JP2002118746A - Image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming method that ensures images, consisting of a small number of data with high image quality with stable number of gradations. SOLUTION: An M-process dither matrix compares a numeral at each of placed dots with image data, to convert the image data into binary data. When the image data are greater than the numeral, the concerned dot is set, and when the image data are equal to or less than the numeral, the concerned dot is cleared. The M-process dither matrix is repeatedly placed on an image, and in the case of uniform density data, the image is filled with dots from places with a smaller numeral, in the order of increasing density, resulting that the dots are regularly scattered in the image plane. When the density is increased, dots adjacent to each isolated dot are produced, resulting in forming a first dot with an increased size. When the density is further increased, dots are generated in the order of being combined with other dots in the main scanning direction to form a line image with 2-dot width in the subscanning direction, thereby forming the line image. Since 4 sub matrices are used to sequentially add dots to the lines with the 2-dot width at the medium density or higher, the line image is made thick uniformly, as the density is increased. Similar processing applies to Y, C, K processes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method, and more particularly, to an image forming method for converting multi-gradation image data into binary or low-value image data and forming an image based on the data. About the method.

[0002]

2. Description of the Related Art Conventionally, there has been used an image forming method relating to halftone processing which can be applied to an image forming apparatus such as a laser printer, a digital copying machine, a color laser printer, a digital color copying machine, or a display device. ing.

In the conventional halftone processing, a dither method is often used, and it is possible to express gradations and colors even with a binary printer or the like. This dither method is generally a dot type dither for forming dots, and includes a dot concentration type in which dots are collectively arranged and a dot dispersion type in which dots are discretely arranged.

In the case of the dot concentration type dither method, the stability of an image is excellent and the gradation is excellent in an electrophotographic printer or the like, but the character or image edge is liable to rattle. In the case of the dot dispersion type dither method, the resolution is high, but the gradation and stability are lacking, and density unevenness such as banding tends to occur easily.

For example, Japanese Patent Application Laid-Open No. 61-21466 discloses a method for forming a line-based image by dither processing.
No. 2, there is a multi-value writing line image forming a diagonal line-shaped image, in which a plurality of minute dots are formed for one pixel data, and a set of the minute dots forms an oblique direction in the recording direction. It is disclosed that, after forming the dot, the minute dots are increased by increasing the density, and after the maximum density of the pixel, the minute dots of the remaining pixels are similarly increased.

Further, Japanese Patent Application Laid-Open Nos. Hei 10-145626 and Hei 10-257337 disclose that the screen angle direction of a line is changed by 90 degrees for each color plate.

Further, Japanese Patent Application Laid-Open No. 61-21466 described above.
Japanese Patent Application Laid-Open No. 2 (1994) discloses that multi-level lines forming an oblique line image are sequentially and uniformly thickened from above.

[0008]

However, in such a conventional image forming method, a YMCK (yellow, magenta, cyan, and black) color image is formed using, for example, four image forming stations. When the images are sequentially transferred to the transfer paper, deviations of the YMCK image positions are apt to occur, and local fluctuations deviating by several tens of microns within one print are inevitable.

When a color image is formed by using a one-dora type image forming apparatus provided with one image forming means, a four-color image is formed by the same image forming system. The amount can be lower than using four imaging stations, but it does occur to some extent.

In forming a color image in this manner, Y
When a local shift of each image position of MCK occurs, even if images of each color are superimposed by performing a general halftone type dither processing or the like, dots of each color are arranged with a periodicity, Since the dots overlap each other, the degree of dot overlap partially differs. The overlapped portion of the toner dots is observed to be cloudy in color, and the color tone is slightly different from that of the portion formed and separated under the same data conditions. For this reason, in general, a low-frequency periodic position fluctuation occurs in an image, and a phenomenon such as coloring, which is a color change, appears in a color portion having a uniform density.

Therefore, in the printing halftone using the screen angle dither which shifts the direction of the halftone dot for each color of YMCK, the screen angle is generally arranged every 30 degrees. Unusual textures (patterns other than the original image) caused by a screen angle as represented by a rosette pattern were sometimes generated.

For example, Japanese Patent Application Laid-Open No. Hei 10-1456 described above
No. 26 and Japanese Patent Application Laid-Open No. 10-257337,
Since an image is formed by an isolated dot or a halftone dot before the formation of a line in the highlight portion, the image period has a direction perpendicular to the line. For this reason, there has been a problem that color moiré occurs due to misregistration when color plates having a screen angle of 90 degrees are combined in those portions.

