public static Bitmap ChangeGray(Bitmap b)  {   BitmapData bmData = b.LockBits(new Rectangle(0, 0, b.Width, b.Height), ImageLockMode.ReadWrite,    PixelFormat.Format24bppRgb);   int stride = bmData.Stride;   // 掃描的寬度       unsafe   {    byte* p = (byte*)bmData.Scan0.ToPointer(); // 獲取圖像首地址    int nOffset = stride - b.Width * 3;  // 實際寬度與系統寬度的距離    byte red, green, blue;    for (int y = 0; y < b.Height; ++y)    {     for (int x = 0; x < b.Width; ++x)     {      blue = p[0];      green = p[1];      red = p[2];        p[0] = p[1] = p[2] = (byte)(.299 * red + .587 * green + .114 * blue); // 轉換公式      p += 3;  // 跳過3個字節處理下個像素點     }     p += nOffset; // 加上間隔    }   }   b.UnlockBits(bmData); // 解鎖   return b;  }