Dear Arion users.
We are pleased to announce a very important improvement in rendering performance in the upcoming upgrades of Arion:
– Arion stand-alone v2.7.0.
– Arion for Rhinoceros v2.7.0.
– Arion for 3ds Max v3.0.3.
The improvement affects coatings (which are present on nearly every single Arion Material since they were introduced some versions ago).
Until now, the Importance Sampling scheme that was distributing samples between the coating and its substrate was based on the amount of reflectance (which is proportional to the Fresnel value). This used to make perfect sense, but in practice the visual importance of the coated reflection is much higher than the raw amount of reflectance. i.e., because of directionality, a noisy specular reflection is much more disturbing to the eye than a clean reflection with a noisy diffuse substrate.
So we have changed the Importance Sampling scheme, to give much more priority to the coating over the substrate. This results in coatings that render as fast (and usually even faster) than 2-layered materials. Until now, users were reporting that coatings were looking significantly better than the equivalent 2-layered solution, but were leaving much more residual noise. That’s no longer the case. 
It’s hard to measure the impact of this improvement in terms of a speed gain factor. But since most Arion scenes make a heavy use of coatings, it is evident that noise convergence will be significantly better in the upcoming builds.
Thanks for watching!
