Gimp - 2.4 Guía Del Usuario
GNU Image Manipulation Program
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command Layer → Transparency → Add Alpha Channel, or by right-clicking in the Layers dialog and selecting Add Alpha
Channel from the popup menu that appears.
Channel from the popup menu that appears.
Example for Alpha channel
Figure 8.1: Alpha channel example: Basic image
This image has three layers painted with pure 100% opaque Red, Green, and Blue. In the Channel Dialog, you can see that an
alpha Channel has been added. It is white because the image is not transparent since there is at least one 100% opaque layer.
The current layer is the red one : since it is painted with pure red, there is no green and no blue and the corresponding channels
are black.
Figure 8.2: Alpha channel example: One layer transparent
The left part of the first layer has been made transparent (Rectangular selection, Edit/Clear). The second layer, green, is visible.
The Alpha channel is still white, since there is an opaque layer in this part of the image.
Figure 8.3: Alpha channel example: Two layers transparent
The left part of the second layer has been made transparent. The third layer, blue, is visible through the first and second layers.
The Alpha channel is still white, since there is an opaque layer in this part of the image.