The following parameters are added to the list of visible settings available from the Irradiance map rollout when set to the Advanced Render UI Mode. 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: - 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 produces 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, setting the Use camera path option on helps to further reduce any flickering, as the GI sample positions on static geometry does not change.
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Show direct light – Only available when Show calc phase is on. It causes V-Ray to show 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. The 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 (only for GI purposes).
Color threshold (Clr thresh) – 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). Distance threshold (Dist thresh) – 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. Normal threshold (Nrm thresh) – 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.
Detail enhancement is a 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. Detail enhancement – Enables 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. Scale – Determines the units for the Radius parameter: Screen – The radius is in image pixels. World – The radius is in world units. Radius – Determines the radius for the detail enhancement effect. Smaller radius means that smaller parts around the details in the image are sampled with higher precision - this would be faster but may be less precise. Larger radius means that more of the scene uses the higher precision sampling and may be slower, but more precise. This is similar to a radius parameter for an ambient occlusion pass. Subdivs mult. – Determines the number of samples taken for the high-precision sampling as a percentage of the irradiance map Hemispheric subdivs. A value of 1.0 means that the same 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.
Randomize samples – Used during irradiance map calculation. When it is checked, 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. Check sample visibility – Used during rendering. It causes V-Ray to use only those samples from the irradiance map, which are directly visible from the interpolated point. This may be useful for preventing "light leaks" through thin walls with very different illumination on both sides. However it 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 – When enabled, V-Ray makes several passes through the image with progressively finer resolutions, starting with the Min rate and working up towards the Max rate. This typically gives a better sample distribution in the irradiance map and also gives an early preview of the scene. When this is off, V-Ray makes just one pass with the specified Max rate, which is slightly faster, but may produce samples that are aligned in a straight line around the edges of the render regions. Calc. samples – Used during irradiance map calculation. It represents the number of already computed samples that are used to guide the sampling algorithm. Good values are between 10 and 25. Low values may speed the calculation pass, but may not provide sufficient information. Higher values are slower and cause additional sampling. In general, this parameter should be left to the default value of 15. Interpolation type – Used during rendering. It selects the method for interpolating the GI value from the samples in the irradiance map. For more information, see The Interpolation Methods example below. Weighted average – 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. 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. Delone triangulation – All other methods of interpolation are blurry methods - that is, they tend to blur the details in indirect illumination. Also, the blurry methods are prone to density bias (see below for a description). In difference, 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 either by increasing the hemispheric subdivs of the irradiance map samples, or by decreasing the Noise threshold value in the brute force sampler rollout. For more information, see The Delone Triagulation Method example below. 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 its effectiveness is currently somewhat questionable. 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 hide noise and produce a smooth result. It is perfect for scenes with large smooth surfaces. Delone triangulation is a more exact method, which usually requires more hemispheric 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. |
Sample lookup – 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 Sample Look-up example below. Nearest – Chooses those samples from the irradiance map which are closest to the point of interpolation. (How many points are chosen is determined by the value of the Interpolation 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 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). Nearest quad-balanced –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. Precalculated overlapping – 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 – 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.
Don't delete – Enables V-Ray to keep the irradiance map in memory until the next rendering. If unchecked, the irradiance map is deleted when the rendering is complete and can not be saved manually afterwards. Auto save – Enables V-Ray to automatically save the irradiance map to the specified file at the end of the rendering. This mode is particularly useful if you want to send the irradiance map for rendering on a different machine though network rendering. Switch to saved map – Enables V-Ray to automatically set the irradiance map mode to From file and the file name to be that of the map that was just saved. Only available when Auto save is enabled. Browse button – Navigate to, and set path to the file used to save the irradiance map at the end of the rendering if Auto save is enabled. |