add functions for color models and colors based on depth in utils package

utils/depth.go

@@ -0,0 +1,36 @@
+package utils
+
+import "image/color"
+
+func ColorModel(depth int) color.Model {
+	switch depth {
+	case 8:
+		return color.GrayModel
+	case 24, 32:
+		return color.RGBAModel
+	default:
+		return color.Gray16Model
+	}
+}
+
+func WhiteColor(depth int) color.Color {
+	switch depth {
+	case 8:
+		return color.Gray{Y: 255}
+	case 24, 32:
+		return color.RGBA{255, 255, 255, 255}
+	default:
+		return color.White
+	}
+}
+
+func BlackColor(depth int) color.Color {
+	switch depth {
+	case 8:
+		return color.Gray{Y: 0}
+	case 24, 32:
+		return color.RGBA{0, 0, 0, 255}
+	default:
+		return color.Black
+	}
+}