Do modern cameras use advanced auto-exposure beyond simple average metering?
Asked 1/16/2020
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Are current camera auto-exposure systems just based on averaging scene brightness, or do modern cameras use more advanced scene analysis? I’m curious whether today’s metering can recognize situations like a dark subject against a bright background or a very bright scene such as snow, without relying on the user to pick a scene mode. In other words, do cameras use multi-zone analysis or learned exposure patterns rather than only a simple average?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
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are all current autoexposure algorithms really so basic as to just measure the average brightness of the scene?
No.
Do any cameras have advanced auto-exposure algorithms?
Yes.
It would seem that one could get much better results using for example some machine learning system that is trained with real, well exposed photos. It could then more accurately estimate the correct exposure from the preview image, even for the black cat in a coal mine and the white dog on the snow.
Most cameras have multiple metering modes:
Spot – The brightness of a small portion of the image is used to calculate exposure.
Average – The brightness of the entire scene is averaged and used to calculated exposure.
Center-weighted average – The brightness of the entire scene is averaged, but the center is given more weight.
Matrix / Evaluative / etc – This is the mode that attempts to do what you describe. The scene is divided into multiple parts. The brightness of each part is evaluated. The result is used to search a database or fed into an algorithm to determine exposure.
I'm not aware of any camera that currently does so, but matrix data could easily be fed into a neural network. That would allow a camera to learn its owner's exposure preferences. This is the type of tech Google uses to identify cats in YouTube videos.
Originally by user75526. Source · Licensed CC BY-SA 4.0
user75526
6y ago
0
Generated from our catalog & community — verify before relying on it.
Yes. Modern cameras generally do much more than simple average metering. Most offer several metering modes, such as spot, center-weighted, and multi-segment/evaluative/matrix metering. In their more advanced modes, cameras analyze brightness across many areas of the frame and may compare the pattern to built-in scene assumptions developed over many years.
This kind of scene recognition has existed in increasingly sophisticated forms since the film era, and modern digital cameras can also combine it with other image processing decisions. But exposure automation still has limits: the camera cannot know exactly which part of the scene you most want exposed correctly. A snowy scene, backlit subject, or very dark subject can all be interpreted differently depending on your intent.
So the answer is yes—many cameras already use advanced auto-exposure algorithms—but no auto mode can fully replace photographer judgment. Metering mode choice and exposure compensation are still often needed.
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