As mentioned in previous blog posts, Arion’s compositing capabilities have been greatly reviewed and extended for v2.5.0. An example is the new Caustics AOV.
As you probably know, Arion features a ‘Disable caustics’ switch (which you can enable either globally or per-material). This switch dims sampled contributions proportionally to ‘how caustic’ they appear to be. This solution effectively removes caustics from the render.
In general, and in true unbiased/physically-based rendering spirit, one should never want to remove caustics from a render. However, in practice, sometimes most of the noise (or even fireflies) in an image come from caustics.
The ‘Disable caustics’ switch is fine. However, it leaves you with no control in case that you only want to remove only some of the caustics, as it is an all-or-none switch.
So, for v2.5.0 we have done the following:
1- We have improved the way the ‘Disable caustics’ switch works, making it filter caustics more finely than before.
2- We have added a new AOV which gathers the contributions that the ‘Disable caustics’ switch would trim out of the final render. This AOV works regardless of whether the ‘Disable caustics’ switch is ON or OFF.
In other words, now you can render normally, and then deal with caustics separately in post-processing.
To obtain a caustics-less render in v2.5.0 you can:
1- Either render with the ‘Disable caustics’ switch turned ON.
2- Or render normally, and then subtract the Caustics AOV from the Main AOV in post-processing.
Both operations are equivalent. Here’s a little example, where the Caustics AOV has been subtracted from the Main AOV:
Once you have a caustic-less image and a Caustics AOV you can do things such as:
– Denoise or despeckle the Caustics AOV, and then add the result to the Main AOV.
– Dim whichever caustics are bothering you and add the result to the Main AOV.
– Pump the caustics up for artistic effect.
In order for these post-processing operations to work (correctly), you must work with 32-bit raw (untonemapped) EXR output. Additions and subtractions of AOVs only work as they are intended to if they happen in unclamped linear space (a.k.a. Linear Workflow / LWF). Doing operations such as the ones mentioned above with tonemapped 8-bit or 16-bit output would ‘seem to work’ but be technically incorrect, because each channel would be LDR-clamped and gamma-corrected.
A little status update:
We’re still working on Arion stand-alone v2.5.0, MAX LIVE v2.5.0 and RHINO LIVE v2.5.0. We will release each of them as soon as they are ready, which should hopefully happen during the upcoming weeks (Aug/Sep).
Thanks for watching!