Black (0,0,0) is "neutral".  If you think of black as 0, then positive values (+1 max) create raised detail (bas-relief);  negative values (-1 min) engrave.

I often use a map with grey (127,127,127) as the neutral;  multiply it by two, then subtract one, and you have a range from -1 to +1.  With a single map, some areas will be engraved, while others are raised, and after manipulation the map background is 0 (black), so you don't get the "exploded diagram" effect as Geep warns about in his tutorial.

Gimme a little time and I'll post screenshots.

Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5