//木刻效果
public Bitmap PFilterMuKe(Bitmap src)
{
 try
 {
  Bitmap a = new Bitmap(src);
  Rectangle rect = new Rectangle(0, 0, a.Width, a.Height);
  System.Drawing.Imaging.BitmapData bmpData = a.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, System.Drawing.Imaging.PixelFormat.Format24bppRgb);
  int stride = bmpData.Stride;
  unsafe
  {
   byte* pIn = (byte*)bmpData.Scan0.ToPointer();
   byte* P;
   int R, G, B;
   int temp = 0;
   for (int y = 0; y < a.Height; y++)
   {
   for (int x = 0; x < a.Width; x++)
   {
    P = pIn;
    B = P[0];
    G = P[1];
    R = P[2];
    temp = (byte)((B + G + R) / 3);
    if (temp >= 122.5)
    {
    P[2] = 0;
    P[1] = 0;
    P[0] = 0;
    }
    else
    {
    P[2] = (byte)255;
    P[1] = (byte)255;
    P[0] = (byte)255;
    }
    pIn += 3;
   }
   pIn += stride - a.Width * 3;
   }
  }
  a.UnlockBits(bmpData);
  return a;
 }
 catch (Exception e)
 {
  MessageBox.Show(e.Message.ToString());
  return null;
 }
}