There's a tool in Photoshop that allows you to change how many tones the image has. Unfortunately I don't remember what it's called.
Hi there, I'm not sure if this is it, I played around with these setting and got similar stuff.
In the menu bar go:
greyscale (you can choose 8 bit or 16 bit)
Then in mode again choose BITMAP
Then in the method box choose - Halftone screen
On pressing OK It will give you halftone screen settings. play around with these and you will get a similar effect. I think.
I'm trying to think... but nothing happens.