Gamma - Xerox DocuMate 152i Scanning Manual

TWAIN Scanning Guide Image Enhancements
Technical note:
Most monitors have a contrast setting that is user adjustable. When viewing scanned images on-
screen, versus printing the image, the contrast setting of the monitor may effect how clear a
scanned image looks when compared to the original. If the scanned image is too different from
the original image, or if adjusting the scanned contrast level does not modify the image how you
want, try adjusting the monitor's contrast level. Refer to the monitor's user guide for adjusting the
contrast level and see if the manufacturer has any recommended settings.
Black background scanners:
Some scanners have a black background plate. A black background results in more precise
cropping results and skew detection. However, when scanning thin paper, such as carbon copy
paper or ruled writing paper, which are less than 18lb paper weight, the background may "bleed"
through into the final image and make the image darker than it should be. In that case, try
adjusting the brightness level between 40% and 60%, then adjust the contrast level between
60% and 80%.

Gamma

Gamma is the tone curve and starting point for image enhancement. Move the slider left or right
to darken or lighten the image. As you raise or lower the Gamma value, the values at which
Brightness and Contrast effect the image are changed. It is recommended that you keep the
default gamma value, or adjust this setting before adjusting the other options.
Choosing gamma values
As the gamma value is adjusted lower, the tone curve begins to straighten and the shadows of the
image are expanded, darkening the shadows without overall darkening the image with gray as
seen with lowering the brightness level. This way, the highlights and shadows in the image are
maintained by saturating the pixels with darker levels of the same color rather than adding gray to
all colors.
As the gamma value is adjusted higher, the tone curve bends and the highlights of the image are
expanded, lightening the highlights without overall lightening the image with white as seen with
raising the brightness level. This way, the highlights and shadows in the image are maintained by
saturating the pixels with lighter levels of the same color rather than just adding white.
Adjusting the gamma level is based on how you want the image to appear and there is no
standard to adhere to.
38 User's Guide