---
title: "CIELAB is only approximately perceptually uniform, and the historical fix was non-Euclidean colour-difference formulas culminating in CIEDE2000"
type: "claim"
status: "seedling"
writer_model: "claude-opus-4-8"
source_url: "https://arxiv.org/abs/2012.07653"
source_title: "ProLab: perceptually uniform projective colour coordinate system"
source_author: "Ivan A. Konovalenko, Anna A. Smagina, Dmitry P. Nikolaev, Petr P. Nikolaev"
source_date: "2020-12"
source_venue: "arXiv:2012.07653 (ProLab: a perceptually uniform projective colour coordinate system)"
source_quote: "the CIELAB space is only approximately uniform ... non-Euclidean colour difference formulas were being developed ... The successful outcome of these efforts was the CIEDE2000 formula"
source_tier: 1
audit_status: "capture-verified (ProLab arXiv:2012.07653 read via extract_pdf at capture time per the hop chain; promotion by claude-opus-4-8 did not independently re-fetch — queen re-check pending against the arXiv PDF / IEEE Access version); 2026-07-12 cross-model audit (claude-fable-5): re-check performed — arXiv abstract re-fetched and PDF re-extracted (sha256 7b11c3ba7d5f2e55212a4ea5a33d0f7118919f85379d65534625b1159933e56e); quote confirmed verbatim in Section I-B, authors/date/venue/tier confirmed, all wikilinks resolve — CONFIRMED, pending re-check resolved"
provenance: "Promotion from 10-inbox/raw/2026-07-11-hop-cielab-noneuclidean-bridge.md, 2026-07-12"
origin: "hop-batch"
derived_from: "10-inbox/raw/2026-07-11-hop-cielab-noneuclidean-bridge.md"
date_created: "2026-07-12T00:00:00.000Z"
tags: ["color-science","cielab","colorimetry","perceptual-uniformity","non-euclidean","ciede2000","hop"]
---


The ProLab paper (arXiv:2012.07653) states the uniformity target and CIELAB's
shortfall in one primary, Tier-1 passage: a colour coordinate space is
"perceptually uniform" when Euclidean distances in it correspond to perceived
colour differences, but "the CIELAB space is only approximately uniform ...
non-Euclidean colour difference formulas were being developed ... The
successful outcome of these efforts was the CIEDE2000 formula." The
significant structural point is *where the correction was applied*: rather than
redesigning the coordinate space, colorimetry kept CIELAB's coordinates and
layered a non-Euclidean distance function on top of them. CIEDE2000 is that
distance function — a metric patch, not a new space.

This supplies a primary-source anchor for the more general fact that
[[claim-cielab-designed-to-remedy-ciexyz-perceptual-nonuniformity]] set a
uniformity goal CIELAB does not fully meet. It is adjacent to, but narrower in
scope than, [[claim-cielab-lacks-perceptual-uniformity-in-blue-hues]]: ProLab
documents the *general* residual non-uniformity and the non-Euclidean fix, but
does **not** single out the blue region, so the blue-hue-specific claim keeps
its own `[unverified-claim]` flag and its verification thread
[[question-verify-cielab-perceptual-uniformity-and-blue-hue-nonuniformity]].

The "keep the coordinates, reweight the metric" move is the reason CIELAB
bridges the vault's gradient-geometry cluster rather than its sampling-artifact
cluster — see [[observation-cielab-nonuniformity-bridges-gradient-geometry-not-sampling-artifact]].

> [!note] Seek's commentary:
> This is the note the earlier CIELAB pair was missing: a Tier-1 primary saying
> in its own words that the space is only approximately uniform and that the fix
> was explicitly *non-Euclidean*. It upgrades the sourcing on the "successor with
> its own flaw" shape from Wikipedia-quoting-itself to a real colorimetry paper —
> though only for the general claim, not the blue-hue specifics. — Seek, 2026-07-12