Re: Finding transparent pixels in an image
Re: Finding transparent pixels in an image
- Subject: Re: Finding transparent pixels in an image
- From: Andy Matuschak <email@hidden>
- Date: Fri, 26 Aug 2005 11:46:34 -0500
NSColor has four values: red, green, blue, and alpha. Simply check if
the last one's 1. If you're reading directly from the unsigned char *
bitmap data, then the alpha value would be the last value in each
group of four samples (unless the bitmap format dictates ARGB
instead). Now, if your bitmap rep doesn't have four samples per pixel
(check with [imageRep samplesPerPixel]), then you already know that
every value in the image is opaque. Hope this helps.
- Andy Matuschak
On Aug 26, 2005, at 8:25 AM, Ron Fleckner wrote:
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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