Adjusting brightness curves
You can adjust the tonal range of an image with the Curves com-
mand. Unlike the Levels command, which can set the minimum,
maximum, and median values, Curves adjusts the entire range of val-
ues. It lets you map input values to output values according to a line
(curve) on a graph. Curves provides the most control over the tonal
range of an image.
This command is not available when a paint object in Black &
White mode or Indexed mode is selected.
In the Curves dialog box, brightness values range from 0 (black) to
255 (white), or 0 percent (white) to 100 percent (black). To switch
between these scales, click the grayscale bar under the graph.
A typical setting is a gentle S-curve (or inverted S-curve, depending
on the scale you use), which adds contrast to an image without
appearing too harsh.
Levels dialog box
You can use the Levels dialog
box to control different
aspects of brightness levels.
A
Choose an individual color
channel or the composite chan-
nel.
B
Type values in the Input
Levels boxes or drag the slider
under the histogram to set the
minimum input level, midtone
ratio, and maximum input level.
C Enter numbers in the text
boxes or drag the sliders to set
the minimum and maximum
output levels.
D The histogram graphs
brightness levels for the select-
ed channel.
E
Click Auto for Canvas to
map the darkest values in the
selection to black and the light-
est value to white.
E
D
B
A
B
C