Explanation: What you are actually doing here is making the light grey pixels whiter, and the dark grey pixels blacker creating more depth to your photograph.
Let's get started!
1. Open Photoshop
2. Go to File, select Open and browse to the photo you want to edit
2. Browse for the Photo you want to edit
3. Go to the bottom of your layers palette and select the half filled circular icon. This is the adjustment layer icon. Select Levels (If you cannot locate this palette, go to Window, Layers or press F7.)
3. Select the Adjustment Layer icon and select Levels
4. The Levels wizzard will open and shows a graph of the levels of your photograph. The far right represents white, the left, black and the middle, grey. Simply drag in the white and black triangular sliders to the point where the graph gets steep. What you are actually doing here, is making the dark greys appear blacker and the lighter greys appear whiter. Unless you feel the need too, it's not necessary to adjust the middle "grey" slider. It does so automatically.
Hey presto! You're done! And the photo looks so much better than the original!