- From: Chris Lilley via GitHub <sysbot+gh@w3.org>
- Date: Mon, 18 Oct 2021 13:56:41 +0000
- To: public-css-archive@w3.org
For the scaling of _a_ & _b_ , this statement in the [OKlab defining article](https://bottosson.github.io/posts/oklab/#how-oklab-was-derived) did give me slight pause: > The _a_ and _b_ plane is scaled so that around 50% gray the ratio of color differences along the lightness axis and the _a_ and _b_ plane is the same as the ratio for color differences predicted by CIEDE2000 because the formula for deltaE2000 introduces a mean-chroma-dependent asymmetry between _a_ and _b_, strongest right on the neutral axis (recalculated _a_ is **1.5** times _b_) then fading off to below **1.1** at chroma 27 and below **1.01** at chroma 40. https://github.com/w3c/csswg-drafts/blob/b9ec4cb357e2a70596ed6863dff8b2bdde8d4060/css-color-4/deltaE2000.js#L27-L40 (For the curious, the values of Cbar, G, and adash are [tabulated here](https://www.w3.org/Graphics/Color/Workshop/slides/lilley/Cbar-G-adash.txt)) This means that: - scaling OKLab _a_ & _b_ relative to L solely based on deltaE 2000 comparisons on the neutral axis picks the point of maximum CIELAB _a_ & _b_ asymmetry - scaling based on some dataset of color pairs will depend on the distribution of mean chroma in that data set > I was mostly focused on the orthogonality between L, C and h Which is a very useful property of OKLab, for gamut mapping and gradient generation -- GitHub Notification of comment by svgeesus Please view or discuss this issue at https://github.com/w3c/csswg-drafts/issues/6642#issuecomment-945796054 using your GitHub account -- Sent via github-notify-ml as configured in https://github.com/w3c/github-notify-ml-config
Received on Monday, 18 October 2021 13:56:43 UTC