Channel (GIMP)
From Wiki @ Karl Jones dot com
In GIMP, as in many image editing programs, a channel represents alpha transparency.
Contents
Transparency
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Alpha transparency
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Masks
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Exporting channels
Method 1
- Make your green layer as a separate image.
- Add a white layer mask to this image
- Make sure that this is 'active' -- click in the layer mask, active has a white border not active has a black border, not obvious when it is all white.
- Using the "grass image", copy to the clipboard.
- Move back to the green image and paste into the image (ie layer mask).
- Initially it is as a floating layer, anchor this to fix it into the layer mask.
- When ready, export as targa file
- Go to export, put in the filename including the .tga suffix.
Method 2
- Make the B&W mask visible
- Open the Channels dialog, and duplicate one the RGB channels (any will do)
- Make the B&W mask invisible
- Create a new Layer, fill with required color or gradient
- "Layer/Mask/Add layer mask" and initialize to the duplicated channel
- "Layer/Mask/Apply layer mask"
Source: http://gimpforums.com/thread-alpha-channels-and-exporting-transparency
