Test rework, bugfixes and more tests

colorconversion.go

@@ -5,10 +5,13 @@ import (
 	"math"
 )
 
-func rgbtoXYZ(r, g, b uint32) (x, y, z float64) {
-	varR := float64(r) / 255
-	varG := float64(g) / 255
-	varB := float64(b) / 255
+// colorToXYZ returns CIE XYZ representation of color.
+// https://en.wikipedia.org/wiki/Color_model#CIE_XYZ_color_space
+func colorToXYZ(color color.Color) (x, y, z float64) {
+	r, g, b, _ := color.RGBA()
+	varR := float64(r>>8) / 255
+	varG := float64(g>>8) / 255
+	varB := float64(b>>8) / 255
 
 	if varR > 0.04045 {
 		varR = math.Pow((varR+0.055)/1.055, 2.4)
@@ -28,16 +31,15 @@ func rgbtoXYZ(r, g, b uint32) (x, y, z float64) {
 		varB = varB / 12.92
 	}
 
-	varR = varR * 100
-	varG = varG * 100
-	varB = varB * 100
+	x = varR*41.24 + varG*35.76 + varB*18.05
+	y = varR*21.26 + varG*71.52 + varB*7.22
+	z = varR*1.93 + varG*11.92 + varB*95.05
 
-	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
 }
 
+// xyztoLAB converts CIE XYZ color space to CIE LAB color space
+// https://en.wikipedia.org/wiki/Lab_color_space#CIELAB-CIEXYZ_conversions
 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°
 
@@ -68,7 +70,8 @@ func xyztoLAB(x, y, z float64) (l, a, b float64) {
 	return l, a, b
 }
 
+// colorToLAB returns LAB representation of any color (without aplha)
+// https://en.wikipedia.org/wiki/Lab_color_space
 func colorToLAB(color color.Color) (l, a, b float64) {
-	cr, cg, cb, _ := color.RGBA()
-	return xyztoLAB(rgbtoXYZ(cr, cg, cb))
+	return xyztoLAB(colorToXYZ(color))
 }

colorconverson_test.go

@@ -0,0 +1,28 @@
+package colorcrop
+
+import (
+	"image/color"
+	"math"
+	"testing"
+)
+
+func TestColorToLAB(t *testing.T) {
+	tests := []struct {
+		color                           color.Color
+		expectedL, expectedA, expectedB float64
+		gotL, gotA, gotB                float64
+	}{
+		{color: color.RGBA{0, 0, 0, 255}, expectedL: 0.0, expectedA: 0.0, expectedB: 0.0},
+		{color: color.RGBA{0, 0, 255, 255}, expectedL: 32.30258667, expectedA: 79.19666179, expectedB: -107.86368104},
+		{color: color.RGBA{0, 255, 0, 255}, expectedL: 87.73703347, expectedA: -86.18463650, expectedB: 83.18116475},
+		{color: color.RGBA{255, 0, 0, 255}, expectedL: 53.23288179, expectedA: 80.10930953, expectedB: 67.22006831},
+		{color: color.RGBA{255, 255, 255, 255}, expectedL: 100.00000000, expectedA: 0.00526050, expectedB: -0.01040818},
+	}
+
+	for _, test := range tests {
+		test.gotL, test.gotA, test.gotB = colorToLAB(test.color)
+		if math.Abs(test.gotL-test.expectedL) > epsilon || math.Abs(test.gotA-test.expectedA) > epsilon || math.Abs(test.gotB-test.expectedB) > epsilon {
+			t.Errorf("%v: expected {%.8f, %.8f, %.8f}, got {%.8f, %.8f, %.8f}", test.color, test.expectedL, test.expectedA, test.expectedB, test.gotL, test.gotA, test.gotB)
+		}
+	}
+}

