Toshiba e-STUDIO163, Service Manual

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e-STUDIO163/203 © 2005 - 2008 TOSHIBA TEC CORPORATION All rights reserved
IMAGE PROCESSING
7 - 4
7.3.2 Functions of image processing circuit
1) High quality image processing
- Background processing function (Range correction)
This function processes to remove undesirable fog from the background so that the original can
be reproduced appropriately. By using this function, it is possible to cut the background density
down when copying originals which have a certain level of background density, such as newspa-
pers.
<Example>
Fig. 7-3
- Filtering
This function is enabled by low-pass filter processing and high-pass filter processing.
Low-pass filter processing
This processing removes image/electrical noise and decreases moire by performing averaging
operation between the image signals of the targeted pixel and those of the neighboring pixels to
enhance the reproducibility of original.
<Example>
Density of the targeted pixel position is X. Density of pixel positions at front and back of the tar-
geted pixel are “a” and “b” respectively. X is converted to X’ through the low pass filtering.
When the matrix is (3 x 1):
The above averaging operation is performed for all the pixels to accomplish the high reproducibil-
ity of original.
Histogram
Dynamic range
width
Lower Density Higher Lower Density Higher
Text
Back-
ground
After range
adjustment
Extended dynamic range
width
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x' =
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a+b+x