Could be a couple of things.
- incompatible plug-ins (3D Stroke may need a specific CS6 version)
- flakey graphics driver causing issues with Fast Preview and accelerated effects
Check that stuff. use "Final Quality" in teh comp viewer to enforce ful lsoftware rendering. Also of course update AE to the 11.0.2 version if you haven't. Several bugs were fixed in that one (but some otehr bugs introduced).
thank you for your quick replies!
I updated After Effects but the issue is still there.
I found out that:
- it has something to do with the alpha channel, because it only happens when an alpha "set matte" or "track matte" is applied.
- It only becomes visible after a precomposition of the comp (before updating to 11.0.2 also in the comp with alpha channel)
- the issue is gone when the resolution/downsample factor is set to half (in the composition screen)
Where are you Alpha sources coming from? I've seen this issue with wrongly interpreted or damged 3D rendered files, e.g. a straight Alpha in an EXR file that has been misinterpreted as premultiplied may show such behavior... It's strictly limited to float compositing, though. It normally works in 8bpc and 16bpc.
Thanx for your reply.
The alpha's are coming from .eps or .ai files that are imported into After Effects and have enabled the TrackMatte (Alpha matte). Some of them have an alpha through the "set matte" effect.
I set the composition to 16bpc, it was 8bpc. Some of the alpha bugs were gone. There was still one left: when reverse timing a "set matte" effect on a layer the first frame stays blank "no alpha visible" the rest is fine.
Are you using the "retain transparency" option on the layers themselves? that might be anotehr of those conflicts. Otehr than that I can only cite the standard AE mantra: In case of doubt, pre-compose.