colorcrop_test.go

@@ -0,0 +1,72 @@
+package colorcrop
+
+import (
+	"image"
+	"image/color"
+	"image/png"
+	"os"
+	"reflect"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+// epsilon is a maximum permissible error
+const epsilon = 0.00000001
+
+func TestCropRectanle(t *testing.T) {
+	type test struct {
+		filename string
+		expected image.Rectangle
+		got      image.Rectangle
+	}
+
+	comparators := []comparator{CmpRGBComponents, CmpEuclidean, CmpCIE76}
+	thresold := 0.5
+
+	tests := []test{
+		{filename: "01.png", expected: image.Rectangle{image.Point{0, 0}, image.Point{1, 1}}},
+		{filename: "02.png", expected: image.Rectangle{image.Point{1, 0}, image.Point{2, 1}}},
+		{filename: "03.png", expected: image.Rectangle{image.Point{2, 0}, image.Point{3, 1}}},
+		{filename: "04.png", expected: image.Rectangle{image.Point{3, 0}, image.Point{4, 1}}},
+		{filename: "05.png", expected: image.Rectangle{image.Point{0, 1}, image.Point{1, 2}}},
+		{filename: "06.png", expected: image.Rectangle{image.Point{1, 1}, image.Point{2, 2}}},
+		{filename: "07.png", expected: image.Rectangle{image.Point{2, 1}, image.Point{3, 2}}},
+		{filename: "08.png", expected: image.Rectangle{image.Point{3, 1}, image.Point{4, 2}}},
+		{filename: "09.png", expected: image.Rectangle{image.Point{0, 2}, image.Point{1, 3}}},
+		{filename: "10.png", expected: image.Rectangle{image.Point{1, 2}, image.Point{2, 3}}},
+		{filename: "11.png", expected: image.Rectangle{image.Point{2, 2}, image.Point{3, 3}}},
+		{filename: "12.png", expected: image.Rectangle{image.Point{3, 2}, image.Point{4, 3}}},
+		{filename: "13.png", expected: image.Rectangle{image.Point{0, 3}, image.Point{1, 4}}},
+		{filename: "14.png", expected: image.Rectangle{image.Point{1, 3}, image.Point{2, 4}}},
+		{filename: "15.png", expected: image.Rectangle{image.Point{2, 3}, image.Point{3, 4}}},
+		{filename: "16.png", expected: image.Rectangle{image.Point{3, 3}, image.Point{4, 4}}},
+	}
+
+	for _, comparator := range comparators {
+		for _, test := range tests {
+			file, err := os.Open("testimages/" + test.filename)
+			if err != nil {
+				t.Fatal(err)
+			}
+			defer file.Close()
+			image, err := png.Decode(file)
+			if err != nil {
+				t.Fatal(err)
+			}
+			test.got = cropRectanle(image, color.RGBA{255, 255, 255, 255}, thresold, comparator)
+			if !reflect.DeepEqual(test.expected, test.got) {
+				t.Errorf("expected %v, got %v for comparator: %s, file: %s", test.expected, test.got, getFuncName(comparator), test.filename)
+			}
+		}
+	}
+}
+
+func getFuncName(i interface{}) string {
+	s := runtime.FuncForPC(reflect.ValueOf(i).Pointer()).Name()
+	p := strings.LastIndex(s, ".")
+	if p > 0 {
+		return string([]rune(s)[p+1:])
+	}
+	return s
+}

comparators.go

@@ -10,6 +10,7 @@ import (
 type comparator func(color.Color, color.Color) float64
 
 // CmpEuclidean returns Euclidean difference of two colors.
+//
 // https://en.wikipedia.org/wiki/Color_difference#Euclidean
 func CmpEuclidean(color1 color.Color, color2 color.Color) float64 {
 	const maxDiff = 113509.94967402637 // Difference between black and white colors
@@ -29,8 +30,8 @@ func CmpRGBComponents(color1 color.Color, color2 color.Color) float64 {
 	r1, g1, b1, _ := color1.RGBA()
 	r2, g2, b2, _ := color2.RGBA()
 
-	r1, g1, b1 = r1/256, g1/256, b1/256
-	r2, g2, b2 = r2/256, g2/256, b2/256
+	r1, g1, b1 = r1>>8, g1>>8, b1>>8
+	r2, g2, b2 = r2>>8, g2>>8, b2>>8
 
 	return float64((max(r1, r2)-min(r1, r2))+
 		(max(g1, g2)-min(g1, g2))+
@@ -38,15 +39,13 @@ func CmpRGBComponents(color1 color.Color, color2 color.Color) float64 {
 }
 
