Exposure The definitive work on this subject is Ansel Adams' The Negative . These range potentially from pure black to pure white with an even gradation in between. The eye can detect thousands of values.
Photographic film can record several hundred.
Photographic paper can show about a hundred. Print media can show even fewer. The first question, then, is how do you get all those values from the scene represented on paper so that the eye doesn't notice what's missing. Correct Exposure Everybody wants to get a correct exposure when they take a picture. Camera companies spend gobs of money and then charge their customers gobs of money for cameras that will give them correct exposures.