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Independent alpha in gimp

Mar 9, 2012, 19:46
Post: #1
Independent alpha in gimp

I'm making textures for a game, for a material that needs a 24bit RGB for the normal texture, and alpha channel that controls the shinyness, specularity of the material. So in short, the alpha has nothing to do with transparency, but gimp handles it as transparency. However this isn't a real problem since i disable the layer mask, so it won't make the textures transparent.

The problem is: i have multiple layers a plain texture, which is multiplied by a baked ambient occlusion texture. But if i flatten the map to export as a png, then gimp applies the layer mask (alpha) to the layer where it is linked, then this layer gets multiplied with the baked layer, then the result is a 24bit rgb png, without alpha channel.
So is there a way to make alpha independent from any layers, as it controls totally different thing? Or i need to copy layermask delete it, flatten image and make a new layer mask on flattened image and paste the previously copied mask every time when i export the texture?
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Mar 9, 2012, 21:25
Post: #2
RE: Independent alpha in gimp
I fear it could be the latter.

It is also possible that some tool in ImageMagick allows you to copy the alpha channel from another image once you have saved the PNG (possibly by splitting the image into 4 independent images, one for each channel, overwriting the alpha channel one and combining them back). This is pure speculation from my part, but I've never been disappointed by IM so far, there is indeed a lot of power and even some magic in that utility. It may be made even more comfortable by having a small script to save the mask independently just before saving the main image

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