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We will start by creating a "ground truth" image for each renderer. This image is generated by using a very large amount of samples so there is no more apparent noise. We will then render several images with varying amount of samples and measure the RMSE between these images and ground truth. Timings will be taken at each render. Having this data will allow us to draw a conclusion about convergence rate and general performance.
The Renderers
| Arnold | RenderMan/RIS | 3Delight OSL | |
|---|---|---|---|
| Version |
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| Technology | Unidirectional path tracer. | Using unidirectional path tracer. Other options are available but not useful for this test. | Unidirectional path tracer. |
| Shaders | C++ | C++ | OSL |
Notes About Sampling Parameters
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 perfect sense sense from a UI standpoint since the variance follows the inverse of the same 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 samplers per pixel along with the user samples.
RenderMan – We had troubles extracting consistant consistent quality from RenderMan. In Arnold and 3Delight, light samples is are the single "go to" parameter to control image quality when only direct lighting is neededconsidered. In RenderMan/RIS, we had to match light sample count with BxDF sample count to achieve acceptable quality and convergence rates. Using light samples only (or BxDF samples only) produced slowly convergent renders. In RenderMan tables below, "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. Note that we used the path tracer with once bounce instead if the "direct lighting" algorithm since the latest would crash once in a while.
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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| Samples (effective) | 2 (1.23) | 4 (4.91) | 8 (19.64) | 16 (78.56) | 32 (314.29) | 64 (1257.18) |
|---|---|---|---|---|---|---|
| Image |  |
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| Time | 1s | 2s | 6s | 21s | 1:21 | 8:12 |
| TTFP | 0s | 0.35s | 1.2s | 3.2s | 11s | 41s |
| Shadow Rays | 0.678 M | 3.26 M | 10.8 M | 43.4 M | 173.6 M | 694.5 M |
| RMSE | 0.15699 | 0.100115 | 0.0501787 | 0.0242515 | 0.0117413 | 0.00693426 |
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Conclusions
- 3Delight generates light samples that are algorithmically better than both Arnold and RenderMan. In short, for N samples:
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