Toshiba e-STUDIO281c Service Manual page 175

4) High quality image processing
- Background processing function
By using the background adjustment function while manually adjusting the image density, unde-
sirable background of the original can be removed if any, and some necessary but disappeared
background can be recovered. 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>
Dynamic range
Back-
ground
Lower Density
- Image discrimination
By determining the magnitude of density variation in a block (n x n dot), the target pixels are
judged whether they are text or photograph. If they are determined to be text, they are further
judged whether they are black or color text, using the differences in the levels of CMY signals.
- 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):
June 2005 © TOSHIBA TEC
After range
width
adjustment
Text
Higher
Histogram
Fig.7-4
a x b
7 - 5
Extended dynamic range
width
Lower Density
a+b+x
x' =
3
e-STUDIO281c/351c/451c IMAGE PROCESSING
Higher
7