Anomaly when displaying RGB data in the image editor #71482

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Roberto · 2019-11-10T23:35:42+01:00

Roberto commented

2019-11-10 23:35:42 +01:00

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: f6cb5f5449
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.

bug_alpha.blend

**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: `f6cb5f5449` 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. [bug_alpha.blend](https://archive.blender.org/developer/F8023339/bug_alpha.blend)

Roberto commented

2019-11-10 23:35:42 +01:00

Added subscriber: @RobertoAngelino

Jeroen Bakker commented

2019-11-11 12:05:01 +01:00

Added subscriber: @Jeroen-Bakker

Philipp Oeser commented

2019-11-11 13:46:34 +01:00

Added subscriber: @lichtwerk

Philipp Oeser commented

2019-11-11 13:46:34 +01:00

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...

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...

Roberto commented

2019-11-11 15:14:28 +01:00

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 ...

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 ...

Jacques Lucke commented

2020-01-08 17:14:56 +01:00

Added subscriber: @JacquesLucke

Jacques Lucke commented

2020-01-08 17:14:56 +01:00

Changed status from 'Needs Triage' to: 'Archived'

Jacques Lucke closed this issue

2020-01-08 17:14:56 +01:00

Jacques Lucke self-assigned this 2020-01-08 17:14:56 +01:00

Jacques Lucke commented

2020-01-08 17:14:56 +01:00

I think the current behavior is more correct in the current design. Changing it to work as you describe probably requires some deeper thinking about the implications this has for color management in the compositor (which I'm not really able to do so far). In any case, this is out of the scope for a bug report. So I'll close this as invalid because this white border is kind of expected.

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Anomaly when displaying RGB data in the image editor #71482