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Chapter 21. PNG Format > PNG Compression

21.5. PNG Compression

The most notable aspect of PNG compression is that it is "lossless," meaning no information is lost in the compression process. A decompressed PNG image is identical to the original.

PNGs use a "deflate" compression scheme (the same engine used to "zip" files with gzip, WinZip, etc.). Like GIFs, PNG's compression works on rows of pixels, taking advantage of repetition in bytes of information. By use of internal filters, it can take advantage of some vertical patterns as well. PNG's compression engine typically compresses images 5-25% better than GIF (and up to 39% better under optimal conditions). Unfortunately, with the currently available tools, it is difficult to achieve such file savings. See Section 21.7 later in this chapter.


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