Re: [Gimp-user] How to make transparency gradiate?

[Richard Gitschlag <strata_ranger hotmail com>]

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Date: Fri, 3 May 2013 12:48:15 -0500
From: kpurtell imirus com
To: tobias lunte hfg-gmuend de; gimp-user-list gnome org
Subject: Re: [Gimp-user] How to make transparency gradiate?

Tobias, that's a sweet trick. Thanks!

   

Tobias Lunte <tobias lunte hfg-gmuend de> wrote:

Am 03.05.2013 18:55, schrieb Keith Purtell:

A client has supplied a logo for Web display (PNG). The logo background is white and needs to become transparent. I've done this in GIMP no problem with simple graphics. However this one features design elements that cast a pale gray shadow onto the white background. Not sure how to make the transparent background play nice with the shadow area?  

If it helps, the background color where this logo will be displayed is pale gray with a bit of blue tint.

   

Use the fuzzy select tool (magic wand) to select the background. Then go to "select -> grow" and grow by 2 or 3 px to make sure all the antialised edges are within the selection, but make sure that no white part of the logo itself is selected. Now you can simply use "colours -> Colour to alpha" (change the colour in the tools menu to white if necessary) and it will perfectly extract the white from your background.

bw,
Tobias Lunte//Tobl

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You can also achieve the same result using paint tools.

1 - Eyedrop the background color.
2 - Switch to the Paintbrush and the "color erase" blending mode.  Color erase is also a color-to-alpha transition.
3 - Start painting the background.

Note that with any color-to-alpha transition you may wind up with "residual" alpha values (very low transparency) in areas.  If you need to clean these up you can do so with the eraser tool or with a Levels/Curves adjustment (shadow end specifically) on the alpha channel.

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