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.<p>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.<p>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.<p>FLIF is a lossless format, and lossless is a very hard and <i>costly</i> constraint. Images that aren't technically lossless, but <i>look lossless</i> to the naked eye can be half the size.<p>e.g. Monkey image from <a href="https://uprootlabs.github.io/poly-flif/" rel="nofollow">https://uprootlabs.github.io/poly-flif/</a> 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).<p>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.