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README.md

@@ -1 +1,17 @@
 # colorcrop
+
+Go library for cropping images by removing borders with specified color.
+
+## Installation
+
+`go get -u github.com/nxshock/colorcrop`
+
+## Usage
+
+Crop white borders with 50% of thresold:
+
+`croppedImage := colorcrop.Crop(sourceImage, color.RGBA{255, 255, 255, 255}, 0.5)`
+
+## Examples
+
+See in "examples".

colorcrop.go

@@ -0,0 +1,67 @@
+// Go library for cropping images by removing borders with specified color.
+package colorcrop
+
+import (
+	"image"
+	"image/color"
+)
+
+// Crop returns cropped image with default comparator.
+func Crop(img image.Image, color color.Color, thresold float64) image.Image {
+	return CropWithComparator(img, color, thresold, CmpRGBComponentsDiff)
+}
+
+// Crop returns cropped image with specified comparator.
+func CropWithComparator(img image.Image, color color.Color, thresold float64, comparator comparator) image.Image {
+	return img.(interface {
+		SubImage(r image.Rectangle) image.Image
+	}).SubImage(cropRectanle(img, color, thresold, comparator))
+}
+
+// cropRectanle returns rectangle of image without borders.
+func cropRectanle(img image.Image, color color.Color, thresold float64, comparator comparator) image.Rectangle {
+	rectangle := img.Bounds()
+
+TopLoop:
+	for y := rectangle.Min.Y; y < rectangle.Max.Y; y++ {
+		rectangle.Min.Y = y
+		for x := rectangle.Min.X; x < rectangle.Max.X; x++ {
+			if comparator(img.At(x, y), color) > thresold {
+				break TopLoop
+			}
+		}
+	}
+
+BottomLoop:
+	for y := rectangle.Max.Y - 1; y >= rectangle.Min.Y; y-- {
+		rectangle.Max.Y = y + 1
+		for x := rectangle.Min.X; x < rectangle.Max.X; x++ {
+			if comparator(img.At(x, y), color) > thresold {
+				break BottomLoop
+			}
+		}
+	}
+
+LeftLoop:
+	for x := rectangle.Min.X; x < rectangle.Max.X; x++ {
+		rectangle.Min.X = x
+		for y := rectangle.Min.Y; y < rectangle.Max.Y; y++ {
+			if comparator(img.At(x, y), color) > thresold {
+				break LeftLoop
+			}
+		}
+
+	}
+
+RightLoop:
+	for x := rectangle.Max.X - 1; x >= rectangle.Min.X; x-- {
+		rectangle.Max.X = x + 1
+		for y := rectangle.Min.Y; y < rectangle.Max.Y; y++ {
+			if comparator(img.At(x, y), color) > thresold {
+				break RightLoop
+			}
+		}
+	}
+
+	return rectangle
+}

comparators.go

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+package colorcrop
+
+import (
+	"image/color"
+	"math"
+)
+
+// comparator is a function that returns a difference between two colors in
+// range 0.0..1.0.
+type comparator func(color.Color, color.Color) float64
+
+// CmpColorDifference returns difference of two colors
+func CmpSquareRGBComponentsDiff(color1 color.Color, color2 color.Color) float64 {
+	const maxDiff = 113509.94967402637 // Difference between black and white colors
+
+	r1, g1, b1, _ := color1.RGBA()
+	r2, g2, b2, _ := color2.RGBA()
+	return math.Sqrt(math.Pow(float64(r2)-float64(r1), 2.0)+
+		math.Pow(float64(g2)-float64(g1), 2.0)+
+		math.Pow(float64(b2)-float64(b1), 2.0)) / maxDiff
+}
+
+// CmpColorDifference returns difference of two colors.
+func CmpRGBComponentsDiff(color1 color.Color, color2 color.Color) float64 {
+	const maxDiff = 765 // Difference between black and white colors
+
+	r1, g1, b1, _ := color1.RGBA()
+	r2, g2, b2, _ := color2.RGBA()
+	return math.Sqrt(math.Abs(float64(r2)-float64(r1))+
+		math.Abs(float64(g2)-float64(g1))+
+		math.Abs(float64(b2)-float64(b1))) / maxDiff
+}

comparators_test.go

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+package colorcrop
+
+import (
+	"image/color"
+	"reflect"
+	"runtime"
+	"testing"
+)
+
+func TestColorComparators(t *testing.T) {
+	type In struct {
+		color1 color.Color
+		color2 color.Color
+	}
+
+	comparators := []comparator{CmpSquareRGBComponentsDiff, CmpRGBComponentsDiff}
+
+	tests := []struct {
+		in         In
+		out        float64
+		commentary string
+	}{
+		{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"},
+	}
+
+	for _, comparator := range comparators {
+		for _, test := range tests {
+			if CmpSquareRGBComponentsDiff(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, CmpSquareRGBComponentsDiff(test.in.color2, test.in.color1))
+			}
+		}
+	}
+}

example/main.go

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+package main
+
+import (
+	"image/color"
+	"image/png"
+	"log"
+	"os"
+
+	"github.com/nxshock/colorcrop"
+)
+
+func main() {
+	log.SetFlags(0)
+
+	// Read source image
+	sourceFile, err := os.Open("img.png")
+	if err != nil {
+		log.Fatalln(err)
+	}
+	defer sourceFile.Close()
+
+	sourceImage, err := png.Decode(sourceFile)
+	if err != nil {
+		log.Fatalln(err)
+	}
+
+	// Crop image white border with 50% thresold
+	croppedImage := colorcrop.Crop(sourceImage, color.RGBA{255, 255, 255, 255}, 0.5)
+
+	// Save cropped image
+	croppedFile, err := os.Create("cropped.png")
+	if err != nil {
+		log.Fatalln(err)
+	}
+	defer croppedFile.Close()
+
+	err = png.Encode(croppedFile, croppedImage)
+	if err != nil {
+		log.Fatalln(err)
+	}
+}

example_test.go

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+package colorcrop_test
+
+import (
+	"image/color"
+	"image/png"
+	"log"
+	"os"
+
+	"github.com/nxshock/colorcrop"
+)
+
+func Example() {
+	log.SetFlags(0)
+
+	// Read source image
+	sourceFile, _ := os.Open("img.png")
+	defer sourceFile.Close()
+
+	sourceImage, _ := png.Decode(sourceFile)
+
+	// Crop image white border with 50% thresold
+	croppedImage := colorcrop.Crop(sourceImage, color.RGBA{255, 255, 255, 255}, 0.5)
+
+	// Save cropped image
+	croppedFile, _ := os.Create("cropped.png")
+	defer croppedFile.Close()
+
+	png.Encode(croppedFile, croppedImage)
+}