Ricoh VT3500, Service Manual

Page: 135 / 330

9.2.4 Reference Data Correction
[Overview]
The reference data, which are used to digitalize the image data, are
compensated by the following corrections:
1. The image data sent from the CCD do not exactly represent the image for
the following reasons:
•
Because of loss of brightness
towards the ends of the fluorescent
lamp and the edge of lens.
•
Because of variations in sensitivity
among pixels of the CCD.
•
Because of distortions of the light
path. (Stains and/or variations in
reflectivity of reflectors, exposure
glass, mirrors, etc.)
To eliminate such distortions from
the image data, the distorted data
are applied to the reference data.
Thus, the image data are corrected
when they are converted into digital
data.
2. Original Background Correction
The white peak levels (VH) for each
pixel are determined by the
reference data. If a newspaper or
blue print is scanned as an original,
the whitest image datum is much
lower than the white peak level of
the white platen cover. The image
datum is close to the black peak
level (VL). As a result, a dirty
background may appear on prints.
To prevent this, the whitest image
datum of the scanned image is
used as the maximum white peak
level (VH Max.) of the reference
data.
Distortion
1 line
Image Data
Reference Data
VL
VH Max.
VL
Image Data
Reference Data
1 December 1993
2-99