Further, the above-mentioned Japanese Patent Application Laid-Open No. 61-214662 has been disclosed.
As described in Japanese Patent Application Laid-Open Publication No. H11-157, if multi-value writing is performed for each dot, it is possible to easily realize high image quality in which the number of gradations is stable and stable. There was a problem that formation was unstable. Therefore, it is conceivable to use small value data, but there is a problem that a change in texture or thickness becomes easy to recognize due to jaggies of the line lines due to dot addition.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method capable of forming an image with a small number of data and having a stable and sufficient number of gradations and realizing high image quality with little color unevenness, color turbidity or image texture. Is what you do.

[0015]

In order to solve the above-mentioned problems, the invention according to the first aspect of the present invention provides a method for converting multi-gradation image data into two.
In the image forming method of converting an image based on the data, the dither matrix for converting the image is converted so as to form the image in a line tone in a certain direction. The dither matrix is composed of a plurality of sub-matrices connected in at least two directions.
The direction is the same as the line base direction of the image.

According to this, the dither matrix for converting multi-gradation image data into binary or low-value image data is for converting an image so as to form a line tone in a certain direction. And a plurality of sub-matrices connected to each other, and the order of density generation of the sub-matrices is set to be the same as the line keying direction of the image. Therefore, it is possible to form a high-quality image that is stable and has a large number of gradations even with small value data.

According to a second aspect of the present invention, there is provided an image forming method for converting multi-tone image data into binary or low-value image data and forming a multi-color image based on the data. Is converted so as to form an image in a line tone in a certain direction, and the direction of the line tone is a screen angle direction in which each color or at least a combination thereof is different, and each screen angle direction is orthogonal to each other. Are characterized by having a relatively large screen angle difference.

According to this, the dither matrix for converting multi-gradation image data into binary or low-value image data converts an image so as to form a line tone in a certain direction. Is a screen angle direction in which each color or at least a combination thereof is different, and the screen angle directions are not orthogonal to each other and have a somewhat large screen angle difference. For this reason, even in the highlight portion, color unevenness and color turbidity due to misregistration can be suppressed.

According to a third aspect of the present invention, there is provided an image forming method for converting multi-level image data into binary or low-level image data and forming an image based on the data. The dither matrix converts the image so as to form a line tone in a certain direction, and the dither matrix is arranged adjacent to the existing dot with an increase in density, and the growth of the edge portion of the line tone by the dither matrix is performed. It is characterized by being linear.

According to this, the dither matrix for converting multi-gradation image data into binary or low-value image data converts the image so as to form a line tone in a certain direction. In addition, the dots were arranged adjacent to the existing dots, and the growth of the line-based edge portion by the dither matrix was linear. For this reason, it is possible to prevent a thick line or a step from being felt in the parallel line.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings. In the present embodiment, YMCK is used as an image forming apparatus.
An electrophotographic color printer that forms a color image using four colors (yellow, magenta, cyan, and black) is used.

FIG. 1 is a cross-sectional view showing a schematic configuration of an electrophotographic color printer according to the present embodiment. Postscript Explanation The electrophotographic color printer 1 forms four color images in an independent image forming system. Is a four-drum tandem engine type image forming apparatus for synthesizing an image.

As shown in FIG. 1, each of the four color (YMCK) image forming systems of the electrophotographic color printer 1 has a small-diameter OPC drum 2 (yellow), 3 (magenta), 4 (cyan) and 5 (black), and an image forming apparatus in which a charging roller, a developing unit, a cleaning unit, a charge removing unit, and the like are arranged from the upstream side of the image forming so as to surround each of the OPC drums 2 to 5. Blocks 6, 7, 8, and 9 are configured. Further, toner bottle units 10, 11, 12, and 13 for replenishing the respective toners of YMCK are arranged beside the image forming blocks 6 to 9.

Further, on the left side thereof, independent YMCK optical writing units 14, 15, 16, 17 are respectively provided.
Is arranged. For example, the optical writing unit 14
The optical components such as an LD light source 18, a collimating lens 19, and an fθ lens 20, a polygon mirror 21, a return mirror 22, and the like are arranged. A writing optical path is guided to a portion where the OPC drum 5 is charged by a charging roller. I will In the optical writing unit 14, optical writing is performed based on image data corresponding to black.
The other optical writing units 15 to 17 have the same configuration, and optical writing is performed based on each of the yellow, magenta, and cyan image data.

