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Bad alpha value in VSE
Closed, InvalidPublicBUG

Description

System Information
Operating system: Linux-5.3.0-51-generic-x86_64-with-debian-buster-sid 64 Bits
Graphics card: GeForce GTX 670/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21

Blender Version
Broken: version: 2.82 (sub 7), branch: master, commit date: 2020-03-12 05:06, hash: rB375c7dc4caf4
Worked: (optional)

Short description of error
PNG pictures with alpha are wrongly composited in VSE. Same pictures are doing well in Gimp or Blender compositor.



Exact steps for others to reproduce the error
I can't obtain a "normal" result while compositing png with alpha in VSE. "Normal" is the result obtained with Gimp or blender compositor. VSE look like it makes alpha harder. Can't be solve by any tweaking. I have tried to switch
Alpha source setting to Premultiplied, change color spaces, but still not ok.

I have packed the entire process files.
-image-generator.blend : generate the png pictures
-Gimp-ok.xcf : png composited ok in Gimp
-compositor-ok.blend : png composited ok in Blender compositor
-VSE-problem : png wrongly composited in Blender VSE (on the upper left, the good result imported for reference)

Same problem on 2.79/2.81/2.82a/2.83 alpha

Discover that at the end of a project I had to redo my entire VSE editing in Blender compositor to obtain the normal result. Litterally no way out.

Thanks a lot if you can fix it!

Event Timeline

Campbell Barton (campbellbarton) changed the task status from Needs Triage to Needs Information from User.May 5 2020, 7:54 AM

This report is missing:

  • Last version that worked.
  • Exact steps to redo the error.
  • A blend file (unless the steps start from the default startup).
laurent renaud (loranozor) changed the task status from Needs Information from User to Needs Triage.May 5 2020, 8:35 AM
laurent renaud (loranozor) updated the task description. (Show Details)

This report is missing:

  • Last version that worked.
  • Exact steps to redo the error.
  • A blend file (unless the steps start from the default startup).

Sorry, I thought it have to be done on the next page...

Richard Antalik (ISS) changed the task status from Needs Triage to Confirmed.May 5 2020, 1:38 PM
Richard Antalik (ISS) changed the subtype of this task from "Report" to "Bug".

In the provided files the VSE colorspace is set to sRGB. Compositor uses Linear color space. In the color management panel you can select which colorspace to use for the VSE.
There is still a difference, that is related to the view transform that have been set in the image-generator.blend. The compositing does alpha compositing before the view transform. The vse test does the view transform before saving the image and after the vse.

See here for a better comparison.

Jeroen Bakker (jbakker) claimed this task.