bw.close()   // flush to e.w
}

// Options are the encoding parameters.
type Options struct {
	// NumColors is the maximum number of colors used in the image.
	// It ranges from 1 to 256.
	NumColors int

	// Quantizer is used to produce a palette with size NumColors.
	// palette.Plan9 is used in place of a nil Quantizer.
	Quantizer draw.Quantizer

	if err != nil {
		t.Fatal(err)
	}
	img, err := Decode(bytes.NewReader(data))
	if err != nil {
		t.Fatal(err)
	}
	err = Encode(io.Discard, img, &Options{NumColors: 1})
	if err != nil {
		t.Fatal(err)
	}