Comparator rework and fixes

colorconversion.go

@@ -0,0 +1,74 @@
+package colorcrop
+
+import (
+	"image/color"
+	"math"
+)
+
+func rgbtoXYZ(r, g, b uint32) (x, y, z float64) {
+	varR := float64(r) / 255
+	varG := float64(g) / 255
+	varB := float64(b) / 255
+
+	if varR > 0.04045 {
+		varR = math.Pow((varR+0.055)/1.055, 2.4)
+	} else {
+		varR = varR / 12.92
+	}
+
+	if varG > 0.04045 {
+		varG = math.Pow((varG+0.055)/1.055, 2.4)
+	} else {
+		varG = varG / 12.92
+	}
+
+	if varB > 0.04045 {
+		varB = math.Pow((varB+0.055)/1.055, 2.4)
+	} else {
+		varB = varB / 12.92
+	}
+
+	varR = varR * 100
+	varG = varG * 100
+	varB = varB * 100
+
+	x = varR*0.4124 + varG*0.3576 + varB*0.1805
+	y = varR*0.2126 + varG*0.7152 + varB*0.0722
+	z = varR*0.0193 + varG*0.1192 + varB*0.9505
+	return x, y, z
+}
+
+func xyztoLAB(x, y, z float64) (l, a, b float64) {
+	refX, refY, refZ := 95.047, 100.000, 108.883 // Daylight, sRGB, Adobe-RGB, Observer D65, 2°
+
+	varX := x / refX
+	varY := y / refY
+	varZ := z / refZ
+
+	if varX > 0.008856 {
+		varX = math.Pow(varX, (1.0 / 3.0))
+	} else {
+		varX = (7.787 * varX) + (16.0 / 116.0)
+	}
+	if varY > 0.008856 {
+		varY = math.Pow(varY, (1.0 / 3.0))
+	} else {
+		varY = (7.787 * varY) + (16.0 / 116.0)
+	}
+	if varZ > 0.008856 {
+		varZ = math.Pow(varZ, (1.0 / 3.0))
+	} else {
+		varZ = (7.787 * varZ) + (16.0 / 116.0)
+	}
+
+	l = (116 * varY) - 16
+	a = 500 * (varX - varY)
+	b = 200 * (varY - varZ)
+
+	return l, a, b
+}
+
+func colorToLAB(color color.Color) (l, a, b float64) {
+	cr, cg, cb, _ := color.RGBA()
+	return xyztoLAB(rgbtoXYZ(cr, cg, cb))
+}