grayscale option

blend.go

@@ -118,10 +118,10 @@ func encodeImage(imgData *image.RGBA) {
 	log.Println("Done.")
 }
 
-// convert RGBA pixel to grayscale
+// convert RGBA pixel to grayscale. BT.709 luminosity formula
 func grayscale(pixel color.Color) color.Color {
 	c := color.RGBAModel.Convert(pixel).(color.RGBA)
-	gray := uint8((c.R + c.G + c.B) / 3)
+	gray := uint8(0.2126*float64(c.R) + 0.7152*float64(c.G) + 0.0722*float64(c.B))
 	return color.RGBA{
 		R: gray,
 		G: gray,
@@ -167,9 +167,13 @@ func blendColor(color1 color.Color, color2 color.Color) color.Color {
 	g := uint8(blend(oc1.G, oc2.G, oc1.A, oc2.A))
 	b := uint8(blend(oc1.B, oc2.B, oc1.A, oc2.A))
 	a := oc1.A + (1-oc1.A)*oc2.A
-	return color.RGBA{
+	new := color.RGBA{
 		R: r, G: g, B: b, A: a,
 	}
+	if ConfigRegister.Grayscale == true {
+		return grayscale(new)
+	}
+	return new
 }
 
 // creates a new rectangle with the min height and width from both images

config.go

@@ -16,6 +16,7 @@ type Config struct {
 	Dimensions   string `json:dimensions`
 	OutputWidth  int    `json:output_width`
 	OutputHeight int    `json:output_height`
+	Grayscale    bool
 }
 
 // loads configuration values from json file

main.go

@@ -14,6 +14,7 @@ func main() {
 	flag.StringVar(&ConfigRegister.InputDir, "input", "/home/gator/Photos", "Input directory. Where to look the images from")
 	flag.StringVar(&ConfigRegister.BaseImage, "base-img", "", "Path to the base image to work with. Random image if not set")
 	flag.StringVar(&ConfigRegister.Dimensions, "dimensions", "800x600", "Out image dimensions. <width>x<height>")
+	flag.BoolVar(&ConfigRegister.Grayscale, "grayscale", false, "Output image in shade of gray (around 50)")
 	flag.Parse()
 
 	// set output's width and height