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The various color blend mode, like Screen, Multipley, Lighten, etc Do not use the correct Alpha channel
Closed, ResolvedPublic

Description

System Information
Operating system: Windows/Linux
Graphics card: N/A

Blender Version
Broken: 2.79 d75376 (2019-01-23) head
Worked: Never - Incorrect when added in commit 4b4702ab8af6f7

I notices when using the VSE to apply some footage that was shot against a black background and meant to be blended in with Screen, had weird behavior in regards to its alpha channel, essentially clipping what was below it and showing transparency. This is a problem when you are taking that footage and transforming it, and using Screen blend mode on the transform layer.

Here are two screen shots showing the before and after the fix (https://developer.blender.org/D4371) and a simple blend file to test with.

Here is the blend file that was used

Event Timeline

Jacques Lucke (JacquesLucke) triaged this task as Confirmed, Medium priority.

Another note on this: These blending mode should work the same as the Color-Mix node in the compositor which takes the alpha channel from the base/background layer (weirdly the top input). In the VSE case the base/background comes from the sequences below.