V Ray Ingles

8/11/2019 V Ray Ingles

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Plugins Home

While V-Ray works with most of the standard 3ds Max lights,

materials and maps, it also includes several additional pluginswhich offer functionality not found in 3ds Max itself. They arespecially optimized for work with V-Ray and using theminstead of the standard ones can increase rendering speedsignificantly.

The V-Ray rendering system includes the following plugins for3ds Max:

Plugin name Description

V-Ray renderer The V-Ray renderer plugin

VRay2SidedMtl A utility material that allows to create thin translucent surfaces like paper, cloth etc.

VRayOverrideMtl

A utility material that allows to specify different materials to be used for reflections,

GI, refractions and shadows.

VRayLightMtl A material for creating light-emitting objects.

VRayMtl

A specialized V-Ray material supporting (glossy) reflections/refractions, absorption,

sub-surface scattering etc.

VRayMtlWrapper

A specialized V-Ray material that allows you to specify additional rendering

parameters for any material.

VRayLight An area light plugin

VRaySun

A V-Ray sun light with accurate intensity and color based on its position over the

horizon.

VRaySky

A procedural HDR environmap map that works with the VRaySun light to create

realistic daylight environments.

VRayShadow A raytraced shadow plugin (sharp and area shadows)

http://help.chaosgroup.com/vray/help/150SP1/index.htm

http://help.chaosgroup.com/vray/help/150SP1/render_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vray2sided_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vray_overridemtl.htm


http://help.chaosgroup.com/vray/help/150SP1/vray_light_mtl.htm


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm


http://help.chaosgroup.com/vray/help/150SP1/light_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vraysun_sky_param.htm




http://help.chaosgroup.com/vray/help/150SP1/shadow_params.htm














VRayDirt

A procedural texture that can be used for dirt-like effects or for simulating ambient

occlusion.

VRayColor A utility texture that always returns a specified color.

VRayMap A map for adding (glossy) V-Ray reflections/refractions to non-V-Ray materials

VRayHDRI A map for loading HDR images (.hdr file extension) and mapping them as environments

VRayEdgesTex

A map that shows mesh edges (useful for wireframe-style rendering). Can also be used

as a bump map to smooth the sharp edges of mesh objects.

VRayDisplacementMod A modifier that enables the V-Ray displacement for an object

VRayFur A plugin that generates simple render-time fur

VRayProxy

A plugin that allows you to specify render-time geometry that will be loaded from an

external file

VRayPlane A geometry plugin that implements an infinite plane primitive.

VRayToon An atmospheric plugin that produces simple cartoon-style effect.

VRayBmpFilter A plugin for loading texture maps without filtering.

VRayPhysicalCamera A new camera type that allows to simulate the workings of a real-world camera.

VRayFastSSS A material for quick simulation of sub-surface scattering

VRayFastSSS2 An advanced material for quick simulation of sub-surface scattering

VRayEnvironmentFog

An enviromental effect that allows the simulation of participating media like fog or

dust in the atmosphere

VRayBlendMtl A utlity material for efficient layering of several different materials.

http://help.chaosgroup.com/vray/help/150SP1/vraydirt_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vraycolor.htm


http://help.chaosgroup.com/vray/help/150SP1/map_params.htm


http://help.chaosgroup.com/vray/help/150SP1/hdri_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayedgestex_params.htm


http://help.chaosgroup.com/vray/help/150SP1/displMod_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayfur_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayproxy_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayplane_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vraytoon_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vraybmpfilter_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayphysicalcamera_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayenvironmentfog_params.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayblendmtl_params.htm




















General

In addition to rendering to the 3ds Max Rendered FrameWindow (RFW or VFB), V-Ray allows you to render to a V-

Ray specific frame buffer, which has some additionalcapabilities:

Allows you to view all render elements in a single windowand switch between them easily;

Keeps the image in full 32-bit floating-point format; Allows you to perform simple color corrections on the

rendered image;

Allows you to choose the order in which the buckets arerendered.

The V-Ray VFB also has some limitations, which are listed inthe Notes section below.

Parameters

Show last VFB - If you have rendered to the V-Ray VFB, buthave closed it, this button allows you to open it again. The

http://help.chaosgroup.com/vray/help/150SP1/vfb_index.html#notes






same can also be achieved with theshowLastVFB() MaxScript method of the V-Ray renderer.

Enable built-in frame buffer - Enables the use of built-in V-

Ray frame buffer. Due to technical reasons, the original 3dsMax frame buffer still exists and is being created. However,when this feature is turned on - V-Ray will not render any datato the 3ds Max frame buffer. In order to preserve memoryconsumption we recommend that you set the original 3ds Maxresolution to a very low value (like 100x100) and turn off the3ds Max Virtual Frame Buffer from the common 3ds Maxrender settings.

Render to memory frame buffer - this will create a V-Rayframe buffer and will use it to store color data that you canobserve while rendering and afterwards. If you wish to renderreally high resolutions that would not fit into memory or thatmay eat up a lot of your RAM not allowing for the scene torender properly - you can turn this feature off and useonly Render to V-Ray raw image file feature.

Get resolution from 3ds Max - this will cause the V-Ray VFBto take its resolution from the 3ds Max common rendersettings.

Output resolution - this is the resolution that you wish to usewith the V-Ray frame buffer.

Pixel aspect - specifies the pixel aspect for the rendered

image in the V-Ray frame buffer.

Render to V-Ray raw image file - when this is on, V-Raydirectly writes to disk the raw image data as it is beingrendered. It does not store any data in the RAM, so thisfeature is very handy when rendering huge resolutions for

http://help.chaosgroup.com/vray/help/150SP1/render_maxscript.htm






preserving memory. If you wish to see what is being rendered,you can turn on the Generate preview setting. You canspecify either a .v r img or an .exr file for output:

If you specify a .v r img extension, the resulting file can beviewed through the File > View im age... menu of 3dsMax, or converted to an OpenEXR file with the help ofthe vrimg2exr tool.

If you specify an .exr extension, V-Ray will write out atiled OpenEXR file that can be used directly by 3dsMax or other compositing applications. The filecontains all render elements for the image.

Generate preview - this will create a small preview of what isbeing rendered. If you are not using the V-Ray memory framebuffer for conserving memory (i.e. Render to memory framebuffer is o ff ), you can use this feature to see a small image ofwhat is being actually rendered and stop the renderer if thereis anything that looks wrong.

Save separate render channels - this option allows you tosave the channels from the VFB into separate files. Usethe Browse... button to specify the file. This option is availableonly when rendering to a memory frame buffer. If rendering isdone only to a raw image file, the render channels can beextracted from that file after rendering is complete.

Save RGB and Save Alpha - these options allow you to

disable saving of the RGB and Alpha channels respectively.This can be useful if you only want to generate other renderchannels. Note that V-Ray will still generate the RGB and

Alpha channels, however they will not be saved.

Hidden parameters

http://www.openexr.com/



http://help.chaosgroup.com/vray/help/150SP1/tools_vrimg2exr.htm







There are some additional parameters of the VFB, which arenot available in the interface, but are accessible throughMaxScript. These may be useful in certain situations. Beloware listed the MaxScript names of these parameters.

output_renderType - This allows you to override the rendertype, specified in the 3ds Max settings. Possible values are:0 - use 3ds Max render type (default);1 - render the full image;2 - region rendering;3 - crop rendering;4 - blow-up rendering.

output_regxmin - The left coordinate (in pixels) of the regionto render (for region/crop/blow-up rendering);

output_regxmax - The right coordinate (in pixels) of theregion to render (for region/drop/blow-up rendering);

output_regymin - The top coordinate (in pixels) of the regionto render (for region/drop/blow-up rendering);

output_regymax - The bottom coordinate (in pixels) of theregion to render (for region/drop/blow-up rendering);

VFB toolbar

This part of the toolbar sets the currently selected channel, as well as the

preview mode. Choose which channels to see with the help of the buttons.

You can also view the rendered image in monochromatic mode.

This will save the current frame data to a file.You can turn this on and of on-the-fly while rendering.

This will create a 3ds Max virtual frame buffer copy of the current V-Ray frame buffer.You can turn

this on and of on-the-fly while rendering.

This will force V-Ray to render the closest bucket found to the mouse pointer. Drag the mouse over

the V-Ray frame buffer while rendering to see which buckers are rendered first. You can turn this on

and of on-the-fly while rendering.



This option allows you to render regions in the V-Ray VFB

This open permanently the info dialog which will give you information about the pixel you right-

click the mouse pointer on. If you right-click the mouse pointer over a pixel without turning this

setting on - then you will see the info dialog only while yuor mouse button is down

This will open a so called "levels control" dialog which will let you define color corrections ofvarious color channels. It will also show the histogram of the currently contained image data in the

buffer. Click and drag your mid-button in the histogram to interactively scale the preview.

Clears the contents of the frame buffer. Somethimes helpful when starting a new render to prevent

confusion with the previous image.

VFB shortcuts

Here is the list of shortcuts you can use to navigate throughthe VFB image. Please note that VFB window must have the

curent focus for the shortcuts to have effect:

Mouse Description

CTRL+LeftClick,

CTRL+RightClick

Zoom in/Zoom out

Roll the mouse-rollon button

up/down

Zoom in/Zoom out

Double-click LeftButton Zoom to 100%

RightClick Show the info dialog with the properties of the last pixel clicked. In order to

see the info non-stop - turn on the info dialog buttonMidButton dragging view pan (hand tool)

Keyboard Description

+ / - Zoom in/Zoom out

* Zoom to 100%

Arrow keys Pan left, up, right, down

Notes

The V-Ray VFB does not display the G-Buffer layers(like Coverage etc.);

The V-Ray VFB does not work with stripe rendering;



Even though you select the V-Ray VFB as your output,the 3ds Max VFB is still created and thus takes additionalmemory. If you want to reduce that memory, you need touncheck the Get resolution from MAXoption, set the

3ds Мax resolution to a low value like 100 x 100, andthen select your real output resolution in the V-Ray VFBoptions.

If you have selected an output image file fromthe Common tab of the Render Scene dialog, V-Ray willfill out the 3ds Max RFW, and this will be saved as yourimage. If you want to save the V-Ray VFB instead, you

should use the Split render channels or Render to V-Ray raw image file option of the V-Ray VFB.

The OpenEXR file format is an open file format for highdynamic range images originally developed by IndustrialLight and Magic. The official site of the OpenEXR fileformat is http://www.openexr.com/







Global switches

General

The global switches allow you to control various aspects ofthe renderer globally.

Parameters

Geometry

section

Displacement - enables (default) or disables V-Ray's owndisplacement mapping. Note that this has no effect onstandard Max displacement mapping, which can be controlledvia the corresponding parameter in the Render Scene dialog.

Force back face culling - enables or disables (default) backface culling for camera and shadow rays. When this optionis on , the surfaces of objects which are turned away from thecamera (or the light source, when tracing shadows) willappear fully transparent. This allows to look inside closedobjects when the camera is outside.

Lighting section



Lights - enables or disables lights globally. Note that if youuncheck this, V-Ray will use the default lights. If you do notwant any direct lighting in your scene, you must uncheck both

this and the Default lights parameters.

Default lights - allows you to control the default lights in thescene.- Off - the default lights in the scene will be always switchedoff

-On - the default lights are always switched on when there are

no lights in the scene or when you have disabled lightingglobally (see Light parameter).

-Off with GI - the default lights will be switched off only whenthe Global Illumination is enabled or if there are lights in thescene

Hidden lights - enables or disables the usage of hiddenlights. When this is checked, lights are rendered regardless ofwhether they are hidden or not. When this option is o ff , anylights that are hidden for any reason (either explicitly or bytype) will not be included in the rendering.

Shadows - enables or disables shadows globally.

Show GI only - when this option is on , direct lighting will notbe included in the final rendering. Note that lights will still be

considered for GI calculations, however in the end only theindirect lighting will be shown.

Materials section



Reflection/refraction - enables or disables the calculation ofreflections and refractions in V-Ray maps and materials.

Max depth - enables the user to limit globally the

reflection/refraction depth. When this is unchecked, the depthis controlled locally by the materials/maps. When this option ischecked, all materials and maps use the depth specified here.

Maps - enables or disables texture maps.

Filter maps - enables or disables texture map filtering. Whenenabled, the depth is controlled locally by the settings of the

texture maps. When disabled, no filtering is performed.

Filter maps for GI - enable or disable texture filtering duringGI calculations and glossy reflections/refractions.When o ff (the default), texture maps are not filtered for GI andglossy reflections/refractions in order to speed up thecalculations. If this option is on , textures will be filtered inthese cases.

Max. transp levels - this controls to what depth transparentobjects will be traced.

Transp. cutoff - this controls when tracing of transparentobjects will be stopped. If the accumulated transparency of aray is below this threshold, no further tracing will beperformed.

Override mtl - this option allows the user to override thescene materials when rendering. All objects will be renderedwith the chosen material, if one is selected, or with theirdefault wireframe materials if no material is specified.



Override exclude - clicking this button brings up the 3ds MaxInclude/Exclude dialog which allows you to select exactly forwhich objects the material is overridden.

Glossy effects - this option allows the user to replace allglossy reflections in the scene with non-glossy ones; usefulfor test renderings.

Indirect illumination section

Don't render final image - when this option is on, V-Ray willonly calculate the relevant global illumination maps (photon

maps, light maps, irradiance maps). This is a useful option ifyou are calculating maps for a fly-through animation.

Raytracing section

Secondary rays bias - a small positive offset that will beapplied to all secondary rays; this can be used if you haveoverlapping faces in the scene to avoid the black splotchesthat may appear. See the Examples section for ademonstration of the effect of this parameter. This parameteris also useful when using the 3ds Max Render-to-texture feature.

Compatibility section

Legacy sun/sky/camera models - previous versions of V-Ray used slightly different calculation models for

theVRaySun, VRaySky and VRayPhysicalCamera which werenot entirely physically accurate. When this option isoff (thedefault), V-Ray uses improved and more accurate models.When this is on , V-Ray will switch to the old models forcompatibility with old scenes. When an old scene is opened,

http://help.chaosgroup.com/vray/help/150SP1/examples_switches.htm



http://help.chaosgroup.com/vray/help/150SP1/render_baking.htm



















V-Ray will automatically display a dialog asking if you want tochange this setting.

Use 3ds Max photometric scale - when on (the default), this

option alignsthe VRayLight, VRaySun, VRaySkyand VRayPhysicalCamera to the photometric units used by 3ds Max and its photometriclights. When this is off , these plugins operate in the internal V-Ray photometric space, like in older versions of V-Ray.Keeping this option on ensures that a VRayLight with a givenpower will match a 3ds Max photometric light with the samepower.

Image Sampler (Antialiasing)

General

In V-Ray, an image sampler refers to an algorithm for sampling and filtering the image function, andproducing the final array of pixels that constitute the rendered image.

V-Ray implements several algorithms for sampling an image. All image samplers support MAX'sstandard antialiasing filters, although at the cost of increased rendering time. You can choose

between Fixed rate sampler, Adapt ive DMC sampler and Adapt ive subdiv is ion sampler.

Parameters

Image sampler

Type - specifies the image sampler type:

Fixed - this sampler always takes the same number of samples per pixel;
















Adaptiv e DMC - this sampler takes a variable number of samples per pixel depending on thedifference in the intensity of the pixels;

Adapt ive subdiv is ion - this sampler divides the image into an adaptive grid-like structure andrefines depending on the difference in pixel intensity.

Antialiasing filter

This section allows you to choose an antialiasing filter. All standard 3ds Max filters are supportedwith the exception of the Plate Match filter. See the Examples section for more information onantialiasing filters.

Fixed rate sampler

This is the simplest imagesampler, and it takes a fixed number of samples for each pixel.

Subdivs - determines number of samples per pixel. When this is set to 1, one sample at the centerof each pixel is taken. If this is greater than 1, the samples are distributed within the pixel. Theactual number of pixels is the square of this parameter (e.g. 4 subdivs produce 16 samples perpixel).

