Start with your texture

Desaturate as usual

Now go edit and select

That brings up this box.

Change the mode to color and do nothing with the opacity, it’s fine right there.

Now bring up the levels dialogue menu.

Now for fun with the sliders.

Start with 1 (I just don’t remember the proper names for the sliders) move it just to where the histogram begins. Next bring 2 just to the right of where it starts on the left.

The center slider moves to the left or right (left mostly I find) until you are satisfied with the results.

The top bump map is just desaturated. The lower one has been processed using this tut.

Hope this helps with your texturing as much as it did mine.