JP2000216999A - Image output processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent periodical image nonuniformity from being generated, due to the relation between each reflected face which is the periodic features of a polygon mirror for deflection scanning laser beams and the periodic features of image data to be dither-processed by reducing the periodic relation as much as possible, and to reduce image nonuniformity. SOLUTION: When a rotating polygon mirror for scanning laser beams to be modulated according to image data to the rotating axial direction of a photosensitive body which is of an image carrier has 6 faces, the dither processing of image data to be image processed by a dither method is conducted alternately in two kinds of different dither matrix sizes, for example, 2×2 and 3×3. Laser beams modulated based on the dither processed image data are deflection- scanned by the polygon mirror, having 6 faces so that a periodical relation that scanning lines by a dither matrix are made to coincide with the faces of the polygon mirror can be prevented from overlapping as much as possible, with at least 6 rotations of the polygon mirror as the period, and periodic image nonuniformity due to the extreme short period can be reduced as much as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for deflecting and scanning an input multi-valued image data (halftone data) based on image data obtained by dithering the image data by a dither method, thereby forming an image on an image carrier. The present invention relates to an image output processing method that forms an image on a computer and reproduces and records the image.

[0002]

2. Description of the Related Art Conventionally, for example, an image of an original is read,
The read data is used as an input image, and in order to reproduce and output the image on a printer for reproducing the image, for example, a laser printer, a conversion process or the like is performed on data that can be output by the printer. As the data to be reproduced, not only an image of a document is read, but also when image data processed by a personal computer or the like is input, the input image data can be reproduced and output by a printer. Needs to be converted.

At this time, if there is data including a halftone in the image data read as described above or the image data input from another device, it is necessary to reproduce the halftone satisfactorily. The dither method is used to perform dither processing. That is, in a laser printer or the like, a semiconductor laser is driven (modulated) based on binary data indicating whether or not to irradiate a laser. Image processing such as conversion to.

For example, Japanese Patent Application Laid-Open No. Sho 59-111471 discloses a dither process by the above-described dither method for binarizing multi-value image data, that is, image data including a halftone, and the size of the dither matrix. And so on. As the dither matrix size, there are usually 2 × 2, 3 × 3 and 4 × 4 pixel sizes. As shown in FIGS. 6 (a), 6 (b) and 6 (c), multivalued image data is arithmetically processed based on these dither matrix sizes, and binary data is stored in any of the matrices. Is applied. That is, based on these matrix sizes, the image data is corrected in the entire area in the main scanning and sub-scanning directions.

[0005] According to the example of FIG. 6, a state where weighting is simply performed clockwise is shown. At this time, the image data has periodic characteristics. If the period of the matrix size matches the period peculiar to the image data, periodic unevenness of the image such as moiré becomes very noticeable. Therefore, the reproduced image has an image quality that is very difficult to see due to periodic unevenness.

Therefore, conventionally, it has been known to change the weight of the matrix or to change the matrix size according to the characteristics of the image data so that such periodic characteristics do not coincide with each other. 59-1
It has been proposed in Japanese Patent Application Laid-Open No. 11471 and Japanese Patent Application Laid-Open No. 59-176978.

[0007]

By changing the dither matrix size according to the image data input as described above, the matrix size according to the image data is set, and the dither method is used. By performing the image processing, it is possible to eliminate the above-mentioned moiré and the like, and to provide an image of good image quality in reproducing halftones and the like.

On the other hand, according to a printer for reproducing and recording data which has been subjected to image processing using the dither method as described above, that is, according to a laser printer using an electrophotographic system, a semiconductor laser is provided based on the processed image data. Is modulated (driven), the modulated laser light (information light) is deflected, and the surface of the photoconductor provided with the photoconductive layer as the image carrier is scanned. An electrostatic latent image is formed.

As means for deflecting the modulated laser light, there is provided a rotating polygon mirror (polygon mirror) having a plurality of reflecting surfaces, and this is rotated at a predetermined rotation speed, so that the laser light is applied to the photosensitive member. Scanning (main scanning) is performed in the rotation axis direction. Then, the surface of the polygon mirror is sequentially switched at predetermined rotation angles in the direction of rotation, and the sub-scanning is performed in accordance with the rotation of the photoconductor, whereby the entire electrostatic latent image corresponding to the image data is obtained. An image can be formed.
The formed electrostatic latent image is developed (visualized) with a coloring agent such as toner, and the image is transferred to a recording material such as a sheet and output as a hard copy.

When the number of surfaces of the polygon mirror rotated by the printer of this type, that is, the image forming apparatus, and the matrix size by the dither method periodically coincide with each other, the same mirror surface of the rotating polygon mirror is replaced by the dither method. The laser beam modulated based on the image data processed by the above is repeatedly deflected and scanned. As a result, the characteristics of the periodic image are also recorded on the image (latent image or toner image) reproduced on the photoreceptor surface, and the periodic image unevenness is conspicuous. This is particularly noticeable when reproducing and outputting a color image.

The polygon mirror which is the above-described polygon mirror is generally a six-sided mirror shown in FIG. 5A, and is also a polygon mirror shown in FIGS. 5B and 5C. There are even-numbered mirrors as surface mirrors and 12-surface mirrors. Therefore, FIG.
FIG. 7 shows an example of scanning when image processing is performed using the 2 × 2 matrix size shown in FIG.

That is, as described above, as a periodic characteristic of the polygon mirror, the reflection surface scans on the same surface every one rotation. In the dither matrix size, the same processing is executed in the sub-scanning direction at a cycle for each size.

Therefore, as illustrated in FIG. 7A, in the first rotation and the second rotation of the polygon mirror, the image data processed by the dither method corresponds to six lines (three areas of the matrix). In the second rotation of the polygon mirror, each line is scanned on the surface used in the first rotation. Therefore, scanning is performed on each surface of the polygon mirror in a state where the periodic characteristics of the polygon mirror and the characteristics of the dither matrix size are coincident with each other, so that periodic image unevenness is conspicuous and an image is very hard to see. .

FIG. 7 shows an example of the case where dither processing is performed using a diagonal matrix size of 3 × 3 using a polygon mirror having six surfaces, and the first and second rotations of the polygon mirror are compared. In this case, the same line according to the matrix size is always used for each rotation of the polygon mirror,
Scanning on the same surface by the polygon mirror is repeatedly performed. Therefore, by repeatedly performing this, scanning of the same line having the same periodic characteristic processed by the dither method is always performed on the same surface of the polygon mirror.

This is not limited to the examples shown in FIGS. 7A and 7B. The same applies to a 4 × 4 matrix size, and even if an 8 or 12 polygon mirror is used. The same will be repeated. However, in relation to a 4 × 4 dither matrix size using a six-sided polygon mirror, the periodic characteristic does not match every rotation of the polygon mirror.
Even if some improvement can be expected by matching each rotation, an effect as large as the difference cannot be expected.

As described above, when the arithmetic correction processing is performed on the pixel data in the area of the matrix size by the dither method, the pixel data between the adjacent matrices may be determined depending on the processed image data at the boundary portion within each of the airs. A difference (difference) occurs between them, and as a result, periodic unevenness of the image results.

This dither matrix size periodically overlaps with the number of reflecting surfaces of the polygon mirror described above. If one line of the dither matrix having periodic characteristics on the same reflecting surface always overlaps as shown in FIG. In a laser scanning recording apparatus capable of delicate recording / reproduction, even a periodic unevenness of image data dithered by the dither matrix is delicately reproduced. For this reason, in a laser scanning recording apparatus that records a high-resolution image in units of one line by laser scanning, even if the level of unevenness is initially invisible to the human eye, the unevenness occurs periodically. Then, the image is reproduced as a periodic unevenness that can be seen by human eyes, that is, an image unevenness.

According to the present invention, a periodic characteristic of a dither matrix size when an image is processed by a dither method and an information beam modulated in accordance with the dither-processed data are scanned on an image carrier. It is an object of the present invention to provide an output processing method in which the periodic characteristics of the mirror surface of a polygon mirror are set so as not to overlap with each other as much as possible, and a deterioration in image quality due to periodic image unevenness is prevented. .

[0019]

According to a first aspect of the present invention, there is provided an image output processing method for converting image data input according to a dither matrix size determined by a dither method. The information light modulated according to the processed image data is deflected and scanned by a polygon mirror that is rotated at a constant speed in the direction of the rotation axis of the image carrier to be rotated. In the processing method for reproducing and outputting the image, the image carrier is set by setting the periodic characteristic of the polygon mirror and the periodic characteristic of the dither matrix size by the dither method so as not to overlap each other as much as possible. Is scanned.

With such a configuration, the information beam can be scanned on the image carrier without the rotation of the rotating polygon mirror corresponding to the periodic characteristic of the dither matrix size for each rotation. For example, for each rotation cycle of the number of faces of the rotating polygon mirror, especially for six faces, scanning is performed on the same face at least every six revolutions so as to match the periodic characteristic of the dither matrix size. Accordingly, periodic repetition of unevenness does not appear remarkably, and an effect of suppressing image unevenness can be expected.

Therefore, in the image output processing method having the above-mentioned configuration, according to the second aspect of the present invention, the periodic characteristic of the polygon mirror is the number of reflecting surfaces, and the dither matrix size in the sub-scanning direction. The dither matrix size is set such that the period in which the reflection surface of the polygon mirror and the reflection surface of the polygon mirror overlap each other becomes long. In other words, if the relationship is set such that the common divisor does not exist in the dither matrix size and the number of reflecting surfaces of the polygon mirror, the two advantages are obtained at least within the rotation of the number of reflecting surfaces of the polygon mirror. They will not match. Specifically, the following configuration can achieve the object.

