How are camera dynamic range EV figures measured, and what does a 12 EV vs 14 EV rating mean?

Question

I often see dynamic range quoted in EV/stops, but the numbers don’t seem consistent between manufacturers and review sites. For example, some medium-format makers quote around 12–14 EV, while some 35mm camera specs appear much lower, yet DxO reports similar values for both formats.

What are these different dynamic range numbers actually measuring? Are they based on the full range between sensor saturation and the point where any detail is buried in noise, or on some stricter definition of ‘usable’ image data?

In practical terms, if a scene spans about 12 EV from brightest highlight to darkest shadow, would a camera rated at 12 EV let me recover meaningful detail across that whole range? And compared with a camera rated at 14 EV, what real-world difference should I expect?

user1375 · Accepted Answer

The problem is dynamic range is subjective, seeing as the definition of dynamic range (at least in terms of sensors) is the difference between the brightest and darkest details the sensor can record.

The brightest value a sensor can record is easily found by looking at what point the sensor photosites become saturated and thus can't record any extra information. Dynamic range then ultimately comes down to what point all discernible detail is lost to noise.

The benchmarking site DXO-mark defines dynamic range as the difference between saturation of the photosites and the point at which the signal to noise ratio hits 1:1, that is where the signal and noise are equal. It's questionable whether any real detail is visible when the SNR is this bad, however it's a convenient figure to use and easy to measure. You can read about their definitions and test procedure here:

http://www.dxomark.com/index.php/en/Learn-more/DxOMark-database/Measurements/Noise

DPreview also measure DR in a similar way by finding the saturation point and then darkening the image until the noise reaches a certain level, but despite devoting an entire page on the subject, they don't mention what noise figure they consider to be the limit of the dynamic range!

http://www.dpreview.com/news/0011/00111608dynamicrange.asp

Given their DR scores are lower than DXO-mark I assume they are a little stricture and adopt a lower signal to noise threshold. As for the 5-6 EV DR stated for 35mm bodies, that figure will most likely be a qualitative assessment by photographers with a more conservative view on what is an acceptable level of detail. The marginal amount of shadow detail that is detectable by a computer program is unlikely to be categorized as "usable" by photographers. However when benchmarking many sensors you have to have a quantitative measure of at what light level detail is lost so the signal to noise ratio is used.

While we're on the subject of dynamic range it's worth pointing out that the [measured] dynamic range of a sensor in good light will be greater than the dynamic range in poor light. This is simply a result of the fact DR is determined by shadow noise, as noise increases DR decreases.

There are however multiple sources of noise, in good light noise in the shadows is mostly due to the electronics, whereas in poor light noise mostly originates from the discrete nature of light (so called photon noise). Small sensor compact cameras with good electronics will thus have a very respectable dynamic range in good light. It's only when light levels fall that the ability of large sensors to capture more photons that gives them an edge when it comes to DR.

How are camera dynamic range EV figures measured, and what does a 12 EV vs 14 EV rating mean?

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