Thanks David & Michael for your comments. I will try some of the other tools and see if that makes a difference, given the source material. I also have the same issue in after effects with the same kind of footage (i.e. 7D H.264 -> prores converted, with graduated areas). Is there any pre-processing / conversion process that can be applied to minimise this effect?
It’s a really nasty type of artifact as I never really know when it’s going to turn up (mostly shot dependent) and sometimes it doesn’t appear until the final encode (either back to h.264 or other delivery codec).
Declan Smith
https://www.madpanic.tv
FCS3 / After Effects CS4 / Combustion / Canon 7D / Canon XL2