The avatar for @sebastien
Sébastien Pierre
Using Observable for software engineering, programming language and user interface research.
Public
Edited
Nov 20, 2022
Importers
7 stars
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grey = ([r,g,b]) => gamma((degamma(r) + degamma(g) + degamma(b))/3)
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md`Let's try that approach and compute a grey value averaging the three component across the gradient, the first in gamma space and the second in linear space.`
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luma = ([r,g,b]) => 0.2126*r + 0.7152*g + 0.0722*b
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luminance = ([r,g,b]) => 0.2126*degamma(r) + 0.7152*degamma(g) + 0.0722*degamma(b)
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lightness = (rgb)=>{
// This is from: https://stackoverflow.com/a/56678483/4100249
const y = luminance(rgb)
return (y <= (216/24389) ? y * (24389/27) : Math.pow(y,(1/3)) * 116 - 16) / 100.0
}
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huedistance = (a,b) => {
const d = Math.abs(hue(a) - hue(b))
return 2 * (d > 0.5 ? 1 - d : d)
}
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hsl(hex(HSLColor))
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viewof HSLColor = color()
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saturation = rgb => hsl(rgb)[2]
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degammasRGB = _ => _ <= 0.04045 ? _/12.92 : Math.pow( ( _ + 0.055) / 1.055, 2.4)
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gammasRGB = _ => _ <= 0.0031308 ? _ * 12.92 : 1.055 * Math.pow(_, 1.0/2.4) - 0.055
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md`Note that according to the [WCAG](https://www.w3.org/TR/WCAG21/#dfn-relative-luminance), the gamma expansion threshold is different in sRGB, from 0.04045 (what we have in *degammasRGB*) to 0.03928, however that difference should have a negligible impact.`
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stylesheet(Stylesheet)
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