Along the way, Ferrell made something of a breakthrough. "Most of the
reading I did on HDR said that you can't use flash when you shoot HDR
image sets, but I didn't listen. I worked out a technique for flash. I
call it flash merging, and it involves using a flash off-camera, handheld, to
spotlight various areas of a scene."
Ferrell used flash merging techniques for this image. "I
took six images with the flash held in a different position for
each exposure. The images were then merged and tone mapped."
Judging how many exposures to make of a particular scene is an important element
of HDR photography. Ferrell calls that judgment "scene awareness,"
and his guidelines for judging scene contrast involve the direction of the light.
"If the scene is frontlit, or the skies are overcast, the scene will have
low contrast, and you can usually capture that in a short EV range--three
images will probably do the trick." If the scene is sidelit, he classifies
it as a medium contrast scene, and that would require capturing a greater EV
range. Backlit scenes are, he says, pretty much the highest contrast scenes
you're going to see in nature, and for those you'll need to capture
a larger dynamic range. "You might go from three to nine images for a
or an interior, which can have a large range of contrast."
This is the result of six images taken with the flash unit held
in a different position for each exposure. "I took care
to fill in the shadows created from the previous flash exposures,"
Ferrell says, "so a fully illuminated scene would result
The imaging program that Ferrell prefers is Photomatix; he also has experience
with Dynamic Photo HDR, FDRTools, and Artizen and has worked with Photoshop
CS3's "merge to HDR" function. While it may sound like the
imaging programs do all the decision-making, there's plenty of input from
the photographer. In tone mapping, for example, you're given anywhere
from five to 15 sliders to adjust, depending on the program. "Those sliders
control the compression of the image," Ferrell says. "They bring
out shadow detail and smooth the highlights, and there's a range of things
you can control that are similar to the adjustments you'd have in Photoshop.
The tone mapping decisions you make personalize the image."
What makes a scene an HDR candidate? "There are a couple of things,"
Ferrell says. "The contrast of the scene immediately indicates to me that
the digital sensor can't capture all this--I need multiple images
to get the full range of light. So it's typically an image that has sky
and dark shadows. And HDR is great for grungy scenes--a junkyard, urban
decay, graffiti, peeling paint; it just brings out those details."
For this image, a flash was fired from five locations around the
If you're interested in HDR, the best way to learn it is simply to do
it: sit down at your computer with a set of exposures, the software program
you've chosen, and an HDR guide. Ferrell's is one, but there are
others, including Michael Freeman's Mastering HDR Photography; HDR: An
Introduction to High Dynamic Range Photography by Jack Howard; and a DVD from
Ben Willmore titled High Dynamic Range Mastery.