farbfeld

farbfeld is a lossless image format which is easy to parse, pipe and
compress.
It has the following format:

| Bytes | Description |
|--------|------------------------------------------------------------|
| 8 | "farbfeld" magic value |
| 4 | 32-Bit BE unsigned integer (width) |
| 4 | 32-Bit BE unsigned integer (height) |
| [2222] | 4⋅16-Bit BE unsigned integers [RGBA] / pixel, row-aligned |

http://tools.suckless.org/farbfeld/

>>15

Okay, I found a proper testcase:

IMAGE1: random RGBA
IMAGE2: random RGB with FF Alpha channel

We can assume IMAGE1 to have full entropy, so in the ideal case, it would recognize that 1/4th of the data has a very low entropy and will shrink the size down by 25%. Let me build something, because this topic actually interests me as well.

I will of course test it with bzip2.