AR-C150 (serv.man5). ARC150-Basic Manual - Sharp Copying Equipment Service Manual (repair manual). Page 56

a. Outline and purpose
The CCD by its nature outputs a certain level of voltage component even though there is no reception of lights. This voltage component is called the
dark component. Since the dark component must not be included in the image signal, it is stored in advance and must be subtracted from the image
component when images are actually read. .

This operation is called the dark component correction. 

b. Details of operation 
1) With the scanner lamp OFF, the CCD output is read and stored as the dark component. (This operation is performed for every warm-up.)

In an actual image scanning, the dark component is subtracted from the CCD output component, and the remainder is used as the actual image com-
ponent.  

The above operation is performed for the CCD of each color (R, G, B). 

a. Outline and purpose
The CCD output gain is adjusted to the proper level so as to read im-
ages in the wide range of densities correctly. 

b. Details of operation 
1) The scanner lamp is lighted and the shading sheet (white) is read

by the CCD. Adjust the amp gain in the CCD PWB so that the
max. CCD output level is 240, and store the gain. 
The above operation is performed for the CCD element of each
color (R, G, B).

3) In an actual image scanning, the image signals are amplified with

the gain adjusted in the above procedure and are outputted to the
ICU PWB.

a. Outline and purpose
This correction is performed to correct unevenness of the image den-
sity due to the following factors.  

1) Light quantity is decreased as apart from the optical center be-

cause of the optical structure.

2) Unevenness of brightness of the scanner lamp

3) Sensitivity variation in the CCD pixels

b. Details of operation 
1) The scanner lamp is lighted and the shading sheet (white) is read

by the CCD. The max. output level of the CCD at that time is 255.

2) Calculate the correction coefficient from the ratio of the max. out-

put level (Wmax) and each CCD element output level (Wt(n)) and
store it. 

Correction coefficient Wtc(n) = Wmax / Wt(n)

3) Obtain the actual image scanning level (Ioutc(n)) from the CCD

detection level and the correction coefficient in an actual image
scanning. 

Ioutc(n) = Wtc(n) x Iout(n)

Perform the above operation for the CCD element of each color
(R, G, B).

–

=

Original image data

signal(Including dark component)

Dark component(Deduct)

True image data
signal

CCD output level (Dark component)

in the no image condition(Black)

Scanner lamp off

DOCUMENT

CCD

WHITE SHEET

LAMP ON

LAMP OFF

CCD

0

Dark component level (Pdcl)

255

240 (max.)  Adjust the gain
so that the max. level is 240.
(Pmax) 

Ptl' = (Ptl - Pdcl) / (Pmax - Pdcl) 

×

 255

Shading correction is performed for each target
 pixel according to the result of the above calculation.

SHARDING CORRECTION (DARK COMPONENT CORRECTION,WHITE LEVEL CORRECTION)

CCD output level

AR-C150

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