vray manual

5/26/2018 Vray Manual

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VRAY MANUAL

Plugins HomeWhile V-Ray works with most of the standard 3ds Max lights, materials and maps, it also includesseveral additional plugins which offer functionality not found in 3ds Max itself. They are speciallyoptimized for work with V-Ray and using them instead of the standard ones can increase renderingspeed significantly.

The V-Ray rendering system includes the following plugins for 3ds 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.

VRayMtlWrapperA specialized V-Ray material that allows you to specify additional rendering parametersfor any material.

VRayLight An area light plugin

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

VRaySkyA procedural HDR environmap map that works with the VRaySun light to create realisticdaylight environments.

VRayShadow A raytraced shadow plugin (sharp and area shadows)

VRayDirtA procedural texture that can be used for dirt-like effects or for simulating ambientocclusion.

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

VRayProxyA plugin that allows you to specify render-time geometry that will be loaded from anexternal 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


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

VRayEnvironmentFogAn enviromental effect that allows the simulation of participating media like fog or dustin the atmosphere

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

RENDER

V-Ray renderer parameters HomeV-Ray is a renderer plugin for 3ds Max. In order to use V-Ray, you must first select it as your currentrenderer. You can do that by clicking on theAss ign...button in the Current renderersrollout of theRender Scene dialog:

In 3ds Max 9 and later, the V-Ray parameters aredivided into several tabs in the render scenedialog; additionally each tab is divided into several

rollouts:


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FRAME BUFFER

GeneralParametersHidden parametersVFB toolbarVFB shortcutsNotes

Search Keywords:VFB, G-buffer, frame buffer, render pass

GeneralIn addition to rendering to the 3ds Max Rendered Frame Window (RFW or VFB), V-Ray allows you torender to a V-Ray specific frame buffer, which has some additional capabilities:

Allows you to view all render elements in a single window and 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 are rendered.

The V-Ray VFB also has some limitations, which are listed in the Notessection below.

Parameters


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Show last VFB- If you have rendered to the V-Ray VFB, but have closed it, this button allows you toopen it again. The same can also be achieved with the showLastVFB() MaxScriptmethod of the V-Ray renderer.

Enable built-in frame buffer- Enables the use of built-in V-Ray frame buffer. Due to technicalreasons, the original 3ds Max frame buffer still exists and is being created. However, when this

feature is turned on - V-Ray will not render any data to the 3ds Max frame buffer. In order to preservememory consumption we recommend that you set the original 3ds Max resolution to a very low value(like 100x100) and turn off the 3ds Max Virtual Frame Buffer from the common 3ds Max rendersettings.

Render to memory frame buffer- this will create a V-Ray frame buffer and will use it to store colordata that you can observe while rendering and afterwards. If you wish to render really high resolutionsthat would not fit into memory or that may eat up a lot of your RAM not allowing for the scene torender properly - you can turn this feature off and use only Render to V-Ray raw image fil efeature.

Get resolut ion f rom 3ds Max- this will cause the V-Ray VFB to take its resolution from the 3ds Maxcommon render settings.

Output resolution- this is the resolution that you wish to use with 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-Ray directly writes to disk the raw image data asit is being rendered. It does not store any data in the RAM, so this feature is very handy whenrendering huge resolutions for preserving memory. If you wish to see what is being rendered, you canturn on the Generate p reviewsetting. You can specify either a .vrimgor an .exrfile for output:

If you specify a .vrimg extension, the resulting file can be viewed through the File > Viewimage...menu of 3ds Max, or converted to an OpenEXR file with the help of the vrimg2exr

tool.

If you specify an .exrextension, V-Ray will write out a tiled OpenEXR file that can be useddirectly by 3ds Max or other compositing applications. The file contains all render elements forthe image.

Generate p review- this will create a small preview of what is being rendered. If you are not using theV-Ray memory frame buffer for conserving memory (i.e. Render to memory frame bufferis off), youcan use this feature to see a small image of what is being actually rendered and stop the renderer ifthere is anything that looks wrong.

Save separate render channels - this option allows you to save the channels from the VFB intoseparate files. Use the Browse...button to specify the file. This option is available only whenrendering to a memory frame buffer. If rendering is done only to a raw image file, the render channelscan be extracted from that file after rendering is complete.

Save RGB and Save Alpha- these options allow you to disable saving of the RGB and Alphachannels respectively. This can be useful if you only want to generate other render channels. Notethat V-Ray will still generate the RGB and Alpha channels, however they will not be saved.

Hidden parametersThere are some additional parameters of the VFB, which are not available in the interface, but areaccessible through MaxScript. These may be useful in certain situations. Below are listed theMaxScript names of these parameters.

output_renderType- This allows you to override the render type, specified in the 3ds Max settings.Possible values are:

0- use 3ds Max render type (default);1- render the full image;2- region rendering;


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3- crop rendering;4- blow-up rendering.

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

rendering);

output_regxmax - The right coordinate (in pixels) of the region to render (for region/drop/blow-uprendering);

output_regymin- The top coordinate (in pixels) of the region to render (for region/drop/blow-uprendering);

output_regymax- The bottom coordinate (in pixels) of the region to render (for region/drop/blow-uprendering);

VFB toolbarThis 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 of various

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.


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VFB shortcutsHere is the list of shortcuts you can use to navigate through the VFB image. Please note that VFBwindow 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 button

MidButton 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 notdisplay the G-Buffer layers (like Coverageetc.);

The V-Ray VFB does notwork with stripe rendering;

Even though you select the V-Ray VFB as your output, the 3ds Max VFB is still created andthus takes additional memory. If you want to reduce that memory, you need to uncheckthe Get resolution from MAXoption, set the 3ds ax resolution to a low value like 100 x 100,and then select your real output resolution in the V-Ray VFB options.

If you have selected an output image file from the Commontab of the Render Scenedialog,V-Ray will fill out the 3ds Max RFW, and this will be saved as your image. If you want to savethe V-Ray VFB instead, you should use the Split render channelsor Render to V-Ray raw

image fileoption of the V-Ray VFB.


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The OpenEXR file format is an open file format for high dynamic range images originallydeveloped by Industrial Light and Magic. The official site of the OpenEXR file formatis http://www.openexr.com/

Global switches Home Render params Examples

GeneralParametersGeometry sectionLighting sectionMaterials sectionIndirect illumination sectionRaytracing sectionCompatibility section

Search Keywords:switches, global switches

GeneralThe global switches allow you to control various aspects of the renderer globally.

Parameters

Geom et r y sec t i on

Displacement- enables (default) or disables V-Ray's own displacement mapping. Note that this hasno effect on standard Max displacement mapping, which can be controlled via the correspondingparameter in the Render Scene dialog.

Force back face culling - enables or disables (default) back face culling for camera and shadowrays. When this option is on , the surfaces of objects which are turned away from the camera (or thelight source, when tracing shadows) will appear fully transparent. This allows to look inside closedobjects when the camera is outside.

L i gh t i n g s ect i o n

Lights- enables or disables lights globally. Note that if you uncheck this, V-Ray will use the defaultlights. If you do not want any direct lighting in your scene, you must uncheck both this and the Defaultlightsparameters.


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Default ligh ts- allows you to control the default lights in the scene.- Off- the default lights in the scene will be always switched off

-On- the default lights are always switched on when there are no lights in the scene or when youhave disabled lighting globally (see Lightparameter).

