This is a master control for enabling global illumination.
The Global Illumination (GI) system lets you use two separate algorithms to calculate indirect lighting.
For example, you can calculate multiple light bounces with a fast algorithm like Path Tracer, and still calculate the final bounce with Final Gather to get a fast, high quality global illumination render. Both subsystems have individual control of Intensity and Saturation to boost the effects if necessary.
You can also set None for both Primary GI and Secondary GI. For Secondary GI, use None when you don’t need deeper indirect light or if you have a Primary GI that cannot use Secondary GI. Use None for primary global illumination when baking advanced passes that perform their own gather (such as Radiosity Normal Map when not using radiance cache, and the Lua pass). When these passes perform their own gather, only the Secondary GI is sampled, making any primary global illumination useless.
Select from the following algorithms:
This is a brute force GI method that calculates GI by sending rays in a hemisphere around the shading points. No caching is used so a new calculation is done for each shading point. An importance sampling method is used for secondary bounces, so a high number of bounces can be used without exploding the render time. The Monte Carlo method is unbiased and can be used for reference images when used as Primary GI. It can also be used as Secondary GI together with Final Gather to produce a multi-bounce high quality result without light leakage.
The Path Tracer algorithm calculates indirect lighting by tracing a (high) number of rays from the camera into the scene. These rays are bounced and traced further into the scene, depending on the properties of the surfaces they hit. Surfaces with a high diffuse reflectance will have a higher probability to continue the ray paths, hence giving more color bleeding to other surfaces. The path is only terminated when the probability for absorption is high enough.
Illumination from the ray bounces are stored at selected points in the scene, resulting in a set of cache points. A parameter, Cache Point Spacing, is used to set the distance between the cached points. A smaller distance will generate more cache points, and enable better capturing of details, but also higher memory usage and longer rendering time.
Once the pre-render pass completes, the path tracer cache holds an approximation of the indirect light. The quality of the solution depends on the number of paths used and the density of the cache. If the path tracer solution is used as Secondary GI, with Final Gather or Radiance Cache as Primary GI, the settings can be set quite low and still produce good quality.
The cache points can be saved to a map file and reused for successive renderings. Note that the file option Reuse and Refine will load the map from file and then refine the solution by adding the paths from a new pre-render pass to the cache. This improves the solution with each successive each rendering.
Master control for enabling caustics, using caustics photon mapping.
Scales the intensity of the first GI bounce.
Scales the saturation of the first GI bounce.
Scales the intensity of secondary GI bounces.
Scales the saturation of secondary GI bounces.
Scales the intensity of the caustics photon map.
Scales the saturation of the caustics photon map.
A gain for boosting the diffuse material components when used by GI. Can be used to adjust the amount of indirect diffuse lighting. For example, a scene with very dark textures will not get much indirect lighting, but when boosting all diffuse components the indirect effects are increased.
Scales the specular material components when used by GI. Can be used to adjust the amount of indirect lighting from specular effects.
Scales the emissive material components when used by GI. Can be used to adjust the amount of indirect lighting from emissive materials.
Controls whether to clamp materials to preserve physical correctness when used by global illumination. Select from the following options:
Disables material clamping.
Clamp each R, G and B component separately.
Clamp the intensity (HSV Value).
Selects what caching method to use for final gathering. Select from the following options:
Disables caching and performs a new final gathering for every shading point. Gives very accurate results but long render times. Use (for example) for reference images.
(Default.) Caches the irradiance at selected points in the scene and uses interpolation in between the points.
Caches radiance SH functions at selected points in the scene and uses interpolation in between the points. The radiance cache is useful in some advanced baking passes (such as Radiosity Normal Maps), when directional indirect lighting is needed.
Sets the maximum number of rays to use for each final gather sample point. A higher number gives higher quality, but longer rendering time.
Sets the number of indirect light bounces calculated by final gather. A value higher than 1 will produce more global illumination effects, but note that it can be quite slow since the number of rays will increase exponentially with the depth. It’s often better to use a fast method for secondary GI. If a secondary GI is used the number of set final gather bounces will be calculated first, before the secondary GI is called. In most cases, set to 1 when using a secondary GI.
Controls how sensitive the final gather should be for contrast differences between the points during precalculation. If the contrast difference is above this threshold for neighbouring points, more points will be created in that area. This tells the algorithm to place points where they are really needed, e.g. at shadow boundaries or in areas where the indirect light changes quickly. Hence this threshold controls the number of points created in the scene adaptively. Note that if a low number of final gather rays are used, the points will have high variance and hence a high contrast difference, so in that case you might need to increase the contrast threshold to prevent points from clumping together.
