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||Parameters Renderer tab|| > Global Illumination tab
(with the V-Ray Renderer node selected)
Main
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On – Enables/disables indirect illumination.
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Irradiance map – Selects the Irradiance map method for primary diffuse bounces. See the Irradiance Map section Settings page for more information. For even more information, see the Light Bounces example below.
Brute force – Selects the brute force method (direct computation) for primary diffuse bounces. See the Brute Force section Settings page for more information.
Light cache – Selects the light cache method as the primary GI engine. See the Light Cache section Settings page for more information.
Multiplier – Determines the degree to which primary/secondary diffuse bounces contribute to the final image's illumination. Note that the default value of 1.0 produces a physically accurate image. Other values are possible, but not physically accurate.
GI - Advanced – Enables advanced global illumination controls
Saturation – Controls the saturation of the GI. A value of 0.0 means that all color will be is removed from the GI solution and the result will be is 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 uses the value defined by Contrast base. A value of 1.0 means the solution remains unmodified. Values higher than 1.0 boost the contrast.
Contrast Base – Determines the base for the contrast boost. It determines which GI values in the image remain unchanged during contrast calculations, and which are shifted. The default value of 0.5 values 5 values leaves the medium grey values in the GI solution unmodified. When a low Contrast Base value is used in conjunction with a raised Contrast value, the image brightens. When a higher Contrast Base is used with a higher Contrast value, the image darkens.
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The previous three post-processing parameters allow additional modification of the indirect illumination before it is added to the final rendering. The default values ensure a physically accurate result, but values can be changed to modify the way GI looks for artistic purposes. |
Brute Force
This rollout controls the settings for Brute Force GI when it is selected as the Primary Engine or Secondary Engine.
Subdivs – The square of this value, multiplied by the Subdivs Multiplier value on the DMC Sampler tab, sets the number of rays that V-Ray will trace from the camera when Brute Force is used as the primary bounces engine.
Depth – Controls the number of light bounces that will be computed when Brute Force is used as the secondary bounces engine.
Light Cache
These options control the Light cache settings when it is selected as the Primary Engine or Secondary Engine.
Subdivs – Determines how many paths are traced from the camera. The actual number of paths is the square of the subdivs (the default 500 subdivs mean that 250 000 paths will be traced from the camera).
Sample Size – 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 lose detail. This value can be either in world units or relative to the image size, depending on whether or not the World scale option is checked or not.
Show Calc. Phase – Enabling this option 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.
Store Direct Light – When this option is enabled, 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.
World Scale – Determines the unit scale for the Sample size and Filter size parameters.
World – Sizes are fixed in world units everywhere. This can affect the quality of the samples. For example, samples that are close to the camera are sampled more often and appear smoother, while samples that are far away are noisier. This option is often the best choice for fly-through animations, since it forces a constant sample density everywhere.
Screen – 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.
Mode – Determines the rendering mode of the light cache:
Single Frame – Computes a new light cache for each frame of an animation.
Fly-Through – Computes 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 only in the active time segment is taken into consideration. Note that it might be better to have the World Scale option enabled 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 – 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 Mode is set to From file.
Don't Delete – When enabled (the default), the light cache remains in memory after the rendering. Disable this option off to automatically delete the light cache (and thus save memory).
Auto Save – When enabled, 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.
Auto Save File – Specifies the file name to save the light cache to.
Filter Type – 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 below) to decrease the 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 values. 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 Filter 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 Filter size are 2-6 times larger than Sample size. Note that Filter size uses the same scale as the Sample size and its meaning depends on the World Scale check box.
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When V-Ray GPU is chosen as a rendering engine, all unsupported options are hidden from the parameters. |
Prefilter Samples – Controls the number of samples taken during prefiltering.
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Filter Samples – When Filter Type is set to Nearest, this parameter determines how many of the nearest samples to look up from the light cache.
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Use Retrace Threshold – When enabled, this option improves the precision of global illumination in cases where the light cache will produce too large an error. This is especially obvious with the Use light cache for glossy rays option, or near corners where light leaks might be possible because of the light cache interpolation. For glossy reflections and refractions, V-Ray dynamically decides whether to use the light cache or not based on the surface glossiness and the distance from it so that the errors due to the light cache are minimized. Note that enabling this option can increase render time.
Leak Prevention – Enables additional calculations to prevent light leaks and reduce flickering with the light cache. 0.0 disables the leak prevention. The default value of 0.8 should be enough for all cases.
Retrace Threshold – Specifies the threshold amount relative to the light cache sample size.
Irradiance Map
Min Rate – 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 map similar to the direct computation (Brute Force) method. A value of -1 means the resolution will be half that of the final image, and so on. It is recommended that you set this value as a negative number so that GI is quickly computed for large and flat regions in the image. This is the same concept as the Min rate parameter of the Adaptive subdivision image sampler.
Max Rate – Determines the resolution of the last GI pass. This is the same concept as the Max rate parameter of the Adaptive subdivision image sampler.
