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