USA Linux Users Group
Web Site: http://www.usalug.org
Sometimes when working with an image you want to make a certain color transparent. When working with a gif file this would make a round circle look round on any color background. This is actually very simple once you do it once. Finding the information for this took me a while so I thought I would pass it on to anyone that was interested.
1. Open your image in the gimp.
2. Right click the image and go to LAYERS then ADD ALPHA CHANNEL. You won't notice anything happening, but don't be concerned. It basically adds a transparent layer at the bottom of your image so when we erase the colors.....it's shows the transparent layer. Which of course would show whatever was under it on the screen.
3. Right click on the image again and go to SELECT and then down to BY COLOR. A window that is all black opens up. Don't change any of the settings....just use the defaults for now.
4. Now click on the color in the image you want to be transparent. These colors will now show up outlined.
5. Right click on the image again and go to EDIT and then down to CLEAR. This should now erase the outlined color you just picked from the image and the "transparent gimp checkerbox" should show through. This is the Gimps way of showing you that section is now transparent.
6. Right click on the image and choose SAVE AS and make sure to save as a GIF file if you want the transparency to work on the web.
Most of this information was gleaned from this webpage: (link dead, sorry) and of course my Gimp Bible and my Essential Gimp books.
Editor's note: the Washington.edu link above has disappeared. This University of Washington link works as of May 2015.
Another fun feature that can be used while using the SELECT and BY COLOR ..... instead of hitting CLEAR you can FILL W BG COLOR or the other one FILL W FG COLOR ........... this allows you to change the colors over the entire image instantly for the particular pixel color you choose to start with. Very fast and fun once you figure this out.
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