Arnold: Stochastic Transparency

While Arnold already uses a stochastic approach for transparency that comes only as a ‘closure’. Which means that for custom shaders that do not use an all closure approach it is not available, so we had to add one ourselves.

Stochastic transparency makes a huge impact on render times where bounces depth is high. Top image took 12:09, bottom with stochastic (low-discepancy bluenoise) transp just 3:43! Using (native Arnold) adaptive sampling, final variance is the same, without, the latter would be noiser.

In the while we also played with various quasi-random sequences to see what’s the better to accomplish the task.

metal_params_normals
metal_params_normals

Eventually we tested both the ‘mechanics’ of the various samplers (ie. fixed sampling) as well as their convergence rate within an adaptive sampling framework.

Here a final one with a recently introduced R2 sequence which has both blue-noise and low-discrepancy properties and remarkably it’s also progressive that means works very well on multidimensional sampling where different bounces for example needs a new seed’ed sequence that fills the holes of the previous ones. On our tests this is comparable to Pixar/Disney latest PMJ.

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