I am trying to create a map of a building in GIMP . The building is color coded by section with 30% opacity, and the space between the colors is currently white because that is the color of the base image that everything is being built onto.

The layer that is to have the walkway colors was put next to last in the order. It is just a transparent layer. I put it near the bottom of the layer order in effort to use a paint tool to color over the other layers and only paint the Alpha channels without painting any of the department colors. I remember being able to lock upper layers to do this. Every time I've tried, I have locked the pixels, position, and alpha in different combinations. Whenever I've started to paint over the white it paints everywhere. What am I doing wrong?

  • Alpha channels and layers are not the same thing. Can you please edit your question to clarify which on you mean? Maybe uploading a few screencaps to imgur.com and linking to them will help clarify the problem. Feb 12 at 21:25
  • Hi. Could you show us a screeen shot of your image and layers, and show what you are trying to do. Thanks.
    – Billy Kerr
    Feb 13 at 0:23
  • imgur.com/a/B7mjgBB This is the link to an image that I hope explains things
    – designinja
    Feb 13 at 13:15

1 Answer 1


If you wan to paint the transparent pixels and only them, set the paint tool to "Behind" mode. If you want to only paint on the opaque pixels, set the alpha-lock on the layer.

enter image description here

  • This sort of worked. When I painted, it colored the white, but I was also able to see it behind the semi-transparent layers on top. imgur.com/a/B7mjgBB This is an explanation of my project
    – designinja
    Feb 13 at 13:17
  • As I understand it you expect Gimp to guess where the path ways are. I see two ways, to a cumulative alpha-to-selection on the colored areas (could be simpler if they are all in a group) and invert the selection before painting, or use the bucket-fill with "Line-art detection" and specify the other layers for the line art.
    – xenoid
    Feb 13 at 13:47

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