That is, in the image output processing method characterized by the above-mentioned configuration, according to the third aspect of the present invention, the dither matrix of the input image is processed by combining a plurality of different sizes. It is characterized by the following. For example, as shown in FIG. 1, when dither processing is performed by combining 2 × 2 and 3 × 3 as a dither matrix size, when a rotating polygon mirror having six surfaces is used, dither processing is performed every six rotations of the number of surfaces. The lines having the same characteristics are scanned on the same plane. As described above, dither matrices of different sizes are appropriately selected, and this combination is selected from various relations with the number of polygon mirrors to be used. That is, it may be convenient to set a relationship in which there is no common divisor between the two.

Further, in the image output processing method having the above-mentioned configuration, according to the invention of claim 4, various combinations of different dither matrix sizes can be set and instructed. By doing so, it is possible to arbitrarily set a combination in which the reproduced image to be output does not occur as periodic image unevenness. It can be easily obtained.

Further, in the image output processing method characterized by the above-mentioned configuration, according to the fifth aspect of the present invention, the number of reflection surfaces of the polygon mirror is odd, and the number of reflection surfaces of the dither matrix is The dither processing is performed by setting a dither matrix size in which the periodic characteristics with the scanning line in the sub-scanning direction do not match as much as possible. For example, if a polygon mirror having seven or nine surfaces is used as shown in FIG. 2, by selecting an arbitrary dither matrix size, the number of reflection surfaces, for example, seven or nine rotations, can be reduced. By simply matching the characteristics of the dither matrix size with the cycle, extremely noticeable periodic unevenness in one or two rotation cycles can be eliminated as much as possible. Especially when using 9 polygon mirrors,
From the relation with the common divisor, it is important to set and select a matrix size other than at least 3 × 3 shown in FIG.

Finally, in the image output processing method characterized by the above-mentioned configuration, according to the invention of claim 6, if the dither matrix size is set to 5 × 5, a general six-sided polygon mirror is used. That is, even if a polygon mirror is used, only scanning with matching characteristics is performed in six rotation cycles. In addition, even in the case of an odd-numbered polygon mirror, scanning with the same characteristic is performed in the same number of rotation cycles of the surface, and the effect of eliminating the occurrence of periodic unevenness as much as possible is increased.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image output processing method according to the present invention will be described below with reference to the drawings.

FIG. 1 shows a second embodiment according to the first embodiment of the present invention.
FIG. 9 is a diagram illustrating an example in which dither matrices of different types are combined, and image data is processed so that dither processing is performed alternately with different dither matrix sizes. FIG. 2 is a diagram showing a configuration example showing an example of a polygon mirror for explaining a second embodiment of the present invention. FIG. 3 is a configuration diagram illustrating an example of an image forming apparatus according to the image output process according to the present invention.

First, a general configuration of an image forming apparatus for performing an image output process according to the present invention will be described with reference to FIG.

The image forming apparatus shown in FIG. 3 shows the configuration of a digital color copying machine. The present invention is not limited to such a digital copying machine, but inputs image data from outside and reproduces and outputs the image. The present invention can be applied as it is to an image forming apparatus such as a printer.

Therefore, a transparent platen 2 on which a document is placed and an operation panel to be described later are provided on the upper part of the main body of the digital copying machine 1 shown in FIG. Supported in an openable and closable manner with respect to the platen 2;
An automatic document feeder (ADF) 3 is mounted on the document table 2 with a predetermined positional relationship. Inside the main body of the digital copying machine 1, there are provided a reading device 4 for reading an image of a document placed on the document table 2, and an image forming section 10 below the reading device 4.

The automatic document feeder 3 feeds the documents placed on the placing table 3a one by one to the document table 2, and when reading by the reading device 4 is completed, the document is discharged to the discharge tray 3b and at the same time the next document is discharged. The conveyance of the document is started, and the document is automatically sent to the document table 2. In the case of a document having images formed on both sides, the automatic document feeder 3 first conveys one side to the document table 2 and discharges the document when reading of that side is completed. Without reversing the front and back sides, the document is sent to the document table 2 again, and after reading the image on the opposite side of the document, the document is discharged and one side of the next document is fed to the document table 2. ing.

