C#图像灰度级拉伸的方法

//定义图像灰度拉伸函数private static Bitmap GrayLP (Bitmap a){  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;  if (a.PixelFormat == System.Drawing.Imaging.PixelFormat.Format8bppIndexed)  { bytes = a.Width * a.Height; }  else { bytes = a.Width * a.Height * 3; }  byte[] grayValues = new byte[bytes];  System.Runtime.InteropServices.Marshal.Copy(ptr, grayValues, 0, bytes);  byte n = 255, m = 0;  double p;  //计算最大和最小灰度级  for (int i = 0; i < bytes; i++)  {   //计算最小灰度级   if (n > grayValues[i])   {     n = grayValues[i];   }           //计算最大灰度级   if (m < grayValues[i])   {     m = grayValues[i];   }  }  //得到斜率  p = 255.0 / (m - n);  //灰度拉伸  for (int i = 0; i < bytes; i++)  {   grayValues[i] = (byte)(p * (grayValues[i] - n) + 0.5);  }  System.Runtime.InteropServices.Marshal.Copy(grayValues, 0, ptr, bytes);  a.UnlockBits(srcData);  return a;}