Gradation Tool; How To Read The Curve - Microtek ArtixScan 4500t Reference Manual

Gradation tool

The Gradation tool lets you adjust the midtones (the mid-level grays) of the
lightness channel "L" of an image without altering the color itself. This is because
even with changes to the luminance or lightness value, the chroma and hue
values are kept constant.
To prevent color images from losing saturation when adjusting the lightness,
ScanWizard Pro provides a Saturation Range option. With this option, colors
outside of a given chroma range are not affected by the manipulation of the
gradation curve.

How to read the curve

.
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.
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.
Original curve
Modified curve
Reference: The Advanced Image Correction tools 89