Gestetner A265, Service Manual

Page: 59 / 855

IMAGE PROCESSING
SM 2-7 A265/A267
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2.2.3 AUTO IMAGE DENSITY
In the SBU
ADS prevents the background of an original from appearing on copies.
The copier scans the auto image density detection area [A] as shown in the
diagram. This corresponds to a few mm at one end of the main scan line. As the
scanner scans down the page, the IPU on the BICU detects the peak white level
for each scan line. The IPU determines the reference value for the A/D conversion
for a particular scan line using the peak white level for that scan line. Then, the IPU
sends the reference value data to the reference controller on the SBU.
When an original with a gray background is scanned, the density of the gray area
is the peak white level density. Therefore, the original background will not appear
on copies. Because peak level data is taken for each scan line, ADS corrects for
any changes in background density down the page.
As with previous digital copiers, the user can select manual image density when
selecting auto image density mode, and the machine will use both settings when
processing the original.
In the IPU
After the SBU process, the IPU board removes background noise resulting from
the SBU-BICU wiring by adjusting the white level.
“Service Mode” Original Types
If the user selects a “Service Mode” original type with the user tools, these two
ADS process can be either enabled or disabled (SP4-936, SP4-937), and the
amount of white level change for the IPU ADS process can be adjusted (SP4-938).
8 0 m m
2 0 m m
0 . 5 m m
Sub scan direction
A265D502.WMF
[A]
CÓPIA NÃO CONTROLADA
CÓPIA NÃO CONTROLADA