Canon fax basic 2000 서비스 매뉴얼

READING SECTION

3–14

4. IMAGE DATA PROCESSOR

After the document is read by the contact sensor, the resulting image data

undergoes various image data processing at the system controller.

The following shows a block diagram outlining the content of image pro-

cessing.

Fig. 3-17   Block Diagram

4.1

 Various Image Data Processing

After the image data has been read, it undergoes various data processing

before it is sent. The following describes these processing types.

• Pre-scan

By the pre-scan, the base color of the white mylar sheet attached to the

document feed section on the contact sensor is read for one line at the start

of document reading so that the unevenness compensation values for the

output contact sensor are stored to shading memory.

• DC generation

DC generation matches the black side reference voltage of the A/D conver-

sion circuit with that of the contact sensor.

• AGC circuit

AGC (Auto Gain Control) adjusts for unevenness in the reading system

(LED, white mylar sheet and contact sensor) to prevent the maximum

value exceeding the maximum value of the A/D conversion circuit when

the background color of the white mylar sheet is read for one line.

D/A

conversion

circuit

GENESIS

(UHQ)

Contact sensor

Brightness data
(analog signal)

Image processing section

ABC circuit

A/D

conversion

circuit

Gray scale data
(digital signal)

DC

generation

AGC
circuit

Shading
memory

To coding/decoding
processing section

Binary data