I do not understand the Portable Network Graphics format. So the first byte in the raw data is `0x89`, then ASCII for `PNG` for when someone opens a PNG image in a text editor, then `0x0D 0x0A` followed by `0x1A` and `0x0A`, so what do these mean? Also what are the 4 byte ‘chunks?’ How can this be translate this to raw pixel data, like `[R, G, B, A, R, G, B, A, …]`? How does the format work? What do I need to know to effectively be able to edit PNG via a hex editor, or better, writing raw RGB data and ***somehow*** encoding that to PNG? Where is the ‘red pixel’ bytes in the Wikipedia example? `89 50 4E 47 0D 0A 1A 0A 00 00 00 0D 49 48 44 52 00 00 00 01 00 00 00 01 08 02 00 00 00 90 77 53 DE 00 00 00 0C 49 44 41 54 08 D7 63 F8 CF C0 00 00 03 01 01 00 18 DD 8D B0 00 00 00 00 49 45 4E 44 AE 42 60 82`
In: Technology
PNG is a compressed format. It doesn’t store the raw RGBA values, it packs the bits into less space using a special algorithm. It’s not rocket science, but if you wanted to do it for anything larger than a 4×4 it wouldn’t be realistic to do it by hand. It’s meant to be run as an algorithm.
There are several tutorials that explain it at a high level, like this one:
[https://medium.com/@duhroach/how-png-works-f1174e3cc7b7](https://medium.com/@duhroach/how-png-works-f1174e3cc7b7)
Or you can read the full specification in all its gory detail:
[https://www.w3.org/TR/2003/REC-PNG-20031110/](https://www.w3.org/TR/2003/REC-PNG-20031110/)
Can you say anything more about what you want to do? It’s possible another file format like TIFF or XPM might suit your needs better; they allow uncompressed data so you could make one with a hex editor.
The chunks are not 4 bytes. The chunks are arbitrary lengths, but the “start of chunk” has the length of the chunk. So after the 0x0A, you start reading the chunks. The first 4 bytes are the length of the data in the chunk. The next 4 bytes are a chunk “type” identifier. Next is the actual chunk data of X bytes specified at the start of the chunk. After you’ve read X bytes, you have 4 bytes as a CRC checksum to make sure the data hasn’t been corrupted.
So in your example, after the header is 4 bytes of “00 00 00 0D”, so that means your chunk is 13 bytes long. The next 4 bytes are “49 48 44 52”, which means “IHDR” header. That gives the PNG image info (height, width, depth) in that 13 bytes. There’s additional headers in there as well
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