grayscale converter example

pkg/grayscale/main.go

@@ -0,0 +1,41 @@
+package main
+
+import (
+	"image"
+	"image/color"
+	"image/png"
+	"os"
+)
+
+// processImage takes input png image from stdin, processes it with f and outputs it to stdout.
+func processImage(f func(image.Image) image.Image) error {
+	img, err := png.Decode(os.Stdin)
+	if err != nil {
+		return err
+	}
+	err = png.Encode(os.Stdout, f(img))
+	if err != nil {
+		return err
+	}
+	return err
+}
+
+type convert struct {
+	image.Image
+	color.Model
+}
+
+func (c convert) ColorModel() color.Model { return c.Model }
+func (c convert) Bounds() image.Rectangle { return c.Image.Bounds() }
+func (c convert) At(x, y int) color.Color { return c.Model.Convert(c.Image.At(x, y)) }
+
+func grayscale(img image.Image) image.Image {
+	return convert{img, color.GrayModel}
+}
+
+func main() {
+	err := processImage(grayscale)
+	if err != nil {
+		panic(err)
+	}
+}