Facsimile and static presentation processing – Static presentation processing – Attribute control
Reexamination Certificate
2000-06-07
2004-05-11
Rogers, Scott (Department: 2626)
Facsimile and static presentation processing
Static presentation processing
Attribute control
C358S003010, C358S003230, C358S003270, C382S205000, C382S269000
Reexamination Certificate
active
06734990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image formation apparatus that is used as an output unit for outputting multi-value image data that has been generated by a computer or the like. Particularly, the invention relates to an antialiasing technique for improving the picture quality that makes it possible to decrease the zigzag effect of a jaggy (a zigzag of pixels (dots)) that is generated in the image formation of characters or line drawings. The present invention can be applied to any kind of device that can form an image of at least one density in addition to the two values of black and white in pixel units. Examples of the application of the present invention to a printer, particularly, a laser printer, will be explained.
2. Description of Related Art
FIG. 1
is a diagram that shows an example of a structure of a laser beam printer.
A reference number
1
denotes a main body of a laser beam printer. The main body has an optical section
2
and an image formation section
11
. The optical section
2
includes a laser
3
that outputs a laser beam, a polygon mirror
4
that deflects a laser beam so as to repetitively scan the laser beam, a mirror motor
5
that rotationally drives the polygon mirror
4
, and abeam detector
6
that detects a start of the scanning of a laser beam. The image formation section
11
includes a photosensitive drum
7
, a developer
8
, a transfer roller
10
, and a return mirror
9
. The surface of the photosensitive drum
7
is charged with an electric charge, not shown. Thereafter, the photosensitive drum
7
receives a laser beam on this surface. A laser beam signal from the laser
3
is modulated in synchronism with the scanning of the laser beam and the rotation of the photosensitive drum
7
. Then, an optical image corresponding to an image to be printed is drawn on the surface of the photosensitive drum
7
. Static electricity charged onto the surface of the photosensitive drum
7
decreases according to the intensity of the laser beam, so that a static latent image is formed on the surface. When a charged toner is contacted to the surface of the photosensitive drum
7
by the developer
8
, the toner adheres to the surface of the photosensitive drum
7
according to the static latent image so that an image is formed. A sheet of paper is brought into contact with the surface of the photosensitive drum on which the toner image has been formed. The transfer roller
10
rolls the sheet on the surface of the photosensitive drum to transfer the toner image onto the paper. A fixer not shown then fixes the transferred toner image onto the paper. As a result, the printing of the image onto the paper has been completed. After the transfer of the toner image, the surface of the photosensitive drum is cleaned. The surface of the photosensitive drum is charged with an electric charge again, and the above process is repeated.
The print data that has been input from a computer system is expanded as a print image data and is stored in an image memory
12
by an image expander
13
. In general, the image memory
12
is called a bit map memory. In the case of two-value print data, each bit of the bit map memory, that is, one bit, corresponds to a print pixel. In the case of a multi-value print data, a few bits of the bit map memory correspond to a print pixel. For example, in the case of a four-bit print data, the bit map memory also has a four-bit structure. Based on the four-bit print data, it is possible to express
16
gradations in pixel units. An optical modulation signal generator circuit
15
reads out the image data stored in the image memory
12
in synchronism with the processing of the main body, and generates an optical modulation signal and applies it to the laser
3
.
In the single-color two-value printers such as monochromatic laser printers, there has been partly employed a picture-quality improvement processing (a smoothing processing). According to this method, a jaggy that has been generated in the printing of characters and line drawings is automatically judged from the print bit map data expanded on the image memory. The jaggy is then converted into a data of higher resolution than that of the input image data, thereby to decrease the zigzag effect of the jaggy.
FIG. 2A
to
FIG. 2C
are diagrams for explaining an example of the smoothing processing of the two-value image data. As shown in
FIG. 2A
, it is assumed, for example, that there are vertical lines each of which is deviated by one pixel (dot) position in the middle of the line in the print image data stored in the image memory
12
. This deviation is a jaggy. In the smoothing processing, the existence of a jaggy is decided based on a matching of patterns of pixel data including neighboring pixels. At the jaggy pixel positions of the lines, the output timing of the optical modulation signal is adjusted as shown in FIG.
2
B. The image is printed after this adjustment. As shown in
FIG. 2C
, the jaggy portions of the vertical lines are smoothed by decreasing the size of the deviation by a half dot. The above shows an example of a smoothing adjustment carried out based on a half-dot adjustment in the same direction. However, it is also possible to adjust the dots in any direction of left and right. In other words, the smoothing processing is an addition or a deletion of dots at jaggy portions to make it possible to print an image by increasing the resolution of the original image data by an integer times in the main scanning direction of the laser beam.
FIG. 3
shows one example of a structure of a picture quality improvement circuit that carries out a smoothing processing of a two-value print data. As shown in FIG.
3
, an optical modulation signal generator circuit
15
has an image memory reader
16
and a picture quality improvement circuit
17
. Further, the picture quality improvement circuit
17
has a line buffer
18
, an evaluation window extractor
21
, and a correction signal generator
22
.
The image memory reader
16
reads out from an image memory
12
bit map data that is located a few lines before the print data currently under exposure by the laser
3
, and transfers the read-out data to the line buffer
18
. The line buffer
18
consists of a shift register which holds data of a few lines before and after the print data currently under exposure.
The evaluation window extractor
21
extracts data of a rectangular area (this area is called an “evaluation window”)
19
around one focused pixel (this pixel is called a “focused pixel (dot))” in the data that is being held in the line buffer
18
. Then, the evaluation window extractor
21
outputs an extracted-pattern layout signal that expresses a pixel layout in the rectangular area. This extracted-pattern layout signal is input to a correction signal generator circuit
22
. The correction signal generator circuit
22
is a circuit that generates a correction signal for a focused pixel based on a dot layout within the evaluation window shown by the extracted-pattern layout signal. The correction signal generator circuit
22
has a look-up table that stores a neighboring pattern of the focused pixel. The correction signal generator circuit
22
correlates the input extracted-pattern layout signal with the look-up table, and outputs a correction signal that has been stored based on this correlation. For example, when it is not necessary to correct the focused pixel, the correction signal generator circuit
22
generates a modulation signal based on the original pixel data, and outputs this modulation signal as a correction signal. When it is necessary to correct the focused pixel, the correction signal generator circuit
22
generates a correction signal based on a correction data stored in advance, and outputs this correction signal.
FIG. 4A
to
FIG. 4D
are diagrams for explaining the smoothing processing of the dot layout pattern of the image data shown in
FIG. 2A
to FIG.
2
C.
FIG. 4A
shows a pattern of an extracted rectangular area that has been extracted
Fuji 'Xerox Co., Ltd.
Rogers Scott
Westerman Hattori Daniels & Adrian LLP
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