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 will not depend on object proximity at all; higher values place more samples in places where objects are close to each other.
Hemispheric subdivs (HSph. subdivs) - this 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 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.
Interpolation samples - this is 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 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 will actually multiply 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 will actually use 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 .
Interpolation frames - this determines the number of frames that will be 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 - e.g. the default value of 2 means that in total 5 irradiance maps will be 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.
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.
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.
Scale - this determines the units for the Radius parameter:
- Screen - the radius is in image pixels.
- World - the radius is in world units.
Radius - 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.
Subdivs mult . - 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.
Show calc 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.
Show 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).
Show samples - when this option is on, V-Ray will show visually the samples in the irradiance map as small dots in the scene.
Use 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:
- 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 anmations 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 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 VRayMtl, as they will look odd.
Interpolation type - this option is used during rendering. It selects the method for interpolating the GI value from the samples in the irradiance map.
- 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 blochiness in the result.
- 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.
- Delone triangulation - all other methods of interpolation are blurry methods - that is, they will 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 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 either by increasing the hemispheric subdivs of the irradiance map samples, or by decreasing the Noise threshold value in the brute force sampler rollout.
Example: The Delone Triangulation Method
This example shows the triangles used by the Delone triangulation method to interpolate samples in the irradiance map. Note that the triangles are constructed on the fly from the irradiance samples; no actual mesh is ever created. The vertices of the shown triangles correspond to samples in the irradiance map.
On-the-fly Delone Triangulation