The CMOS sensor used in this machine is a 1-line linear image sensor consisting of 7488 photocells. After completion of photoelectric conversion in the light-

receiving block, the signals are output to the AP circuit in the reader controller PCB in parallel for each channel (total four channels) of the CMOS sensor array.

4.3.6.3 CMOS Sensor Output Gain Correction and Offset Correction

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The analog video signals output from the CMOS sensor are corrected so that they will have a specific gain level (gain correction), and the output voltages generated

in the absence of incident light are also corrected so that they it will have a specific offset level (offset correction).

4.3.6.4 CMOS Sensor Output A/D Conversion

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After completion of the above corrections, the analog video signals are converted to digital signals corresponding to individual pixel voltage levels by the A/D

converter.

4.3.6.5 Shading Correction (Outline)

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The CMOS sensor outputs are necessary even for the following reasons even when the density of the original is uniform:

(1) Variation in sensitivity among CMOS sensor pixels

(2) Variation in light intensity of rod lens array

The machine performs shading correction to even out the CMOS sensor output.

There are two types of shading correction: shading adjustment performed in the Service mode and shading correction performed for each job.

4.3.6.6 Shading Adjustment

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The machine measures the density of the standard white plate, and stores the measured density data. It then processes the stored data to use it as the target value for

shading correction.

Contact image sensor (CIS)

CMOS sensor (1 line)

Analog image signal

IC1

Analog image

processing

A/D

- Gain correction

conversion

- Offset correction

CMOS sensor 4