Universal V-Ray 1.5 Settings

General

Setting the V-Ray renderer

Notes

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General

The "universal" settings comprise a set of settings that we have found to work very well for still images in many situations. Please note that these settings are not optimal, in the sense that with enough tweaking, you can probably get similar quality with faster render times. The beauty of these settings though, is that they require almost no tweaking and you are guaranteed to get a good result in the end.

The advantages of these settings are:

very little parameters for controlling render quality vs speed (essentially, only the Noise threshold);

they work for a very large number of scenes; they typically produce high-quality results.

Of course, there is a disadvantage: the scene may render quite slow. With tweaking, you may get faster results.

These settings work, because the high AA subdivs essentially cause all the sampling to be performed by the image sampler. It will take as many samples per pixel as required to achieve the specified noise threshold. In many ways, this is similar to PPT (progressive path tracing), but is done on a per-bucket basis and the number of samples is adaptive for each pixel.

Setting the V-Ray renderer

1. Set V-Ray as the current rendering engine (with the default V-Ray settings).

2. In the Image sampler rollout, switch the image sampler Type to Adaptive DMC. Set the Max. subdivs to 100 (one hundred). Leave the Min. subdivs to 1.

4. In the Indirect illumination rollout, Turn GI on, set the Primary GI engine to Brute force. Do not change the Subdivs. Set the Secondary GI engine to Light cache.

5. In the Light cache rollout, set the light cache Interpolation samples to 5.

6. In the Color mapping rollout, make sure that the Clamp output and Sub-pixel mapping options are off.

7. In the DMC sampler rollout, set the Adaptive amount parameter to 1.0. Typically you will also need to adjust the Noise threshold as the default may produce too much noise. A good value is, for example, 0.005.

8. You can also control the noise directly from the Image sampler rollout, if you uncheck the Use DMC sample thresh. parameter, and adjust the Clr. thresh instead (e.g. to 0.005).  

Notes

Leave all subdivs anywhere at their default values. They won't have any effect anyways - the 100 AA subdivs will almost certainly override everything else. 

Avoid using sharpening AA filters. They can make the noise more apparent.

 

Image Sampler (Antialiasing)General

Parameters

Fixed rate sampler

Adaptive DMC sampler

Adaptive subdivision sampler

Notes

General

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

V-Ray implements several algorithms for sampling an image. All image samplers support MAX's standard antialiasing filters, although at the cost of increased rendering time. You can choose between Fixed rate sampler, Adaptive DMC sampler and Adaptive subdivision sampler.

Parameters

Image sampler

Type - specifies the image sampler type:

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

Adaptive DMC - this sampler takes a variable number of samples per pixel depending on the difference in the intensity of the pixels;

Adaptive subdivision - this sampler divides the image into an adaptive grid-like structure and refines depending on the difference in pixel intensity.

Antialiasing filter

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

Fixed rate sampler

This is the simplest image sampler, 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 of each pixel is taken. If this is greater than 1, the samples are distributed within the pixel. The actual number of pixels is the square of this parameter (e.g. 4 subdivs produce 16 samples per pixel). 

Adaptive DMC sampler

This sampler makes a variable number of samples per pixel based on the difference in intensity between the pixel and its neighbors. 

This is the preferred sampler for images with lots of small details (like VRayFur, for example) and/or blurry effects (DOF, motion blur, glossy reflections etc). It also takes up less RAM than the Adaptive subdivision sampler.

Min subdivs - determines the initial (minimum) number of samples taken for each pixel. You will rarely 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 of this number (e.g. 4 subdivs produce 16 samples per pixel).

Max subdivs - determines the maximum number of samples for a pixel. The actual maximum number of sampler is the square of this number (e.g. 4 subdivs produces a maximum of 16 samples). Note that V-Ray may take less than the maximum number of samples, if the difference 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 specified in the DMC sampler to determine if more samples are needed for a pixel. When this is off, the Color threshold parameter 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.

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

Adaptive subdivision sampler

This is an advanced image sampler capable of undersampling (taking less than one sample per pixel). In the absence of blurry effects (direct GI, DOF, glossy reflection/refraction 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 as the other image samplers. However, with detailed textures and/or blurry effects, it can 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 per pixel; -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, 1 means four samples, 2 means eight samples etc.

