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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. Those effective samples are gather gathered from Arnold's diagnostics files.

RenderMan/RIS – In Arnold and 3Delight, light samples are the single "go to" parameter to control image quality when only direct lighting is consideredneeded. 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 results data, "N samples" means N samples for both light and BxDF.   We did all the tests with the "advanced (mode 4)" light sampler since  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 one bounce instead of the "direct lighting" algorithm for one of the images because of a crash (quality and speed did not  seem suffer although there were some minor differences). 

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  • 3Delight is slower to generate these samples. For draft renders (high variance), Arnold is fastest. For final renders (low variance) 3Delight becomes increasingly faster with increasing samples.
  • Arnold and RenderMan/RIS draw samples at about the same speed, but the quality of Arnold samples is better. 
  • Both Arnold and RenderMan/RIS produce biased images at low sample counts. More specifically: images are darker. 3Delight manages to keep the same energy overall independently of sample counts.
  • Arnold, 3Delight and RenderMan/RIS rely on acceleration data structures to sample the geometric area lights. In Arnold and RenderMan/RIS, the algorithmic complexity to build those data structures is tied – linearly, as the graph shows –  to the linearly 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 arewere).  



Resources



RenderMan/RISArnold3Delight
Images and Stats


Maya Scene

Remarks
The same scene works with both 3Delight and Arnold