Gimp — combine alpha from one layer, with rgb image of another

gimp

I am using Gimp, I have an RGB image on one layer (alpha unused), I then created another layer it now has the alpha I want (RGB) unused.

I can not work out how to get the alpha to the other layer. How can I get the alpha from one layer into another layer?

Best Answer

For each layer...

  1. Select the layer.
  2. Go to Layer > Mask > Add Layer Mask...
  3. In the menu that pops up, choose Transfer layer's alpha channel.

Now you should see that both layers have two "preview" boxes in the Layers panel.

Now...

  1. Select (left click) the right box on the layer that only uses the alpha channel.
  2. Select all (Ctrl + A)
  3. Copy (Ctrl + C)
  4. Select the right box on the layer that doesn't use the alpha channel.
  5. Paste (Ctrl + V)
  6. Go to Colors > Invert to inver the colors on the new alpha channel.

This should provide you with the results you want. I would also delete the layer (or at least make it invisible) that doesn't use RGB at all after this, but I suppose it's not necessary since it's transparent.

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