Canon Vizcam 1000, Service Manual

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COPYRIGHT © 2001 CANON INC. CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
3-51
3. OPERATION AND TIMING
j. Logarithmic Correction and BGR
→ → → → →
YMC Conversion
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.
Figure 3-325 Figure 3-326
b) BGR
→
YMC Conversion
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).
Table 3-301
Figure 3-327 Figure 3-328
Black White
CCD output
255
0
Original density
0 255
Output level
255
0
Input level
Light
Toner
B
G
R
Y
Absorbed
Reflected
Reflected
M
Reflected
Absorbed
Reflected
C
Reflected
Reflected
Absorbed
B G R
400 500 600 700
Wavelength (nm)
Transmission through filter
Y M C
400 500 600 700
Wavelength (nm)
Reflection by toner