Oce 3121 Technical & Service Manual page 298

In this manner, the density of the background and the density of the image are
measured to classify the document into any of the following three types:
Background Type Document
1
Documents which are white, or light in density, carrying text.
Reversal Type Document
2
Documents which are coloured, or light in density, carrying light text or re-
versed text.
Other Documents
3
Documents with slight variation in density (e.g., photos).
Depending on the type of document, one of the following three AE tables is
selected to generate a correction table suitable for density correction of the
document.
Adjustment of the "priority on image" function in service mode (*3*); see
(((((()
When AE is executed using the RDF, AE is initiated for each document which
is picked up.
In page separation, a signal AE scan is used to check the density of all docu-
ments for the selection of an AE table.
Copy density
AE Table for Background Type
Binary Processing
The binary processing circuit converts multiple-value image signals into bina-
ry signals. The method used is called the PD method, which enables better re-
production of highlight areas than the median density (MD) retention method.
Binary processing is executed in text mode, and text and photo mode.
D-A Conversion
The D-A conversion circuit is used to convert multiple-value image signals
into analogue signals. D-A conversion is executed in photo mode.
522 TSM Océ 3121
Copy density
Density of document
Density of document
AE Table for Reversal Type AE Table for Other Type
Copy density
Density of docu-
Functional description