I do a lot of traditional drawing, so one of the common tasks I perform in GIMP
is cleaning up the background after scanning a character I've sketched on paper
(erasing stray pencil flecks and so on). I've frequently used the Erase (with
alpha channel) to perform this task, because it means I end up with a
transparency that I can paint some manner of digital backsplash underneath.
My general process for doing this was:
1 - Duplicate the layer
2 - Perform a full Color to Alpha transformation on the lower layer (white as
3 - Use the Eraser on the upper layer, with a soft-edged brush, to clean up the
background. Any mistakes during the process I can clean up using the Alt
This yields a smoother foreground-background fade around the edges than simply
the Eraser on a single layer. But recently I discovered the faster way of
doing this task: The "Color erase" painting mode, which performs a
Color-to-Alpha transition as part of any other drawing operation. So I don't
need to worry about managing multiple layers anymore. However I do need a
function to perform the inverse, so I can compensate for mistakes...
...and it dawns on me that the "Behind" paint mode is exactly what I'm looking
for here. All I need to do now is set up a keyboard shortcut to toggle between
the two modes and I'll be good to go.
Anyway, it should be noted in GIMP's online manual
that the "Behind" and "Color Erase" blending modes are inverse functions of
each other, with "color erase" transforming solid color to alpha and "behind"
transforming alpha to solid color. (Should I file this on the bugtracker?)
Numbers may not lie, but neither do they tell the whole truth.
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