Is HTJ2K lossy in OpenEXR 3.5.2? Corrected: only the HTJ2K256 and HTJ2K32 compression names are lossless; the lossy LJ2K compression also uses the High-Throughput block coder, so 'HTJ2K is lossless' holds only for those two names.

Problem. The earlier finding answers 'is HTJ2K lossy?' by saying the lossy mode is a separate compression called LJ2K, which can read as if HTJ2K coding is never lossy. Conditions. OpenEXR v3.5.2 attribute list. Method. The compression-type list describes HTJ2K256_COMPRESSION and HTJ2K32_COMPRESSION as lossless JPEG 2000 coding with the High-Throughput blocker, and LJ2K_COMPRESSION as lossy JPEG 2000 coding that also uses the High-Throughput block coder and introduces distortion. Failure modes. An agent that tells a user 'HTJ2K is lossless' may route LJ2K files as lossless; choose by the EXR compression name, not by the HTJ2K label. Limitations. Statement is taken from the attribute documentation, not from encoder behaviour; no file was written or measured. Version and date. OpenEXR v3.5.2 docs fetched 2026-10-23. Curator qualifications: All cited documentation excerpts located on the live pages by curator GET; no video sources. Correction of earlier record(s) C2-B05-B-06 from a discovery re-fetch on 2026-10-23; the curator re-located the cited excerpts by GET. Limitations: Verdict (c) missing limitation, minor: the original facts (lossless names, separate LJ2K with its own lossyHTJ2KQuality attribute) are correct; only the implied 'HTJ2K is never lossy' reading is misleading. Encoder behaviour not tested. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://github.com/AcademySoftwareFoundation/openexr/blob/v3.5.2/website/StandardAttributes.rst",
      "note": "Compression list, LJ2K_COMPRESSION entry (L154-L156)"
    }
  ]
}