It’s a phrase we hear over and over in photography – high dynamic range, the sensor’s dynamic range – but what exactly is dynamic range and why is it important to understand how it affects your photography?
What is Dynamic Range?
Well, let’s start with the fact that all audio and visual sensing devices have a dynamic range. That includes our very own eyes and ears. In visual terms, dynamic range is the ratio between the minimum and maximum light levels that a particular sensor can measure. In the case of our eyes, that range is immense – we can determine a vast amount of tones but not the full range. Imagine sitting in a dark room with one large window and a very bright sunny view outside. If you look at the view, your eyes will not see anything in the room, it will be too dark. Conversely, if you look inside the room, the view outside will be too bright to decipher anything. This is demonstrating the dynamic range of your eyes. Your camera sensor, unfortunately, has significantly less dynamic range than your eyes, but by understanding it we can deal with lighting that exceeds the dynamic range of our camera sensors.
The Limitations of Your Camera Sensor
We have all come across the limitations of our camera sensors, many times. It manifests itself, in particular, with blown highlights – those areas of intense brightness within an image that were too bright for the camera’s sensor to deal with. They appear in the final shot as pure white and no matter how you try to process the image, nothing will ever pull the detail back, all that will happen is that you make that pure white grey. This happens because your camera’s exposure meter is tuned to work out an average for the scene and if there is too much contrast it cannot expose the entire dynamic range. This is quite a common scenario in photography, direct light casting dark shadows, reflections on dark surfaces, a dark dog on white snow, all of these and many more can exceed the sensor’s capabilities. So how can we control this issue and extend the dynamic range of our photos?
Unrecoverable highlights. Image by Andrew Butitta, on Flickr
How to Extend the Dynamic Range
1. Shoot Raw – Because Raw files give us only the pure data from the sensor, we are getting the full dynamic range capabilities from that sensor. Jpg files go through internal processing before being saved and this invariably clips off some of the dynamic range at one end of the scale or the other. By using a Raw file we can carefully manipulate the image in post production, attempting to get the maximum range that the shot offers.
2. Shoot Low ISO – As you increase your ISO, not only does the noise level increase but also the dynamic range decreases. For each step up in ISO, there will be a small but discernible drop in the dynamic range of your image. If the light is low, it is better to use a tripod and low shutter speed than hand holding at higher ISO.
High ISO also reduces dynamic range. Image by Nguyen Hoang on Flickr
3. Shoot HDR – HDR some times gets a bad press due to some of the overly garish images it produces. However, it is in fact a tool for increasing the dynamic range of your images but keeping them natural looking. By shooting a range of exposures and carefully combining them in Photoshop or an HDR program, you can dramatically increase your dynamic range without making the image look unnatural.
Shoot HDR to extend your dynamic range. Image by Ben Jackson, on Flickr
4. Learn Your Histogram – The key to getting the optimum exposure from your sensor is to understand your histogram. Put simply, that little graph on your screen can show you if you are exceeding dynamic range. If the graph falls off to the left, then you are losing dynamic range in the shadows, if it falls to the right your loss is in the highlights. Bear in mind, most histograms are based on a jpg version of the shot, a RAW file might be able to recover some of the detail at either end.
5. Shoot to the Right – This is complicated subject but in it’s simplest terms, camera sensors are more efficient at the brighter end of a dynamic range. By shifting our histogram to the right end of the graph, by increasing our exposure we can make sure we are getting the best dynamic range from the sensor. The key is not to allow any of the histogram to fall off the right side of the graph as these will become the “unrecoverable” highlights.
6. Use a Graduated Filter – One of the key problems with dynamic range is found in landscape photography, where the sky is often too bright to maintain detail if the landscape is exposed correctly. To counter this we can use a graduated filter, which effectively reduces that dynamic range to something that the sensor can deal with.
Using a graduated filter can reduce the the dynamic range to within the sensor's tolerances. Image by Steve Maw, on Flickr
Dynamic range is an important subject in photography. By understanding the limitations of our sensors and how to counter an excessive dynamic range, we can create quality shots with a full range of tones and colors.