Ricoh Aficio Color 4006, Service Manual

Page: 88 / 487

24 February, 1999 IMAGE PROCESSING
2-39
Detailed
Descriptions
2.5.5 IPU SECTION
Picture Element Correction and Scanner Gamma Correction
(1) Picture Element Correction
The Picture Element Correction circuit does two things.
1. Completion of the Scan Line Correction process
The discrepancy in the spacing of the RGB signals from the CCD in the sub-scan
direction is corrected by the line correction circuit in the scanner section (refer to
Scanner Section – Scan Line Correction). However, if the correction data
corresponding to the magnification ratio is not an integer, then further correction is
needed to synchronize the RGB signals.
2. Correction if the CCD is not perpendicular to the light
If the CCD board is not perpendicular to the light axis, the position of each pixel is
different from the original image position. This difference becomes larger towards
the ends. Under this condition, vertical black lines (in the sub-scan direction) at the
left and right edges of the original are colored because the Y, M, and C toner dots
are not properly positioned. (This can be checked by looking at the vertical lines at
the right and left edges of a copy of the C4 color chart.)
Therefore, the CCD line spacing is also corrected here. The target areas for this
correction are shown above. The green CCD line is taken as a standard, and the
ends of the red and blue lines are corrected.
Adjust SP modes 4-932-001 to 4-932-004 to change the vertical line correction
level.
R
G
B
A259D803.WMF
Picture Element Correction