Further, on the right side of the image forming blocks 6 to 9, a series of transfer belt units 24 for superimposing the four color toner images formed on the OPC drums 2 to 5 on the transfer belt 23 are provided.
Are arranged in contact with the OPC drums 2 to 5, and the toner image is transferred onto the transfer paper while holding the transfer paper (not shown).

On the lower side of the apparatus, there is provided a paper feed tray 25 for accommodating transfer paper, and when the paper is fed one by one in a horizontal direction by a pickup roller 26, the transfer paper has an image forming system. The transfer belt 2 is transported in the vertical direction.
The toner image electrostatically attracted and held on the transfer sheet 3 is transferred to a transfer sheet. The transferred paper is transferred to the fixing unit 2 on the upper side of the apparatus.
7, the toner is fixed on the transfer paper by heat and pressure, and the discharge tray 2 on the upper part of the electrophotographic color printer 1
The paper is discharged to the printer 8 with the image side down.

Electrophotographic color printer 1 of the present embodiment
Uses four imaging stations as described above for YM
Since this is an image forming method in which CK images are individually formed and transferred to transfer paper, the printing speed is excellent.

However, since image forming systems are different from each other, each image position of YMCK may be shifted by several tens of microns due to a position error of an optical system or a structure, a shape error of an image forming drum or the like. Even if the displacement is accurately adjusted, the position of the optical component may fluctuate due to the environment, aging, and the like. In addition, depending on the accuracy of parts, local fluctuations deviating by several tens of microns may not be avoided even in one print. For this reason, 1 provided with one image forming means
Since the four-color image is formed by the same image forming system in the Dora type image forming apparatus, the amount of misregistration for each color can be suppressed lower than that of the four Dora type, but it still occurs to some extent.

In addition, in the case of a color image, when a local shift of each image position of YMCK occurs, for example, when a general halftone type dither process is performed and the images of the respective colors are superimposed, the respective colors are shifted. Since the dots are arranged with a periodicity and overlap in the image, the degree of dot overlap partially differs. That is, although dots of a certain color are overlapped with each other, they are arranged apart in a certain portion.

FIG. 2 is a diagram showing a state in which dots of two different colors are formed and arranged using halftone dot dither. As shown in FIG. 2, here, a case where an image is created by halftone dithering of magenta and cyan dots, and where dots substantially overlap each other as shown in FIG. There is a portion where dots partially overlap as shown in FIG. 3B and a portion where dots do not overlap as shown in FIG.
For this reason, ((a), (b)) colors are observed to be turbid in the portion where the toner dots overlap, and the color tone of the portion (c) formed under the same data condition and separated is slightly delicate. Will be observed differently. Generally, a low-frequency periodic position fluctuation occurs in an image, and a phenomenon such as coloring, which is a color change, appears in a color portion having a uniform density.

Therefore, in the electrophotographic color printer 1 of the present embodiment, the dither method is used for the halftone processing. The dither is a line screen angle dither in which the basic tone of the image of each color of YMCK is linear and the line directionality is different for each color. This line screen angle dither can form a stable image by concentration of dots by the line image, so that it is possible to reduce color unevenness due to misregistration due to the screen angle as described above.
In the halftone type dither, the dots are arranged in four directions and have two directions perpendicular to each other. Therefore, the screen angles of the four colors must be set within 90 degrees, and each of the screen angles is set to 30 degrees. Or, it is generally 15 degrees.

Electrophotographic color printer 1 of the present embodiment
The diagonal screen angle dither adopted by the company has a 4-line screen angle of 180 because the direction of the parallel line is one direction.
Since the angle can be set within degrees, the degree of freedom of the screen angle is increased, and an angle with less texture can be selected.

(Embodiment 1) In Embodiment 1, an embodiment will be described in the case where the line screen angle dither is 1200 × 600 dpi / 1 bit. FIG. 3 shows K (black), C (cyan), M (magenta), and Y (yellow) of the dither matrix.
FIG. 4 is a diagram showing specifications relating to each version.

