---
title: "Ahrens et al. 2024's own abstract does not mention Gaussian curvature or the CIELAB ab-plane, and its full text was unreachable this session behind a nominally open-access license"
type: "claim"
status: "seedling"
source_url: "https://api.semanticscholar.org/graph/v1/paper/DOI:10.1002/col.22897"
source_title: "A machine learning approach to color space Euclidisation"
source_author: "Lia Ahrens, Julian Ahrens, Hans D. Schotten (abstract text reproduced by Semantic Scholar from the publisher record)"
source_date: "2023-09-15 (record accessed 2026-07-28)"
source_quote: "the Euclidisation task consists in finding an injective transformation from the original color space into a real vector space and the corresponding inverse transformation, such that the Euclidean distances in the embedded color space align with the reference color distances. [...] Comparative evaluation is carried out on well‐established color distance laws, including the CIELAB‐based DE2000 color difference formula."
source_tier: 3
audit_status: "capture-verified (Semantic Scholar API `abstract` field read directly at capture time 2026-07-28, not a search-summary rendering; promotion by claude-sonnet-5 did not independently re-fetch — a Tier 3 aggregator ceiling applies regardless, so no independent re-check is required to clear this note's own claim); 2026-07-31 cross-model audit (claude-fable-5): Semantic Scholar record re-fetched — abstract matches the source_quote verbatim and contains no mention of Gaussian curvature, isometric embedding, or the ab-plane, confirming the note's negative-evidence claim; corrected the title spelling from 'Euclidization' to 'Euclidisation' to match the publisher record as reproduced by Semantic Scholar (the abstract's own British spellings — 'Euclidisation', 'optimisation' — corroborate)"
provenance: "Promotion from 10-inbox/raw/2026-07-28-verify-against-a-primary-source-that-the-cielab.md, 2026-07-29"
origin: "batch"
derived_from: "10-inbox/raw/2026-07-28-verify-against-a-primary-source-that-the-cielab.md"
date_created: "2026-07-29T00:00:00.000Z"
writer_model: "claude-sonnet-5"
tags: ["cielab","gaussian-curvature","ahrens-2024","color-space","primary-source-gap","euclidization"]
---


Lia Ahrens, Julian Ahrens, and Hans D. Schotten (DFKI, Kaiserslautern) published "A machine learning approach to color space Euclidisation" in *Color Research & Application*, DOI 10.1002/col.22897, first published online 2023-09-15. The paper is real and locatable, but its body text could not be read this session across four independent routes: Wiley's full-text page (HTTP 402), Wiley's bare DOI-resolved page (HTTP 402), and both the `pdfdirect` and `epdf` PDF endpoints (HTTP 403 via `extract_pdf`) — this despite Unpaywall and Semantic Scholar both confirming the article carries a CC-BY open-access license. ResearchGate's mirror listing also returned HTTP 403, no Wayback Machine snapshot exists, and no preprint could be located.

The one piece of the paper's own text that *was* reachable — its abstract, via the Semantic Scholar API's structured `abstract` field — describes a neural-network methodology for approximating a Euclidean embedding of a reference color-difference law (evaluated on CIEDE2000 among others), framed as an improvement "over previous contributions." It makes no mention of Gaussian curvature, isometric-embedding obstruction, or the ab-plane specifically. This is negative evidence, not a refutation: the claim could still appear in the paper's body (most plausibly as motivating background, the place such a claim usually lives), but nothing in the one part of the text this session could reach supports it.

See [[question-verify-cielab-ab-plane-gaussian-curvature]] for the open verification this leaves outstanding, and [[claim-cielab-only-approximately-uniform-fixed-by-noneuclidean-formulas]] for the broader vault claim this would, if confirmed, supply a geometric mechanism for.

> [!note] Seek's commentary:
> The tell here isn't that the paper was unreachable — paywalls are routine — it's that this one is CC-BY and *still* unreachable, on the publisher's own venue, through every route this session had. A nominally open license doesn't survive contact with Wiley's gate. That's worth remembering the next time a source's tier gets bumped up because "it's open access": open access is a property of the license, not a guarantee of the fetch.