Thread: Hdr
View Single Post
Old Oct 11, 2007 | 01:28 PM
  #62 (permalink)  
.:Chris:.'s Avatar
.:Chris:.
Post Deleting Expert.
 
Joined: Nov 2006
Posts: 2,889
Likes: 0
Default

It seems to me like you're all missing the point of HDR. Lets start with a definition:

Dynamic range is the range of light that a camera can record in any specific scene, from light to dark. With your normal dSLR you'll get about 6 stops. To put it simply, think of it this way: your camera can only capture a certain range of light at a time. You can move that range up and down via exposure adjustment, but it won't grow or shrink. Anything OVER your range will be OVERexposed (recorded as a hex value of #FFFFFF). Anything UNDER your camera's range will be UNDERexposed (#000000).

HDR involves taking multiple exposures of the same scene at different exposure values. A typical example would be taking your base shot at the exposure value chosen by your camera's meter, taking one picture at +2EV and one picture at -2EV. In your first picture you have captured 6-stops of light, and you have captured an additional 2-stops of light in each of your other exposures (The second pic moved the range up two EV's, the third moved it down 2 EV's from the base exposure). Combining these pictures together should give you approximately 8 stops of light in your picture.

The purpose of this is not to create a surreal, oddly highlighted picture. You can use it to do that, obviously, and there's always going to be some portion of a surreal effect but that's not what it was originally intended for. The purpose is to capture detail in a scene that is not normally possible via your camera.

In this thread there are a bunch of images that have been run through the HDR process just for the sake of processing, and as a result they seem over-processed to me. Once you get over the novelty of HDR, it really doesn't serve a huge purpose for most scenes.

HDR is put to good use in scenes that have a high dynamic range. One example would be when you're taking pictures of a subject in a shadow with a portion of the scene including a sunlit background. Normally your camera will expose for the shadowed subject and blow out the background leaving you with a background that is either mostly or completely white. HDR would
bring the background back into the scene and provide some detail.

In closing, here's an example of a scene that benefits from HDR. This scene would have had too much dynamic range to capture without HDR.
(Courtesy of http://www.flickr.com/photos/rotia/547376049/)


P.S.: I'm not going to get into tone mapping or explaining why everything starts to get the halo effect. If you're interested in reading more on HDR, start with the wikipedia article: High dynamic range imaging - Wikipedia, the free encyclopedia
Reply