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Section III Digital Postprocessing
Adjusting Overall Exposure
Most images, even those that are generally
well-exposed, will require some adjustments for
best appearance. The basic refinement made to an
image is to adjust its tonal range using the
Levels
adjustment command. The
Levels
command can be
used on the
Background
layer, but making changes
using an adjustment layer is preferable. To create a
Levels
adjustment layer, click on the
Layers
icon in
the
Adjustments
panel. The
Levels
histogram will
appear, and a new layer (Levels 1) will be shown on
the
Layers
palette. See Figure 15-21.
As described in Chapter 8, Making Exposure
Decisions, the histogram is a graphic display of the
number and distribution of tones in the image.
The horizontal dimension, from 0 to 255,
represents the 256 possible shades of gray in
the 8-bit image. The “peaks and valleys” are
representations of the actual number of pixels
of each shade, from 0 (pure black) at left to 255
(pure white) at right. A photo with a full range of
tones will show smaller numbers of pixels at the
extremes and a large number distributed through
the middle tones.
If the histogram displays empty areas at
either end (indicating no pixels at the lowest or
highest values), the image’s black point and white
point can be adjusted to distribute tones over
the full tonal range. This is done by positioning
the small triangular sliders at either end below
the lowest and highest values shown on the
histogram. See Figure 15-22. This will reassign
the valuesa of the pixels, so that the darkest value
will become 0 and the lightest, 255. All other
pixel values in the image will be redistributed
to provide a full tonal range. The effects of such
Figure 15-21. Using the
Adjustments
panel. A—Click
on the Levels icon to create a new adjustment layer.
B—The Levels histogram will appear in the
Adjust-
ments
panel, and a new layer, labeled Levels 1, will
be shown above the
Background
layer on the Layers
palette. Note the basically empty area at the right side
of the histogram. This indicates that the image is dark
and underexposed.
A
B
Figure 15-22.
Moving the slider below the right side
of the histogram toward the left will adjust the white
point, distributing image tones over the full tonal range.
Compare the histogram and the brightness of the image
in this illustration with the histogram and image in
Figure 15-21.
Move
slider