This page provides information on the Irradiance Map in the GI tab.
These options control settings for the Irradiance map when it is selected as the Primary Engine in the GI tab.
||Renderer tab|| > Global Illumination tab
(with the V-Ray Renderer node selected)
Min Rate – Determines the resolution for the first GI pass. A value of 0 means the resolution is the same as the resolution of the final rendered image, which makes the irradiance map similar to the direct computation (Brute Force) method. A value of -1 means the resolution is 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 a 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 are 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 are used to interpolate the indirect illumination at a given point. Larger values tend to blur the detail in GI although the result is smoother. Smaller values produce results with more detail, but might produce blotchiness if the Subdivs value is low.
Color Threshold – 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 – 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 – Controls how sensitive the irradiance map is to distance between surfaces. A value of 0.0 means the irradiance map does 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 calculates 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.
If you use this option, you should not use interpolated glossy reflections/refractions in V-Ray Material as they will not render accurately.
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 computes 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 computes a new full-image irradiance map for the first rendered frame; for all other frames, V-Ray tries 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 computes and refines its own local irradiance map.
From File – In this mode, V-Ray simply loads the irradiance map from the supplied file at the start of the rendering sequence and uses this map for all the frames in the animation. No new irradiance map is computed. This mode can be used for fly-through animations, and works well in network rendering mode.
Add Тo Current Map – In this mode, V-Ray 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 that this mode is not supported for distributed rendering.
Incremental Add To Current Map – In this mode, V-Ray uses the irradiance map that is already in memory and only refines 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. Refer to the Tutorials section for more information.
Interp. Frames – The number of frames that are used to interpolate GI when Mode is set to Animation (rendering). In this mode, 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 a total of 5 irradiance maps are interpolated. Higher values slow down the rendering and might cause light to appear to lag behind its actual location when the animation is viewed. Lower values render faster but might increase flickering.
File – Specifies the irradiance map file which will be loaded if the From File mode is selected.
Don't Delete from Memory – When enabled, the map is not deleted from the memory at the end of the rendering.
Auto Save – 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.
Auto Save File – Specifies the file path for the irradiance map to be saved.
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 Interpolation 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 Detail 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 uses 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 is used as for the regular irradiance map samples. Lower values 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 visually shows the samples in the irradiance map as small dots in the scene.
Show Calculation Phase – When enabled, V-Ray shows the irradiance map passes as the irradiance map is calculated. This gives 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. For more information, see the Interpolation Modes example below.
Local Delone Triangulation – All other methods of interpolation are blurry methods; that is, they 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 preserves the detail while avoiding density bias. Since it is non-blurry, the result might look more noisy (blurring tends to hide noise). More samples are 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 tries 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 does 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 blochiness 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 hides noise and produces 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. For more information, see the Lookup Mode example below.
Quad-Balanced (good) – This is an extension of the nearest look-up 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 look-up, 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 (draft) – This method simply chooses 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 Interpolation Samples parameter.) This is the fastest look-up 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 picks 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 (very good/fast) – 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 chooses 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 (best) – 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 uses 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 also slows the rendering, since V-Ray traces additional rays to determine sample visibility. For more information, see the Check Sample Visibility example below.
Multipass – This is used during irradiance map calculation. When checked, this causes V-Ray to use all irradiance map samples computed so far. Unchecking it allows V-Ray to use only samples collected during previous passes, but not those computed earlier during the current pass. Keeping this checked usually causes V-Ray to take less samples (and therefore compute the irradiance map faster). That means that on multiprocessor machines, several threads are 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 are randomly jittered. Unchecking it produces 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.
Example: Interpolation Modes
The following examples show the main differences between a blurry interpolation method (Least squares fit) and a non-blurry one (Delone triangulation). Notice how the images in the first column are more blurry, while the images in the second column are sharper.
Blurry method (Least Squares Fit)
|Non-blurry method (Delone Triangulation)|
The scene is a simple cube on a sphere as seen from above, lit by a HDRI map. Low hemispheric subdivs and low irradiance map rates 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 Delone 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: Lookup Mode
The following examples show the differences between the three sample lookup methods and more specifically, their behavior in areas with changing sample density.
This is the test scene, the left image shows the final image and the right image shows the samples in the irradiance map (the image was rendered with the Show Samples option enabled). The scene itself is a sphere on a plane, lit by a V-Ray area light and a small degree of skylight. The area light had the Store with irradiance map option enabled.
The samples in the irradiance map
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
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 Precalculated 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 Delone Triangulation interpolation method.
Nearest lookup method
Quad-Balanced lookup method
The images are nearly identical. This is because the Delone Triangulation method, being a non-blurry method, is less sensitive to the samples that are being looked up, so long as the Delone Trianglulation can be performed successfully from them.
Being the fastest of the three methods, Nearest look-up may be used for preview purposes. Nearest quad-balanced performs fairly well in the majority of cases. Pre-calculated 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 that the look-up method is mostly important when using a blurry interpolation method. When using Delone 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 checked. The two images are rendered with the Medium irradiance map preset.
Check Sample Visibility is off
Check Sample Visibility is on
Notice the light leak in the first image. This happens because near the thin wall, V-Ray uses samples from both sides. When the Check Sample Visibility option is turned on, V-Ray discards the samples from the wrong side.
As a comparison, here is the same image rendered with the High irradiance map preset and Check Sample Visibility turned off.
High irradiance map preset, Least Squares Fit
High irradiance map preset, Delone Triangulation
The light leak effect is negligible in the left image, and completely absent in the right one. This is because the High irradiance map preset causes V-Ray to take additional samples at the base of the thin wall, thus decreasing the leaking effect. Using a non-blurry interpolation method (Delone triangulation) further limits this effect.
The conclusion is that turning on Check Sample Visibility is only useful for low irradiance map settings. Also note that this option may not work very well for curved objects.
- For animated irradiance maps, GI samples on different objects are not shared, which might lead small objects to appear black in final renders. A simple solution to this issue is to group those objects together, because GI samples are shared for objects which are part of the same group.