Canon imageRUNNER ADVANCE 715 series Service Manual page 35

Table of Contents

Scanner Unit (Front)

3 Line Sensor

Analog Image

- Gain Correction

- Offset Correction

Scanner Unit (Back)

3 Line Sensor

Analog Image

- Gain Correction

- Offset Correction

■ Shading Correction

Even if the original density is even, output of the CIS Reading Sensor in the Scanner Unit may not become even. A control that

corrects variations in the output is shading correction.

Main causes of uneven output of the Reading Sensor are shown below.

• Variation in sensitivity of pixel of the Reading Sensor

• Uneven light intensity of the lens

• Uneven light intensity of the LED and light guide plate

• Deterioration of the LED

• Variations in luminance between at the position of the Standard White Plate and at the reading position

To correct unevenness of the Reading Sensor output, shading correction is performed.

In shading correction, there is a type of shading correction that is executed per job.

● Shading Correction (Common to Reader and ADF)

Shading correction is performed for each scanning of original.

With this operation, light of LED Lamp is emitted to the Standard White Plate, and the reflected light is converted into digital data

at the analog image processing part of the Scanner Unit PCB. The amount of digitized reflected light is input to the shading

correction circuit in the Main Controller PCB as the shading coefficient. In the shading correction circuit, the stored target value

and the shading coefficient are compared, and the difference is determined as the shading correction value.

With this shading correction value, variation of pixel of the Reading Sensor of each scan is corrected to make the image density

Main Controller PCB

Shading Correction

MTF Correction

Image signal

Color Displacement

2. Technology

Control signal