//定义肤色检测函数（可供人脸检测等研究使用）
public Bitmap SkinDetect1(Bitmap a)
{
  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;
   double r, g, Fupr,Flor,Wrg;
   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];
     if (R + G + B == 0)
     {
       r = 0;
       g = 0;
     }
     else
     {
       r = (R / (R + G + B));
       g = (G / (R + G + B));
     }
     Fupr = (1.0743 * r + 0.1452-1.3767 * r * r) ;
     Flor = (0.5601 * r + 0.1766-0.776 * r * r);
     Wrg = (r - 0.33) * (r - 0.33) + (g - 0.33) * (g - 0.33);  
     if ((R - G >= 45) && ((R > G) && (G > B)) && (Fupr > g) && (Wrg >= 0.0004))
     {
        P[0] = (byte)B;
        P[1] = (byte)G;
        P[2] = (byte)R;  
     }
     else
     {
       P[0] = 0;
       P[1] = 0;
       P[2] = 0;
     }
     pIn += 3;
     
     }
     pIn += stride - a.Width * 3;
   }
  }
  a.UnlockBits(bmpData);
  return a;
}