 // CmpCIE76 returns difference of two colors defined in CIE76 standart.
+//
 // https://en.wikipedia.org/wiki/Color_difference#CIE76
 func CmpCIE76(color1 color.Color, color2 color.Color) float64 {
-	const maxDiff = 149.95514755026548 // Difference between blue and white colors
+	const maxDiff = 149.95514755 // Difference between blue and white colors
 
-	r1, g1, b1, _ := color1.RGBA()
-	r2, g2, b2, _ := color2.RGBA()
-
-	cl1, ca1, cb1 := xyztoLAB(rgbtoXYZ(r1/256, g1/256, b1/256))
-	cl2, ca2, cb2 := xyztoLAB(rgbtoXYZ(r2/256, g2/256, b2/256))
+	cl1, ca1, cb1 := colorToLAB(color1)
+	cl2, ca2, cb2 := colorToLAB(color2)
 
 	return math.Sqrt(distance(cl2, cl1)+distance(ca2, ca1)+distance(cb2, cb1)) / maxDiff
 }
@@ -55,6 +54,7 @@ func distance(x, y float64) float64 {
 	return (x - y) * (x - y)
 }
 
+// min is minimum of two uint32
 func min(a, b uint32) uint32 {
 	if a < b {
 		return a
@@ -62,6 +62,7 @@ func min(a, b uint32) uint32 {
 	return b
 }
 
+// max is maximum of two uint32
 func max(a, b uint32) uint32 {
 	if a > b {
 		return a

comparators_test.go

@@ -2,40 +2,102 @@ package colorcrop
 
 import (
 	"image/color"
-	"reflect"
-	"runtime"
+	"math"
 	"testing"
 )
 
-func TestColorComparators(t *testing.T) {
-	type In struct {
-		color1 color.Color
-		color2 color.Color
-	}
-
+func TestLinearComparators(t *testing.T) {
 	comparators := []comparator{CmpEuclidean, CmpRGBComponents}
 
 	tests := []struct {
-		in         In
-		out        float64
-		commentary string
+		color1   color.Color
+		color2   color.Color
+		expected float64
+		got      float64
 	}{
-		{in: In{color.RGBA{0, 0, 0, 255}, color.RGBA{255, 255, 255, 255}},
-			out:        1.00,
-			commentary: "Difference between black and white colors"},
-		{in: In{color.RGBA{255, 255, 255, 255}, color.RGBA{255, 255, 255, 255}},
-			out:        0.00,
-			commentary: "Difference between same colors"},
-		{in: In{color.RGBA{255, 255, 255, 0}, color.RGBA{255, 255, 255, 255}},
-			out:        0.00,
-			commentary: "Difference between same colors with different transparency"},
+		{color1: color.RGBA{0, 0, 0, 255}, color2: color.RGBA{0, 0, 0, 255}, expected: 0.00},             // same black colors
+		{color1: color.RGBA{255, 255, 255, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 0.00}, // same white colors
+		{color1: color.RGBA{0, 0, 0, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 1.00},       // different (black and white) colors
+		{color1: color.RGBA{255, 255, 255, 255}, color2: color.RGBA{0, 0, 0, 255}, expected: 1.00},       // different (white and black) colors
+		{color1: color.RGBA{255, 255, 255, 0}, color2: color.RGBA{255, 255, 255, 255}, expected: 0.00},   // must ignore alpha channel
 	}
 
