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Incorrect RGB display in Image Viewer when not viewing alpha channel
Confirmed, NormalPublicBUG


Version: 2.82a (Linux 64)

How to reproduce:

  1. Open the attached file and render the frame.
  2. In the display_channels menu in the header of the Image Viewer, select "Color" (Not "Color and Alpha")
  3. Mouse over the pixels of the image and Compare the RGB values with the displayed values.
  4. Display the individual RGB color channels as well

The above image looks as though the rim of the shape is solid grey, but in fact the explicit RGB values do fade from grey to black, due to the blur node.

When viewing an image in Color without alpha, or in Red, Green, or Blue Display mode, the image viewer seems to "pre-divide", or perhaps "un-premultiply" the RGB values, which causes incorrect values to display. This makes it very difficult for the user to work with alpha channels!

Adding an Alpha Convert node makes matters even worse:

Now, the explicit RGB values really are a solid grey, but in the image view the rim is displayed as getting brighter! Not a good workflow at all!

Event Timeline

The color that is read in the ibuf comes with alpha premultiplied.
I don't quite understand why it happens, but I imagine it is important for the final image.

(This is an area that I'm not familiar with).

Thankyou, @Germano Cavalcante (mano-wii) . It doesn't seem to affect the final image. If, for instance, you save the image to a file, the saved image will have the correct colors (the values explicitly stated when you mouse over the pixels), whether or not you enable alpha. It will not look like the result displayed in the viewer. The viewer is showing RGB values which don't seem to relate with how the final image looks.

T74586 Switching between passes in the image editor can make the channel selector invalid.

Germano Cavalcante (mano-wii) changed the task status from Needs Triage to Confirmed.Tue, Mar 24, 1:50 PM
Germano Cavalcante (mano-wii) changed the subtype of this task from "Report" to "Bug".

It deserves an investigation.
I'm confirming as a bug.