High Dynamic Range (HDR) photography, also known as High Dynamic Range Imaging (HDRI), is a way to combine multiple photographs of the same scene into a single photo that has better brightness detail. The technique can be used to produce more realistic photographs, or it can be used to produce surreal photographs which look like an artist’s painting.
Suppose we are photographing an outdoor scene. We might find that a photo captures little detail in the deep shadows, which are almost black, and has “washed out” bright areas, which are almost white. We seek to produce a better image; one that shows good detail in the lowlights, middle ranges and highlights.
The starting point for an HDR photo is a set of photos of the same scene, taken at different exposures. Any number of photos can be used, but three is quite workable. One photo is taken at normal exposure, one is underexposed so that it shows good detail in the bright areas, and one is overexposed so that it shows good detail in the dark areas. Some cameras can automatically take this bracketed set of exposures, and in many other cameras the bracketing can be set manually.
It’s important that the variation in exposure is obtained by changing the shutter speed, and not by changing the apeture, so that the photos will all have the same depth of field.
The photos are then combined using a software application such as Photomatix or Photoshop CS2.
HDR photos can be used for artistic purposes, but they also have utilitarian functions. A real estate agent, for example, can photograph the interior of a house on a sunny day without the scenery in the windows becoming washed out, or can photograph the outside of a house at dusk and also capture an attractive light coming from the indoor illumination.
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