FLIF, a new “Free Lossless Image Format”:
FLIF is a novel lossless image format which outperforms PNG, lossless WebP, lossless BPG and lossless JPEG2000 in terms of compression ratio.
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Even if the best image format was picked out of PNG, JPEG 2000, WebP or BPG for a given image, depending on the type of image (photograph, line art, etc), then FLIF still beats that by an average of 10% in our comparisons.
Source code is available at https://github.com/FLIF-hub/FLIF.
The million dollar question is if browsers will ever support this format.