go-color/contrast.go at master · dominikh/go-color

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package color

// TODO:

// APCA

// Lstar

// Michelson

// WCAG21

// Weber

// DeltaPhiStar

func luminance(c Color) float64 {

return c.Convert(XYZ_D65).Values[1]

}

// ContrastWeber computes the Weber luminance contrast.

func ContrastWeber(c1, c2 Color) float64 {

y1 := max(luminance(c1), 0)

y2 := max(luminance(c2), 0)

if y2 > y1 {

y1, y2 = y2, y1

}

if y2 == 0 {

// the darkest sRGB color above black is #000001 and this produces a

// plain Weber contrast of ~45647. So, setting the divide-by-zero result

// at 50000 is a reasonable max clamp for the plain Weber

return 50_000

} else {

return (y1 - y2) / y2

}

// ContrastMichelson computes the Michelson contrast.

func ContrastMichelson(c1, c2 Color) float64 {

y1 := max(luminance(c1), 0)

y2 := max(luminance(c2), 0)

if y2 > y1 {

y1, y2 = y2, y1

}

if y1+y2 == 0 {

return 0

}

return (y1 - y2) / (y1 + y2)

}