Toshiba 4580, Service Manual

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6570/5570 IMAGE PROCESSING 6 - 4 Mar. 1999 © TOSHIBA TEC
6.3 SLG Board (PWA-F-SLG-300)
6.3.1 Features
(1) The image processing ASICs are controlled by CPU on the SLG board (PWA-F-SLG-300).
(2) The image processing functions of the SLG board implement
the following functions:
•
High quality image processing
•
Image memory editing
•
Editing processing
•
Gamma correction
•
Tone processing
•
External output system interfacing
6.3.2 Functional description of the image processing circuit
An ASIC mounted on the SLG PC board implement the functions described below.
(1) High quality image processing
(A) Range correction
This function converts image signals to density range width and corrects it to match each original
document’s image. When copying the images of an original having a certain amount of background
(such as appear in newspapers), it reduces the background density.
<Example>
Histogram
Dynamic range width
Smaller No. of pixels Larger
Lower
Density
Higher
Smaller No. of pixels Larger
Lower
Density
Higher
Text
Back-
ground
After range
correction
Extended dynamic range width