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RenderMan/RIS – In Arnold and 3Delight, light samples are the single "go to" parameter to control image quality when only direct lighting is considered. In RenderMan/RIS, we had to match light sample count with BxDF sample count to achieve acceptable quality and satisfactory convergence rates. Using light samples only – or BxDF samples only – produced slowly convergent renders. In RenderMan/RIS result data, "N samples" means N samples for both light and BxDF. We did all the test with the "advanced (4)" light sampler — other samplers did not provide acceptable results for this test case. The samples used by the renderer are the ones entered in the UI and are not squared as in Arnold. Note that we used the path tracer with once one bounce instead if the "direct lighting" algorithm for one of the images because of a crash (quality and speed do did not differ).
3Delight – We have only one control for the general quality of the render. In the case of direct lighting, 3Delight "understands" that samples are best used for light sampling and that's what it does. As tests will show, those samples have a linear impact on perceived noise levels.
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