Oce 3121 Technical & Service Manual page 282

Shading Automatic Correction
Shading automatic correction is executed by using service mode (* 4 *; FUNC-
TION).
In this type of correction, the density of blank paper and the density of the ex-
posure reference strip is measured and stored in memory. The stored data is
computed and, subsequently, used as the "target value" for shading correction.
Exposure reference strip
Scanning lamp
mirror 2
mirror 1
CCD
Lens
mirror 3
Shading Correction
Shading correction is executed during the scanning of each document.
The light from the exposure lamp is directed at the exposure reference strip.
The reflected light is turned into digital signals by the analogue image process-
ing block. The reflected light data, which was converted into digital signals, is
sent to the shading circuit of the image processor PBA.
The shading circuit compares the pre-determined target value and shading data
and computes the difference as the shading correction value.
The shading correction value is used to correct variations among CCD pixels
that occur during the scanning. This is to ensure a specific image density level.
506 TSM Océ 3121 Functional description