Shading Correction - Canon imageRUNNER ADVANCE C350 series Service Manual

2
Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
● Shading Correction
Due to the characteristics of each of the elements in the CIS, variations occur in the reading
level in the horizontal scanning direction.
Reading is therefore performed with the LED on and with the LED off to correct the white and
black levels for each horizontal scanning position and obtain a uniform reading level.
There are two types of shading correction: white shading and black shading.
White shading (for copyboard reading)
The White Plate is illuminated by switching between R, G, and B at designated intervals to
read and the luminance.
The reading of the white level in the horizontal scanning direction is made uniform by
calculating the correction coefficient of the white level for each horizontal scanning position.
255
RED
luminance
0
Horizontal scanning position
Related error code:
E301-0001: Surface light intensity error
2 Technical Explanation > Original Exposure and Feed System > Image Processing > Image Processing by the Main Controller PCB (Reader ASIC)
RED shading target
Luminance value before correction
Correction coefficient
F-2-20
White shading (for stream reading)
The shading correction of stream reading is performed using the white level adjustment value
(factory adjustment value).
White level correction of each horizontal scanning position is performed so that the value will
match the factory adjustment value, which is regarded as a target value.
Black shading
The White Plate is read with the LED off, and the correction coefficient of black level for each
horizontal scanning position is calculated to make the black level reading in the horizontal
scanning direction uniform.
255
Luminance
0
Horizontal scanning position
Related error code:
E301-0002: Surface light intensity error
2-17
Luminance value before correction
Correction coefficient
F-2-21
2-17