一种图象二值化的算法（C#）

源代码：
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;

namespace Nobugz {
  static class Util {
    public static Bitmap BitmapTo1Bpp(Bitmap img) {
      int w = img.Width;
      int h = img.Height;
      Bitmap bmp = new Bitmap(w, h, PixelFormat.Format1bppIndexed);
      BitmapData data = bmp.LockBits(new Rectangle(0, 0, w, h), ImageLockMode.ReadWrite, PixelFormat.Format1bppIndexed);
      for (int y = 0; y < h; y++) {
        byte[] scan = new byte[(w + 7) / 8];
        for (int x = 0; x < w; x++) {
          Color c = img.GetPixel(x, y);
          if (c.GetBrightness() >= 0.5) scan[x / 8] |= (byte)(0x80 >> (x % 8));
        }
        Marshal.Copy(scan, 0, (IntPtr)((int)data.Scan0 + data.Stride * y), scan.Length);
      }
      return bmp;
    }
  }
}
调用方法：
Bitmap bmp = Nobugz.Util.BitmapTo1Bpp(new Bitmap(@"c:\temp\test1.bmp"));
bmp.Save(@"c:\temp\test.bmp", System.Drawing.Imaging.ImageFormat.Bmp);
说明：
A few remarks with this code.  Sadly, I couldn't avoid the pointer arithmetic in the Marshal.Copy() call, the code is not going to work in 64-bit apps.  And it is not going to be terribly fast, Bitmap.GetPixel() is slow.  Hope it works for you.