Premultiplication issue with two jpeg sequences I have two (rgb) jpeg sequences one with the alpha information (black and white) the other one with the green screen footage. I keyed them with Keylight and they look perfect in AE before exporting.



When I import the jpeg sequences back in AE and apply the alpha, I get a green hallow.



It seems to be some premultiplication issue. What did I do wrong exporting / importing the jpeg sequences?
Part of it may be the fact you are using JPEG sequences.  JPEG isn't a pixel accurate format and you are going to have some differences in block quantization that could potentially result in mismatches.

I don't think that is the only issue since it is a bit too regular for it to be the only issue, but I'd try to use an intermediate format that is a bit more lossless for doing things that need to be pixel accurate match up.