Adapt ive DMC sampler

This sampler makes avariable number of samples per pixel based on the difference in intensity between the pixel and itsneighbors.

This is the preferred sampler for images with lots of small details (like VRayFur , for example) and/orblurry effects (DOF, motion blur, glossy reflections etc). It also takes up less RAM thanthe Adapt ive subdiv is ion sampler.

Min subdivs - determines the initial (minimum) number of samples taken for each pixel. You willrarely need to set this to more than 1, except if you have very thin lines that are not capturedcorrectly, or fast moving objects if you use motion blur. The actual number of pixels is the square ofthis number (e.g. 4 subdivs produce 16 samples per pixel).

Max subdivs - determines the maximum number of samples for a pixel. The actual maximumnumber of sampler is the square of this number (e.g. 4 subdivs produces a maximumof 16 samples). Note that V-Ray may take less than the maximum number of samples, if thedifference in intensity of the neighbouring pixels is small enough.

Use DMC sampler threshold - when this is on (the default), V-Ray will use the threshold specifiedin the DMC sampler to determine if more samples are needed for a pixel. When this is off, the Colorthreshold parameter will be used instead.

http://help.chaosgroup.com/vray/help/150SP1/examples_image_sampler.htm






http://help.chaosgroup.com/vray/help/150SP1/render_params_dmc.htm








Color threshold - the threshold that will be used to determine if a pixel needs more samples. Thisis ignored if the Use DMC sampler threshold option is on.

Show samples - if this is on, V-Ray will show an image where the pixel brightness is directlyproportional to the number of samples taken at this pixel. This is useful for fine-tuning theantialiasing of the image.

Adapt ive subdiv is ion sampler

This is an advancedimage sampler capable of undersampling (taking less than one sample per pixel). In the absence ofblurry effects (direct GI, DOF, glossy reflection/reftaction etc) this is the best preferred imagesampler in V-Ray. On average it takes fewer samples (and thus less time) to achieve the same

image quality as the other image samplers. However, with detailed textures and/or blurry effects, itcan be slower and produce worse results than the other two methods.

Also note that this sampler takes up more RAM than the other two samplers - see the Notes below.

Min. rate - controls minimum number of samples per pixel. A value of zero means one sample perpixel; -1 means one sample every two pixels; -2 means one sample every 4 pixels etc.

Max. rate - controls maximum number of samples per pixel; zero means one sample per pixel, 1means four samples, 2 means eight samples etc.

Color threshold - determines the sensitivity of the sampler to changes in pixel intensity. Lowervalues will produce better results, while higher values will be faster, but may leave some areas ofsimilar intensity undersampled.

Randomize samples - displaces the samples slightly to produce better antialiasing of nearlyhorizontal or vertical lines.

Object outline - this will cause the image sampler to always supersample object edges (regardlessof whether they actually need to be supersampled). This option has no effect if DOF or motion bluris enabled.

Normals - this will supersample areas with sharply varying normals. This option has no effect ifDOF or motion blur is enabled.

Show samples - if this is on, V-Ray will show an image where the pixel brightness is directlyproportional to the number of samples taken at this pixel. This is useful for fine-tuning the

antialiasing of the image.

Notes

Which sampler to use for a given scene? The answer is best found with experiments, buthere are some tips:

http://help.chaosgroup.com/vray/help/150SP1/render_params_imagesampler.htm#ram






o For smooth scenes with only a few blurry effects and smooth textures,the Adapt ive subdiv is ion sampler with its ability to undersample the image isunbeatable.

o For images with detailed textures or lots of geometry detail and only a few blurryeffects, theAdapt ive DMC sampler performs best. Also in the case of animationsinvolving detailed textures, theAdapt ive subdiv is ion sampler might produce jittering which the Adapt ive DMC sampler avoids.

o For complex scenes with lots of blurry effects and/or detailed textures, the Fixed

rate sampler performs best and is very predictable with regards to the quality andrender time.

A note on RAM usage: image samplers require substantial amount of RAM to storeinformation about each bucket. Using large bucket sizes may take a lot of RAM. This isespecially true for the Adapt ive subdiv is ion sampler, which stores all individual sub-samples taken within a bucket. The Adapt ive DMC sampler and the Fixed rate sampler onthe other hand only store the summed result of all sub-samples for a pixel and so usuallyrequire less RAM.

Indirect illumination (GI)

General

Approaches to indirect illumination

V-Ray implements several approaches for computing indirect

illumination with different trade-offs between quality andspeed:

Brute force - this is the simplest approach; indirectillumination is computed independently for each shadedsurface point by tracing a number of rays in differentdirections on the hemisphere above that point.

Advantages:o this approach preserves all the detail (e.g. small

and sharp shadows) in the indirect lighting;o it is free from defects like flickering in animations;o no additional memory is required;



o indirect illumination in the case of motion-blurredmoving objects is computed correctly.

Disadvantages:

o the approach is very slow for complex images (e.g.interior lighting);

o it tends to produce noise in the images, which canbe avoided only by shooting a larger number ofrays, thus slowing it even more.

Irradiance map - this approach is based on irradiancecaching; the basic idea is to compute the indirect

illumination only at some points in the scene, andinterpolate for the rest of the points.

Advantages:o the irradiance map is very fast compared to direct

computation, especially for scenes with large flatareas;

o the noise inherent to direct computation is greatlyreduced;

o the irradiance map can be saved an re-used tospeed up calculations of different views for thesame scene and of fly-through animations;

o the irradiance map can also be used to acceleratedirect diffuse lighting from area light sources.

Disadvantages:

o some details in indirect lighting can be lost or

blurred due to the interpolation;o if low settings are used, flickering may occur when

rendering animations;o the irradiance map requires additional memory;



o indirect illumination with motion-blurred movingobjects is not entirely correct and may lead to noise(although in most cases this is not noticeable).

Photon map - this approach is based on tracing particlesstarting from the light sources and bouncing around thescene. This is useful for interior or semi-interior sceneswhith lots of lights or small windows. The photon mapusually does not produce good enough results to beused directly; however it can be used as a roughapproximation to the lighting in the scene to speed thecalculation of GI through direct computation or irradiance

map.

Advantages:o the photon map can produce a rough approximation

of the lighting in the scene very quickly;o the photon map can be saved an re-used to speed

up calculation of different views for the same sceneand of fly-through animations;

o the photon map is view-independent.

Disadvantages:

o the photon map usually is not suitable for directvisualization;

o requires additional memory;o in V-Ray's implementation, illumination involving

motion-blurred moving objects is not entirely correct(although this is not a problem in most cases).

o the photon map needs actual lights in order to work;it cannot be used to produce indirect illuminationcaused by environment lights (skylight).

Light cache - light caching is a technique forapproximating the global illumination in a scene. It is very



similar to photon mapping, but without many of itslimitations. The light map is built by tracing many manyeye paths from the camera. Each of the bounces in thepath stores the illumination from the rest of the path into

a 3d structure, very similar to the photon map. The lightmap is a universal GI solution that can be used for bothinterior or exterior scenes, either directly or as asecondary bounce approximation when used with theirradiance map or the brute force GI method.

Advantages:o the light cache is easy to set up. We only have the

camera to trace rays from, as opposed to thephoton map, which must process each light in thescene and usually requires separate setup for eachlight.

o the light-caching approach works efficiently with anylights - including skylight, self-illuminated objects,non-physical lights, photometric lights etc. Incontrast, the photon map is limited in the lightingeffects it can reproduce - for example, the photonmap cannot reproduce the illumination from skylightor from standard omni lights without inverse-squarefalloff.

o the light cache produces correct results in cornersand around small objects. The photon map, on theother hand, relies on tricky density estimationschemes, which often produce wrong results inthese cases, either darkening or brightening those

areas.o in many cases the light cache can be visualized

directly for very fast and smooth previews of thelighting in the scene.

Disadvantages:



o like the irradiance map, the light cache is view-dependent and is generated for a particular positionof the camera. However, it generates anapproximation for indirectly visible parts of the

scene as well - for example, one light cache canapproximate completely the GI in a closed room;

o currently the light cache works only with V-Raymaterials;

o like the photon map, the light cache is not adaptive.The irradiance is computed at a fixed resolution,which is determined by the user;

o the light cache does not work very well with bump

maps; use the irradiance map or brute force GI ifyou want to achieve better results with bump maps.

o lighting involving motion-blurred moving objects isnot entirely correct, but is very smooth since thelight cache blurs GI in time as well (as opposed tothe irradiance map, where each sample iscomputed at a particular instant of time).

Which method to use? That depends on the task at hand.The Examples section can help you in choosing a suitablemethod for your scene.

Primary and secondary bounces

The indirect illumination controls in V-Ray are divided into twolarge sections: controls concerning primary diffusebounces and controls concerning secondary diffuse bounces.

A primary diffuse bounce occurs when a shaded point isdirectly visible by the camera, or through specular reflective orrefractive surfaces. A secondary bounce occurs when ashaded point is used in GI calculations.

Parameters

http://help.chaosgroup.com/vray/help/150SP1/examples_GI.htm






On - turnindirectillumination onand off.

GI caustics

GI causticsrepresent lightthat has gonethrough onediffuse, andone or several specular reflections (or refractions). GI causticscan can be generated by skylight, or self-illuminated objects,

for example. However, caustics caused by direct lights cannotbe simulated in this way. You must use theseparate Caustics section to control direct light caustics. Notethat GI caustics are usually hard to sample and may introducenoise in the GI solution.

Refractive GI caustics - this allows indirect lighting to passthrough transparent objects (glass etc). Note that this is not

the same as Caustics, which represent direct light goingthrough transparent objects. You need refractive GI causticsto get skylight through windows, for example.

Reflective GI caustics - this allows indirect light to bereflected from specular objects (mirrors etc). Note that this isnot the same as Caustics, which represent direct light goingthrough specular surfaces. This is off by default, becasereflective GI caustics usually contribute little to the finalillumination, while often they produce undesired sublte noise.

Post-processing

These controls allow additional modification of the indirectillumination, before it is added to the final rendering. Thedefault values ensure a physically accurate result; however

http://help.chaosgroup.com/vray/help/150SP1/render_params_caustics.htm






the user may want to modify the way GI looks for artisticpurposes.

Saturation - controls the saturation of the GI; a value

of 0.0 means that all color will be removed from the GIsolution and will be in shades of grey only. The default valueof 1.0 means the GI solution remains unmodified. Valuesabove 1.0 boost the colors in the GI solution.

Contrast - this parameter works together with Contrastbase to boost the contrast of the GI solution. When Contrastis 0.0 , the GI solution becomes completely uniform with the

value defined by Contrast base. A value of 1.0 means thesolution remains unmodified. Values higher that 1.0 boost thecontrast.

Contrast base - this parameter determines the base for thecontrast boost. It defines the GI values that remain unchangedduring the contrast calculations.

Ambient occlusion

These controls allow you to add an ambient occlusion term tothe global illumination solution.

On - enable or disable ambient occlusion.

Amount - the amount of ambient occlusion. A value of 0.0 willproduce no ambient occlusion.

Radius - ambient occlusion radius.

Subdivs - determines the number of samples used forcalculating ambient occlusion. Lower values will render faster,but might introduce noise.



Primary diffuse bounces

Multiplier - this value determines how much primary diffusebounces contribute to the final image illumination. Note thatthe default value of 1.0 produces a physically accurate image.

Other values are possible, but not physically plausible.

Primary GI engine - the list box specifies the method to beused for primary diffuse bounces.

Irradianc e map - selecting this will cause V-Ray to use anirradiance map for primary diffuse bounces. Seethe Irradiance map section for more information.

Global photon map - selecting this option will cause V-Ray touse a photon map for primary diffuse bounces. This mode isuseful when setting up the parameters of the global photonmap. Usually it does not produce good enough results for finalrenderings when used as a primary GI engine. See the Globalphoton map section for more information.

Bru te force - selecting this method will cause V-Ray to use

direct computation for primary diffuse bounces. See the bruteforce GI section for more information.

Light cache - this chooses the light cache as the primary GIengine. See the Light cache section for more information.

Secondary diffuse bounces

Multiplier - this determines the effect of secondary diffusebounces on the scene illumination. Values close to 1.0 may

tend to wash out the scene, while values around 0.0 mayproduce a dark image. Note that the default value of 1.0produces physically accurate results. While other values arepossible, they are not physically plausible.

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Secondary diffuse bounces method - this parameterdetermines how V-Ray will calculate secondary diffusebounces.

None - no secondary bounces will be computed. Use thisoption to produce skylit images without indirect color bleeding.

Global photon map - selecting this option will cause V-Ray touse a photon map for primary diffuse bounces. This mode isuseful when setting up the parameters of the global photonmap. Usually it does not produce good enough results for finalrenderings when used as a primary GI engine. See the Global

photon map section for more information.

Bru te force - selecting this method will cause V-Ray to usedirect computation for primary diffuse bounces. See the Bruteforce GI section for more information.

Light cache - this chooses the light cache as the primary GIengine. See the Light cache section for more information.

Notes

V-Ray does not have a separate skylight system. Theskylight effect can be achieved by setting the backgroundcolor or environment map in the 3ds Max environmentdialog, or in V-Ray's own Environment rollout.

You will get physically accurate lighting if you set both

the primary and secondary GI multipliers to their defaultvalue of 1.0. While other values are possible, they willnot produce a physically accurate result.



















Brute force GI Home Render params Examples

Search Keywords : brute force, direct calculation, GI

General

This section is available only if you have chosen Bruteforce as either the primary or the secondary GI engine.

The brute force method for computing global illuminationrecomputes the GI values for every single shaded pointseparately and independently from other points. While very

slow, this method is very accurate, especially if you havemany small details in the scene.

To speed up brute force GI, you can use a faster method (thephoton map or the light map) for approximating secondary GIbounces, while using the brute force method for the primarybounces.

Parameters

Subdivs - thisdetermines the number of samples used to approximate GI.Note that this is not the exact number of rays that V-Ray willtrace. The number of rays is proportional to the square of thisnumber, but also depends on the settings in the DMC

sampler rollout.

Secondary bounces - this parameter is available only if bruteforce GI is selected as a secondary GI engine. It controls thenumber of light bounces that will be computed.
























Irradiance map Home Render params Examples

General

Parameters Built-in presets Basic parameters Options Detail enhancement

Advanced options Mode On render end Notes

General

This section allows the user to control and fine-tune variousaspects of the irradiance map. This section is enabled onlywhen the irradiance map is chosen as the GI method forprimary diffuse bounces.

Some background for understanding how the irradiance mapworks is necessary in order to grasp the meaning of theseparameters.

Irradiance is a function defined for any point in the 3D spaceand represents the light arriving at this point from all possibledirections. In general, irradiance is different in every point and

in every direction. However, there are two useful restrictionsthat can be made. The first is the surface irradiance - which isthe irradiance arriving at points which lie on the surface ofobjects in the scene. This is a natural restriction since we areusually interested in the illumination of objects in the scene,and objects are usually defined through their surface. The



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second restriction is that of diffuse surface irradiance - whichis the total amount of light arriving at a given surface point,disregarding the direction from which it comes.

In more simple terms, one can think of the diffuse surfaceirradiance as being the visible color of a surface, if we assumethat its material is purely white and diffuse.

In V-Ray, the term irradiance map refers to a method ofefficiently computing the diffuse surface irradiance for objectsin the scene. Since not all parts of the scene have the samedetail in indirect illumination, it makes sense to compute GI

more accurately in the important parts (e.g. where objects areclose to each other, or in places with sharp GI shadows), andless accurately in uninteresting parts (e.g. large uniformly litareas). The irradiance map is therefore built adaptively. Thisis done by rendering the image several times (each renderingis called a pass) with the rendering resolution being doubledwith each pass. The idea is to start with a low resolution (saya quarter of the resolution of the final image) and work up tothe final image resolution.

