Canon 1000 Service Manual page 95

Logarithmic Correction and BGR → → → → → YMC Conversion
j.
a) Logarithmic Conversion
The CCD output has a linear characteristic in relation to the light reflected by an original. However, the
density as perceived by the eye is not linear in relation to the reflected light.
Figure 3-325 shows the relationship between the density of an original and the output of the CCD as
perceived by the eye.
To compensate for the discrepancy, level conversion is executed as shown in Figure 3-326.
CCD output
255
0
Black
Original density
Figure 3-325
BGR → YMC Conversion
b)
The circuit generates Y, M, and C signals
taking advantage of the fact that B, G, and R (light)
are complementary to Y, M, and C (toner).
Transmission through filter
B
400 500
Figure 3-327
COPYRIGHT © 2001 CANON INC.
White
G R
600 700
Wavelength (nm)
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
3. OPERATION AND TIMING
Output level
255
0
0
Figure 3-326
Light
Y
Toner
B Absorbed
G Reflected
R Reflected
Table 3-301
Reflection by toner
Y
400 500
Wavelength (nm)
Figure 3-328
255
Input level
M C
Reflected Reflected
Absorbed Reflected
Reflected Absorbed
M C
600 700
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