> Date: Tue, 1 Mar 2016 10:08:50 +0000
> From: dereksalt1...@gmail.com
> To: firstname.lastname@example.org
> Subject: [Gimp-user] Problems creating layer masks
> I hope that you can help me. For a long time I have been trying to make
> layer masks of fine details, such as leafless trees full of twigs, using
> Gimp 2.8. I can make what looks like a perfect black and white image for
> the mask but when I apply it to the photo all the twigs come out with a
> white halo around them. I have tried selecting the image, growing,
> shrinking, and feathering it, the copying and pasting but nothing works.
> Working on solid areas such as a building gives no problems.
> Any suggestions please.
> Derek Salt
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Not quite sure what you're trying to do based on this description but let's see
... is it safe to assume that the object you're trying to mask was originally
shot against some kind of white backdrop? Then the white "halos" you see are
pixels that are originally some mix (think alpha blending) of foreground and
background, and GIMP has no way of automatically 'knowing' what the original,
non-blended color of that pixel was supposed to be.
So you'll probably need to do something along the lines of a color-to-alpha
transition. However, instead of going to the menus to look for this function,
switch to your Paintbrush tool and select the "color erase" painting mode from
the toolbox -- color erase is effectively a color-to-alpha function but as a
painting mode. Very useful! Make sure you've added an alpha channel to the
layer. Then eyedrop your background color (the one to be erased) and start
using the brush to "paint" around the edges of your object. If you make any
mistakes, you can undo this by setting the painting mode to "behind" (Behind
and Color Erase are opposite modes) and painting back over the area.
Numbers may not lie, but neither do they tell the whole truth.
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