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, or reflected light) 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.

EVs represent an exposure for a given brightness using the camera’s shutter speed and current aperture (usually relative to 100 ISO). The EV chart is not relative, it is absolute. Each EV is a static brightness level. In other words, EV 0 is always the same brightness, no matter where you are or what you’re doing.

The EV scale isn’t something you need to memorize, it is just a good idea to understand it as it shows very literally how camera settings relate to scene brightness.

It’s also a good thing to keep in mind for understanding the quality of a camera. 10 years ago a high quality camera would have around 12 stops of dynamic range. Now there are still cameras with nearly 15 stops of dynamic range. You might be thinking, well, that’s just 3 stops more than 10 years ago right? Just remember that each stop is a doubling of the light power. So if we say the 12th stop of brightness was 100,000 lux (full sunlight), then the 13th stop is 200,000 lux, the 14th is 400,000 lux, and the 15th is 800,000 lux… It means that a modern camera with ~15 stops of DR can take a picture with a light source 8 times brighter than the sun and maintain the same exposure as a camera with ~12 stops of dynamic range.

Of course this also works in reverse, given the exposure is made for the highlights in the scene, the modern camera will resolve details in dark areas of the image that are 8 times less bright than the older camera.

This is part of what makes understanding EVs a powerful tool for you as a photographer. It can give you the ability to more rationally explain why one camera is better for a certain use than another one is. It can also help you understand how to light your scene.

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 high end digital camera’s have a dynamic range in the ~15-16 stop range. That means they can handle blacks as dark as 0 EV and white’s as bright as ~15-16 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 reasonably contained within one carefully exposed image from the highest quality digital cameras.

Dynamic Range in cameras

As mentioned earlier most current generation full frame cameras are in the 15-16 EV range at their base ISO. 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 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 in a scene. A camera’s dynamic range refers to the range of brightness that the camera is capable of capturing. The highest I know of for still cameras is 14.8 stops/EVs in a single picture (always achieved at base ISO). Higher DR does not necessarily equate to higher quality pictures. A variety of things can contribute to picture quality and DR is but one specification. What high DR does do for photographers is allow them to capture more of the highlights and more of the shadows in any given exposure (at base ISO).