-Off with GI - the default lights will be switched off only when the Global Illumination is enabled or ifthere are lights in the scene

Hidden lights - enables or disables the usage of hidden lights. When this is checked, lights arerendered regardless of whether they are hidden or not. When this option is off, any lights that arehidden for any reason (either explicitly or by type) will not be included in the rendering.

Shadows- enables or disables shadows globally.

Show GI only- when this option is on , direct lighting will not be included in the final rendering. Notethat lights will still be considered for GI calculations, however in the end only the indirect lighting willbe shown.

M a t e r i a l s s ect i o n

Reflection/refraction - enables or disables the calculation of reflections and refractions in V-Raymaps and materials.

Max depth- enables the user to limit globally the reflection/refraction depth. When this is unchecked,the depth is controlled locally by the materials/maps. When this option is checked, all materials andmaps use the depth specified here.

Maps- enables or disables texture maps.

Filter maps- enables or disables texture map filtering. When enabled, 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 during GI calculations and glossyreflections/refractions. When off(the default), texture maps are not filtered for GI and glossyreflections/refractions in order to speed up the calculations. If this option is on , textures will be filteredin these cases.

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

Transp. cutoff - this controls when tracing of transparent objects will be stopped. If the accumulated

transparency of a ray is below this threshold, no further tracing will be performed.

Override mt l- this option allows the user to override the scene materials when rendering. All objects

will be rendered with the chosen material, if one is selected, or with their default wireframe materials ifno material is specified.

Override exclude - clicking this button brings up the 3ds Max Include/Exclude dialog which allowsyou to select exactly for which objects the material is overridden.

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

I n d i r ect i l l um i n a t i o n sect i o n

Don't render final image- when this option is on, V-Ray will only calculate the relevant globalillumination maps (photon maps, light maps, irradiance maps). This is a useful option if you arecalculating maps for a fly-through animation.


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Ray t r a c i n g sect i o n

Secondary rays bias- a small positive offset that will be applied to all secondary rays; this can beused if you have overlapping faces in the scene to avoid the black splotches that may appear. Seethe Examplessection for a demonstration of the effect of this parameter. This parameter is also usefulwhen using the 3ds Max Render-to-texturefeature.

Com pa t i b i l i t y sect i o n

Legacy sun/sky/camera models- previous versions of V-Ray used slightly different calculationmodels for theVRaySun, VRaySkyand VRayPhysicalCamerawhich were not entirely physicallyaccurate. When this option isof f(the default), V-Ray uses improved and more accurate models.When this is on , V-Ray will switch to the old models for compatibility with old scenes. When an old

scene is opened, V-Ray will automatically display a dialog asking if you want to change this setting.

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

the VRayLight, VRaySun, VRaySkyand VRayPhysicalCamerato the photometric units used by 3dsMax and its photometric lights. When this is of f, these plugins operate in the internal V-Rayphotometric space, like in older versions of V-Ray. Keeping this option on ensures that a VRayLight

with a given power will match a 3ds Max photometric light with the same power.

Image Sampler Antialiasing)

General

Parameters

Fixed rate sampler

Adaptive DMC samplerAdaptive subdivision sampler

Notes

GeneralIn V-Ray, an image samplerrefers 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 choosebetween Fixed ratesampler,Adaptive DMCsampler andAdapt ive subdivision sampler.

Parameters


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Im age sam p l e r

Type- specifies the image sampler type:

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

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

Adapt ive subdiv ision- this sampler divides the image into an adaptive grid-like structure and refinesdepending on the difference in pixel intensity.

An t i a l i a s i n g f i l t er

This section allows you to choose an antialiasing filter. All standard 3ds Max filters are supported withthe exception of the Plate Matchfilter. See the Examplessection for more information on antialiasingfilters.

Fixed ratesampler

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 center ofeach pixel is taken. If this is greater than 1, the samples are distributed within the pixel. The actualnumber of pixels is the square of this parameter (e.g. 4subdivs produce 16samples per pixel).

Adapt ive DMCsampler

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 than theAdaptivesubdivisionsampler.

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 captured

correctly, or fast moving objects if you use motion blur. The actual number of pixels is the square ofthis number (e.g. 4subdivs produce 16samples per pixel).

Max subdivs- determines the maximum number of samples for a pixel. The actual maximum numberof sampler is the square of this number (e.g. 4subdivs produces a maximum of 16samples). Notethat V-Ray may take less than the maximum number of samples, if the difference in intensity of theneighbouring pixels is small enough.

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

Color threshold- the threshold that will be used to determine if a pixel needs more samples. This is

ignored if the Use DMC sampler threshold option is on.


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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 antialiasingof the image.

Adapt ive subdivis ionsampler

This is an advanced imagesampler capable of undersampling (taking less than one sample per pixel). In the absence of blurryeffects (direct GI, DOF, glossy reflection/reftaction etc) this is the best preferred image sampler in V-Ray. On average it takes fewer samples (and thus less time) to achieve the same image quality asthe other image samplers. However, with detailed textures and/or blurry effects, it can be slower andproduce worse results than the other two methods.

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

Min. rate - controls minimum number of samples per pixel. A value of zeromeans one sample perpixel; -1means one sample every two pixels; -2means one sample every 4pixels 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. Lower valueswill produce better results, while higher values will be faster, but may leave some areas of similarintensity 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 (regardless ofwhether they actually need to be supersampled). This option has no effect if DOF or motion blur isenabled.

Normals- this will supersample areas with sharply varying normals. This option has no effect if DOFor 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 antialiasingof the image.

Notes Which sampler to use for a given scene? The answer is best found with experiments, but here

are some tips:

o For smooth scenes with only a few blurry effects and smooth textures, theAdaptivesubdivisionsampler with its ability to undersample the image is unbeatable.

o For images with detailed textures or lots of geometry detail and only a few blurryeffects, theAdapt ive DMCsampler performs best. Also in the case of animationsinvolving detailed textures, theAdaptive subdivision sampler might produce jitteringwhich theAdaptive DMCsampler 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.


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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 theAdaptive subdivision sampler, which stores all individual sub-samplestaken within a bucket. TheAdaptive DMCsampler and the Fixed ratesampler on the otherhand only store the summed result of all sub-samples for a pixel and so usually require lessRAM.

Indirect illumination (GI)

GeneralApproaches to indirect illuminationPrimary and secondary bouncesParametersNotes

General

Approaches to indirec t i llumination

V-Ray implements several approaches for computing indirect illumination with different trade-offsbetween quality and speed:

Brute force- this is the simplest approach; indirect illumination is computed independently foreach shaded surface point by tracing a number of rays in different directions on thehemisphere above that point.

Advantages:

o this approach preserves all the detail (e.g. small and sharp shadows) in the indirectlighting;

o it is free from defects like flickering in animations;o no additional memory is required;o indirect illumination in the case of motion-blurred moving 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 can be avoided only by shooting a

larger number of rays, thus slowing it even more.

Irradiance map- this approach is based on irradiance caching; the basic idea is to computethe indirect illumination only at some points in the scene, and interpolate for the rest of thepoints.