A reading device 4 for reading an image of a document sent to the document table 2 by the automatic document feeder 3 comprises:
A first scanning unit 5 and a second scanning unit 6 that are reciprocated in parallel with the document table 2 are provided. First
The scanning unit 5 supports an exposure lamp that illuminates the original, a mirror that reflects light reflected from the original to a target position, and the like. Further, the second scanning unit 6 includes a pair of reflecting mirrors for reflecting the reflected light image reflected by the above-mentioned mirror to the CCD 8 which is a reading element via the imaging lens 7 constituting the reading device 4. Supported.

The first scanning unit 5 runs at a predetermined scanning speed from a home position (left side in FIG. 3) when reading an image of a document. Then, the second scanning unit 6 travels in the same direction at half the scanning speed. As a result, the image of the document is sequentially formed on the CCD 8 via the image forming lens 7, and the CCD 8 outputs read data that has been photoelectrically converted. The CCD 8 is provided with R, G, and B CCDs for color-separating the image if the original is color, or a color separation filter or the like is arranged in the optical path to read the color-separated image. Output data. CC
The read data output from D8 is converted into image data by the image forming unit 1 through a processing circuit that performs image processing for forming a color image or the like in the image forming unit 10 as described later.
Transferred to 0.

The image forming section 10 for reproducing the image data obtained through the reading device 4 as a visible image on a sheet has a sheet feeding device 11 provided below. The sheet feeding device 11 is provided with a sheet feeding unit that stores the sheets S in a sheet feeding cassette or a tray and separates and feeds the sheets one by one. The sheet sent out by the sheet feeding device 11 includes a registration roller 1 disposed in front of an image forming position.
It is sent to 2. The registration roller 12 is a well-known one, and is configured to convey a sheet to an image forming position in a timely manner.

An image forming unit 10 is provided above the sheet feeding device 11.
A transport belt mechanism 14 for movably holding a transfer belt 13 as a sheet holding member constituting the image forming apparatus is provided. The transport belt mechanism 14 includes a drive roller 15 that stretches the transfer transport belt 13 formed in an endless shape, and a driven roller 16. The transfer transport belt 13 is configured to transport the sheet P by electrostatically attracting the sheet P. Therefore, the driven roller 16 is moved to the registration roller 12 side.
The charging roller 17 is disposed so as to be in contact with the driven roller 16 and is pressed against the driven roller 16 via the transfer / conveying belt 13.

A fixing device 18 for transferring a toner image transferred on a sheet S, which will be described later, to the sheet is disposed on the side of the drive roller 15 of the transport belt mechanism 14. As the sheet S passes between the fixing roller nips of the fixing device 18, the toner on the surface is melted and fused and fixed on the sheet surface. The sheet S is transferred to the fixing device 18.
Is fixed and transported in the transport direction switching gate 1
The paper is then discharged by a discharge roller 20 to a paper discharge tray 21 provided so as to protrude out of the main body of the copying machine 1.

The switching gate 19 selectively switches between discharging the fixed sheet to the discharge tray 21 as described above or re-supplying the sheet to the image forming position of the image forming section 10 again. The conveyance path of the sheet S is switched. If image formation on both sides of the sheet S is selected, the switching gate 19 is controlled so as to guide the sheet S to the switchback transport path 22. As a result, the sheet S is again conveyed to the registration roller 12 just before the image forming position in the image forming unit 10 after the sheet S is turned upside down via the switchback conveyance path 22.

On the other hand, the image forming unit 10 is arranged above the transport belt mechanism 14, in particular, the linear portion (horizontal portion) of the transfer transport belt 13, in the order from the upstream in the transport direction in the vicinity of the transfer transport belt 13. The first, second, third and fourth image forming stations Pa, Pb, Pc and Pd are arranged side by side. The transfer conveyance belt 13 is stretched between the driving roller 15 and the driven roller 16 as described above, and is driven to run in the arrow Z direction by the rotation of the driving roller 16. Then, the sheet conveyed through the registration roller 12 is transferred to the transfer conveyance belt 13 by the action of the charging roller 17.
To be held electrostatically. The sheet S is sequentially conveyed to each of the image forming stations Pa, Pb, Pc, and Pd as the transfer conveyance belt 13 travels.

Each image forming station Pa, Pb, P
c and Pd have substantially the same configuration, and are a photosensitive member 23 which is a drum-shaped image carrier that is driven to rotate in the direction of arrow F in the figure.
a, 23b, 23c, and 23d. Chargers 24a, 24b, 24 for uniformly charging the photosensitive members are provided around the respective photosensitive members 23a, 23b, 23c, 23d.
c and 24d, and a developing device 25a according to the present invention for visualizing the electrostatic latent image formed on the photoconductor with toner of each color.
Transfer means 25b, 25c, 25d and a transfer means 2 for transferring the developed toner image to a sheet, which are provided in contact with the back surface of the transfer / transport belt 13 to constitute the transfer device of the present invention.
6a, 26b, 26c, 26d, and a cleaning device 27a, which removes toner remaining on the photoreceptor surface after transfer.
27b, 27c and 27d are sequentially arranged along the rotation direction of the photoconductor.

