Canon iR2018 Series, Service Manual

Page: 115 / 348

Chapter 4
4-15
4.3.6.6 Shading Adjustment
0017-2641
The machine measures the density of the standard white plate, and stores the measured density data. It then processes the stored data to use it as the target value for
shading correction.
4.3.6.7 Shading Correction
0017-2642
The machine performs shading correction for each scan. It measures the density of the standard white plate, and compares the measured value with the target value
stored in the shading correction circuit to use the difference between the two as the shading correction value. The machine uses this shading correction value to
correct the variation among CMOS sensor pixels when scanning the original, thus evening out the image density level.
F-4-28
CMOS
sensor
output
Original density
Standard white plate
Characteristics
before correction
Target
value
Measurement
value
Characteristics
after correction
White