Regression: some Alpha Representation types of some images in Cycles appears to only unmultiple, and not re-multiple #102942
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Reference: blender/blender#102942
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System Information
Operating system: tested on
macOS-10.13.6-x86_64-i386-64bit
,macOS-13.0.1-arm64-arm-64bit
andWindows-10-10.0.22621-SP0
Graphics card:
ATI Radeon HD 5750 OpenGL Engine ATI-1.68.25
;Apple M1 Pro Metal - 83
;NVIDIA GeForce RTX 3060 Laptop GPU/PCIe/SSE2 NVIDIA 516.94
Blender Version
Broken: 3.3.1, branch: master, commit date: 2022-10-04 18:35, hash:
b292cfe5a9
Worked: 3.2.2
Short description of error
Some Alpha images (Like the ones generated by Photoshop) in Cycles Shader editor displays Alpha, Straight and Premultiplied with the same issue.
Exact steps for others to reproduce the error
Sample file 1 (simpler):
cycles_alpha__bug.blend
Sample file 2:

#102942 3.2.2.blend
Added subscriber: @FilipMond
#103289 was marked as duplicate of this issue
PSD Alpha ignored as Straightto PSD Alpha ...Added subscriber: @EAW
Changed status from 'Needs Triage' to: 'Confirmed'
Thank you for the report, and thank you for adding additional information to try and clarify.
I will have to eliminate some of this report to focus it on the Cycles material issue, but I have attempted to answer your other points below.
I don't think this is specific to PSDs, but part of a previously reported bug. The compositor having bright edges might have the same cause as #102484 (PNG 8bit and 16bit loads differently in compositor), which would mean that the Compositor Input Node doesn't do any Straight to Associated (premultipied) conversion for any loaded from disk 8 bit per channel images, and not just pngs.
In Cycles, whenever the alpha channel of the Image texture node is connected to another node, the image in unpremultiplied, so that the colors are correct when the alpha is then remultiplied back into the colors in the mixing with the transparent BSDF.
See D4807#110723 and D4807#110765
It appears that the re-multiplying isn't occurring as it was in 3.2.2.
An fortunate (because it at least gives you a workaround) side effect of
3b23b5c638
I believe. Setting the Alpha Channel to Channel Packed prevents Cycles from un-premultiplying the color channels.This issue I could not repeat, the viewport updated for me whenever I changed the alpha type, both in 3.3.0 and 3.5.0 alpha.
PSD Alpha ...to PSD Image with Alpha in Cycles shader editor appears to only unmultiple, and not re-multiple like in 3.2.2This reminds me of #99565 (Discrepancy in Cycles rendering result appears when "Pack Resources" on tga file) and #101810 (Cycles produces glowing artifacts around the alpha clipped area of the texture).
@EAW Thanks for taking time to give me more insight into it :) Reading Brecht's notes sounds like a nightmare ...
Ad to Refreshing lag I will test it on another machine later.
PSD Image with Alpha in Cycles shader editor appears to only unmultiple, and not re-multiple like in 3.2.2to Regression: some Alpha Representation types of some images in Cycles appears to only unmultiple, and not re-multipleAdded subscriber: @Alaska
This issue was referenced by
3029bd2b0c
This issue was referenced by
b314d92e7d
Changed status from 'Confirmed' to: 'Resolved'
Upstream patch:
https://github.com/OpenImageIO/oiio/pull/3750