Advantages:o the irradiance map is very fast compared to direct computation, especially for scenes

with large flat areas;o the noise inherent to direct computation is greatly reduced;o the irradiance map can be saved an re-used to speed up calculations of different

views for the same scene and of fly-through animations;o the irradiance map can also be used to accelerate direct 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;


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o the irradiance map requires additional memory;o indirect illumination with motion-blurred moving objects 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 particles starting from the light sources andbouncing around the scene. This is useful for interior or semi-interior scenes whith lots of

lights or small windows. The photon map usually does not produce good enough results to beused directly; however it can be used as a rough approximation to the lighting in the scene tospeed the calculation 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 scene and of fly-through animations;o the photon map is view-independent.

Disadvantages:

o the photon map usually is not suitable for direct visualization;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 illumination caused by environment lights (skylight).

Light cache - light caching is a technique for approximating the global illumination in a scene.It is very similar to photon mapping, but without many of its limitations. The light map is builtby tracing many many eye paths from the 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. Thelight map is a universal GI solution that can be used for both interior or exterior scenes, eitherdirectly or as a secondary bounce approximation when used with the irradiance map or thebrute 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 the photon map, which must process each light in the scene and usuallyrequires separate setup for each light.

o the light-caching approach works efficiently with any lights - including skylight, self-illuminated objects, non-physical lights, photometric lights etc. In contrast, the photonmap is limited in the lighting effects it can reproduce - for example, the photon mapcannot reproduce the illumination from skylight or from standard omni lights withoutinverse-square falloff.

o the light cache produces correct results in corners and around small objects. Thephoton map, on the other hand, relies on tricky density estimation schemes, which

often produce wrong results in these cases, either darkening or brightening thoseareas.o in many cases the light cache can be visualized directly for very fast and smooth

previews of the lighting in the scene.

Disadvantages:o like the irradiance map, the light cache is view-dependent and is generated for a

particular position of the camera. However, it generates an approximation forindirectly 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-Ray materials;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 orbrute force GI if you want to achieve better results with bump maps.


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o lighting involving motion-blurred moving objects is not entirely correct, but is verysmooth since the light cache blurs GI in time as well (as opposed to the irradiancemap, where each sample is computed at a particular instant of time).

Which method to use? That depends on the task at hand. The Examplessection can help you inchoosing a suitable method for your scene.

Primary and secondary bouncesThe indirect illumination controls in V-Ray are divided into two large sections: controlsconcerningprimary diffuse bouncesand controls concerning secondary diffuse bounces. A primarydiffuse bounce occurs when a shaded point is directly visible by the camera, or through specularreflective or refractive surfaces. A secondary bounce occurs when a shaded point is used in GIcalculations.

ParametersOn- turn indirectillumination on and off.

GI causticsGI caustics represent lightthat has gone through onediffuse, and one or severalspecular reflections (orrefractions). GI causticscan can be generated byskylight, or self-illuminatedobjects, for example.However, caustics causedby direct lights cannot be

simulated in this way. You must use the separate Causticssection to control direct light caustics. Notethat GI caustics are usually hard to sample and may introduce noise in the GI solution.

Refractive GI caustics- this allows indirect lighting to pass through transparent objects (glass etc).Note that this is not the same as Caustics, which represent direct light going through transparentobjects. You need refractive GI caustics to get skylight through windows, for example.

Reflective GI caustics- this allows indirect light to be reflected from specular objects (mirrors etc).Note that this is not the same as Caustics, which represent direct light going through specularsurfaces. This is offby default, becase reflective GI caustics usually contribute little to the finalillumination, while often they produce undesired sublte noise.

Post-processing

These controls allow additional modification of the indirect illumination, before it is added to the finalrendering. The default values ensure a physically accurate result; however the user may want tomodify the way GI looks for artistic purposes.

Saturation - controls the saturation of the GI; a value of0.0means that all color will be removed fromthe GI solution and will be in shades of grey only. The default value of 1.0means the GI solutionremains unmodified. Values above 1.0boost the colors in the GI solution.

Contrast- this parameter works together with Contrast baseto boost the contrast of the GI solution.When Contrast is 0.0, the GI solution becomes completely uniform with the value defined by Contrastbase. A value of1.0 means the solution remains unmodified. Values higher that 1.0 boost the contrast.

Contrast base- this parameter determines the base for the contrast boost. It defines the GI values

that remain unchanged during the contrast calculations.


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Ambient occ lusion These controls allow you to add an ambient occlusion term to the global illumination solution.

On- enable or disable ambient occlusion.

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

Radius- ambient occlusion radius.

Subdivs- determines the number of samples used for calculating ambient occlusion. Lower valueswill render faster, but might introduce noise.

Primary diffuse bouncesMultiplier- this value determines how much primary diffuse bounces contribute to the final image

illumination. Note that the default value of 1.0 produces a physically accurate image. Other values arepossible, but not physically plausible.

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

Irradiance map- selecting this will cause V-Ray to use an irradiance map for primary diffusebounces. See the Irradiance mapsection for more information.

Global photon map- selecting this option will cause V-Ray to use a photon map for primary diffuse

bounces. This mode is useful when setting up the parameters of the global photon map. Usually itdoes not produce good enough results for final renderings when used as a primary GI engine. Seethe Global photon mapsection for more information.

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffusebounces. See the brute force GIsection for more information.

Light cache- this chooses the light cache as the primary GI engine. See the Light cachesection formore information.

Secondary diffuse bouncesMultiplier- this determines the effect of secondary diffuse bounces on the scene illumination. Valuesclose to 1.0 may tend to wash out the scene, while values around 0.0 may produce a dark image.Note that the default value of 1.0 produces physically accurate results. While other values arepossible, they are not physically plausible.

Secondary diffuse bounces method- this parameter determines how V-Ray will calculatesecondary diffuse bounces.

None - no secondary bounces will be computed. Use this option to produce skylit images withoutindirect color bleeding.

Global photon map- selecting this option will cause V-Ray to use a photon map for primary diffusebounces. This mode is useful when setting up the parameters of the global photon map. Usually itdoes not produce good enough results for final renderings when used as a primary GI engine. Seethe Global photon mapsection for more information.

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffusebounces. See the Brute force GIsection for more information.

Light cache- this chooses the light cache as the primary GI engine. See the Light cachesection formore information.


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Notes V-Ray does not have a separate skylight system. The skylight effect can be achieved by

setting the background color or environment map in the 3ds Max environment dialog, or in V-Ray's own Environment rollout.

You will get physically accurate lighting if you set both the primary and secondary GImultipliers to their default value of 1.0. While other values are possible, they will not produce aphysically accurate result.

Brute force GI

Search Keywords:brute force, direct calculation, GI

GeneralThis section is available only if you have chosenBrute forceas either the primary or the secondaryGI engine.

The brute force method for computing global illumination recomputes the GI values for every singleshaded point separately and independently from other points. While very slow, this method is veryaccurate, especially if you have many small details in the scene.

To speed up brute force GI, you can use a faster method ( the photon mapor the light map) forapproximating secondary GI bounces, while using the brute force method for the primary bounces.

Parameters

Subdivs- this determines

the number of samples used to approximate GI. Note that this is not the exact number of rays that V-Ray will trace. The number of rays is proportional to the square of this number, but also depends onthe settings in the DMC samplerrollout.

Secondary bounces- this parameter is available only if brute force GI is selected as a secondary GIengine. It controls the number of light bounces that will be computed.

