Date: Jun 8, 2011
High dynamic range (HDR) photography creates images with an extremely large range from the darkest to the lightest areas of the photograph. The resulting images more accurately reflect the wide range or intensity levels found in the real world — and are visually stunning. In this article, Michael Miller, author of Photopedia: The Ultimate Digital Photography Resource, shows you how to create HDR images using your own digital camera and Adobe Photoshop.
Want to create images that have a wider range of brightness and contrast? Want your digital photos to pop off the page?
Then you need to learn about high dynamic range (HDR) imaging, a special type of digital photography designed to capture the largest possible range between the dark and bright areas of a photograph. HDR imaging involves taking multiple shots of a subject at different exposure levels, then merging the different shots into a single photographic image. All you need is a digital camera than allows for manual exposure and a digital image editing program with an HDR merge function — like Adobe Photoshop CS. The result is eye-popping images that look unlike anything you’ve taken before!
Understanding HDR Imaging
HDR stands for high dynamic range, and HDR imaging is just as the name implies — a way to create digital images with a high dynamic range in terms of luminance (brightness). That is, with HDR imaging, the range between the lightest and darkest areas of a photograph is greater than with traditional photography or digital imaging.
The wide dynamic range of an HDR image makes the picture almost pop from the page. At the most basic, HDR images more accurately represent the range of brightness levels found in real life; when applied properly, HDR brings a kind of hyperrealism to your photographs.
As an example, Figure 1 shows a digital photograph shot and edited using traditional methods. Figure 2 shows the same image captured with HDR imaging. As you can see, the HDR image is more vivid, almost surreal in its range between dark and bright areas. HDR affects everything about the picture, resulting in more defined details, sharper contrast, and more vivid colors.
Figure 1 A cloud shot using traditional imaging techniques.
Figure 2 The same cloud shot, processed with HDR imaging techniques – note the enhanced contrast, color, and dynamic range.
The increased dynamic range in an HDR image is a result of merging multiple photographs of the same subject, taken at different exposures. The exposure determines how much light is captured by the camera, and is measured in terms of exposure value, or EV. (One EV unit is equivalent to one f/stop on your camera.) An increase of one EV doubles the amount of light captured.
Taking a series of photos at different exposures is called exposure bracketing. A typical HDR image is composed of three or more images with exposures at least one EV away from each other. A dark exposure captures detail in bright areas of the scene; a light exposure captures detail in mid-tones and shadows. The over- and under-exposed shots are combined to create a finished image with more overall tonal detail than is possible with a single (proper) exposure.
The best HDR photos involve a scene of extreme contrast, in terms of brightness. That is, HDR is best shown off with photos that have both extremely bright and dark areas, such as the sun behind a darkened wall, or a dark room with bright light shining in from the windows.
By the way, HDR imaging isn’t a new phenomenon, although it has acquired a new life in this new age of digital imaging. The concept of merging several exposures dates back to the “combination printing” of French photographer Gustave Le Gray in the 1850s, and is closely related to the sophisticated burning and dodging techniques popularized by Ansel Adams in his high contrast nature photography. With the advent of digital photography and digital image editing, however, it is now feasible to accomplish HDR by combining multiple images shot at different exposures.
Shooting an HDR Photo
The key to digital HDR photography is to take multiple photographs of the same scene, each at a different exposure value. In HDR photography, you change the exposure by adjusting the aperture (the size of the lens opening), while maintaining the same shutter speed; this ensures you’ll have the same depth of field in all the shots.
To take HDR photographs, then, you need a digital camera that allows you to manually adjust the aperture or f/stop setting. This may be accomplished by a simple over- or underexposure setting that you manually change between shots. Some more sophisticated digital cameras offer auto exposure bracketing, where the camera automatically “brackets” a normal exposure with additional shots at higher and lower EVs.
Naturally, when you take multiple photographs of the same scene, you need to do so quickly, to reduce any movement in the photo. (This is where auto exposure bracketing is nice, as the shots follow automatically in rapid succession.) HDR photography, then, is best suited for images without any natural motion; it’s better for landscapes than for sports action, for example.
How many shots do you need to take? You’ll need to shoot at enough different exposure levels to capture all the brightness levels in the scene. This means putting the darkest values in the scene no lower than the mid-range of your camera sensor’s sensitivity range. In practice, that means no fewer than three separate exposures, and perhaps as many as five to seven — or even more. Each shot should be taken at between one and two EVs apart.
The best way to approach this is to position your camera on a tripod, so that it won’t move between shots. Switch your camera into manual exposure mode (sometimes called aperture priority mode) and turn off the autofocus. Then take a series of shots at 1-EV increments by changing your camera’s aperture with each shot. Start with a “normal” exposure, then bracket it with one shot 1 EV lower and another shot 1 EV higher. What you end up with is one shot properly exposed, one underexposed, and one overexposed; it’s this combination that generates the HDR image.
If this series of shots doesn’t achieve the dynamic range you want, repeat the process but shoot two shots at higher EVs and two shots at lower EVs, instead. You may also want to experiment with shooting at 2-EV increments instead of 1-EV increments.
For best results, shoot in camera RAW mode, if you can. You want to record the shot with the least compression and highest possible resolution, so you don’t lose any of that dynamic range.
Editing HDR Images in Photoshop
Once you’ve shot your images at different exposure levels, you now need to merge those photos into a single HDR image. The easiest way to do this is by using Adobe Photoshop and its Merge to HDR function.
For purposes of this article I’m using Photoshop CS5, which includes an enhanced Merge to HDR Pro function. If you have an older version of Photoshop (CS2, CS3, or CS4), you have the basic Merge to HDR functionality, which does a good job but offers fewer adjustments during the merge process.
Here’s how to do it:
- From within Photoshop CS5, select File > Automate > Merge to HDR Pro. (In older versions, select File > Automate > Merge to HDR.)
- When the Merge to HDR dialog box appears, click the Browse button.
- When the Open dialog box appears, hold down the Ctrl button to select the multiple files you want to merge, then click Open.
- Back in the Merge to HDR dialog box, check the Attempt to Automatically Align Source Images box. (This will help to minimize any changes in your pictures in the multiple shots.)
- Click the OK button. Photoshop now loads the files you selected and begins processing them; depending on the size and number of photos selected, this may take several minutes.
- Photoshop now displays a temporary merged image, in a new window; the individual photographs that comprise the merged image are displayed on the bottom of the window. You can remove individual exposures from this merged image by deselecting them at this point.
- If you’re using Photoshop CS5, you now have a range of adjustments you can make to the merged photo. Perhaps the best way to start is to pull down the Preset list at the top right of the window and select from one of the available configurations: Flat, Monochromatic (artistic, high contrast, or low contrast), Photorealistic (low contrast or high contrast), Surrealistic (low contrast or high contrast), Saturated, or More Saturated.
- You can also adjust any of the other available controls, such as edge glow, gamma, exposure, detail, shadow, highlight, and color vibrance and saturation. Experiment with what each control does, and how it affects the picture.
- You will be saving this 32-bit merged image as a 16-bit image, for printing and screen display purposes. Make sure the Mode (at the top right of the window) is set to 16 Bit Local Adaptation.
- Click the OK button when ready to proceed.
- Photoshop now displays the final merged image. Select File > Save As to save this image.
Figure 3 Selecting the files to merge.
Figure 4 Viewing the merged image in Photoshop CS5.
Note that you may need to clean up the merged image a bit. Some HDR images exhibit a color cast, and there may be various types of distortion visible. Use the appropriate tools to edit the image as necessary.
The result should be a stunning image, unlike anything you’ve shot traditionally. Once you get going with HDR photography, it’s easy to get hooked; have fun experimenting with different shots, exposure levels, and Photoshop adjustments!