add algo for RGB to GrayScale

README.md

@@ -76,6 +76,8 @@ The ePub include as a first page:
 # go-comic-converter -h
 
 Usage of go-comic-converter:
+  -algo string
+    	Algo for RGB to Grayscale: luster, default, mean, luma (default "default")
   -author string
     	Author of the epub (default "GO Comic Converter")
   -input string

internal/epub/core.go

@@ -15,6 +15,7 @@ type ImageOptions struct {
 	ViewWidth  int
 	ViewHeight int
 	Quality    int
+	Algo       string
 }
 
 type EpubOptions struct {

internal/epub/image_processing.go

@@ -80,6 +80,7 @@ func LoadImages(path string, options *ImageOptions) ([]*Image, error) {
 					options.ViewWidth,
 					options.ViewHeight,
 					options.Quality,
+					options.Algo,
 				)
 				name := fmt.Sprintf("OEBPS/Images/%d.jpg", img.Id)
 				if img.Id == 0 {

internal/image-converter/core.go

@@ -6,11 +6,50 @@ import (
 	"image/color"
 	"image/jpeg"
 	"io"
+	"sort"
 
 	"golang.org/x/image/draw"
 )
 
-func Load(reader io.ReadCloser) *image.Gray {
+var AlgoGray = map[string]func(color.Color) color.Color{
+	"default": func(c color.Color) color.Color {
+		return color.GrayModel.Convert(c)
+	},
+	"mean": func(c color.Color) color.Color {
+		r, g, b, _ := c.RGBA()
+		y := float64(r+g+b) / 3 * (255.0 / 65535)
+		return color.Gray{uint8(y)}
+	},
+	"luma": func(c color.Color) color.Color {
+		r, g, b, _ := c.RGBA()
+		y := (0.2126*float64(r) + 0.7152*float64(g) + 0.0722*float64(b)) * (255.0 / 65535)
+		return color.Gray{uint8(y)}
+	},
+	"luster": func(c color.Color) color.Color {
+		r, g, b, _ := c.RGBA()
+		arr := []float64{float64(r), float64(g), float64(b)}
+		sort.Float64s(arr)
+		y := (arr[0] + arr[2]) / 2 * (255.0 / 65535)
+		return color.Gray{uint8(y)}
+	},
+}
+
+func toGray(img image.Image, algo string) *image.Gray {
+	grayImg := image.NewGray(img.Bounds())
+	algoConv, ok := AlgoGray[algo]
+	if !ok {
+		panic("wrong gray algo")
+	}
+
+	for y := img.Bounds().Min.Y; y < img.Bounds().Max.Y; y++ {
+		for x := img.Bounds().Min.X; x < img.Bounds().Max.X; x++ {
+			grayImg.Set(x, y, algoConv(img.At(x, y)))
+		}
+	}
+	return grayImg
+}
+
+func Load(reader io.ReadCloser, algo string) *image.Gray {
 	defer reader.Close()
 	img, _, err := image.Decode(reader)
 	if err != nil {
@@ -21,9 +60,7 @@ func Load(reader io.ReadCloser) *image.Gray {
 	case *image.Gray:
 		return imgt
 	default:
-		newImg := image.NewGray(img.Bounds())
-		draw.Draw(newImg, newImg.Bounds(), img, image.Point{}, draw.Src)
-		return newImg
+		return toGray(img, algo)
 	}
 }
 
@@ -120,8 +157,8 @@ func Get(img *image.Gray, quality int) []byte {
 	return b.Bytes()
 }
 
-func Convert(reader io.ReadCloser, crop bool, w, h int, quality int) ([]byte, int, int) {
-	img := Load(reader)
+func Convert(reader io.ReadCloser, crop bool, w, h int, quality int, algo string) ([]byte, int, int) {
+	img := Load(reader, algo)
 	if crop {
 		img = CropMarging(img)
 	}

main.go

@@ -7,6 +7,8 @@ import (
 	"path/filepath"
 	"strings"
 
+	imageconverter "github.com/celogeek/go-comic-converter/internal/image-converter"
+
 	"github.com/celogeek/go-comic-converter/internal/epub"
 )
 
@@ -61,6 +63,7 @@ type Option struct {
 	Title   string
 	Quality int
 	NoCrop  bool
+	Algo    string
 	LimitMb int
 }
 
@@ -88,6 +91,7 @@ Options:
     Title   : %s
     Quality : %d
     Crop    : %v
+	AlgoGray: %s
     LimitMb : %s
 `,
 		o.Input,
@@ -100,6 +104,7 @@ Options:
 		o.Title,
 		o.Quality,
 		!o.NoCrop,
+		o.Algo,
 		limitmb,
 	)
 }
@@ -114,6 +119,10 @@ func main() {
 			p.Description,
 		))
 	}
+	availableAlgo := make([]string, 0)
+	for a := range imageconverter.AlgoGray {
+		availableAlgo = append(availableAlgo, a)
+	}
 
 	opt := &Option{}
 	flag.StringVar(&opt.Input, "input", "", "Source of comic to convert: directory, cbz, zip, cbr, rar, pdf")
@@ -123,6 +132,7 @@ func main() {
 	flag.StringVar(&opt.Title, "title", "", "Title of the epub")
 	flag.IntVar(&opt.Quality, "quality", 85, "Quality of the image")
 	flag.BoolVar(&opt.NoCrop, "nocrop", false, "Disable cropping")
+	flag.StringVar(&opt.Algo, "algo", "default", fmt.Sprintf("Algo for RGB to Grayscale: %s", strings.Join(availableAlgo, ", ")))
 	flag.IntVar(&opt.LimitMb, "limitmb", 0, "Limit size of the ePub: Default nolimit (0), Minimum 20")
 	flag.Usage = func() {
 		fmt.Fprintf(os.Stderr, "Usage of %s:\n", filepath.Base(os.Args[0]))
@@ -192,6 +202,12 @@ func main() {
 		opt.Title = filepath.Base(defaultOutput[0 : len(defaultOutput)-len(ext)])
 	}
 
+	if _, ok := imageconverter.AlgoGray[opt.Algo]; !ok {
+		fmt.Fprintln(os.Stderr, "algo doesn't exists")
+		flag.Usage()
+		os.Exit(1)
+	}
+
 	fmt.Fprintln(os.Stderr, opt)
 
 	if err := epub.NewEpub(&epub.EpubOptions{
@@ -205,6 +221,7 @@ func main() {
 			ViewHeight: profile.Height,
 			Quality:    opt.Quality,
 			Crop:       !opt.NoCrop,
+			Algo:       opt.Algo,
 		},
 	}).Write(); err != nil {
 		fmt.Fprintf(os.Stderr, "Error: %v\n", err)