Save a 32-bit Bitmap as 1-bit .bmp file in C#

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

?

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

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.