Irradiance mapGeneralParametersBuilt-in presetsBasic parametersOptionsDetail enhancementAdvanced optionsModeOn render endNotes


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GeneralThis section allows the user to control and fine-tune various aspects of the irradiance map. Thissection is enabled only when the irradiance map is chosen as the GI method for primary diffusebounces.

Some background for understanding how the irradiance map works is necessary in order to grasp themeaning of these parameters.

Irradiance is a function defined for any point in the 3D space and represents the light arriving at thispoint from all possible directions. In general, irradiance is different in every point and in everydirection. However, there are two useful restrictions that can be made. The first is the surfaceirradiance- which is the irradiance arriving at points which lie on the surface of objects in the scene.This is a natural restriction since we are usually interested in the illumination of objects in the scene,

and objects are usually defined through their surface. The second restriction is that of diffuse surfaceirradiance- which is the total amount of light arriving at a given surface point, disregarding thedirection from which it comes.

In more simple terms, one can think of the diffuse surface irradiance as being the visible color of a

surface, if we assume that its material is purely white and diffuse.

In V-Ray, the term irradiance map refers to a method of efficiently computing the diffuse surfaceirradiance for objects in the scene. Since not all parts of the scene have the same detail in indirectillumination, it makes sense to compute GI more accurately in the important parts (e.g. where objectsare close to each other, or in places with sharp GI shadows), and less accurately in uninterestingparts (e.g. large uniformly lit areas). The irradiance map is therefore built adaptively. This is done byrendering the image several times (each rendering is called a pass) with the rendering resolutionbeing doubled with each pass. The idea is to start with a low resolution (say a quarter of the resolutionof the final image) and work up to the final image resolution.

The irradiance map is in fact a collection of points in 3d space (a point cloud) along with the computedindirect illumination at those points. When an object is hit during a GI pass, V-Ray looks into the

irradiance map to see if there are any points similar in position and orientation to the current one.From those already computed points, V-Ray can extract various information (i.e. if there are anyobjects close by, how fast the indirect illumination is varying etc). Based on that information, V-Raydecides if the indirect illumination for the current point can be adequately interpolated from the pointsalready in the irradiance map, or not. If not, the indirect illumination for the current point is computed,and that point is stored in the irradiance map. During the actual rendering, V-Ray uses a sophisticatedinterpolation method to derive an approximation of the irradiance for all surfaces in the scene.


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PARAMETER

Built-in presets

Current preset- thisdropdown list allows youto choose from several

presets for some of theirradiance mapparameters. You can usethese to quickly set thecolor, normal and distancethresholds, as well as themin/max rates. Thefollowing presets areavailable:

Very low- thispreset is onlyuseful for previewpurposes to showthe generallighting in thescene.

Low- a low-quality preset forpreview purposes

Medium- amedium qualitypreset; works finein many situationsin scenes which

have don't smalldetails.

Mediumanimation- amedium qualitypreset targeted atreducing flickeringin animations -the Distance thresholdis higher.

High- a high-quality preset that works in most situations, even for scenes with small detailsas well as for most animations.

High animation- a high-quality preset that can be used if the High preset produces flickeringin animations - the Distance thresholdis higher.

Very high - a very high quality preset; can be used for scenes with extremely small andintricate details.

Note that the presets are targeted for a typical 640x480 image. Larger images usually can do withlower Min/Max rates than those specified in the presets.

Basic parametersMin rate- this value determines the resolution for the first GI pass. A value of 0 means the resolution

will be the same as the resolution of the final rendered image, which will make the irradiance mapsimilar to the direct computation method. A value of -1means the resolution will be half that of thefinal image and so on. You would usually want to keep this negative, so that GI is quickly computedfor large and flat regions in the image. This parameter is similar to (although not the same as) the Minrateparameter of theAdapti ve subdivision image sampler.


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Max rate- this value determines the resolution of the last GI pass. This is similar to (although not thesame as) the Max rateparameter of theAdaptive subdiv isionimage sampler.

Color threshold (Clr thresh)- this parameter controls how sensitive the irradiance map algorithm is

to changes in indirect lighting. Larger values mean less sensitivity; smaller values make the irradiancemap more sensitive to light changes (thus producing higher quality images).

Normal threshold (Nrm thresh) - this parameter controls how sensitive the irradiance map is tochanges in surface normals and small surface details. Larger values mean less sensitivity; smallervalues make the irradiance map more sensitive to surface curvature and small details.

Distance threshold (Dist thresh) - this parameter controls how sensitive the irradiance map is todistance between surfaces. A value of 0.0 means the irradiance map will not depend on objectproximity at all; higher values place more samples in places where objects are close to each other.

Hemispheric subdivs (HSph. subdivs)- this controls the quality of individual GI samples. Smallervalues make things faster, but may produce blotchy result. Higher values produce smoother images.This is similar to theSubdivsparameter for direct computation. Note that this is not the actual numberof rays that will be traced. The actual number of rays is proportional to the square of this value and

also depends on the settings in the DMC sampler rollout.

Interpolation samples- this is the number of GI samples that will be used to interpolate the indirectillumination at a given point. Larger values tend to blur the detail in GI although the result will besmoother. Smaller values produce results with more detail, but may produce blotchiness iflow Hemispheric subdivsare used. Note that if you use interpolated irradiance maps (i.e.the Modeis set toAnimation (rendering)), V-Ray will actually multiply this value by the number ofirradiance maps used. For example, if you have the Interpolation samplesset to 20, andthe Interpolation framesto 2, V-Ray will actually use 100 samples to interpolate. This is done inorder to preserve the blurring of the GI solution compared to a single frame irradiance map, howeverit also slows down the rendering. To speed up the rendering in that case, you can decrease this valueto 10or 5.

Interpolation frames- this determines the number of frames that will be used to interpolate GI whenthe Modeis set toAnimation (rendering). In this mode, V-Ray interpolates the irradiance from themaps of several adjacent frames to help smooth out any flickering. Note that the actual number offrames used is 2*(interp. frames)+1- e.g. the default value of 2means that in total 5irradiance mapswill be interpolated. Higher values slow down the rendering and may produce "lagging" effect. Lowervalues render faster but may increase flickering. Note that increasing this value also increases thenumber of samples used for interpolation from the irradiance map - see the note for the Interpolationsamplesparameter.

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

irradiance map is calculated. This will give you a rough idea of the indirect illumination even beforethe final rendering is complete. Note that turning this on slows the calculations a little bit, especially forlarge images. This option is ignored when rendering to fields - in that case, the calculation phase isnever displayed.

Show direct light- this option is only available when Show calc phaseis on. It will cause V-Ray toshow direct lighting for primary diffuse bounces in addition to indirect lighting while the irradiance mapis being calculated. Note that V-Ray does not really need to compute this. The option is only forconvenience. This does not mean that direct lighting is not calculated at all - it is, but only forsecondary diffuse bounces (only for GI purposes).

Show samples- when this option is on, V-Ray will show visually the samples in the irradiance map

as small dots in the scene.

Use camera path- when this option is on , V-Ray will calculate the irradiance map samples for theentire camera path, instead of just the current view. This is useful in the following cases:


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Calculating irradiance maps for short fly-through animations in one go. Instead of usingthe Incremental add to current map mode and rendering the animation every Nth frame,you can turn the Use camera path optionon , and render just one single frame - this willproduce information for the entire camera path.

