sepia, general filter function

blend.go

@@ -159,6 +159,42 @@ func grayscale(pixel color.Color) color.Color {
 	}
 }
 
+// sepia toning filter
+func sepia(pixel color.Color) color.Color {
+	c := color.RGBAModel.Convert(pixel).(color.RGBA)
+
+	var npr uint8
+	var npg uint8
+	var npb uint8
+
+	tr := float64(c.R)*0.393 + float64(c.G)*0.769 + float64(c.B)*0.189
+	tg := float64(c.R)*0.349 + float64(c.G)*0.686 + float64(c.B)*0.168
+	tb := float64(c.R)*0.272 + float64(c.G)*0.534 + float64(c.B)*0.131
+
+	npr = uint8(math.Min(255, tr))
+	npg = uint8(math.Min(255, tg))
+	npb = uint8(math.Min(255, tb))
+
+	return color.RGBA{
+		R: npr,
+		G: npg,
+		B: npb,
+		A: c.A,
+	}
+}
+
+// if a filter is specified, apply it to the pixel, if not returns it unchanged
+func filter(pixel color.Color) color.Color {
+	if ConfigRegister.Grayscale {
+		return grayscale(pixel)
+	}
+
+	if ConfigRegister.Sepia {
+		return sepia(pixel)
+	}
+	return pixel
+}
+
 func darken(fc uint8, bc uint8, fa uint8) float64 {
 	return math.Min(float64(fc), float64(bc))
 }
@@ -199,10 +235,7 @@ func blendColor(color1 color.Color, color2 color.Color) color.Color {
 	new := color.RGBA{
 		R: r, G: g, B: b, A: a,
 	}
-	if ConfigRegister.Grayscale == true {
-		return grayscale(new)
-	}
-	return new
+	return filter(new)
 }
 
 // creates a new rectangle with the min height and width from both images

config.go

@@ -18,6 +18,7 @@ type Config struct {
 	OutputWidth  int    `json:output_width`
 	OutputHeight int    `json:output_height`
 	Grayscale    bool
+	Sepia        bool
 	Amount       int
 	Quiet        bool
 }
@@ -53,6 +54,7 @@ func initConfigRegister() {
 	flag.StringVar(&ConfigRegister.BaseImage, "base-img", "", "Path to the base image to work with. Random image if not set")
 	flag.StringVar(&ConfigRegister.Dimensions, "dimensions", "1280x1024", "Out image dimensions. <width>x<height>")
 	flag.BoolVar(&ConfigRegister.Grayscale, "grayscale", false, "Output image in shade of gray (around 50)")
+	flag.BoolVar(&ConfigRegister.Sepia, "sepia", false, "Output image with sepia tone")
 	flag.IntVar(&ConfigRegister.Amount, "amount", 2, "Number of images to blend together")
 	flag.BoolVar(&ConfigRegister.Quiet, "quiet", false, "No progress messages")
 	flag.Parse()