The irradiance map is in fact a collection of points in 3d space(a point cloud) along with the computed indirect illumination atthose points. When an object is hit during a GI pass, V-Raylooks into the irradiance map to see if there are any pointssimilar in position and orientation to the current one. Fromthose already computed points, V-Ray can extract variousinformation (i.e. if there are any objects close by, how fast the

indirect illumination is varying etc). Based on that information,V-Ray decides if the indirect illumination for the current pointcan be adequately interpolated from the points already in theirradiance map, or not. If not, the indirect illumination for thecurrent point is computed, and that point is stored in theirradiance map. During the actual rendering, V-Ray uses a



sophisticated interpolation method to derive an approximationof the irradiance for all surfaces in the scene.

Parameters

Built-in presets

Currentpreset - thisdropdown listallows you tochoose fromseveral presetsfor some of the

irradiance mapparameters.You can usethese toquickly set thecolor, normaland distancethresholds, as

well as themin/max rates.The followingpresets areavailable:

Very

low - this

preset is only useful for preview purposes to show thegeneral lighting in the scene. Low - a low-quality preset for preview purposes Medium - a medium quality preset; works fine in many

situations in scenes which have don't small details.



Medium animation - a medium quality preset targeted atreducing flickering in animations - the Distancethreshold is higher.

High - a high-quality preset that works in most situations,

even for scenes with small details as well as for mostanimations.

High animat ion - a high-quality preset that can be usedif the High preset produces flickering in animations -the Distance threshold is higher.

Very hig h - a very high quality preset; can be used forscenes with extremely small and intricate details.

Note that the presets are targeted for a typical 640x480image. Larger images usually can do with lower Min/Maxrates than those specified in the presets.

Basic parameters

Min rate - this value determines the resolution for the first GIpass. A value of 0 means the resolution will be the same asthe resolution of the final rendered image, which will make theirradiance map similar to the direct computation method. A

value of -1 means the resolution will be half that of the finalimage and so on. You would usually want to keep thisnegative, so that GI is quickly computed for large and flatregions in the image. This parameter is similar to (althoughnot the same as) the Min rate parameter of the Adapt ive

subdiv is ion image sampler.

Max rate - this value determines the resolution of the last GIpass. This is similar to (although not the same as) the Maxrate parameter of the Adapt ive subdiv is ion image sampler.

Color threshold (Clr thresh) - this parameter controls howsensitive the irradiance map algorithm is to changes in indirectlighting. Larger values mean less sensitivity; smaller values



make the irradiance map more sensitive to light changes (thusproducing higher quality images).

Normal threshold (Nrm thresh) - this parameter controls

how sensitive the irradiance map is to changes in surfacenormals and small surface details. Larger values mean lesssensitivity; smaller values make the irradiance map moresensitive to surface curvature and small details.

Distance threshold (Dist thresh) - this parameter controlshow sensitive the irradiance map is to distance betweensurfaces. A value of 0.0 means the irradiance map will not

depend on object proximity at all; higher values place moresamples in places where objects are close to each other.

Hemispheric subdivs (HSph. subdivs) - this controls thequality of individual GI samples. Smaller values make thingsfaster, but may produce blotchy result. Higher values producesmoother images. This is similar to theSubdivs parameter fordirect computation. Note that this is not the actual number ofrays that will be traced. The actual number of rays isproportional to the square of this value and also depends onthe settings in the DMC sampler rollout.

Interpolation samples - this is the number of GI samples thatwill be used to interpolate the indirect illumination at a givenpoint. Larger values tend to blur the detail in GI although theresult will be smoother. Smaller values produce results withmore detail, but may produce blotchiness if low Hemispheric

subdivs are used. Note that if you use interpolated irradiancemaps (i.e. the Mode is set to An imat ion (render ing) ), V-Raywill actually multiply this value by the number of irradiancemaps used. For example, if you have the Interpolationsamplesset to 20 , and the Interpolation frames to 2 , V-Raywill actually use 100 samples to interpolate. This is done in






order to preserve the blurring of the GI solution compared to asingle frame irradiance map, however it also slows down therendering. To speed up the rendering in that case, you candecrease this value to 10 or 5 .

Interpolation frames - this determines the number of framesthat will be used to interpolate GI when the Modeis setto An imat ion (render ing) . In this mode, V-Ray interpolatesthe irradiance from the maps of several adjacent frames tohelp smooth out any flickering. Note that the actual number offrames used is 2*(int erp. frames)+1 - e.g. the default valueof 2 means that in total 5 irradiance maps will be interpolated.

Higher values slow down the rendering and may produce"lagging" effect. Lower values render faster but may increaseflickering. Note that increasing this value also increases thenumber of samples used for interpolation from the irradiancemap - see the note for the Interpolation samples parameter.

Options

Show calc phase - when this option is on, V-Ray will showthe irradiance map passes as the irradiance map is

calculated. This will give you a rough idea of the indirectillumination even before the final rendering is complete. Notethat turning this on slows the calculations a little bit, especiallyfor large images. This option is ignored when rendering tofields - in that case, the calculation phase is never displayed.

Show direct light - this option is only available when Showcalc phase is on. It will cause V-Ray to show direct lightingfor primary diffuse bounces in addition to indirect lighting whilethe irradiance map is being calculated. Note that V-Ray doesnot really need to compute this. The option is only forconvenience. This does not mean that direct lighting is notcalculated at all - it is, but only for secondary diffuse bounces(only for GI purposes).



Show samples - when this option is on, V-Ray will showvisually the samples in the irradiance map as small dots in thescene.

Use camera path - when this option is on , V-Ray willcalculate the irradiance map samples for the entire camerapath, instead of just the current view. This is useful in thefollowing cases:

Calculating irradiance maps for short fly-throughanimations in one go. Instead of using the Incremental

add to cu rrent map mode and rendering the animation

every N th frame, you can turn the Use camera pathoption on , and render just one single frame - this willproduce information for the entire camera path.

Using irradiance maps for anmations with moving objectswhere the camera also moves - either in Single frame ,or Animat ion (prepass) mode. In this case, settingthe Use camera path option on will help to furtherreduce any flickering, as the GI sample positions onstatic geometry will not change.

If you use this option, you should not use interpolated glossyreflections/refractions in VRayMtl, as they will look odd.

Detail enhancement

Detail enhancement is a method for bringing additional detailto the irradiance map in the case where there are small detailsin the image. Due to its limited resolution, the irradiance maptypically blurs the GI in these areas or produces splotchy andflickering results. The detail enhancement option is a way tocalculate those smaller details with a high-precision brute-force sampling method. This is similar to how an ambientocclusion pass works, but is more precise as it takes intoaccount bounced light.







On - turns on detail enhancement for the irradiance map. Notethat an irradiance map calculated in this mode should not beused without the detail option. When detail enhancement

is On , you can use lower irradiance map settings andhigher Interpolation samples. This is because the irradiancemap is only used to capture the general far-off lighting, whiledirect sampling is used for the closer detail areas.

Scale - this determines the units for the Radius parameter:Screen - the radius is in image pixels.World - the radius is in world units.

Radius - this determines the radius for the detailenhancement effect. Smaller radius means that smaller partsaround the details in the image are sampled with higherprecision - this would be faster but may be less precise.Larger radius means that more of the scene will use thehigher precision sampling and may be slower, but moreprecise. This is similar to a radius parameter for an ambientocclusion pass.

Subdivs mult. - this determines the number of samples takenfor the high-precision sampling as a percentage of theirradiance map Hemispheric subdivs. A value of 1.0 meansthat the same number of subdivs will be used as for theregular irradiance map samples. Lower values will make thedetail-enhanced areas more noisy, but faster to render.

Advanced options

Interpolation type - this option is used during rendering. Itselects the method for interpolating the GI value from thesamples in the irradiance map.

Weighted average - this method will do a simple blendbetween the GI samples in the irradiance map based on the



distance to the point of interpolation and the difference in thenormals. While simple and fast, this method tends to producea blochiness in the result.

Least squares f i t - the default method; it will try to compute aGI value that best fits in among the samples from theirradiance map. Produces smoother results than the weightedaverage method, but is slower. Also, ringing artifacts mayappear in places where both the contrast and density of theirradiance map samples change over a small area.

Delone tr iangulat ion - all other methods of interpolation are

blurry methods - that is, they will tend to blur the details inindirect illumination. Also, the blurry methods are proneto density bias (see below for a description). In difference, theDelone triangulation method is a non-blurry method and willpreserve the detail while avoiding density bias. Since it is non-blurry, the result might look more noisy (blurring tends to hidenoise). More samples will be needed to get a sufficientlysmooth result. This can be done either by increasing thehemispheric subdivs of the irradiance map samples, or bydecreasing the Noise threshold value in the brute forcesampler rollout.

Least sq uares w i th Voronoi weights - this is a modificationof the least squares fit method aimed at avoiding the ringing atsharp boundaries by taking in consideration the density of thesamples in the irradiance map. The method is quite slow andits effectiveness is currently somewhat questionable.

Although all interpolation types have their uses, it probablymakes most sense to use either Least squares f i t or Delonetr iangulat ion . Being a blurry method, Least squares f i t willhide noise and will produce a smooth result. It is perfect forscenes with large smooth surfaces. Delone tr iang ulat ion is a



more exact method, which usually requires more hemisphericsubdivs and high Max irradiance map rate (and thereforemore rendering time), but produces accurate results withoutblurring. This is especially obvious in scenes where there are

a lot of small details.

Sample lookup - this option is used during rendering. Itselects the method of choosing suitable points from theirradiance map to be used as basis for the interpolation.

Nearest - this method will simply choose those samples fromthe irradiance map which are closest to the point of

interpolation. (How many points will be chosen is determinedby the value of the Interpolation samplesparameter.) This isthe fastest lookup method and was the only one available inearly versions of V-Ray. A drawback of this method is that inplaces where the density of the samples in the irradiance mapchanges, it will pick more samples from the area with higherdensity. When a blurry interpolation method is used, this leadsto the so-called density bias which may lead to incorrectinterpolation and aritfacts in such places (mostly GI shadowboundaries).

Nearest quad-balanced - this is an extension of the nearestlookup method aimed at avoiding density bias. It divides thespace about the interpolated point in four areas and tries tofind an equal number of samples in all of them (hence thename quad-balanced ). The method is a little slower than thesimple Nearest lookup, but in general performs very well. A

drawback is that sometimes, in its attempt to find samples, itmay pick samples that are far away and not relevant to theinterpolated point.

Precalculated over lapping - this method was introduced inan attempt to avoid the drawbacks of the two previous ones. It



requires a preprocessing step of the samples in the irradiancemap during which a radius of influence is computed for eachsample. This radius is larger for samples in places of lowdensity, and smaller for places of higher density. When

interpolating the irradiance at a point, the method will chooseevery sample that contains that point within its radius ofinfluence. An advantage of this method is that when used witha blurry interpolation method it producses a continuous(smooth) function. Even though the method requires apreprocessing step, it is often faster than the other two. Thesetwo properties make it ideal for high-quality results. Adrawback of this method is that sometimes lonely samples

that are far-away can influence the wrong part of the scene. Also, it tends to blur the GI solution more than the othermethods.

Density-based - the default method; it combinesthe Nearest and the Precalculated over lapping methodsand is very effective in reducing ringing artifacts and artifactsdue to low sampling rates. This method also requires apreprocessing step in order to compute sample density, but itperforms a nearest neighbour look-up to choose the mostsuitable samples while taking sample density in account.

Being the fastest of the three methods, Nearest lookup maybe used for preview purposes. Nearest quad-

balanced performs fairly well in the majority ofcases. Precalculated over lapping is fast and in many casesperforms very well, but may tend to blur the GI solution.

The Density-based method produces very good results in themajority of cases and is the default method.

Note that the lookup method is mostly important when using ablurry interpolation method. When using Delone



t r iangulat ion , the sample lookup method does not influencethe result very much.

Calc. pass interpolation samples - this is used during

irradiance map calculation. It represents the number ofalready computed samples that will be used to guide thesampling algorithm. Good values are between 10 and 25. Lowvalues may speed the calculation pass, but may not providesufficient information. Higher values will be slower and willcause additional sampling. In general, this parameter shouldbe left to the default value of 15.

Use current pass samples - this is used during irradiancemap calculation. When checked, this will cause V-Ray to useall irradiance map samples computed so far. Unchecking it willallow V-Ray to use only samples collected during previouspasses, but not those computing earlier during the currentpass. Keeping this checked will usually cause V-Ray to takeless samples (and therefore compute the irradiance mapfaster). That means that on multiprocessor machines, severalthreads will be modifying the irradiance map at the same time.Because of the asynchronous nature of this process, there isno guarantee that the rendering the same image twice willproduce the same irradiance map. Normally this is not aproblem at all and it is recommended to keep this optionchecked.

Randomize samples - this is used during irradiance mapcalculation. When it is checked, the image samples will be

randomly jittered. Unchecking it will produce samples that arealigned in a grid on the screen. In general, this option shouldbe kept checked in order to avoid artifacts caused by regularsampling.



Check sample visibility - this is used during rendering. It willcause V-Ray to use only those samples from the irradiancemap, which are directly visible from the interpolated point.This may be useful for preventing "light leaks" through thin

walls with very different illumination on both sides. However itwill also slow the rendering, since V-Ray will trace additionalrays to determine sample visibility.

Mode

Mode - this groups of controls allow the user to select the waythe irradiance map is (re)used.Bucket mode - in this mode, a separate irradiance map isused for each rendered region ("bucket"). Note that since

each bucket is computed independently of the others, theremay be differences at the bucket edges. They can be reducedby using higher settings for the irradiance map(the High preset, more hemispheric subdivs and/orsmaller Noise thresho ld for the DMC sampler).

Single frame - the default mode; a single irradiance map iscomputed for the whole image, and a new irradiance map is

computed for each frame. This is the mode to use whenrendering animations of moving objects. In doing so one mustmake sure that the irradiance map is of sufficiently high qualityto avoid flickering.

Mult i f rame incremental - this mode is useful when renderinga sequence of frames (not necessarily consequtive) whereonly the camera moves around (so-called fly-throughanimations). V-Ray will compute a new full-image irradiancemap for the first rendered frame; for all other frames V-Raywill try to reuse and refine the irradiance map that has beencomputed so far.

From f i le - in this mode V-Ray will simply load the irradiancemap from the supplied file at the start of the rendering



sequence and will use this map for all the frames in theanimation. No new irradiance map will be computed. Thismode can be used for fly-through animations and will workwell in network rendering mode.

Add to current map - in this mode V-Ray will compute acompletely new irradiance map and will add it to the map thatis already in memory. This mode is useful when compiling anirradiance map to render multiple views of a static scene. Notethat this mode is not supported for distributed rendering.

Incremental add to cu rrent map - in this mode V-Ray will

use the irradiance map that is already in memory and will onlyrefine it in places that don't have enough detail. This mode isuseful when compiling an irradiance map to render multipleviews of a static scene or a fly-through animation.

Animat ion (prepass) - in this mode V-Ray calculatesirradiance maps to be used later on for final rendering withthe Animat ion (render ing) mode. One irradiance map iscreated for each frame and written into a separate file. Notethat in this mode you have to render one map for each frame(i.e. you cannot render every Nth frame). V-Ray automaticallydisables rendering of the final image in this mode - onlyirradiance map prepasses are calculated.

An imat ion (render ing) - in this mode V-Ray renders a finalanimation using irradiance maps created with theAnimat ion

(prepass) mode. Irradiance maps from several adjacent

frames are loaded together and blended so as to reduceflickering. The number of irradiance maps that are interpolatedis determined by the Interp. frames parameter.

The irradiance map mode that should be used depends on theparticular rendering task - a static scene, a static scene

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rendered from multiple views, a fly-through animation or ananimation with moving objects. Refer to thetutorials section formore information.

Irradiance map control buttons

There are some more buttons in this group that allow one toperform certain operations on the irradiance map:

Browse - this button allows the user to select the irradiancemap file which will be loaded if the From f i le mode isselected. Alternatively, the user can enter the path and nameof the file directly in the edit box.

Save to file - this will save to file the irradiance map which iscurrently in memory. Note that the Don't deleteoption inthe On render end group must be turned on. Otherwise V-Ray will automatically delete the irradiance map at the end ofthe rendering process.

