This is a little complicated, but bear with me:
1: Desaturate the image (make greyscale while staying in RGB space)
2: Invert the image
3: Copy the image
4: Bring up layers dialogue
5: Add a layer and fill it with red
6: Add a mask to this layer
7: Paste into the mask
8: Apply the mask
That
Hi Eric,
This is the problem I solved in the Color To Alpha
filter - it should be in any recent gimp. Simply
select the background color and go. Note that your
image will need to have an alpha channel for the
plug-in to run, and it works best with solid color
backgrounds.
Regards,
Seth
