Tuesday, July 17, 2012

Dynamic Range, Eye vs. Display

The human eye has a much greater dynamic range than any film or digital display. By dynamic range I mean, roughly, the ability to discrimate between slighly different light values over a wide range of light values. This photograph illustrates the problem:


There's a large area at left center where we see a well-articulated image, three water towers and some other stuff (including the Empire State Building) against the sky. The surrounding area, however, is lost in dark murk. But, I assure you, I wasn't standing in the dark when I took the shot. I could see my surroundings perfectly well.

Now, a digital camera can register a greater dynamic range than any display or film can present. So it is possible rebalance the pixel values so that the foreground structure is nicely articulated:


The foreground structure is now nicely articulated, but the background appears washed out. The image is also grainy. That problem can be solved with a better camera, but the problem of the overall dynamic range is not a camera problem. It's a presentation problem. Here's a somewhat better balance:


And, if you are willing to do without color, you can realize the image in black and white, where the washed out background may not be so bothersome:


There is no way to print an image that will have a dynamic range that matches the eye's capacity. Monitors and panel displays have the same problem. The lightest light isn't as bright as the eye can register--we can, after all, look directly into lights and fires if they're not too bright--and no black can be ask dark as a room without any light at all. So, some compromise is necessary when making images, a problem Ernst Gombrich discusses in Art and Illusion. And that compromise provides room for endless tinkering, though I wouldn't recommend it.

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