Using irradiance maps for anmations with moving objects where the camera also moves -

either in Single frame, orAnimation (prepass)mode. In this case, setting the Use camerapathoption on will help to further reduce any flickering, as the GI sample positions on staticgeometry will not change.

If you use this option, you should not use interpolated glossy reflections/refractions in VRayMtl, asthey will look odd.

Detail enhancementDetail enhancement is a method for bringing additional detail to the irradiance map in the case wherethere are small details in the image. Due to its limited resolution, the irradiance map typically blurs theGI in these areas or produces splotchy and flickering results. The detail enhancement option is a wayto calculate those smaller details with a high-precision brute-force sampling method. This is similar tohow an ambient occlusion pass works, but is more precise as it takes into account bounced light.

On- turns on detail enhancement for the irradiance map. Note that an irradiance map calculated inthis mode should not be used without the detail option. When detail enhancement is On, you can uselower irradiance map settings and higher Interpolation samples. This is because the irradiance mapis only used to capture the general far-off lighting, while direct sampling is used for the closer detailareas.

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 detail enhancement effect. Smaller radius means thatsmaller parts around the details in the image are sampled with higher precision - this would be fasterbut may be less precise. Larger radius means that more of the scene will use the higher precisionsampling and may be slower, but more precise. This is similar to a radius parameter for an ambientocclusion pass.

Subdivs mult. - this determines the number of samples taken for the high-precision sampling as a

percentage of the irradiance map Hemispheric subdivs. A value of 1.0 means that the same numberof subdivs will be used as for the regular irradiance map samples. Lower values will make the detail-enhanced areas more noisy, but faster to render.

Advanced optionsInterpolation type- this option is used during rendering. It selects the method for interpolating the GIvalue from the samples in the irradiance map.

Weighted average- this method will do a simple blend between the GI samples in the irradiance mapbased on the distance to the point of interpolation and the difference in the normals. While simple andfast, this method tends to produce a blochiness in the result.

Least squares fit - the default method; it will try to compute a GI value that best fits in among thesamples from the irradiance map. Produces smoother results than the weighted average method, butis slower. Also, ringing artifacts may appear in places where both the contrast and density of theirradiance map samples change over a small area.

Delone triangulation- all other methods of interpolation are blurry methods - that is, they will tend to

blur the details in indirect illumination. Also, the blurry methods are prone to density bias(see belowfor a description). In difference, the Delone triangulation method is a non-blurry method and will

preserve the detail while avoiding density bias. Since it is non-blurry, the result might look more noisy(blurring tends to hide noise). More samples will be needed to get a sufficiently smooth result. This


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can be done either by increasing the hemispheric subdivs of the irradiance map samples, or bydecreasing the Noise threshold value in the brute force sampler rollout.

Least squares with Voronoi weights- this is a modification of the least squares fit method aimed at

avoiding the ringing at sharp boundaries by taking in consideration the density of the samples in theirradiance map. The method is quite slow and its effectiveness is currently somewhat questionable.

Although all interpolation types have their uses, it probably makes most sense to use either Leastsquares fitorDelone triangulation. Being a blurry method, Least squares fitwill hide noise and willproduce a smooth result. It is perfect for scenes with large smooth surfaces. Delone triangulationisa more exact method, which usually requires more hemispheric subdivs and high Max irradiance maprate (and therefore more rendering time), but produces accurate results without blurring. This isespecially obvious in scenes where there are a lot of small details.

Sample lookup - this option is used during rendering. It selects the method of choosing suitablepoints from the irradiance map to be used as basis for the interpolation.

Nearest- this method will simply choose those samples from the irradiance map which are closest tothe point of interpolation. (How many points will be chosen is determined by the value of

the Interpolation samplesparameter.) This is the fastest lookup method and was the only oneavailable in early versions of V-Ray. A drawback of this method is that in places where the density ofthe samples in the irradiance map changes, it will pick more samples from the area with higher

density. When a blurry interpolation method is used, this leads to the so-called density biaswhichmay lead to incorrect interpolation and aritfacts in such places (mostly GI shadow boundaries).

Nearest quad-balanced- this is an extension of the nearest lookup method aimed at avoidingdensity bias. It divides the space about the interpolated point in four areas and tries to find an equalnumber of samples in all of them (hence the name quad-balanced). The method is a little slower thanthe simple Nearest lookup, but in general performs very well. A drawback is that sometimes, in itsattempt to find samples, it may pick samples that are far away and not relevant to the interpolatedpoint.

Precalculated overlapping- this method was introduced in an attempt to avoid the drawbacks of thetwo previous ones. It requires a preprocessing step of the samples in the irradiance map during whicha radius of influence is computed for each sample. This radius is larger for samples in places of lowdensity, and smaller for places of higher density. When interpolating the irradiance at a point, themethod will choose every sample that contains that point within its radius of influence. An advantageof this method is that when used with a blurry interpolation method it producses a continuous(smooth) function. Even though the method requires a preprocessing step, it is often faster than theother two. These two properties make it ideal for high-quality results. A drawback of this method isthat sometimes lonely samples that are far-away can influence the wrong part of the scene. Also, ittends to blur the GI solution more than the other methods.

Density-based- the default method; it combines the Nearestand the Precalculatedoverlappingmethods and is very effective in reducing ringing artifacts and artifacts due to low

sampling rates. This method also requires a preprocessing step in order to compute sample density,but it performs a nearest neighbour look-up to choose the most suitable samples while taking sampledensity in account.

Being the fastest of the three methods, Nearestlookup may be used for preview purposes. Nearestquad-balancedperforms fairly well in the majority of cases. Precalculated overlappingis fast and inmany cases performs very well, but may tend to blur the GI solution. The Density-basedmethodproduces very good results in the majority of cases and is the default method.

Note that the lookup method is mostly important when using a blurry interpolation method. Whenusing Delone triangulation, the sample lookup method does not influence the result very much.

Calc. pass interpolation samples- this is used during irradiance map calculation. It represents the

number of already computed samples that will be used to guide the sampling algorithm. Good valuesare between 10 and 25. Low values may speed the calculation pass, but may not provide sufficient


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information. Higher values will be slower and will cause additional sampling. In general, thisparameter should be left to the default value of 15.

Use current pass samples- this is used during irradiance map calculation. When checked, this will

cause V-Ray to use all irradiance map samples computed so far. Unchecking it will allow V-Ray touse only samples collected during previous passes, but not those computing earlier during the current

pass. Keeping this checked will usually cause V-Ray to take less samples (and therefore compute theirradiance map faster). That means that on multiprocessor machines, several threads will bemodifying the irradiance map at the same time. Because of the asynchronous nature of this process,there is no guarantee that the rendering the same image twice will produce the same irradiance map.Normally this is not a problem at all and it is recommended to keep this option checked.

Randomize samples- this is used during irradiance map calculation. When it is checked, the imagesamples will be randomly jittered. Unchecking it will produce samples that are aligned in a grid on thescreen. In general, this option should be kept checked in order to avoid artifacts caused by regularsampling.

Check sample visibili ty- this is used during rendering. It will cause V-Ray to use only those samplesfrom the irradiance map, 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 it willalso slow the rendering, since V-Ray will trace additional rays to determine sample visibility.

