dithering done :)

util/stdio.go

@@ -0,0 +1,14 @@
+package imageutils
+
+// ProcessImage takes input png image from stdin, processes it with f and outputs it to stdout.
+func ProcessStdio(f func(image.Image) image.Image) {
+      	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
+}