Capture ¶

High dynamic range images have a large range of brightness in the scene—some light areas, some dark areas. By blending an underexposed image that captures detail in bright areas of the scene with an overexposed image that captures detail in dark areas of the scene you can capture a range of brightness that would not be possible with a single photograph.

In the picture above, taken on the pinto arch trail in Moab, Utah, there are two exposures of one scene: the immediate surroundings are in a shadow, the sky and butte in the distance are in the bright sunlight. Below I’ve blended the shots into a single scene with a wide range of brightness – an HDR image:

I captured the image above using the following equipment:

• Nikon D610
• Samyang Optics / Rokinon AF 14 mm f/2.8 FE

And that’s it: no tripod and no filters. I shot the image handheld at f/11 ISO 200.

The shutter speed for underexposed photo was 1/400 sec. For the overexposed photo it was 1/60 sec. I varied the shutter speed using the exposure bracketing feature of the Nikon D610.

Processing ¶

After capturing my under- and over-exposed photos I use the following software programs:

• align_image_stack which is part of the hugin package
• enfuse which is part of the enblend family of FOSS photo tools
• Darktable to make final edits and lens correction
• exiftool to manage metadata

First, I import my images using a bash script I wrote that maintains a strict file structure. Next, I use Darktable to do lens correction (based on the astounding achievement that is the lensfun database) then I export as 16-bit tif files.

At this point, since I shot the images without a tripod, they have minor misalignments. align_image_stack corrects the misalignments and creates a perfect stack of images:

#!/usr/bin/env bash

# align.sh
# ---
# By default align image stack tries to find 8 control points in a 5x5 grid
# This finds 16 control points in a 10x10 grid.
align_image_stack \
    -a aligned_ -v -m \
    -g 10 -c 16 -C \
    "$@"

I use the command align.sh *.tif with the above script to create aligned images.

This command creates precisely aligned, stackable tif files with the prefix aligned_ in the current directory.

Notice in the image above – taken just East of Moran Point at the Grand Canyon in Arizona – that the underexposed image shows more detail in the clouds and the sun, whereas in the overexposed image shows much more detail in the canyon and on the rocks in the foreground.

Now I use the enfuse command to produce a not-offensively-garish HDR image of the aligned images: enfuse -o out.tif aligned_000* .

In the final image, we retain both the detail of the sun and clouds in the sky as well as a clear view of the canyon (and its grandeur) and the rocks in the foreground.

This is a technique I use constantly to capture shots that would be impossible any other way, AND(!) it uses tools and techniques that are useful for all FOSS photography nerds. Best of all? No high-falutin cellular phone required.