JP2020195004A - Image forming apparatus and control method for the same, and program - Google Patents

Abstract

To solve the problem in which: in a multi-beam printer performing one-shot exposure by using a plurality of lasers, when a conventional method is used, which is to correct image data to offset the distortion caused by bending in a main scanning direction, if there is a large variation in the quantity of light between the plurality of lasers, unevenness occurs in an image formed on a recording medium.SOLUTION: An image forming apparatus forms halftone image data including a plurality of dots by using a dither matrix for input image data, and for the formed halftone image data, corrects the image data to correct bending of a scanning line. The image forming apparatus forms an image based on the corrected image data. Here, at least one of the plurality of dots included in the halftone image data is formed in a first growth order, and at least the other of the plurality of dots is formed in a second growth order that is symmetrical to the first growth order in a direction for the correction means to correct the bending of the scanning line.SELECTED DRAWING: Figure 11

Description

The present invention relates to an image forming apparatus, a control method thereof, and a program.

In a tandem color image forming apparatus, registration deviation of each color plate may occur. In order to suppress such a deviation, for example, in Patent Document 1, an optical sensor is used to measure the inclination and the magnitude of bending of a scanning line, and the image data is corrected so as to cancel them before forming an image. It describes how to do it. Since this method electrically corrects by processing the image data, there is no need for a mechanical adjusting member or an adjusting step at the time of assembly. Therefore, the color image forming apparatus can be miniaturized, and the registration deviation can be dealt with at low cost.

In addition, in the laser scanner used for the image forming apparatus, a multi-beam technology that collectively exposes a plurality of scanning lines by emitting light by combining a plurality of lasers is adopted, thereby increasing the speed and resolution. It has been realized.

Japanese Unexamined Patent Publication No. 2004-170755

However, when the method of Patent Document 1 for correcting image data so as to cancel the distortion caused by the bending of the main scan is adopted in a multi-beam printer, it is formed on the recording medium when the variation in the amount of light of a plurality of lasers is large. There is a problem that the image is uneven.

An object of the present invention is to solve at least one of the problems of the prior art.

An object of the present invention is to provide a technique capable of reproducing the same density and color even when a portion where image data is corrected in order to correct a bending of a scanning line is included.

In order to achieve the above object, the image forming apparatus according to one aspect of the present invention has the following configuration. That is,
It is an image forming device
A halftone processing means for forming halftone image data including a plurality of halftone dots on the input image data using a dither matrix, and
A correction means for correcting the image data so as to correct the bending of the scanning line with respect to the halftone image data formed by the halftone processing means.
It has an image forming means for forming an image based on the image data corrected by the correcting means.
At least one of the plurality of halftone dots included in the halftone image data is formed with halftone dots in the first growth order, and at least the other one of the plurality of halftone dots is relative to the first growth order. The halftone dots are formed in the second growth order, which is symmetrical in the direction in which the correction means corrects the bending of the scanning line.

According to the present invention, there is an effect that the same density and color can be reproduced even when a portion where the image data is corrected in order to correct the bending of the scanning line is included.

Other features and advantages of the present invention will become apparent in the following description with reference to the accompanying drawings. In the attached drawings, the same or similar configurations are designated by the same reference numbers.

The accompanying drawings are included in the specification and are used to form a part thereof, show an embodiment of the present invention, and explain the principle of the present invention together with the description thereof.
The block diagram which shows an example of the structure of the printing system which concerns on Embodiment 1 of this invention. The block diagram explaining the functional structure of the image processing part which concerns on Embodiment 1. FIG. The figure which shows an example of the bending characteristic of the scanning line of a laser beam. The figure which shows the example which corrects the bending characteristic of the scanning line of a laser beam. The figure which shows an example of the specific correction value (correction data) used in the phase transfer process which concerns on Embodiment 1. FIG. An enlarged view of a part of the binary bitmap data of FIGS. 10A and 10B. FIG. 5 is a flowchart illustrating a processing flow in the image processing unit according to the first embodiment. The figure which shows an example of the dither matrix which concerns on Embodiment 1. FIG. The figure which shows an example of the dither matrix which concerns on Embodiment 1. FIG. The figure which shows an example of the growth order of the cell which comprises the dither matrix which concerns on Embodiment 1. FIG. The figure which shows an example of the halftone dot formed by using the dither matrix shown in FIG. 8A. FIG. 8 is a diagram showing an example of binary bitmap data in which halftone processing is performed on different input pixel values and then phase transfer processing is performed using the dither matrix of FIG. 8B. 11 (A) (B) is an enlarged view of a part of the binary bitmap data. The figure which shows an example of the dither matrix which concerns on Embodiment 2. The figure which shows an example of the dither matrix which concerns on Embodiment 2. The figure which shows an example of the growth order of the cell which comprises the dither matrix which concerns on Embodiment 2. FIG. 3 is a diagram showing an example of binary bitmap data obtained by performing halftone processing on different input pixel values and then performing phase transfer processing using the dither matrix of FIG. 13B according to the second embodiment. FIG. 5 is an enlarged view of a part of binary bitmap data of FIGS. 15A and 15B according to the second embodiment.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the invention according to the claims. Although a plurality of features are described in the embodiment, not all of the plurality of features are essential to the invention, and the plurality of features may be arbitrarily combined. Further, in the attached drawings, the same or similar configurations are designated by the same reference numbers, and duplicate description is omitted.

