Modern digital cameras can do a lot of things that their predecessors even as recently as 10 years ago could not do, but they're still not perfect. And one of the challenges that digital photography manufacturers have always faced is producing cameras that are capable of capturing a full range of tones in a high dynamic range situation. Even today, the best DSLRs on the market still can't achieve this in every situation. But there's good news—many newer model cameras have an automatic mode designed to combat this problem. It's called "Auto HDR," but just what does it do and more importantly, should you use it? Keep reading to find out.
[ Top image Railyard ABQ HDR 6-1-14-1894-3 by Flickr user Joseph j7uy5]
What is dynamic range?
Before you can completely understand how modern cameras cope with high dynamic range situations, you need to understand a little bit about what exactly "dynamic range" means. Essentially, dynamic range is the difference between the brightest parts of the scene and the darkest parts of the scene. An image with high dynamic range will have a much broader range of tones between black and white than an image with low dynamic range will have. When you compare the dynamic range of your own eyes to the dynamic range of your camera's image sensor, your camera's image sensor is going to fall a little bit short of what your eyes can do. What this means is that you, with your human eyes, can look at a very brightly lit scene and discern detail even in the darkest shadows and the brightest highlights. Your camera, however, cannot do the same thing. Even the most expensive professional-grade DSLRs fall short of being able to capture every detail in very bright situations. So what happens when you take a photo in bright conditions is that you get lost detail in the shadows or highlights, which may render as completely black or completely white, respectively. We call this phenomena "clipping;" if it happens in the brightest parts of the scene you may have also heard it referred to as "blown out highlights.”
There are a lot of different tactics you can use to cope with very high dynamic range situations. The first and simplest is to simply underexpose or overexpose your photograph deliberately, accepting that clipping is going to happen in either the shadows or the highlights, depending on the scene. Obviously this is not ideal, but it is often the most convenient way of coping with the problem. If your subject is mobile, another option is to move him or her into a shaded area, where the light is more even. You can also use tools such as fill flash or a reflector to bounce light into the shadows, which has the overall effect of evening out the light and reducing the dynamic range.
Another technique photographers use to deal with high dynamic range is to shoot a high dynamic range photograph. Traditionally this is done with landscapes or other non-moving subjects, and a tripod is required. To create a high dynamic range image, you shoot at least three different photos: one at the optimal exposure, or the exposure your camera recommends, one at a stop or so under the optimal exposure and one at a stop or so over the optimal exposure. The shots are then loaded into a post-processing program and combined so that highlight details will come from the underexposed shot, midtone details will come from the photo shot at the optimal exposure and shadow detail will come from the overexposed shot. The result is an image with that complete range of tones that you could see with your own eye, but that your camera could not capture in a single exposure.
If you've never tried shooting HDR before, you can probably see why the technique is not enormously popular amongst beginners. HDR photography requires a certain amount of finesse, a good understanding of the way exposure works, and a tripod—but most of all, it requires you to feel comfortable working with post-processing software. If all of that sounds to you like a little too much trouble, you're not alone. A lot of people stay away from HDR because the learning curve is just a little too steep.
But here's the good news—many camera manufacturers now make an "auto HDR" mode standard even in less-expensive model cameras. The auto HDR mode works exactly like standard HDR works, except all of the processing is done in camera, which eliminates the need for knowledge of post-processing or special post-processing software. Every manufacturer has its own way of doing things, but generally speaking when you select the auto HDR mode, your camera will shoot at least one photo at the optimal exposure and at least one photo on either side, depending on the conditions. In the default setting, your camera may attempt to correct the exposure difference automatically, or you can choose to set the exposure difference (or the number of shots to combine) based on your own visual interpretation of the scene.
One of the cool things about auto HDR is that, depending on your camera model, you may not need to use a tripod to create an HDR image. The camera takes a quick burst of exposures, which limits the alignment differences between shots, and then adds correction for any changes in camera position that did happen between frames. But auto HDR modes do fall short in other areas. While some HDR software can produce HDR images that include moving subjects (the moving subject is isolated from one frame in the series and the other frames are used to render non-moving elements) the in-camera software is not going to be able to correct for motion that happens within the scene itself, so you can't shoot an HDR image of your kid scoring a goal at his soccer game. You could try, but your camera won't be able to align all of the different images of the moving person, and you'll end up with a sort of ghosting or double imaging effect. The same is true for an otherwise static scene that includes moving elements, such as windblown treetops or a crashing surf. But the good news is that if you have ever found yourself wishing for better dynamic range but not wanting to take that step of learning HDR techniques, then auto HDR is a great way to get your feet wet.
The Lock House, Great Haywood by Flickr user William Hook
There are other drawbacks to using auto HDR that you should be aware of before you decide to try it out—many cameras do not use the RAW file format for auto HDR, so you can only shoot in JPEG. That might be a concern if you need to make simple adjustments to your white balance setting or if you want to try pulling details out of the highlights or shadows that the auto HDR mode was not able to capture. And many auto HDR modes will throw out the original exposures and produce only a single image, which is great if you love the single image and not so great if you'd like to do some tweaks or change the way photos are combined. Of course, this is more advanced level HDR, so for beginners it may not even be a relevant concern. However do keep in mind that you get what you get with most auto HDR photos, so if you think you might want to do processing at the multi-image level you’ll probably want to practice HDR the old-fashioned way instead.
Some cameras make the decision-making process simple by giving you two shots to compare—a standard JPEG and the final HDR version. If you don't like the results, you can then reshoot, but of course you can't make any manual tweaks in camera; you have to save that for post-processing. Processing those images automatically in-camera also takes some time, so you won't be shooting any images in rapid succession if you're using the auto HDR mode.
Of course the real question is if those in-camera HDR files are really superior to a standard HDR or a RAW file. The ultimate answer to that question depends of course on the camera model, so generally speaking it's a good idea to run some tests with your camera's auto HDR mode to see where it falls on the spectrum. You may find that images shot with just two frames, or a two-step exposure range, are going to look better than a standard JPEG, but may not look as good as the RAW version of the same scene. The RAW file format tends to be a lot better at capturing high dynamic range scenes then JPEG is, so it already has a natural ability to include that missing detail that you are trying to get with the auto HDR feature. That doesn't mean you shouldn't use auto HDR, but if you're not noticing an improvement in quality over a similar RAW image you should go for shots with a three stop exposure range or higher.
Painted Driftwood by Flickr user Allen McGregor
Like all camera features, you'll probably need to experiment with your camera's auto HDR mode to see if it's worth using. If you shoot lots of photos outdoors on bright, sunny days, you may find that it's just a lot more convenient to use auto HDR than it is to pack a tripod along with you and shoot every landscape three times, only to have to create that combined HDR image later on in post-processing. If you're just not the sort of person who likes to spend a lot of time in front of the computer screen, auto HDR may be a good choice for you, but you'll never know unless you give it a try.
- How to cope with high dynamic range
- Under or over expose
- Shoot HDR
- Auto HDR
- Let your camera choose the exposure difference or choose it manually
- Avoid scenes that have motion
- Compare your auto HDR photos to your RAW photos
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