In a nutshell, gamma correction is about having contrast in an image. That's not everything to know about gamma correction, but it's essentially the desired result. There should be a deep black in an image and a bright white in an image (if the image has a black and a white). A typical Poser render tends to not have either and the end result is a murky look to an image that lacks the kind of crispness that it should have.

It's something that can either be corrected in Poser to a degree or through a photoediting program. My preference is the latter because there are more controls that allow the correction to be made in real time and allows a great deal more experimentation. Doing it in Poser is a global render. If that doesn't look right, something has to be tweaked and rendered again in a non-real time process.

My visual indexes of Poser content are at http://www.sharecg.com/pf/rgagnon