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Finding transparent pixels in an image

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Finding transparent pixels in an image

Subject: Finding transparent pixels in an image
From: Ron Fleckner <email@hidden>
Date: Fri, 26 Aug 2005 23:25:29 +1000

Hi,

I want to be able to determine if a pixel in an NSBitmapImageRep is transparent so I can change it to white. I thought I could do it if the value read from the pixel was red:0 green:0 blue:0. That actually works, but unfortunately, black pixels also give the same value, so my altered image has white not only where the original had transparency, but also where the original had pure black.

How can I tell the difference between black and transparent pixels?

Thanks for any answers/pointers/clues.

Ron
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