Gestetner A193 Service Manual page 73

IMAGE PROCESSING
3. Main Scan Magnification/Reduction
Reduction and enlargement in the sub scan direction are done by changing
the scanner speed. However, reduction and enlargement in the main scan
direction are handled by the IPU chip. The processing for main scan
magnification/reduction is the same as in the previous digital machines.
[A]
A193D504.wmf
When making a copy using the ADF, the magnification circuit creates a
mirror image. This is because the scanning starting position in the main scan
direction is at the other end of the scan line in ADF mode (as compared with
platen mode). In platen mode, the original is placed face down on the
exposure glass, and the corner at [A] is at the start of the main scan. The
scanner moves down the page. In ADF mode, the ADF feeds the leading
edge of the original to the DF exposure glass, and the opposite top corner of
the original is at the main scan start position.
To convert the mirror image, the CPU stores the main scan line data in the
LIFO (Last In First Out) memory of the magnification block, from the last
pixel. When loading the main scan line data from the LIFO memory, the CPU
loads the first pixel of the main scan line.
(A193) 2-12 SM