The Quite OK Image Format for Fast, Lossless Compression

Created on 2023-06-27T04:02:44-05:00

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A simple lossless image format meant to require very little source code to implement support for.

Performance is approximal to an unoptimized PNG (libpng's output) but is about 2-3x faster to load.

Consists of a header and a number of instructions to reconstruct the original image. An interpreter walks over each instruction and decants the raw pixel data from there.

When a pixel is decoded it is hashed and stored in a 64-bucket hash table. These are the colors of recent memory, and can be referenced by opcodes to repeat a color.

RGBA: Sets a full RGBA pixel.

RGB: Sets a raw RGB pixel, retaining the current alpha channel.

Index: Reference one of the 64 colors in recent memory.

Diff: Stores the difference between the previous pixel and this one. Does not encode the alpha channel.

Luma: Stores difference of the previous green channel and this one. Then the (smaller) difference of the green channel to red, and difference of green to blue.

Run: Invoke the previous pixel a given number of times; run length encoding.