switch cb {
		case cbG8:
			if gray != nil {
				offset := (y - b.Min.Y) * gray.Stride
				copy(cr[0][1:], gray.Pix[offset:offset+b.Dx()])
			} else {
				for x := b.Min.X; x < b.Max.X; x++ {
					c := color.GrayModel.Convert(m.At(x, y)).(color.Gray)
					cr[0][i] = c.Y
					i++
				}
			}
		case cbTC8:
			// We have previously verified that the alpha value is fully opaque.
			cr0 := cr[0]

	defer w.Close()
	bounds := png.Bounds()
	cm := png.ColorModel()
	var bitdepth int
	switch cm {
	case color.RGBAModel, color.NRGBAModel, color.AlphaModel, color.GrayModel:
		bitdepth = 8
	default:
		bitdepth = 16
	}
	cpm, _ := cm.(color.Palette)
	var paletted *image.Paletted
	if cpm != nil {
		switch {
		case len(cpm) <= 2:
			bitdepth = 1

	if !(Point{x, y}.In(p.Rect)) {
		return
	}
	i := p.PixOffset(x, y)
	p.Pix[i] = color.GrayModel.Convert(c).(color.Gray).Y
}

func (p *Gray) SetRGBA64(x, y int, c color.RGBA64) {
	if !(Point{x, y}.In(p.Rect)) {
		return
	}
	// This formula is the same as in color.grayModel.
	gray := (19595*uint32(c.R) + 38470*uint32(c.G) + 7471*uint32(c.B) + 1<<15) >> 24
	i := p.PixOffset(x, y)

	var d decoder
	if _, err := d.decode(r, true); err != nil {
		return image.Config{}, err
	}
	switch d.nComp {
	case 1:
		return image.Config{
			ColorModel: color.GrayModel,
			Width:      d.width,
			Height:     d.height,
		}, nil
	case 3:
		cm := color.YCbCrModel
		if d.isRGB() {
			cm = color.RGBAModel
		}
		return image.Config{
			ColorModel: cm,

				break
			}
		} else {
			if d.stage >= dsSeenIHDR {
				break
			}
		}
	}

	var cm color.Model
	switch d.cb {
	case cbG1, cbG2, cbG4, cbG8:
		cm = color.GrayModel
	case cbGA8:
		cm = color.NRGBAModel
	case cbTC8:
		cm = color.RGBAModel
	case cbP1, cbP2, cbP4, cbP8:
		cm = d.palette
	case cbTCA8:
		cm = color.NRGBAModel
	case cbG16: