Shading Compensation - Toshiba e-STUDIO 160 Service Manual

7.6.2 Shading compensation

The following problems effect the voltage values obtained by photo-voltaic conversion by the CCD:
As a light distribution of light source is varied.
The reflected light is collected by a lens (the light path is shortest at the CCD center and longest
at the ends), there is a difference in the intensities of light reaching the CCD.
The photo-voltaic capacities of each of the 7,450 CCD elements are uneven.
Consequently, these problems must be compensated. This is called "shading compensation." Shad-
ing compensation involves normalizing optical energy according to the following equation based
on already known scanned black data and white data, and compensating for uneven illuminance
of the image data and device unevenness.
I = k x
where,
k: Coefficient
S: Image data before compensation
K: Black data (in black memory)
W: White data (in white memory)
December 2002 TOSHIBA TEC
(S - K)
(W - K)
7 - 13 e-STUDIO160/200/250 SCANNER