What is the easiest way to convert and save a 32-bit Bitmap to a 1-bit (black/white) .bmp file in C#?

This code will get the job done

using System.Drawing.Imaging;using System.Runtime.InteropServices;...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);  byte[] scan = new byte[(w + 7) / 8];  for (int y = 0; y < h; y++) {    for (int x = 0; x < w; x++) {      if (x % 8 == 0) scan[x / 8] = 0;      Color c = img.GetPixel(x, y);      if (c.GetBrightness() >= 0.5) scan[x / 8] |= (byte)(0x80 >> (x % 8));    }    Marshal.Copy(scan, 0, (IntPtr)((long)data.Scan0 + data.Stride * y), scan.Length);  }  bmp.UnlockBits(data);  return bmp;}

　　

You can speed it up, if necessary, by using unsafe code to replace the GetPixel() method.