Reset irradiance map - this will clear the irradiance map frommemory.

On render end

This group of controls instructs V-Ray what to do with theirradiance map at the end of the rendering process.

Don't delete - the default for this option is on, which meansthat V-Ray will keep the irradiance map in memory until the

next rendering. If this option is cleared, V-Ray will delete theirradiance map when rendering is complete. This means thatyou will not be able to save the map manually afterwards.

Auto save - if this option is set, V-Ray will automatically savethe irradiance map to the specified file at the end of the

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rendering. This mode is particularly useful if you want to sendthe irradiance map for rendering on a different machinethrough network rendering.

Switch to saved map - this option is only available ifthe Auto save option is turned on. If Switch to saved map ison, then V-Ray will also automatically set the irradiance mapmode to From f i le and will set the file name to be that of themap that was just saved.

Notes

You can view, merge and save irradiance maps withthe irradiance map viewer tool.

For animated irradiance maps, GI samples on differentobjects are not shared; this may lead to small objects toappear black in the final renders. To solve this issue,group those objects together - this will work as GIsamples are shared for objects which are part of thesame group.

Global photon map Home Render params Examples

General Parameters

Notes

General

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The global photon map is somewhat similar to the irradiancemap. It is also used to represent the lighting in the scene, andit is a collection of points in 3D space (a point cloud).However, the photon map is built in a different way. It is built

by tracing particles (photons) emitted by the scene lights.Those photons bounce around the scene and hit varioussurfaces. The hit points are stored in the photon map.

Reconstructing the illumination from the photon map is alsodifferent from the irradiance map. With the irradiance map, asimple interpolation is used to blend the nearby GI samples.With the photon map, we need to estimate the

photon density at a given point. The idea of density estimationis central to the photon map. V-Ray can use several methodsfor density estimation, each with its own advantages anddisadvantages. Usually these methods are based on lookingfor the photons that are nearest to the shaded point.

Note that in general, the photon map provides a less accurateapproximation of the scene illumination than the irradiancemap, espcially when it comes to small details. The irradiancemap is built adaptively, whereas the photon map is not. Also amajor disadvantage of the photon map is the boundary bias.This unwanted effect is mostly visible around corners andobject edges, which appear darker than they should be. Theirradiance map can also exhibit boundary bias, however itsadpative nature allows one to decrease the effect greatly.

Another disadvantage of the photon map is that it cannotsimulate illumination from skylight. This is because the

photons need an actual surface to be emitted from. Theskylight, at least in V-Ray, is not a surface actually present inthe scene.

On the other hand, the photon map is view-independent andcan be computed relatively quickly. This makes it ideal for



approximating the scene illumination when used together withmore accurate methods like direct computation or theirradiance map.

Parameters

Note that thebuilding of the photon map is also controlled by the photon

settings of individual lights in the scene. See the Light settingsdialog for more information.

Bounces - this parameter controls the number of lightbounces approximated by the photon map. More bouncesproduce a more reallistic result, but take more time andmemory.

Auto search dist - when this ison , V-Ray will try to compute asuitable distance within which to search for photons.Sometimes the computed distance is ok, in other cases itmight be too big (which will slow down the rendering) or toosmall (which will produce a more noisy result).

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Search dist - this option is only available when Auto searchdist is off. It allows you to specify the photon search distancemanually. Keep in mind that this value depends on the size ofyour scene. Lower values will speed up the rendering but may

produce more noisy results. Larger values will slow down therendering but may produce smoother results.

Max photons - this option specifies how many photons will betaken into consideration when approximating the irradiance atthe shaded point. More photons mean a smoother (and moreblurry) result and may also slow down the rendering. Smallervalues mean a more noisy result but will render faster. When

this value is 0 , V-Ray will use all the photons in the givensearch range.

Multipler - this allows you to control the brightness of thephoton map.

Max density - this parameter allows you to limit the resolution(and thus the memory) of the photon map. Whenever V-Rayneeds to store a new photon in the photon map, it will firstlook if there are any other photons within a distance specifiedby Max density. If there is already a suitable photon in themap, V-Ray will just add the energy of the new photon to theone in the map. Otherwise, V-Ray will store the new photon inthe photon map. Using this options allows you to shoot manyphotons (and thus get smoother results) while keeping thesize of the photon map manageable.

Convert to irradiance map - this will cause V-Ray toprecompute the irradiance at the photon hit points stored inthe photon map. This allows fewer photons to be used wheninterpolated the irradiance during rendering, while keeping theresult relatively smooth. It is important to note that the



resulting map stores irradiance, but is not the same as theirradiance cache used by V-Ray for primary diffuse bounces.

Interp. samples - this controls how many irradiance samples

will be taken from the photon map once it is converted to anirradiance map. Larger values produce smoother results, butmay be slower; smaller values produces more noisy resultsbut rendering is faster.

Convex hull area estimate - when this is o ff , V-Ray will usea simplified algorithm for computing the area, covered by anumber of photons (by only taking the distance to the farthest

photon). This algorithm may cause corners to be darker.Using the convex hull area estimate avoids the dark cornersproblem, but is slower and not as robust.

Store direct light - when this is on , V-Ray will store directillumination in the photon map as well. This may speed up theirradiance map or brute force GI, when used as a primaryengine, and there are lots of lights in the scene. When thisis o ff , direct lighting will be computed always by tracing thenecessary rays. This may slow things down if there are lots oflights in the scene.

Retrace threshold - when this is greater than 0.0, V-Ray willuse brute force GI near corners, instead of the photon map, inorder to obtain a more accurate result and to avoid splotchesin these areas. This may slow down the rendering. When thisis 0.0, the photon map will be used always, which will be

faster, but may produce artifacts near corners or in placeswhere objects are close to each other.

Retrace bounces - controls how many bounces will be madewhen retracing corners. If Retrace threshold is 0.0, then this



parameter is ignored. Typically this should be equal tothe Bounces parameter.

Notes

The photon map cannot simulate secondary illuminationdue to skylight. The photon map is mostly useful forinterior scenes with artificial lighting or relatively smallwindows.

The photon map works only with V-Ray materials.Standard materials will receive GI, but will not generateany photons.

Light cache Home Render params Examples

General

Parameters

Calculation parameters Reconstruction parameters

Mode

On render end

Notes

General

Light caching (sometimes also called light mapping) is atechnique for approximating the global illumination in a scene.This method was developed originally by Chaos Groupspecifically for the V-Ray renderer. It is very similar to photonmapping, but without many of its limitations.



http://help.chaosgroup.com/vray/help/150SP1/examples_lightcache.htm


http://help.chaosgroup.com/vray/help/150SP1/render_params_lightmap.htm#general


http://help.chaosgroup.com/vray/help/150SP1/render_params_lightmap.htm#parameters


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The light cache is built by tracing many many eye paths fromthe camera. Each of the bounces in the path stores theillumination from the rest of the path into a 3d structure, very

similar to the photon map. On the other hand, in a sense, it isthe exact opposite of the photon map, which traces paths fromthe lights, and stores the accumulated energy from thebeginning of the path into the photon map.

Although very simple, the light-caching approach has manyadvantages over the photon map:

It is easier to set up. We only have the camera to trace

rays from, as opposed to the photon map, which mustprocess each light in the scene and usually requiresseparate setup for each light.

The light-caching approach works efficiently with anylights - including skylight, self-illuminated objects, non-physical lights, photometric lights etc. In contrast, thephoton map is limited in the lighting effects it canreproduce - for example, the photon map cannot

reproduce the illumination from skylight or from standardomni lights without inverse-square falloff.

The light cache produces correct results in corners andaround small objects. The photon map, on the otherhand, relies on tricky density estimation schemes, whichoften produce wrong results in these cases, eitherdarkening or brightening those areas.

In many cases the light cache can be visualized directlyfor very fast and smooth previews of the lighting in thescene.



Even with these advantages, light caching is similar in speedto the photon map and can produce approximations to theglobal lighting in a scene very quickly. In addition, the lightcache can be used successfully for adding GI effects to

animations.

Of course, the light cache has some limitations: Like the irradiance map, it is view-dependent and is

generated for a particular position of the camera.

Like the photon map, the light cache is not adaptive. Theillumination is computed at a fixed resolution, which is

determined by the user.

The light cache does not work very well with bump maps.

Parameters



Calculation parameters

These parameters affect the calculation phase of the lightcache; they do not affect the final rendering.

Subdivs - this determines how many paths are traced fromthe camera. The actual number of paths is the square of thesubdivs (the default 1000 subdivs mean that 1 000 000 pathswill be traced from the camera).

Sample size - this determines the spacing of the samples inthe light cache. Smaller numbers mean that the samples willbe closer to each other, the light cache will preserve sharp

details in lighting, but it will be more noisy and will take morememory. Larger numbers will smooth out the light cache butwill loose detail. This value can be either in world units orrelative to the image size, depending on lightcache Scale mode.

Scale - this parameter determines the units of the Samplesize and the Filter size:Screen - the units are fractions of the final image (a value of

1.0 means the samples will be as large as the whole image).Samples that are closer to the camera will be smaller, andsamples that are far away will be larger. Note that the units donot depend on the image resolution. This value is best suitedfor stills or animations where the light cache needs to becomputed at each frame.

World - the sizes are fixed in world units everywhere. This

can affect the quality of the samples - samples that are closeto the camera will be sampled more often and will apearsmoother, while samples that are far away will be noisier. Thisvalue might work better for fly-through animations, since it willforce constant sample density everywhere.



Number of passes - the light cache is computed in severalpasses, which are then combined into the final light cache.Each pass is rendered in a separate thread independently ofthe other passes. This ensures that the light cache is

consistent across computers with different number of CPUs.In general, a light cache computed with smaller number ofpasses may be less noisy than a light cache computed withmore passes, for the same number of samples; however smallnumber of passes cannot be distributed effectively acrossseveral threads. For single-processor non-hyperthreadingmachines, the number of passes can be set to 1 for bestresults.

Store direct light - with this option, the light cache will alsostore and interpolate direct light. This can be useful for sceneswith many lights and irradiance map or direct GI method forthe primary diffuse bounces, since direct lighting will becomputed from the light cache, instead of sampling each andevery light. Note that only the diffuse illumination produced bythe scene lights will be stored. If you want to use the lightcache directly for approximating the GI while keeping thedirect lighting sharp, uncheck this option.

Show calc. phase - turning this option on will show the pathsthat are traced. This does not affect the calculation of the lightcache and is provided only as a feedback to the user. Thisoption is ignored when rendering to fields - in that case, thecalculation phase is never displayed.

Use camera path - when this option is on , V-Ray willcalculate the light cache samples for the entire camera path,instead of just the current view, in the same way as this isdone for the Fly- through mode. This is useful when renderinganimations with moving objects where the camera also movesand the light cache needs to be inSingle frame mode. In this



case, setting the Use camera path option on will help toreduce any flickering, as the GI sample positions on staticgeometry will not change.

Adaptive tracing - when this option is on, V-Ray will storeadditional information about the incoming light for each lightcache sample, and try to put more samples into the directionsfrom which more light coming. This may help tp reduce thenoise in the light cache, particularly in the case of caustics.

Use directions only - this option is only available whenthe Adaptive tracing option is on. It causes V-Ray to only

use the optimized directions, generated from the light cachesamples, rather than the accumulated irradiance from thesamples themselves. This produces more accurate results,but also a noisier light cache.

Reconstruction parameters

These parameters control how the light cache is used in thefinal rendering, after is has been calculated.

Pre-filter - when this is turned on, the samples in the lightcache are filtered before rendering. Note that this is differentfrom the normal light cache filtering (see below) whichhappens during rendering. Prefiltering is performed byexamining each sample in turn, and modifying it so that itrepresents the average of the given number of nearbysamples. More prefilter samples mean a more blurry and lessnoisy light cache. Prefiltering is computed once after a newlight cache is computed or loaded from disk.

Filter - this determines the type of render-time filter for thelight cache. The filter determines how irradiance isinterpolated from the samples in the light cache.None - no filtering is performed. The nearest sample to theshaded point is taken as the irradiance value. This is the



fastest option, but it may produce artifacts near corners, if thelight cache is noisy. You can use pre-filtering (see above) todecrease that noise. This option works best if the light cacheis used for secondary bounces only or for testing purposes.

Nearest - this filter looks up the nearest samples to theshading point and averages their value. This filter is notsuitable for direct visualization of the light cache, but is usefulif you use the light cache for secondary bounces. A propertyof this filter is that is adapts to the sample density of the lightcache and is computed for a nearly constant time.The Interpolation samples parameter determines how many

of the nearest samples to look up from the light cache.

Fixed - this filter looks up and averages all samples from thelight cache that fall within a certain distance from the shadedpoint. This filter produces smooth results and is suitable fordirect visualization of the light cache (when it is used as theprimary GI engine). The size of the filter is determined bythe Filter size parameter. Larger values blur the light cacheand smooth out noise. Typical values for the Filter size are 2-6 times larger than the Sample size. Note that Filtersize uses the same scale as the Sample size and itsmeaning depends on the Scale parameter.

Use light cache for glossy rays - if this option is on , the lightcache will be used to compute lighting for glossy rays as well,in addition to normal GI rays. This can speed up rendering ofscenes with glossy reflections quite a lot.

Mode

Mode - determines the rendering mode of the light cache:Progress ive path trac ing - in this mode, the light cachealgorithm is used to sample the final image progressively. Fora discussion of this mode see the tutorial.

http://help.chaosgroup.com/vray/help/150SP1/tutorials_pathtracing.htm






Single frame - this will compute a new light cache for eachframe of an animation.

Fly- through - this will compute a light cache for an entire fly-

through animation, assuming that the cameraposition/orientation is the only thing that changes. Themovement of the camera in the active time segment only istaken in consideration. Note that it may be better touse World Scale for fly-through animations. The light cache iscomputed only at the first rendered frame and is reusedwithout changes for subsequent frames.

From f i le - in this mode the light cache is loaded from a file.The light cache file does not include the prefiltering of the lightcache; prefiltering is performed after the light cache is loaded,so that you can adjust it without the need to recompute thelight cache.

File - specifies the file name to load the light cache from,when the Mode is set to From f i le .

Save to file - this button allows to save the light cache to a fileon disk, for later re-use. Note that the Don't delete optionmust be on for this to work - otherwise, the light cache will bedeleted as soon as rendering is complete and it will not bepossible to save it.

On render end

This group of controls determine what happens with the lightcache after rendering is complete.

Don't delete - when on (the default), the light cache remainsin memory after the rendering. Turn this option o ff toautomatically delete the light cache (and thus save memory).



Auto save - when on , the light cache will be automaticallywritten to the specified file. Note that the light cache will bewritten as soon as it is calculated, rather than at the actualend of the rendering.

Switch to saved map - when on , after the rendeing iscomplete, the light cache Mode will be automatically setto From f i le and the name of the auto-saved light cache filewill be copied to the File parameter.

Notes

Do not set the Adaptive amount in the DMCsampler rollup to 0.0 when using the light cache, as thiswill cause excessive render times.

Do not apply perfectly white or very close to whitematerials to a majority of the objects in the scene, as thiswill cause excessive render times. This is because theamount of reflected light in the scene will decrease verygradually and the light cache will have to trace longer

paths. Also avoid materials that have one of their RGBcomponents set to maximum (255 ) or above.

If you want to use the light cache for animation, youshould choose a large enough value for the Filter sizeinorder to remove the flickering in the GI.

There is no difference between light caches computedfor primary bounces (direct visualization) and forsecondary bounces. You can safely use light cachescomputed in one of these modes for the other.

Similar to the photon map, you can get "light leaks" withthe light cache around very thin surfaces withsubstantially different illumination on both sides.









Sometimes it may be possible to reduce this effect byassigning different GI Surface ID's to the objects on bothsides of the thin surface (see the Object settingsdialog);the effect can also be reduced by decreasing

the Sample size and/or the filtering.

Caustics Home Render params Examples

General

Parameters

Notes

General

V-Ray supports the rendering of the caustics effects. In orderto produce this effect you must have proper causticsgenerators and caustics receivers in the scene (forinformation how to make an object a causticsgenerator/receiver read the Object settings and Lightssettings sections in Render parameters > System>Object/Light settings. The settings in this parameter sectioncontrol the generation of the photon map (an explanation ofthe photon map can be found in the Terminology section).

In order to calculate the caustics effects, V-Ray uses atechnique known as photon mapping. It is a two-passtechnique. The first pass consists of shooting particles(photons) from the light sources in the scene, tracing them as

they bounce around the scene, and recording the placeswhere the photons hit the object surfaces. The second pass isthe final rendering, when the caustics are calculated byusing density estimation techniques on the photon hits storedduring the first pass.

http://help.chaosgroup.com/vray/help/150SP1/global_settings.htm




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Parameters

On - turnsrendering of causticson and o ff .

Multiplier - this multiplier controls the strength of the caustics.It is global and applies to all light sources that generatecaustics. If you want different multipliers for the different lightsources then you should use the local light settings.Note: thismultiplier is cumulative with the multipliers in the local lightsettings.

Search distance - when V-Ray needs to render the causticseffect at a given surface point, it searches for a numberphotons on that surface in the area surrounding the shadedpoint (search area). The search area in fact is a circle withcenter the original photon and its radius is equal to theSearchdistance value. Smaller values produce sharper, but perhaps

more noisy caustics; larger values produce smooher, butblurrier caustics.

Max photons - this is the maximum number of photons thatwill be considered when rendering the caustics effect on asurface. Smaller values cause less photons to be used and



the caustucs will be sharper, but perhaps noisier. Largervalues produce smoother, but blurrier caustics. The specialvalue of 0 means that V-Ray will use all the photons that it canfind inside the search area.

Max density - this parameter allows you to limit the resolution(and thus the memory) of the caustics photon map. WheneverV-Ray needs to store a new photon in the caustics photonmap, it will first look if there are any other photons within adistance specified by Max density. If there is already asuitable photon in the map, V-Ray will just add the energy ofthe new photon to the one in the map. Otherwise, V-Ray will

store the new photon in the photon map. Using this optionsallows you to shoot many photons (and thus get smootherresults) while keeping the size of the caustics photon mapmanageable.

Mode - controls the mode of the irradiance map:New map - when this option is selected a new photon mapwill be generated. It will overwrite any previous photon mapleft over from previous rendering.

Save to fi le - hit this button if you want to save an alreadygenerated photon map in a file.

From f i le - when you enable this option V-Ray will notcompute the photon map but will load it from a file. Hitthe Browse button on the right to specify the file name.

File - the file name with the caustics photon map to be loadedwhen the Mode is set to From f i le .

Don't delete - when checked, V-Ray will keep the photonmap in memory after the scene rendering has finished.



Otherwise the map will be deleted and the memory it takeswill be freed. This option can be especially useful if you wantto compute the photon map for a particular scene only onceand then reuse it for further rendering.

Auto save - when this is turned on, V-Ray will automaticallysave the caustics photon map to the provided file whenrendering is complete.

Switch to saved map - this option is only available if Autosave is on. It will cause V-Ray to automatically setthe Mode to From f i le with the file name of the newly saved

map.

Notes

Caustics also depend on the individual light settings(see Light settings dialog).

Environment Home Render params

General

Parameters

GI Environment (skylight)

Reflection/Refraction environment

Refraction environment

Notes

General






http://help.chaosgroup.com/vray/help/150SP1/render_params_environment.htm#general


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http://help.chaosgroup.com/vray/help/150SP1/render_params_environment.htm#gi_env


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The Environment section in V-Ray render parameters iswhere you can specify a color and a texture map to be usedduring GI and reflection/refraction calculations. If you don'tspecify a color/map then the background color and map

specified in the 3ds Max Environment dialog will be used bydefault.

Parameters

GI Environment (skylight)

This group allows you to override the 3ds Max Environmentsettings for indirect illumination calculations. The effect ofchanging the GI environment is similar to skylight.

On - turns on and o ff the GI environment override.

Color - lets you specify the environment (skylight) color. Notethat this is ignored if there is an environment texture specified.

Multiplier - a multiplier for the color value. Note that themultiplier does not affect the environment texture (if present).Use an Output map to control the brightness of theenvironment map if the map itself does not have brightnesscontrols.

Texture - lets you choose a GI environment texture. Note thatif present, the texture overrides the specifiedColor .



Reflection/refraction environment

This group allows you to override the 3ds Max Environmentsettings when reflections and refractions are calculated. Notethat you can also override the reflection/refraction

environment on a per material basis (seeVRayMtl) or a permap basis (see VRayMap). If you do not enable theRefraction override, this group of controls affects bothreflections and refractions. If you enable the Refractionoverride, then this group affects only reflections.

On - with this option turned on V-Ray will use thespecified Color and Texture during reflection/refraction

calculations.

Color - lets you specify the environment color forreflections/refractions. This is ignored, if there is anenvironment texture specified.

Multiplier - a multiplier for the color value. Note that themultiplier does not affect the environment texture (if present).Use an Output map to control the brightness of the

environment map, if the map itself does not have brightnesscontrols.

Texture - lets you choose an environment texture texture.Note that if specified, this texture overrides the Color .

Refraction environment

This group allows to override the environment for refractionrays only. When this override is disabled, V-Ray will use the

environment specified in the Reflection/refraction group whencalculating refractions.

On - enables the refraction environment override.









Color - specifies the environment color for refractions. Thiscolor is ignored if there is an environment texture specified.

Multiplier - a multiplier for the Color value. Note that themultiplier does not affect the environment texture (if present).Use an Output map to control the brightness of theenvironment map, if the map itself does not have brightnesscontrols.

Texture - specifies the environment texture for refractions.Note that if present, this texture overrides the specified Color .

DMC sampler Home Render params Examples

General Parameters References

General

Monte Carlo (MC) sampling is a method for evaluating "blurry"values (anitaliasing, depth of field, indirect illumination, arealights, glossy reflections/refractions, translucency, motion bluretc). V-Ray uses a variant of Monte Carlo samplingcalled deterministic Monte Carlo (DMC). The differencebetween pure Monte Carlo sampling and deterministic Monte

Carlo is that the first uses pseudo-random numbers which aredifferent for each and every evaluation (and so re-rendering asingle image will always produce slightly different results inthe noise), while deterministic Monte Carlo uses a pre-definedset of samples (possibly optimized to reduce the noise), whichallows re-rendering an image to always produce the exact



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same result. By default, the deterministic Monte Carlo methodused by V-Ray is a modficiation of Schlick sampling,introduced by Christophe Schlick in [1] (seethe References section below for more information).

Note that there exists a sub-set of DMC sampling called quasi Monte Carlo (QMC) sampling, in which the samples areobtained from sequences of numbers, called low-discrepancysequences, which have special numeric properties. V-Ray,however, does not use this technique.

Instead of having separate sampling methods for each of the

blurry values, V-Ray has a single unified framework thatdetermines how many and what exactly samples to be takenfor a particular value, depending on the context in which thatvalue is required. This framework is called the "DMCsampler".

The actual number of samples for any blurry value isdetermined based on three factors:

The subdivs value supplied by the user for a particularblurry effect. This is multiplied by the Global subdivsmultiplier (see below).

The importance of the value (for example, dark glossyreflections can do with fewer samples than bright ones,since the effect of the reflection on the final result issmaller; distant area lights require fewer samples than

closer ones etc). Basing the number of samplesallocated for a value on importance is called importancesampling.

The variance (think "noise") of the samples taken for aparticular value - if the samples are not very different

http://help.chaosgroup.com/vray/help/150SP1/render_params_dmc.htm#ref1










from each other, then the value can do with fewersamples; if the samples are very different, then a largernumber of them will be necessary to get a good result.This basically works by looking at the samples as they

are computed one by one and deciding, after each newsample, if more samples are required. This technique iscalled early termination or adaptive sampling.

For more information on the relationship and effects of theseparameters, please refer to the tutorials section.

Parameters

Amount - controls the extent to which the number of samplesdepends on the importance of a blurry value. It also controlsthe minimum number of samples that will be taken. A value of

1.0 means full adaptation; a value of 0.0 means noadaptation.

Min samples - determines the minimum number of samplesthat must be made before the early termination algorithm isused. Higher values will slow things down but will make theearly termination algorithm more reliable.

Noise threshold - controls V-Ray's judgement of when ablurry value is "good enough" to be used. This directlytranslates to noise in the result. Smaller values mean lessnoise, more samples and higher quality. A value of 0.0 meansthat no adaptation will be performed.







Global subdivs multiplier - this will multiply all subdivsvalues everywhere during rendering; you can use this toquickly increase/decrease sampling quality everywhere. Thisaffects everything, except for the lightmap, photon map,

caustics and aa subdivs. Everything else (dof, moblur,irradiance map, brute-force GI, area lights, area shadows,glossy reflections/refractions) is affected by this parameter.

Time independent - when this option is On , the samplingpattern will be the same from frame to frame in an animation.Since this may be undesirable in some cases, you can turnthis option Off to make the samping pattern change with time.

Note that re-rendering the same frame will produce the sameresult in both cases.

Path sampler - specifies what algorithm to use to generate

sample values. V-Ray uses a modification of Schlick

sampling (see the References section below for more details).

References

More information on deterministic Monte Carlo sampling forcomputer graphics can be found from the sources listedbelow.

[1] C. Schlick, An Adaptive Sampling Technique forMultidimensional Integraton by Ray Tracing, inSecond Eurographics Workshop on Rendering (Spain),1991, pp. 48-56Describes deterministic MC sampling for antialiasing,motion blur, depth of field, area light sampling and glossyreflections.

[2] K. Chiu, P. Shirley and C. Wang, Multi-JitteredSampling, in Graphics Gems IV, 1994







Describes a combination of jittered and N-rooks samplingfor the purposes of computer graphics.

[3] Masaki Aono and Ryutarou Ohbuchi, Quasi-Monte

Carlo Rendering with Adaptive Sampling, IBM TokyoResearch Laboratory Technical Report RT0167,November 25, 1996, pp.1-5

An online version can be found athttp://www.kki.yamanashi.ac.jp/~ohbuchi/online_pubs/eg96_html/eg96.htm Describes an application of low discrepancy sequencesto area light sampling and the global illumination

problem.

[4] M. Fajardo, Monte Carlo Raytracing in Action,in State of the Art in Monte Carlo Ray Tracing forRealistic Image Synthesis, SIGGRAPH 2001 Course21, pp. 151-162;

An online version can be found athttp://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/papers/Monte Carlo/Monte Carlo SIGGRAPH

Course.pdf Describes the ARNOLD renderer employing randomizedquasi-Monte Carlo sampling using low discrepancysequences for pixel sampling, global illumination, arealight sampling, motion blur, depth of field, etc.

[5] E. Veach, December, Robust Monte Carlo Methodsfor Light Transport Simulation, Ph. D. dissertation for

Stanford University, 1997, pp. 58-65 An online version can be foundat http://graphics.stanford.edu/papers/veach_thesis/ Includes a description of low discrepancy sequences,quasi-Monte Carlo sampling and its application to solvingthe global illumination problem.

http://www.kki.yamanashi.ac.jp/~ohbuchi/online_pubs/eg96_html/eg96.htm



http://www.cs.virginia.edu/~gfx/Courses/2003/ImageSynthesis/papers/Monte%20Carlo/Monte%20Carlo%20SIGGRAPH%20Course.pdf




http://graphics.stanford.edu/papers/veach_thesis/











[6] L. Szirmay-Kalos, Importance Driven Quasi-MonteCarlo Walk Solution of the Rendering Equation,Winter School of Computer Graphics Conf., 1998

An online version can be found

at http://www.fsz.bme.hu/~szirmay/imp1_link.html Describes a two-pass method for solving the globalillumination problem employing quasi-Monte Carlosampling, as well as importance sampling using lowdiscrepancy sequences.

Color Mapping Home Render params Examples

General Parameters Notes

Search keyword s: color mapping, tone mapping, burn-out, overexpose

General

Color mapping (also called tone mapping) can be used toapply color transformations on the final image colors.Sometimes an image can contain a higher range of colors thatcan be displayed on a computer screen. Color mapping hasthe task of re-mapping the image values to be suitable fordisplay purposes.

Parameters

Type - this isthe type oftransformationused. These

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are the possible types:Linear mu lt ip ly - this mode will simply multiply the final imagecolors based on their brightness are. Color components thatare too bright (above 1.0 or 255) will be clipped. This can

result in burnt out spots near bright light sources.

Exponent ia l - this mode will saturate the colors based ontheir brightness. This can be useful to prevent burn-outs invery bright areas (for example around light sources etc). Thismode will not clip bright colors, but will instead saturate them.

HSV exponential - this mode is very similar to

the Exponent ia l mode, but it will preserve the color hue andsaturation, instead of washing out the color towards white.

Intensi ty exponent ia l - this mode is similar tothe Exponent ia l one, but it will preserve the ratio of the RGBcolor components and will only affect the intensity of thecolors.

Gamm a correc t ion - this mode applies a gamma curve to thecolors. In this case, the Dark multiplier is a general multiplierfor the colors before they are gamma-corrected. The Brightmultiplier is the inverse of the gamma value (f.e. forgamma 2.2 , the Bright multiplier must be 0.4545 ).

Intensi ty gamma - this mode applies a gamma curve to theintensity of the colors, instead of each channel (r/g/b)independently.

Reinhard - this mode is a blend between exponential-stylecolor mapping and linear mapping. If the Burn value is 1.0, theresult is linear color mapping and if the Burn value is 0.0, theresult is exponential-style mapping.



Dark multiplier - this is the multiplier for dark colors.

Bright multiplier - this is the multiplier for bright colors.

Gamma - this parameter allows the user to control the gammacorrection for the output image regardless of the colormapping mode. Note that the value here is the inverse of theone used for the Gamma correct ion color mapping type. Forexample, to correct the image for a 2.2-gamma display, youshould set the Gammaparameter simply to 2.2 .

Sub-pixel mapping - this option controls whether color

mapping will be applied to the final image pixels, or to theindividual sub-pixel samples. In older versions of V-Ray, thisoption was always assumed to be on , however its defaultvalue is now o ff as this produces more correct renderings,especially if you use the universal settingsapproach.

Clamp output - if this is on , colors will be clamped after colormapping. In some situations, this may be undesirable (forexample, if you wish to antialias hdr parts of the image, too) -in that case, turn clamping o ff .

Clamp level - this option specifies the level at which colorcomponents will be clamped if the Clamp outputoption is on .

Affect background - if this is o ff , color mapping will not affectcolors belonging to the background.

Don't affect colors (adaptation only) - when this parameteris on, the color mapping will not be applied to the final image,however V-Ray will proceed with all its calculations as thoughcolor mapping is applied (e.g. the noise levels will becorrected accordingly). This can be useful, for example, if you

http://help.chaosgroup.com/vray/help/150SP1/tutorials_unisettings.htm





know that you will apply some color correction to the imagelater on, but wish to keep the rendering itself in linear spacefor compositing purposes. Note that the Clamp output optionwill have an effect regardless of the value of the Don't affect

colors option.

Linear workflow - when this option is checked V-Ray willautomatically apply the inverse of the Gamma correction thatyou have set in the Gamma field to all VRayMtl materials inyour scene. Note that this option is intended to be usedonly for quickly converting old scenes which are not setup with proper linear workflow in mind. This option is not

a replacement for proper linear workflow.

Camera Home Render params Examples

General Parameters Camera type

Depth of field Motion blur General motion blur parameters Notes

General

The camera rollout controls the way the scene geometry isprojected onto the image. Note that if you usetheVRayPhysicalCamera in your scene, most of theparameters in this section are ignored, with the exception ofsome of the motion blur parameters (those on the right-handside of the dialog),






http://help.chaosgroup.com/vray/help/150SP1/examples_camera.htm


http://help.chaosgroup.com/vray/help/150SP1/render_params_camera.htm#general


http://help.chaosgroup.com/vray/help/150SP1/render_params_camera.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/render_params_camera.htm#cameratype


http://help.chaosgroup.com/vray/help/150SP1/render_params_camera.htm#dof


http://help.chaosgroup.com/vray/help/150SP1/render_params_camera.htm#mblur


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Parameters

Camera type

The cameras in V-Ray generally define the rays that are castinto the scene, which essentially is how the scene is projectedonto the screen. V-Ray supports several camera

types: Standard ,Spherical , Cylindrical (point),Cylindrical(ortho), Box and Fish eye. Orthographic views are supportedtoo.