ModeMode - this groups of controls allow the user to select the way the irradiance map is (re)used.Bucket mode- in this mode, a separate irradiance map is used for each rendered region ("bucket").

Note that since each bucket is computed independently of the others, there may be differences at thebucket edges. They can be reduced by using higher settings for the irradiance map (the Highpreset,more hemispheric subdivs and/or smaller Noise thresholdfor the DMC sampler).

Single frame- the default mode; a single irradiance map is computed for the whole image, and a newirradiance map is computed for each frame. This is the mode to use when rendering animations ofmoving objects. In doing so one must make sure that the irradiance map is of sufficiently high quality

to avoid flickering.

Multiframe incremental- this mode is useful when rendering a sequence of frames (not necessarilyconsequtive) where only the camera moves around (so-called fly-through animations). V-Ray willcompute a new full-image irradiance map for the first rendered frame; for all other frames V-Ray willtry to reuse and refine the irradiance map that has been computed so far.

From file- in this mode V-Ray will simply load the irradiance map from the supplied file at the start of

the rendering sequence and will use this map for all the frames in the animation. No new irradiancemap will be computed. This mode can be used for fly-through animations and will work well in networkrendering mode.

Add to current map- in this mode V-Ray will compute a completely new irradiance map and will addit to the map that is already in memory. This mode is useful when compiling an irradiance map torender multiple views of a static scene. Note that this mode is not supported for distributed rendering.

Incremental add to current map- in this mode V-Ray will use the irradiance map that is already inmemory and will only refine it in places that don't have enough detail. This mode is useful whencompiling an irradiance map to render multiple views of a static scene or a fly-through animation.

Animation (prepass) - in this mode V-Ray calculates irradiance maps to be used later on for finalrendering with theAnimation (rendering)mode. One irradiance map is created for each frame andwritten into a separate file. Note that in this mode you have to render one map for each frame (i.e. youcannot render every Nth frame). V-Ray automatically disables rendering of the final image in thismode - only irradiance map prepasses are calculated.

Animation (rendering)- in this mode V-Ray renders a final animation using irradiance maps createdwith theAnimation (prepass)mode. Irradiance maps from several adjacent frames are loaded


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together and blended so as to reduce flickering. The number of irradiance maps that are interpolatedis determined by the Interp. framesparameter.

The irradiance map mode that should be used depends on the particular rendering task - a staticscene, a static scene rendered from multiple views, a fly-through animation or an animation withmoving objects. Refer to thetutorialssection for more information.

I r r a d i a n c e ma p co n t r o l bu t t o n s

There are some more buttons in this group that allow one to perform certain operations on theirradiance map:

Browse- this button allows the user to select the irradiance map file which will be loaded if the Fromfilemode is selected. Alternatively, the user can enter the path and name of the file directly in the editbox.

Save to fi le- this will save to file the irradiance map which is currently in memory. Note that the Don'tdeleteoption in the On r ende r end group must be turned on. Otherwise V-Ray will automatically

delete the irradiance map at the end of the rendering process.

Reset i rradiance map- this will clear the irradiance map from memory.

On render endThis group of controls instructs V-Ray what to do with the irradiance map at the end of the renderingprocess.

Don't delete- the default for this option is on, which means that V-Ray will keep the irradiance map inmemory until the next rendering. If this option is cleared, V-Ray will delete the irradiance map whenrendering is complete. This means that you will not be able to save the map manually afterwards.

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

at the end of the rendering. This mode is particularly useful if you want to send the irradiance map forrendering on a different machine through network rendering.

Switch to saved map- this option is only available if theAuto saveoption is turned on. If Switch tosaved map is on, then V-Ray will also automatically set the irradiance map mode to From fileandwill set the file name to be that of the map that was just saved.

Notes You can view, merge and save irradiance maps with the irradiance map viewertool.

For animated irradiance maps, GI samples on different objects are not shared; this may leadto small objects to appear black in the final renders. To solve this issue, group those objects

together - this will work as GI samples are shared for objects which are part of the samegroup.


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Global photon map

General

Parameters

Notes

GeneralThe global photon map is somewhat similar to the irradiance map. It is also used to represent thelighting in the scene, and it is a collection of points in 3D space (a point cloud). However, the photonmap 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 various surfaces. The hit points are stored in thephoton map.

Reconstructing the illumination from the photon map is also different from the irradiance map. Withthe irradiance map, a simple interpolation is used to blend the nearby GI samples. With the photonmap, we need to estimate the photon densityat a given point. The idea of density estimation iscentral to the photon map. V-Ray can use several methods for density estimation, each with its own

advantages and disadvantages. Usually these methods are based on looking for the photons that arenearest to the shaded point.

Note that in general, the photon map provides a less accurate approximation of the scene illuminationthan the irradiance map, espcially when it comes to small details. The irradiance map is builtadaptively, whereas the photon map is not. Also a major disadvantage of the photon map isthe boundary bias. This unwanted effect is mostly visible around corners and object edges, whichappear darker than they should be. The irradiance map can also exhibit boundary bias, however itsadpative nature allows one to decrease the effect greatly. Another disadvantage of the photon map isthat it cannot simulate illumination from skylight. This is because the photons need an actual surfaceto be emitted from. The skylight, at least in V-Ray, is not a surface actually present in the scene.

On the other hand, the photon map is view-independent and can be computed relatively quickly. Thismakes it ideal for approximating the scene illumination when used together with more accuratemethods like direct computation or the irradiance map.

Parameters

Note that the building of thephoton map is also controlled by the photon settings of individual lights in the scene. See the Lightsettings dialogfor more information.


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Bounces - this parameter controls the number of light bounces approximated by the photon map.More bounces produce a more reallistic result, but take more time and memory.

Auto search dist - when this ison , V-Ray will try to compute a suitable distance within which tosearch for photons. Sometimes the computed distance is ok, in other cases it might be too big (which

will slow down the rendering) or too small (which will produce a more noisy result).Search dist- this option is only available whenAuto search dist is off. It allows you to specify thephoton search distance manually. Keep in mind that this value depends on the size of your scene.Lower values will speed up the rendering but may produce more noisy results. Larger values will slowdown the rendering but may produce smoother results.

Max photons- this option specifies how many photons will be taken into consideration whenapproximating the irradiance at the shaded point. More photons mean a smoother (and more blurry)result and may also slow down the rendering. Smaller values mean a more noisy result but will renderfaster. When this value is 0, V-Ray will use all the photons in the given search range.

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

Max density- this parameter allows you to limit the resolution (and thus the memory) of the photonmap. Whenever V-Ray needs to store a new photon in the photon map, it will first look if there are anyother photons within a distance specified by Max density. If there is already a suitable photon in themap, V-Ray will just add the energy of the new photon to the one in the map. Otherwise, V-Ray willstore the new photon in the photon map. Using this options allows you to shoot many photons (andthus get smoother results) while keeping the size of the photon map manageable.

Convert to irradiance map - this will cause V-Ray to precompute the irradiance at the photon hitpoints stored in the photon map. This allows fewer photons to be used when interpolated theirradiance during rendering, while keeping the result relatively smooth. It is important to note that theresulting map stores irradiance, but is not the same as the irradiance cache used by V-Ray forprimary diffuse bounces.

Interp. samples- this controls how many irradiance samples will be taken from the photon map onceit is converted to an irradiance map. Larger values produce smoother results, but may be slower;smaller values produces more noisy results but rendering is faster.

Convex hull area estimate- when this is off, V-Ray will use a simplified algorithm for computing thearea, covered by a number of photons (by only taking the distance to the farthest photon). Thisalgorithm may cause corners to be darker. Using the convex hull area estimate avoids the darkcorners problem, but is slower and not as robust.

Store direct ligh t- when this is on , V-Ray will store direct illumination in the photon map as well. This

may speed up the irradiance map or brute force GI, when used as a primary engine, and there arelots of lights in the scene. When this is of f, direct lighting will be computed always by tracing thenecessary rays. This may slow things down if there are lots of lights in the scene.

Retrace threshold- when this is greater than 0.0, V-Ray will use brute force GI near corners, insteadof the photon map, in order to obtain a more accurate result and to avoid splotches in these areas.This may slow down the rendering. When this is 0.0, the photon map will be used always, which willbe faster, but may produce artifacts near corners or in places where objects are close to each other.

Retrace bounces - controls how many bounces will be made when retracing corners. If Retracethresholdis 0.0, then this parameter is ignored. Typically this should be equal tothe Bouncesparameter.

Notes The photon map cannot simulate secondary illumination due to skylight. The photon map is

mostly useful for interior scenes with artificial lighting or relatively small windows.


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The photon map works only with V-Ray materials. Standard materials will receive GI, but willnot generate any photons.

Light cache

General

Parameters

Calculation parameters

Reconstruction parameters

Mode

On render end

Notes

GeneralLight caching (sometimes also called light mapping) is a technique for approximating the globalillumination in a scene. This method was developed originally by Chaos Group specifically for the V-Ray renderer. It is very similar to photon mapping, but without many of its limitations.

The light cache is built by tracing many many eye 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 photonmap. On the other hand, in a sense, it is the exact opposite of the photon map, which traces pathsfrom the lights, and stores the accumulated energy from the beginning of the path into the photon

map.

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

It is easier to set up. We only have the camera to trace rays from, as opposed to the photonmap, which must process each light in the scene and usually requires separate setup for eachlight.

The light-caching approach works efficiently with any lights - including skylight, self-illuminated objects, non-physical lights, photometric lights etc. In contrast, the photon map islimited in the lighting effects it can reproduce - for example, the photon map cannot reproducethe illumination from skylight or from standard omni lights without inverse-square falloff.

The light cache produces correct results in corners and around small objects. The photon

map, on the other hand, relies on tricky density estimation schemes, which often producewrong results in these cases, either darkening or brightening those areas.

In many cases the light cache can be visualized directly for very fast and smooth previews ofthe lighting in the scene.

Even with these advantages, light caching is similar in speed to the photon map and can produceapproximations to the global lighting in a scene very quickly. In addition, the light cache can be usedsuccessfully 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 thecamera.


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Like the photon map, the light cache is not adaptive. The illumination is computed at a fixedresolution, which is determined by the user.

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

Parameters

Calculation parametersThese parameters affect the calculation phase of the light cache; they do not affect the finalrendering.

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

Sample size- this determines the spacing of the samples in the light cache. Smaller numbers meanthat the samples will be closer to each other, the light cache will preserve sharp details in lighting, butit will be more noisy and will take more memory. Larger numbers will smooth out the light cache but

will loose detail. This value can be either in world units or relative to the image size, depending onlight cache Scalemode.

Scale- this parameter determines the units of the Sample s izeand 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, and samples that are faraway will be larger. Note that the units do not depend on the image resolution. This value is bestsuited for stills or animations where the light cache needs to be computed at each frame.

World - the sizes are fixed in world units everywhere. This can affect the quality of the samples -samples that are close to the camera will be sampled more often and will apear smoother, whilesamples that are far away will be noisier. This value might work better for fly-through animations,since it will force constant sample density everywhere.


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Number of passes- the light cache is computed in several passes, which are then combined into thefinal light cache. Each pass is rendered in a separate thread independently of the other passes. Thisensures that the light cache is consistent across computers with different number of CPUs. In general,a light cache computed with smaller number of passes may be less noisy than a light cache computedwith more passes, for the same number of samples; however small number of passes cannot bedistributed effectively across several threads. For single-processor non-hyperthreading machines, the

number of passes can be set to 1 for best results.

Store direct light- with this option, the light cache will also store and interpolate direct light. This canbe useful for scenes with many lights and irradiance map or direct GI method for the primary diffusebounces, since direct lighting will be computed from the light cache, instead of sampling each andevery light. Note that only the diffuse illumination produced by the scene lights will be stored. If youwant to use the light cache directly for approximating the GI while keeping the direct lighting sharp,uncheck this option.

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

Use camera path- when this option is on , V-Ray will calculate the light cache samples for the entirecamera path, instead of just the current view, in the same way as this is done for the Fly-throughmode. This is useful when rendering animations with moving objects where the camera alsomoves and the light cache needs to be inSingle framemode. In this case, setting the Use camerapathoption on will help to reduce any flickering, as the GI sample positions on static geometry willnot change.

Adapt ive tracing- when this option is on, V-Ray will store additional information about the incominglight for each light cache sample, and try to put more samples into the directions from which morelight coming. This may help tp reduce the noise in the light cache, particularly in the case of caustics.

Use directions only- this option is only available when theAdapt ive t racingoption is on. It causesV-Ray to only use the optimized directions, generated from the light cache samples, rather than the

accumulated irradiance from the samples themselves. This produces more accurate results, but alsoa noisier light cache.

Reconstruct ion parametersThese parameters control how the light cache is used in the final rendering, after is has beencalculated.

Pre-filter- when this is turned on, the samples in the light cache are filtered beforerendering. Note

that this is different from the normal light cache filtering (see below) which happens during rendering.Prefiltering is performed by examining each sample in turn, and modifying it so that it represents theaverage of the given number of nearby samples. More prefilter samples mean a more blurry and lessnoisy light cache. Prefiltering is computed once after a new light cache is computed or loaded fromdisk.

Filter - this determines the type of render-time filter for the light cache. The filter determines howirradiance is interpolated from the samples in the light cache.None- no filtering is performed. The nearest sample to the shaded point is taken as the irradiancevalue. This is the fastest option, but it may produce artifacts near corners, if the light cache is noisy.You can use pre-filtering (see above) to decrease 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 the shading point and averages their value. Thisfilter is not suitable for direct visualization of the light cache, but is useful if you use the light cache forsecondary bounces. A property of this filter is that is adapts to the sample density of the light cacheand is computed for a nearly constant time. The Interpolation samplesparameter determines howmany of the nearest samples to look up from the light cache.


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Fixed - this filter looks up and averages all samples from the light cache that fall within a certaindistance from the shaded point. This filter produces smooth results and is suitable for directvisualization of the light cache (when it is used as the primary GI engine). The size of the filter isdetermined by the Filter size parameter. Larger values blur the light cache and smooth out noise.Typical values for the Filter size are 2-6 times larger than the Sample size. Note that Filter sizeusesthe same scale as the Sample sizeand its meaning depends on the Scaleparameter.

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

ModeMode- determines the rendering mode of the light cache:Progressive path tracing- in this mode, the light cache algorithm is used to sample the final imageprogressively. For a discussion of this mode see the tutorial.