As shown in FIG. 3, the screen ruling of each color is common to 190 lines, so that a relatively high-resolution image can be formed. The gradation of each color is composed of 80 matrix values as described later, and the number of gradations is 81 gradations. The line screen angle direction of each color is configured, for example, as shown in FIG. 4, and line images are arranged at intervals of 30 degrees or more for each color as shown in FIG. Also,
The basic matrix is composed of 20 dots as shown in the matrix of each of the YMCK plates in FIGS. 5 to 8, and the above gradation (81 gradation) is expressed by four sub-matrices.

Regarding the repetition matrix in the image,
Although not shown, each has a period of 40 × 20 dots, and the dither matrix is arranged in a printer controller of the image forming apparatus or a printer driver such as a PC connected thereto in the form of a dither conversion table.

FIGS. 5 to 8 are diagrams showing the dither matrix of each plate at 1200 × 600 dpi / 1 bit dither. FIG.
Is an M-version dither matrix, which compares the numerical value in each dot arrangement with image data and converts it into binary data.
Here, when the image data is larger, the dot is turned ON, and when the image data is smaller or equal, the dot is turned OFF. The dither matrix of the M plane in FIG. 5 is repeatedly arranged on the image as shown in FIG.

Therefore, in the case of the uniform density data, the dots are buried from the place where the numerical value is small in the order of increasing density, and at first, isolated dots are generated near the center of the four sub-matrices, and the dots are regularly arranged on the image plane. Will be scattered around.

Next, when the density increases, a dot is generated adjacent to the isolated dot, and the first dot becomes larger. In this case, if the writing exposure period of one dot is set to be full, the resolution in the sub-scanning direction is set to 1200 dpi at 1200 dpi.
The writing signal for the dots is continuous, and stable dots with large potential attenuation of the latent image due to exposure can be formed.

When the density is further increased, dots are generated in such an order that they are combined with the dots in the main scanning direction, and the sub-scanning direction changes to a line-shaped image having a width of 2 dots. As a result, a line image in which the dots are combined is formed in the line direction shown in FIG.

Thereafter, after the middle density portion, unlike the previous dot growth order, dots are sequentially added to the two-dot width line by four sub-matrices as shown by the numerical values of the matrix. In addition, the line image becomes evenly thicker as the density increases.

The Y-version dither matrix shown in FIG. 6 is composed of a basic matrix of 20 dots of the same shape, and forms a line screen in the 4:00 direction of the timepiece (see FIG. 4). Then, as the density increases, the number of dots is sequentially increased in the sub-scanning direction from the center of each matrix to form a line in the sub-scanning direction within the matrix. Thereafter, by extending the previous line so as to extend in the main scanning direction of the next matrix with respect to the upper and lower stages of the line in the sub-scanning direction, the line image can be grown so as to become thicker.

The C-plate dither matrix shown in FIG.
Has a horizontal line symmetrical structure with respect to the Y plane dither matrix shown in FIG. The C version dither matrix is the same
It is composed of a basic matrix of dots and forms a line screen in the 2 o'clock direction of the watch (see FIG. 4). In this case as well, as the density increases, the dots are sequentially increased from the center of each matrix in the sub-scanning direction, and lines in the sub-scanning direction are formed in the matrix. Thereafter, by extending the previous line so as to extend in the main scanning direction of the next matrix in the upper and lower stages in the sub-scanning direction of the line, the line image can be grown so as to become thicker.

The K-version dither matrix shown in FIG.
Has an axisymmetric vertical line structure with respect to the M-plate dither matrix shown in FIG. The K version dither matrix is the same
It consists of a basic matrix of 0 dots,
A line screen in the 1 o'clock direction is formed (see FIG. 4). Then, as the density increases, a line having a width of 2 dots in the sub-scanning direction is formed from the center of each matrix. Thereafter, the number of dots is increased for each dot so as to be connected in the main scanning direction of the line, and the line image is thickened so as to be a uniform straight line.

FIG. 9 is a diagram showing the arrangement of sub-matrices of the M version. The blocks of each matrix are arranged as shown, and the order of the sub-matrices is the same as the line direction of the image, that is, the sub-matrix. 1, 2 and 3 and 4 are screen directions. The matrix shape is the same for each color plate shown in FIGS. 6 to 9, and the order of the sub-matrix and the screen direction are the same.

Specifically, in the M-version dither matrix of FIG. 5, thresholds 1, 4, 7, and 10 are arranged in the highlight portion as shown in FIG. 9, and thereafter, the sub-matrix order of FIG. Increases the matrix value. This allows
For example, in a highlight portion having a data level of about 5, 1
Dots are formed only in the portions 4 and 4, and the dots are arranged in the same linear direction as the parallel line direction formed in the other middle and high density portions,
Since no dots are formed at the threshold values of 7 and 10, an image pattern having a double cycle is obtained. As the density increases, the dots are aligned in the sub-matrix, and the line is based on the 190 discrete dots. However, since the directionality is the same, the change in texture is reduced.

As described above, according to the first embodiment,
Since a plurality of adjacent sub-matrices are configured to increase in a specific order in accordance with the increase in density, it is possible to secure a stable and large number of gradations even with small value data, and to form a high quality image. it can.

Embodiment 2 In Embodiment 2, a line screen angle dither in the case where the writing density is 1200 × 600 dpi / 2 bits will be described. FIG. 10 shows K (black), C (cyan), M (magenta), and Y of the dither matrix.
It is a figure showing the specification about each version of (yellow). FIG.
As shown in FIG. 0, the screen ruling of the K and Y plates is 1
90 lines, but the screen frequency of the C and M versions is 2
The number of lines is 10, and a high-resolution image can be formed.
The gradation of each color is composed of a total of 160 matrix values, and the number of gradations is 161 gradations. In the line screen angle direction of each color, as shown in FIG. 10, line images are arranged at intervals of 30 degrees or more for each color. The basic matrix is composed of 20 dots, each of which has 2 dots.
The above gradation (161 gradation) is expressed by one sub-matrix and four-valued multivalued number of each dot. Although not shown, the repetition matrix in the image has a cycle of 40 × 20 dots and a cycle of 20 × 8 dots, respectively, and is similarly arranged in the form of a dither conversion table.

FIGS. 11 to 13 are diagrams showing a K-version dither threshold matrix of 1200 × 600 dpi / 2 bit dither. These matrices are deformed blocks as shown in the figure, and their numerical values indicate the dot generation order of the K plane. 2b
In writing the it data, it is possible to perform 0 and 3 level exposure within a dot of 1200 × 600 dpi. Here, the PWM (pulse width modulation) system for controlling the exposure time of the LD is adopted as the write modulation system, but the present invention is not limited to this. For example, a PM (power modulation) system for modulating the exposure power, or a combination of both systems Of course, it is also possible to use LD modulation of a different modulation method or a multi-level number.

The threshold value matrix is expressed by N-
It has a threshold table of one, compares the numerical value of each threshold with image data, and converts it into multi-value data that falls within the threshold section. For example, in the case of 2-bit data, if the image data is smaller than the threshold table 1 shown in FIG. 11, the data is set to “0”. If the image data is smaller than the threshold table 2 shown in FIG. Data is "1"
The image data is smaller than the threshold value table 3 shown in FIG. 13, and the data is “2” when the image data is equal to or more than FIG. 12, and the data is “3” when the image data is equal to or more than FIG.
It is converted into four values from “0” to “3”.

Then, with this converted data, 0 to 100% of the PWM is modulated and written as described above. PWM
The values may be equal, such as 0, 33, 66, and 100%, respectively, or may be set differently.
Further, the maximum duty of PWM may be set to 100% or less. In this way, the image is converted into four different exposure levels including OFF, and image formation with different dot sizes is performed.

As shown in the K-plate dither threshold matrices in FIGS. 11 to 13, the arrangement is repeated on the image.
Therefore, in the case of data having a uniform density, small dots in FIG. 11 are generated from the place where the numerical value is small in the order of increasing density, and initially, isolated dots are generated near the center of the two sub-matrices. Start to scatter regularly.

Next, when the density increases, the minute dot portion becomes a medium size dot at the next exposure level, and a large size stable dot is formed at the next level. In this case, if the writing exposure period of one dot is set to be full, it becomes an isolated dot of one dot at 1200 × 600 dpi.

When the density is further increased, as shown in the figure, the dots are sequentially generated from the small dots in such an order that they are combined in the sub-scanning direction, and grow into large dots. As a result, 1
The transition to the next dot is performed in a state where the density of each dot is saturated, and the transition to a linear image is made as shown in the figure.

Thereafter, the line image becomes evenly thicker as the density increases with respect to the lines even after the middle density portion. In this case, the two sub-matrix directions are different from the line direction of the lines, and are orthogonal to the lines.

FIG. 14 is a diagram showing the matrix order of the M version of 2-bit dither as described above. This indicates the order in which dots are generated, but actually, as shown in the K-version dither matrix shown in FIGS.
The structure is converted into a matrix with two threshold tables.

The 2-bit dither M-plate matrix shown in FIG. 14 is composed of a rectangular basic matrix of 20 dots, and forms a line screen in the 2 o'clock direction of the watch (see FIG. 4). In this case, the dot period has a shape that is not an accurate square. As the density increases, small dots grow sequentially from large dots to large dots in the same manner as described above, and shift to the next dot in a state where the density of one dot unit is saturated. The dots are sequentially increased in the sub-scanning direction from the end of each matrix to form a line. Thereafter, the line image is grown so as to be fat.

Although not shown, the Y-version dither matrix has a structure which is line-symmetric with respect to the K-version dither matrix shown in FIGS. The Y-version dither matrix is composed of the same basic matrix of 20 dots, and forms a line screen in the 11 o'clock direction of the watch (see FIG. 4). The same applies to the image formation accompanying the density increase by the dither matrix. The dot grows sequentially from the small dot to the large dot, and shifts to the next dot when the density of one dot unit is saturated.

The C-plate dither matrix has a structure which is line-symmetric with respect to the M-plate dither matrix shown in FIG. The C version dither matrix is
It is composed of the same basic matrix of 20 dots,
A line screen at 10 o'clock of the watch is formed (see FIG. 4). The image formation accompanying the density increase by the dither matrix is the same as above, and the dots grow sequentially from small dots to large dots, and shift to the next dot in a state where the density of one dot unit is saturated.

With respect to the line screen angle dither shown in FIG. 3 and FIG. 15 described later, 1200 × 600 dpi / dither shown in FIG.
The screen angle of each color is not orthogonal to each other and different from each other, and is set to have a certain angle, as shown in the specification of the line diagonal screen angle dither by writing 2 bits. Up to this, the period of the dots or lines of the image does not overlap.

As described above, according to the second embodiment,
An appropriate screen angle is formed for each color plate over the entire area of the medium and high density area that forms line images and the highlight area that is formed by isolated dots and halftone dots before line images are formed. Therefore, color unevenness and color turbidity due to misregistration can be suppressed.

Embodiment 3 In Embodiment 3, a line screen angle dither in the case where the writing density is 1200 × 1200 dpi / 1 bit will be described. FIG. 15 shows the dither matrices K (black), C (cyan), M (magenta),
It is a figure which shows the specification regarding each plate of Y (yellow). As shown in FIG. 15, the screen ruling of each of the K, C, M, and Y plates is common to 223 lines, and a high-resolution image can be formed. The gradation of each color is composed of a total of 116 matrix values, and the number of gradations is 117 gradations. As for the line screen angle direction of each color, as shown in FIG. 15, the line images are arranged so as to be sufficiently separated by 40 degrees or more for each color. The basic matrix is composed of 29 dots, and each of the four sub-matrices expresses the above-mentioned gradation (117 gradations). Although not shown, the repetition matrix in the image has a cycle of 58 × 58 dots, and is similarly arranged in the form of a dither conversion table.

Although not shown, M in the first embodiment is not shown.
A plate dither threshold matrix that is symmetrical with respect to the vertical line in FIG. 16 is referred to as a Y plate matrix, and a plate dither threshold line symmetrically with respect to the 45-degree direction line is referred to as a K plate matrix. The symmetrical one is similarly configured as a C-plate matrix. Also, the screen angle is the same in the second embodiment, and the dither matrixes for the M, Y, and K planes are configured to be line-symmetric with respect to FIG.

FIG. 16 shows that the writing density is 1200 × 1200 dpi.
FIG. 19 is a diagram showing an M-version dither threshold matrix in the first mode of / 1 bit, and FIG.
FIG. 9 is a diagram showing a plate dither threshold matrix. In any case, the dither specifications are as shown in FIG. 15 and are common as described above.

