Gestetner G060 Service Manual page 640

IMAGE PROCESSING
Black Level Correction
• Improves image reproduction for high-density areas.
• Reads the black video level at black elements on the CCD. These pixels are
masked off, and should produce a pure black signal.
• This is subtracted from the value of each pixel.
• Calculated for each scan line.
• Corrects the image data for any changes in black level with time, as the machine
scans down the page.
Adjustments
The properties of the scanner unit, which are necessary for controlling the scanner
VPU (video processing unit), are not stored in the memory of the printer
mainframe. These properties are stored in the EEPROM on the SBU.
After replacing the SBU, adjust the following:
SP4–008 Scanner sub-scan magnification
SP4–010 Scanner leading edge registration
SP4–011 Scanner side-to-side registration
VPU Test Mode
To make sure the scanner VPU control is functioning, output the VPU test pattern
with SP4-907. ( "4. Troubleshooting" for details)
G570 6-8 SM