What is HDR? How useful is it?

What is HDR? How useful is it?

To understand HDR and its use cases you need to familiarize yourself with what dynamic range is.

Our eyesight is a super advanced and adaptive mechanism polished by evolution over millions of years. It adapts really quickly to different lighting conditions and brightness levels of objects around us. We can easily discern detail in very dark objects in twilight or brightly lit snowscapes in the sun (seemingly) at the same time.

Dynamic range is just how big a spread between superdark and superbright we can register while still distinguishing detail, a quality of handling ranges of brightness. Our eyesight has a very wide dynamic range, but camera sensors can’t match that due to their physical qualities and the processing bit depths, which dictate only so many registrable gradations of brightness (further complicated by the gamma adjustment, but that’s a different story). Meaning we can either have them capture the detail in brightly lit objects, or on dark objects, but not at the same time, as it takes very different exposure settings (think of your eyes adjusting to bright daylight after exiting a dark room).

So for very contrasty scenes (those with wide DR) that will mean either pictures with good detail in the shadows, with all brighter parts in solid overexposed white, or detailed brights, with all shadow parts as a solid black mess.

What if you could take those good brights and good darks, and combine them together from several shots made with different exposures? Well now that’s just what the HDR technique in digital photography does.

Now that you understand this, think about some usecases. HDR will definitely help with high-contrast scenes. The lower the contrast, the smaller the advantage, although you might like the creative effect.

The more dynamic your scene is (fast movement, windy weather, etc), the worse your chances are, as objects change position between shots and start producing artifacts (multiplying around the moving edges; some software algorithms can mitigate that, but that’s usually the domain of desktop or cloud software). Same goes for cases when you move yourself and can’t stand still, and with phone cameras that’s a serious concern, since even tiny moves in relation to tiny lenses represent a considerable movement percentage-wise.

Also HDR can be tricky for subjects with large continuous tone areas with sharp borders. This has to do with algorithms outlining areas to pick from several shots. Joining them with hard edges would look terrible so there’s a lot of masking going on with feathered edges of masks blending into each other. At those sharp borders, e.g. edges of buildings, this results in halos appearing, especially with the simpler algorithms in smartphone apps, which have to work quickly with limited resources.

With all its pluses HDR processing can and often does produce eerie unnatural results that look flat, so like any creative technique it’s best taken with a grain of salt. Often you don’t want all that detail, your shots may turn out much more expressive if you keep the natural contrast so any backgrounds don’t stand out too much and distract from your real subject.

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HDR stands for HIGH DYNAMIC RANGE imaging, and it’s an old photography practice recently introduced to cameraphones like the iPhone and some Android devices (or with the use of special apps ). You’re on the right track: it’s supposed to make your pictures look better, but it depends on when you use it.

How HDR Works

HDR, as its name implies, is a method that aims to add more “dynamic range” to photographs, where dynamic range is the ratio of light to dark in a photograph. Instead of just taking one photo, HDR uses three photos, taken at different exposures. You can then use image editing software to put those three images together and highlight the best parts of each photo. In the case of HDR on smartphones, your phone does all the work for you—just snap your picture and it’ll spit out one regular photo and one HDR photo. The result is something that should look more like what your eyes see, rather than what your camera sees.

This is why, when you turn HDR mode on, your phone takes a little longer to take the photo. It’s actually taking three pictures, rather than just one. Check out the image above for an example. It wasn’t taken with a cameraphone, but it’s a good demonstration of what HDR can do.

When you should use HDR

As we said, HDR is designed to help you take better-looking photos, especially in certain situations. Here’s where you should try using HDR:

When You Shouldn’t Use HDR

Of course, as you’ve discovered, sometimes HDR actually makes your pictures look worse. Here are some situations in which HDR is better off ignored:

Luckily, most HDR cameraphones will give you two images: one with HDR turned off, and one with it turned on. That means that you can always give HDR a shot and see what the comparison looks like before turning it off altogether (as long as you have time to sit through the extra few seconds of photo-taking). As with all things photography, you can’t go wrong experimenting! These guidelines should help you out, but don’t be afraid to snap a few photos and look at them later. Once you get the hang of it, HDR can be a great tool for getting better pictures.

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