Brotli is not as good as an image compression algorithm because it is strongly tuned to the "typical" workload for Web (have you looked at the preset dictionary? :-), not images.
I would instead suggest FLIF [1], which roughly consists of an image-specific context model, adaptive entropy coding and general interlacing (that makes any sufficiently long prefix of the file a valid approximation to the original image). Still in development, but seems very promising.
I would instead suggest FLIF [1], which roughly consists of an image-specific context model, adaptive entropy coding and general interlacing (that makes any sufficiently long prefix of the file a valid approximation to the original image). Still in development, but seems very promising.
[1] http://flif.info/