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/

Could someone show the tradeoff? I thought bzip2 of raw image files was competitive with PNG?

The difference between bzip2 and gzip (used by png internally) is in favor of bzip2 but is not that big. However png passes an image through a predictor first (several actually, and the encoder chooses that which gives the best compressible result) which really helps on certain kinds of images (with gradients for most prominent example).

You're welcome to test it yourself, of course.