+ Just stumbled upon this great photoshop tutorial, which gives you a detailed insight on using Levels tool in Photoshop for enhancing lighting in any digital images. This is a very handy tutorial for photographers / image editing professional and can be used with other image editing programs. Basically the levels tool can move and stretch brightness levels in a histogram using three main components: a black point, white point and mid-tone slider. The position of the black and white point sliders redefine the histogram's "Input Levels", so they are mapped to the "Output Levels" (default is black (0) or white (255), respectively), whereas the mid-tone slider redefines the location of middle gray (128).
Using "Levels" in Photoshop - Tutorial Link
