2004-04-10 19:11:02 +02:00
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The pngquant utility converts 32-bit RGBA PNGs to 8-bit RGBA-palette PNGs (or
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fewer than 8 bits, if you want), via quantization and ordered or diffusion
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(Floyd-Steinberg) dithering. You can also use it on RGB or even palette images
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(for example, to further color-reduce them to 16 colors). It does:
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2002-04-02 18:52:20 +02:00
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- nice reduction of all PNG image types to 256-color (or smaller) palette
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- automatic optimization of tRNS chunks
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- batch conversion of multiple files (e.g., "pngquant 256 *.png")
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- Unix-style command-line filtering (e.g., "... | pngquant 16 | ...")
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It does still lack a few features:
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- no ancillary chunk preservation (except gAMA)
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- no preservation of significant-bits info after rescaling (sBIT chunk)
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- no mapfile support
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- no "native" handling of 16-bit-per-sample files or gray+alpha files
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2004-04-10 19:11:02 +02:00
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(all samples are truncated to 8 bits and all images are promoted
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2002-04-02 18:52:20 +02:00
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to RGBA before quantization)
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By the way, be sure to check "before" and "after" file sizes, preferably with
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pngcrush (http://pmt.sourceforge.net/pngcrush/); dithered palette images may
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2004-04-10 19:11:02 +02:00
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be four times smaller to begin with, but they do not compress nearly as well
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2002-04-02 18:52:20 +02:00
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as grayscale and truecolor images. Some images, such as Henri Sivonen's alpha
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button (http://www.pp.htv.fi/hsivone1/css-test/bitmapstyle.html), can be made
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smaller as full 32-bit RGBA images (4076 bytes in this case) than as either
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FS-dithered palette (4550 bytes) or ordered-dither palette (4482 bytes) images.
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WWW: http://www.libpng.org/pub/png/apps/pngquant.html
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2004-04-10 19:11:02 +02:00
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Greg Roelofs <newt@pobox.com>
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