After a short vacation where I used my iPhone as my only camera (no sense dragging around a big Canon DSLR for just a couple of days) I found myself with a small dilemma: after capturing many photos, both in regular mode and in HDR, I stared wondering: “how do I recognize HDR photos?” On the device there is a small overlay when browsing photos, but after downloading them on the PC there doesn’t seem to be any way to distinguish them. Sure, the HDR version is always saved after the original capture, so you can look for two identical images and the one with the higher file name will be in HDR. But that only works if the device is set to keep the original version; and there are lots of other ways this can fail, for example if you delete one of them directly on the device or if you rename photos on the computer. Since the iPhone clearly knows which is which, how does it do it and how can I discover than piece of information on the PC?
After some searching on Google I came across a forum discussion with the answer: the iPhone camera adds a custom EXIF tag called ‘Custom Rendered’ to both files. The field has a value of 4 for the original image and 3 for HDR. As a bonus, Panorama-photos also have this tag set with a value of 6 – though they are much easier to recognize due to their different aspect ratio. The only photo-processing software I found that shows this tag to the end-user is Picasa: select the photo and activate the ‘Properties Panel’. Unfortunately there doesn’t seem to be a way to search by custom fields, so you are still left to check each photo one by one, but this is at least a clear criteria to recognize and organize HDR files.
Personally I’m not entirely convinced HDR offers better results that classic photos; sometimes there is better contrast in HDR – clouds and sky are usually overexposed in normal photos and HDR fixes this – other times the HDR version looks ‘fake’, unnatural, with wrong colors or exposure. That’s one of the main reasons I prefer to have both photos and decide later which to keep. Another article I found during my search suggests you can get better results by exposing for the darkest part of the scene before shooting and I will certainly give it a try to see if it makes any difference.