You're right about the interpolation method (bilinear vs nearest-neighbor), it's indeed not a fair comparison in that respect. However, I do think that most PNG

You're right about the interpolation method (bilinear vs nearest-neighbor), it's indeed not a fair comparison in that respect. However, I do think that most PNG viewers use nearest-neighbor (at least that's what my viewer did when I gave it a partial PNG file). But it's not just the interpolation that makes a difference: PNG interlaces full RGB pixels (all 3 channels at the same time), while FLIF gives priority to luma so you get a chroma subsampling effect on partial files. Also GIF only has vertical interlacing and PNG only does 7 passes of 2D interlacing, which means that for huge images, the first pass can still take a while. Another point: I am proposing to use progressive decoding to avoid having to download the full lossless image (so a browser supporting FLIF would need some mechanism to stop downloading the image file when "enough" detail is available). Repeated re-rendering is not necessary. E.g. on a mobile phone you would rather just download some prefix of the file (the size of the prefix could depend on the available bandwidth) and render it once, at least until the user zooms in on the image, or saves or prints it or something -- then the download should be resumed in order to load more/all detail.