HDR stands for High Dynamic Range imaging,
and it's an old photography practice recently introduced to camera phones 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. Here's a quick primer on how HDR
works, and when you should—and shouldn't—turn it on.
How it 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
take your picture and it will give 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 at a time, rather than just one. Check out the image above
for an example.
HDR Sensors
More and more
CMOS image sensors now have high dynamic range capability within the pixels
themselves. Such pixels are intrinsically non-linear (by design) so that the
wide dynamic range of the scene is non-linearly compressed into a smaller
dynamic range electronic representation inside the pixel. Such sensors are used
in extreme dynamic range applications like welding or automotive.
Some other
sensors designed for use in security applications can automatically provide two
or more images for each frame, with changing exposure. For example, a sensor
for 30fps video will give out 60fps with the odd frames at a short exposure
time and the even frames at a longer exposure time. Some of the sensor may even
combine the two images on-chip so that a wider dynamic range without in-pixel
compression is directly available to the user for display or processing.
-source Wikipedia
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