Capture: CIELAB's perceptual-uniformity design intent and blue-hue shortfall, verified against the primary CIE technical report

Bottom line up front: Both halves of the topic question are now confirmed against a genuine Tier-1 primary source — CIE 15:2004, Technical Report: Colorimetry, 3rd edition (the CIE's own official technical report, prepared by CIE Technical Committee 1-48 and approved by the CIE Board of Administration), fetched as a full PDF from the Internet Archive's copy of the U.S. federal incorporation-by-reference deposit and read in full via extract_pdf. This closes the gap left open in question-verify-cielab-perceptual-uniformity-and-blue-hue-nonuniformity, which had flagged both claim-cielab-designed-to-remedy-ciexyz-perceptual-nonuniformity and claim-cielab-lacks-perceptual-uniformity-in-blue-hues as resting on a single Tier-4 Wikipedia citation. A second Tier-1 source — Sharma, Wu & Dalal (2005), the CIEDE2000 implementation-notes paper, fetched from the University of Rochester's own hosting of the authors' paper — independently corroborates the blue-region mechanism with a specific hue-angle figure (~275°).

Claim: CIE 15:2004 confirms CIELAB was recommended by the CIE explicitly to give a perceptually more uniform alternative to CIEXYZ

Claim type: definitional/historical (what CIELAB was for). Sourcing floor: Tier 3–4 acceptable; Tier 1 achieved — this is the CIE's own technical report stating its own recommendation.

Section 8.2, "CIE 1976 uniform colour spaces," opens: "Pending the development of an improved coordinate system, the use of one of the following coordinate systems is recommended whenever a three-dimensional spacing perceptually more nearly uniform than that provided by the XYZ system is desired." Section 8.2.1.1 then defines CIELAB itself as: "Three-dimensional, approximately uniform, colour space produced by plotting in rectangular coordinates, L*, a*, b*..."

This directly upgrades claim-cielab-designed-to-remedy-ciexyz-perceptual-nonuniformity from a Tier-4 Wikipedia paraphrase to the CIE's own primary wording: the space was recommended specifically because CIEXYZ's spacing is not perceptually uniform, and CIELAB is offered as a (self-described "approximately") uniform successor. Note the CIE's own qualifier "approximately uniform," appearing in the space's very definition — the CIE's technical report does not claim CIELAB achieves perfect uniformity, only that it is intended to approximate it better than CIEXYZ.

Claim: CIE 15:2004 documents CIELAB's residual non-uniformity in the blue region by name, as the specific motivation for the CIEDE2000 rotation term

Claim type: technical-mechanism (how the space actually behaves, and how the corrective formula addresses it). Sourcing floor: Tier 1–2 required. Tier 1 achieved.

Section 8.3.1, "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 blue region specifically as the site of a distinct geometric distortion: "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 that 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.

Claim: An independent peer-reviewed CIEDE2000 paper corroborates that the blue-region correction is localized around a hue angle of ~275°

Claim type: quantitative (a specific hue-angle figure) + technical-mechanism. Sourcing floor: Tier 1–2 required. Tier 1 achieved — the authors' own paper, hosted on the corresponding author's University of Rochester page, published in Color Research & Application.

Sharma, Wu & Dalal, "The CIEDE2000 Color-Difference Formula: Implementation Notes, Supplementary Test Data, and Mathematical Observations," Color Research & Application 30(1):21–30 (2005), discusses the rotation term's impact 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 independently derives that the rotation term's discontinuity effects are "localized around a mean hue of 275°," consistent with the location the CIE 15:2004 report itself describes only qualitatively ("the blue region").

This gives the blue-hue claim a second, independent Tier-1 corroboration and supplies the specific numeric hue angle (~275°) that neither the CIE report's qualitative description nor the previously-cited Wikipedia sentence provided with sourcing this strong.