 	for _, comparator := range comparators {
 		for _, test := range tests {
-			if comparator(test.in.color2, test.in.color1) != test.out {
-				t.Errorf("%s: %s: expected %.2f, got %.2f", runtime.FuncForPC(reflect.ValueOf(comparator).Pointer()).Name(), test.commentary, test.out, comparator(test.in.color2, test.in.color1))
+			test.got = comparator(test.color1, test.color2)
+			if math.Abs(test.got-test.expected) > epsilon {
+				t.Errorf("%v %v: expected %.8f, got %.8f", test.color1, test.color2, test.expected, test.got)
 			}
 		}
 	}
 }
+
+func TestCmpCIE76(t *testing.T) {
+	type test struct {
+		color1   color.Color
+		color2   color.Color
+		expected float64
+		got      float64
+	}
+
+	tests := []test{
+		{color1: color.RGBA{0, 0, 0, 255}, color2: color.RGBA{0, 0, 0, 255}, expected: 0.00000000 / 149.95514755},             // same black colors
+		{color1: color.RGBA{255, 255, 255, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 0.00000000 / 149.95514755}, // same white colors
+		{color1: color.RGBA{0, 0, 0, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 100.00000068 / 149.95514755},     // different (black and white) colors
+		{color1: color.RGBA{255, 255, 255, 255}, color2: color.RGBA{0, 0, 0, 255}, expected: 100.00000068 / 149.95514755},     // different (white and black) colors
+		{color1: color.RGBA{255, 0, 0, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 114.55897602 / 149.95514755},   // different (red and white) colors
+		{color1: color.RGBA{0, 255, 0, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 120.41559907 / 149.95514755},   // different (green and white) colors
+		{color1: color.RGBA{0, 0, 255, 255}, color2: color.RGBA{255, 255, 255, 255}, expected: 149.95514755 / 149.95514755},   // different (blue and white) colors
+	}
+
+	for _, test := range tests {
+		test.got = CmpCIE76(test.color1, test.color2)
+		if math.Abs(test.got-test.expected) > epsilon {
+			t.Errorf("%v %v: expected %.8f, got %.8f", test.color1, test.color2, test.expected, test.got)
+		}
+	}
+}
+
+func TestMin(t *testing.T) {
+	type test struct {
+		x        uint32
+		y        uint32
+		expected uint32
+		got      uint32
+	}
+
+	tests := []test{
+		{x: 1, y: 2, expected: 1},
+		{x: 3, y: 2, expected: 2},
+		{x: 4, y: 4, expected: 4},
+	}
+
+	for _, test := range tests {
+		test.got = min(test.x, test.y)
+		if test.got != test.expected {
+			t.Errorf("min(%d, %d): expected %d, got %d", test.x, test.y, test.expected, test.got)
+		}
+	}
+}
+
+func TestMax(t *testing.T) {
+	type test struct {
+		x        uint32
+		y        uint32
+		expected uint32
+		got      uint32
+	}
+
+	tests := []test{
+		{x: 1, y: 2, expected: 2},
+		{x: 3, y: 2, expected: 3},
+		{x: 4, y: 4, expected: 4},
+	}
+
+	for _, test := range tests {
+		test.got = max(test.x, test.y)
+		if test.got != test.expected {
+			t.Errorf("max(%d, %d): expected %d, got %d", test.x, test.y, test.expected, test.got)
+		}
+	}
+}

example_test.go

@@ -1,3 +1,6 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
 package colorcrop_test
 
 import (
@@ -9,7 +12,7 @@ import (
 	"github.com/nxshock/colorcrop"
 )
 
-func Example() {
+func ExampleBasicUsage() {
 	log.SetFlags(0)
 
 	// Read source image
@@ -18,8 +21,34 @@ func Example() {
 
 	sourceImage, _ := png.Decode(sourceFile)
 
-	// Crop image white border with 50% thresold
-	croppedImage := colorcrop.Crop(sourceImage, color.RGBA{255, 255, 255, 255}, 0.5)
+	// Crop white border with 50% thresold
+	croppedImage := colorcrop.Crop(
+		sourceImage,                    // for source image
+		color.RGBA{255, 255, 255, 255}, // crop white border
+		0.5) // with 50% thresold
+
+	// Save cropped image
+	croppedFile, _ := os.Create("cropped.png")
+	defer croppedFile.Close()
+
+	png.Encode(croppedFile, croppedImage)
+}
+
+func ExampleCustomComparator() {
+	log.SetFlags(0)
+
+	// Read source image
+	sourceFile, _ := os.Open("img.png")
+	defer sourceFile.Close()
+
+	sourceImage, _ := png.Decode(sourceFile)
+
+	// Crop white border with 50% thresold
+	croppedImage := colorcrop.CropWithComparator(
+		sourceImage,                    // for source image
+		color.RGBA{255, 255, 255, 255}, // crop white border
+		0.5,                // with 50% thresold
+		colorcrop.CmpCIE76) // using CIE76 standart for defining color difference
 
 	// Save cropped image
 	croppedFile, _ := os.Create("cropped.png")