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Image Editor "Erase Alpha" brush blending mode affects all channels
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Description

System Information
Operating system: Linux 64-bit

Blender Version
2.92

Short description of error
When used on floating point images, the "Erase Alpha" brush blend mode erases not only the Alpha channel, but the RGB channels as well. This makes it impossible for the user to paint the alpha channel of an image without affecting the RGB channels. Although this is not the case with non-float images, it may appear to be at first glance; this will be submitted as a second but related bug.


Exact steps for others to reproduce the error

  1. Open the attached file. Note that both images have an alpha channel but are currently viewed in RGB and not RGBA.
  2. Use the default brush in "Erase Alpha" mode to erase a hole in the floating-point image on the right.
  3. Use shift-click to sample the pixel-values of the image to confirm that the RGB channels have been multiplied/reduced.
  4. This is also apparent when you try to use "Add Alpha" to un-erase the image- the completely erased parts do not come back.