High Pass FIlter

http://strobist.blogspot.com/2010/02/after-light-high-pass-post-production.html

  

With Hi Pass

A good review by Stobist of the High Pass Filter in Photoshop to add pop and mid range contrast to your photos. After making a background copy, you will find this filter under filter; Other; High Pass.  I use overlay or soft light (instead of hard light) to merge these layers and then adjust the opacity for the effect I want.