Regression: some Alpha Representation types of some images in Cycles appears to only unmultiple, and not re-multiple #102942

New Issue

System Information
Operating system: tested on macOS-10.13.6-x86_64-i386-64bit, macOS-13.0.1-arm64-arm-64bit and Windows-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

Open one the following files in 3.2.2 and 3.3.0 or later.
Sample file 1 (simpler):
cycles_alpha__bug.blend

Sample file 2:
#102942 3.2.2.blend

**System Information** Operating system: tested on `macOS-10.13.6-x86_64-i386-64bit`, `macOS-13.0.1-arm64-arm-64bit` and `Windows-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. |![#102942 3.2.2.png](https://archive.blender.org/developer/F13994930/T102942_3.2.2.png)|![#102942 3.3.1.png](https://archive.blender.org/developer/F13994931/T102942_3.3.1.png) | -- | -- | ![image.png](https://archive.blender.org/developer/F14073827/image.png) **Exact steps for others to reproduce the error** - Open one the following files in 3.2.2 and 3.3.0 or later. Sample file 1 (simpler): [cycles_alpha__bug.blend](https://archive.blender.org/developer/F14073844/cycles_alpha__bug.blend) Sample file 2: [#102942 3.2.2.blend](https://archive.blender.org/developer/F13994937/T102942_3.2.2.blend) ![ExampleAlpha_v02.psd](https://archive.blender.org/developer/F13992423/ExampleAlpha_v02.psd)

Added subscriber: @FilipMond

#103289 was marked as duplicate of this issue

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.

Material Cycles- Here we don't have such nodes (like in Compositor). Also semitransparent pixels here appear extensively bright.
Same for Alpha Straight or Premultiply.

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.

Material - What fixed the issue here was set Alpha > Channel Packed, that is weird for me, since I understood it was designed for different purpose.

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.

Another issue (probably for a new report if not reported already) is lack of refreshing Render display mode in viewport. To get viewport refreshed after Alpha type change I have to switch display modes. I'm mentioning it here just to let you know, that what you see is not what it is :)

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.

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. >Material Cycles- Here we don't have such nodes (like in Compositor). Also semitransparent pixels here appear extensively bright. >Same for Alpha Straight or Premultiply. 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](https://archive.blender.org/developer/D4807)#110723 and [D4807](https://archive.blender.org/developer/D4807)#110765 It appears that the re-multiplying isn't occurring as it was in 3.2.2. >Material - What fixed the issue here was set Alpha > Channel Packed, that is weird for me, since I understood it was designed for different purpose. 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. >Another issue (probably for a new report if not reported already) is lack of refreshing Render display mode in viewport. To get viewport refreshed after Alpha type change I have to switch display modes. I'm mentioning it here just to let you know, that what you see is not what it is :) 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.

This 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.

@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.

Added subscriber: @Alaska

This issue was referenced by 3029bd2b0c

This issue was referenced by 3029bd2b0cd15cc5d08cf7d8f8fd492879b8438b

This issue was referenced by b314d92e7d

This issue was referenced by b314d92e7dbeefee5edd6e65d90e560b215fd992

Changed status from 'Confirmed' to: 'Resolved'

Upstream patch:
https://github.com/OpenImageIO/oiio/pull/3750

Upstream patch: https://github.com/OpenImageIO/oiio/pull/3750

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Regression: some Alpha Representation types of some images in Cycles appears to only unmultiple, and not re-multiple #102942