Curve Tool; How To Read The Curve - Microtek ScanMaker IIG User Manual

Curve tool

Usage
To adjust the midtones,
or mid-level grays, of
an image.

How to read the curve

Original curve: Straight
diagonal line
The curve shows the relationship
of the brightness changes across
the middle pixels between the
resulting image and the original.
When you open the Curves dialog
box, the line on the graph is
diagonal because the Input and
Output values are the same.
The x axis of the graph represents
the original brightness values of
the pixels, from 0 to 255; the y axis
represents the new brightness
values. Clicking on the diagonal
line then plots a point that can be
adjusted.
The Curve tool lets you control the gamma,
which measures the intensity affecting the mid-
level grays (midtones) of an image. Adjusting
the gamma lets you change the values of the
middle range of gray tones without dramatically
altering the shadows and highlights.
In many ways, the Curve tool gives you the
most control for adjusting an image's values, but
novice users may take some time to master its
intricacies. The Curve tool applies to grayscale
and color images and is not available for use
with line art or halftone scan modes.
Modified curve with
points moved up
When the curve is moved up or
down, the relationship between
input value and output value
changes accordingly.
• In areas where the curve is
moved down, pixels in that
portion of the image are
darkened.
• In areas where the curve is
moved up, pixels in that portion
of the image are lightened.
Contrast in an image can be seen
by the angle of the line. The
steeper the slope, the higher the
contrast. The closer the line is to
horizontal, the lower the contrast.
Reference: The Settings Window 5-67