Using a free Photoshop Action from Inkjetgoodies
You can download it at http://inkjetgoodies.com/main/psactions.htm

It is a combination of several techniques and does the following:

1. Create New Hue/Saturation Adjustment Layer with the
   following properties:
   Mode: Saturation
   Hue: -180
   Saturation: -100
   Lightness: +100
2. Convert LAB Color. Choose the Flatten Option if given.
3. Open the Channels Window and delete Channels 'A' and 'B'
4. Convert to Grayscale.