Image Processing - Konica Minolta bizhub C250 Service Manual

Theory of operation ver. 3.0 Aug. 2006

23. Image processing

23.1 Scanner section image processing block diagram
1. Photoelectric conversion
2. Analog-to-digital conversion
3. Shading correction
4. Line-to-line variation correction/color aberration correction
5. Zoom/movement processing
To the MFP control board
• The following detail the image processing operations performed by the scanner section.
1. A reduction type CCD sensor is used to read the light reflected off the original and
convert the optical data to a corresponding electric signal. To make data process-
ing faster, data transfer and output are done through two channels, one for even-
numbered pixels and the other for odd-numbered pixels.
2. The odd and even analog signals output from the CCD sensor chips are synthe-
sized to form a single string of signal data which is in turn converted to 8-bit digital
signals (256 gradation levels).
3. A correction is made of errors that occur due to variations in sensitivity of each
CCD chip and the light distribution varying along the length of the exposure lamp.
The shading correction is made by holding the peak value, i.e., the maximum value
of readings taken of multiple lines, to prevent adverse effects on the image due to
dust on the shading sheet.
4. Memory called FIFO is employed to compensate for a deviation in the scanning
position of the original, which represents a gap between two adjacent CCD chips,
thereby matching the output timing of R, G, and B data. Also, the color aberration of
the lens is compensated at this time.
5. FIFO memories are used to enlarge or reduce the image. The image is enlarged by
increasing the number of data readings and reduced by decreasing the number of
data readings.
6. The scanning are is divided into multiple blocks. The ratio of color or monochrome
is calculated for each of these blocks. The machine then determines whether the
entire original is colored or monochrome. A histogram of lightness is also created
for later AE processing.
• The image data is transmitted to MFP control board on the write section through the
interface cable
CCD sensor board
Image processing board
6. ACS processing
23. Image processing
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