I tried compressing with bzip2 and xz, (both set to maximum compression with -9). I know xz to be slower, but I have measured it to have the least bloat when fed random data to compress.
With "clean" low-noise images, it would seem that bzip2 is out-performing xz markedly, hence your recommendation. Also, both ff+xz and ff+bzip2 out-perform PNG. However, on noisier images, such as those from a camera, it would seem that although PNG outperforms farbfeld wrapped with either compression algorithm, xz is now out-performing bzip2, although less markedly than when the reverse is true on cleaner images. I intend to do some more widespread testing on a large sample of different images which I can share the results on. But I can confirm that as it stands bzip2 looks likely to be the best candidate. Cheers
