FLIF – Free Lossless Image Format
Everyone loves the "responsive loading" feature, but that's not even the novel thing about the format (JPEG 2000 did it even better — 16 years ago)! The novel feature of this format is better entropy coding.FLIF decoder adds interpolation to make incomplete scans look nicer than in PNG, but that's a feature of the decoder, not the file format, so there's nothing stopping existing PNG decoders from copying that feature.Note that it's generally not desirable to have FLIF used on the Web. A decent-quality JPEG will load at full resolution quicker than it takes FLIF to show a half-resolution preview.FLIF is a lossless format, and lossless is a very hard and costly constraint. Images that aren't technically lossless, but look lossless to the naked eye can be half the size.e.g. Monkey image from https://uprootlabs.github.io/poly-flif/ is 700KB in FLIF, but 300KB in high-quality JPEG at q=90 without chroma subsampling (i.e. settings good even for text/line-art), and this photo looks fine even at 140KB JPEG (80% smaller than FLIF).So you want FLIF for archival, editing and interchange of image originals, but even the best lossless format is a waste of bytes when used for distribution to end users.