color/internal/helper/oklab_test.go

package helper

import (
	"fmt"
	"image/color"
	"math"
	"testing"
)

func TestLMSToXYZ(t *testing.T) {
	for c := range Enum(true, false, true) {
		want := collect3(LRGBtoXYZ(RGBtoLRGB(uint32(c.R), uint32(c.G), uint32(c.B))))

		if got := collect3(LMStoXYZ(XYZtoLMS(want[0], want[1], want[2]))); !EqFloat64SliceFuzzy(want[:], got[:]) {
			t.Errorf("LMStoXYZ(XYZtoLMS(%v)) = %v, want unchanged", want, got)
			return
		}
	}
}

func TestLMSToLRGB(t *testing.T) {
	for c := range Enum(true, false, true) {
		want := collect3(RGBtoLRGB(uint32(c.R), uint32(c.G), uint32(c.B)))

		l, m, s := LRGBtoLMS(want[0], want[1], want[2])

		// test via the optimized LMStoLRGB function.
		if got := collect3(LMStoLRGB(l, m, s)); !EqFloat64SliceFuzzy(want[:], got[:]) {
			t.Errorf("LMStoLRGB(LRGBtoLMS(%v)) = %v, want unchanged", want, got)
			return
		}

		// make sure this is equivalent to going through the XYZ colourspace.
		if got := collect3(XYZtoLRGB(LMStoXYZ(l, m, s))); !EqFloat64SliceFuzzy(want[:], got[:]) {
			t.Errorf("XYZtoLRGB(LMStoXYZ(LRGBtoLMS(%v))) = %v, want unchanged", want, got)
			return
		}
	}
}

func TestOKLabToLMS(t *testing.T) {
	for c := range Enum(true, false, true) {
		want := collect3(LRGBtoLMS(RGBtoLRGB(uint32(c.R), uint32(c.G), uint32(c.B))))
		if got := collect3(OkLabToLMS(LMStoOkLab(want[0], want[1], want[2]))); !EqFloat64SliceFuzzy(want[:], got[:]) {
			t.Errorf("OkLabToLMS(LMStoOKLab(%v)) = %v, want unchanged", want, got)
			return
		}
	}
}

func TestOkLabExamplePairs(t *testing.T) {
	// The page https://bottosson.github.io/posts/oklab/ lists example XYZ and OkLab pairs,
	// with the results rounded to three decimal places.
	examples := []struct{ xyz, lab [3]float64 }{
		{[3]float64{0.950, 1.000, 1.089}, [3]float64{1.000, 0.000, 0.000}},
		{[3]float64{1.000, 0.000, 0.000}, [3]float64{0.450, 1.236, -0.019}},
		{[3]float64{0.000, 1.000, 0.000}, [3]float64{0.922, -0.671, 0.263}},
		{[3]float64{0.000, 0.000, 1.000}, [3]float64{0.153, -1.415, -0.449}},
	}

	round := func(x float64) float64 {
		return math.Round(x*1000) / 1000
	}

	round3 := func(a, b, c float64) [3]float64 {
		return [3]float64{round(a), round(b), round(c)}
	}

	for i, e := range examples {
		if gotLab := round3(LMStoOkLab(XYZtoLMS(e.xyz[0], e.xyz[1], e.xyz[2]))); gotLab != e.lab {
			t.Errorf("pair %d: computed lab=%v, want=%v", i+1, gotLab, e.lab)
		}

		// note that the example table isn't suitable fo testing OkLab to XYZ conversion due to
		// the errors introduced by rounding.
		//
		// we are depending the round trip conversions being correct, which is verified by TestLMSToXYZ and TestOKLabToLMS.
	}
}

type testNXYZAColor [4]float64

func (c testNXYZAColor) RGBA() (_, _, _, _ uint32) {
	panic("should not be called")
}

func (c testNXYZAColor) NXYZA() (_, _, _, _ float64) {
	return c[0], c[1], c[2], c[3]
}

type testNOkLabAColor [4]float64

func (c testNOkLabAColor) RGBA() (_, _, _, _ uint32) {
	panic("should not be called")
}

func (c testNOkLabAColor) NOkLabA() (_, _, _, _ float64) {
	return c[0], c[1], c[2], c[3]
}

func TestColorToNOkLabA(t *testing.T) {
	tests := []struct {
		input color.Color
		want  [4]float64
	}{
		{
			// test special NRGBA handling.
			color.NRGBA{0x01, 0x23, 0x45, 0x67},
			[4]float64{0.25462381167525894, -0.02293028913883799, -0.07098467472369072, float64(0x6767) / 0xffff},
		}, {
			// test special NRGBA64 handling.
			color.NRGBA64{0x0123, 0x4567, 0x89ab, 0},
			[4]float64{0.39601873251000413, -0.03369278598612779, -0.12401844116020128, 0},
		}, {
			// test a colour that can return its linear NRGBA values directly.
			testNLRGBA{color.NRGBA64{0x0123, 0x4567, 0x89ab, 0xcdef}},
			[4]float64{0.39601873251000413, -0.03369278598612779, -0.12401844116020128, float64(0xcdef) / 0xffff},
		}, {
			// test conversion of the values from a a colour that can return NXYZA values directly.
			testNXYZAColor{0.95, 1., 1.089, .5},
			// these were from the canonical test pairs, these values are 1, 0, 0 when rounded to the nearest thousandth.
			[4]float64{0.9999686754143632, -0.0002580058168537569, -0.00011499756458199784, .5},
		}, {
			// test that we get the values from a colour that can return NOkLabA directly.
			testNOkLabAColor{math.Inf(1), math.NaN(), math.Inf(-1), -1},
			[4]float64{math.Inf(1), math.NaN(), math.Inf(-1), -1},
		},
	}
	for _, tt := range tests {
		t.Run(fmt.Sprintf("%#+v", tt.input), func(t *testing.T) {
			if got := collect4(ColorToNOkLabA(tt.input)); !EqFloat64SliceFuzzy(got[:], tt.want[:]) {
				t.Errorf("ColorToNOkLabA(%#+v) = %v, want %v", tt.input, got, tt.want)
			}
		})
	}
}