What HDR means for iPhone photos

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One hotly anticipated feature rolling out in next week's iOS 4.1 update is the new HDR (high dynamic range) option in the iPhone's built-in Camera app. The results are subtly improved and realistic looking photos, as opposed to the fake, over-processed look that is often the hallmark of HDR.

A high dynamic range image combines a series of photographs, each shot at a different exposure: underexposed where everything is darker, overexposed where it's lighter, and properly exposed in the middle. The best parts of these images are put together into one shot that brings out details in both the shadows and the highlights—information that would normally be lost in a single exposure though visible to the human eye.

For example, an HDR image of a cityscape with a bright sky and dark foreground will combine an underexposed sky with an overexposed foreground to show more details across the board.

A normal iPhone image (left) and an HDR iPhone image (right).

Apple's version of HDR combines three images taken with the iPhone's back camera in quick succession. When iOS 4 is installed, a new HDR button appears to the right of the camera's flash button. Tapping it turns HDR on or off. In the iPhone's settings under Photos, there is a new HDR setting below the Slideshow controls. Turning it on means your camera will save a copy of the regular photo in addition to the HDR image in your camera roll. Turn it off if you only want the HDR images saved. There aren't any adjustment options for HDR images beyond on or off.

There are a number third-party of HDR apps already available in the App store, but they typically only combine two photos together, not three. Some only take one photo and then add a filter to mimic the HDR look, like the $1.99 HDR Camera app. If you can't wait until the iOS update is released check out the Pro HDR and TrueHDR apps (both $1.99), which combine two photos with varying results.

HDR photography isn't loved by everyone. The final products can be garish, and when everything in an image is perfectly exposed the scene can look fake. Apple's HDR appears to avoid this pitfall by dialing down the overall effect. It's so mild that some iPhone photographers might choose to leave the setting on all the time.

[Image via neven]

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