If you've ever photographed a subject against a backlight, you know how difficult it is. If you underexpose, the background will look clear but the subject will be a dark silhouette. If you overexpose, the subject will show up but the background will be completely blown out by the lighting. It's exactly that sort of problem for which
HDR photography is suited. HDR, or high dynamic range, photography merges multiple exposures of a subject together, combining the best details from overexposures and underexposures to produce a composite picture that shows off everything without shadows or blow-out.
HDR isn't a catch-all solution to bad lighting, though. In fact, it's often more suited as an artistic photography method than a serious go-to tool.
When used casually, when the lighting doesn't justify it, HDR shots gain an almost dreamlike quality, because it brings out the most vivid details of all exposures. When there are a lot of colors in the frame, the HDR image can look super-saturated and bright. Unless the lighting makes it nearly impossible to catch the scene with one exposure, HDR isn't the best technique to simply take a picture of a subject. It might produce a pretty and detail-rich image, but it won't be an "accurate" image.
A small handful of digital cameras already offer in-camera HDR processing. The
Sony a500 and a550 SLRs and the
Canon PowerShot S95 compact camera all feature HDR systems. Sony's cameras merge just two exposures into one, and Canon has yet to explain exactly how the S95 handles HDR. Conventional HDR photography can take 5, 7, or even 15 exposures and merge them together, so even with in-camera processing there could be some value to doing it yourself.
If your camera or portable device can't handle HDR photography, don't fret; as long as you can change the exposure value of your shots, you can make your own HDR photos at home out of auto-bracketed or manually adjusted (adjust the aperture one stop for each shot) exposures. Photoshop
has had an automated HDR function since CS2. Once you've taken a few photos spread across a range of exposure values, go to File > Automate > Merge to HDR... and select them.
The program will automatically merge all your exposures into a single HDR image and present you with the composite. If it doesn't look quite right, you can disable certain exposures to change how the merged image looks. Once you're done, the resulting picture will have a dynamic range far beyond your monitor's ability to display it. At that point, you should crank the photo's bit depth down to 16 bits by going into Image > Mode > 16 Bits/Channel... and adjusting the Exposure and Gamma settings to fit.
Surprisingly, Apple is joining the world of HDR photography. The final version of iOS 4.1 for the iPhone 4
will be able to capture and render HDR photos, a first for such a portable device. The iOS 4.1 HDR uses only three exposures, but it's still two exposures more than most digital cameras or cell phones can process and merge. While it's not a game-changing feature, it has the potential of letting users take better photos in awkward lighting, and could entice them to enter the wide world of HDR photography with a dedicated camera.
Have you experimented with HDR? If so, share your photos in the comments!
Image credits: gdgt, flickr user yourdon
