Ricoh B121 Service Manual page 281

γ)
Scanner Gamma (
The CCD output is not proportional to the quantity of light received. Scanner γ
correction corrects the CCD output so that grayscale data is proportional to the
quantity of light received.
The machine has two possible scanner gamma curves: Text and Photo. When
selecting Text, the machine does not use scanner γ correction. As a result, the
output is darker than the image density on the original. The advantage of this is
that the machine can bring out gradations in paler areas. The disadvantage is that
the machine cannot bring out gradations in darker areas, i.e. differences in shades
of dark colors are hard to distinguish.
When selecting Photo, the machine uses scanner γ correction. One advantage of
this is that the machine can bring out gradations in dark areas of photo image
originals. The disadvantage is that it in some cases images come out lighter than
the customer desires.
Output
Density
SM
Correction
Text
6-23
IMAGE PROCESSING
Photo
Original Density
B121D921.WMF
B121 Series/B259 Series