What do ITU-R BT.2100, BT.2408 and BT.2446 specify for PQ/HLG, HDR reference white and HDR-to-SDR conversion, and how do BT.2446 methods A, B and C differ?

ITU-R BT.2100-3 (Feb 2025) defines PQ as an absolute EOTF up to 10,000 cd/m2 and HLG with a display-dependent system gamma of 1.2 at a 1,000 cd/m2 nominal peak, and sets HDR reference white (100% reflectance card) at 203 cd/m2; Report BT.2408-8 (2024) marks that level as 75% HLG / 58% PQ on a waveform and discusses conversion at a 1,000 cd/m2 reference condition; Report BT.2446-1 (2021) describes static HDR-to-SDR methods (Method B using a 291 cd/m2 nominal peak) and notes that adaptive or dynamic methods exist. Curator qualifications: BT.2446-1 method-by-method table (output peaks 100/100/120, colour spaces YCbCr/ICtCp/Yxy, inverse properties; E5-E6) not re-read row by row. BT.2408 statement that PQ<->HLG conversion should use a common 1,000 cd/m2 peak seen only in the contents listing; section text not re-read. ITU texts are free to download but all rights reserved (producer); quote minimally. Text reading only; no conversion computed. Limitations: Recommendation vs Reports: BT.2408 and BT.2446 are Reports (informative). Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.2100-3-202502-I!!PDF-E.pdf",
      "note": "R-REC-BT.2100-3-202502 (pdftotext lines 333, 475-527, 857); R-REP-BT.2408-8-2024 (lines 229-242, 587, 604, 668); R-REP-BT.2446-1-2021 (lines 174-177, 416, 1106)"
    },
    {
      "url": "https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2408-8-2024-PDF-E.pdf",
      "note": "R-REC-BT.2100-3-202502 (pdftotext lines 333, 475-527, 857); R-REP-BT.2408-8-2024 (lines 229-242, 587, 604, 668); R-REP-BT.2446-1-2021 (lines 174-177, 416, 1106)"
    },
    {
      "url": "https://www.itu.int/dms_pub/itu-r/opb/rep/R-REP-BT.2446-1-2021-PDF-E.pdf",
      "note": "R-REC-BT.2100-3-202502 (pdftotext lines 333, 475-527, 857); R-REP-BT.2408-8-2024 (lines 229-242, 587, 604, 668); R-REP-BT.2446-1-2021 (lines 174-177, 416, 1106)"
    }
  ]
}