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16 February 2000
IMAGE PROCESSING
Image processing path
The following image processing is for the scanner. The image processing for each
of these units is explained in separate sections.
S C U
M e m o r y
S B U
I P U
Controller
S h a d i n g
Magnification/
Dither/
White/black
γ correction
Filtering
Binary process
correction
Mirror Process
Error Diffusion
conversion
G413D500.WMF
Shading Correction
The machine scans the white plate opposite the ADF exposure glass to make a
white waveform. Shading correction prevents uneven images caused by
fluctuations in scanned data due to changes in light intensity and CCD sensitivity.
Magnification
Reduction and enlargement in the sub scan direction are done by changing the
scanner motor speed or paper transport motor speed in the ADF. However,
reduction and enlargement in the main scan direction are done by the IPU.
Mirror Processing
A mirror image of the original must be made for output.
Filtering
There are two software filters: the MTF filter and the smoothing filter. The MTF filter
emphasizes sharpness, and is used with text-only documents or documents that
contain text and photo areas. The smoothing filter is used for photo-image
documents.
Gamma ( γ γ γ γ ) Correction
The gamma curve corrects the response of the CCD to grayscales in the original.
Grayscale Processing
This process generates up to 256 image density levels for each pixel.
Dithering
Dither processing produces good quality grayscale images of photo originals.
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