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I am searching for a software that will allow me to reduce the number of colors for PNG-24 transparent (as in photoshop) files. Photoshop doesn't allow me any control over the amount of colors the PNG is saved, having this kind of software/plugin would be great.

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... i'm afraid you might be out of luck on this one. If you're thinking in terms of reducing the size of the file by limiting colors that won't happen. I think there are some ways / utilities to optimize png sizes, but color reduction 'gif-style' isn't one of them. –  vector Aug 7 '11 at 21:34

2 Answers 2

You could use ImageMagick's convert application with the -color flag.

http://www.imagemagick.org/script/command-line-options.php?ImageMagick=fv5ffdto8nt4revt54g3ba7ne7#colors

i.e: convert something.png -color 256

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Thanks, but is their anything like a visual GUI instead of command line? –  Idan Shechter Aug 7 '11 at 21:45
    
You could use the gimp gimp.org/windows which is a bit more geeky than Photoshop. But many would argue that their UI is pretty ugly. –  John Mitchell Aug 15 '11 at 0:29

There are two tools:

  • pngquant which creates 256-color PNGs with alpha channel. That greatly reduces file sizes (60-70%). In latest versions it may have better quality and smaller file size than Photoshop's Save For Web (even for images without alpha).

  • mediancut posterizer reduces number of unique colors in 24/32-bit PNG files. This can reduce file sizes by 20-30%, and again is smarter than posterizing colors in Photoshop as it also posterizes alpha channel and is smarter about selecting posterization levels.

Both of those programs have a GUI: ImageAlpha.

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