Adaptive Sampling doesn't work on AOVs or even Alpha

[toby.gainesQTXCX]

- unless there's value in the RGB channels. Things like separated aov renders, or black matte objects with alpha, must have the min. camera AA set to max. Which renders much slower and doesn't match the AA of the beauty renders, creating edges in comp. I don't see any options for this in the aov's attributes, is there no way to make this work? 

[david.ostler2WSX9]

I had an issue with this a while back in solaris and found that I needed to have an RGBA pass in order for adaptive sampling to work correctly.  It seems like I saw a note that this was fixed in one of the recently Arnold releases.  Are you using the latest version?

[toby.gainesQTXCX]

No but I have no control over that anyway - but if it's a known issue / no workaround, that answers my question, thanks.

[toby.gainesQTXCX]

This must be what you saw - it's not a fix or addition of a feature, just a warning that Adaptive won't work.
Arnold 7.1.4.0 ;
"Warn when adaptive sampling is enabled and there is no RGBA AOV: Adaptive sampling will only run on the RGBA (beauty) AOV. If there is no AOV with the name RGBA, then adaptive sampling is disabled. This can be particularly confusing when IPR has a display window and so adaptive sampling is used, but the batch render is done without display (kick -dw for instance) and adaptive sampling stopped working. We now emit a warning when this occurs so this issue can be easily detected. (ARNOLD-12521)"

Vray had an option to sample aov's on each aov node, at least 5 years ago. I used it in early 2017.

[Stephen.Blair]

Also, "color" will be automatically renamed to "RGBA" under the covers.