What is HDR on the iPhone?
I’ve talked to quite a few people who have the new iPhone 4 and do not even know about the HDR functionality build into the camera. The acronym HDR often makes people think that it has something to do with High Definition or something similar, but this is not the case. HDR stands for High Dynamic Range and it is a trick that pro photographers have been using for years that is now built in to the iPhone. It is worth mentioning that this feature is NOT built into the 4th generation iTouch.
Dynamic Range is an indicator of the range of brightness a person (or camera) is capable of processing. The human eye has a much higher dynamic range than a camera does. This is what allows us to stand in a dimly lit room and be able to clearly see indoor areas that are in shadow as well as brightly lit outdoor areas. Cameras, with their limited range have to ‘expose’ for one or the other. If you set your exposure to produce a clear image of the outdoors, the shadows will be black. If you expose for the shadows, the bright outdoors will be ‘blow out’ and devoid of any detail. The HDR feature on the iPhone addresses this limitation.
Here is how HDR works. When you have HDR enabled on your iPhone, the camera actually takes 3 pictures in rapid succession. It then uses an internal algorithm to combine the three images into a single image, using the properly exposed areas of each to make a final image with a higher dynamic range than any of the originals. Photographers often use ‘bracketing’ to take multiple shots of a scene with high contrast and then combine them later in PhotoShop. The iPhone does it on its own.
Here are a couple of sample images to demonstrate the difference. I just snapped these off right from my reading room so cut me some slack. They aren’t high quality photos or anything — they just demonstrate the HDR. Actually, they are both a little dark 
This first image from my iPhone shows the shot without HDR. Notice how the room is basically black and the detail outside is blow out beyond recognition.
iPhone 4 - HDR Off
And this second was taken with HDR turned on. In this image, you can see some of the detail in the room and can clearly see the trees outside. Pretty cool hunh?
iPhone 4 - HDR On
One caveat to be aware of with HDR however is this. Since it is taking 3 pictures in ‘rapid’ succession, if you subject is moving, you will get at best a blurry image and, at worst, an extra eye, nose or mouth on their face
-john
No related posts.
Thanks a bunch for this post john. I just got my iPhone 4 not long ago and wondered what HDR meant. I also didn’t know why I was getting two of every photo and why sometimes the second photograph had overlapping features. Your Graphics blog post on HDR on the iPhone was greatly needed and proved extremely valuable to me personally. Thanks again.
Shelly
Thanks John, for this helpful information about using HDR on the iPhone. It sounds like this is a great new feature on the iPhone especially when you have very bright or very dark areas in a photograph which you would like to expose properly. It takes a lot of work to accomplish this same thing with a regular camera.