Graphics Programs Reference
In-Depth Information
Exposure
Starting with Photoshop CS2, support was added for 32-bit
images. Generally referred to as high dynamic range (HDR), these
images offer great flexibility in exposure. These images can better
handle re-creating the wide range of exposures found in outdoor
scenes or intense lighting conditions. The Exposure adjustment is
usually used on images that exist in 32-bit space and is said to be
a 32-bit floating point operation (often shortened to
loat
).
Creating an HDR image is a combination of shooting techniques
and a Photoshop command. It requires that the camera be secured
firmly to a tripod and that you be careful when triggering or
adjusting the camera to not move it (or allow anything to move in
the shot either). Several photos at various exposures are taken of
the same scene (a minimum of three; usually five to seven is ade-
quate). The camera should have its auto-bracket and ISO features
disabled. Each shot should be about two f-stops apart. The user
then harnesses the Merge to HDR command (File > Automate >
Merge to HDR) to create the 32-bit image. You'll create an HDR
image later in the topic, but for now let's jump ahead to an HDR
image that's already built.
1.
Close any open files, and
then open the file Ch10_
HDR1.tif. If you click in
your menus, you'll notice
that several features are
grayed out. Most image
adjustments do not work for
a 32-bit image. This image
was taken in a very low-
light environment, but by
combining multiple expo-
sures together into the HDR
image, I captured a much
better photo.
2.
Click the Exposure icon in the Adjustments panel. This com-
mand makes tonal adjustments by performing calculations in
a linear color space (Gamma 1.0) rather than the current color
space. This offers extreme flexibility for future changes.