Each of the photoconductors 23a, 23b, 23c,
A dot light (information light) modulated according to the image data processed by the dither method according to the present invention is provided on the upper part of 23d.
, A deflecting device for deflecting light from the semiconductor laser device in the main scanning direction, and an f-θ lens for forming (exposing) the laser light deflected by the deflecting device on the surface of the photoreceptor. Laser irradiators 28a, 28b, 28c, 28d constituted by exposure means are provided respectively. The deflecting device is generally provided with polygon mirrors 30a to 30d, which are rotating polygon mirrors, and incorporates mirror motors 31a to 31d for rotating the polygon mirror at a predetermined speed at a high speed.

The laser irradiation device 28a receives image data corresponding to a color component image of a color original image corresponding to the color of the developing device 25a mounted. That is, when the developing device 25a contains the toner corresponding to yellow (Y), the laser irradiation device 28a supplies R (red) input from the reading device 4 to the image processing device (not shown) as described above. ), G (green), and B (blue) color image data, data conversion for reproducing yellow is performed, and the converted yellow image data is input, and image exposure is performed by the input.

The laser irradiation device 28b receives image data corresponding to a color component image of a color original image corresponding to the color of the developing device 25b. That is, the developing device 25b
Contains magenta (M) toner, the laser irradiation device 28b receives R,
Data conversion is performed to reproduce magenta from the G and B components, and magenta image data is input, and image exposure is performed.

Further, the laser irradiation device 28c receives image data corresponding to the color component image of the color original image corresponding to the color of the developing device 25c. That is, the developing device 25c
Contains cyan (C) toner, the laser irradiation device 28c receives R, R of the input color image data.
The G and B components are converted into data for reproducing cyan, the cyan image data is input, and image exposure is performed.

The laser irradiation device 28d receives image data corresponding to the color component image of the color original image corresponding to the color of the developing device 25d. That is, the developing device 25
When d contains black (BK) toner, black image data converted corresponding to black is input to the laser irradiation device 28d, thereby performing image exposure. In particular, for black image data, the input R, G, and B components are substantially the same.
The image is input to the laser irradiation device 28d in order to perform black development.

As a result, the photosensitive member 23 at each image forming position
On the a, 23b, 23c, and 23d, an electrostatic latent image corresponding to the color of the color-converted document is formed. Then, the developing device 25 of each image forming station Pa, Pb, Pc, Pd
a, developing device 25b, developing device 25c, developing device 25d
, And is reproduced as a toner image corresponding to the color image of the document.

The first image forming station Pa
And a registration roller 12 for adsorbing the sheet to the transfer belt 13 as described above.
7, the sheet S sent through the registration roller 12 is reliably electrostatically attracted to the transfer / conveyance belt 13, and in this state, the conveyance belt mechanism 14 is used.
, The paper is sequentially conveyed to the first to fourth image forming stations Pa, Pb, Pc, and Pd without shifting. Therefore, the sheet S is formed by the photoconductors 23 formed at the image forming stations Pa, Pb, Pc, and Pd.
The toner images of the respective colors on a, 23b, 23c, and 23d are transferred so as to be sequentially superimposed, and a color image is reproduced.

Then, the fourth image forming station Pd
Between the fixing device 18 and the fixing device 18, a neutralizer 29 is provided almost directly above the drive roller 15 of the transport belt mechanism 14. Therefore, the sheet S that has passed through the fourth image forming station Pd has three colors of yellow, magenta, and cyan.
The toner images of four colors including color or black are superposed and transferred, and the electrostatic attraction state with the transfer belt 13 is released by the operation of the charge eliminator 29. 13 and sent to the fixing device 18. The static eliminator 29 is supplied with an AC voltage and performs an AC corona discharge to remove the charged charges.

In the color digital copying machine 1 having the above-described configuration, the sheet S is accommodated in a sheet feeding cassette or a tray constituting the sheet feeding mechanism 11 in order to form an image on the sheet. Are sent one by one. The fed sheet S is fed via a transport roller or the like provided in a transport path to the registration roller 12 in order to feed the toner image to each transfer position of the toner image in each of the image forming stations Pa, Pb, Pc, and Pd. . The leading edge of the fed sheet P is detected by a sensor (not shown) or the like, and is temporarily stopped at the position of the registration roller 12 by a signal output from the sensor. Then, at a timing with each of the image forming stations Pa, Pb, Pc, and Pd, the sheet is fed to the transfer / conveying belt 13 rotating in the arrow Z direction shown in FIG.

