What I have:
- [A] a sequence of RGB images
- [B] a sequence of grayscale alpha images (but also in RGB)
What I want:
- a sequence of RGBA images that have untouched RGB channels from the [A] sequence, and the alpha channel created from the [B] sequence.
Is there a way to do this using Blender's sequence editor?
EDIT: I'm almost there. The trick is to load both sequences as Movie Clips, add these to the compositor using the Movie Clip node, and combine channels.
The remaining problem is the way the alpha is handled - I want straight all the way (so that the RGB channels are not touched), but I can't find any settings for that, and I get a white outline, such as often appears when there is straight/premultiplied alpha mismatch: