//定义图像反色函数
private static Bitmap PContray (Bitmap a)
{
 int w = a.Width;
 int h = a.Height;
 Bitmap dstBitmap = new Bitmap(a.Width, a.Height, 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;
  int r, g, b;
  for (int y = 0; y < h; y++)
  {
   for (int x = 0; x < w; x++)
   {
   p = pIn;
   r = p[2];
   g = p[1];
   b = p[0];
   pOut[2] = (byte)(255 - r);
   pOut[1] = (byte)(255 - g);
   pOut[0] = (byte)(255 - b);
   pIn += 3;
   pOut += 3;
   }
   pIn += srcData.Stride - w * 3;
   pOut += srcData.Stride - w * 3;
  }
  a.UnlockBits(srcData);
  dstBitmap.UnlockBits(dstData);
  return dstBitmap;
 }
}