Gestetner A294 Service Manual page 80

IMAGE PROCESSING
Main Scan Magnification/Reduction
However, reduction and enlargement in the main scan direction are handled by the
IPU chip on the SICU board.
Scanning and laser writing are done at a fixed pitch (the CCD elements cannot be
squeezed or expanded). So, to reduce or enlarge an image, imaginary points are
calculated that would correspond to a physical enlargement or reduction of the
image. The correct image density is then calculated for each of the imaginary
points based on the image data of the nearest four true points. The calculated
image data then becomes the new (reduced or enlarged) image data.
Main scan magnification can be disabled with SP4-903-5 to test the IPU chip.
Sub Scan Magnification
When the selected magnification is 50% or larger, the image magnification in the
sub scan direction is changed by changing the scanner speed. (As the
magnification ratio increases, the scanner speed is reduced.)
However, when a magnification ratio smaller than 50% is selected, the required
scanner speed exceeds the limit of the scanner motor. So, the scanner speed is
reduced to half of the required speed for that reduction ratio. As a result, there are
twice as many scan lines as needed. So alternate lines are removed.
For example, if a 49% magnification ratio is selected, the scanner speed is the
same as the speed of 98% magnification, but the number of sub scan lines used
for the image is half of that for 98% magnification.
A294/A295
CÓPIA NÃO CONTROLADA
2-30
CÓPIA NÃO CONTROLADA
A294D646.WMF
SM