Re: [csswg-drafts] [css-color-4] Define epsilon (or range of valid epsilons) for determining when Lab/OKLab should be considered achromatic (#11706)

So it is now clear that ε should be chosen to encompass the narrow range of values close to the central axis where the hue angle is ill-conditioned and replaced with `none`.

In many spaces (but not all) that is also where achromatic colors converted from some RGB space where R=G=B fall. For the spaces where that is not true, that is because of color appearance; the eye is not fully adapted and so neutrals gradually diverge from the central axis as the neutral gets brighter. But the hue angle is not ill-conditioned and the ε should not be made artificially large so as to encompass these colors.

Given that, I think we can firm up the distastefully wooly prose we currently have:

> User agents <em>may</em> treat a component as [=powerless=]
 if the color is "sufficiently close" to the precise conditions specified.
 For example, a gray color converted into ''lch()'' may,
 due to numerical errors,
 have an <em>extremely small</em> chroma rather than precisely ''0%'';
 this can, at the user agent's discretion,
 still treat the hue component as [=powerless=].
 It is intentionally unspecified exactly what "sufficiently close" means for this purpose.

In particular, dropping that last sentence and giving specific guidance on ε.

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Received on Tuesday, 18 March 2025 14:36:57 UTC