code: func (p *ycc) YCbCr() *image.YCbCr {
  	ycbcr := image.NewYCbCr(p.Rect, p.SubsampleRatio)
  	switch ycbcr.SubsampleRatio {
  	case ycbcrSubsampleRatio422:
  		return p.ycbcr422(ycbcr)
  	case ycbcrSubsampleRatio420:
  		return p.ycbcr420(ycbcr)
  	case ycbcrSubsampleRatio440:
  		return p.ycbcr440(ycbcr)
  	case ycbcrSubsampleRatio444:
  		return p.ycbcr444(ycbcr)
  	case ycbcrSubsampleRatio411:
  		return p.ycbcr411(ycbcr)
  	case ycbcrSubsampleRatio410:
  		return p.ycbcr410(ycbcr)
  	}
  	return ycbcr
  }
docs: // YCbCr converts ycc to a YCbCr image with the same subsample ratio
  // as the YCbCr image that ycc was generated from.