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

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

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

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

Show samples - if this is on, V-Ray will show an image where the pixel brightness is directly proportional 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, but here are some tips: 

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

o For images with detailed textures or lots of geometry detail and only a few blurry effects, the Adaptive DMC sampler performs best. Also in the case of animations involving detailed textures, the Adaptive subdivision sampler might produce jittering which the Adaptive 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 and render time. 

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

Indirect illumination (GI)General

Approaches to indirect illumination

Primary and secondary bounces

Parameters

Notes

General

Approaches to indirect illumination

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

Brute force - this is the simplest approach; indirect illumination is computed independently for each shaded surface point by tracing a number of rays in different directions 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-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 compute the indirect illumination only at some points in the scene, and interpolate for the rest of the points.

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; 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 and 

bouncing 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 be used directly; however it can be used as a rough approximation to the lighting in the scene to speed 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 built by tracing many many eye paths from the camera. Each of the bounces in the path stores the illumination from the rest of the path into a 3d structure, very similar to the photon map. The light map is a universal GI solution that can be used for both interior or exterior scenes, either directly or as a secondary bounce approximation when used with the irradiance 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 the photon map, which must process each light in the scene and usually requires 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 photon map is limited in the lighting effects it can reproduce - for example, the photon map cannot reproduce the illumination from skylight or from standard omni lights without inverse-square falloff. 

o 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 produce wrong results in these 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 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 for indirectly visible parts of the scene as well - for example, one light cache can approximate 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 or 

brute force GI if you want to achieve better results with bump maps. o lighting involving motion-blurred moving objects is not entirely correct, but is very 

smooth since the light cache blurs GI in time as well (as opposed to the irradiance map, where each sample is computed 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 suitable method for your scene.

Primary and secondary bounces

The indirect illumination controls in V-Ray are divided into two large sections: controls concerning primary diffuse bounces and controls concerning secondary diffuse bounces. A primary diffuse bounce occurs when a shaded point is directly visible by the camera, or through specular reflective or refractive surfaces. A secondary bounce occurs when a shaded point is used in GI calculations.

Parameters

On - turn indirect illumination on and off.

GI caustics

GI caustics represent light that has gone through one diffuse, and one or several specular reflections (or refractions). GI caustics can can be generated by skylight, or self-illuminated objects, for example. However, caustics caused by direct lights cannot be simulated in this way. You must use the separate Caustics section to control direct light caustics. Note that 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 transparent objects. 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 specular surfaces. This is off by default, because reflective GI caustics usually contribute little to the final illumination, while often they produce undesired subtle noise.

Post-processing

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

Saturation - controls the saturation of the GI; a value of 0.0 means that all color will be removed from the GI solution and will be in shades of grey only. The default value of 1.0 means the GI solution remains unmodified. Values above 1.0 boost the colors in the GI solution.

Contrast - this parameter works together with Contrast base to boost the contrast of the GI solution. When Contrast is 0.0, the GI solution becomes completely uniform with the value defined by Contrast base. A value of 1.0 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. 

Ambient occlusion

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 0.0 will produce no ambient occlusion.

Radius - ambient occlusion radius. 

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

Primary diffuse bounces

Multiplier - 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 are possible, 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 diffuse bounces. See the Irradiance map section 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 it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffuse bounces. See the brute force GI section for more information.

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

Secondary diffuse bounces

Multiplier - this determines the effect of secondary diffuse bounces on the scene illumination. Values close 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 are possible, they are not physically plausible.

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

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

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 it does not produce good enough results for final renderings when used as a primary GI engine. See the Global photon map section for more information.

Brute force - selecting this method will cause V-Ray to use direct computation for primary diffuse bounces. See the Brute force GI section for more information.

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

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 GI multipliers 

to their default value of 1.0. While other values are possible, they will not produce a physically accurate result.

Light CacheGeneral

Parameters

  Calculation parameters

  Reconstruction parameters

  Mode

  On render end

Notes

General

Light caching (sometimes also called light mapping) is a technique for approximating the global illumination 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 the path stores the illumination from the rest of the path into a 3d structure, very similar to the

photon map. On the other hand, in a sense, it is the exact opposite of the photon map, which traces paths from 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 photon map, which must process each light in the scene and usually requires separate setup for each light. 

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 is limited in the lighting effects it can reproduce - for example, the photon map cannot reproduce the 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 produce wrong 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 of the lighting in the scene.

Even with these advantages, light caching is similar in speed to the photon map and can produce approximations to the global lighting in a scene very quickly. In addition, the light cache 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. The illumination 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 light cache; they do not affect the final rendering.

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

Sample size - this determines the spacing of the samples in the light cache. Smaller numbers mean that the samples will be closer to each other, the light cache will preserve sharp details in lighting, but it 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 on light cache Scale mode.

Scale - this parameter determines the units of the Sample size 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, and samples that are far away will be larger. Note that the units do not depend on the image resolution. This value is best suited 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 appear smoother, while samples that are far away will be noisier. This value might work better for fly-through animations, since it will force constant sample density everywhere.

Number of passes - the light cache is computed in several passes, which are then combined into the final light cache. Each pass is rendered in a separate thread independently of the 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 of passes may be less noisy than a light cache computed with more passes, for the same number of samples; however small number of passes cannot be distributed 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 can be useful for scenes with many lights and irradiance map or direct GI method for the primary diffuse bounces, since direct lighting will be computed from the light cache, instead of sampling each and every light. Note that only the diffuse illumination produced by the scene lights will be stored. If you want 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 the calculation of the light cache and is provided only as a feedback to the user. This option is ignored when 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 entire camera path, instead of just the current view, in the same way as this is done for the Fly-through mode. This is useful when rendering animations with moving objects where the camera also moves and the light cache needs to be in Single frame mode. In this case, setting the Use camera path option on will help to reduce any flickering, as the GI sample positions on static geometry will not change.

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

Use directions only - this option is only available when the Adaptive tracing option is on. It causes V-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 also a noisier light cache.

Reconstruction parameters

These parameters control how the light cache is used in the final rendering, after is has been

calculated.

Pre-filter - when this is turned on, the samples in the light cache are filtered before rendering. 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 the average of the given number of nearby samples. More prefilter samples mean a more blurry and less noisy light cache. Prefiltering is computed once after a new light cache is computed or loaded from disk.

Filter - this determines the type of render-time filter for the light cache. The filter determines how irradiance 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 irradiance value. 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 cache is 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. This filter is not suitable for direct visualization of the light cache, but is useful if you use the light cache for secondary bounces. A property of this filter is that is adapts to the sample density of the light cache 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 the light cache that fall within a certain distance from the shaded point. This filter produces smooth results and is suitable for direct visualization of the light cache (when it is used as the primary GI engine). The size of the filter is determined 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 size uses the same scale as the Sample size and its meaning depends on the Scale parameter.

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

Mode

Mode - determines the rendering mode of the light cache:

Progressive path tracing - in this mode, the light cache algorithm is used to sample the final image progressively. 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 active time segment only is taken in consideration. Note that it may be better to use World Scale for fly-through animations. The light cache is computed only at the first rendered frame and is reused without 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 can adjust it without the need to recompute the light cache.

File - specifies the file name to load the light cache from, when the Mode is 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 that the Don't delete option 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 end

This 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 this option off to 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 the light 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 rendering is complete, the light cache Mode will be automatically set to From file and the name of the auto-saved light cache file will be copied to the File parameter.

Notes

Do not set the Adaptive amount in the DMC sampler rollup to 0.0 when 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 the scene, as this will cause excessive render times. This is because the amount of reflected light in 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 for the Filter size in order to remove the flickering in the GI. 

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

Similar to the photon map, you can get "light leaks" with the light cache around very thin surfaces 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 the thin surface (see the Object settings dialog); the effect can also be reduced by decreasing the Sample size and/or the filtering.

Color MappingGeneral

Parameters

Search keywords: color mapping, tone mapping, burn-out, overexpose

General

Color mapping (also called tone mapping) can be used to apply color transformations on the final image colors. Sometimes an image can contain a higher range of colors that can be displayed on a computer screen. Color mapping has the task of re-mapping the image values to be suitable for display purposes.

Parameters

Type - this is the type of transformation used. These are the possible types: 

Linear multiply - this mode will simply multiply the final image colors based on their brightness are. Color components that are too bright (above 1.0 or 255) will be clipped. This can result in burnt out spots near bright light sources.

Exponential - this mode will saturate the colors based on their brightness. This can be useful to prevent burn-outs in very bright areas (for example around light sources etc). This mode will not clip bright colors, but will instead saturate them.

HSV exponential - this mode is very similar to the Exponential mode, but it will preserve the color hue and saturation, instead of washing out the color towards white.

Intensity exponential - this mode is similar to the Exponential one, but it will preserve the ratio of the RGB color components and will only affect the intensity of the colors.

Gamma correction - this mode applies a gamma curve to the colors. In this case, the Dark multiplier is a general multiplier for the colors before they are gamma-corrected. The Bright multiplier is the inverse of the gamma value (f.e. for gamma 2.2, the Bright multiplier must be 0.4545).

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

Reinhard - this mode is a blend between exponential-style color mapping and linear mapping. If the Burn value is 1.0, the result is linear color mapping and if the Burn value is 0.0, the result 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 gamma correction for the output image regardless of the color mapping mode. Note that the value here is the inverse of the one used for the Gamma correction color mapping type. For example, to correct the image for a 2.2-gamma display, you should set the Gamma parameter simply to 2.2.

Sub-pixel mapping - this option controls whether color mapping will be applied to the final image pixels, or to the individual sub-pixel samples. In older versions of V-Ray, this option was always assumed to be on, however its default value is now off as this produces more correct renderings, especially if you use the universal settings approach.

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

Clamp level - this option specifies the level at which color components will be clamped if the Clamp output option is on.

Affect background - if this is off, color mapping will not affect colors belonging to the

background.

Don't affect colors (adaptation only) - when this parameter is on, the color mapping will not be applied to the final image, however V-Ray will proceed with all its calculations as though color mapping is applied (e.g. the noise levels will be corrected accordingly). This can be useful, for example, if you know that you will apply some color correction to the image later on, but wish to keep the rendering itself in linear space for compositing purposes. Note that the Clamp output option will have an effect regardless of the value of the Don't affect colors option.

Linear workflow - when this option is checked V-Ray will automatically apply the inverse of the Gamma correction that you have set in the Gamma field to all VRayMtl materials in your scene. Note that this option is intended to be used only for quickly converting old scenes which are not set up with proper linear workflow in mind. This option is not a replacement for proper linear workflow.

DMC SamplerGeneral

Parameters

References

General

Monte Carlo (MC) sampling is a method for evaluating "blurry" values (antialiasing, depth of field, indirect illumination, area lights, glossy reflections/refractions, translucency, motion blur etc). V-Ray uses a variant of Monte Carlo sampling called deterministic Monte Carlo (DMC). The difference between pure Monte Carlo sampling and deterministic Monte Carlo is that the first uses pseudo-random numbers which are different for each and every evaluation (and so re-rendering a single image will always produce slightly different results in the noise), while deterministic Monte Carlo uses a pre-defined set of samples (possibly optimized to reduce the noise), which allows re-rendering an image to always produce the exact same result. By default, the deterministic Monte Carlo method used by V-Ray is a modification of Schlick sampling, introduced by Christophe Schlick in 1991 (see the References section below).

Note that there exists a sub-set of DMC sampling called quasi Monte Carlo (QMC) sampling, in which the samples are obtained from sequences of numbers, called low-discrepancy sequences, 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 that determines how many and what exactly samples to be taken for a particular value, depending on the context in which that value is required. This framework is called the "DMC sampler".

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

The subdivs value supplied by the user for a particular blurry effect. This is multiplied by the Global subdivs multiplier (see below). 

The importance of the value (for example, dark glossy reflections can do with fewer samples than bright ones, since the effect of the reflection on the final result is smaller; distant area lights require fewer samples than closer ones etc). Basing the number of samples allocated for a value on importance is called importance sampling. 

The variance (think "noise") of the samples taken for a particular value - if the samples are not very different from each other, then the value can do with fewer samples; if the samples are very different, then a larger number 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 new sample, if more samples are required. This technique is called early termination or adaptive sampling. 

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

Parameters

Amount - controls the extent to which the number of samples depends on the importance of a blurry value. It also controls the minimum number of samples that will be taken. A value of 1.0 means full adaptation; a value of 0.0 means no adaptation.

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

Noise threshold - controls V-Ray's judgment of when a blurry value is "good enough" to be used. This directly translates to noise in the result. Smaller values mean less noise, more samples and higher quality. A value of 0.0 means that no adaptation will be performed.

Global subdivs multiplier - this will multiply all subdivs values everywhere during rendering; you can use this to quickly increase/decrease sampling quality everywhere. This affects 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 sampling pattern will be the same from frame to frame in an animation. Since this may be undesirable in some cases, you can turn this option Off to make the samping pattern change with time. Note that re-rendering the same frame will produce the same result 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 for computer graphics can be found from the sources listed below.