The matrix shown in FIG. 16 is composed of the matrix values of the density generation order as shown in the figure, and the dot generation from the highlight portion is shown in FIGS. 17 and 18. The threshold value matrix determines the ON / OFF of the dot by comparing the numerical value of each threshold value and the image data in the same manner as described above. FIG. 17 shows an example of conversion of image data when the image data is uniform at 17 levels. The illustrated 8 dots are arranged on a straight line and are generated discretely.

Next, FIG. 18 is a diagram showing an example of conversion of image data when the image data is uniform at 43 levels. As shown, dots are arranged on a straight line to form a line image. I have. Thereafter, dots are sequentially connected to the line of one dot size, and the line image is grown so that the line image becomes thicker as the density increases. 1200dpi 21
Approximately 30-40 for dot writing pitch of μm
Although dots having a diameter of about μm are formed, in the first embodiment, an isolated dot is formed from the highlight portion, and the dot or line is resolved based on visual characteristics because the dot is based on a one-dot line. It can be less noticeable.

The matrix shown in FIG. 19 is made up of matrix values having different density generation orders from the case shown in FIG. 16, and the dot generation from the highlight portion is shown in FIGS. 20 and 21. The threshold value matrix determines the ON / OFF of the dot by comparing the numerical value of each threshold value and the image data in the same manner as described above. The matrix in FIG. 19 is arranged so that adjacent dots in the main scanning direction are generated from isolated dots in each basic matrix, and then adjacent dots in the sub-scanning direction are combined.

FIG. 20 is a diagram showing an example of conversion of image data when the image data is uniform at 35 levels, and has an arrangement on a halftone dot where four dots are connected as shown.

Next, dots are generated in the sub-scanning direction from the portion connected thereto, and in FIG.
FIG. 9 is a diagram illustrating an example of image data conversion in the case of uniformity at seven levels, where dots are arranged in a straight line having a width of two dots as illustrated. Thereafter, dots are sequentially combined with the two-dot size line, and the line image is grown so that the line image becomes thicker as the density increases.

In the second mode, the dots are arranged in the highlight portion in the dot main scanning direction so that the electrophotographic color printer 1 can form stable dots. Further, as described above, the exposure period of one dot is set to one.
By setting the duty to 00%, the writing optical signal becomes continuous, which is more effective. Thereafter, since the image is based on the two-dot line pattern, a stable line image is formed, and density unevenness and color unevenness hardly occur.

When the density is increased from the state shown in FIG. 18 in the order of 62, 80, 53, and 71 from the position of the upper threshold 45 in the sub-matrix, local thickening in the line image is achieved. Is generated, and a step corresponding to a size of 2 dots is generated at a lower portion when 80 is filled. On the other hand, as shown in FIG.
7, 53, and 56 are in contact with the existing lines, and the threshold is set so that each dot is discretely generated.

Further, in the example shown in FIG. 21, as the density increases, 89, 91, 97,.
100 is in contact with the existing line, each dot is discretely generated, and a threshold is set so as to shift to a three-dot line. As a result, the line image does not become locally thick, and a smooth line image can always be formed.

As described above, according to the third embodiment,
With regard to changes in texture and thickness due to jagged line lines due to dot addition, which is likely to occur in line dither systems using binary or small value data, high image quality with less texture can be realized by the growth order of line patterns. it can.

[0073]

As described above, according to the first aspect of the present invention, the dither matrix for converting multi-gradation image data into binary or small-valued image data is obtained by converting an image into a line in a certain direction. It is converted so as to form a base tone, and is constituted by a plurality of sub-matrices connected in at least two directions, and the density generation order of the sub-matrices is set in the same direction as the line tone direction of the image, so that the low-value data Even with this, it is possible to form a stable and high-quality image with many gradations.

According to the second aspect of the present invention, the dither matrix for converting multi-gradation image data into binary or low-value image data is converted so that the image is formed in a line tone in a certain direction. The direction of the line tone is a screen angle direction for each color or at least a combination of the colors, and since the screen angle directions are not orthogonal to each other and have a somewhat large screen angle difference, highlighting is performed. Even in the part, color unevenness and color turbidity due to misregistration can be suppressed.

According to the third aspect of the present invention, the dither matrix for converting multi-gradation image data into binary or low-value image data converts the image so that the image is formed in a line tone in a certain direction. It is arranged adjacent to the existing dots with the increase in density, and the growth of the line-based edge part by the dither matrix is made linear, so that the thin lines and steps of the line are not felt. be able to.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an electrophotographic color printer according to an embodiment.