At this time, due to the action of the charging roller 17, the transfer / conveying belt 13 is given a predetermined charge, and the sheet S is electrostatically attracted to the transfer belt 13. Thereby, while passing through the image forming stations Pa, Pb, Pc, and Pd, stable conveyance is performed in a sucked state,
The toner images of each color formed in each station are sequentially transferred and superimposed.

That is, each image forming station Pa, P
b, Pc, and Pd, the toner image of each color is
3a, 23b, 23c, and 23d, which are sequentially superimposed and transferred onto the surface of the conveyed sheet P electrostatically attracted by the transfer / conveyance belt 13. Then, finally, the fourth image forming station Pd
When the transfer of the toner image is completed, the sheet S is separated from the transfer and conveyance belt 13 by the action of the charge remover 29 from the leading end of the sheet S. Then, the peeled sheet S is guided to the fixing device 18, and the color toner image superimposed and transferred on the sheet S is melted and fixed, and is output to the paper discharge tray 21.

(First Embodiment of the Present Invention) In the color digital copying machine 1 as shown in FIG. 3, the read data read by the reading device 4 as described above is transferred to the image forming stations Pa, An image processing circuit (not shown) is provided to reproduce Pb, Pc, and Pd as a toner image. Normally, the read data from the reading device 4 is R
(Red), G (green), and B (blue) color-separated read data that can be processed by the image forming unit 10 is Y
(Yellow), M (magenta), C (cyan), BK
(Black) color image data. Therefore, in order to perform the color conversion processing and the like, the digital copying machine 1 is provided with a well-known image processing circuit (not shown).

As described above, in the image processing circuit, each of the image forming stations Pa, Pb, Pc, P
The image data is sent to the image data d. In the image processing, dither processing by the dither method is also performed in order to achieve good halftone reproducibility, and the image data after the processing is applied to the above-described Y, M for each color. , C and BK as color image data,
Each of the target laser irradiation devices 28a to 28d is sent.

Therefore, the polygon mirror 30 of the laser irradiators 28a to 28d according to the present invention (hereinafter, one laser irradiator will be described as 28) is rotated at a predetermined speed and modulated according to the image data. Especially ON-O
The laser beam from the semiconductor laser driven by the FF is used as information light to deflect the surface of the photoreceptor 23 in the direction of the rotation axis and scan.

According to the present invention, the polygon mirror 30
A case where a six-sided mirror is used as shown in FIG. 5A will be described below. In the dither matrix size by the dither method, at least two dither matrices having different sizes in the sub-scanning direction are alternately combined as shown in FIG.
Dither processing is performed. In the example shown in FIG. 1, the dither matrix sizes are 2 × 2 and 3 ×
Alternately combine dither matrices of size 3
The image processing by dither processing is executed.

In the case where a six-plane polygon mirror 30 is used for the image data shown in FIG. 1, each surface of the polygon mirror 30 by the first rotation scan and the seventh rotation scan has a periodic dither matrix. It matches the characteristics, but the matching period is very long. In other words, the matching period is
If the rotation of the polygon mirror 30 is used as a reference, the cycle is six rotations. If the common divisor does not exist between the dither matrix size and the number of mirrors (reflection surfaces) of the polygon mirror 30, the cycle is determined by the dither matrix size or the number of mirrors of the polygon mirror 30 (the larger one). The scans will match by number.

Therefore, as shown in the example of FIG. 1, the period can be lengthened by variously changing the combination of dither matrices and selecting such that the surface of the polygon mirror 30 and the common divisor do not exist.

For example, when a six-sided polygon mirror 30 is used, the dither matrix size to be selected is 3
By combining the × 3 and 4 × 4 matrices, the polygon mirror 30 performs scanning with a period of 7 rotations so as to match the periodic characteristic of the dither matrix.

In the case where a 12-sided polygon mirror 30 shown in FIG. 5C is used for the image processed by the dither matrix size shown in FIG. 1, the mirror of the polygon mirror 30 is used. Since the number is 12, the line scans having the same characteristics match in the larger number of 12 rotation cycles. In this case, the scanning lines are every 60 lines, and the effect of eliminating the periodic unevenness is further enhanced.

Further, since the result of the image processing by the dither method differs depending on the characteristics of the image data input to the image forming apparatus, too much image unevenness is considered from the result of the reproduced image actually output (recorded). If so,
Various combinations of dither matrix size are changed,
Image reproduction and output processing can be performed in a state where periodic image unevenness is less noticeable.

As described above, the setting of the dither matrix size can be changed by combining the dither matrix size on an operation panel arbitrarily operated by an operator provided in the image forming apparatus 1 as shown in FIG. There is provided a setting key or the like for instructing to change the setting. The combination can be arbitrarily set and operated with the setting key. Thus, when the image unevenness is anxious, the user operates the setting key to change the dither matrix size, for example, as shown in FIG.
Is changed to a combination of 3 × 3 and 4 × 4, or the combination shown in FIG.
And 2 × 2, dither processing is performed on the input image data, and reproduction and output by a combination of arbitrary matrix sizes can be performed.

