Joe's How-To

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Joe’s How-To

High Dynamic Range Photography

By Joe Doherty

On Christmas Day 1977, when I was 18, I was delighted to receive a gift of three Ansel Adams books: The Negative, The Print, and The Camera. If you are not familiar, these volumes are about the craft of photography rather than the art of photography. While some of the lessons are archaic, the overarching themes are still relevant. Of these, I think the most accessible to contemporary audiences is the idea behind the photography term “High Dynamic Range.”

High Dynamic Range (HDR) refers to scenes in which there are extremes of light and shadow. Think of the interior of a cathedral, with bright stained glass windows near the ceiling and wooden statues hidden in the recesses of the chapel. The challenge in such a scene is how to capture the relevant detail at the high end of the range without sacrificing detail at the low end. It’s a challenge faced by architectural and landscape photographers everywhere.

Adams used techniques like pre-fogging or a water bath to capture the dynamic range of his images. Lynn Radeka uses sophisticated masking in printing. Galen Rowell used graduated neutral density filters in front of the lens to lower the intensity of light in certain areas of a scene, like a snow-capped mountain. Modern photographers take advantage of digital tools by bracketing exposures and blending them in post-processing. It is therefore interesting to know that efforts to overcome the challenges of HDR are at least 170 years old.

The photographer Edouard Baldus, in an effort to make photographs that captured what he could see with his naked eye, foreshadowed several methods used in digital photography: exposure blending, focusstacking, and panorama stitching. For one image he puzzled together no fewer than ten separately exposed and focused negatives to capture the detail of the cloister of Saint-Trophime, at Arles, France in 1851 (Figure 1). Baldus had the same goal as Adams, Radeka, and Rowell. He wanted to make a realistic image of a place by overcoming the limitations of his tools.

I point this out because HDR has gotten a bad reputation. It has been used to create many images that are garish, unrealistic, and better described as illustrations than photographs. But like many things in life, these examples stick out because they are so obvious. The use of HDR in non-obvious ways is seldom mentioned or noticed because the craft takes a back seat to the art. And the craft of HDR has a long history in photography.

So how do we know when to use it, and how to use it? To answer the first question I draw upon what I learned from Adams’ books; I need to use HDR techniques

Fig. 1

when the camera cannot readily capture what I see with my naked eye. My naked eye compensates for a lot. It can see a mountain peak against a blue sky over an aspen grove, and clearly make out the tree trunks in the shadows. My camera isn’t as adaptable. It measures the sky as many stops brighter than the shadowy tree trunks, and if it isn’t capable of capturing both ends of the range it will drop one or the other (or both).

So what do we do? There are two strategies. The first is to see if the in-camera exposure can be “dialed-in” to record sufficient information at both ends of the range, from highlights and shadows. In the digital age we call this “exposing to the right.” We can then balance the extremes in processing. Your camera will not do this automatically. While there is variation among brands and settings, all cameras average the exposure across a scene, to balance the highs and lows, even if that means that the highs and lows are clipped off. This isn’t what we want. We use the histogram in the camera to determine the exposure needed for the shot.

Figure 2 illustrates what the camera’s average exposure for the scene looks like, and the accompanying histogram. Notice that the sky is a nice shade of blue, the mountains are correctly exposed, and the histogram indicates that there is no clipping at the bottom or the top of the exposure range. In other words, this entire scene is within the capabilities of the camera sensor. But also notice that there is a lot of “room” on the right side of the histogram, and that a lot of the data is clumped near the bottom end. That clump includes aspen trunks in the shadows on the left. We want to increase the exposure so that the trunks are better exposed, with the data clumped as far to the right as possible without clipping. This will give us more information (and thus more separation) in the mid-tones and shadows.

Fig. 2

Figure 3 (below) illustrates what “exposing to the right” means. It is two stops brighter than the earlier exposure (1/10th sec. compared to 1/40th sec.). The image is decently exposed for the foreground, but the mountains and sky are quite bright and not at all pleasing. The histogram reveals, however, that the highlights aren’t clipped (except for two small patches of white snow), which means that they contain usable information. We can use that information in processing to try to recreate what our eyes see.

Fig. 3

From here the process is relatively straightforward. We want to bring the highlights back into the range that looks like what our eyes saw. In Lightroom I use the Graduated Filter (like Rowell did) to lower the exposure on the sky and the mountains by one stop (-1.00) (Figure 4). Lightroom gives us the ability to selectively apply the filter using a Range Mask (it’s at the bottom of the Graduated Filter panel). I apply my one stop adjustment only to values that are at the top of the luminance range (50 to 100), so that my adjustment won’t apply to the shadows. Try it, it’s very cool.

I then finished the process by using the Dehaze slider to simultaneously increase overall contrast, darken the sky, and bring out the wisp of clouds (Figure 5). Evidence for this transformation is in the histogram. There is significant separation across the entire exposure range, and no values are clipped. This was all possible because we overrode the camera’s settings and “overexposed” the image. There is no blending of multiple images, just a purposeful strategy to utilize the inherent range of the technology. It’s a process that would be familiar to Adams and Rowell, and envied by Baldus.

Some might object that this is not HDR, because it doesn’t combine multiple frames of different exposures. I think this objection misses the point, by placing the emphasis on the process and not on the problem. The scene has a high dynamic range, and had I encountered it with my Nikon D70 in 2006 I would have needed multiple frames of different exposures. Once combined, I still would have had to make the same creative decisions I made here. In 2021, the Nikon D850 is inherently capable of recording a broader range of light than the D70. The scene did not change.

My D850 is not magical, however. Some scenes are beyond its capabilities, and a second strategy is needed. Exposure blending is to be used when the inherent range of the camera cannot capture what the naked eye sees. I use for my example a recent image from the North Rim of the Grand Canyon, as an approaching thunderstorm was about the chase us back to camp. The sun was setting behind a squall line to our right, its light penetrating the distant canyons, while clouds swirled overhead. My eye clearly saw the disk of the sun, the glowing canyons, and the majestic clouds. Like Baldus, I had my doubts about whether the camera would see as clearly as I did.

Fig. 5

Fig. 4

I set up my camera to do a 3-frame bracket, with each exposure two stops apart. In practice this meant shooting at 1/20th, 1/80th, and 1/5th of a second (Figures 6a, 6b, and 6c). Each frame shows a significant amount of clipping, but each also contains an important part of the image. The darkest one gives me the disk of the sun and some of the drama in the storm, the brightest gives me detail and luminance in the canyons, and the medium gives me clouds and the contours of the landscape.

Where Baldus had to manually cut and paste his negatives, I have the luxury of pushing a few buttons. In Lightroom I selected all three frames, went into the Develop Module, and used the Photo/Merge/HDR option (Ctrl-H) to automatically combine them. This gave me a file with a massive amount of information (much more than my Nikon D850 could produce), which I could use to edit the image. Had I used any single frame I would not have been able to capture the moment; the camera was not capable of it. Using this method, though, I was as unconstrained as a painter to convey the grandeur and the terror of the imminent storm (Figure 7).

I consider myself a realist. I photograph what I see. But what I see and what the camera captures are not always the same thing. My education in the craft of photography allows me to appreciate that the constraints of the medium rarely disappear, they are just transformed by new technology and equipment. We are always – from Baldus to Adams to Rowell to us -- striving for ways to overcome them. High Dynamic Range photography, used wisely, helps us to keep it real.

Fig. 6a Fig. 6b Fig. 6c

Fig. 7