Graphics Programs Reference
In-Depth Information
Chapter Thirteen — HDR
Overview
HDR
stands for
H
igh
D
ynamic
R
ange. This refers to the range of tonal values that are
present in an image.
Digital cameras can only record a portion of the tonal values present in a scene. When we
look at an object in the shade, our eyes allow us to clearly see objects in the shadows as well
as objects in the bright sunshine that surrounds it.
When there are bright lights and dark shadows in a scene and we adjust the exposure on
our cameras, we can only set the exposure to have one or the other properly exposed. If the
shadows are bright enough to see details, the light areas will be overexposed. If we get the
exposure correct for the bright areas, the shadows will just look like black areas without any
detail.
In the past this could be compensated for by using a graduated ND filter to cover the bright
areas when the image is captured. It could also be adjusted in the film developing process
with a great deal of effort.
More recently, the digital solution involved dodging and burning, as well as the use of ex-
tensive selections, layers, and layer masks.
Now we can accomplish the same thing by combining several photos at different exposures.
Common practice is to take 3 to 7 shots of the same scene with a range of exposure settings.
Many DSLR cameras can do this automatically. Using a tripod during the shoot is imperat-
ive for image alignment when the images are combined and processed.
This is another task that Photoshop has dramatically simplified. Just open the files and tell
Photoshop to create the composite image.
The process is outlined in the illustrations that follow.
