Please note that this documentation space offers information for V-Ray 3.6! For most up-to-date documentation, refer to V-Ray Next for Modo help.

This page provides information on the Irradiance Map rollout of the V-Ray GI Render Settings.

 

Section Contents

Page Contents

 

Overview


This section controls and fine-tunes various aspects of the irradiance map. This section is enabled only when the irradiance map is chosen as the GI method for primary diffuse bounces. For more details on the theories behind this GI type, please see the Irradiance Map GI page in these docs.

 


 

UI Path: ||V-Ray GI render settings|| > Irradiance Map rollout

 

Irradiance Map Parameters


 


 

 

Irradiance map preset – A number of presets are available which automatically set the numeric parameters in this section. A manual change to these values sets the preset to Custom.

Min rate – Determines the resolution for the first GI pass. A value of 0 sets the resolution to that of the final rendered image, resulting in an irradiance map similar to the direct computation method. A value of -1 sets the resolution to half the size of the final image, and so on. It is usually best to keep this value negative so that GI is quickly computed for large, flat regions in the image. This parameter is similar to (although not the same as) the Min rate parameter of the Adaptive subdivision image sampler.

Max rate – Determines the resolution of the last GI pass. This is similar to (although not the same as) the Max rate parameter of the Adaptive subdivision image sampler.

Subdivs – Controls the quality of individual GI samples. Smaller values speed up the process, but may produce a blotchy result. Higher values produce smoother images. This is similar to the Subdivs parameter for direct computation. 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.

Interp. samples – Specifies 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 may produce blotchy results if Subdivs is set to a low value. 

Interp. frames – Determines the number of frames used to interpolate GI when the Mode is set to Animation (rendering). V-Ray interpolates the irradiance from the maps of several adjacent frames to help smooth out any flickering. Note that the actual number of frames used is 2*(interp. frames)+1. For example, the default value of 2 means that in total, 5 irradiance maps will be interpolated. Higher values slow down the rendering and may produce a "lagging" effect, where objects appear to lag in movement from one frame to the next. Lower values render faster but may increase flickering. 

Color threshold – Controls the sensitivity of the irradiance map algorithm to changes in indirect lighting. Larger values lessen sensitivity; smaller values make the irradiance map more sensitive to light changes (thus producing higher quality images). 

Normal threshold – Controls the sensitivity of the irradiance map to changes in surface normals and small surface details. Larger values lessen sensitivity; smaller values make the irradiance map more sensitive to surface curvature and small details. 

Distance threshold – Controls the sensitivity of the irradiance map to the 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 enabled, V-Ray calculates the irradiance map samples for the entire camera path instead of just the current view. This is useful in the following cases:

  • When calculating irradiance maps for short fly-through animations all at once. Enabling the Use camera path option and rendering a single frame will produce information for the entire camera path. This method is an alternative to using Incremental add to current map as the Mode and rendering the animation every nth frame.
  • When 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 reduce flickering, as the GI sample positions on static geometry will not change.

 

Mode – Specifies the method for (re)using the irradiance map. The irradiance map mode that that is best for the task depends whether the rendering is a static scene, a static scene rendered from multiple views, a fly-through animation, or an animation with moving objects.

Single frame – The default mode. Computes a single irradiance map for the whole image and a new irradiance map for each frame. During distributed rendering, each render server will compute its own full-image irradiance map. This mode is best used when rendering animations of moving objects. The irradiance map must be 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, as with a fly-through animation. V-Ray computes 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 to avoid flickering, this mode can also be used in network rendering, where each rendering server will compute and refine its own local irradiance map.
From file – Loads the irradiance map from the supplied file at the start of the rendering sequence and uses it for all the frames in the animation. New irradiance maps are not computed. This mode can be used for fly-through animations and will work well in network rendering mode.
Add to current map – Computes a completely new irradiance map and adds 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: This mode is not supported for distributed rendering.
Incremental add to current map – Uses the irradiance map that is already in memory and only refines it in places that lack 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 – Uses a separate irradiance map 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, artifacts may result, which 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) – Calculates irradiance maps to be used later for final rendering with Animation (rendering) mode. One irradiance map is created for each frame and then written into a separate file. In this mode consecutive frames must be rendered, as opposed to rendering every nth frame. V-Ray automatically disables rendering of the final image in this mode, and only irradiance map prepasses are calculated and saved.
Animation (rendering) – Renders a final animation using irradiance maps created with 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.

Auto save – When enabled, V-Ray automatically saves the irradiance map to the specified file at the end of the rendering. This mode is particularly useful when sending the irradiance map to a different machine through network rendering.

Auto save file – Specifies where to save the irradiance map when Auto save is enabled.

Save – Save an already generated irradiance map in a file.

Reset – Removes stored irradiance map from memory.

Don't delete – When enabled (default setting), V-Ray keeps the irradiance map in memory until the next rendering. When disabled, V-Ray deletes the irradiance map when rendering is complete, meaning the map cannot be manually saved afterwards.

