CHAPTER 3 MAIN CONTROLLER
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2001 CANON INC. 2000 2000 2000 2000 CANON iR8500/7200 REV.1 AUG. 2001
2.2.7 Binary Processing (dither screen method)
The dither screen method controls the texture by binary processing so that the data will be
best suited for printing. The 8-bit image density signal for film photo mode is converted into
a 1-bit images density signal (binary).
Although the image is expressed in binary, the use of a dither screen method of 12×12
pixels enables its reproduction in 144 gradations.
2.3 Controlling the Image Memory
The image memory is used for binary image data as follows:
2.3.1 Compression/Expansion, Rotation, and Enlargement/Reduction
The image stored in binary is subjected to the following: compression/expansion (for
electronic sorting), rotation, and conversion different resolution.
2.3.2 SDRAM
The image data is temporarily stored.
2.3.3 HDD
As opposed to its function as an image server, the HDD is also used for storage of image
data for the Box function.
2.4 Processing Output Image
The output image data to be sent to the printer unit is processed as follows:
2.4.1 Smoothing
a. Output of the Read Image
In the case of text or text/photo mode, the input image of 600×600 dpi is subjected to
smoothing, thereby expressing it at a resolution of 1200 (equivalent) × 600 dpi.
In smoothing, the image data is compared against several hundred templates of 7×7-pixel
pattern matrixes for replacement of the pixel in question.
Notch processing and the like are also executed here as patterns unique to read images.
b. Output of Printer Image (PDL)
The image data is subjected to smoothing suited to PDL, in which a resolution of
300×300 or 600×600 dpi used for each mode is converted into 2400 (equivalent) ×600 dpi.
2.4.2 Thickening (PDL output only)
If selected by the printer driver, thickening processing is executed to enhance the repro-
duction of fine lines.
The PDL output image is processed so that each horizontal line is given additional 1/2
pixels (1200 dpi) in up/down direction and each vertical line is given 1/2 pixels (1200 dpi)
in left/right direction.
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