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Data flow (flowchart)
30.
FIFO
31.
GA2
(Area
separation)
GA2
32.
(MTF
correction)
Gamma
33.
correction SRAM
(Irregular drive
countermeasure)
Laser pulse
34.
width modulation
35.
ECL circuit
36.
LSU
30. FIFO
This line memory (FIFO) is used for area separation and MTF correction.
31. Gate array 2
Performs area separation. In area separation, the characteristics of the target pixel and
the neighboring pixels are judged to perform the optimum process. For example, judge-
ment is made to identify that the area is a photo area or a hatched area such as
newspaper photos.
32. Gate array 2
Corrects blurs in images in the main scanning direction and the sub scanning direction.
Details are as follows.
MTF meas Modulation Transfer Function of the optical system.
a: Theoretical value
ICU PWB
b: Value received by the CCD element (N)
The optical system provides out of focus even the focus adjustment is perfectly com-
pleted. When the CCD elements receive reflected light from the document, the light
leaks to the neighboring pixels by the optical system characteristics. On the contrary,
light come in from the neighboring pixels. Correction is made by adding the leaked lights
and subtracting the lights from the neighboring pixels. This correction is called the MTF
correction.
(In actual, this process includes calculation of the effect on the pixels by the preceding
and the following lines.
The MTF correction performs process to provide clear characters by edge emphasis if
the area separation result is a character area, and to provide less emphasis if the result
is a hatched area, and to provide smooth images if the result is a photo area.
When the soft photo mode is selected, the area separation and the MTF correction are
not performed, but the multi-value dithering is performed instead. The size of dither
matrix in multi-value dithering can be selected by simulation.
33. Gamma correction SRAM
Gamma correction is performed to make optimum copying of image data. In the photo
mode, gamma correction is made to reproduce clear half tone images. In the manual
mode, gamma correction is performed to provide clear copying of characters.
Image data before correction are of 8 bit as well as image data after correction. (0 ∼
255)
In the photo mode, line alignment is performed, where the gamma correction curve of
the odd number pixels and the even number pixels in the main scanning direction are
changed to reduce fluctuations in drive of the machine.
In combination with the above area separation, it reduces bad effects of line alignment
process for hatched documents.
The gamma correction SRAM performs the highlight process.
34. Laser pulse width modulation
The image data which are subjected to the gamma correction are converted into laser
pulse signals (which varies the laser radiating time for each pixel.)
Radiating time of laser can be changed in the unit of 1/256.
35. ECL circuit
The laser pulse width signal is sent to the LSU at ECL level.
36. LSU
The laser scan unit performs printing.
Content
a
b
1 pixel (N)
1 – 7
Original
CCD
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