Toshiba e-STUDIO163 Service Manual page 91

Optoelectronic conversion
The CCD is a one-chip optoelectronic conversion device, comprised of several thousand light-receiving
elements arranged in a line, each one of them is a few microns square. This equipment has a CCD with
7,084 light-receiving elements.
Each element of the light-receiving section consists of semiconductive layers P and N. When the light
irradiates the element, the light energy produces a minus (-) charge in the layer P; the amount of the
charge produced is proportional to the energy and irradiating time. The charge produced in the light
receiving section is then sent to the transfer section where it is shifted by transfer clock from left to right
as shown in the figure below, and is finally output from the CCD. At this time, to increase the transfer
speed of the CCD, the charge is separated into four transfer sections and output in parallel via two
channels.
Transfer section 3
Transfer section 1
Light-receiving section
Transfer section 2
Transfer section 4
Shift register
Shading correction
A variation is caused by the following factors in the CCD output.
1) The light source has a variation in its light distribution.
2) Each of the 7,084 elements varies in optoelectronic conversion efficiency.
These differences need to be corrected and this correction is referred to as a shading correction. The
shading correction is performed by applying a normalization process using the following formula on the
black data and the white data obtained in advance to correct the lighting variance and element variation
of the image data.
( S-K)
I = k
x
( W- K)
k: Coefficient
S: Image data before correction
K: Black data (stored in "Black" memory)
W: White data (stored in "White" memory)
December 2005 © TOSHIBA TEC
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Fig. 6-4
Fig. 6-5
6 - 7
Transfer clock
Light energy
7083 7084
Details of light-receiving section
Transfer clock
Layer N
Layer P
e-STUDIO163/203 SCANNER
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