public void Test()
        {
            Console.WriteLine("--- BinaryPayload ---");
            var sw = new System.Diagnostics.Stopwatch();

            // 画像の平均輝度を取得(C#)
            sw.Restart();
            double csy = ImagePath.GetAverageY();

            Console.WriteLine($"C#  AverageY={csy:f2}  {sw.Elapsed} sec");

            // 画像の平均輝度を取得(PInvoke)
            sw.Restart();
            double cppy;

            using (var bitmap = new Bitmap(ImagePath))
            {
                var rect       = new Rectangle(0, 0, bitmap.Width, bitmap.Height);
                var bitmapData = bitmap.LockBits(rect, ImageLockMode.ReadOnly, bitmap.PixelFormat);
                try
                {
                    var payload = new ImagePayload(bitmap, bitmapData);
                    cppy = GetImageAllY(payload);
                }
                finally { bitmap.UnlockBits(bitmapData); }
            }
            Console.WriteLine($"C++ AverageY={cppy:f2}  {sw.Elapsed} sec");
        }
 private extern static double GetImageAllY(ImagePayload imagePayload);