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Edit only alpha channel

Nov 9, 2011, 09:50
Post: #1
Edit only alpha channel
I'm trying to create an image which emulates a solar corona (it's basically just a blurry circle). It's as easy as making one brush stroke in gimp, but my problem is that i can't get all the channels to be correctly set.

Ultimately i just want to edit the alpha channel, NOT the RGB ones. They should all be pure white, or 255, 255, 255. But for some reason, no matter how much masking or color selection or clicking only the alpha channel and not the RGB ones or anything that i do, i cannot keep the RGB white while editing the alpha channel, every stroke that affects alpha seems to invariably affect the other three.

How can i edit ONLY the alpha channel?
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Nov 9, 2011, 10:26
Post: #2
RE: Edit only alpha channel
This is exactly what a "layer mask" is. Editing the layer mask is editing the alpha-channel of the layer. "Layer/Mask/Add layer mask", or in the right-click menu of the Layers list.

As an example, see the images I posted in this topic: . In the Layers dialog, you have a thumbnal of the layer, and a thumbnail of the mask. I just paint the layer to decide how much of the bottom image I want to show.

Now answering your questions on
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