(Under Exposed) -2...-1...0...+1...+2 (Over Exposed)
|High Dynamic Range - HDR|
An HDR photo is is basically a picture that has "high dynamic range" of luminance (light) between the lightest and darkest areas of an image (you can see into the shadows). A typical HDR photo requires three or more different exposures. One exposure is under exposed (dark), one normal (typical photo), and one over exposed (too much light). These stages of photos are then combined and tone-mapped with software program e.g. Photomatix Pro (which I use). Once these images are combined and tone-mapped, you're left with the HDR image.