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Comment by yoru-sulfur | Hacker News Reader

What will really blow your mind is that you can cat a png and a zip together and the resulting file is both a valid png that looks identical to the image and a zip that contains the same contents as the archive.

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This is how these self extracting archives work, it’s just an exe (that allows adding random data to the end) and a zip (that allows random data to be prepended) added together.

more specifically the executable part contains the logic to decompress the remainder of the file, while still allowing a decompression program to be able to open and decompress the file (ignoring the executable portion of that file).

This may be also the trick used by the fantasy console PICO-8[0] which games run by png-based cartridges[1].

[0]: https://www.lexaloffle.com/pico-8.php

[1]: https://www.lexaloffle.com/bbs/?cat=7&carts_tab=1#sub=2&mode...

Apparently, Pico8 encodes the compressed app data directly in the PNG pixel data. They use 2 least significant bits of each color channel to encode a single byte of data per color. The pixel count of pico8 cartridges is what creates the console's 32,800 byte size limit.

https://pico-8.fandom.com/wiki/P8PNGFileFormat