High Dynamic Range (HDR) images are all the rage nowadays. A quick scroll through this showcase
of HDR photography shows why: HDR images can be dramatic and hyper-realistic.
HDR images exhibit a greater range between the lightest and darkest areas of an image than normally captured by a camera. The goal is to embue the image with the same dynamic range that the human eye can record (or even more, if the desired effect is artistic rather than realistic).
HDR images can be created in several different ways. The most common method is to merge normal, standard dynamic range photos in such a way as to capture the lightest and darkest details in the merged image. This merging is done via software, and we'll talk more about this approach in a moment.
The other alternative is hardware based. More digital cameras now include an HDR feature that allows in-camera processing and creation of an HDR image. This is generally accomplished when the camera takes multiple exposures of the scene - each exposure being "underexposed" or "overexposed" - and then using onboard processing to generate a single image that incorporates the details from the extremes.
In the end, all HDR imaging is software based, whether done in the camera or in the computer. Analysis of the lightest and darkest ends of the range of luminance is necessary in order to make sure details aren't lost in the final image.
In addition, all HDR imaging requires at least two source images - again, one that emphasizes the darker end of the luminance range of the scene, and one that emphasizes the brighter end of the range. The most common method of capturing these contrasting photos with a digital camera is by using a bracketing method of exposure. Photograph a scene with the camera set for one or more stops under "normal" and then take a second photo of the same scene with a setting of one or more stops over "normal." (Obviously, unless you have a camera that can simultaneously capture multiple F-stops with one shutter click, you'll probably need to use a tripod to ensure that the photos are capturing the identical scene.)
The tricky part of the process comes after the images are captured. How can you best combine them to create the HDR image?
There are a number of applications that can be used to generate HDR images. Photoshop CS5 has a couple of different approaches ("Merge to HDR" and "HDR Toning"), but it's expensive and is overkill if all you want is a quick method of creating an HDR image.
In that case, your best bet is a dedicated application geared specifically toward HDR imaging. There are several to choose from. I've tested Photomatix
by HDRsoft ($99; Mac/Windows) and it's fairly straightforward and yields good results.
A similar, less-expensive alternative to Photomatix is HDRFactory
($69; Mac/Windows), one of the many image processing applications offered by Akvis, a Russian software company. I was recently offered the chance to test and review HDRFactory 1.0, which I installed on my Mac Pro running OS 10.6.7 (Snow Leopard).
My source images were taken using a tripod-mounted Canon Digital Rebel XT. I used the camera's auto exposure bracketing feature to take three photos, one normally exposed, and two bracketed with -2 and +2 F-stops. (For those who obsess over metadata, the -2 was F/10, the normal was F/5, and the +2 was F/4.5. All photos were 1/1000 sec. and ISO100; 31mm focal length.)
Here are the source images (normal on top):
After transferring the photos to my hard drive, I opened HDRFactory (there doesn't appear to be a way to import photos directly from a camera into the application, although that's not a big deal) and selected the photos for processing. The program handles at least sixteen different file formats, including proprietary RAW formats for all major camera manufacturers. My photos happened to be plain vanilla, 7-megapixel JPGs.
Those accustomed to the elegant interfaces of most Mac OS X-native applications will find HDRFactory's layout a bit Windows-centric (I even flashed back to Mac OS 6). The interface is functional and intuitive, but hardly slick. Here's a screenshot of the basic window:
Lots of icons and control bars. Fortunately, the application's tooltip function works well, providing a summary in the yellow box of the purpose of each icon and option as you move your cursor over each of them.
And HDRFactory is all about options. The sheer number of detailed parameter combinations and settings is staggering, and I don't profess to either understand or have tested all or even most of them. For this reason, the program is easy to use, but difficult to master - true mastery requires a solid grasp of the principles of digital imaging in general, and HDR imaging in particular. This makes it a solid choice for pros, but the ability to quickly experiment (or to use the program's built-in presets) also make it a non-intimidating option for beginners and those who just want to play around with HDR to see what can be done. For my test, I stayed with the "AKVIS Default" preset.
Of course, the true measure of image processing software is in the quality of its output. Below are comparisons of the HDR output from the three programs I mentioned above: Photoshop CS5 (two images), Photomatix, and HDRFactory. All images were generated using each program's default settings.
Photoshop CS5 - HDR Toning
Photoshop CS5 - Merge to HDR Pro
HDRFactory - "AKVIS Default"
As you can see, the results vary widely, and "the best" result is a matter of personal preference. However, I did notice more artifacts in the HDRFactory image (look closely at the sky around the upper branches of the tree and you'll see the subtle white pixelated artifacts; they're missing from the other versions). The HDRFactory image is also 10-20% larger than the others.
Again, I didn't experiment much with the myriad of options available in HDRFactory, but there's not a single significant technical aspect of the image that can't be easily tweaked via the program's settings. And once you find a combination of settings that you like, you can save that combination as a default option, saving considerable time for future use.
If you already have Photoshop and don't often work with HDR images, a standalone program like HDRFactory may not be attractive, but the price and control of the program make it almost irresistible for those who want a standalone HDR application. (And if you want to use it seamlessly in conjunction with Photoshop, HDRFactory comes with a plugin option. Mac users have to buy it separately; it's bundled with the standalone Windows app.)