Turtle - Global Illumination
Global Illumination
New Final Gather Algorithm
The algorithm for Final Gather has been redesigned. The new method uses a progressive scheme where new samples are added based on contrast difference to neighboring samples. The new method is much better at handling sharp edges in the illumination and it is better at eliminating artifacts due to geometric discontinuities where the old method often failed. The old FG method can still be used if needed by enabling the Legacy checkbox.
Final Gather Attenuation
A new feature for attenuating FG rays has been added. Two type of attenuation is supported; Falloff Attenuation, where the light is decreased with distance, and Occlusion Attenuation, where the light is decreased for shorter rays, which enhances the occlusion and shadowing effect of final gather. Occlusion Attenuation is very useful for giving more contrast and depth to the lighting, especially if multi-bounce Global Illumination is used, where the result can look flat and washed out in areas of strong illumination.
Radiance Cache unified with Final Gather
The Radiance Cache light integrator has been integrated into Final Gather. In the Final Gather settings you can now choose what cache type to use. If you select RadianceSH a Radiance Cache will be used.
New Final Gather Mode
Final Gather has a new mode for brute force sampling. This is enabled by choosing None when selecting Cache Type. In this mode a new hemisphere sampling is performed for every shading point, which gives a very exact result. The render time is often long so it’s mostly suitable for rendering reference images.
New Monte Carlo Global Illumination
There is a new light integrator called Monte Carlo. It’s very similar to the brute force FG method but handles secondary bounces more efficiently, so a high number of bounces can be used without exponentially increasing the render time. This integrator can also be used as Secondary GI.
Cache Direct Light
Final Gather, Path Tracer and Photon Mapping have a new checkbox for Cache Direct Light. When enabled they will cache both indirect light and direct light from the light sources. This increases performance since fewer direct shading calculations are needed. This is an approximation so it can affect the quality of the result. For instance indirect lighting from specular highlights might be lost. Previously a similar method was used when selecting Approximate GI shading method. But now this can be controlled per integrator instead. Note that caching direct light is only valid when using Path Tracer and Photon Map as secondary integrators or when multi-bounce Final Gather is used.
New Method for Light Leak Problems
To eliminate light leak problems new functionality for checking visibility between cached sample points has been added. This makes sure that samples from different sides of geometry are not used together, causing light leakage. This is added to both Final Gather and Path Tracer. By enabling Check Sample Visibility all light leakage is removed. It comes with a small performance hit so make sure you use this only when you need to.
Improved Color Balance
The color balance system for Global Illumination has been unified and now supports color balance to every output, including Spherical Harmonics and RNM. Color balance now affects Global Illumination caches, previously it was just a post process. The Intensity and Saturation controls have been modified so that primary now affects the first bounce and secondary all other bounces, independent of what Global Illumination methods are selected. So for example if you use multi-bounce Final Gather you can now adjust the contribution from the first and the secondary bounces separately.
The override controls for Intensity and Saturation has been moved from the shapes in Maya and is now located on each shader instead. The shader local values are multiplied by the global values.
New color balance controls have been added. You can now modify the diffuse, specular and emissive contributions independently for Global Illumination. These controls are available both globally and locally on each material shader.
New Prepasses
The precalculation pass for Final Gather and Occlusion is now progressive and runs in a number of passes, each pass with a higher detail level. Under Anti-Aliasing -> Prepass you can set the min and max sample rate which controls the number of passes that will be rendered. Another difference is that the visualization of the prepass now shows the indirect lighting, instead of the full shaded result. This increases performance and gives a better visualization of the indirect lighting.
The Path Tracer prepass has also been modified to show the indirect lighting. It now shows a direct visualization of the path tracer cache, instead of the noisy path tracer solution.
GI Transparency Depth
A new control, GI Transparency Depth, has been added for limiting the number of transmissions a Global Illumination ray can do. This will affect rays spawned by Final Gather, Monte Carlo and Occlusion sampling.
Performance Improvements
Major performance improvement has been done with multi-bounce Final Gather. Previously there was a massive performance hit when using FG Depth higher than 1. But that has now been optimized.
Overall performance of global illumination has been improved and it now scales better on multi-core systems.
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