internal/png/stdlibwriter.go
func Encode(w io.Writer, m image.Image) error {
	var e Encoder
	return e.Encode(w, m)
}
func Encode(w io.Writer, m image.Image) error {
	var e Encoder
	return e.Encode(w, m)
}
// Encode writes the Image m to w in PNG format. Any Image may be
// encoded, but images that are not image.NRGBA might be encoded lossily.