如何使用asp.net实现上传图片时判断图片的模式GRB或CMYK？

Bitmap bmp = new Bitmap(allow_fileStream); //文件路径
allowUpload = stringHelper.IsCMYK(bmp) == "true" ? false : true; //返回true字符串则图片不是RGB模式的
public string IsCMYK(System.Drawing.Image img)
{
  string isCmyk;
  if ((GetImageFlags(img).IndexOf("Ycck") > -1) || (GetImageFlags(img).IndexOf("Cmyk") > -1))
  {
   isCmyk = "true";
  }
  else
  {
   isCmyk = "false";
  }
  return isCmyk;
}
public string GetImageFlags(System.Drawing.Image img)
{
  ImageFlags FlagVals = (ImageFlags)Enum.Parse(typeof(ImageFlags), img.Flags.ToString());
  return FlagVals.ToString();
}