By Jim Zuckerman
Published by SekonicHigh-dynamic-range imaging can bring out highlight and shadow detail in your photos and let you apply a range of styles, from the realistic to the surreal. Jim Zuckerman explains how to capture the exposures you need to work creatively with HDR.
HDR is the abbreviation for “high dynamic range.” The dynamic range of a photograph describes the ratio between the maximum and minimum measurable light intensities. In photography, the dynamic range is often described in terms of stops, reflecting the range of exposure values a sensor or a light-sensitive medium such as film is capable of responding to. In other words, dynamic range defines how much detail we can see in the highlights and how much detail is distinguishable in the shadows. Dynamic range is also sometimes referred to as a contrast ratio.
Contrast is a big deal in photography because digital sensors (as well as film) are not as sophisticated as our eye/brain combination. We can see incredible detail in the deepest of shadows and the brightest of highlights. We have built into us a tremendous dynamic range. Digital sensors have a much more limited dynamic range. When you photograph contrasty subjects with a digital camera, your images will tend to be very dark or even black in the shadows, while the highlights may very well become so overexposed that they lose most or all texture and detail. This is what “blowing out the highlights” means.
A case in point is the photo of a bed and breakfast establishment in Mexico, image 1. Notice the extreme contrast in this picture. The courtyard was open to the sky, and during midday it’s very bright. The doors on the left were under a large overhang and in deep shadow. When I exposed correctly for the doors, the courtyard became completely blown out. This is not what I saw at all, of course. In reality, I saw a perfectly “exposed” scene with good detail everywhere. The way the picture turned out is not a function of the way I metered the scene; rather, it is entirely a function of the inability of the digital sensor to record a good exposure throughout this very contrasty situation.
When I took another photo and exposed for the highlights (image 2) the shadows went so dark that along the left edge of the frame they are black with no detail. To “expose for the highlights” means to use exposure settings that will make the brightest areas of a scene appear with full detail and no blown-out areas. Before the HDR technique was possible, photographers using a digital camera or black-and-white film usually exposed for the highlights and then lightened shadow areas to reveal more detail, either with raw image processing software or in a chemical darkroom. Sometimes we compromised between extremes of light and shadow and just tried to find a satisfactory middle ground. The compromise was never ideal, so we just accepted the limits of the medium.
The HDR technique revolutionized photography in that it allowed photographers to retain detail throughout a contrasty image. You can see this in image 3. HDR is indeed a remarkable new tool. As I say to my students all the time, it’s a great time to be a photographer.
It is important to note that the HDR technique is not a special effect in the normal way we think of these things. Instead, it is a technique designed to overcome the limitations of the photographic process and reveal the dynamic range in a scene as we can see it with our eyes. For those of you who are uncomfortable manipulating photographic images, HDR does not change reality. It does quite the opposite. It replaces the unrealistic contrast of photographic images with the contrast range we perceive with our eyes and brain.
To create an HDR image, you need to take several exposures of the contrasty subject or scene from a tripod. The exposures should be one or two f/stops apart, and the same lens aperture must be used for each shot. When all of those pictures are opened on your desktop (with no post-processing to tweak the exposure), they are assembled together using either Photoshop or the program Photomatix. Most photographers use Photomatix because it does a better job than Photoshop in terms of blending the images and then giving you additional controls to manipulate the final composite.
The number of exposures you take will vary depending on how much contrast there is in the shot. For #3, I took a total of six separate images, and for the entrance of a small hotel in Prague, #4, I used five images. You can see the five exposures in #5.
If you are not allowed to use a tripod, some other firm support has to be used – a railing, the floor, a ball head resting on a table. In the stunning St. Mary’s cathedral in Krakow, Poland, #6, I rested the camera on the floor and used a 14mm lens to take three exposures two f/stops apart for the HDR composite.
The typical HDR image is done with the first exposure measured for middle gray, and then this is followed by two overexposed variations (by one and two f/stops) and then two underexposed shots (by one and two f/stops). That usually encompasses the entire dynamic range. Sometimes, though, with extreme contrast additional exposures are required. When I photographed from a porch looking into the sun, #7, the difference in exposure between the brilliant sky and the underside of the overhanging roof was at least eight f/stops. I used eight exposures to create this composite.
On the other hand, you can have extreme contrast between two parts of a photo but only two different exposures of it are necessary to make a perfect composite. In #8, the lighting on the interior of the barn was even and it was very easy to obtain a good exposure. However, the outside scenes visible through the windows were quite a bit brighter. There was a five f/stop discrepancy between the exterior and the interior. I took two pictures – one in which I exposed for the sunny exterior (using the spot mode on the hand held meter) and one where I exposed for the weathered wood (again using spot mode). You can see that the resulting composite is perfect.
In #9, the ornate interior of the oldest university in Europe, the University of Wroclaw, Poland, was similarly fairly uniform in exposure. Even though the day was overcast, the architect seen through the window was grossly overexposed to the point of being distracting. Two different exposures were all that was necessary to make this look like what I saw with my eyes.
HDR can be used in all kinds of situations as long as the camera doesn’t move between the exposures and your subjects don’t move, too. I used it in a 19th barn in Missouri when I photographed an old buggy. Note in the original photo, #10, how dark the back of the barn is compared to the foreground. In the HDR composite, #11, which consists of five separate exposures, the exposure is perfect throughout the image and we can see complete detail in the weathered wood in the rear of the barn and in the underside of the carriage, and the highlights in the foreground are not bordering on overexposure.
The photograph I took in the spectacular St. Patrick’s cathedral in Dublin, Ireland, #12, has quite a bit of highlight and shadow, and this is exactly what I saw. Had I not used HDR, the shadow areas would have been very dark with little or no detail.
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