Adobe PHOTOSHOP 5.0 User Manual page 125

Setting the highlights and shadows using
the Levels sliders
You can also set the highlights and shadows in an
image by moving the Levels input sliders to the
first group of pixels on both ends of the histogram.
Doing so maps these pixels—the darkest and
lightest pixels in each channel—to black and
white, increasing the tonal range of the image. The
corresponding pixels in the other channels are
adjusted proportionately to avoid altering the
color balance.
Less exact than assigning target values or using the
Curves dialog box, this method often gives good
results, especially if you want to maintain a color
cast in the highlights and shadows. (For more
information, see "Using the Curves command" on
page 120.)
In many images, eliminating the color cast is
useful. But in other images, using the Levels sliders
to set the highlights and shadows may produce
better results precisely because it does not affect the
color balance.
For a color illustration of color cast, see
figure 6-2 on page 225.
To set the highlights and shadows using the Levels
sliders:
Open the Levels dialog box (see "Using color
1
adjustment commands" on page 105).
The Levels dialog box displays a histogram of the
image. (See "Step 2: Check the scan quality and
tonal range" on page 112.)
If the image has more than one color channel,
2
choose the channel (or channels) you want to
adjust from the Channel menu. (See "Using the
Channels palette" on page 240.)
To edit a combination of color channels at the
same time, Shift-select the channels in the
Channels palette before choosing the Levels
command. The Channel menu then displays the
abbreviations for the target channels—for
example, CM for cyan and magenta. The menu
also contains the individual channels for the
selected combination.
Drag the Input Levels sliders to the edge of the
3
first group of pixels on either end of the histogram.
For example, suppose you want to increase the
contrast in an image with pixels that currently
cover a range of only 0–233. If you drag the Input
Levels white triangle to 233, pixels with brightness
values of 233 and higher (in each channel of the
image) are mapped to 255, pixels with lower
brightness values are mapped to corresponding
lighter values. This remapping lightens the image,
increasing the contrast in highlight areas.
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User Guide