Further leads

• CIE Publication No. 142-2001, "Improvement to industrial colour-difference evaluation" (Vienna: Central Bureau of the CIE) — the actual CIEDE2000 standard document CIE 15:2004 cites (CIE, 2001a); not yet fetched directly, would be the single most-authoritative primary for the CIEDE2000 formula's own wording. (Cited in CIE 15:2004 references list.)
• Luo, M.R., Cui, G. & Rigg, B. (2001), "The development of the CIE 2000 colour-difference formula: CIEDE2000," Color Research & Application 26(5):340–350 — the original methodology paper the CIEDE2000 formula and the Sharma et al. implementation notes both build on; not fetched this run (see Entity candidates below — this is the paper whose earlier work the blue-region correction actually rests on).
• CIE Publication No. 15.2-1986 (2nd edition, predecessor to CIE 15:2004) and CIE Publication No. 116-1995, "Industrial colour difference evaluation" — cited in CIE 15:2004's reference list as intermediate steps between original 1976 CIELAB and CIEDE2000; not fetched.
• Kuehni, R.G. (2002), "CIEDE2000: milestone or final answer?" and Luo, Cui & Rigg (2002), "Further comments on CIEDE2000" — both Color Research & Application short pieces cited by Sharma et al. as addressing perceptual-uniformity/applicability questions the implementation-notes paper explicitly declined to cover ("does not in any way address psychophysical evaluation of the formula, attempt to improve its uniformity, or define its domain of applicability").
• Sharma, Wu & Dalal (2005) also documents three distinct mathematical discontinuities in the CIEDE2000 formula itself (mean-hue computation, hue-difference sign, and hue rollover at 360°) — a distinct, narrower technical thread from the blue-hue-uniformity question, worth its own capture if the CIEDE2000 cluster grows.
• CIE 15:2004 Section 8.2.3, Note 1 notes that "anomalous values of h_ab may be obtained" from the linear CIELAB formulae for transparent object colours of low luminance factor near the spectrum locus or purple line (McLaren, 1980) — a separate documented CIELAB edge case, not investigated further here.

Central question: [RESOLVED]

Both parts of the topic question are confirmed against CIE 15:2004, the CIE's own primary technical report: (a) CIELAB was explicitly recommended by the CIE for perceptual uniformity, offered as a "three-dimensional spacing perceptually more nearly uniform" than CIEXYZ; and (b) the same report documents a specific, named non-uniformity in the blue region — a chroma/hue-difference interaction tilting the color-difference ellipsoid off the constant-hue direction — which the CIE's own CIEDE2000 correction (Section 8.3.1) was built to address. A second independent Tier-1 source (Sharma, Wu & Dalal 2005) corroborates the blue-region location with the specific figure of ~275° hue angle. This closes question-verify-cielab-perceptual-uniformity-and-blue-hue-nonuniformity and should be used to lift the [unverified-claim] flag on both claim-cielab-designed-to-remedy-ciexyz-perceptual-nonuniformity and claim-cielab-lacks-perceptual-uniformity-in-blue-hues at promotion.

Entity candidates

• Luo, Cui & Rigg (2001), "The development of the CIE 2000 colour-difference formula: CIEDE2000" — person/paper — flagged first, deliberately: this is the FOUNDATIONAL paper the blue-region correction in CIE 15:2004 and the Sharma et al. implementation notes both rest on and measure themselves against; not yet read directly, and the vault's known blind spot is under-flagging exactly this kind of ancestor.
• CIE (International Commission on Illumination) — concept/organization — the standards body itself; already implicit throughout the vault's CIELAB cluster but never has its own entity page; worth one given how load-bearing "CIE recommends X" is across five existing claim-notes.
• CIE 15:2004 (Technical Report: Colorimetry, 3rd edition) — document/concept — the primary technical report itself; distinguishing it from CIE 15.2-1986 and CIE 142-2001 (the actual CIEDE2000 standard) matters because this capture cites the 2004 report's summary of CIEDE2000, not the 2001 standard directly.
• Gaurav Sharma, Wencheng Wu, Edul N. Dalal — persons — authors of the CIEDE2000 implementation-notes paper cited here; the paper's own co-authors, per the vault's noted blind-spot pattern of over-catching co-authors relative to foundational ancestors.
• CIEDE2000 — concept — already an unresolved wikilink referenced by three existing claim-notes in this cluster; this capture adds primary-source (not just secondary) grounding for its blue-region rotation term.
• CIE Technical Committee 1-48 (Division 1, "Colour and Vision") — concept/body — the specific committee (chaired by J.D. Schanda, per the report's own front matter) responsible for CIE 15:2004; relevant if the vault ever wants to track CIE technical-committee provenance as its own thread.