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November 2003 © TOSHIBA TEC 7 - 5 e-STUDIO3511/4511 IMAGE PROCESSING
7
7.3.2 Functions of image processing circuit
The image processing section on the SYS board realizes the followings:
(1) ACS (Auto Color Selection)
This function determines whether the original to be scanned is colored or monochrome, based on
the analysis of the R, G and B signals output from the CCD.
(2) Color conversion (CMY image data processing)
When functioning the copier, the RGB image data is converted to CMY image data. (When functioning
the scanner, it is converted to RGB image data.)
The image data taken in by the scanner represents the intensities of reflection from the three primary
colors of light (Red, Green and Blue). These RGB values are then color-converted to the respective
amounts of toners corresponding to the three colors (Yellow, Magenta and Cyan) for printing (=CMY
image data processing).
(3) Black component generation
K (Black) signal is generated from the CMY image data. Based on this K signal, the CMY image data
is corrected to suppress hue on reproducing grays or to make the black look more real.
(4) High quality image processing
(a) Background processing function
By using the background adjustment function while manually adjusting the image density,
undesirable 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 newspapers.
<Example>
DensityLower Higher DensityLower Higher
Back-
ground
Tex t
LargerNo. of pixelsSmaller
LargerNo. of pixelsSmaller
Histogram
Fig. 7-301
(b) 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.
After background
processing
Dynamic range
width
Extended dynamic
range width