Canon CANOSCAN FB330 series Service Manual page 44

CHAPTER 2
Calibration is performed when CanoScan FB330P/FB630P has received calibration
command from the host computer. Calibration is to compose black shading data and white
shading data by reading and averaging the black mark and white mark on the back of the
document glass as color references for the proper color reading.
1) Black shading data composition
Black shading data is composed by reading and averaging total 18 lines (6 lines x 3 times) of
output from the scanning unit with the LED turned OFF.
2) LED exposure control
LED exposure period is set for proper image output. The peak value of image signal output
from each red, green and blue LED exposure is checked if it is in the range of a preset value. If
the peak value is out of the range, LED exposure time is changed. Proper LED exposure period
is set by reading 1 line of an image and checking if it is properly output comparing to the
preset value.
3) White shading data composition
White shading data is composed by reading 6 lines of each red, green and blue of the white
mark, making the highest output 4 lines as sample data. This is repeated 3 times and total 12
lines of sample data is averaged to be the white shading data.
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COPYRIGHT © 1999 CANON INC. CANOSCAN FB330/FB630 SERIES REV.0 OCT. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)