EXR Multilayer Alpha Channel Issues from Blender

Report · Apr 11, 2023

I'm having some trouble with getting AE to recognize the correct alpha channel from a multilayer EXR exported from a Blender project I am working on. Blender's compositor is showing below with proper alpha channels. However, when I check "convert premultiplied", the alpha channel is speckled.

Now - when I bring this EXR into AE and use ExtractR, I get this -

ahah! It appears AE is doing the same "convert premultiplied" that Blender's compositor has the option to do.

Unfortunately, there is no way to access the alpha channels options of this openEXR - they should appear next to floating point - even though it certainly has one and it shows up in ExtractR.

I've posted a similar question in the Blender forums as I know it might just be how Blender exports alpha channels within EXR files. I'm new to the EXR workflow and could use some tips! Thanks all, appreciate the read.

Report · Apr 12, 2023

This has never been different. In a multichannel file the Alpha becomes "just another channel" and the default assumed channel order no longer really matters. This is in accordance with how the EXR spec is designed. Other programs just act smarter like Nuke retaining the order of the first four channels even on complex EXRs. Anyway, you have to fix it on the Blender side of things and/ or extract the Alpha as a separate layer, then treat it with effects and re-introduce it to your footage with Channel Combiner, Set Matte or simply as a track matte.

Mylenium