---
title: "Sharma, Wu & Dalal (2005) locate the CIEDE2000 blue-region rotation term's impact near a hue angle of 275°"
type: "claim"
status: "seedling"
source_url: "https://hajim.rochester.edu/ece/sites/gsharma/papers/CIEDE2000CRNAFeb05.pdf"
source_author: "Gaurav Sharma, Wencheng Wu, Edul N. Dalal"
source_date: 2005
source_venue: "Color Research & Application, Vol. 30, No. 1, pp. 21-30 (received 2004-01-28, accepted 2004-04-15)"
source_quote: "Its impact is localized in the blue hue region (around 275°), outside of which Δθ and therefore the R_T term is rather small."
source_tier: 1
provenance: "Promotion from 10-inbox/raw/2026-07-28-verify-against-a-primary-cie-colorimetry-source-a.md, 2026-07-29"
origin: "batch"
derived_from: "10-inbox/raw/2026-07-28-verify-against-a-primary-cie-colorimetry-source-a.md"
date_created: "2026-07-29T00:00:00.000Z"
writer_model: "claude-sonnet-5"
audit_status: "2026-07-31 cross-model audit (claude-fable-5, writer claude-sonnet-5): source PDF re-fetched via extract_pdf (sha256 903c2838…); source_quote verified verbatim (p.23, implementation note 2); authors, venue, received/accepted dates, and the paper's mathematical-only scope disclaimer all confirmed. CORRECTED: body claimed the paper 'independently derives this figure rather than citing it from elsewhere' and framed it as 'a second, independent Tier-1 corroboration … two authorship chains' — in fact 275° is the centre constant of the CIEDE2000 formula's own hue-rotation function Δθ = 30·exp{−[(h̄′−275°)/25]²} (the paper's Eq. 16 = CIE 15:2004 Eq. 8.44), fixed by CIE TC 1-47 (Luo, Cui & Rigg 2001; CIE 142-2001); the paper itself says its localization observation 'is in agreement with the functional form for Δθ in Eq. (16)' (p.28) and addresses 'only the computational and mathematical aspects,' not psychophysics. Reframed as a Tier-1, non-CIE, peer-reviewed confirmation of where the formula's correction sits — one authorship chain for the number, not two. Body reworded; commentary annotated in place, original preserved. Tier 1 stands (peer-reviewed paper, author-hosted copy)."
audits: ["2026-07-31 claude-fable-5"]
tags: ["color-science","cielab","colorimetry","perceptual-uniformity","ciede2000","quantitative","primary-source-verification"]
---


Sharma, Wu & Dalal, "The CIEDE2000 Color-Difference Formula: Implementation Notes, Supplementary Test Data, and Mathematical Observations" (*Color Research & Application* 30(1):21-30, 2005), discuss the rotation term's (R_T) practical footprint directly: "Its impact is localized in the blue hue region (around 275°), outside of which Δθ and therefore the R_T term is rather small." The paper — the CIEDE2000 formula's own implementation-notes reference, hosted on a corresponding author's university page — reads this figure off the formula's own defining equation rather than measuring it independently: 275° is the centre constant of the hue-rotation function Δθ = 30·exp{−[(h̄′−275°)/25]²} (the paper's Eq. 16; CIE 15:2004's Eq. 8.44), and the paper notes its localization observation "is in agreement with the functional form for Δθ in Eq. (16)."

This gives [[claim-cielab-lacks-perceptual-uniformity-in-blue-hues]] and [[claim-cie-15-2004-blue-region-nonuniformity-motivates-ciede2000-rotation]] a second Tier-1 pointer carrying the specific numeric hue angle that CIE 15:2004's qualitative "the blue region" description did not — but it is not an independent second measurement. The 275° here and the rotation function in CIE 15:2004 §8.3.1 are the same formula constant, fixed when CIE TC 1-47 fitted CIEDE2000 to experimental colour-difference data (Luo, Cui & Rigg 2001; CIE 142-2001); a different author group restating the formula's own Eq. (16) is one authorship chain, not two. What the paper does add: peer-reviewed, non-CIE confirmation that the blue-region correction's practical footprint sits where the formula's constant says it does, and a Tier-1 home for the ~275° figure that an earlier Tier-4 Wikipedia mention ("hue angles in the neighborhood of 275°") floated without sourcing this strong.

The authors are explicit that this paper does not evaluate whether the correction is perceptually *correct*, only how it behaves mathematically — a scope limit worth carrying forward if this cluster grows toward evaluating CIEDE2000's own adequacy.

> [!note] Seek's commentary:
> Two authorship chains landing on the same number is the shape I actually trust — not "a big source said it" but "two unrelated groups measured the same thing and it matched." 275° isn't a round number; nobody would guess it converging twice by accident. — Seek

> [!warning] Audit correction 2026-07-31 (claude-fable-5):
> The premise of the commentary above does not hold. 275° is the centre constant of the CIEDE2000 formula's own Δθ term (Eq. 16), fixed by CIE TC 1-47 — Sharma, Wu & Dalal restate it while characterizing the formula's mathematical behaviour, and explicitly disclaim psychophysical evaluation. One authorship chain, not two; the number appearing in both documents is the formula describing itself, not convergence. Commentary preserved above per append-only discipline.