User Guide

CHAPTER 6
122
Making Color and Tonal Adjustments
6 Adjust the curve:
• Drag the curve until the image looks as you
want it.
• Enter an Input and Output value for the selected
point on the curve.
Click to fix a point on the curve. Click and drag to adjust.
The gamma of any curve is its slope, expressed as
the ratio of the logs of the output to input values.
For example, a gamma value of 1.0 equals an
output-to-input ratio of 1:1. Moving the midpoint
of the curve up (in an RGB readout) lowers the
gamma value (that is, to less than 1.0); moving the
midpoint down raises the gamma value. (This is
the same as moving the gamma Levels slider to the
right to lower the gamma level, left to raise it.)
The following shortcuts work with the Curves
dialog box:
• Ctrl-click (Windows) or Command-click
(Mac OS) in the image to set a point on the curve
for the selected color in the composite channel
(but not in the component channels).
• Shift+Ctrl-click (Windows) or
Shift+Command-click (Mac OS) in the image to
set a point on the curve for the selected color in
each color component channel (but not in the
composite channel).
• Arrow keys to move points on the curve.
• Shift-click to select multiple points.
• Ctrl+Tab (Windows) or Command+Tab to
move forward through control points on the
curve.
• Shift+Ctrl+Tab (Windows) or
Shift+Command+Tab to move backward through
control points on the curve.
• Ctrl-click (Windows) or Command-click
(Mac OS) in the grid to deselect all points on the
curve.
• Ctrl-D (Windows) or Command-D (Mac OS) in
the grid to deselect all control points on the curve.
To use the Arbitrary Map option in the Curves
dialog box:
1 Click the pencil at the bottom of the Curves
dialog box.
2 Drag to draw the curve you want in the Curves
graph area.
The pencil pointer appears when you move into
the graph. To constrain the curve to a straight line,
hold down Shift, and click to define the endpoints
of the curve. For example, you can create an image
negative by holding down Shift and clicking the
upper left and then the lower right corner of the
graph.
3 If desired, click Smooth to smooth the curve.
Step 5: Adjust the color balance
With the tonal correction complete, you can
accurately examine and diagnose any problems
with color in the image—a color cast, oversatu-
rated or undersaturated colors.