Why don’t cameras automatically choose the full HDR bracketing range?
Asked 2/9/2016
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2 answers
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Some cameras offer HDR modes or exposure bracketing, but why don’t more cameras automatically determine how many bracketed shots are needed?
For example, after putting the camera on a tripod and enabling an HDR bracketing mode, the camera could take a test shot, inspect the image or histogram, then keep adding frames at +1 EV and -1 EV (using shutter speed changes only) until highlights are no longer clipped in the brightest-preserving frame and shadows are no longer clipped in the darkest-preserving frame.
This is about automating the bracket capture, not tone-mapping or merging the HDR image in-camera. Why isn’t this kind of automatic HDR bracketing common in cameras?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
10y ago
2 Answers
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Because photography is about a lot more than just proper exposure. The camera can't read your mind to see how you wish the final image to turn out.
Imagine a scene that would be properly exposed at ISO400, 1/125 second, and f/5.6. You could also expose the same scene at the same level using ISO 400, 1/1000 second, and f/2. Or ISO 400, 1/15 second, and f/16. Or ISO 100, 1/250 second, and f/16. ISO 1600, 1/8000 second, and f/1.4. Etc...
If anything in the scene is moving, or of there are elements in the scene that are closer and farther from the camera than other elements, each of these sets of settings are all going to look very different in the final result even though they are all exposed at the same level.
How does your camera know the result at which you are aiming?
Originally by user15871. Source · Licensed CC BY-SA 4.0
user15871
10y ago
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It’s possible, but camera makers usually leave it to the photographer because bracketing isn’t just a technical clipping problem.
Even if exposure could be expanded automatically by checking a histogram, the camera still doesn’t know your intent. Exposure settings affect more than brightness: shutter speed changes motion rendering, aperture changes depth of field, and ISO affects noise. Those choices are creative, not just corrective.
Also, the feature would mainly help a narrow group of users: people advanced enough to shoot HDR brackets, but not so advanced that they prefer to control the range themselves. That makes it a lower-priority feature for manufacturers compared with simpler auto modes or more broadly useful tools.
It’s also not true that this can’t be done. Some third-party firmware, such as Magic Lantern on certain Canon cameras, has offered automatic HDR bracketing based on histogram/RAW analysis, along with related features like Auto-ETTR. So the main reason it’s uncommon is likely product design and cost/benefit priorities, not technical impossibility.
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