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Note that the presets are targeted for a typical 640x480 image. Larger images usually can do with lower Min/Max rates than those specified in the presets.
Basic ParametersMin rate – This value 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 method. A value of -1 means the resolution is half that of the final image and so on. You would usually want to keep this negative, so that GI is quickly computed for large and 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 – This value 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. Hemispheric subdivs (HSph. subdivs) – This controls the quality of individual GI samples. Smaller values make things faster, but may produce blotchy results. 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 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. Color threshold (Clr thresh) – 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 (Nrm thresh) – 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 (Dist thresh) – This parameter 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. Interp. samples – This is the number of GI samples that is 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 may produce blotchiness if low Hemispheric subdivs are used. Note that if you use interpolated irradiance maps (i.e. the Mode is set to Animation (Rendering)), V-Ray actually multiplies this value by the number of irradiance maps used. For example, if you have the Interpolation samples set to 20, and the Interpolation frames to 2, V-Ray uses 100 samples to interpolate. This is done in order to preserve the blurring of the GI solution compared to a single frame irradiance map, however it also slows down the rendering. To speed up the rendering in that case, you can decrease this value to 10 or 5. Interp. frames – This option is only available when the Mode is set to Animation (Rendering). It determines the number of frames that is used to interpolate GI when the 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, meaning the default value of 2 means that in total 5 irradiance maps are interpolated. Higher values slow down the rendering and may produce "lagging" effect. Lower values render faster but may increase flickering. Note that increasing this value also increases the number of samples used for interpolation from the irradiance map - see the note for the Interpolation samples parameter. Advanced OptionsInterp. type – This option is used during rendering. It selects the method for interpolating the GI value from the samples in the irradiance map.
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 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. Lookup mode – This option is used during rendering. It selects the method of choosing suitable points from the irradiance map to be used as basis for the interpolation.
Being the fastest of the three methods, Nearest lookup 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 that the lookup method is mostly important when using a blurry interpolation method. When using Delone triangulation, the sample lookup method does not influence the result very much. Calc. interp. samples – This is used during irradiance map calculation. It represents the number of already computed samples that will be 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 will be slower and will cause additional sampling. In general, this parameter should be left to the default value of 15. Multipass – When this is turned on, V-Ray will make 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. Randomize samples – This is used during irradiance map calculation. When it is checked, 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. Check sample – This is used during rendering. It will cause 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 will also slow the rendering, since V-Ray will trace additional rays to determine sample visibility.
Detail EnhancementDetail 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. On – 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. R – This 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 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. Subdivisions – This 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 will be used as for the regular irradiance map samples. Lower values will make the detail-enhanced areas more noisy, but faster to render. Scale – This determines the units for the Radius parameter: Screen – The radius is in image pixels.
ShowCalc. phase – When this option is on, 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. Direct light – This option is only available when Show calc phase is on. It will cause 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). Samples – When this option is on, V-Ray will show visually the samples in the irradiance map as small dots in the scene.
OptionsUse camera path – When this option is on, V-Ray will calculate the irradiance map samples for the entire camera path, instead of just the current view. This is useful in the following cases:
If you use this option, you should not use interpolated glossy reflections/refractions in VRmat, as they will look odd.
Files
Auto save – If – If this option is set, V-Ray will 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 through network rendering.
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