Adobe PHOTOSHOP 5.0 User Manual page 129

The horizontal axis of the graph represents the
original brightness values of the pixels (Input
levels); the vertical axis represents the new
brightness values (Output levels). In the default
diagonal line, no pixels have been mapped to new
values, so all pixels have identical Input and
Output values.
Note: For RGB images, Curves displays brightness
values from 0 to 255, with shadows (0) on the left.
For CMYK images, Curves displays percentages from
0 to 100, with highlights (0) on the left. To reverse the
curve and change the display at any time, click the
double arrow beneath the curve.
2 If the image has more than one color channel,
choose the channel (or channels) you want to
adjust from the Channel menu.
To edit a combination of color channels at the
same time, Shift-select the channels in the
Channels palette before choosing the Curves
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.
For more information on choosing channels, see
"Using the Channels palette" on page 240.
3 To make the Curves grid finer, hold down Alt
(Windows) or Option (Mac OS), and click the
grid. Alt/Option-click again to make the grid
larger.
4 Click the part of the curve you want to adjust.
A set of direction arrows marks the pixel's position
on the graph, and the Input and Output values
appear at the bottom of the dialog box.
Clicking in the image displays the pixel values and
location on the curve.
Drag through the image to determine the
lightest and darkest areas in the composite
channel of an RGB, Lab, or grayscale image, or
in individual channels of all images. This is
particularly useful in Windows when the
threshold function in Levels is unavailable.
Click any points on the curve that you want to
5
remain fixed. For example, if you want to adjust
the midtones while minimizing the effect on the
highlights and shadows, click the quarter and
three-quarter points on the curve.
You can add up to 14 points to the curve, locking
those values. To remove a fixed point, drag it off
the graph; select it and press Delete; or Ctrl-click
(Windows) or Command-click (Mac OS) it. You
cannot delete the endpoints of the curve.
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User Guide