In this case, the matrix size has been described by taking two types of combinations as an example, but it goes without saying that the present invention can be carried out in the same manner in three or four types of combinations.

Furthermore, it is possible to use a single dither matrix size instead of a combination of dither matrix sizes. For example, a dither matrix having a size of 5 × 5 as shown in FIG.
Even when the polygon mirror 30 is changed and scanned by the six-sided polygon mirror 30, the polygon mirror 30 has a period of six rotations and coincides with the period of the dither matrix, and the same result as the case shown in FIG. 1 can be obtained. Becomes

Therefore, by using a dither matrix size of 7 × 7 or the like, the effect of suppressing periodic image unevenness is further increased. However, if the matrix size is increased excessively, the whole image becomes smoother, but the resolution of the image may be deteriorated. Therefore, it can be said that a dither matrix size of about 5 × 5 as shown in FIG. 4 is optimal.

(Second Embodiment of the Present Invention)
According to the embodiment, the plurality of combinations having different dither matrix sizes by dither processing are used to minimize the possibility that scanning by each surface of the polygon mirror 30 coincides with the periodic characteristic based on the dither matrix size. is there. Instead of such an example, it is also possible to perform scanning on the polygon mirror 30 side so that the specifics do not overlap as much as possible.

For this reason, the polygon mirror 30 is used as shown in FIG.
It is effective to configure an odd-numbered surface instead of an even-numbered surface as shown in FIG. In other words, FIG. 2A shows an example of a polygon mirror 30 having seven surfaces, and FIG. 2B shows an example of a polygon mirror 30 having nine surfaces.

Therefore, when the semiconductor laser of the laser irradiation device 28 is modulated (driven) in accordance with the image data which has been dithered using the 4 × 4 dither matrix size, the seven polygons shown in FIG. If scanning is performed using the mirror 30, the scanning line having the periodic characteristic of the dither matrix coincides every seven rotation cycles of the polygon mirror 30. Therefore, the period becomes as large as possible, and it can be expected that periodic image unevenness can be reduced.

In the nine-sided polygon mirror 30 shown in FIG. 2B, there are nine rotation cycles. However, when the dither matrix size is 3.times.3, scanning is performed on scanning lines having the same feature in three rotation cycles. Therefore, it is necessary to set in consideration of the number of faces of the polygon mirror 30 and the size of the dither matrix.

For example, the set dither matrix size, particularly the number of lines in the sub-scanning direction, and the polygon mirror 3
It is effective to set the relationship such that the common divisor does not exist such that the number of mirrors of 0 is not divisible from each other. Therefore, when the polygon mirror 30 is an even-numbered surface, for example, a six-surfaced polygon mirror, if the size is 2 × 2, 3 × 3, or 4 × 4, there are 2 or 3 common divisors. Therefore, if a relationship where there is no common divisor, that is, 5 × 5 or the like is set as the dither matrix size, the matching cycle can be lengthened even if each polygon mirror 30 shown in FIG. 5 is used.

It is needless to say that the same effect can be expected for the polygon mirror 30 having the odd number of mirrors shown in FIG. 2 by setting the above-mentioned 5 × 5 dither matrix size.

(Other Embodiments of the Present Invention) In the description of the first and second embodiments described above, light corresponding to image data deflected and scanned by the rotating polygon mirror 30, ie, light The description has been made assuming that the number of information beams (laser beams) is one.

However, when there are a plurality of, for example, two information beams (laser beams) simultaneously deflected and scanned by each surface of the polygon mirror 30, the number of information beams (two) and the number of mirrors (for example, six surfaces, The relationship is set so that the periodic characteristic (either 8 or 12 surfaces) and the periodic characteristic of dither matrix size (for example, 5 × 5) do not overlap (do not coincide) as much as possible. With this arrangement, it is possible to lengthen the cycle of repeatedly performing deflection scanning with the same mirror surface (mirror surface), and to suppress the periodic image unevenness.

Further, by combining both the first and second embodiments, the effect can be further promoted. That is, as an example shown in FIG. 1, by using a combination of different matrix sizes and using the polygon mirror 30 of the odd-numbered mirror shown in FIG.
, It is possible to lengthen the rotation cycle at which the periodic characteristics coincide with each other.

As described above, according to the image output processing method of the present invention, in the combination of the number of mirrors (the number of reflection surfaces) of the polygon mirror 30 and the dither matrix size by the dither method, the mirrors on the same surface are used. The relationship is set so that the scanning repetition period, that is, the repetition period of the scanning line having the periodic characteristic of the matrix size is prevented from overlapping as much as possible. This allows
Since periodic image unevenness can be suppressed as much as possible, it is possible to favorably output reproduction in halftones and output high quality images without unevenness.

