Active-D Lighting is a Nikon term for a technology that expands the dynamic range of your camera’s sensor. A number of the major camera manufacturers employ similar technology – Canon’s variant is known as Auto Lighting Optimiser. The thing all of these technologies have in common is that they attempt to increase the details in the highlights and/or the shadow regions of an image. Most commonly this is applied to scenes of high contrast where the sensor’s default dynamic range cannot cope with the difference between the brightest and darkest parts of the scene.
What is Dynamic Range?
We should look at dynamic range before we delve into the technologies that try to expand it. In any one scene there is going to be a brightest point, the point closest to pure white and a darkest point, the closest to pure black. The closer those points are to the pure white or black the higher the contrast of the scene. Our eyes are pretty good at capturing that range – we can typically see up to 15 stops difference. Camera sensors however are not quite so adept at it, seeing more like 9-12 stops in the best cases.
That’s why when we see an image taken in an extremely contrasty situation, it looks wrong to our eyes. The black, shadow areas often go so black we cannot see any detail in them, whilst the highlights “blow.” Blown highlights are where the bright parts of the scene are so bright, that the camera’s sensor records them as pure white, even though they are not. There is no way to recover these blown highlights, trying to pull them back in post production just leaves us with odd looking flat grey colours.
So how does Active-D counter this problem and how do I use it?
It's all about the Curves. Many of you that use Photoshop or similar will know about curves. Curves allow the editor to reduce highlights or increase shadow detail of a shot, after it was taken (and assuming the detail is there). Active-D and its cousins work on the same principle only in camera and before the shot is taken. If you have Active-D selected in the menu, when you half press the shutter, the exposure meter measures the scene. If the scene is of a particularly high contrast it will then attempt to adjust the tone curve of that scene, reducing the highlights and boosting the shadows.
Depending on your camera’s manufacturer you will be able to choose from several levels of D Lighting adjustments ranging from a very low level to high level.
Of course whilst this technology might sound amazing, in reality there is always a trade off. The main issue is that the overall contrast of the image will be lowered, possibly leading to a flat look from what was originally a bright contrasty scene. As with any exposure manipulation there is the possibility of an increase in noise, particularly in the shadow areas. Also because the camera is doing the calculations, other than the presets you have little control over the function. Also D-Lighting is only available when shooting JPEG files.
What are the Alternatives to Active D Lighting?
Active-D and Auto Light Optimisers can be considered sledge hammers to crack a walnut. There are a few, more subtle and controllable ways to deal with excess contrast in a scene.
Shooting RAW – By shooting RAW, you are utilising the full dynamic range of your sensor, it is not going through any post production and compression as a JPEG file would. This means that by careful manipulation in post production, you can restore detail to blown highlights and dark shadow areas.
Custom Tone Curves. Some cameras allow you to create your own custom curves to deal with difficult lighting conditions. Effectively the same process as Active-D lighting, except you can actually define how the curve will deal with the shadows and the highlights. You might create a curve purely to tone down the excessively bright regions in the highlights.
Shooting HDR – HDR, high dynamic range photography has always been about recreating the scene in front of the camera with as much dynamic range as is needed to look natural. Often this is more than the sensor can deal with in a single shot so in HDR photography we take a range of shots around the correct exposure and merge them together to give us one final shot with a higher dynamic range.
Active-D lighting can be useful when starting out in photography or shooting in rapidly changing lighting conditions. It can allow us to flatten out extreme contrast in our shots and give a more natural looking image. However as our knowledge of both camera and photographic technique improves, we can easily replicate Active-D using other more controllable techniques.