 

Irradiance Map - Advanced Parameters


 

 

 

Detail enhancement is a method for bringing additional detail to the irradiance map when 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 since it accounts for bounced light. 

Detail enhancement – Enables detail enhancement for the irradiance map. When detail enhancement is enabled, it is possible to use a lower irradiance map preset 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: If irradiance map was previously calculated and saved with Detail Enhancement enabled, this option should be enabled again when the irradiance map is used later.

Detail scale – Determines the units for the Detail radius parameter:

Screen – Sets the radius units to image pixels.
World – Sets the radius units to world units. 

Detail radius [px] – 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 - this may be faster but less precise overall. A larger radius means that more of the scene will use the higher precision sampling and may be slower, but more precise. This is similar to a radius parameter for an ambient occlusion pass. 

Detail subdivs mult. – Determines the number of samples taken for the 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 make the detail-enhanced areas more noisy, but faster to render.

Show samples – When enabled, V-Ray displays the samples in the irradiance map as small dots in the scene.

Show calc phase – When enabled, V-Ray shows the irradiance map passes as the irradiance map is calculated. This gives a rough idea of the indirect illumination even before the final rendering is complete. Enabling this option slows down calculations, especially for large images.

Show direct light – When enabled, V-Ray shows direct lighting for primary diffuse bounces in addition to indirect lighting while the irradiance map is being calculated. This option is provided as a convenience; V-Ray does not need to compute this, as direct lighting is ordinarily calculated only for secondary diffuse bounces for GI purposes. This option is only available when Show calc phase is enabled.

Interpolation mode – Used during rendering. Specifies the method for interpolating the GI value from the samples in the irradiance map. For more information, see Example: Interpolation Methods.

Weighted average – Performs 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, it tends to produce blotchy results.
Least squares fit – The default method. Attempts to compute a GI value that best fits with 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.
Local Delaunay triangulation – The only non-blurry method of interpolation that preserves detail while avoiding density bias. The result might have noise (due to lack of blurring), and more samples may be needed to produce a sufficiently smooth result. This can be done either by increasing the Subdivs of the irradiance map samples, or by decreasing the Noise threshold value in the Image sampler rollout. In comparison, the other methods of interpolation tend to blur the details in indirect illumination and are prone to density bias, where more samples from high-density areas can lead to artifacts. 
Least squares with Voronoi weights
– 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 may not produce effective results.

Although all interpolation types have their uses, most cases will benefit from using either Least squares fit or Local Delaunay triangulation. The blurring method of Least squares fit will hide noise and produce a smooth result. It is suitable for scenes with large smooth surfaces. Local Delaunay triangulation is a more exact method, which usually requires more Subdivs and a high irradiance map Max rate (and therefore more rendering time), but produces accurate results without blurring. It is suitable for scenes with a high amount of small details.

Lookup mode – Used during rendering. Specifies the method of choosing suitable points from the irradiance map to be used as basis for the interpolation. For more information, see Example: Sample Lookup.

Nearest (draft) – Chooses samples from the irradiance map that are closest to the point of interpolation. The number of interpolation points is set by the Interp. samples parameter. This is the fastest look-up method and was the only one available in early versions of V-Ray. This method has a notable drawback: In places where the density of the samples changes in the irradiance map, this method will pick more samples from the areas with higher density. When a blurry interpolation method is used, this density bias (getting more samples from high-density areas) might lead to incorrect interpolation and artifacts, mostly in GI shadow boundaries.
Quad-balanced (good) – 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 the Nearest method, but generally performs very well. A drawback is that sometimes, in its attempt to find samples, it might pick samples that are far away and not relevant to the interpolated point.
Overlapping (very good/fast) – This method was introduced to overcome the drawbacks of the Nearest and Quad-balanced lookup methods. It requires a preprocessing step 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 Nearest and Quad-balanced. A drawback of this method is that sometimes a far sample can influence the wrong part of the scene. Also, it tends to blur the GI solution more than the other methods.
Density-based (best) – The default method. It combines the Nearest and 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 lookup to choose the most suitable samples while taking sample density into account.

Check sample visibility – Used during rendering. Causes V-Ray to use only the samples from the irradiance map that are directly visible from the interpolated point. This can be useful for preventing "light leaks" through thin walls with very different illumination on both sides. However, it also slows rendering since V-Ray traces additional rays to determine sample visibility. For more information, see Example: Check Sample Visibility.

Multipass – Used during irradiance map calculation. When enabled, V-Ray uses all irradiance map samples computed so far. When disabled, V-Ray only uses samples collected during previous passes, but not those computed earlier in the current pass. Keeping this enabled usually causes V-Ray to take less samples and therefore compute the irradiance map faster. This option is provided because of the asynchronous nature of the irradiance map calculation process on multiprocessor machines, where several threads modify the irradiance map at the same time. Because of this, there is no guarantee that rendering the same image twice will produce exactly the same irradiance map. However, this does not usually lead to problems in the rendering, and it is usually best to keep this option enabled. 

