Re: [Gimp-user] Problems creating layer masks

[Richard <strata_ranger hotmail com>]

> Date: Tue, 1 Mar 2016 10:08:50 +0000
> From: dereksalt1159 gmail com
> To: gimp-user-list gnome 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.

-- Stratadrake
strata_ranger hotmail com
--------------------
Numbers may not lie, but neither do they tell the whole truth.