Sets the number of final gather points to interpolate between. A higher value will give a smoother result, but can also smooth out details. If light leaks through walls as this value increases, checking the sample visibility can solve the problem. See Check Sample Visibility below.
Controls a scaling of Final Gather with Ambient Occlusion which can be used to boost shadowing and get more contrast in your lighting. The value controls how much Ambient Occlusion to blend into the Final Gather solution.
Max distance for occlusion. Beyond this distance a ray is considered to be unoccluded. Can be used to avoid full occlusion for closed scenes.
Can be used to adjust the contrast for ambient occlusion. Increase this value to make bright surfaces brighter and dark surfaces darker.
A scaling of the occlusion values. Can be used to increase or decrease the shadowing effect.
When on, a single Ambient Occlusion pass will be rendered, to visualize the AO effect. All other render passes are ignored. This can be useful while tuning your AO settings.
Controls how sensitive the final gather should be for differences in the points normals. A lower value will give more points in areas of high curvature.
Controls how the irradiance gradient is used in the interpolation. Each point stores its irradiance gradient which can be used to improve the interpolation. However in some situations using the gradient can result in white ”halos” and other artifacts. This threshold can be used to reduce those artifacts.
The max distance a ray can be traced before it’s considered to be a “miss”. This can improve performance in very large scenes. If the value is set to 0.0 the entire scene is used. The distance is measured in Maya units.
When on, final gather also caches lighting from light sources. This increases performance since fewer direct light calculations are needed. It gives an approximate result, and hence can affect the quality of the lighting. For instance indirect light bounces from specular highlights might be lost. However this caching is only done for depths higher than 1, so the quality of direct light and shadows in the light map will not be reduced.
Turn this on to clamp the sampled values to [0, 1]. This will reduce low frequency noise when Final Gather is used together with other Global Illumination algorithms.
Turn this on to reduce light leakage through walls. When points are collected to interpolate between, some of them can be located on the other side of geometry. As a result light will bleed through the geometry. So to prevent this Turtle can reject points that are not visible.
Sets the number of paths that are traced for each sample element (pixel, texel or vertex). For preview renderings, you can use a low value like 0.5 or 0.1, which means that half of the pixels or 1/10 of the pixels will generate a path. For production renderings you can use values above 1.0 if needed to get good quality.
Sets the average number of bounces in the Path Tracer solution. The maximum depth is 40. A lower Depth will result in a faster but noisier solution, but the overall intensities will be the same. How far light actually bounces is much dependent on your materials, brighter materials lets light spread further than dark materials.
Sets the maximum distance between the points in the path tracer cache. If set to 0.0 a value will be calculated automatically based on the size of the scene. The automatic value will be printed out during rendering, which is a good starting value if the point spacing needs to be adjusted.
Selects the filter to use when querying the cache during rendering. None will return the closest cache point (unfiltered).
Sets the size of the filter as a multiplier of the Cache Point Spacing value. For example, a value of 3.0 uses a filter that is three times larger then the cache point spacing. If this value is below 1.0 there is no guarantee that any cache point is found. If no cache point is found the Default Color will be returned instead for that query.
Prefilters the cache points before the final pass starts. This can increase the performance using the final render pass and is especially useful when Check Sample Visibility is enabled, or the filter kernel is large.
When on, final gather also caches lighting from light sources. This increases performance since fewer direct light calculations are needed. It gives an approximate result, and hence can affect the quality of the lighting. For instance indirect light bounces from specular highlights might be lost. However this caching is only done for depths higher than 1, so the quality of direct light and shadows in the light map will not be reduced.
Turn this on to reduce light leakage through walls. When points are collected to interpolate between, some of them can be located on the other side of geometry. As a result light will bleed through the geometry. So to prevent this Turtle can reject points that are not visible.
Sets the number of rays to use for each calculation. A higher number gives higher quality, but longer rendering time.
Sets the average number of indirect light bounces calculated by Monte Carlo. A lower number means a noisier but faster solution, although the overall intensities will be the same.
The maximum distance a ray can be traced before it’s considered to be a “miss”. This can improve performance in very large scenes. If the value is set to 0.0 the entire scene will be used. The distance is measured in Maya units.
Caustics effects are handled with a special photon map in Turtle. You must explicitly emit caustics photons from light sources.
Influences the number of photons to use when calculating caustics effects, a higher number take more photons into account. Default value is 1.0.
Sets the maximum search radius to use when searching for photons during lighting calculations for caustics effects. If the Photon Radius is set to r, photons within a sphere of radius r around the sample point will be used to calculate the light. The radius is given in Maya units.
Sets the maximum number of bounces a caustics photon can take before it is absorbed.