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List:       gimp-user
Subject:    Re: transparency question...
From:       Jason Murray <lather () electrografix ! com>
Date:       1999-04-16 18:56:47
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lyle@ltaylor.users.xmission.com wrote:
> 
> On 16 Apr, Stewart #7 wrote:
> >
> >    I want to take a picture, make the white background transparent
> > (I guess this is how to do it..), and then overlay the drawing on a
> > new background... err... can GIMP do this ?
> >
> > stu7
> 
> You should be able to do this fairly easily.  What I might try first
> (and this may not be the best way) would be to copy the picture in a
> new layer over the new background that you want, use "Select by color"
> and select the white that you want to be transparent, and then delete
> it.  The new background should show through where you deleted the
> white.  If you end up deleting too much, I believe you might be able to
> set a threshold on what determines what a single color is, or you can
> manually deselect the areas that should not be selected.
> 
> Like I said, it may not be the best way, but it may do what you want.
> 
> Hope that help.
> 
> Lyle

If there is a lot of white in the body of the picture, not just the
background, you may want to use fuzzy select instead of selection by
colour.

If either does not get everything, or if you do not want to
bother with it at all, you can also do this yourself with either the
erase tool, or, probably more preferably, add a layer mask to the
layer from which you want to remove the white. Set the layer mask
to full opacity and use your paint brush tool to mask out the areas
of the background which you do not want. You can use undo or erase
tool to get it back. Apply the mask, merge layers, and flatten.

To add the mask, right click on the layer name in the layer dialog
and find "add layer mask". Then you can apply the mask by going to
that same dialog.

Ctrl-click on the layer mask's preview in the Layers dialog
toggles the effect of the layer mask.

Good luck. Regards,
Jason

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