How is this PNG image file partially animated ?

From what I can tell, the PNG is more than what meets the eye, but only on certain platforms.

What I think is happening, (because of course it's unclear since it deals with an esoteric part of programming no one thinks of) is:

PNGs are made up of chunks, basically as you'd figure it. IHDR, header for the file, giving specifications to it's contents. PLTE, color palette. Then the important one IDAT, Image Data.

So, to what's happening. When the PNG is being decompressed and rendered on certain platforms, or in certain code families, rather than decompressing as it's supposed to, it enters a loop of image data. Thus giving the visual of animation, even though it's only animation in the technical sense.

That's my interpretation anyways, because that's a mystery to me, since by all accounts it shouldn't be possible.

Unless there's something more technical going on here that's beyond my paygrade.

/r/gamedev Thread