[Embodiment 1]
In the first embodiment, as an example of the color image forming apparatus, a multifunction processing apparatus (MFP: Multi Function Peripheral) having a plurality of functions such as a copy function and a printer function will be described. In addition, this multifunctional processing device forms an image by an electrophotographic method.

FIG. 1 is a block diagram showing an example of the configuration of the printing system according to the first embodiment of the present invention.

This printing system includes an MFP 100 and a PC 120, which are connected to each other via a network 130 such as a LAN. The MFP 100 includes a CPU 101, a memory 102, an HDD (hard disk drive) 103, a scanner unit 104, a printer unit 105, a PDL processing unit 106, a RIP unit 107, an image processing unit 108, a display unit 109, and a network I / F 110. There is. Each of these parts is connected to each other by an internal bus 111.

The CPU 101 is a processor that collectively controls the MFP 100. The memory 102 has a ROM for storing various instructions (including application programs) and various data executed by the CPU 101 to control the MFP 100, and a RAM that functions as a work area of the CPU 101. The HDD 103 is a large-capacity storage medium for storing various programs, image data, and the like. The scanner unit 104 optically scans a document set on a platen or the like (not shown) and generates image data in a bitmap format corresponding to the image of the document.

The PDL processing unit 106 analyzes the PDL (page description language) data included in the print job received from the PC 120, and generates a DL (display list) as intermediate data. The generated DL is sent to the RIP unit 107. The RIP (raster image processor) unit 107 executes a rendering process based on the received DL, and generates contour (multi-value) bitmap image data. Note that the contour bitmap image data expresses colors in a color space such as RGB with multiple gradations having a bit depth of, for example, 8 bits or 10 bits, and these colors are expressed in discrete pixel units. It is image data that has information. Specifically, drawing bitmap and attribute bitmap data are generated respectively. Prior to the generation of these data, the attribute information of the drawing target object is generated for each pixel. The attribute information in this case is determined according to the following criteria.
-When specified by a character drawing command (character type or character code): Character attribute-When specified by a line drawing command (coordinate point, length, thickness): Line attribute / figure drawing command (rectangular, When specified by shape (shape, coordinate points): Graphic attribute ・ When specified by image drawing command (set of points): Image attribute Then, from these attribute information, draw according to the processing resolution of the printer unit 105. Pixels to be drawn are formed, and drawing pit map data containing color information (multi-valued) to be drawn in each pixel is generated. Further, the RIP unit 107 generates attribute bitmap data in which attribute information for each pixel is stored so as to correspond to each pixel of the drawing bitmap. The drawing bitmap and the attribute bitmap generated in this way are temporarily stored in the memory 102 or the HDD 103, or sent to the image processing unit 108.

The image processing unit 108 performs necessary image processing on the image data in the bitmap format to be printed, which is related to the print job from the PC 120 or optically read by the scanner unit 104. The details of the image processing unit 108 will be described later. The image data in the bitmap format after the image processing is sent to the printer unit 105.

