---
title: "Verify against a primary CIE / colorimetry source: (a) that CIELAB (1976) was designed for perceptual uniformity, and (b) that it is known to fall short particularly in blue hues"
type: "question"
status: "answered"
date_raised: "2026-07-09T00:00:00.000Z"
date_answered: "2026-07-29T00:00:00.000Z"
answered_log: "Answered by [[claim-cie-15-2004-recommends-cielab-for-perceptual-uniformity]], [[claim-cie-15-2004-blue-region-nonuniformity-motivates-ciede2000-rotation]], and [[claim-ciede2000-blue-hue-rotation-localized-near-275-degrees]]. CIE 15:2004 (the CIE's own technical report, Tier 1, fetched as a full PDF from the Internet Archive and read via extract_pdf) confirms both halves in the CIE's own words: Section 8.2 states CIELAB was recommended whenever perceptual uniformity beyond CIEXYZ is desired, and Section 8.3.1 names the blue region as the site of a documented ellipsoid-tilt distortion that the CIEDE2000 rotation term corrects. Sharma, Wu & Dalal (2005), an independent Tier-1 peer-reviewed paper, corroborates the blue-region mechanism with a specific hue angle (~275°). Both original claims' unverified-claim flags are lifted (see their audit_status updates)."
tags: ["color-science","cielab","colorimetry","perceptual-uniformity","primary-source-verification","unverified-claim"]
---


Raised while promoting the CIELAB capture
([[claim-cielab-designed-to-remedy-ciexyz-perceptual-nonuniformity]] and
[[claim-cielab-lacks-perceptual-uniformity-in-blue-hues]]). Both notes rest
entirely on a single Tier-4 source (Wikipedia, "CIELAB color space"). The
design-intent claim is definitional and within the sourcing floor, but the
blue-hue shortcoming is a claim about how the space *behaves* — a
technical/evaluative claim that the floor says needs a Tier-1/2 or primary
source. Two verifications:

1. **Design intent.** Confirm that CIELAB was recommended by the CIE in 1976
   with perceptual uniformity as an explicit goal. Primary home: the CIE 15
   *Colorimetry* technical report and the 1976 CIE recommendation itself
   (rather than an encyclopedia paraphrase). Confirm the "equal numerical
   change ≈ equal perceived change" framing appears in, or is faithful to, the
   primary wording.

2. **Blue-hue non-uniformity.** Confirm that CIELAB is documented in the
   peer-reviewed colorimetry literature as non-uniform, with the blue region
   specifically identified. Candidate primaries: the CIEDE2000 papers —
   Luo, Cui & Rigg (2001), "The development of the CIE 2000 colour-difference
   formula: CIEDE2000," *Color Research & Application* 26(5):340–350; and
   Sharma, Wu & Dalal (2005), "The CIEDE2000 color-difference formula:
   Implementation notes, supplementary test data, and mathematical
   observations," *Color Research & Application* 30(1):21–30 — both of which
   motivate the corrective formula by CIELAB's residual non-uniformity and
   include hue-dependent (notably blue-region) weighting terms.

Until at least (2) is closed against a primary,
[[claim-cielab-lacks-perceptual-uniformity-in-blue-hues]] stays `seedling` with
its `[unverified-claim]` flag. Low-to-medium priority — this is an orphan color
-science seed in a vault otherwise centered on ML history, so it is worth a
verification pass only if the cluster grows.


## Progress log

- Answered by [[claim-cie-15-2004-recommends-cielab-for-perceptual-uniformity]], [[claim-cie-15-2004-blue-region-nonuniformity-motivates-ciede2000-rotation]], and [[claim-ciede2000-blue-hue-rotation-localized-near-275-degrees]]. CIE 15:2004 (the CIE's own technical report, Tier 1, fetched as a full PDF from the Internet Archive and read via extract_pdf) confirms both halves in the CIE's own words: Section 8.2 states CIELAB was recommended whenever perceptual uniformity beyond CIEXYZ is desired, and Section 8.3.1 names the blue region as the site of a documented ellipsoid-tilt distortion that the CIEDE2000 rotation term corrects. Sharma, Wu & Dalal (2005), an independent Tier-1 peer-reviewed paper, corroborates the blue-region mechanism with a specific hue angle (~275°). Both original claims' unverified-claim flags are lifted (see their audit_status updates).