Sometimes a scene that you want to photograph has a wide range of light in it, for example, a strong sunlight and some deep shadows. As you look at that scene, your eyes can quickly adjust to that range of light to see each part correctly. But a camera only has a limited range of operable exposure to deal with in any one image. To handle these types of scenes, we need a more advanced method to correctly capture a good image.
High Dynamic Range (HDR) photography is a technique that uses multiple photos taken at different exposures and then combined in software to produce one photo with a wider range of exposure, thus capturing a much wider range of light in a composite image. This one image can then be adjusted using post processing to adjust each area to give the desired effect.
The scene below is a waterfall in Hocking Hills, Ohio. It is located at the end of a deep gorge such that during strong daylight hours the top part has bright sunlight while the area next to and under the falls is in deep shadow. The center photo below was taken just as the camera chose the exposure for the shot. The sensor saw the bright light at top and that determines how it would record the scene. However, you can see that deep shadows and very dark and, upon closer inspection, you would see that they are very grainy because of underexposure.
Therefore, 3 exposures of the the same waterfall were taken typically 2 stops apart – one average, 1 brighter, and one darker. This insures that one shot will properly expose the bright part, while the other shot will best expose the dark shadows. It is important that the range of exposure is done by adjusting the exposure time and not the f-stop so that the focus remains uniform across each image. To insure the images are all aligned, a tripod is mandatory for this kind of work unless the exposure times are very short. When in doubt, just bring the tripod.
We can then combine the images in software. I used Adobe Lightroom for this example to get one composite image that can now be adjusted to give less exposure on the bright part at the top, a little exposure in the shadows, and some highlights on the water itself. Since each area of the photo, from bright sunlight to deep shadow has image information from the best available rendition in the properly exposed photo, we get quality rendering in each area – the highlights are not blown out and the shadows are not grainy from underexposure.
The are several good software packages to do this, but I use Lightroom since it is now a built in feature and I do not need to pay extra for another software tool.
It is interesting to note that some smartphones can do a version of HDR in their own software. I will cover iPhone photography in another post.