---
title: "CIE 15:2004 names the blue region as the site of CIELAB's residual non-uniformity, and states the CIEDE2000 rotation term exists to correct it"
type: "claim"
status: "seedling"
source_url: "https://ia802802.us.archive.org/23/items/gov.law.cie.15.2004/cie.15.2004.pdf"
source_author: "CIE Technical Committee 1-48, International Commission on Illumination"
source_date: 2004
source_venue: "CIE 15:2004, Technical Report: Colorimetry, 3rd edition, Section 8.3.1, p.20 (Equations 8.43-8.45)"
source_quote: "Visual colour-difference perception data show an interaction between chroma difference and hue difference in the blue region that is observed as a tilt of the major axis of a colour-difference ellipsoid from the direction of constant hue angle. To account for this effect, a rotation function is applied to weighted hue and chroma differences."
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): body wording corrected — was 'An independent peer-reviewed source corroborates the same mechanism with a specific hue-angle figure'; now states the Sharma, Wu & Dalal 2005 paper supplies the ~275° figure (the CIEDE2000 formula's own Δθ centre constant) but is mathematical-only and does not second the perceptual data. This note's own source claim (CIE 15:2004 §8.3.1, verified verbatim in the 2026-07-31 pass-1 audit) is unaffected."
audits: ["2026-07-31 claude-fable-5"]
tags: ["color-science","cielab","colorimetry","perceptual-uniformity","ciede2000","cie","primary-source-verification"]
---


Section 8.3.1 of CIE 15:2004, "CIEDE2000 total colour difference formula," states plainly that the correction exists because CIELAB is non-uniform: "The CIEDE2000 total colour difference formula corrects for the non-uniformity of the CIELAB colour space for small colour differences under reference conditions." It then identifies the mechanism and its location: "Visual colour-difference perception data show an interaction between chroma difference and hue difference in the blue region that is observed as a tilt of the major axis of a colour-difference ellipsoid from the direction of constant hue angle. To account for this effect, a rotation function is applied to weighted hue and chroma differences." The report then gives the rotation term itself (R_T, built from a hue-rotation function Δθ) as Equations 8.43-8.45.

This is the primary-source confirmation [[claim-cielab-lacks-perceptual-uniformity-in-blue-hues]] needed: not a Wikipedia paraphrase but the CIE's own technical report naming the blue region as the location of a specific, documented perceptual distortion — a hue/chroma-difference interaction tilting the color-difference ellipsoid off the constant-hue direction — addressed by a dedicated correction term in the CIE's own recommended formula. An independent peer-reviewed implementation-notes paper supplies the specific hue-angle figure for the correction's centre (~275°, the constant of the formula's own Δθ function), though it is mathematical-only and does not second the perceptual data: see [[claim-ciede2000-blue-hue-rotation-localized-near-275-degrees]]. [[entity-ciede2000]] collects the formula's other appearances across the vault.

> [!note] Seek's commentary:
> "A tilt of the major axis of a colour-difference ellipsoid from the direction of constant hue angle" is a sentence doing an enormous amount of quiet work — it's the CIE admitting, in its own geometry, that blue doesn't sit where the coordinate system says it should. The 1976 space drew a grid; the ellipsoid is where the eye actually lives. — Seek