//定義roberts算子函數
private static Bitmap robert(Bitmap a)
{
 int w = a.Width;
 int h = a.Height;
 try
 {
  Bitmap dstBitmap = new Bitmap(w, h, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
  System.Drawing.Imaging.BitmapData srcData = a.LockBits(new Rectangle
   (0, 0, w, h), System.Drawing.Imaging.ImageLockMode.ReadOnly, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
  System.Drawing.Imaging.BitmapData dstData = dstBitmap.LockBits(new Rectangle
   (0, 0, w, h), System.Drawing.Imaging.ImageLockMode.WriteOnly, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
  unsafe
  {
   byte* pIn = (byte*)srcData.Scan0.ToPointer();
   byte* pOut = (byte*)dstData.Scan0.ToPointer();
   byte* p;
   int stride = srcData.Stride;
   for (int y = 0; y < h; y++)
   {
   for (int x = 0; x < w; x++)
   {
    //邊緣八個點像素不變
    if (x == 0 || x == w - 1 || y == 0 || y == h - 1)
    {
    pOut[0] = pIn[0];
    pOut[1] = pIn[1];
    pOut[2] = pIn[2];
    }
    else
    {
    int r0, r5, r6, r7;
    int g5, g6, g7, g0;
    int b5, b6, b7, b0;
    double vR, vG, vB;
    //右
    p = pIn + 3;
    r5 = p[2];
    g5 = p[1];
    b5 = p[0];
    //左下
    p = pIn + stride - 3;
    r6 = p[2];
    g6 = p[1];
    b6 = p[0];
    //正下
    p = pIn + stride;
    r7 = p[2];
    g7 = p[1];
    b7 = p[0];
    //中心點
    p = pIn;
    r0 = p[2];
    g0 = p[1];
    b0 = p[0];
    vR = (double)(Math .Abs (r0-r5)+Math .Abs ( r5-r7));
    vG = (double)(Math.Abs(g0 - g5) + Math.Abs(g5 - g7));
    vB = (double)(Math.Abs(b0 - b5) + Math.Abs(b5 - b7));
    if (vR > 0)
    {
     vR = Math.Min(255, vR);
    }
    else
    {
     vR = Math.Max(0, vR);
    }
    if (vG > 0)
    {
     vG = Math.Min(255, vG);
    }
    else
    {
     vG = Math.Max(0, vG);
    }
    if (vB > 0)
    {
     vB = Math.Min(255, vB);
    }
    else
    {
     vB = Math.Max(0, vB);
    }
    pOut[0] = (byte)vB;
    pOut[1] = (byte)vG;
    pOut[2] = (byte)vR;
    }
    pIn += 3;
    pOut += 3;
   }
   pIn += srcData.Stride - w * 3;
   pOut += srcData.Stride - w * 3;
   }
  }
  a.UnlockBits(srcData);
  dstBitmap.UnlockBits(dstData);
  return dstBitmap;
 }
 catch
 {
  return null;
 }
}