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Anomaly when displaying RGB data in the image editor
Open, Needs Triage by DeveloperPublic


System Information
Operating system: Windows-10-10.0.18362 64 Bits
Graphics card: GeForce GTX 760/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 441.12

Blender Version
Broken: version: 2.80 (sub 75), branch: master, commit date: 2019-07-29 14:47, hash: rBf6cb5f54494e
Worked: (optional)

I point out an anomaly "(most likely) that I noticed during the compositing phase. When I display RGB (and not RGBA) data in the image editor (or in the backdrop) I get an incorrect result where the alpha is gray Here is an example.

-I have set a resolution of 1024x1024 at 100% in the properties.

-I created an "Image" node in the compositor and generated a UV grid with a 1024X1024 resolution without alpha channel to have any image (RGB).

-I created a matte, using "Box Mask" to get any alpha.

-I connected the "Box Mask" node output to a Blur and softened the mask slightly.

-I created a "Set Alpha" node and connected the UV grid of the Image node to the RGB and the Blur output to the Alpha.

When I visualized both in the image editor and in the background the result of the "set alpha" I obtained the UV grid of the shaded by the alpha, so far But when I changed from "Color and Alpha" to "Color" from the Display I got an "anomalous" image: the Uv grid with the (white) edges of the matte above.
I get the same result also using Separate RGB + Combine RGB, connecting the UV grid in RGB and the blurred Matte in A when I display the RGB in the image editor.



Event Timeline

Isnt this because Use Alpha is checked on the Viewer / Composite nodes?
(Colors are treated as alpha premultiplied then). Need to check again how this is supposed to be looking...

Of course, if I turn off the alpha in the viewer it "seems" to work but at this point if I want to see "only" the alpha channel I can't. In theory, if I want to see only RGB using a node that does not "multiply" as Set Alpha or SeparateRGB + Combine RGB I would expect to see the "RGB" (and not "RGBA") data intact without the influence of the alpha ( alpha which seems to be added more than multiplied). The alpha channel, however, should be kept waiting for a node like "Convert Alpha" which multiplies by RGB.

Then I don't know if it's normal for behavior ... but if it is I don't understand the sense ...