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The post makes sense and is good. > Lossless ones are basically just ZIP, Let's go down one more level of abstraction, it's crucial for understanding why it's

The post makes sense and is good. > Lossless ones are basically just ZIP, Let's go down one more level of abstraction, it's crucial for understanding why it's byte-level patterns: Deflate, not ZIP. See http://www.libpng.org/pub/png/spec/1.2/PNG-Compression.html http://www.libpng.org/pub/png/spec/1.2/PNG-Compression.html. > image compression algorithms are generally terrible at finding patterns. The core of deflate is pattern recognition, inter alia: - Duplicate series of bytes (a pattern of repeated bytes in series). - Huffman coding (a pattern of high frequency repeated bytes that could be replaced by another repeated byte string) See https://en.wikipedia.org/wiki/Deflate https://en.wikipedia.org/wiki/Deflate > There are certain patterns that PNG can efficiently detect, like repeating pixels from the line above PNG uses deflate. General byte-level patterns. It does not do bespoke image-specific stuff. > This is certainly entirely explained by the chosen (in this case, default) compression level of the ZIP file and PNG files. Probably.

jncraton 3y ago
> PNG uses deflate. General byte-level patterns. It does not do bespoke image-specific stuff. That's not quite the whole story. PNG does include simple filters to represent a line as a difference from the line above, and that may be what the original post is referring to. [1] [1] https://en.wikipedia.org/wiki/PNG#Filtering https://en.wikipedia.org/wiki/PNG#Filtering
crazygringo 3y ago
> PNG uses deflate. General byte-level patterns. It does not do bespoke image-specific stuff. That's exactly what I meant, sorry if I wasn't clear. It's not "finding patterns in images". It's finding byte-level patterns, not visual (image) patterns -- which are inherently dimensional in a way that a stream of bytes isn't. Which is why the post doesn't make any sense. Its entire premise is that there's something about lossless image compression which is different from zip/deflate and similar byte stream compression algorithms.

jncraton 3y ago

> PNG uses deflate. General byte-level patterns. It does not do bespoke image-specific stuff. That's not quite the whole story. PNG does include simple filters to represent a line as a difference from the line above, and that may be what the original post is referring to. [1] [1] https://en.wikipedia.org/wiki/PNG#Filtering https://en.wikipedia.org/wiki/PNG#Filtering

crazygringo 3y ago

> PNG uses deflate. General byte-level patterns. It does not do bespoke image-specific stuff. That's exactly what I meant, sorry if I wasn't clear. It's not "finding patterns in images". It's finding byte-level patterns, not visual (image) patterns -- which are inherently dimensional in a way that a stream of bytes isn't. Which is why the post doesn't make any sense. Its entire premise is that there's something about lossless image compression which is different from zip/deflate and similar byte stream compression algorithms.