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non-HDR versus HDR versions.
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High Dynamic Range (HDR) Imaging
A relatively new process has come onto the scene, called High Dynamic Range Imaging (HDRI). HDRI allows the camera to capture a large dynamic range of exposures into one image resulting in a full range of intensity levels found in real scenes. This is particularily dramatic when the scene contains both bright sunlit areas as well as deep shadows. A good description and backgrounder is available in this Wikipedia article. In addition, there are several other websites which contain galleries of what is possible with this technique. This collection of photos of Cambridge University is particularily stunning.
There are several software packages to achieve an HDR image. I use both Photomatix and easyHDR. I am very pleased with the results as have many others who have published work on the web. There are several good tutorials; see the links in the sidebar column.
Using either easyHDR or Photomatix, I have been able to have some success with both techniques supported by the software. First is the ability to combine multiple RAW, TIFF, or JPG images taken at multiple exposures into one HDR image file. This is typically done with a tripod although multiple images can be aligned in the software in case a tripod is not available. Secondly is the ability to process one image taken in RAW mode into an HDR image. The ability to post process a raw image is exploited by the software in generating the HDR image. This is effective for scenes that do not have a very wide range of exposures. I believe that if 3 shots bracketed 1 F-stop apart can cover the range of light intensities in the scene, an HDR from a single RAW image will yield acceptable results. This is also the only option possible if the subject is moving such as an action scene. The critical processing step is called tone mapping. This is a process to squeeze all of the range of intensities into the available display's capability. Again, see the Wikipedia article for a good description. There are many controls to manipulate the effect of the image as explained in the tutorials mentioned above.
The HDR technique solves many of the tough exposure challenges. The images on the right of this page are 4 examples of what HDR processing can do. First is a single image of a pond taken in the RAW format which was converted to an HDR image. The range of light intensity was such that good results could be achieved with a single image. In a similar fashion, action shots can benefit from HDR processing using 1 RAW image. The second example is a backlit scene which has a wide range of bright sun to deep shadows. The HDR image is constructed from 3 RAW images taken 2 F-stops apart. Similar results can also be obtained from 3 JPG images. The third example was constructed from 5 shots taken 1 EV apart to capture the full exposure range from bright treetops to deep shadows in the cave.
Perhaps the most dramatic results come from photographs were were simply known to be "impossible" up until now because of the wide range of light intensities in the scene. The final example is by Allan Haskell. The inside of a cathedral exhibits a wide range of shadows to very bright windows. The HDR photo is generated from 8 images 1 F-stop apart.