HDR Photography Workshop

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    Dynamic Range

    Practical Effects of Limited Dynamic Range

    Traditional Solutions

    The HDR Solution

    Pete Carr

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  • 4This property is also known as the contrast ratio of the scene. Dynamic range can be characterized by the terms of exposure value (EV) levels, zones, levels, or stops of range.

    First, look at a scene with a reasonably low dynamic range, as shown in Figure 1-1. Here, you see a winter scene looking down a lane bordered on both sides by ice-covered trees, some of which have been damaged by a recent ice storm. The

    On the surface, High Dynamic Range (HDR) photography is about overcoming technological limitations. Cameras, whether film-based or digi-tal, dont perform as well as eyes and brains when it comes to collecting and interpreting light. You dont even have to think about it your eyes adjust to the ever-changing amount of light around you, and youre able to discern details in deep shadows and bright highlights automatically.

    When you take a photograph, however, you have one fleeting chance to collect what details the camera can capture. You must learn to deal with its limitations as you try to balance shadows and light in a single exposure. Many photographers spend their lives working to achieve this balance.

    HDR photography is a relatively new technique that overcomes the limitations of a single photo by using multiple exposures to produce an image that illustrates a high dynamic range scene (real-ity) with low dynamic range data. It is a powerful way to extend the cameras responsiveness to light. You find out how to do that in this book, beginning with this chapter.

    Digging deeper, HDR photography is an exciting avenue of artistic expression. Many choose to push the limits of photography with HDR, while others prefer to present their subjects very natu-rally. There is no absolute right or wrong approach its up to you and your audience.

    DYNAMIC RANGEWithin the context of photography, dynamic range refers to the range of brightness (from very little to a lot or from a lot to even more) in the scene to be photographed. ABOUT THIS PHOTO An example of a scene with a smaller

    dynamic range. (ISO 160, f/8.0, 1/100 second, Sony 18-70mm f/3.5-5.6 at 60mm) Robert Correll

    1-1

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    HDR PHOTOGRAPHY PHOTO WORKSHOP / Dynamic Range and Digital Photography

    lights, or with reflections pushes highlights to the extreme. Anchoring the low end of the spectrum are shadows and other less well-lit areas in the scene.

    The exposure challenge in a scene like that shown in 1-2 is to rein in the highlights in the sky and clouds while exposing the rest of the scene well enough so that it can be seen. Careful RAW file processing was essential to presenting this photo. The clouds and other highlights were protected and the foliage on the riverbanks was

    light-gray sky is barely visible. The street, trees, and sky are all fairly light, but there are no intense highlights. Dark tones are represented by a bit of foliage and tree branches. All in all, this scene was easily captured by the camera. In fact, contrast was enhanced during RAW file process-ing to balance the highs and lows.

    Some scenes, such as that shown in 1-2, clearly have a greater contrast ratio, or dynamic range, than others. Shooting during midday, into the sun during the Golden Hour, around bright

    ABOUT THIS PHOTO Scenes such as this one push the dynamic range of your camera and require careful processing. (ISO 100, f/8.0, 1/250 second, Sigma 10-20mm f/4-5.6 at 14mm) Robert Correll

    1-2

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  • 6The dynamic range of a camera tells you how many stops of brightness it can capture in a single exposure. For example, can it capture the sun and shadows in one photo? In the case of 1-4 and 1-5, the answer is no. The photo in 1-4 was underex-posed by four stops in order to capture the sun, and reduce or eliminate detail-hiding glare. This photo illustrates the peak of the upper end of this scenes dynamic range. The next exposure, 1-5, captures the opposite end of the scenes dynamic range. In this case, the bridge and other dark ele-ments in the foreground and in the distance are visible, but the sun and sky are washed out by glare. This is closer to how the scene looked in person, although the meter indicated the photo was overexposed by 4 stops (+4 EV).

    brightened. In other words, the dynamic range of the scene was captured reasonably well by the camera raw exposure, but these highs and lows had to be squeezed to fit into the file format required for viewing and printing.

    The challenge when shooting in shadow, such as inside a building, on a cloudy day, or during either predawn or dusk, is to capture details in low light, as shown in 1-3. The underside of the bridge is in shadow, which presents an exposure dilemma. You must capture darker details by increasing ISO, aperture, or slowing the shutter, all without causing the scene outside the bridge to be overexposed. Quite often, this is impossible in a single photograph without resorting to flash or extra lighting.

    ABOUT THIS PHOTO Standing under a bridge, the outside is perfectly exposed, but the image lacks detail inside the bridge. (ISO 200, f/13, 3 seconds, Nikon 14-24mm f/2.8 at 14mm) Pete Carr

    1-3

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    HDR PHOTOGRAPHY PHOTO WORKSHOP / Dynamic Range and Digital Photography

    your camera has a dynamic range often inade-quate to the task at hand can have undesirable effects on your photos.

    This section briefly illustrates what happens when highlights are too bright, shadows are too dark, or both.

    PRACTICAL EFFECTS OF LIMITED DYNAMIC RANGEHDR is not meant to replace, nor is it always a good substitute for, the single-exposure photogra-phy that were all used to. However, the fact that

    ABOUT THIS PHOTO One photo isnt enough to capture this range of light. Compare this version, underexposed by four stops, with 1-5. (ISO 100, f/8.0, 1/4000 second, Sigma 10-20mm f/4-5.6 at 18mm) Robert Correll

    ABOUT THIS PHOTO This photo and 1-4 illustrate the large dynamic range of this scene. Compare details in the sun, sky, and bridge. (ISO 100, f/8.0, 1/60 second, Sigma 10-20mm f/4-5.6 at 18mm) Robert Correll

    1-4 1-5

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  • 8necessary, try to fix the problems in processing. HDR, however, presents another way. The point of HDR is to enable you to bring out more detail in scenes that demand more dynamic range than your camera has, as shown in 1-7.

    BLOWN-OUT HIGHLIGHTSBlown-out details, quite often skies, are the result of limited dynamic range. Too much light over-exposes parts of the scene and the camera literally cannot measure any more light. The resulting image has no details in the overexposed areas.

    A bright sky is notoriously hard to capture well and not ruin the rest of the photo. For example, when given a choice between capturing a nice building at the cost of a blown-out sky or captur-ing a building that is too dark but has a nice exposed sky, most photographers (and their cam-eras) choose a blown-out sky. Why? Because, although blowing out a sky runs contrary to most digital photography guidelines, the building is the subject of the photo.

    This dilemma is illustrated in 1-6. The cathedral is the subject of the photo and, as such, deserves to be well exposed. The sky, however, limits the amount that you can raise the exposure without blowing it out. The camera does not have enough dynamic range to capture both at the same time. Notice that the ISO was raised to capture details on the darker building. Although you could choose to lengthen the exposure time, that was impractical in this case due to people moving around next to the building.

    When you know you cant expose both the build-ing and the sky correctly, you have a choice: Shoot for the building or shoot for the sky, and if

    ABOUT THIS PHOTO An example of a blown-out sky. The building is nicely exposed but the background is completely lost, or blown out. (ISO 640, f/8.0, 1/100 second, Nikon 24-70mm f/2.8 at 29mm) Pete Carr

    1-6

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    HDR PHOTOGRAPHY PHOTO WORKSHOP / Dynamic Range and Digital Photography

    DETAILS LOST IN SHADOWAt the opposite end of the scale is when you lose details in the shadows or the dark areas of your photos. Silhouettes caused by sunsets are the usual cause when shooting land- and cityscapes, although you also run into this problem when shooting indoors in dark spaces or any other time your subject is backlit.

    What happens in this case is the camera (or the photographer) decides to expose for the bright areas of the scene, underexposing everything else. This protects the sky but turns the foreground to silhouette and shadow. In the case of 1-8, the ship and quay in the foreground, plus