What is dynamic range in photography?

If you are familiar with audio you’ve probably heard the words “dynamic range” used to describe speakers or recording systems. Light and sound are actually described in much the same ways. Where dynamic range in sound means the difference between quiet and loud, dynamic range in photography refers to the difference in brightness.

It’s a complicated subject, but here goes an attempt at explaining “dynamic range”.

In a sense dynamic range is the difference between white and black, but that isn’t the whole story. In theory, the difference between white and black can be near .1 lux or 1 billion trillion trillion lux. (Lux is a measurement of light intensity on a surface, not the intensity of the light source) For instance, imagine the difference in brightness of your surroundings at night vs the day, nighttime scenes are usually around 1 lux brightness whereas midday sun can reach 100,000 lux. But what is white at night isn’t nearly as bright compared to what is white in midday.

In photography we don’t use lux, although lux is an accurate measurement of reflected light we use a different system in photography that makes finding the multiples of different scenes easier. That system is called EV which stands for Exposure Value. The difference between every EV is equivalent to a doubling of the amount of light in a scene. Since every EV is double the light of the previous EV, it means that the EV scale is exponential. For instance, if one scene meters at 10EV, and another meters at 15EV, the 15EV scene is 32 times brighter than the 10EV scene.

The important thing about EV’s is that they’re defined according to the correct exposure for a given brightness using the camera’s shutter speed and current aperture (usually relative to 100 ISO). This means that every EV corresponds to a specific camera setting. Below is a chart listing out the camera settings for some EV’s.

It’s fair to say that to be using 1/32000 of a second at f/8 and 100 ISO, you’re probably photographing something insanely bright, like pointing the camera straight at the sun at the equator at noon.

Looking at this chart I can tell that an EV of 15 is probably bright midday sun, and an EV of -1 is a typical nighttime exposure. I know that just from thinking about previous pictures I’ve taken using similar settings. And that is what makes the EV scale so useful, it’s easy to relate to actual camera settings. If you take the time to remember the scale it can be a condensed way of telling another photographer what settings you’re using.

Dynamic Range

Dynamic range in a photograph is the number of EV’s that can fit inside a single photo. It ends up being the difference between black and white, but black and white in one camera can relate to a different EV range than black and white in another camera.

Modern digital camera’s have a dynamic range in the 18 stop range. That means they can handle blacks as dark as 0 EV and white’s as bright as 18 EV all contained in one scene.

Typically the absolute brightest outdoor scenes will have a maximum EV differential of about 18 stops of meaningful information. This can usually be contained within one carefully exposed image from the highest quality digital cameras.

Some cinema cameras are capable of 16-17 stops of dynamic range which puts them very close to the absolute maximum needed for most photography or videography on planet Earth.

Dynamic Range in cameras

As mentioned earlier most current generation full frame cameras are in the 16-18 EV range at ISO 100. The limiting factor in most cameras is something called the “noise floor”. The noise floor is the point at which the signal from the light is too small to overcome the self-noise in the sensor. Therefore, the Dynamic Range is the brightness range from the noise floor (darkest pixels) up to the brightest possible light that causes the sensor to clip to pure white (brightest pixels).

Due to the small size of sensors there is a limit to how much circuitry can be realistically placed into the sensor. This means that changing the sensitivity of the sensor in hardware is difficult to do. Some modern sensors have multiple built in amplification circuits which allow the sensor to maintain high dynamic range at multiple ISO settings.

Most sensors still do not have multiple gain circuits which means that the signal from the base gain circuit of 100 ISO must be amplified to achieve higher sensitivity settings.

To imagine how this works imagine that each pixel in the sensor is like a cup, and that the light going in the pixel is like water entering a cup.

At 100 ISO we can imagine that each pixel/cup starts off empty, and we can accurately measure how much light/water enters the pixel/cup with each exposure.

However, increase the ISO to 1,600, and now there is more noise in the image. Essentially you can think of the noise as “pre-filling” the cup with some random amount of dirt and junk. Now the pixel “fills up” faster, and it is harder to tell how much “light” was captured because of all the random junk that is mixed up in the “cup”.

Increasing dynamic range has the side benefit of increasing the accuracy of the camera as the differences between color brightness levels becomes more clearly delineated.

Final Thoughts

Dynamic range refers to the difference between the brightest highlights and darkest shadows a camera can capture in a single image. This essentially means the camera captures more information about the whole scene than a camera with lower dynamic range does. To use the cup analogy from earlier, a camera with high dynamic range has bigger “cups” that gather more light information about the scene. More light gathered = more information about the scene captured = higher quality pictures.