//定義sobel算子函數(shù)
private static Bitmap sobel(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, r1, r2, r3, r4, r5, r6, r7, r8;
    int g1, g2, g3, g4, g5, g6, g7, g8, g0;
    int b1, b2, b3, b4, b5, b6, b7, b8, b0;
    double vR, vG, vB;
    //左上
    p = pIn - stride - 3;
    r1 = p[2];
    g1 = p[1];
    b1 = p[0];
    //正上
    p = pIn - stride;
    r2 = p[2];
    g2 = p[1];
    b2 = p[0];
    //右上
    p = pIn - stride + 3;
    r3 = p[2];
    g3 = p[1];
    b3 = p[0];
    //左
    p = pIn - 3;
    r4 = p[2];
    g4 = p[1];
    b4 = p[0];
    //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];
    // 右下 
    p = pIn + stride + 3;
    r8 = p[2];
    g8 = p[1];
    b8 = p[0];
    //中心點
    p = pIn;
    r0 = p[2];
    g0 = p[1];
    b0 = p[0];
    //使用模板
    vR = (double)(Math .Abs (r1+2*r4+r6-r3-2*r5-r8)+Math .Abs (r1+2*r2+r3-r6-2*r7-r8));
    vG = (double)(Math .Abs (g1+2*g4+g6-g3-2*g5-g8)+Math .Abs (g1+2*g2+g3-g6-2*g7-g8));
    vB = (double)(Math .Abs (b1+2*b4+b6-b3-2*b5-b8)+Math .Abs (b1+2*b2+b3-b6-2*b7-b8));
    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;
 }
}