In this case, since the number of surfaces of the polygon mirror 30 and the dither matrix size are different from each other, the scanning on the same surface is prevented from being matched as much as possible, and the combination can be changed variously. Thus, periodic image unevenness can be suppressed as much as possible.

Further, by setting the number of surfaces of the polygon mirror 30 to an odd number, it is possible to minimize the coincidence of scanning surfaces when scanning according to dithered image data. For example, good results can be obtained by using the dither matrix size shown in FIG.

Further, by setting the dither matrix size as shown in FIG. 4, even if the polygon mirror 30 has an even or odd number of mirrors, scanning can be performed so as to minimize the occurrence of periodic image unevenness. .

[0077]

According to the image output processing method of the present invention, the relationship between the matrix size used for improving the reproducibility of the halftone by the dither method as the image processing and the number of reflecting surfaces of the rotary polygon mirror is determined. Considering the matrix size and the number of mirror surfaces so as not to have a periodic relationship as much as possible, it is possible to minimize periodic image unevenness. Thereby, it is possible to output a faithful reproduced image without affecting the image quality of the entire image.

In particular, when periodic image unevenness is conspicuous, by taking into account the combination of matrix sizes, it can be eliminated and the operator can set it arbitrarily.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a combination based on a dither matrix size according to a dither method for describing a first embodiment of the present invention.

FIG. 2 shows a polygon mirror for deflecting and scanning information light for explaining a second embodiment of the present invention.
FIG. 3 is a top view of a polygon mirror having seven surfaces, and FIG.

FIG. 3 is a configuration diagram showing an internal structure of a digital copying machine as an image forming apparatus for performing image output according to the present invention.

FIG. 4 is a diagram showing an example of a dither matrix with a size of 5 × 5 according to the dither method according to the present invention.

FIG. 5 shows a general structure of a polygon mirror according to the present invention, wherein (a) shows a polygon mirror having six surfaces,
(B) is a diagram showing a polygon mirror having eight surfaces, and (c) is a diagram showing a polygon mirror having twelve surfaces.

FIG. 6 shows an example of a dither matrix size by the dither method according to the present invention, where (a) is 2 × 2 and (b)
FIG. 4 is a diagram showing a 3 × 3 matrix size, and FIG. 4C is a diagram showing a 4 × 4 matrix size.

7A and 7B are diagrams for explaining a periodic relationship between a conventional dither matrix size and each surface of a polygon mirror. FIG. 7A illustrates a relationship between a 2 × 2 matrix size and a six-surface polygon mirror. (B) is a diagram showing the relationship between a 3 × 3 matrix size and six polygon mirrors.

[Explanation of symbols]

 Reference Signs List 1 digital copying machine (image output processing unit) 4 reading device (image input unit) 10 image forming unit (output unit) 13 transfer / conveying belt 23 photoconductor 24 charging device 25 developing device 26 transfer means 28 laser irradiation device 30 polygon mirror ( Polyhedral mirror) 31 Mirror motor

Continued on the front page (72) Inventor Toshio Yamanaka 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Hidekazu Sakagami 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation F term (reference) 5C072 AA03 BA17 HA13 UA17 XA01 XA05 5C077 LL04 MP08 NN09 PP05 PP68 PQ08 TT03 TT06

Claims (6)

[Claims] An image data input according to a dither matrix size determined by a dither method is subjected to dither processing, and an information beam modulated according to the processed image data is transmitted to an image carrier of a rotated image carrier. In a processing method for reproducing and outputting an image corresponding to an input image by deflecting and scanning with a polygon mirror rotated at a constant speed in a rotation axis direction, a periodic characteristic of the polygon mirror and a dither matrix by a dither method An image output processing method, wherein the image carrier is scanned by setting such that the periodic characteristics of the size do not overlap each other as much as possible. 2. The periodic characteristic of the polygon mirror is the number of reflection surfaces, and the period in which the sub-scanning direction of the dither matrix size and the reflection surface of the polygon mirror overlap each other becomes long.
2. The image output processing method according to claim 1, wherein a dither matrix size is set. 3. An image output processing method according to claim 1, wherein the dither processing of the input image is performed by combining a plurality of different sizes of the dither matrix. 4. The image output processing method according to claim 3, wherein various combinations of different dither matrix sizes can be designated. 5. The number of reflection surfaces of the polygon mirror is odd, and a dither matrix size is set so that the periodic characteristic of the dither matrix does not coincide with the scanning line in the sub-scanning direction as much as possible. 2. The image output processing method according to claim 1, wherein dither processing is performed. 6. The dither matrix size is 5 × 5.
3. The image output processing method according to claim 2, wherein: