HDR IMAGERY

A few years ago, while visiting Tim Tyson’s blog, I discovered a kind of photography I had previously been unaware of, one that opens up a whole new type of imagery.

I speak of High Dynamic Range (HDR) photography, which combines the data contained in multiple digital images taken at different exposures to create a single photograph. The results can be remarkable, even surrealistic.

No photography - from the earliest daguerreotypes to the latest high-resolution digital imaging - is capable of covering the extreme range of lighting conditions our eyes can perceive. We can see by starlight on a moonless night, and we can see on bright sunny days - a dynamic range of about a billion-to-one. But as soon as you try to crush that huge spread between the darkest darks and the brightest whites down to something you can capture on film (or on a digital sensor), you’re giving something up.

The newest digital light sensors can capture a dynamic range of about 11,000:1. You lose a lot of that when you display your image on an LCD screen, which is capable of about 1000:1 range... but even that is way better than a paper print’s 100:1.

Back when people still used film to take photographs, you could improve the dynamic range of your display by using transparency film - slides - instead of print film. But you had to get the exposure just right. Transparency film has little room for exposure errors: no latitude. With contrasty films like Kodachrome 64, you had to be within a half-stop of dead center. If you were making prints, you could use techniques such as dodging or burning to jack up the dynamic range of an image, darkening highlights or bringing out shadow detail. Not an exercise for the timid or lazy.

With digital imaging technology, though, we now have the ability to take three, five, or more separate exposures, each shot with different exposure values in order to “bracket” the main shot, and combine them to capture the brightest whites, the blackest blacks, and pretty much everything in between. The mashed-up image files are huge 32-bit jobbies with a huge amount of visual information; to display them, they have to be crunched down to 8-bit files using a process called tone-mapping. The results still can’t compete with the dynamic range of the human eye - not by a long shot - but they can have a certain aesthetic appeal.

The latest versions of Photoshop incorporate HDR imaging capability, but I have found that Photomatix, a stand-alone HDR imaging program, does a much better job. I’ve been screwing around with HDR for several years now, off and on - here are a few I’ve done...



Depending on how broad your exposure bracketing is, and depending on the specific settings you use during the tone-mapping process, your results will vary from somewhat normal-appearing to otherworldly. Give it a try!