高效取得图片数据GetImgByte，返回结果数组和像素一一对应

     // 性能最高，其数组和像素一一对应   
        public static byte[] GetImgByte(this Bitmap bmp)
        {
            BitmapData bitmapData = bmp.LockBits(new System.Drawing.Rectangle(new Point(0, 0), bmp.Size),
                ImageLockMode.ReadWrite, PixelFormat.Format24bppRgb);
            byte[] res = new byte[bitmapData.Stride * bitmapData.Height];

            IntPtr Ptr = bitmapData.Scan0;
            System.Runtime.InteropServices.Marshal.Copy(Ptr, res, 0, res.Length);

            bmp.UnlockBits(bitmapData);
            return res;
        }