Schlick, C., 1991, An Adaptive Sampling Technique for Multidimensional Integraton by Ray Tracing, in Second Eurographics Workshop on Rendering (Spain), pp. 48-56Describes deterministic MC sampling for antialiasing, motion blur, depth of field, area light sampling and glossy reflections.

Masaki Aono and Ryutarou Ohbuchi, November 25, 1996, Quasi-Monte Carlo Rendering with Adaptive Sampling, IBM Tokyo Research Laboratory Technical Report RT0167, pp.1-5;online version can be found hereDescribes an application of low discrepancy sequences to area light sampling and the global illumination problem.

Fajardo, M., August 13, 2001, Monte Carlo Raytracing in Action, in State of the Art in Monte Carlo Ray Tracing for Realistic Image Synthesis, SIGGRAPH 2001 Course 21, pp. 151-162;online version can be found hereDescribes the ARNOLD renderer employing randomized quasi-Monte Carlo sampling using low discrepancy sequences for pixel sampling, global illumination, area light sampling, motion blur,

depth of field, etc.

Veach, E., December, 1997, Robust Monte Carlo Methods for Light Transport Simulation, Ph. D. dissertation for Stanford University, pp. 58-65online version can be found hereIncludes a description of low discrepancy sequences, quasi-Monte Carlo sampling and its application to solving the global illumination problem.

Szirmay-Kalos, L., 1998, Importance Driven Quasi-Monte Carlo Walk Solution of the Rendering Equation, Winter School of Computer Graphics Conf., 1998online version can be found hereDescribes a two-pass method for solving the global illumination problem employing quasi-Monte Carlo sampling, as well as importance sampling using low discrepancy sequences.

Image Sampler (Antialiasing)General

Parameters

Fixed rate sampler

Adaptive DMC sampler

Adaptive subdivision sampler

Notes

General

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

V-Ray implements several algorithms for sampling an image. All image samplers support MAX's standard antialiasing filters, although at the cost of increased rendering time. You can choose between Fixed rate sampler, Adaptive DMC sampler and Adaptive subdivision sampler.

Parameters

Image sampler

Type - specifies the image sampler type:

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

Adaptive DMC - this sampler takes a variable number of samples per pixel depending on the difference in the intensity of the pixels;

Adaptive subdivision - this sampler divides the image into an adaptive grid-like structure and refines depending on the difference in pixel intensity.

Antialiasing filter

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

Fixed rate sampler

This is the simplest image sampler, 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 of each pixel is taken. If this is greater than 1, the samples are distributed within the pixel. The actual number of pixels is the square of this parameter (e.g. 4 subdivs produce 16 samples per

pixel). 

Adaptive DMC sampler

This sampler makes a variable number of samples per pixel based on the difference in intensity between the pixel and its neighbors. 

This is the preferred sampler for images with lots of small details (like VRayFur, for example) and/or blurry effects (DOF, motion blur, glossy reflections etc). It also takes up less RAM than the Adaptive subdivision sampler.

Min subdivs - determines the initial (minimum) number of samples taken for each pixel. You will rarely 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 of this number (e.g. 4 subdivs produce 16 samples per pixel).

Max subdivs - determines the maximum number of samples for a pixel. The actual maximum number of sampler is the square of this number (e.g. 4 subdivs produces a maximum of 16 samples). Note that V-Ray may take less than the maximum number of samples, if the difference 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 specified in the DMC sampler to determine if more samples are needed for a pixel. When this is off, the Color threshold parameter 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.

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

Adaptive subdivision sampler

This is an advanced image sampler capable of undersampling (taking less than one sample per pixel). In the absence of blurry effects (direct GI, DOF, glossy reflection/refraction 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 as the other image samplers. However, with detailed textures and/or blurry effects, it can 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 per pixel; -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, 1 means four samples, 2 means eight samples etc.

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

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

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

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

Show samples - if this is on, V-Ray will show an image where the pixel brightness is directly proportional 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, but here are some tips: 

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

o For images with detailed textures or lots of geometry detail and only a few blurry effects, the Adaptive DMC sampler performs best. Also in the case of animations involving detailed textures, the Adaptive subdivision sampler might produce jittering which the Adaptive 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 and render time. 

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