[supertackyman]

I had done some thinking on this and allthough it seems like you and tamlin have worked it out i still wanna put in my 2 cents.

I seem to have stumbled upon a very easy way.
first, I opened my color pic.
then i converted it to b&w (im not sure hoe you pefer to but i simplt desaturated the image.)
lastly, I set my art history brush to erase to the first step, chose a brushtip that was about half as big as the pic and erased one side using the shift key to keep my stroke straight.

the end result.





P.S. im on 7 also