Maniphest T101063

Wrong alpha saving as render
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Authored By
Vyacheslav (hitrpr)
Sep 14 2022, 2:37 PM
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  • BF Blender
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Brecht Van Lommel (brecht)
Omar Emara (OmarSquircleArt)
Vyacheslav (hitrpr)
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Description

System Information
Operating system: Windows-10-10.0.17763-SP0 64 Bits
Graphics card: NVIDIA GeForce RTX 3060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 512.95

Blender Version
Broken: version: 3.3.0, branch: master, commit date: 2022-09-06 15:39, hash: rB0759f671ce1f
After saving picture with alpha, I got very different result (comparing preview)

saved as rgb

saved as rgba… (barely visible, huge color loss)

Open file, render, save as png rgba, compare with preview/viewport.

untitled2.blend637 KBDownload

Expected WYSIWYG

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Event Timeline

Vyacheslav (hitrpr) created this task.Sep 14 2022, 2:37 PM
Paul Kotelevets (1D_Inc) awarded a token.Sep 14 2022, 2:51 PM
Omar Emara (OmarSquircleArt) added a subscriber: Omar Emara (OmarSquircleArt).Sep 14 2022, 3:49 PM

Testing the following simple 4x4 image which contains the color (0.0, 0.0, 0.5, 0.1). Saving it as an 8-bit PNG produces an image with the color (0.0, 0.0, 1.0, 0.1020). I can't make sense of why the blue channel became 1. So I will leave this to someone more familiar with this area.

alphaTest.exr401 BDownload

Brecht Van Lommel (brecht) closed this task as Archived.Sep 14 2022, 4:33 PM
Brecht Van Lommel (brecht) added a subscriber: Brecht Van Lommel (brecht).

This is another variation of T81199: Some effects [bloom, smoke, fire, ..] still don't save in PNG with transparent background (occlusion vs. emission).

In fact no matter what we do, this image can't be represented well as a PNG file. It can't represent pixels that are both very transparent and bright.

Vyacheslav (hitrpr) added a comment.Sep 14 2022, 5:14 PM
In T101063#1417174, @Brecht Van Lommel (brecht) wrote:

This is another variation of T81199: Some effects [bloom, smoke, fire, ..] still don't save in PNG with transparent background (occlusion vs. emission).
In fact no matter what we do, this image can't be represented well as a PNG file. It can't represent pixels that are both very transparent and bright.

But we can suppress alpha to achieve proper result, same as we see at preview!
Appearance is much more important than «ground digital programmer`s truth» esp for png, where artist want to have same picture and can tune alpha manually.