For V-Ray versions prior to SP3 the parameters in this sectionare ignored, if you are rendering from aVRayPhysicalCamera. V-Ray SP3 and later version take the settings in this menuinto consideration.

Override FOV - with this setting you can override the 3dsMax's FOV angle. This is because some V-Ray camera typescan take FOV ranges from 0 to 360 degrees, whereas thecameras in 3ds Max are limited to 180 degrees.






FOV - here you specify the FOV angle (only when OverrideFOV is turned on and the current camera type supports FOVangle).

Height - here you can specify the height of the Cyl indr ical(or tho) camera. This setting is available only whenthe Type is set to Cyl indr ical (or tho ) .

Auto-fit - this setting controls the auto-fit option of the Fish-eye camera. When Auto-fit is enabled V-Ray will calculatethe Dist value automatically so that the rendered image fitshorizontally with the image's dimensions.

Dist - this setting applies only to the Fish-eye camera.The Fish-eye camera is simulated as a Standard camerapointed to an absolutely reflective sphere (with a radius of 1.0)that reflects the scene into the camera's shutter.The Dist value contorts how far is the camera from thesphere's center (which is how much of the sphere will becaptured by the camera). Note: this setting has no effectwhen the Auto-fit option is enabled.

Curve - this setting applies only to the Fish-eye camera. Thissetting contorts the way the rendered image is warped. Avalue of 1.0 corresponds to a real world Fish-eye camera. Asthe value approaches 0.0 the warping is increased. As thevalue approaches 2.0 the warping is reduced. Note: in factthis value controls the angle at which rays are reflected by thevirtual sphere of the camera.

Type - from this list you can select the type of the camera.See the Examples section for a more detailed discussion oncamera types.Standard - this is a standard pinhole camera.







On - turns the depth-of-field effect on .

Aperture - this is the size of the virtual camera aperture, inworld units. Small aperture sizes reduce the DOF effect,

larger sizes produce more blur.

Center bias - this determines the uniformity of the DOF effect. A value of 0.0 means that light passes uniformly through theaperture. Positive values mean that light is concentratedtowards the rim of the aperture, while negative valuesconcentrate light at the center.

Focal distance - determines the distance from the camera atwhich objects will be in perfect focus. Objects closer or fartherthan that distance will be blurred.

Get from camera - when this option is on, the Focaldistance is determined from the camera target, if therendering is done froma camera view.

Sides - this option allows you to simulate the polygonal shapeof the aperture of real-world cameras. When this option is o ff ,the shape is assumed to be perfectly circular.

Rotation - specifies the orientation of the aperture shape.

Anisotropy - this option allows the stretching of the bokeheffect horizontally or vertically. Positive values stretch theeffect in the vertical direction. Negative values stretch it in the

horizontal direction.

Subdivs - controls the quality of the DOF effect. Lower valuesare computed faster, but produce more noise in the image.Higher values smooth out the noise, but take more time torender. Note that the quality of sampling also depends on the



settings of the DMC sampler as well as on the chosen Imagesampler .

Motion blur

On - turns motion blur on.

Duration - specifies the duration, in frames, during which thecamera shutter is open.

Interval center - specifies the middle of the motion blurinterval with respect to the 3ds Max frame. A valueof 0.5 means that the middle of the motion blur interval ishalfway between the frames. A value of 0.0 means that the

middle of the interval is at the exact frame position.

Bias - this controls the bias of the motion blur effect. A valueof 0.0 means that the light passes uniformly during the wholemotion blur interval. Positive values mean that light isconcentrated towards the end of the interval, while negativevalues concentrate light towards the beginning.

General mo tion blu r parameters

These parameters are used whether you are rendering from astandard camera or from a VRayPhysicalCamerawith motionblur enabled.

Prepass samples - this controls how many samples in timewill be computed during irradiance map calculations.

Blur particles as mesh - this option controls the blurring of

particle systems. When this is on , particles will be blurred likenormal meshes. However, many particle systems change thenumber of particles between frames. You can turn off thisoption to compute the motion blur from the velocity of theparticles instead.




http://help.chaosgroup.com/vray/help/150SP1/render_params_imagesampler.htm












Geometry samples - this determines the number of geometrysegments used to approximate motion blur. Objects areassumed to move linearly between geometry samples. Forfast rotating objects, you need to increase this to get correct

motion blur. Note that more geometry samples increase thememory consumption, since more geometry copies are kept inmemory. You can also control the number of geometrysamples on a per-object basis from the Object settings dialog.

Subdivs - determines the quality of the motion blur. Lowervalues are computed faster, but produce more noise in theimage. Higher values smooth out the noise, but take more

time to render. Note that the quality of sampling also dependson the settings of the DMC sampler as well as on thechosen Image sampler .

Default displacement Home Render params

General

Parameters

Notes

General

This section allows you to control displacement of objects withdisplacement materials, which do nothave aVRayDisplacementMod modifier applied.

Parameters












http://help.chaosgroup.com/vray/help/150SP1/render_params_displacement.htm#general


http://help.chaosgroup.com/vray/help/150SP1/render_params_displacement.htm#parameters


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OverrideMax's - when this option is on , V-Ray will render objects withdisplacement materials using its own internal microtriangledisplacement. When this option is o ff , the objects will berendered with the standard 3ds Max displacement.

Edge length - this determines the quality of the displacement.Each triangle of the original mesh is subdivided into a number

of subtriangles. More subtriangles mean more detail in thedisplacement, slower rendering times and more RAM usage.Less subtriangles mean less detail, faster rendering and lessRAM. The meaning of Edge length depends on the View-dependent parameter below.

View-dependent - when this is on, Edge length determinesthe maximum length of a subtriangle edge, in pixels. A valueof 1.0 means that the longest edge of each subtriangle will beabout one pixel long when projected on the screen. WhenView-dependent is off, Edge length is the maximumsubtriangle edge length in world units.

Max. subdivs - this controls the maximum subtrianglesgenerated from any triangle of the original mesh. The value isin fact the square root of the maximum number ofsubtriangles. For example, a value of 256 means that at

most 256 x 256 = 65536 subtriangles will be generated for anygiven original triangle. It is not a good idea to keep this valuevery high. If you need to use higher values, it will be better totesselate the original mesh itself into smaller triangles instead.From build 1.45.20 onward, the actual subdivisions for atriangle are rounded up to the nearest power of two (this



makes it easier to avoid gaps because of different tesselationon neighboring triangles).

Tight bounds - when this is on, V-Ray will try to compute the

exact bounding volume of the displaced triangles from theoriginal mesh. This requires pre-sampling of the displacementtexture, but the rendering will be faster, if the texture has largeblack or white areas. However, if the displacement texture isslow to evaluate and varies a lot between full black and white,if may be faster to turn this option off. When it is off, V-Ray willassume worst-case bounding volumes, and will not presamplethe texture.

Amount - this is a scaling parameter for the defaultdisplacement. Values larger than 1.0 increase thedisplacement amount, while values lower than 1.0 reduce it.

Relative to bbox - if this parameter is on , the actualdisplacement amount is based on the bounding box of theobjects, like this is done by 3ds Max itself by default. If thisoption is off , the displacement is expressed in generic worldunits where white areas in the displacement map correspondto displacement of 1 generic unit. You can usethe Amount parameter to increase or decrease displacementamount.

System Home Render params

General Parameters Raycaster parameters Render region division Distributed rendering



http://help.chaosgroup.com/vray/help/150SP1/render_params_system.htm#general


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Frame stamp Object settings Light settings Presets

V-Ray log Other parameters

Search keywords : System, VRay System, raycaster, frame stamp,

geometry

General

In this section you can adjust a variety of V-Ray parametersrelated to the overall operation of the renderer.

Parameters

http://help.chaosgroup.com/vray/help/150SP1/render_params_system.htm#frameStamp


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http://help.chaosgroup.com/vray/help/150SP1/render_params_system.htm#presets


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Raycaster parameters

Here you can control various parameters of V-Ray's BinarySpace Partitioning (BSP) tree.

One of the basic operations that V-Ray must performisraycasting - determining if a given ray intersects anygeometry in the scene, and if so - identifying that geometry.The simplest way to implement this would be to test the rayagainst every single render primitive (triangle) in the scene.Obviously, in scenes with thousands or millions of trianglesthis is going to be very slow. To speed this process, V-Rayorganizes the scene geometry into a special data structure,

called a binary space partitioning (BSP) tree.

The BSP tree is a hierarchical data structure, built bysubdividing the scene in two parts, then looking at each ofthose two parts and subdividing them in turn, if necessary andso on. Those "parts" are callednodes of the tree. At the top ofthe hierarchy is the root node - which represents the boundingbox of the whole scene; at the bottom of the hierarchy arethe leaf nodes - they contain references to actual triangles

from the scene.

Max tree depth - the maximum depth of the tree. Largervalues will cause V-Ray to take more memory, but therendering will be faster - up to some critical point. Valuesbeyond that critical point (which is different for every scene)will start to slow things down. Smaller values for thisparameter will cause the BSP tree to take less memory, but

rendering will be slower.

Min leaf size - the minimum size of a leaf node. Normally thisis set to 0.0, which means that V-Ray will subdivide the scenegeometry regardless of the scene size. By setting this to a



Dynamic memory limit - the total RAM limit for the dynamicraycasters. Note that the memory pool is shared between thedifferent rendering threads. Therefore, if geometry needs tobe unloaded and loaded too often, the threads must wait for

each other and the rendering performance will suffer.Render region division

Here you can control various parameters of V-Ray's renderingregions (buckets). The bucket is an essential part of thedistributed rendering system of V-Ray. A bucket is arectangular part of the currently rendered frame that isrendered independently from other buckets. Buckets can besent to idle LAN machines for processing and/or can be

distributed between several CPUs. Because a bucket can beprocessed only by a single processor the division of the framein too small a number of buckets can prevent the optimalutilization of computational resources (some CPUs stay idleall the time). However the division of the frame in too manybuckets can slow down the rendering because there is asome time overhead related with each bucket (bucket setup,LAN transfer, etc).

X - determines the maximum region width in pixels (RegionW/H is selected) or the number of regions in the horizontaldirection (when Region Count is selected)

Y - determines the maximum region height in pixels (RegionW/H is selected) or the number of regions in the verticaldirection (when Region Count is selected)

Region sequence - determines the order in which the regionsare rendered. Note that the default Triangulat ion sequence isbest if you use a lof of dynamic geometry (displacement-mapped objects, VRayProxy or VRayFur objects), since itwalks through the image in a very consistent manner so thatgeometry that was generated for previous buckets can be










used for the next buckets. The other sequences tend to jumpfrom one end of the image to another which is not good withdynamic geometry.

Reverse sequence - reverses the region sequence order.

Previous render - this parameter determines what should bedone with the previous image in the virtual frame buffer whenrendering starts. Note that this parameter has no effect on thefinal result of the rendering; it is implemented simply as aconvenient way to distinguish between parts from the currentframe being rendered, and part left over from the previousrendering. The possible values are:Unchanged - no changes will be made - the virtual framebuffer remains the same;

Cross - every second pixel of the image will be set to black;

Fields - every other line of the image will be set to black;

Darken - the colors in the image will be darkened.

Blue - the previous image is tinted in blue.

Distributed rendering

Distributed rendering is the process of computing a singleimage over several different machines. Note that this isdifferent from distributing the frame over several CPU's in asingle machine, which is called multithreading. V-Ray

supports multithreading, as well as distributed rendering.

Before you can use the distributed rendering option, you mustdetermine the machines that will take part in thecomputations. Both 3ds Max and V-Ray need to be properlyinstalled on those machines, although they don't need to be



authorized. You must make sure that the V-Ray spawnerapplication is running on those machines - either as a service,or as a stand-alone application. Refer to the Installationsection for more details on configuring and running the V-Ray

spawner.

For additional information on distributed rendering, pleaserefer to the dedicated Distributed rendering section.

Distributed rendering - this checkbox specifies whether V-Ray will use distributed rendering.

Settings... - this button opens the V-Ray distributedrendering settings dialog. See the Distributedrenderingsection for more information.

Frame stamp

The frame stamp is a convenient way to put some short textover the rendered images. It can be useful in many ways - forexample, in network rendering, to quickly determine whichframes were rendered by which machine. The frame stamp is

one line of text, which appears at the bottom of the image.

Checkbox - turns the frame stamp on and off.

Edit box - here you enter the text you wish to appear in theimages. You can also use some special keywords, all of whichbegin with the percent symbol (%). The keywords arereplaced by V-Ray with the corresponding value:

Keyword Meaning

%vrayversion the current version of V-Ray

%filename the name of the current scene file

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%frame the number of the current frame

%primitives * the number of unique intersectable primitives generated fo

%rendertime the render time for the current frame

%computername the network name of the computer

%date the current system date

%time the current system time

%w the width of the image in pixels

%h the height of the image in pixels

%camera the name of the camera for this frame (if rendering from a

%"<maxscript parameter name>"the value of any V-Ray parameter, given its MaxScript nam

parameter name in quotation marks ("). Also note that this

%ram the amount of physical memory (in KBytes) installed on the

%vmem the amount of virtual memory (in KBytes) available on the s

%mhz the clock speed of the system CPU(s)

%os the operating system

* An intersectable primitive is a primitive that provides a directmethod for intersection with a ray (such as a triangle, theinfinite plane generated by a VRayPlane plugin etc). Most

often, the number of these primitives is the same as thenumber of triangles (faces) processed by V-Ray for thecurrent frame. Note that this may be different from the totalnumber of triangles in the scene. With the dynamic raycaster,only geometry that is actually needed is generated and







accounted for. Geometry that is not generated is not includedin this count.

Font - this button allows you to choose a font and font

attributes for the text in the frame stamp.

Full width - when this option is checked, the frame stamp willtake the whole width of the image, otherwise the stamp will beonly as wide as the text is.

Justify - specifies the position of the stamp:Left - the stamp is placed on the left of the image.

Center - the stamp is centered.Right - the stamp is placed on the right side of the image.

Object Settings / Light Settings

These buttons bring up the dialogs for the local object andlight settings.

Presets

This button brings up the presets dialog.

V-Ray log

These parameters controlthe V-Ray messages window. During rendering, V-Ray writesvarious information in the file C:\VRayLog.txt. The messageswindow shows some of that information so that you can view itwithout the need to manually open that file.





http://help.chaosgroup.com/vray/help/150SP1/presets.htm








Each message can fall into one of four categories, which arecolored in a different way in the messages window. Thosecatergories are errors (colored in red), warnings (colored in

green), informative messages (colored in white) and debugmessages (colored in black).

Show window - when this is turned on, V-Ray will show themessages window at the start of every render.

Level - this determines what kind of messages will be showedin the window:

1 - only error messages2 - error and warning messages3 - errors, warnings and informative messages4 - all messages

Log file - this parameter determines the location and thename of the log file. The default log file is C:\VRayLog.txt

Other parameters

MAX-compatible ShadeContext - V-Ray carries all itscomputations in world space. However, some 3ds Max

plugins (notably atmospherics) take it as granted that the

renderer works in camera space, because this is what the

default scanline renderer does. To preserve compatibility with

such plugins, V-Ray emulates work in camera space by

converting the various points and vectors passed to and from

other plugins. In addition to slowing down V-Ray by forcing itto convert values all the time, working in camera space

messes up with camera modifiers such as the Technical

camera script. This why you have the option of turning off the

camera-space emulation.



