Canon GP215 Service Manual page 102

3. OPERATIONS AND TIMING
6. Density Processing
a. Logarithmic Correction
The CCD output has linear characteristics in
relation to the light reflected by an original.
However, the density of an original as perceived
by the human eye does not show linear charac-
teristics in relation to the light reflected by the
original.
The relationship between the density as per-
ceived by the naked eye and the output of the
CCD are as shown in Figure 3-336.
CCD output
255
0
Black
Density od original
Figure 3-336
To correct the discrepancy, the correction
curve shown in Figure 3-337 is used to execute
level conversion.
Output level
255
0
0
Input level
Figure 3-337
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COPYRIGHT © 1996 CANON INC.
White
255
CANON GP215/200 REV.0 JULY 1996 PRINTED IN JAPAN (IMPRIME AU JAPON)
b. Density Processing
The correction curve for density processing
varies according to the following:
1) Setting of the Copy Density key on the control
panel.
2) Results of AE measurement
3) Selection of text/photo, photo mode
4) Results of photosensitive drum resistance
According to the setting of the Copy Density
key, the curve will be for darker or lighter as in
Figure 3-338.
When text/photo or photo mode is selected,
the curve shown in Figure 3-339 will be selected
to ensure good gradation and faithful reproduction
of the density of an original.
Copy density
Darker
Figure 3-338
Copy density
Text mode
Figure 3-339
Lighter
Text mode
Density of original
Text / photo
and photo mode
Density of original