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

Fly-through - this will compute a light cache for an entire fly-through animation, assuming that the

camera position/orientation is the only thing that changes. The movement of the camera in the activetime segment only is taken in consideration. Note that it may be better to use WorldScalefor fly-through animations. The light cache is computed only at the first rendered frame and is reusedwithout changes for subsequent frames.

From file- in this mode the light cache is loaded from a file. The light cache file does not include the

prefiltering of the light cache; prefiltering is performed after the light cache is loaded, so that you canadjust it without the need to recompute the light cache.

File- specifies the file name to load the light cache from, when the Modeis set to From file.

Save to file - this button allows to save the light cache to a file on disk, for later re-use. Note thatthe Don't deleteoption must be on for this to work - otherwise, the light cache will be deleted as soon

as rendering is complete and it will not be possible to save it.

On render endThis group of controls determine what happens with the light cache after rendering is complete.

Don't delete- when on (the default), the light cache remains in memory after the rendering. Turn thisoption offto automatically delete the light cache (and thus save memory).

Auto save- when on , the light cache will be automatically written to the specified file. Note that thelight cache will be written as soon as it is calculated, rather than at the actual end of the rendering.

Switch to saved map- when on , after the rendeing is complete, the light cache Modewill beautomatically set to From fileand the name of the auto-saved light cache file will be copied tothe Fileparameter.

Notes Do not set theAdapt ive amountin the DMC samplerrollup to 0.0when using the light

cache, as this will cause excessive render times.

Do not apply perfectly white or very close to white materials to a majority of the objects in thescene, as this will cause excessive render times. This is because the amount of reflected lightin the scene will decrease very gradually and the light cache will have to trace longer paths.Also avoid materials that have one of their RGB components set to maximum (255) or above.

If you want to use the light cache for animation, you should choose a large enough value forthe Filter sizein order to remove the flickering in the GI.


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There is no difference between light caches computed for primary bounces (directvisualization) and for secondary bounces. You can safely use light caches computed in one ofthese modes for the other.

Similar to the photon map, you can get "light leaks" with the light cache around very thinsurfaces with substantially different illumination on both sides. Sometimes it may be possible

to reduce this effect by assigning different GI Surface ID's to the objects on both sides of thethin surface (see the Object settingsdialog); the effect can also be reduced by decreasingthe Sample sizeand/or the filtering.

Caustics

General

Parameters

Notes

GeneralV-Ray supports the rendering of the caustics effects. In order to produce this effect you must haveproper caustics generators and caustics receivers in the scene (for information how to make an objecta caustics generator/receiver read the Object settingsand Lights settingssections in Renderparameters > System >Object/Light settings. The settings in this parameter section control thegeneration of the photon map (an explanation of the photon map can be found inthe Terminologysection).

In order to calculate the caustics effects, V-Ray uses a technique known as photon mapping. It is atwo-pass technique. The first pass consists of shooting particles (photons) from the light sources inthe scene, tracing them as they bounce around the scene, and recording the places where the

photons hit the object surfaces. The second pass is the final rendering, when the caustics arecalculated by using density estimationtechniques on the photon hits stored during the first pass.

Parameters

On- turns rendering ofcausticson and of f.

Multiplier- this multiplier controls the strength of the caustics. It is global and applies to all lightsources that generate caustics. If you want different multipliers for the different light sources then you


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should use the local light settings.Note: this multiplier is cumulative with the multipliers in the locallight settings.

Search distance- when V-Ray needs to render the caustics effect at a given surface point, it

searches for a number photons on that surface in the area surrounding the shaded point (searcharea). The search area in fact is a circle with center the original photon and its radius is equal to

theSearch distancevalue. Smaller values produce sharper, but perhaps more noisy caustics; largervalues produce smooher, but blurrier caustics.

Max photons- this is the maximum number of photons that will be considered when rendering thecaustics effect on a surface. Smaller values cause less photons to be used and the caustucs will besharper, but perhaps noisier. Larger values produce smoother, but blurrier caustics. The special valueof 0means that V-Ray will use all the photons that it can find inside the search area.

Max densit y- this parameter allows you to limit the resolution (and thus the memory) of the causticsphoton map. Whenever V-Ray needs to store a new photon in the caustics photon map, it will firstlook if there are any other photons within a distance specified by Max density. If there is already asuitable photon in the map, V-Ray will just add the energy of the new photon to the one in the map.Otherwise, V-Ray will store the new photon in the photon map. Using this options allows you to shoot

many photons (and thus get smoother results) 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 map will be generated. It will overwrite anyprevious photon map left over from previous rendering.

Save to file- hit this button if you want to save an already generated photon map in a file.

From file- when you enable this option V-Ray will not compute the photon map but will load it from afile. Hit the Browsebutton on the right to specify the file name.

File - the file name with the caustics photon map to be loaded when the Modeis set to From file.

Don't delete- when checked, V-Ray will keep the photon map in memory after the scene renderinghas finished. Otherwise the map will be deleted and the memory it takes will be freed. This option canbe especially useful if you want to compute the photon map for a particular scene only once and thenreuse it for further rendering.

Auto save - when this is turned on, V-Ray will automatically save the caustics photon map to theprovided file when rendering is complete.

Switch to saved map- this option is only available ifAuto saveis on. It will cause V-Ray toautomatically set the Modeto From filewith the file name of the newly saved map.

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


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ENVIRONMENT

General

Parameters

GI Environment (skylight)

Reflection/Refraction environment

Refraction environment

Notes

GeneralThe Environment section in V-Ray render parameters is where you can specify a color and a texturemap to be used during GI and reflection/refraction calculations. If you don't specify a color/map thenthe background color and map specified in the 3ds Max Environment dialog will be used by default.

Parameters

GI Environment (skylight)This group allows you to override the 3ds Max Environment settings for indirect illuminationcalculations. The effect of changing the GI environment is similar to skylight.

On- turns on and of fthe GI environment override.

Color- lets you specify the environment (skylight) color. Note that this is ignored if there is anenvironment texture specified.

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

itself does not have brightness controls.

Texture - lets you choose a GI environment texture. Note that if present, the texture overrides thespecifiedColor.

Reflection/refraction environmentThis group allows you to override the 3ds Max Environment settings when reflections and refractionsare calculated. Note that you can also override the reflection/refraction environment on a per materialbasis (seeVRayMtl) or a per map basis (see VRayMap). If you do not enable the Refraction override,this group of controls affects both reflections and refractions. If you enable the Refraction override,then this group affects only reflections.

On- with this option turned on V-Ray will use thespecified Colorand Textureduring reflection/refraction calculations.

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


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Multiplier - a multiplier for the color value. Note that the multiplier does not affect the environmenttexture (if present). Use an Outputmap to control the brightness of the environment map, if the mapitself does not have brightness controls.

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

the Color.

Refraction environmentThis group allows to override the environment for refraction rays only. When this override is disabled,V-Ray will use the environment specified in the Reflection/refraction group when calculatingrefractions.

On- enables the refraction environment override.

Color- specifies the environment color for refractions. This color is ignored if there is an environmenttexture specified.

Multiplier- a multiplier for the Colorvalue. Note that the multiplier does not affect the environmenttexture (if present). Use an Outputmap to control the brightness of the environment map, if the mapitself does not have brightness

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