Check for missing files - when this is on, V-Ray will try tofind any missing files in the scene and will put up a dialoglisting them, if there are any. The missing files will also be

printed to the C:\VRayLog.txt file. If this option is on, and yourender the scene with distributed rendering, and if a renderservers detects missing files, it will refuse to render the scene.

Optimized atmospheric evaluation - normally in 3ds Max,atmospherics are avaluated after the surface behind them hasbeen shaded. This may be unnecessary if the atmospheric isvery dense and opaque. Turning this option on will cause V-

Ray to first evaluate the atmospheric effects, and shade thesurface behind them only if the atmospherics are sufficientlytransparent.

Low thread priority - turning this on will cause V-Ray to usethreads of lower priority when rendering.

VRayMtl parameters

Home Examples

General Parameters Basic parameters Diffuse Reflection Refraction

Translucency BRDF Options Maps Reflect interpolation Refract interpolation


http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#basic


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#diffuse


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#reflection


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http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#sss


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#brdf


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#options


http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#maps


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Notes

General

A special material - the VRayMtl - is provided with the V-Rayrenderer. This allows for better physically correct illumination(energy distribution) in the scene, faster rendering, moreconvenient reflection and refraction parameters. Withinthe VRayMtl you can apply different texture maps, control thereflections and refractions, add bump and displacement maps,force direct GI calculations, and choose the BRDF for thematerial.

Parameters

http://help.chaosgroup.com/vray/help/150SP1/material_params.htm#notes





Basic parameters

Diffuse

Diffuse - this is the diffuse color of the material. Note theactual diffuse color of the surface also depends on thereflection and refraction colors. See the Energypreservation parameter below.

Rougness - this parameter can be used to simulate roughsurfaces or surfaces covered with dust (for example, skin, or

the surface of the Moon).Example

Reflection

Reflect - reflection color. Note that the reflection color dimsthe diffuse surface color based on theEnergypreservation option. Example

http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#roughness



http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#reflection_color







Fresnel reflections - checking this option makes thereflection strength dependent on the viewing angle of thesurface. Some materials in nature (glass etc) reflect light in

this manner. Note that the Fresnel effect depends on theindex of refraction as well. Example

Fresnel IOR - the IOR to use when calculating Fresnelreflections. Normally this is locked to theRefractionIOR parameter, but you can unlock it for finer control.

Hilight glossiness - this determines the shape of the hilight

on the material. Normally this parameter is locked tothe Reflection glossiness value in order to producephysically accurate results.

Reflection glossiness - controls the sharpness of reflections. A value of 1.0 means perfect mirror-like reflection; lowervalues produce blurry or glossy reflections. Usethe Subdivs parameter below to control the quality of glossyreflections. Example

Subdivs - controls the quality of glossy reflections. Lowervalues will render faster, but the result will be more noisy.Higher values take longer, but produce smoother results.

Use interpolation - V-Ray can use a caching scheme similarto the irradiance map to speed up rendering of glossyreflections. Check this option to turn caching on. See

the Reflection interpolation section for more details.

Max depth - the number of times a ray can be reflected.Scenes with lots of reflective and refractive surfaces mayrequire higher values to look right.

http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#fresnel


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returned. When this is off, the ray will not be refracted, but willbe continued without changes. Example

Fog color - the attenuation of light as it passes through the

material. This option allows to simulate the fact that thickobjects look less transparent than thin objects. Note that theeffect of the fog color depends on the absolute size of theobjects and is therefore scene-dependent. The fog color alsodetermines the look of the object when usingtranslucency. Example

Fog multiplier - the strength of the fog effect. Smaller values

reduce the effect of the fog, making the material moretransparent. Larger values increase the fog effect, making thematerial more opaque. In more precise terms, this is theinverse of the distance at which a ray inside the object isattenuated with am amount equal to the Fog color . Example

Fog bias - this parameter allows to change the way the fogcolor is applied; by adjusting this parameter you can makethin parts of the object to appear more transparent thannormal, or less transparent than normal.

Affect shadows - this will cause the material to casttransparent shadows, depending on the refraction color andthe fog color. This only works with V-Ray shadows and lights.

Affect Channels - Allows you to specifiy which channels aregoing to be affected by the transperency of the material

- Color Only - the transperency will affect only the RGBchannel of the final render

- Color+alpha - this will cause the material to transmit thealpha of the refracted objects, instead of displaying an opaquealpha. Note that currently this works only with clear (non-

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glossy) refractions.

-Al l channels - all channels and render elements will beaffected by the transperency of the material

Translucency

Type - selects the algorithm for calculating translucency (alsocalled sub-surface scattering). Note that refraction must beenabled for this effect to be visible. Currently only single-bounce scattering is supported. The possible values are:None - no translucency is calculated for the material;

Hard (wax) model - this model is specifically suited for hard

materials like marble;

Soft (water) model - this model is mostly for compatibility witholder V-Ray versions (1.09.x);

Hybr id model - this is the most realistic sss model and issuitable for simulating skin, milk, fruit juice and othertranslucent materials.

Back-side color - normally the color of the sub-surfacescattering effect depends on the Fog color; this parameterallows you to additionally tint the SSS effect.

Thickness - this limits the rays that will be traced below thesurface. This is useful if you do not want or don't need to tracethe whole sub-surface volume.

Light multuplier - a multiplier for the translucent effect.

Scatter coefficient - the amount of scattering inside theobject. 0.0 means rays will be scattered in alldirections; 1.0 means a ray cannot change its direction insidethe sub-surface volume.



Forward/backward coefficient - controls the direction ofscattering for a ray. 0.0 means a ray can only go forward(away from the surface, inside the object); 0.5 means that a

ray has an equal chance of going forward orbackward; 1.0 means a ray will be scattered backward(towards the surface, to the outside of the object).

BRDF

The BRDF parameters determine the type of the hilights andglossy reflections for the material. There parameters have aneffect only if the reflection color is different from black andreflection glossiness is different than 1.0.

Type - this determines the type of BRDF (the shape of thehilight): Example

Phong - Phong hilight/reflections

Bl inn - Blinn hilight/reflections

Ward - Ward hilight/reflections

Anisotropy - determines the shape of the hilight. A value of0.0 means isotropic hilights. Negative and positive valuessimulate "brushed" surfaces. Example

Rotation - determines the orientation of the anisotropic effectin degrees (rotation in degrees). Different brushed surfacescan be simulated by using a texture map for the anisotropyrotation parameter. Example

http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#brdf_type



http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#aniso



http://help.chaosgroup.com/vray/help/150SP1/examples_material.htm#aniso_rotation








Local axis - controls how the direction for the anisotropiceffect is chosen:Loc al axis - the direction is based on the selected local objectaxis.

Map channel - the direction is based on the selected mappingchannel.

Options

Trace reflections - if this is o ff , reflections will not be traced,even if the reflection color is greater than black. You can turnthis off to produce only hilights. Note that when this is off, thediffuse color will not be dimmed by the reflection color, aswould happen normally.

Trace refractions - if this is o ff , refractions will not traced,even if the refraction color is greater than black.

Cutoff - this is a threshold below which reflections/refractionswill not be traced. V-Ray tries to estimate the contribution ofreflections/refractions to the image, and if it is below thisthreshold, these effects are not computed. Do not set this to0.0 as it may cause excessively long render times in some

cases.

Environment priority - this specifies how to determine theenvironment to use if a reflected or refracted ray goes throughseveral materials each of which has an environment override.



Double-sided - if this is true, V-Ray will flip the normal forback-facing surfaces with this material. Otherwise, the lightingon the "outer" side of the material will be computed always.You can use this to achieve a fake translucent effect for thin

objects like paper.

Reflect on back side - if this is true, reflections will becomputed for back-facing surfaces too. Note that this affectstotal internal reflections too (when refractions are computed).

Use irradiance map - if this is true, the irradiance map will beused to approximate diffuse indirect illumination for the

material. If this is off, brute force GI will be used. You can usethis for objects in the scene which have small details and arenot approximated very well by the irradiance map.

Treat glossy rays as GI rays - this specifies on whatoccasions glossy rays will be treated as GI rays:Never - glossy rays are never treated as GI rays.

Only fo r GI rays - glossy rays will be treated as GI rays only

when GI is being evaluated. This can speed up rendering ofscenes with glossy reflections and is the default.

Always - glossy rays are always treated as GI rays. A sideeffect is that the Secondary GI engine will be used for glossyrays. For example, if the primary engine is irradiance map,and the secondary is light cache, the glossy rays will use thelight cache (which is a lot faster).

Energy preservation mode - determines how the diffuse,reflection and refraction color affect each other. V-Ray tries tokeep the total amount of light reflected off a surface to be lessthat or equal to the light falling on the surface (as this happensin the real life). For this purpose, the following rule is applied:



Refract interpolation

These determine the options for the interpolation of glossyreflections. They are very similar to the options for theirradiance map. Note that it is not recommended to useinterpolation for animations, since this may cause severeflickering.

Notes

Use the VRayMtl whenever possible in your scenes.This material is specifically optimized for V-Ray and oftenGI and lighting is computed much faster for V-Raymaterials than for standard 3ds Max materials. Many V-Ray features (e.g. light cache, photon mapping, renderelements) are guaranteed to work properly onlywith VRayMtl and other V-Ray compliant materials.

VRayMtl can produce reflections/refractions for matte

objects - see VRayMtlWrapper .

VRay2SidedMtl parameters Home Examples

General Parameters Notes

Search Keywords : 2Sided, backlight, VRay2SidedMtl

General







http://help.chaosgroup.com/vray/help/150SP1/render_elements.htm








http://help.chaosgroup.com/vray/help/150SP1/examples_vray2sided.htm


http://help.chaosgroup.com/vray/help/150SP1/vray2sided_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vray2sided_params.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/vray2sided_params.htm#notes














The VRay2SidedMtl material is a utility material provided withthe V-Ray renderer. The material allows seeing the light onthe backside of the objects. Use this material to simulate thintranslucent surfaces like paper, cloth curtains, tree leaves etc.

For further info see the Example sections.

Parameters

Front material - this is the material which is going to be usedfor front-side faces as defined by the object normals.

Back material - this is the material V-Ray will use for back

side faces as defined by their normals.

Use back material checkbox - when this is o ff , V-Ray willconsider both sides assigned with the front material. Whenthis is on , you can assign a different material from the frontone. For further info see the Example sections.

Translucency - this determines which side (front or back)relative to the camera is more visible in the rendering process.By default this value is 0.5 , which means that both the sidefacing the camera, and the one facing away from it, will bevisible to the same degree. When this parameter is closerto 0.0 the more of the material facing the camera is going beseen. When it is closer to1.0 , the more of the back material isseen.











Force single-sided sub-materials - when is is on (thedefault), the sub-materials will render as one-sided materials.Turning this option off is not recommended.

VRayOverrideMtl parameters Home Examples

General Parameters

Notes

Search Keywords : Override material, VRayOverrideMtl

General

The VRayOverr ideMtl is a utility material provided with the V-Ray renderer. It allows a surface to look in a different waydepending on whether it is seen through reflections,

refractions or GI. With this material you can get a fine controlover the color bleeding, reflections, refractions and shadowsof the objects. For more info see theExample section.

Parameters


http://help.chaosgroup.com/vray/help/150SP1/examples_vray_overridemtl.htm


http://help.chaosgroup.com/vray/help/150SP1/vray_overridemtl.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vray_overridemtl.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/vray_overridemtl.htm#notes




http://help.chaosgroup.com/vray/help/150SP1/images/examples/vray_overridemtl/00_start01.png









Base material - this is the material V-Ray will use whilerendering the object.

GI material - this is the material V-Ray will use whilecalculating the GI solution.

Reflect material - this is the material V-Ray will use to renderthe object with, when the object is seen in reflections.

Refract material - this is the material V-Ray will use to renderthe object with, when the object is seen through refractions.

Shadow material - this is the material that will be used torender shadows cast from the object.

VRayLightMtl parameters Home Examples

General Parameters

Direct illumination Notes

Search Keywords : light material, self-illumination

General


http://help.chaosgroup.com/vray/help/150SP1/examples_vraylightmtl.htm


http://help.chaosgroup.com/vray/help/150SP1/vray_light_mtl.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vray_light_mtl.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/vray_light_mtl.htm#direct


http://help.chaosgroup.com/vray/help/150SP1/vray_light_mtl.htm#notes










The VRayLightMt l is a special material provided with the V-Ray renderer. This material is generally used for producingself-illuminated surfaces. It also allows faster rendering ratherthan with a Standard 3ds Max material with self-illumination

enabled. It also allows to turn an object into an actual meshlight source.

Parameters

Color - this is the self-illumination color of thematerial.

Multiplier - this is themultiplier for the Color .Note that this does notaffect the texture map, ifspecified.

Texture - a texture map to use for the self-illumination color.

Opacity - a texture to use as opacity for the material. Notethat making the material less opaque does not affect theintensity of the self-illumination color. This is so that you cancreate perfectly transparent materials that nevertheless stillemit light.

Emit light on back side - checking this option makes theobject emit light from its back side as well. If this is off, the

material is rendered as black on the back sides.

Displace - allows the user to add a displacement map to theV-Ray Light Material.



Direct illumination

The controls in this section allow you to turn the objects whichhave this VRayLightMt l material applied into actual directmesh light sources. The effect is equivalent to creating

a VRayLight in Mesh mode for the same object. The controlsin this section are intentionally simple; if you need morecontrol over the light source (exclude objects from illuminationetc), it is better to use a VRayLight instead.

There are currently some restrictions on using these options.For more details, please see the Notes section below.

On - when enabled, turns any objects with the same materialinto mesh light sources. Note that this currently does not workif the material is inside a Mult i /Sub-object material.

Subdivs - controls the number of samples used for directsampling of the mesh light. Lower values may be faster tocalculate, but may introduce noise in the image. Higher valuesreduce the noise, but increase render times.

Notes

You can use the VRayLightMt l as a light sourceassigned to an object. Increasing the multiplier will affectthe GI solution and will produce more light. Note thatoverbright colors may look the same as pure white butthe GI results will be different. For more information seethe Examples section.

If you know the photometric power of a self-illuminatedobject in lumens (e.g. 1700 lm for a 100-watt bulb) youcan calculate the multiplier for VRayLightMt l if youdivide the lumens by the surface area of the object inmeters (the 3ds Max Measure utility can be used for


















this), provided that the self-illuminated color is purewhite.

The direct illumination options currently only work

properly if the VRayLightMt l material is the only materialapplied on the object. They will not work if the material ispart of a complex material like a Mult i /sub-

object material or a VRayBlendMtl material. Thisrestriction will probably be removed in a future release.

The direct illumination options do not work properly if theobject with the VRayLightMt l has motion blur. This willbe corrected in a future release.

VRayMtlWrapper Home

General Parameters

Additional surface properties

Matte properties Miscellaneous

General

The VRayMtlWrapper can be used to specify additionalsurface properties per material. These properties are alsoavailable in the Object settings dialog. However, the settingsfrom the VRayMtlWrapper override those from the Object

settings.

Parameters


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm#parameters


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm#additional


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm#matte


http://help.chaosgroup.com/vray/help/150SP1/mtlWrapper_params.htm#misc




















Base material - this is theactual surface material.

Additional surface properties

Generate GI - controls the GI generated by the material.

Receive GI - controls the GI received by the material.

Generate caustics - turn this off, if the material should not

generate caustics.

Receive caustics - turn this off if the material should notreceive caustics.

Caustics multiplier - determines the effect of caustics on thematerial.

Matte properties

Matte surface - makes the material appear as a mattematerial, which shows the background, instead of the basematerial, when viewed directly. Note that the base material isstill used for things like GI, caustics, reflections etc.



Alpha contribution - determines the appearance of theobject in the alpha channel of the rendered image. A value of1.0 means the alpha channel will be derived from thetransparency of the base material. A value of 0.0 means the

object will not appear in the alpha channel at all and will showthe alpha of the objects behind it. A value of -1.0 means thatthe transparency of the base material will cut out from thealpha of the objects behind. Matte objects are typically givenan alpha contribution of -1.0. Note that this option isindependent of the Matte surface option (i.e. a surface canhave an alpha contribution of -1.0 without being a mattesurface).

