support grayscale or color mode

grayscale is on by default
as the conversion is mainly
useful for eInk device.

internal/converter/converter.go

@@ -101,6 +101,7 @@ func (c *Converter) InitParse() {
 	c.AddSection("Config")
 	c.AddStringParam(&c.Options.Profile, "profile", c.Options.Profile, fmt.Sprintf("Profile to use: \n%s", c.Options.AvailableProfiles()))
 	c.AddIntParam(&c.Options.Quality, "quality", c.Options.Quality, "Quality of the image")
+	c.AddBoolParam(&c.Options.Grayscale, "grayscale", c.Options.Grayscale, "Grayscale image. Ideal for eInk devices.")
 	c.AddBoolParam(&c.Options.Crop, "crop", c.Options.Crop, "Crop images")
 	c.AddIntParam(&c.Options.CropRatioLeft, "crop-ratio-left", c.Options.CropRatioLeft, "Crop ratio left: ratio of pixels allow to be non blank while cutting on the left.")
 	c.AddIntParam(&c.Options.CropRatioUp, "crop-ratio-up", c.Options.CropRatioUp, "Crop ratio up: ratio of pixels allow to be non blank while cutting on the top.")

internal/converter/options/converter_options.go

@@ -23,6 +23,7 @@ type Options struct {
 	// Config
 	Profile                    string `yaml:"profile"`
 	Quality                    int    `yaml:"quality"`
+	Grayscale                  bool   `yaml:"grayscale"`
 	Crop                       bool   `yaml:"crop"`
 	CropRatioLeft              int    `yaml:"crop_ratio_left"`
 	CropRatioUp                int    `yaml:"crop_ratio_up"`
@@ -64,6 +65,7 @@ func New() *Options {
 	return &Options{
 		Profile:                    "",
 		Quality:                    85,
+		Grayscale:                  true,
 		Crop:                       true,
 		CropRatioLeft:              1,
 		CropRatioUp:                1,
@@ -174,6 +176,7 @@ func (o *Options) ShowConfig() string {
 		{"ViewRatio", fmt.Sprintf("1:%s", strings.TrimRight(fmt.Sprintf("%f", profiles.PerfectRatio), "0"))},
 		{"View", viewDesc},
 		{"Quality", o.Quality},
+		{"Grayscale", o.Grayscale},
 		{"Crop", o.Crop},
 		{"CropRatio", fmt.Sprintf("%d Left - %d Up - %d Right - %d Bottom", o.CropRatioLeft, o.CropRatioUp, o.CropRatioRight, o.CropRatioBottom)},
 		{"Brightness", o.Brightness},

internal/epub/imageprocessor/epub_image_processor.go

@@ -6,6 +6,7 @@ package epubimageprocessor
 import (
 	"fmt"
 	"image"
+	"image/draw"
 	"os"
 	"sync"
 
@@ -126,6 +127,37 @@ func (e *EPUBImageProcessor) Load() (images []*epubimage.Image, err error) {
 	return images, nil
 }
 
+func (e *EPUBImageProcessor) createImage(src image.Image, r image.Rectangle) draw.Image {
+	if e.Options.Image.GrayScale {
+		return image.NewGray(r)
+	}
+
+	switch t := src.(type) {
+	case *image.Gray:
+		return image.NewGray(r)
+	case *image.Gray16:
+		return image.NewGray16(r)
+	case *image.RGBA:
+		return image.NewRGBA(r)
+	case *image.RGBA64:
+		return image.NewRGBA64(r)
+	case *image.NRGBA:
+		return image.NewNRGBA(r)
+	case *image.NRGBA64:
+		return image.NewNRGBA64(r)
+	case *image.Alpha:
+		return image.NewAlpha(r)
+	case *image.Alpha16:
+		return image.NewAlpha16(r)
+	case *image.CMYK:
+		return image.NewCMYK(r)
+	case *image.Paletted:
+		return image.NewPaletted(r, t.Palette)
+	default:
+		return image.NewNRGBA64(r)
+	}
+}
+
 // transform image into 1 or 3 images
 // only doublepage with autosplit has 3 versions
 func (e *EPUBImageProcessor) transformImage(src image.Image, srcId int) []image.Image {
@@ -177,7 +209,7 @@ func (e *EPUBImageProcessor) transformImage(src image.Image, srcId int) []image.
 	// convert
 	{
 		g := gift.New(filters...)
-		dst := image.NewGray(g.Bounds(src.Bounds()))
+		dst := e.createImage(src, g.Bounds(src.Bounds()))
 		g.Draw(dst, src)
 		images = append(images, dst)
 	}
@@ -204,7 +236,7 @@ func (e *EPUBImageProcessor) transformImage(src image.Image, srcId int) []image.
 			epubimagefilters.CropSplitDoublePage(b),
 			epubimagefilters.Resize(e.Image.View.Width, e.Image.View.Height, gift.LanczosResampling),
 		)
-		dst := image.NewGray(g.Bounds(src.Bounds()))
+		dst := e.createImage(src, g.Bounds(src.Bounds()))
 		g.Draw(dst, src)
 		images = append(images, dst)
 	}
@@ -213,11 +245,11 @@ func (e *EPUBImageProcessor) transformImage(src image.Image, srcId int) []image.
 }
 
 // create a title page with the cover
-func (e *EPUBImageProcessor) CoverTitleData(img image.Image, title string) (*epubzip.ZipImage, error) {
+func (e *EPUBImageProcessor) CoverTitleData(src image.Image, title string) (*epubzip.ZipImage, error) {
 	// Create a blur version of the cover
 	g := gift.New(epubimagefilters.CoverTitle(title))
-	dst := image.NewGray(g.Bounds(img.Bounds()))
-	g.Draw(dst, img)
+	dst := e.createImage(src, g.Bounds(src.Bounds()))
+	g.Draw(dst, src)
 
 	return epubzip.CompressImage("OEBPS/Images/title.jpg", dst, e.Image.Quality)
 }

internal/epub/options/epub_options.go

@@ -30,6 +30,7 @@ type Image struct {
 	Manga               bool
 	HasCover            bool
 	View                *View
+	GrayScale           bool
 }
 
 type Options struct {

main.go

@@ -114,6 +114,8 @@ $ go install github.com/celogeek/go-comic-converter/v%d@%s
 		DryVerbose:                 cmd.Options.DryVerbose,
 		Quiet:                      cmd.Options.Quiet,
 		Image: &epuboptions.Image{
+			Quality:   cmd.Options.Quality,
+			GrayScale: cmd.Options.Grayscale,
 			Crop: &epuboptions.Crop{
 				Enabled: cmd.Options.Crop,
 				Left:    cmd.Options.CropRatioLeft,
@@ -121,7 +123,6 @@ $ go install github.com/celogeek/go-comic-converter/v%d@%s
 				Right:   cmd.Options.CropRatioRight,
 				Bottom:  cmd.Options.CropRatioBottom,
 			},
-			Quality:             cmd.Options.Quality,
 			Brightness:          cmd.Options.Brightness,
 			Contrast:            cmd.Options.Contrast,
 			AutoRotate:          cmd.Options.AutoRotate,