| Gimp: Alpha Channel | |
| Transparent textures and the alpha channel. Sometimes you want a picture like the one on the right. Thinkerer Melville with a feather in his cap. I made this feather with the alpha channel. Think of the alpha channel as like the red, green, and blue channels of a color image. Those channels tell each pixel what color to display. The alpha channel tells a pixel how transparent it should be. |
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| 1. You can easily get a picture of a feather. We were working on one of those in Gimp 101. |
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| 2. You want to change the background from black to transparent. |
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| 3. Add a transparent layer to the image. You'll get used to thinking about digital images as having several layers. | |
| 3. You want to make the black area transparent. The best tool for that is "Select regions by color." That lets you select all black areas. Note the tools menu: hand selecting a color. |
| 4. After you select the area.
you erase the selected region with Ctrl K. That lets the alpha
(transparent) layer show through. By convention, the alpha
layer is represented by a checkerboard in light and dark grey.
This area will be transparent in the finished image. Notice the little dotted line around the feather. That indicates the boundary of the selected area. On screen, the dots crawl a bit. Here I wanted to select the black area. If I had wanted to select the feather, I could have used Select option in the menu and found the Inverse option in the dropdown. |
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| 5. You must export the image to .tga (targa) format.
That format allows the alpha channel. When you tell Gimp to Save
as.., put the extension .tga after the name.
Right: Thinkerer compares the original .jpg image with the .tga image. Both images are the same shape. |
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| 6. Upload and use the image just as you do with a .jpg image. |
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The Thinkerer
05/01/2008 Copyright (c) D. F. Dansereau & S. H. Evans |
LOD | ||
| Famous fables | |||