Re:PNG Is Back
by wongarsu on Wednesday June 25, 2025 @02:19PM
(#44380331)
PNG's basic idea is to store the difference between the current pixel and the pixel above it, left of it or to the top-left (chosen once per row), then apply standard deflate compression to that. The first step basically turns gradients into repeating patterns of small numbers, which compress great. You can get decent improvements by just switching deflate for zstd
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> You can get decent improvements by just switching deflate for zstd
Maybe I sounded too critical of zstd. To be clear: I use it for general-purpose compression where available, the only exception would be where eeking out the last % gain is important and slow decompression is acceptable and it has one of these patterns that Bzip2 does better in the first place
That it's better than deflate (afaik aka gzip and zlib, just with different header fields) is not surprising since that was iirc the defined goal of Zstandard project