Determine if Alpha Channel is Used in an Image

Posted by Otaku on Stack Overflow See other posts from Stack Overflow or by Otaku
Published on 2010-06-17T19:16:47Z Indexed on 2010/06/17 19:33 UTC
Read the original article Hit count: 289

Filed under:

c#

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.NET

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gdi+

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transparency

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system.drawing.imaging

As I'm bringing in images into my program, I want to determine if:

they have an alpha-channel
if that alpha-channel is used

#1 is simple enough with using Image.IsAlphaPixelFormat. For #2 though, other than looping through every single pixel, is there a simple way I can determine if at least one of the pixels has an alpha channel that is used (i.e. set to some other value than 255)? All I need back is a boolean and then I'll make determination as to whether to save it out to 32-bit or 24-bit.

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