Auto Background Correction - Ricoh JP5000 Service Manual

IMAGE-PROCESSING 1 July, 1998

2.2.2 AUTO BACKGROUND CORRECTION

[A]
C229D097.WMF
Auto background correction mode can be used in Photo/Letter, Photo, and Tint
modes. The default setting does not allow the user to select auto background
correction mode. (Use SP 2-31 to enable this mode.)
Auto background correction prevents the background of an original from appearing
on copies.
While scanning the original, the background density detection area [A] is also
scanned. This area [A] is a narrow strip at the start of the main scan line, as shown.
As the scanner scans down the page, the IPU on the MPU detects the peak white
level for each scan line, within this narrow strip only. From this peak white level, the
IPU determines the reference value for the A/D conversion for the scan line. The
IPU then sends the reference value 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. This feature corrects any changes in background density down the
page, because peak level data is taken for each line scanned.
2-6