Sunday, October 19, 2008

Starkweather Creek Bike Path at night: Notes on how this photograph was made

How This Photograph Was Made
Night shooting in the city under streetlights with a tripod is always interesting, even though the scenes often exceed the dynamic range of the camera sensor -- that is, the range from the lightest to darkest tones. That's part of what gives night photos their unique look, especially in black and white -- the extreme range from impenetrable black shadows to completely blown out white highlights with no detail. But sometimes you want to hold some of that detail, either in the shadows or the highlights, or both.

One way to do that is with what's called HDR (High Dynamic Range) Software. It enables users to take multiple exposures of the same scene (often three: shadow, midtones and highlights) from exactly the same point (this is usually done on a tripod, but can be done manually if you're careful). The software then merges all the exposures (users can control the mix) into one final image that retains detail across the tonal range, because it blends exposures appropriate to each tone. People often say of the result, "That looks like a painting" -- which is understandable, because painters rarely paint shadows all black, or all white highlights. HDR is used more often for color images than black and white, although the same principles apply to both. This may be because black and white has a long tradition of conventions regarding tonal range to express different effects or moods that goes back more than a century, and which was developed working within the limitations of photographic emulsions, not electronic image sensors. Many serious black and white shooters like to work within those conventions. In contrast, in color digital photography there's often more of a wide-open, "anything goes" spirit that welcomes computerized experimentation.

There are close to 1 million photos tagged HDR on Flickr. Personally, I'm usually not fond of the results. Often they strike me as unnatural, or surreal in an unpleasant sense. But there are exceptions, and I've seen some that I like very much, in which the processing is carried out with subtlety and sensitivity. And in some cases, it's simply a valuable tool. For example, if you're shooting architectural interiors in daytime, it's a great way to balance the indoor lighting with the view through the windows without having to illuminate the interior to daylight levels.

Still, since I haven't personally been confronted by a situation where I feel I need HDR software, I haven't bought it or experimented with it. But there are situations which come close. This photo of the Starkweather Creek Bike Path overpass over east Washington Ave. in Madison is an example. I figured I would expose for the shadows and the midtones and let the highlights blow out. I thought I would like the bright, flaring effect, and mostly I did. There was only one problem: That delicate, Frank Lloyd Wright-influenced patterning on the big lights atop the bridge piers is a signature design detail of this bridge. The patterns are easily visible to the eye at night. But in a photograph exposed for shadow detail, the detail is lost entirely. There's nothing there.

So what did I do with this image that I really liked otherwise? Fortunately, I had bracketed the exposure, and in another frame the rest of the bridge was too dark, but the lights looked fine. I selected the lights in the darker photo, feathered the edges a bit and darkened the lights a bit more. Then I pasted them over the blown-out lights in the other image, did a bit of touch-up around the edges, and that was that. Maybe I could call what I did "pseudo HDR."

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