August 3, 2006

Basics

Was It Done With a Lens, or a Brush?

By IAN AUSTEN

Like many amateur photographers, Joe Dejesus posts his photos online and compares them to the work of others on the photo-sharing site Flickr. At some point last year, a number of landscape photos caught his eye with their vibrant tones and colors.

Their secret was a software technology known as H.D.R., for high dynamic range photography. And Mr. Dejesus quickly became one of its practitioners.

“You can get different combinations of colors you cannot achieve with photos,” said Mr. Dejesus, who lives in Granada Hills, Calif., and posts his work under the pseudonym Kris Kros at www.flickr.com/photos/kros. “You can easily come up with something that looks like a painting.”

H.D.R. is one of many digital darkroom techniques catching the fancy of amateur photographers. With the rising popularity of digital single-lens reflex cameras and more powerful personal computers has come a growing interest in visual experiments.

At the same time, software makers like Adobe are increasingly automating many of those processes, including H.D.R. While they may not always be straightforward, tricky digital techniques no longer require months of experience or hours of study.

Although H.D.R. photos are often compared to paintings, they are an attempt by software makers to allow photography to more accurately mimic human vision.

Dynamic range measures how great a difference between light and dark can be captured by a digital camera or film. Relative to the human eye, all photography has a limited dynamic range, and digital photography suffers even more than film.

It is this limitation that leads to landscape photos where a dramatic sky appears as a washed-out smudge. A classic example of the problem is trying to photograph a room’s interior while still capturing the view outside its windows. In that case, photographers are usually forced to choose either the room or its view as their subject.

While it is certainly possible to darken skies and lighten shadows using Photoshop and other image editing programs, even Adobe, the company that makes Photoshop, acknowledges that those methods fall short.

“You’re just not going to get access to the whole range of the scene,” said John Peterson, a senior computer scientist at Adobe who helped develop Photoshop.

The problem, quite simply, is that the data image editors need is not captured by cameras, even if the image was saved as a RAW file, which holds more data than a conventional JPEG photo.

The concept of H.D.R. photography is fairly simple. It starts with a photographer harvesting every bit of difference in brightness by taking several different photos of the same scene, with large exposure differences between them. Software then sorts through the resulting images, which range from underexposed views that are nearly black to washed-out overexposures, to calculate the full dynamic range of the view. Using that vast amount of data, it then constructs a single, high dynamic range photo.

At least that’s the theory. While the actual practice can be highly automated, it is slightly more complicated.

While Adobe did not invent the idea of H.D.R., it popularized it by making it a feature in Photoshop CS2, the $650 professional version of its program introduced last year. (H.D.R. is not part of Photoshop Elements, the considerably less expensive consumer version of the program.)

Mr. Dejesus uses PhotomatixPro, which is available for $100 from a French company, HDR Software (www.hdrsoft.com). And a German programmer, who prefers to call the process full dynamic range photography, sells a program called FDRTools for $53 (www.fdrtools.com).

After a software package, the next thing aspiring H.D.R. photographers need is a sturdy tripod. While the programs try to align the multiple images, a task Photoshop performs most successfully, they have limitations. A single exposure that is too far out of line can cause an unpleasantly blurry final photo.

For perhaps obvious reasons, H.D.R. photography works best with motionless subjects — very motionless subjects. Disturbed waters or winds strong enough to move clouds and flutter leaves and flags between exposures can create effects that are, depending on the viewer, either curiously artistic or unpleasantly peculiar.

There is no absolute rule for the ideal number of photos or their exposure differences. Some experimentation, however, showed that three photos, each two exposure values apart, usually did the trick. (Two exposure values is the equivalent of two f-stops on a lens, but it’s best to get the same effect by changing the shutter speed instead to avoid variations in focus.)

Seven or eight exposures were involved in efforts to create a scene where interiors and exteriors matched. But more pictures usually led to greater alignment problems.

Processing the pictures is a two-step affair. After the programs go through the selected images, they produce a true high dynamic range photo. Unfortunately, because current monitors and printers cannot render H.D.R. pictures, this generally looks terrible.

The next step, tone mapping, creates a useable photo that can be saved in a common format like TIFF or JPEG.

FDRTools, at least in its Macintosh version, is an unpolished and sluggish piece of software, which is probably why Photoshop CS and Photomatix appear to be more popular among people who post their work on sites like Flickr.

The H.D.R. pictures produced by Photoshop CS and Photomatix vary in much the same way as photos taken with different brands of film. The Photoshop images are technically more accurate and make details visible in all areas of the photo, regardless of their lightness or darkness.

Photomatix pictures after one mapping are far more dramatic, although sometimes at the expense of some details and an increase in image noise. (The Photomatix tone mapper is available separately as a Photoshop plug-in.)

Géraldine Joffre, the managing director of HDRSoft, said that while Photomatix was popular with amateur photographers, some professionals told the company they found its results unnatural.

But Ms. Joffre’s theory is that the pros’ assessments are based on photography’s traditional limitations — in effect, how people think photos should look, rather than the actual dynamic range of scenes.

“People sometimes say it doesn’t look like a photograph, it looks like a painting,” Ms. Joffre said. “But if your camera was perfect it would take an H.D.R. image.”