Movie Making Manual/Cinematography/Cameras and Formats/Human Visual System

=Human Visual System=

Yes, this article is a bit tongue-in-cheek! Of course it's not possible to produce a concrete list of "specifications" for the human visual system because it functions in such a fundamentally different way to a man-made-camera. Oh, and there's the small issue that we didn't design the eye. If we're being completely honest then we have to admit that our understanding of the human visual system is patchy. That said, it is useful and interesting to compare the human eye to man-made cameras. Not least because an important aim of photography and cinematography is to exploit and mimic the various eccentricities of the human visual system.

Dynamic Range
At any given instant, the retina can resolve a contrast ratio of around 100:1 (about 6 1/2 stops). As soon as your eye moves (saccades) it re-adjusts its exposure both chemically and by adjusting the iris. This is like having a camera on auto exposure. Hence, over time, you can resolve a contrast ratio of about 1,000,000:1 (about 20 stops).

The challenge for photographic systems is to display far more than the eye can instantaneously resolve, so that we can "read" a scene.

Typically a screen-projected image (film, DLP, whatever) won't ever have a brightness range of more than 1,000:1 and often less. If you make brighter highlights then scattered light from those areas of the screen will light up the shadows. This is where curve shaping (the S shape of film stocks etc) comes in to pack more original scene brightness in at each end of the range without apparently reducing the contrast of the mid-tones.

WikiPedia Articles

 * Human Eye