Randomize samples – Used during irradiance map calculation. When enabled, the image samples are randomly jittered to help avoid artifacts caused by evenly-spaced samples. Disabling it will produce samples that are aligned in a grid on the screen. In general, this option should be enabled. 

Calc. interp. samples – Used during irradiance map calculation to determine the number of already-computed samples that will be used to guide the sampling algorithm. Values between 10 and 25 generally work well. Low values may speed the calculation pass, but may not provide sufficient information. Higher values will be slower and cause additional sampling. In general, this parameter should be left at the default value of 10.

 



 

Example: Interpolation Methods

 

 

The following examples show the main differences between a blurry interpolation method (Least squares fit) and a non-blurry one (Local Delaunay triangulation). Notice how the images in the first column are more blurry, while the images in the second column are sharper.

 

Comment

Blurry method (Least squares fit)

Non-blurry method (Local Delaunay triangulation)
The scene is a simple cube on a sphere as seen from above, lit by a HDRI map. Low irradiance map rates and subdivs were used intentionally so that the difference is more obvious. Both images were rendered with exactly the same irradiance map.

This scene shows the ability of the Local Delaunay triangulation method to preserve detail. Notice that the shadows in the right image are sharper. Both images used the same irradiance map.

A close-up of the previous scene. The irradiance map is exactly the same as for the two previous images (it was saved and then loaded from disk).

 

 


 

Example: Sample Lookup

 

The following examples show the differences between the sample lookup methods, and more specifically, their behavior in areas with changing sample density.

 

 


Test scene

 


Samples in the irradiance map

 

 

This is the test scene. The left image shows the final image and the right image shows the samples in the irradiance map (it was rendered with the Show samples option checked). The scene itself is a sphere on a plane, lit by a V-Ray area light and a little skylight. The area light had the option Store with irradiance map checked.

As one can notice, the density of the samples is quite different in the uniformly lit areas and in the shadow transition area.

 

The following three images used exactly the same irradiance map with the Least squares fit interpolation method.

 

 


Nearest lookup method

 


Quad-balanced lookup method

 

 

 


Overlapping lookup method

 


Density-based lookup method

 

 

 

You can see the ringing artifacts (the white halo around the shadow) caused by the different sample density in the first two images. The third image, rendered with the Overlapping method, is free from those artifacts. It also rendered faster than the previous two images. The last image was rendered using the Density-based method. This method yields the best result but is slower than the Overlapping method.

As a comparison, here is the same image rendered with the Local Delaunay triangulation interpolation method.

 

 


Nearest lookup method

 


Quad-balanced lookup method

 

 

 


Overlapping lookup method

 


Density-based lookup method

 

 

The images are nearly identical. This is because the Local Delaunay triangulation method, being a non-blurry method, is less sensitive to the samples that are being looked up, so long as the Local Delaunay triangulation can be performed successfully from them.

Being the fastest of the three methods, Nearest may be used for preview purposes. Nearest quad-balanced performs fairly well in the majority of cases. Precalculated overlapping is fast and in many cases performs very well, but may tend to blur the GI solution. The Density-based method produces very good results in the majority of cases and is the default method.

Note: The lookup method is mostly important when using a blurry interpolation method. When using Local Delaunay triangulation, the sample look-up method does not influence the result very much.

 

 

 


 

Example: Check Sample Visibility

 

The following examples demonstrate the effect of the Check sample visibility parameter. The scene is a thin wall lit on the two sides by two V-Ray area lights with different colors. Both lights had the Store with irradiance map option enabled. The two images are rendered with the Irradiance map preset set to Medium.

 

 


Check sample visibility = disabled

 


Check sample visibility = enabled

 

 

Notice the light leak in the first image, where some of the green light leaks through the wall to the red side. This happens because near the thin wall, V-Ray will use samples from both sides. When Check sample visibility is enabled, V-Ray will discard the samples from the other side of the wall.

As a comparison, here is another set of images rendered with Irradiance map preset set to High and Check sample visibility disabled.

 

 


High preset, Least squares fit lookup method

 


High preset, Local Delaunay triangulation lookup method

 

 

 

The light leak effect is negligible in the first image, and completely absent in the second one. This is because the High preset will cause V-Ray to take additional samples at the base of the thin wall, thus decreasing the leaking effect. Using a non-blurry interpolation method (such as Local Delaunay triangulation) further limits this effect.

The conclusion is that enabling Check sample visibility is only useful for low irradiance map settings. Also note that this option might not work very well for curved objects.

 

 


 

Notes


  • For more details on how the Irradiance Map engine works, please see the Irradiance Map GI page.
  • You can view, merge and save irradiance maps with the Irradiance Map Viewer | imapviewer tool.
  • For animated irradiance maps, GI samples on different objects are not shared; this may lead to 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 same group.