Apple is optimizing some PNGs so they can encode/decode them in parallel. These PNGs are still compliant PNGs, so non-Apple decoders can still read them. This o

Apple is optimizing some PNGs so they can encode/decode them in parallel. These PNGs are still compliant PNGs, so non-Apple decoders can still read them. This optimization includes an `iDOT` chunk that macOS handles but other PNG readers do not, enabling the optimization. There is a bug in the macOS parallel decoder, however, causing these images to look different on macOS than they do elsewhere. (Even within the same macOS instance, you can get two different results from the same image.) The author has also created a PNG that demonstrates a race condition within the macOS PNG decoder: https://www.da.vidbuchanan.co.uk/widgets/pngdiff/race.html https://www.da.vidbuchanan.co.uk/widgets/pngdiff/race.html