A Simplified HDR Technique
By Ellis Vener
There were three major problems to solve for this view of the State Capitol Building in Atlanta, Georgia:
- It is a large multi-level space with lots of fine detail.
- There were multiple light sources: daylight, fluorescent and tungsten.
- The interior composition spanned a broad EV range with important detail at both ends.
Solving the first two problems was straightforward, solved with a Nikon D3 and an AF-S 14-24mm f/2.8G ED Nikkor lens set to f/8 at 14mm. I chose f/8 for depth of field and optimal resolution. I set the Nikon D3 to manual focus, ISO 200, and aperture priority 3-D Matrix metering. Once I secured, checked and doubled-checked the camera settings and position, I took seven exposures, bracketing from +3 to -3 stops in one-stop increments. Given the total spectrum hash of light sources, I thought it best to give Auto White Balance a try.
Image ©2007 Ellis Vener
Based on earlier conversations with architectural photographer Christopher Campbell, I decided to experiment with a modified version of the two-exposure HDR (High Dynamic Range) technique discussed in Mark Galer’s book Photoshop CS3 Essential Skills. I selected two frames in Adobe Photoshop Lightroom: an under exposed one for the best highlight detail and an over exposed one for best shadow detail. I set the Clarity slider to 10 and turned off sharpening, leaving the white balance setting “As Shot.”
I exported the two frames as 16-bit per channel TIFFs in the Pro Photo color space, opened the files in Photoshop CS3, and copied and pasted the darker exposure as a new layer on top of the lighter exposure.
I set the blending mode for the top layer was to Difference to check the alignment of the two layers. Once alignment was confirmed I switched the blending mode back to Normal.
I lowered the opacity on the top layer until both the image on the monitor and the histogram looked right, with clipping only in the very deepest shadows and the visible lightbulbs.
I created a Levels Adjustment Layer (Levels > New Adjustment Layer > Levels…) in the top layer. By holding down the opt/alt key and clicking on the black and white point sliders, you can see where clipping occurs. It helps to view your image at 50% or 100% magnification. In this case I tweaked the mid-tones slightly.
Once it looked right, I saved this file as a master, duplicated it, and flattened the duplicate. I applied PhotoKit Sharpener’s Capture Expert Sharpener (set to High Resolution/ Fine Edge mode). I checked the overall sharpening at 50% magnification and again at 100% looking for halos. Satisfied and with the file adequately backed up to other locations, I flattened it and saved again.
See images below for large view and details.
This image (above) was the best single frame. The image below is the end result of the HDR technique.