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Index › Programming Questions & Help › OpenGL and 3D Libraries › straight alpha/no premultiply HELP!
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straight alpha/no premultiply HELP! (Read 369 times)
glenn
straight alpha/no premultiply HELP!
Sep 7th, 2008, 5:57pm  
Hi
I've been using PNGs of simple sprites textured onto quads, but they are appearing with white halos around them, as if premultiplied - I need to apply them with straight alpha.

I searched through the forums and found similar problems, but couldn't figure out the opengl code.  Any help or work arounds appreciated, thanks,
Glenn.
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glenn
Re: straight alpha/no premultiply HELP!
Reply #1 - Sep 8th, 2008, 11:23am  
okay, managed to narrow down the specific problem,

the white fringing only occurs when you see the sprite at a distance, but when viewed up close to around its orginal size, it's absolutely fine.  So something to do with the scaling in opengl is affecting the accuracy of the alpha channel at small sizes.
so now i have to sort this out somehow, any advice welcome as usual.
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glenn
Re: straight alpha/no premultiply HELP!
Reply #2 - Sep 8th, 2008, 12:43pm  
Well I think i've figured it out, I've just made sure that when I'm making the sprites in Photoshop, I'm doing it against a black background, and saving out as a TGA with alpha channel, so that it is premultiplied to black, the same as my sketch background.  Not %100 technically sure what's going with everything, but at least i've found a solution.
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