Am 19.10.2025 um 04:57 schrieb Aaron M. Ucko: Hi Adam,
I have found that when a PNG image's row width does not correspond to a whole number of bytes, the low-order bits of the last byte in each uncompressed row can fluctuate between pdflatex runs, at least when libpng can perform SIMD-assisted decompression, yielding nondeterministic output even when arranging to supply predetermined timestamps. (Moreover, this fluctuation can affect the length of the resulting compressed stream, slightly shifting the file position of subsequent content.)
Note sure, if you are subscribed to that bug in the meantime and follow the discussion. Meanwhile it seems to be sure, that we look at a design flaw in the libpng library. Norbert has forwarded the issue description + reproduction instructions to [1]. I'm subscribed to the discussion and will follow it.
Hilmar [1] https://github.com/pnggroup/libpng/discussions/864 -- sigfault
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