I seem to be missing a basic concept. If I open an image with alpha
channel, I can't find any way to edit the alpha channel. I end up
using other software to save the alpha as a grayscale and editing that.
That requires converting my 24 bit image to grayscale too so I can
load the alpha as a layer for editing. What I want is to keep the
24 bit rgb image and edit the alpha as an 8 bit layer.
FWIW, I generally use 32 bit targa format for editing image with
alpha., because I don't have any filter for directX compressed
formats (DXT1, DXT3).
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