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

	}
}

func (s *StackSet) assignColors() {
	// Assign different color indices to different packages.
	const numColors = 1048576
	for i, src := range s.Sources {
		pkg := packageName(src.FullName)
		h := sha256.Sum256([]byte(pkg))
		index := binary.LittleEndian.Uint32(h[:])
		s.Sources[i].Color = int(index % numColors)
	}

	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)
	}

		{"GIF.Delay", Field, 0},
		{"GIF.Disposal", Field, 5},
		{"GIF.Image", Field, 0},
		{"GIF.LoopCount", Field, 0},
		{"Options", Type, 2},
		{"Options.Drawer", Field, 2},
		{"Options.NumColors", Field, 2},
		{"Options.Quantizer", Field, 2},
	},
	"image/jpeg": {
		{"(FormatError).Error", Method, 0},
		{"(UnsupportedError).Error", Method, 0},
		{"Decode", Func, 0},
		{"DecodeConfig", Func, 0},