HDR conversion checks on the GPU: ΔE-ITP, PU21 and CAMBI in one workflow #2145

Summary. Quality checks for SDR↔HDR conversion and tone mapping: colour difference (ΔE-ITP), PQ-aware fidelity (PU21) and banding (CAMBI), on the GPU, as one workflow with a report. No HDR VMAF model is assumed (none is published); scoring an HDR rendition with an SDR model after tone mapping is not offered as an HDR measure.

Scope.

• GPU twins of PU21 and ΔE-ITP (New metrics: ΔE-ITP, PU21, NIQE, BRISQUE, Y-FUNQUE+ #1247, GPU and SIMD twins for the new metrics #1248).
• A CLI / vmaf-tune preset that runs the three metrics on an HDR master against its SDR or HDR derivative, with thresholds the user sets.
• Docs explaining what each metric does and does not measure.

Plan (2026-10-07)

Phase RC8 (#1245, workflow check on RC5 twins). Depends on the exact PU21 and ΔE-ITP twins (#2458, #2457) and CAMBI on the GPU (exists). Acceptance (failing first): a master/derivative fixture pair with a planted tone-mapping shift fails the thresholds and names the metric; the report states what each metric does not measure. Size M.