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The "Premultiplied" setting for Alpha on the Image input node in the compositor doesn't seem to work correctly for png image with alpha #115014

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opened 2023-11-16 20:48:49 +01:00 by T-112 · 2 comments
T-112 commented 2023-11-16 20:48:49 +01:00
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System Information
Operating system: macOS-13.6-arm64-arm-64bit 64 Bits
Graphics card: Metal API Apple M1 Pro 1.2

Blender Version
Broken: version: 4.0.0, branch: blender-v4.0-release, commit date: 2023-11-13 17:26, hash: 878f71061b8e
Worked: (don't know)

Short description of error
A png with alpha does not look correct when viewed using the compositor viewer node. Setting the Alpha to "Premultiplied" does not work, but using an Alpha Convert node does.

Exact steps for others to reproduce the error

  • Have a png image with alpha
  • Use an Image input node in the compositor with default settings
  • The image has a rough border with incorrect looking alpha when viewed via a viewer node in the compositor
    • The image has correct looking alpha when using the Image Editor to view it
  • In order to get correct looking alpha view the viewer node, I have to add an Alpha Convert node set to "To Premultiplied"
  • Setting the Alpha to "Premultiplied" on the Image input node gives a completely different and broken looking result
**System Information** Operating system: macOS-13.6-arm64-arm-64bit 64 Bits Graphics card: Metal API Apple M1 Pro 1.2 **Blender Version** Broken: version: 4.0.0, branch: blender-v4.0-release, commit date: 2023-11-13 17:26, hash: `878f71061b8e` Worked: (don't know) **Short description of error** A png with alpha does not look correct when viewed using the compositor viewer node. Setting the Alpha to "Premultiplied" does not work, but using an Alpha Convert node does. **Exact steps for others to reproduce the error** - Have a png image with alpha - Use an Image input node in the compositor with default settings - The image has a rough border with incorrect looking alpha when viewed via a viewer node in the compositor - The image has correct looking alpha when using the Image Editor to view it - In order to get correct looking alpha view the viewer node, I have to add an Alpha Convert node set to "To Premultiplied" - Setting the Alpha to "Premultiplied" on the Image input node gives a completely different and broken looking result
Screenshot 2023-11-16 at 11.45.08 AM.png
2.3 MiB
premultiplied_bug.blend
2.7 MiB
Screenshot 2023-11-16 at 11.45.08 AM.png
T-112 added the
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Pratik Borhade commented 2023-11-17 06:07:54 +01:00
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Hi, thanks for the report. Yes, can confirm. But this appears to be fixed already in current main/4.1

Hi, thanks for the report. Yes, can confirm. But this appears to be fixed already in current main/4.1
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Pratik Borhade added
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Omar Emara commented 2024-03-11 10:05:17 +01:00
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Closing since this is already fixed in 4.1 which will be release soon.

Closing since this is already fixed in 4.1 which will be release soon.
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Reference: blender/blender#115014
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