While not everyone will know what HDR even stands for, many have seen these initials in the Camera settings of their iPhone photo app. For the iPhone, the HDR setting essentially takes three photos and merges them into one photo for the user [*]. While I will leave out the details of the algorithm [*], this intuitively makes sense for certain types of photos: scenery or still-life pictures. This concept wont make much sense for moving shots and quick photos-of-the-moment for fairly obvious reasons; and therefore HDR photography will never be well suited to most iPhone users.
HDR, short for High Dynamic Range, is a photographic technique where multiple exposures of one scene are taken and then added together to form a new, composite image with better dynamic range. So if you take a photo with a bright sky and dark forest, a single image will either have a white/bright sky or a dark/black forest with no detail in whichever one’s the extreme. An HDR image will take a photo where the forest is richly detailed and the sky is white and washed-out and then another photo with the forest appearing dark and black with rich detail and contrast now appearing in the sky and clouds. (Typically an intermediate will also be taken for a third point of reference.) The various photos will be stitched together incorporating the areas of detail and contrast from each image into the final photograph. This is the theory behind HDR photography.
HDR was both glorified and demonized when it first came out, and it has fared no better or worse as time goes on. Some claimed it as a golden tool of rich, popping scenery while others called it digital trickery and equivalent to a photoshop hack. The battle is still ongoing in several different corners, but the technology is out there, so for better or worse we better learn to live with it.
But enough of the background on HDR photography, let’s actually move onto a concrete example. Here are a series of images I took on my most recent trip to the Kelly-Hubbard Farm:
While the exposure values (EV number) are fairly self-explanatory, let me point out the salient features of the HDR image through its benefits and limitations. The primary benefit here is the level of detail in the cloud. Notice the intricate patterns within the cloud as well as the smooth gradients between the pure white sections to the nearly completely transparent perimeter. This region of the image is a direct result of the first source image, the EV -1.30 exposure. Both of the other two exposures display the cloud as a smooth, pure white object with very little definition. Likewise–but perhaps not too clearly seen in this image–most of the detail in the HDR picture for the area under the overhang stems from the information within the overexposed, EV +1.30 exposure. In the middle, EV 0 picture the overhang is virtually black throughout, but some detail is to be found within the EV +1.30. The main drawback to such a multi-composition can be seen in the tree region of the HDR picture. The muddled details is a direct result of both the movement of the tree (and me) and the change in focal length through the aperture change. While shooting in aperture priority would remedy that effect, it would be made up in either iso noise or increased blur from a long exposure. It comes down to the inherent difficulty in achieving such a wide bracketing of exposures. There are many situations where this effect can be prevented (like with a tripod or a faster lens), it boils down to the inherent issue of using HDR in real-life situations where conditions are constantly changing and timing is critical.
I could continue to breakdown HDR photography–especially with examples, but I hope this fashions you with an idea of how HDR photography works, both in theory and practice, while also highlighting the primary benefits and limitations to this technique. I hope it’s another tool you’ll add to your practice.