luma_limited_u8 — IMGMETRICS `iqa` op

• Data kinds: any → any

• Call: import fullseye as fs; fs.ledger.luma_limited_u8(rgb) -> 'np.ndarray' (to call the implementation directly, import iqatid; iqatid.luma_limited_u8(rgb) -> 'np.ndarray'; from the registry, opsimgmetrics.get("luma_limited_u8"))

Usage

> This operator's description has not been translated yet. The original text follows as it is.

RGB (H, W, 3) uint8 → Y′ = round(16 + (65.481 R + 128.553 G + 24.966 B) / 255) の uint8 (H, W)。

ITU-R BT.601 の limited range(studio swing)の輝度。黒 (0,0,0) → 16、白 (255,255,255) → 235。full range の

Y = 0.299 R + 0.587 G + 0.114 B(黒 0・白 255)とは別の量で、PSNR(peak 255 のまま)は 20 log10(255/219) = 1.321 dB

低く出る。TID2013 の作者値 psnr.txt(「luminance component」)と ssim.txt は この規約で 4 桁一致した(10 組、2026-10-04。

full range だと PSNR −1.3 dB・SSIM 最大 0.05 ずれ、丸めないと PSNR が +0.002〜0.07 dB ずれる)。ページにも readme にも

どの輝度かは書かれておらず、実測で特定した規約。丸めは `np.round`(半偶数)。輝度が ちょうど k.5 に落ちる画素は丸めの向きが

算術の順序で変わり、作者と 1 LSB 食い違うことがある(TID2013 では参照 I12 の 28 画素。彩度変化 5 組で作者 = 完全一致、ここでは 86.6 dB。

半切り上げでも float32 でも揃わない)。PSNR が 60 dB を超える領域だけの話で、それ以外の 2,995 組は 0.0005 dB 以内。

Raises `ValueError`: 形が (H, W, 3) でない、dtype が uint8 でない。

Detailed usage guide

• image_difference_metrics family guide

References (sample data, literature)

• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).

• Operator provenance and references — the sources of the research/methods this op family came from.

• The canonical algorithm (author, year) and its uses are named in the family usage guide above.

Runnable examples (verified samples that actually call this op)

• poc_iqa_tid2013 — py -3.11 examples/poc_iqa_tid2013.py

Ops the type connects to (they accept `any` as input)

rgb_to_lab · lab_to_rgb · rgb_to_xyz · xyz_to_lab · delta_e_2000 · delta_e_76 · delta_e_map · mse

Same category (`iqa`)

rank_data · rank_spearman · rank_kendall_b · tid2013_published · tid2013_root · tid2013_index · tid2013_metric_values · tid2013_evaluate

*Provenance: iqatid.py — IMGMETRICS operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

luma_limited_u8 — IMGMETRICS iqa op