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Fix progressive AC refinement JPEG decoding#565

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fix-progressive-ac-refinement-jpeg
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Fix progressive AC refinement JPEG decoding#565
treeform wants to merge 1 commit intomasterfrom
fix-progressive-ac-refinement-jpeg

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@treeform treeform commented Mar 28, 2026

  • fix progressive JPEG AC refinement decoding when an EOB run is active by refining through spectralEnd instead of stopping one coefficient early
  • correct the SOS progressive validation check to reject spectralStart > spectralEnd
  • add tests/fileformats/jpeg/masters/chair_normal.jpg as a regression case in the JPEG suite

Pixie was skipping the last coefficient during progressive AC refinement when eobRun was active. That left one refinement bit unread, desynchronized the entropy bitstream, and caused a later Huffman decode to fail even though the JPEG itself was valid.

Progressive AC refinement scans were skipping the last coefficient during EOB-run handling, which left the bitstream misaligned and caused later Huffman decode failures on valid JPEGs. Add the chair_normal regression image to keep this case covered.

Made-with: Cursor
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