Subdivs – Controls the quality of individual GI samples. Smaller values make things faster, but may produce blotchy result. Higher values produce smoother images. This is similar to the Subdivs parameter for the Brute Force method. Note that this is not the actual number of 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 – The number of GI samples that will be used to interpolate the indirect illumination at a given point. Larger values tend to blur the detail in GI although the result will be smoother. Smaller values produce results with more detail, but might produce blotchiness if the Subdivs value is low.
Color Threshold – Color threshold. This parameter controls how sensitive the irradiance map algorithm is to changes in indirect lighting. Larger values mean less sensitivity; smaller values make the irradiance map more sensitive to light changes (thus producing higher quality images).
Normal Threshold – Normal threshold. This parameter controls how sensitive the irradiance map is to changes in surface normals and small surface details. Larger values mean less sensitivity; smaller values make the irradiance map more sensitive to surface curvature and small details.
Distance Threshold – Distance threshold. This parameter controls how sensitive the irradiance map is to distance between surfaces. A value of 0.0 means the irradiance map will not depend on object proximity at all; higher values place more samples in places where objects are close to each other.
Use Camera Path – When this option is enabled, V-Ray will calculate the irradiance map samples for the entire camera path instead of just the current view. This is useful for:
- Calculating irradiance maps for short fly-through animations in one go. Instead of using the Incremental add to current map mode and rendering the animation every Nth frame, you can turn the Use Camera Path option on, and render just one single frame - this will produce information for the entire camera path.
- Using irradiance maps for animations with moving objects where the camera also moves, either in Single Frame or Animation (Prepass) mode. In this case, enabling the Use camera path option will help to further reduce any flickering, as the GI sample positions on static geometry will not change.
Mode – This group of controls selects the way the irradiance map is (re)used.
Single Frame – The default mode; a single irradiance map is computed for the whole image, and a new irradiance map is computed for each frame. During distributed rendering, each render server will compute its own full-image irradiance map. This is the mode to use when rendering animations of moving 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 necessarily consecutive) where only the camera moves around (such as a fly-through animation). V-Ray will compute a new full-image irradiance map for the first rendered frame; for all other frames, V-Ray will try to reuse and refine the irradiance map that has been computed so far. If the irradiance map is of sufficiently high quality as to avoid flickering, this mode can also be used in network rendering; each rendering server will compute and refine its own local irradiance map.
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 irradiance map will be computed. This mode can be used for fly-through animations, and will work well in network rendering mode.
Add to Current Map – In this mode, V-Ray will compute a completely new irradiance map and will add it to the map that is already in memory. This mode is useful when compiling an irradiance map to render 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 in memory and will only refine it in places that don't have enough detail. This mode is useful when compiling an irradiance map to render multiple views of a static scene or a fly-through animation.
Bucket Mode – In this mode, a separate irradiance map is used for each rendered region ("bucket"). This is especially useful since it allows the irradiance map computations to be effectively distributed among several computers when using Distributed Rendering. Bucket mode can be slower than Single frame mode since an additional border must be computed around each region in order to reduce edge artifacts between neighboring regions. Even so, there may be such artifacts. They can be further reduced by using higher settings for the irradiance map (the High preset, more Subdivs and/or smaller Noise threshold for the DMC sampler).
Animation (Prepass) – In this mode, V-Ray calculates irradiance maps to be used later on for final rendering with the Animation (rendering) mode. One irradiance map is created for each frame and written into a separate file. Note that in this mode you have to render one map for each frame (i.e. you cannot render every Nth frame). V-Ray automatically disables rendering of the final image in this mode - only irradiance map prepasses are calculated.
Animation (Rendering) – In this mode, V-Ray renders a final animation using irradiance maps created with the Animation (prepass) mode. Irradiance maps from several adjacent frames are loaded together and blended so as to reduce flickering. The number of irradiance maps that are interpolated is determined by the Interp. frames parameter.
The choice of irradiance map mode depends on the particular rendering task - a static scene, a static scene rendered from multiple views, a fly-through animation or an animation with moving objects.
File – Specifies the irradiance map file which will be loaded if the From File mode is selected.
Don't Delete – When this option is enabled, V-Ray keeps the irradiance map in memory until the next rendering, meaning the irradiance map can be saved with the Save option for later use. If this option is disabled, V-Ray deletes the irradiance map when rendering is complete.
Auto Save – When enabled, automatically saves the irradiance map to the specified Auto Save File at render end.
Auto Save File – If this option is enabled, V-Ray automatically saves 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 to a different machine for network rendering.
Enable Detail Enhancement – Turns on detail enhancement for the irradiance map. Note that an irradiance map calculated in this mode should not be used without the detail option. When detail enhancement is On, you can use lower irradiance map settings and higher Interp. samples. This is because the irradiance map is only used to capture the general far-off lighting, while direct sampling is used for the closer detail areas.
Note: This is method for bringing additional detail to the irradiance map in the case where there are small details in the image. Due to its limited resolution, the irradiance map typically blurs the GI in these areas or produces splotchy and flickering results. The detail enhancement option is a way to calculate those smaller details with a high-precision brute-force sampling method. This is similar to how an ambient occlusion pass works, but is more precise as it takes into account bounced light.
Scale – Determines the units for the Radius setting:
Screen – The radius is expressed as image pixels.
