1) Student has answered yr question with lots of technicality. In short, its known as push processing.Originally Posted by user12343
2) er... it depends on how much underexposed. in B & W, i managed to print with 2 stops either over or underexposed but image turn out flat, as in low contrast. 1 stop difference not so bad. as for color, very small margin. 1 shop difference n the pic's flat. with some adjustments, it can still look properly exposed but image quality will definately drop.