Image Processing Functions - Canon CANOSCAN N1220U Service Manual

CHAPTER 2
B. Image Processing Functions
1. Contact image sensor
The gate array outputs clock signals based on the command from the control program to the
contact image sensor. The contact image sensor lights the LED in order of red, green and blue
according to the clock signals, then outputs 1 line of image signal proportional to the light
intensity received by the phototransistor.
2. A/D conversion
Analog image signals output from the contact image sensor are converted into the digital
image data of 14 bits each by A/D converter in the gate array in order of red image signal,
green image signal, and blue image signal.
3. Resolution conversion
1) Resolution conversion in the horizontal scanning direction
Basic resolution of CanoScan N650U/N656U is 600 dpi, and selective at 600 dpi, 300 dpi,
150 dpi, 75 dpi. Basic resolution of CanoScan N1220U is 1200 dpi, and selective at 1200 dpi,
600 dpi, 300 dpi, 150 dpi, 75 dpi. Resolution conversion in the horizontal scanning direction
is performed by averaging the thinned data and output data.
Example: To change the resolution to 1/2, image data is converted as shown in Figure 2-16.
2) Resolution conversion in the vertical scanning direction
The control program changes the scanning unit moving speed to change the resolution in
the vertical scanning direction. When increasing the resolution, the scanning unit moves at a
low speed to read more lines as shown in Figure 2-18.
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COPYRIGHT 2000 CANON INC.
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Figure 2-16
Sampling point
Moving direction
Scanning unit
Figure 2-17
Sampling point
Moving direction
Scanning unit
Figure 2-18
CANOSCAN N650U/N656U/N1220U REV.0 JUNE 2000 PRINTED IN JAPAN (IMPRIME AU JAPON)
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