World – The radius is expressed in world units.
Radius – Determines the radius for the detail enhancement effect. A smaller radius means that smaller parts around the details in the image are sampled with higher precision, which is faster but might be less precise. A larger radius means that more of the scene will use the higher precision sampling and might be slower, but more precise. This value is similar to a radius parameter for an ambient occlusion pass.
Subdivs Multiplier – Determines the number of samples taken for high-precision sampling as a percentage of the irradiance map subdivs. A value of 1.0 means that the same number of 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.
Enable Irradiance Map - Advanced – Enables advanced Irradiance Map controls.
Show Samples – When enabled, V-Ray will visually show the samples in the irradiance map as small dots in the scene.
Show Calculation Phase – When enabled, 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 before the final rendering is complete. Note that turning this on slows the calculations a little bit, especially for large images. This option is ignored when rendering to fields - in that case, the calculation phase is never displayed.
Show Direct Light – Only available when Show calc phase is enabled. When enabled, V-Ray shows direct lighting for primary diffuse bounces in addition to indirect lighting while the irradiance map is being calculated. Note that V-Ray does not really need to compute this. This option is only for convenience. This does not mean that direct lighting is not calculated at all - it is, but only for secondary diffuse bounces (for GI purposes).
Interpolation Mode – Used during rendering. It selects the method for interpolating the GI value from the samples in the irradiance map.
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 the irradiance map. The method is quite slow and its effectiveness is currently somewhat questionable.
Delone Triangulation – All other methods of interpolation are blurry methods; that is, they will tend to blur the details in indirect illumination. Blurry methods are prone to density bias (see below for a description).Conversely, 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 can be done by increasing the Subdivs of the irradiance map samples.
Least Squares Fit – The default method; it will try to compute a GI value that best fits in among the samples from the irradiance map. Produces smoother results than the weighted average method, but is slower. Also, ringing artifacts may appear in places where both the contrast and density of the irradiance map samples change over a small area.
Weighted Average – This method will do a simple blend between the GI samples in the irradiance map based on the distance to the point of interpolation and the difference in the normals. While simple and fast, this method tends to produce a blotchiness in the result.
Although all interpolation types have their uses, it probably makes most sense to use either Least squares fit or Delone triangulation. Being a blurry method, Least squares fit will hide noise and will produce a smooth result. It is perfect for scenes with large smooth surfaces. Delone triangulation is a more exact method, which usually requires more subdivs and high Max irradiance map rate (and therefore more rendering time), but produces accurate results without blurring. This is especially obvious in scenes where there are a lot of small details.
Lookup Mode – Used during rendering. It selects the method of choosing suitable points from the irradiance map to be used as basis for the interpolation.
Quad-Balanced – this is an extension of the nearest lookup method aimed at avoiding density bias. It divides the space about the interpolated point in four areas and tries to find an equal number of samples in all of them (hence the name quad-balanced). The method is a little slower than the simple Nearest lookup, but in general performs very well. A drawback is that sometimes, in its attempt to find samples, it may pick samples that are far away and not relevant to the interpolated point.
Nearest – this method will simply choose those samples from the irradiance map which are closest to the point of interpolation. (How many points will be chosen is determined by the value of the Interp. samples parameter.) This is the fastest lookup method and was the only one available in early versions of V-Ray. A drawback of this method is that in places where the density of the 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 bias which may lead to incorrect interpolation and artifacts in such places (mostly GI shadow boundaries).
Overlapping – this method was introduced in an attempt to avoid the drawbacks of the two previous ones. It requires a preprocessing step of the samples in the irradiance map during which a radius of influence is computed for each sample. This radius is larger for samples in places of low density, and smaller for places of higher density. When interpolating the irradiance at a point, the method will choose every sample that contains that point within its radius of influence. An advantage of this method is that when used with a blurry interpolation method it produces a continuous (smooth) function. Even though the method requires a preprocessing step, it is often faster than the other two. These two properties make it ideal for high-quality results. A drawback of this method is that sometimes lonely samples that are far-away can influence the wrong part of the scene. Also, it tends to blur the GI solution more than the other methods.
Density-Based – the default method; it combines the Nearest and the Precalculated overlapping methods 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 neighbor look-up to choose the most suitable samples while taking sample density in account.
Check Sample Visibility – When enabled, V-Ray will use only those samples from the irradiance map that are directly visible from the interpolated point during rendering. This may be useful for preventing "light leaks" through thin walls with very different illumination on both sides. However it will also slow the rendering, since V-Ray will trace additional rays to determine sample visibility.
Multipass – 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 to use only samples collected during previous passes, but not those computed earlier during the current pass. Keeping this checked will usually cause V-Ray to take less samples (and therefore compute the irradiance map faster). That means that on multiprocessor machines, several threads will be modifying the irradiance map at the same time. Because of the asynchronous nature of this process, there is no guarantee that 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 setting is used during irradiance map calculation. When this option is enabled, the image samples will be randomly jittered. Unchecking it will produce samples that are aligned in a grid on the screen. In general, this option should be kept checked in order to avoid artifacts caused by regular sampling.
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This example shows the effect of the number of light bounces on an image:
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