Channel (GIMP)

In GIMP, as in many image editing programs, a channel represents alpha transparency.

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

See also

• Alpha transparency
• GIMP