Human eye can expose quite wide dynamic range. If you look a sunset view, you can easily pick dark details on the ground and still see vivid colors of the sky. Camera sensor, however, is not able to pick both ends of the light levels at the same time. This usually results a dark ground or overexposed sky in the photographs.
HDR is about taking multiple pictures exactly from the same position, with different exposure settings. First, take a picture to expose sky, then another picture to expose the ground. The next step is to combine these two shots by using properly exposed parts of both images.
HDR photographs can be “manufactured” either manually with a photo manipulation software, like Photoshop, or use a HDR feature in a camera or a HDR camera application. Modern SLRs have a HDR mode, thus making the process automatic. There are plenty of HDR camera applications available for smart phones, too.
The application itself is easy to use. Just remember to start Pro HDR app instead the native camera application. There are few differences how buttons have positioned compared to iPhone Camera app, but this causes no confusion. The app starts in the automatic mode by default, but you go manual and choose two exposure points.
The shooting happens in two stages: first expose the raw snapshots and then process those into a resulting photo. When you press the shutter button, the exposing starts. It takes five seconds in manual mode to take needed two shots, ten seconds in the automatic mode.
Here we observe the biggest drawback in the HDR photography. During the exposure stage, there should be minimal camera movement and no moving subjects in front of the camera to make good results. The best subject for HDR is obviously a scenic view, and using tripod would be always good idea. The wind can also decrease the end result quality if there are trees in the picture.
For camera phones, tripod is not usually there. Going handheld, the camera easily moves between the two snapshots, and this can result shadows in the resulting HDR picture, as shown on the image left.
After shooting, it takes about 12 seconds to process the two shots into a one (with iPhone 4S). You cannot do much anything meanwhile. Before save, you can review the results on full screen, but unfortunately you cannot zoom to confirm sharpness and other detail.
This is the point where I observed a bit of bad user interface design in Pro HDR app: If you press Done button, a dialog pops up saying: “you have not saved you picture, continue to camera anyway? Cancel/OK”. If you want to save the picture, press cancel, then Save button, then Done again to take next picture. Although you learn to press Save directly, in action situation I stumbled couple of times first pressing the Done button.
What about the results? There are many situations where Pro HDR shines and gives easily great results. It is huge bonus that you don’t need to download photos first to laptop, process them for HDR. Now you can take nice HDR shots, and share those from the iPhone right away.
Sometimes the moderate optics in iPhone can cause issues. For example, when the subject has bright areas, the brightness bleeds to nearby areas in image. This is also visible in HDR images quite often. One issue, although rare, is variation in color temperature, as illustrated image on left.
Sometimes the results are more artistic than photo realistic, but this is something you have to accept when doing photography with a smart phone and letting the software do the work. Besides, this kind of results can be almost beautiful: