save bitmap image as grayscale image in C#
<p>This is my bitmap code</p>

<pre><code>Bitmap b = new Bitmap(columns, rows, PixelFormat.Format24bppRgb);
BitmapData bmd = b.LockBits(new Rectangle(0, 0, columns, rows), ImageLockMode.ReadWrite, b.PixelFormat); 
</code></pre>

<p>How can i save this as a grayscale image ?</p>

<p>Well iam specifically interested in the saving part. How do i save it as a file ?</p>
