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My name is Elefterios and I am studying photography and audiovisuals. Currently I'm on my last year doing my thesis project related to timelapse. On the HDR Timelapse chapter I'm writing a short introduction explaining dynamic range.

As funny as it sounds I've been really confused when it comes to dynamic range measured in EV, or dynamic range stops, that a sensor can capture and I can't find an easy and simple explainable answer online.

So I'll try and make my question as clear as possible.

So basically I want to understand: what do these numbers really mean? For example in a single frame, 13 stops of dynamic range means 13 stops inside the light meter of the camera? If that's the case I think in reality that's way too much. It's like saying that from 1 second of exposure I go all way up to 1/8000 of a second with my Canon 5D Mark III to be able to get an image with 13 stops of dynamic range.

At least that's what I understand with the term "13 stops of dynamic range".

When I shoot an HDR image of -3, 0, +3 exposure values, what is the dynamic range of that image? Because if my saying above is correct then an HDR image of -3, 0, +3 has a dynamic range of 6 stops.

  • How did you arrive at the conclusion that -3, 0, +3 leads to 6 stops total? – null Apr 10 '16 at 16:43
  • let's say I have a value of 1/125 as 0. If i move all the way to -3 my under exposure image will be 1/1000. From 0 if I move to +3 my exposure will be 1/15. So from 1/1000 all the way up to 1/15 thats a total of 6 stops. Atleast that's how I understand it. – Elefterios H Apr 10 '16 at 17:04
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Yes, the stops are the same measurement, but you are misunderstanding what is meant by dynamic range. Dynamic range is not the same as an exposure setting.

Dynamic range is everything from black to white (i.e., the points at which you lose detail into black and white) that your camera can capture. So, if you have to think of it in exposure terms, if you take a picture that encompasses black and white, and if you were to expose the black so it appeared as middle gray, and then exposed the white so it appeared as middle gray, the difference in your exposures would be whatever the sensor's dynamic range is. That's why the difference is so large. Think in terms of the ends of your histogram, not the middle.

In terms of how -3, 0, +3 is only 6EV, well, it's a 6EV variance, but of the entire dynamic range. So, if say, you have a sensor with 12EV DR, you've taken that 12EV and shifted it a total of 6EV, so you've got 18EV of dynamic range possible in your HDR image. But it really depends on the scene you're shooting as to whether or not you actually used all of that range. Simply shifting exposure by a set amount in both directions is no guarantee you've covered the entire dynamic range of the scene. Or that your scene requires any bracketing at all to cover its dynamic range. Not all scenes have a dynamic range outside the capabilities of the sensor.

This is why some HDR folks will use the histogram to make sure they need to bracket, as well as to see that they've covered the data to extinction at both ends. And why the MagicLantern HDR nuts have found a way to automate this. :)

See also: Cambridge in Colour's "Understanding Dynamic Range" article.

  • Thank you for your response. So, the dynamic range of an image taken with bracketing (-3, 0, +3) depends on the cameras sensor dynamic range? For example if the cameras dynamic range is 10 I add 6 which gives me an image of 16 stops of dynamic range? But still thats not an accurate result because it all ends up whether or not the scene requires that amount of dynamic range to capture? So basically we can't specify the dynamic range of an HDR image just by looking at the exposure values. You first need to see the histogram, check and make sure the scene requires that amount of expos. difference – Elefterios H Apr 10 '16 at 17:47
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    @ElefteriosH yes, that's pretty much it. BTW, since this is SE, not a messageboard, comments are more like footnotes, not for discussion (that's what chat is for). You may want to take time to read the Tour, and learn how to accept and vote up when you get enough rep . :) – inkista Apr 10 '16 at 17:52
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Dynamic range in digital terms is following: the ratio between the brightest adequately recorded gray (D65 gray, for example) colour and the darkest adequately recorded gray colour both recorded with one exposure.

The quality of record is mostly unaffected (except probably with sensor blooming (charge leakage)) in the bright end of tonal range.

The quality of record is affected by sensor noise (circuit noise and photon noise) in the dark end of tonal range. The noise may be calculated and it is said that a dark tone is recorded adequately if the noise is less than arbitrary value. Different arbitrary values may be used, so it is not reliable to compare dynamic range specifications unless the threshold value is specified alongside.

The dynamic range being 14 stops means that camera is able to record object with power X and the object with power X/2^14 adequately simultaneously.

The stops of dynamic range are similar to stops of metering.

To calculate the dynamic range of RAW material you should sum the exposure scatter size with dynamic range of a camera calculated at ISO value which you use. The scatter of series -3,0,+3 is 6 stops.

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From the very beginning, photographers defined the unit of exposure as the “stop”. This stems from the fact that early camera lenses did not have a mechanically adjustable aperture. They made lens caps with holes in the center, each with a different hole diameter. The hole size or “aperture” (Latin for opening) was nicknamed “stop”.

The best sequence of hole sizes is a doubling or halving of surface area. Since we are dealing with circles, we must fall back on the math of circles. Factorial: If multiply the diameter of a circle by the square root of 2 which is 1.414, you compute a revised circle with twice the surface area. The key is the square root of 2 (it’s OK to round this to simply 1.4)

What happens when you use the 1.4 factor is, a series of circles, each allowing twice the light energy to pass to film or digital sensor. The sequence or number set is: The f/numbers 1 – 1.4 – 2 – 2.8 – 4 – 5.6 – 8 – 11 – 16 – 22 – 32 Each going right is its neighbor on the left multiplied by 1.4. Going the other way, it’s the neighbor on the right divided by 1.4. Such a number set creates a series of circles, each double or half its neighbor in surface area. This allows photographers to adjust exposure in a logical 2X sequence.

Dynamic range for both film and digital is measured in terms of stops. A typical film has a range of about 10 f/stops. f/stop is short for focal ratio. We divide the focal length of the lens by the working aperture diameter to compute the f/stop. This clever system is universal. Any lens set to the same f/stop number allows the same light energy to play on film or digital sensor. The f/stop system takes the chaos out of setting your camera exposure. It also gives us a universal method to talk about the magnitude of our exposure.

Talking about the dynamic range of a typical film of 10 f/stops, since each f/stop represents a doubling of light energy we can say that the light level change is: 1 – 2 – 4 - 8 – 16 – 32 – 64 – 128 – 512 – 1024 That’s the light level range . Think this way 1 watt light bulb thru a 1000 watt light bulb. Also you should know that the unaided human eye naturally spans 10x more range.

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