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interface Color {
red: number,
green: number,
blue: number,
}
export function parse(str: string): Color {
return {
red: parseInt(str.slice(1,3), 16),
green: parseInt(str.slice(3,5), 16),
blue: parseInt(str.slice(5,7), 16),
}
}
// https://www.w3.org/TR/2008/REC-WCAG20-20081211/#contrastratio
export function contrastRatio(c1: Color, c2: Color): number {
const r1 = relativeLuminance(c1)
const r2 = relativeLuminance(c2)
return r1 > r2
? (r1 + 0.05) / (r2 + 0.05)
: (r2 + 0.05) / (r1 + 0.05)
}
function relativeLuminance(c: Color): number {
return (
0.2126 * fromSRGB(c.red / 255)
+ 0.7152 * fromSRGB(c.green / 255)
+ 0.0722 * fromSRGB(c.blue / 255))
}
function fromSRGB(sRGB: number): number {
return sRGB <= 0.03928
? sRGB / 12.92
: Math.pow(((sRGB + 0.055) / 1.055), 2.4)
}
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