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Eevee not rendering alpha modes as it should
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Description

System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce RTX 2060/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.38

Blender Version
Broken: version: 2.91.0 Alpha, branch: master, commit date: 2020-10-05 08:29, hash: rBa4f8b2ad7653
Worked: (newest version of Blender that worked as expected)

Short description of error
Import via Image as Planes a transparent PNG as emit or shaderless and alpha mode as STRAIGHT (as it should be for a PNG).
In the viewport and in Eevee renders we can see white fringes in the transparency border. At the Image Editor, it is ok.
Cycles renders it correctly.

If we import as Premultiplied, the problem inverts: Not ok at Image Editor, ok in Eevee and viewport.

Event Timeline

I think this isn't a bug, you change the image interpolation in the image node


Yes you can change, my point is that STRAIGT should work for Image Editor and Eevee render the same way.
I think Eevee is not properly dealing with alpha mode.
Cycles is ok.

This is because in Cycles the image is always pre-multiplied by alpha.
This makes black where there is no alpha in the image.

It reminds me of T72677: Alpha Channel Darkens the Colors
Strange that in Eevee the image is no longer being pre-multiplied.

In my opinion Eevee and Cycles should behave the same in this matter of textures with alpha channel.
Perhaps it would be nice to have an option to make the premultiplication optional.

This seems to be the same problem in T76187: Cycles Image Texture Alpha conversion inconsistency with EEVEE and Image Editor (but I didn't understand the description there).

I think T69106 is closer duplicate for this. I will merge these reports.