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Due to the PNG signature ("magic bytes"), every PNG file starts with the sequence "89 50 4E 47 0D 0A 1A 0A". In ASCII: "[\x89]PNG\r\n[SUB]\n" Is there any inf

by dbrgn 4y ago

Due to the PNG signature ("magic bytes"), every PNG file starts with the sequence "89 50 4E 47 0D 0A 1A 0A". In ASCII: "[\x89]PNG\r\n[SUB]\n" Is there any information on the origin of these bytes? Why were they chosen like that?

blueflow 4y ago
So you'd get "PNG" printed out when you accidentally "type"ed that file in MS-DOS. The 1A was the EOF character for text data back then.
- dbrgn 4y ago
  Ah, that makes a lot of sense! So what's 0x89 at the start? It's outside the ASCII range.
  - blueflow 4y ago
    So when a 7-bit transfer masks out all highest bits, it becomes a invalid signature instead of the pixel data getting silently corrupted.
edflsafoiewq 4y ago
They are explained in detail on the Wikipedia page: https://en.wikipedia.org/wiki/Portable_Network_Graphics#File_header https://en.wikipedia.org/wiki/Portable_Network_Graphics#File...