To produce a HDE image aof a scene with an excessively high luminance range you udst capture a number of 8 or 16 bpc (bits per channel) images using different exposures, and merge them into a single DHR 32 bpc image. The number of images required will depend on the lumanance range of the scene.
A 32 bpc HDR image file contains far too many tones to be viewed on a monitor or sent to a printer. It is only possile to view a small range of tones at a time. Tone Mapping is a process of controlling how the extended range of tones in a 32 bpc HDR image file are compressed and manipulated to produce a conventional 8 or 16 bpc image, which can be viewed or printed.
(Above was taken from the Technology 3 handout High Dynamic Range Imagery)
My Canon EOS 5D Mark II as do most Canon SLR camera have Auto Exposure Bracketing (AEB) settings that allows the camera to automatically bracket exposure up to ± 2 stops in 1/3 stop increments for three successive shots. In addition to the exposure bracketing, the user can set the exposure compensation so the bracketting can be shifted to the ± 4 stop exposure but still only bracket within 2 stops.
(Canon Inc. 2009, Canon EOS 5D Mark II Instruction Manual, pg 97)
I have seen discussions on various web forums about the number of shots that are needed to producing HDR and there seems to be differing opinions if 3 are sufficient or more should be used due to the dynamic range of the scene. Those wanting to expose more than 3 images complain about the Canon's ability to shoot only a 3 shot bracket. There does appear to be a relatively easy work around as follows.
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Ridiculous. AEB can also be used very easily for bracketing for HDR. Manually adjusting each exposure can certainly be done, but increases the chances of movement between frames.Even with Canon's 3-exposure AEB limit, I can bracket 9 to 12 shots extremely rapidly -- much, MUCH faster than I could manually shot-by-shot. For shots that include the sky (in which the clouds are ALWAYS moving), this can mean the difference between virtually unnoticeable ghosting in the clouds and an unusable final image.
Getting more than 3 shots isn't really all that complicated. Your exposure meter in your viewfinder shows you where all three brackets are placed. I use 1-stop brackets most of the time (because I found that with the software I use, the smaller gap between exposures produces better results).Meter your shot as you would for a single exposure. If you normally "expose to the right," ignore that and meter for "0" in your viewfinder for HDR work. Set your camera to bracket 3 shots. Set your dial to jump in 1-stop increments. Dial your exposure until the longest exposure of your bracket (the notch on the left) is two stops above "0" (to the right) of your meter. Take three shots. Dial back to put your center notch at "0." Take three shots. Dial back to put the shortest exposure (the notch on the right) two stops below (to the left) of "0."
9 exposures, from -4 to +4, in 1-stop increments. That will give you a pretty good range for most scenes and just adjust how many brackets you need accordingly.
With a little practice, you can take a 9-bracket set like this without losing much more time than someone shooting a camera capable of more bracketed shots.
If you choose to bracket at something different than 1-stop increments, you may have to adjust your math a bit to determine how far to dial for your starting bracket, but the basic concept remains the same.
(Flickr 2012. flickr canon photography/ discuss group AEB setting. (Using the Auto Exposure Bracket), viewed 18 March 2012 <http://www.flickr.com/groups/canon_photography/discuss/72157627494534787/ viewed 19 March 2012>