FIG. 2 is a diagram illustrating a state in which an image is formed and arranged with dots of two different colors using halftone dot dither.

FIG. 3 shows K, C,
It is a figure showing the specification about each version of M and Y.

FIG. 4 is a diagram showing a line screen angle direction of each color.

FIG. 5 is a diagram illustrating an M-plate dither matrix according to the first embodiment.

FIG. 6 is a diagram illustrating a Y-version dither matrix according to the first embodiment.

FIG. 7 is a diagram illustrating a C-plate dither matrix according to the first embodiment.

FIG. 8 is a diagram illustrating a K-plate dither matrix according to the first embodiment.

FIG. 9 is a diagram illustrating an arrangement of an M-version sub-matrix according to the first embodiment.

FIG. 10 illustrates a dither matrix K, according to the second embodiment.
FIG. 4 is a diagram showing specifications relating to each of C, M, and Y versions.

FIG. 11 is a diagram illustrating a matrix of a 2-bit dither threshold 1 according to the second embodiment.

FIG. 12 is a diagram illustrating a matrix of a 2-bit dither threshold value 2 according to the second embodiment.

FIG. 13 is a diagram illustrating a matrix of a 2-bit dither threshold value 3 according to the second embodiment.

FIG. 14 is a diagram illustrating an M-plate matrix order of 2-bit dither.

FIG. 15 shows K of a dither matrix according to the third embodiment.
FIG. 4 is a diagram showing specifications relating to each of C, M, and Y versions.

FIG. 16 is a diagram illustrating an M-plate dither matrix according to the first embodiment of the third embodiment.

17 is a diagram illustrating an example of conversion of image data when image data is uniform at 17 levels for dot generation from a highlight portion of the M-plate dither matrix in FIG. 16;

18 is a diagram illustrating an example of conversion of image data in a case where dot data from a highlight portion of the M-plate dither matrix in FIG. 16 is uniform at 43 levels.

FIG. 19 is a diagram illustrating an M-plate dither matrix according to a second embodiment of the third embodiment.

20 is a diagram illustrating an example of conversion of image data in a case where dot data from a highlight portion of the M-plate dither matrix in FIG. 19 is uniform at 35 levels.

21 is a diagram illustrating an example of conversion of image data in a case where image data is uniform at 87 levels for dot generation from a highlight portion of the M-plate dither matrix in FIG. 19;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Electrophotographic color printer 2,3,4,5 OPC drum 6,7,8,9 Image forming block 10,11,12,13 Toner bottle unit 14,15,16,17 Optical writing unit 18 LD light source 19 Collimating lens Reference Signs 20 fθ lens 21 Polygon mirror 22 Folding mirror 23 Transfer belt 24 Transfer belt unit 25 Paper feed tray 26 Pickup roller 27 Fixing unit 28 Paper discharge tray

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/52 H04N 1/46 BF term (Reference) 2C262 AA04 AA24 AA26 AB13 BB03 BB06 BB22 BB25 BB27 5B057 BA29 CA01 CA08 CA12 CA16 CB01 CB07 CB12 CB16 CE13 5C077 LL19 MP08 NN04 NN08 PP33 PP39 RR02 TT03 TT06 5C079 HB03 LA12 LA34 LC04 LC07 LC14 NA02 NA05 PA02 PA03

Claims (3)

[Claims] 1. An image forming method for converting multi-gradation image data into binary or low-value image data and forming an image based on the data, wherein the dither matrix for converting the image includes an image. The dither matrix is composed of a plurality of sub-matrices connected in at least two directions, and the density generation order of the sub-matrices is the same as the line tone direction of the image. An image forming method comprising: 2. An image forming method for converting multi-gradation image data into binary or low-value image data and forming a multi-color image based on the data, wherein the dither matrix for converting the image includes: The image is converted so as to form a line tone in a certain direction, and the direction of the line tone is different for each color, or at least a combination thereof is a different screen angle direction. An image forming method having a large screen angle difference. 3. An image forming method for converting multi-tone image data into binary or low-value image data and forming an image based on the data, wherein the dither matrix for converting the image includes an image. The dither matrix is arranged so as to be adjacent to an existing dot with an increase in density, and the growth of the edge portion of the line based on the dither matrix is linear. Image forming method.