//定义图像线性运算函数（y=kx+v）
private static Bitmap LinearOP(Bitmap a, double k, double v)
{
  Rectangle rect = new Rectangle(0, 0, a.Width, a.Height);
  System.Drawing.Imaging.BitmapData srcData = a.LockBits(rect, System.Drawing.Imaging.ImageLockMode.ReadWrite, a.PixelFormat);
  IntPtr ptr = srcData.Scan0;
  int bytes = 0;
  bytes = srcData.Stride * a.Height;
  byte[] grayValues = new byte[bytes];
  System.Runtime.InteropServices.Marshal.Copy(ptr, grayValues, 0, bytes);
  int temp = 0;
  for (int i = 0; i < bytes; i++)
  {
   temp = (int)(k * grayValues[i] + v + 0.5);
   temp = (temp > 255) ? 255 : temp < 0 ? 0 : temp;
   grayValues[i] = (byte)temp;
  }
  System.Runtime.InteropServices.Marshal.Copy(grayValues, 0, ptr, bytes);
  a.UnlockBits(srcData);
  return a;
}