LPE
Local Palette Encoding (LPE) is a lossy image compression format that provides a compression ratio of 6.4:1 in most cases and acceptable image quality using only simple integer math. Its method of operation is quite simple, the image is split into 8x8 blocks and a palette of 2 values is picked for each channel, the image is then dithered using those local palettes.
I have written a portable encoding/decoding library (liblpe) as well as some simple utilities (lpe-utils) which can create and convert LPE files.
Here are two images encoded in LPE:
Here's a cool thing, these images have been decoded locally by your browser, thanks to liblpe compiled to WASM and a bit of a hacky script to achieve this: lpe-web