Working with 32–bit floating–point HDR files requires a completely different mind–set altogether. We are no longer working with a fixed value of a pixel trying to force it up or down the histogram scale with either levels or curves (which often leads to various imaging artifacts). Instead, in an HDR file every pixel has a complete range of data that we are simply cycling through (or re–exposing) by applying different adjustments. In a way, we are no longer working with pixels at all; we are working with light itself.
The first image below shows a freshly merged HDR file from 6 different exposures. Using the concept outlined above we can relight the scene (to a reasonable extent) as long as the file is kept in 32–bit. Since an HDR file knows exactly how the scene looks like either really under or over–exposed (and everything in between) we can use that information to simulate various lighting by adjusting tone, contrast, and color of a specific area.
Here the lights in the frame are turned on and basic illumination is created, which will be refined in subsequent steps. HDR allows for brighter areas to have great local contrast without blowing out—something that would never be possible in either 8 or 16–bit modes. The black shadows on the right side of the frame will later be restored without any loss in quality.
More virtual light sources are added outside the frame to illuminate both shadows and the foreground. A mercury vapor light, which gives off a cyan cast, is added to illuminate the High Line in the center of the image. The lights in the windows are turned on all at the same time as well.
At this point it was time to place in the model on a motorcycle, which were shot as a separate single exposure and processed out to a 16–bit file where a mask was created. The only advantage by bringing a 16–bit file over to a 32–bit working space is that it allowed us to keep the background in HDR for further tweaking. The 16–bit file does not gain any extra information from this process, however. The color and contrast were then adjusted to seamlessly blend the two elements together.
All the layers were then stamped together and part of the new layer was flipped and put in perspective to create the billboard on the side of the building. By staying in 32–bit it was possible to simulate a very realistic colorcast as well as hot spots on the sign. At this point all the work in 32–bit was done and the file was converted to 16–bit where minor finishing touches were made, including adding the glow to the lights. Rollover the final image below to see the original HDR file; larger version is available in the gallery section.
By staying in 32–bit mode and avoiding a common practice of tone mapping down to either 8 or 16–bit opens up a whole new way of looking at and working with photographs. The result is a much cleaner, more dimensional image with incredible level of detail and contrast throughout the entire tonal range.
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All photographs © Gregor Halenda, 2008. All Rights Reserved.
Imaging work by DOT Editions.