Copy content of channels into other ones

[Ofnuts]

(10-23-2025, 04:43 PM)top1r Wrote: Hi, I would like to know how to copy the content of colors channels RGB (Red, Green and Blue) into Green, then copy the content of Alpha channel into Red ?

I tried it on PS and it was quite easy, but I can't manage to reproduce it on Gimp.

Thanks and have a good day !

For the first one, two solutions:

Solution 1:

• Colors > Components > Channel mixer, and set the target channel from 100% of one of the source channels, and 0% of the rest.
  

Solution2:

1. From the channels list,  drag the relevant R/G/B channel thumbnail to the canvas. This creates grayscale layer which is a copy of the channel
   
2. Edit > Copy to copy the layer to the clipboard
   
3. In the Channels list, deselect the other channels, leaving only the target channel enabled (but you can keep all channels visible)
   
4. In the Layers list, hide/remove the B&W layer, select your original image
   
5. Edit > Paste as > Floating data (in Gimp 2.10, you can do a plain Edit > Paste)
   
6. Layer > Anchor
   
7. Don't forget to re-enable channels before continuing.
   

For the second one

1. Alpha to selection
   
2. Add a layer filled with black
   
3. Bucket-fill selection with white
   
4. Process as with solution 2 above from Step #2.