Shadows - turn this on to make shadow visible on the mattesurface.

Affect alpha - turn this on to make shadows affect the alphacontribution of the matte surface. Areas in perfect shadow willproduce white alpha, while completely unoccluded areas willproduce black alpha. Note that GI shadows (from skylight) arealso computed, however GI shadows on matte objects are notsupported by the photon map and the light map GI engines,when used as primary engines. You can safely use those withmatte surfaces as secondary engines.

Color - an optional tint for the shadows on the matte surface.

Brightness - an optional brightness parameter for theshadows on the matte surface. A value of 0.0 will make the

shadows completely invisible, while a value of 1.0 will showthe full shadows.

Reflection amount - shows the reflections from the basematerial. This only works if the base material is directlya VRayMtl.







Refraction amount - shows the refractions from the basematerial. This only works if the base material is directlya VRayMtl.

GI amount - determines the amount of GI shadows.

No GI on other mattes - this will cause the object to appearas a matte object in reflections, refractions, GI etc for othermatte objects. Note that if this is on , refractions for the matteobject might not be calculated (the object will appear a matteobject to itself and will not be able to "see" the refractions on

the other side).Miscellaneous

GI surface ID - this number can be used to prevent theblending of light cache samples across different surfaces. Iftwo objects have different GI surface IDs, the light cachesamples of the two objects will not be blended. This can beuseful to prevent light leaks between objects of vastly differentillumination.

VRayFastSSS material Home







http://help.chaosgroup.com/vray/help/150SP1/images/examples/vrayfastsss/vrayfastsss1.png






General VRayFastSSS parameters Notes

Search keyword s: sub-surface scattering, sss, skin, wax

General

VRayFastSSS is a material that calculates a sub-surfacescattering effect. Since it uses a simplified algorithm, it istypically faster than the sub-surface scattering optionof VRayMtl and may be easier to control. NotethatVRayFastSSS does not include diffuse and glossy effects.To add these, create a VRayBlendMtl materialwithVRayFastSSS as a base material and a VRayMtl as acoat material.

VRayFastSSS simulates the effect of three sub-surface layers- a shallow layer over a deep layer over a back-scatteringlayer. You can control these separately to achieve differentlooks for the surface.

VRayFastSSS parameters

http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss_params.htm#parameters_dirt


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss_params.htm#notes














Prepass rate -

VRayFastSSS approximates the sub-surface scattering byprecomputing the surface lighting at different points on thesurface and then interpolating between these points. Thisparameter determines the resolution at which surface lightingis precomputed during the prepass phase. A value of 0 meansthat the prepass will be at the final image resolution; a valueof -1 means half the image resolution, and so on. For highquality renders it is recommended to set this to 0 .

Interpolation samples - this parameter determines howmany samples will be used when smoothing the surfacelighting. For very translucent surfaces, there must be enoughsamples to blur the lighting across a large portion of thesurface and so you may need to increase this parameter.Less translucent surfaces can do with fewer samples, whichalso makes the calculations faster.

Diffuse roughness - this parameter controls the surfaceroughness for the material. A value of 0.0 produces a diffusematerial, while higher values give the surface a translucentquality.



Back color - the color for the back-scattering effect. Note thatboth the Shallow color and Deep color are used as filters ontop of the Back color .

Notes

VRayFastSSS uses the V-Ray prepass system tosimulate and interpolate the sub-surface scattering.During other GI calculations (e.g. light cache or photonmapping), the material is calculated as a diffuse one.

VRayFastSSS does not require that the object has anyactual volume; it relies purely on surface lighting.

VRayFastSSS2 material Home Examples

General Parameters General parameters Diffuse and sub-surface layers parameters Specular layer parameters Options Notes References and links


http://help.chaosgroup.com/vray/help/150SP1/examples_vrayfastsss2.htm


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#params


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#parameters_sss2


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#diffuse


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#specular

http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#options


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#notes


http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#references


http://help.chaosgroup.com/vray/help/150SP1/images/examples/vrayfastsss2/vrayfastsss2.png




http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#specular









Search keyword s: sub-surface scattering, sss, skin, wax, marble

General

VRayFastSSS2 is a material that is primarily designed forrendering of translucent materials like skin, marble etc. Theimplementation is based on the concept of BSSRDF originallyintroduced by Jensen et al . (see the references below) and isa more or less physically accurate approximation of the sub-surface scattering effect, while still being fast enough to beused in practice.

In difference from theoriginal VRayFastSSS material, VRayFastSSS2 is a completematerial with diffuse and specular components that can beused directly, without the need of a VRayBlendMtl material.More exactly, the material is composed of three layers: aspecular layer, a diffuse layer, and a sub-surface scatteringlayer. The sub-surface scattering layer is comprised of singleand multiple scattering components. Single scattering occurswhen light bounces once inside the material. Multiple

scattering results from light bouncing two or more timesbefore leaving the material.

Parameters

General parameters

Preset - allows you tochoose one of several available preset materials. Most of thepresets are based on measured data provided by Jensen etal.in [3].







http://help.chaosgroup.com/vray/help/150SP1/vrayfastsss2_params.htm#ref3








Prepass rate - VRayFastSSS2 accelerates the calculation ofmultiple scattering by precomputing the lighting at differentpoints on the surface of the object and storing them in astructure called an illumination map, which is similar to the

irradiance map used to approximate global illumination, anduses the same prepass mechanism built into V-Ray that isalso used for e.g. interpolated glossy reflections/refractions.This parameter determines the resolution at which surfacelighting is computed during the prepass phase. A valueof 0 means that the prepass will be at the final imageresolution; a value of -1 means half the image resolution, andso on. For high quality renders it is recommended to set this

to 0 or higher, as lower values may cause artifacts orflickering in animations. If the chosen prepass rate is notsufficient to approximate the multiple scattering effectadequately, VRayFastSSS2 will replace it with a simplediffuse term. This can happen, for example, for objects thatare very far away from the camera, or if the subsurfacescattering effect is very small. This simplification is controlledby the Prepass blur parameter.

Scale - additionally scales the subsurface scattering radius.Normally, VRayFastSSS2 will take the scene units intoaccount when calculating the subsurface scattering effect.However, if the scene was not modelled to scale, thisparameter can be used to adjust the effect. It can also beused to modify the effect of the presets, which resetthe Scatter radius parameter when loaded, but leavethe Scale parameter unchanged.

IOR - the index of refraction for the material. Most water-based materials like skin have IOR of about 1.3 .

Diffuse and sub-surface scattering layers parameters



Overall color - controlsthe overall coloration forthe material. This colorserves as a filter for both

the diffuse and the sub-surface component.

Diffuse color - the colorof the diffuse portion of the material.

Diffuse amount - the amount for the diffuse component of thematerial. Note that this value in fact blends between the

diffuse and sub-surface layers. When set to 0.0 , the materialdoes not have a diffuse component. When set to 1.0 , thematerial has only a diffuse component, without a sub-surfacelayer. The diffuse layer can be used to simulate dust etc. onthe surface.

Sub surface color - the general color for the sub-surfaceportion of the material.

Scatter color - the internal scattering color for the material.Brighter colors cause the material to scatter more light and toappear more translucent; darker colors cause the material tolook more diffuse-like.

Scatter radius - controls the amount of light scattering in thematerial. Smaller values cause the material to scatter lesslight and to appear more diffuse-like; higher values make the

material more translucent. Note that this value is specifiedalways in centimeters (cm); the material will automatically takecare to convert it into scene units based on the currentlyselected system units.



Phase function - a value between -1.0 and 1.0 thatdetermines the general way light scatters inside the material.Its effect can be somewhat likened to the difference betweendiffuse and glossy reflections from a surface, however the

phase function controls the reflection and transmittance of avolume. A value of 0.0 means that light scatters uniformly inall directions (isotropic scattering); positive values mean thatlight scatters predominantly forward in the same direction as itcomes from; negative values mean that light scatters mostlybackward. Most water-based materials (e.g. skin, milk) exhibitstrong forward scattering, while hard materials like marbleexhibit backward scattering. This parameter affects most

strongly the single scattering component of the material.Positive values reduce the visible effect of single scatteringcomponent, while negative values make the single scatteringcomponent generally more prominent.

Specular layer parameters

Specular color -determines the specular

color for the material.

Specular amount -determines the specularamount for the material. Note that there is an automaticFresnel falloff applied to the specular component, based onthe IOR of the material.

Specular glossiness - determines the glossiness (hightlightsshape). A value of 1.0 produces sharp reflections, lowervalues produce more blurred reflections and highlights.

Specular subdivs - determines the number of samples thatwill be used to calculate glossy reflections. Lower valuesrender faster, but may produce noise in the glossy reflections.



Higher values reduce the noise, but may be slower tocalculate.

Specular reflections - enables the calculations of glossy

reflections. When o ff , only hilights will be calculated.

Specular trace depth - the number of reflection bounces forthe material.

Options

Single scatter - controlshow the single scattering

component is calculated:

None - no singlescattering component iscalculated.

Simple - the single scattering component is approximatedfrom the surface lighting. This option is useful for relatively

opaque materials like skin, where light penetration is normallylimited.

Raytraced (sol id) - the single scattering component isaccurately calculated by sampling the volume inside theobject. Only the volume is raytraced; no refraction rays on theother side of the object are traced. This is useful for highlytranslucent materials like marble or milk, which at the sametime are relatively opaque.

Raytraced (refract ive) - similar to the Raytraced

(sol id) mode, but in addition refraction rays are traced. Thisoption is useful for transparent materials like water or glass. Inthis mode, the material will also produce transparentshadows.



Single scatter subdivs - determines the number of samplesto make when evaluating the single scattering componentwhen the Single scatter mode is set to Raytraced

(sol id) or Raytraced (refract ive) .

Refraction depth - this determines the depth of refractionrays when the Single scatter parameter is set toRaytraced(refractive) mode.

Front lighting - enables the multiple scattering component forlight that falls on the same side of the object as the camera.

Back lighting - enables the multiple scattering component forlight that falls on the opposite side of the object as thecamera. If the material is relatively opaque, turning this o ff willspeed up the rendering.

Scatter GI - controls whether the material will accuratelyscatter global illumination. When o ff , the global illumination iscalculated using a simple diffuse approximation on top of thesub-surface scattering. When on, the global illumination isincluded as part of the surface illumination map for multiplescattering. This is more accurate, especially for highlytranslucent materials, but may slow down the rendering quitea bit.

Prepass blur - controls if the material will use a simplifieddiffuse version of the multiple scattering when the prepass

rate for the direct lighting map is too low to adequatelyapproximate it. A value of 0.0 will cause the material to alwaysuse the illumination map. However, for objects that are faraway from the camera, this may lead to artifacts or flickeringin animations. Larger values control the minimum required



samples from the illumination map in order to use it forapproximating multiple scattering.

Notes

When using either Raytraced (sol id) or Raytraced(refractive) mode for the Single scatter parameter, youneed to use VRayShadows for standard lights in order toget correct results.

VRayFastSSS2 uses the V-Ray prepass system tosimulate and interpolate the sub-surface scattering.During other GI calculations (e.g. light cache or photonmapping), the material is calculated as a diffuse one.

For the reason explained above, VRayFastSSS2 willrender as a diffuse one with the progressive path tracingmode of the light cache.

References and links

Here is a list of links and references used when buildingthe VRayFastSSS2 material.

[1] H. C. Hege, T. Hollerer, and D. Stalling, VolumeRendering: Mathematical Models and Algorithmicaspects

An online version can be foundat http://www.cs.ucsb.edu/~holl/publications.html Defines the basic quantities involved in volumetricrendering and derives the volumetric and surfacerendering equations.

[2] T. Farrell, M. Patterson, and B. Wilson, A DiffusionTheory Model of Spatially Resolved, Steady-stateDiffuse Reflectance for the Noninvasive



http://www.cs.ucsb.edu/~holl/publications.html






Determination of Tissue Optical Properties in v ivo ,Med. Phys. 19(4), Jul/Aug 1992Describes an application of the diffusion theory to thesimulation of sub-surface scattering; derives the base

formulas for the dipole approximation used by Jensen etal. (see below).

[3] H. Jensen, S. Marschner, M. Levoy, and P.Hanrahan, A Practical Model for Subsurface LightTransport, SIGGRAPH'01: Computer GraphicsProceedings, pp. 511-518

An online version of this paper can be found

at http://www-graphics.stanford.edu/papers/bssrdf/ Introduces the concept of BSSRDF and describes a practial method for calculating sub-surface scatteringbased on the dipole approximation derived by Farrell etal. (see above).

[4] H. Jensen and J. Buhler, A Rapid HierarchicalRendering Technique for Translucent Materials,SIGGRAPH'02: Computer Graphics Proceedings, pp.

576-581 An online version of this paper can be foundat http://graphics.ucsd.edu/~henrik/papers/fast_bssrdf/ Introduces the idea of decoupling the calculations ofsurface illumination and the sub-surface scattering effectin a two-pass method; describes a fast hierarchicalapproach for evaluating subsurface scattering and

proposes a reparametrization of the BSSRDF

parameters for easier user adjustment.

[5] C. Donner and H. Jensen, Light Diffusion in Multi-Layered Translucent Materials, SIGGRAPH'05: ACMSIGGRAPH 2005 Papers, pp. 1032-1039

An online version of this paper can be found

http://www-graphics.stanford.edu/papers/bssrdf/



http://graphics.ucsd.edu/~henrik/papers/fast_bssrdf/







at http://graphics.ucsd.edu/papers/layered/ Provides a concise description of the original BSSRDFsolution method presented by Jensen et al; extends themodel to multi-layered materials and thin slabs using

multipole approximation.

VRayBlendMtl material Home

General Parameters

Notes

Search keyword s: layered material, car paint, shellac, blend, skin

General

VRayBlendMtl can be used to layer several V-Raycompatible materials in an efficient

manner. VRayBlendMtl takes full advantage of the shadingpipeline of the V-Ray renderer and is typically faster than thestandard Blend ,Shellac and Compos i te materials of 3dsMax. It also keeps the physical correctness of the finalmaterial while offering similar functionality to the standard 3dsMax ones. It can be used to create complex materials like car

http://graphics.ucsd.edu/papers/layered/




http://help.chaosgroup.com/vray/help/150SP1/vrayblendmtl_params.htm#general


http://help.chaosgroup.com/vray/help/150SP1/vrayblendmtl_params.htm#parameters_dirt


http://help.chaosgroup.com/vray/help/150SP1/vrayblendmtl_params.htm#notes


http://help.chaosgroup.com/vray/help/150SP1/images/examples/vrayblendmtl/vrayblendmtl.png








paints, human skin (when used with VRayFastSSS as a basematerial) etc.

An advantage of VRayBlendMtl is that you can use

the VRayMtlSelect render element to split the different sub-materials of VRayBlendMtl into different render elements.

VRayBlendMtl takes a base material and applies othermaterials (coatings) on top of it. This works like a stack, whereeach coat material blends between its own shading and thatof the materials below it in the stack.

Parameters

Base material - the base material over which other materialsare layered. If this is not specified, the base material will beassumed to be a perfectly transparent material.

Coat materials - these specify materials to use as coatings.



Blend amount - this color specifies how much of the finalresult is contributed by the corresponding coating material,and the rest of the materials below it. If the Blend amount iswhite, the final result is comprised of the coat material only,

and other materials below it are blocked. If the Blendamount is black, a coat material has no effect on the finalresult. This parameter can also be controlled by a texturemap.

Additive (shellac) mode - checking this optionmakes VRayBlendMtl to behave like a multi-layered Shellac material. Note that this would often result in a

physically incorrect material (e.g. a material that reflects morelight than falls on it). It is not recommended to use this optionunless you know what you are doing.

Notes

VRayBlendMtl is specifically designed for the V-Rayshading API and can only support V-Ray compatiblematerials (VRayMtl , VRayFastSSS etc). Additional V-

Ray compatible materials can be developed with the V-Ray Shading SDK.

V Ray Ingles

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