Page History

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Notes About Sampling Parameters and Other Remarks

Arnold — For light samples, Arnold uses effective sample counts that are proportional – within a constant –  to the square of the user specified value.  As we will see, this makes  sense from a UI standpoint since the variance follows the inverse of the same rule in the case of Arnold. This makes the light samples slider linear in term of perceived noise. In the Arnold tables below, we will specify the effective samples per pixel along with the user samples.

RenderMan – We had troubles extracting consistent quality from 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 – or BxDF samples only ) produced –  produced slowly convergent renders.  In RenderMan tables below/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 bounce instead if the "direct lighting" algorithm since the latest would crash once in a whilefor one of the images because of a crash (quality and speed do not differ). 

3Delight – 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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• 3Delight is slower to generate these samples. Meaning that for draft (high variance) renders Arnold and RenderMan/RIS are faster. For final renders (low variance) 3Delight becomes increasingly faster with increasing samples.
• Both Arnold and RenderMan/RIS produce biased images at low sample counts. More specifically: images are darker. This explains higher RMSE with low sample counts. 3Delight manages to keep the same energy overall independent on sample counts.
• Arnold, 3Delight and RenderMan/RIS rely on acceleration data structures to sample the geometric area lights. In Arnold and RenderMan, the algorithmic complexity to build those data structures is tied – linearly, as the graph shows –  to the number of samples (as well as the complexity of the light). In 3Delight, only to the complexity of the light matters (time to first pixel for 3Delight was 2-3 seconds no matter how many samples there are).