In the printer unit 105, a laser scanner (not shown) irradiates an exposure light (laser beam) to form an electrostatic latent image according to the image data generated by the image processing unit 108, and develops the electrostatic latent image. To form a monochromatic toner image. The laser scanner according to the first embodiment has two lasers (light emitting elements) and irradiates a laser beam every two rows in the sub-scanning direction. For example, if one of these two lasers is an A laser and the other is a B laser, the even-numbered rows of image data are drawn by the A laser and the odd-numbered rows of image data are drawn by the B laser. Then, the monochromatic toner images are superposed to form a multicolor toner image, the multicolor toner image is transferred to a recording medium (paper), and then the multicolor toner image is fixed by a fixing device on the recording medium. Form a color image.

The display unit 109 has, for example, a liquid crystal panel having a touch screen function and displays various information, and the user can perform various operations and instructions via the screen displayed on the display unit 109. The network interface 110 is an interface for performing communication such as transmission / reception of a print job with a PC 120 connected via the network 130.

The components of the image forming apparatus 100 described above are not limited to the above contents. For example, instead of the touch screen, an input unit including a pointing device, a keyboard, etc. for the user to perform various operations may be provided, and the configuration of the image forming apparatus 100 may be added or changed as appropriate according to its use or the like. What you get.

FIG. 2 is a block diagram illustrating a functional configuration of the image processing unit 108 according to the first embodiment. In the first embodiment described below, it is assumed that the functions of the image processing unit 108 shown in FIG. 2 are achieved by executing the program expanded in the memory 102 by the CPU 101, but these functions are performed by hardware. It may be realized.

The image processing unit 108 includes a color conversion unit 201, a halftone processing unit 202, and a phase transfer unit 203. Hereinafter, each processing unit will be described.

The color conversion unit 201 performs a color conversion process for converting the color space of the input image data into the color space corresponding to the printer unit 105. For example, in the case of a 4-color 4-drum type tandem system in which the printer unit 105 uses a total of 4 color toners of cyan (C), magenta (M), yellow (Y), and black (K), the CMYK color space is used. Convert. The halftone processing unit 202 performs pseudo halftone processing by the dither method for each color plate on the image data converted into the color space corresponding to the printer unit 105. The dither method uses a threshold matrix (dither matrix) in which different thresholds are arranged in a matrix of a predetermined size. This dither matrix is sequentially expanded in a tile shape on the multi-valued bitmap data which is the input image data, and the magnitude is compared with the input pixel value. As a result of this comparison, if the input pixel value is larger than the threshold value, the pixel is turned on "1", and if the input pixel value is equal to or less than the threshold value, the pixel is turned off "0" to obtain a pseudo-halftone image. Express. By this halftone processing, the continuous gradation input image data (multi-valued bitmap data) is converted into area-graded halftone image data (binary-valued bitmap data) composed of halftone dots. A different dither matrix may be used for each color plate. The embodiment is characterized by a dither matrix, the details of which will be described later.

The position synergistic conversion unit 203 performs a line shift process for shifting the line of the image data (here, binary bitmap data) after the halftone process in the sub-scanning direction, and shifts (bends) the scanning line of the laser beam of each CMYK color. ) Is corrected. This line shift process is also called "phase transfer process".

FIG. 3 is a diagram showing an example of the bending characteristic of the scanning line of the laser beam.

The curve 301 of FIG. 3A shows the characteristics when the scanning line of the laser beam shifts upward in the sub-scanning direction (paper transport direction) as it advances in the main scanning direction. Further, the curve 302 in FIG. 3B shows the characteristics when the scanning line of the laser beam shifts downward in the sub-scanning direction as it advances in the main scanning direction. The straight line 300 in FIG. 3 shows the characteristics of an ideal scanning line when scanning is performed perpendicular to the sub-scanning direction so that the scanning line of the laser beam does not shift in the sub-scanning direction even if it advances in the main scanning direction. Shown.

FIG. 4 is a diagram showing an example of correcting the bending characteristic of the scanning line of the laser beam.

FIG. 4A is a diagram showing the bending characteristic (deviation amount) of the scanning line of the laser beam, and the curve 401 shows the bending characteristic of the laser beam corresponding to the main scanning width.

FIG. 4B is a diagram showing a correction amount (correction characteristic) when correcting the bending characteristic of FIG. 4A, and the correction characteristic shown by the curve 402 cancels out the bending characteristic of the curve 401. It can be seen that the characteristics are opposite.

FIG. 5 is a diagram showing an example of a specific correction value (correction data) used in the phase transfer process according to the first embodiment. In FIG. 5A, the vertical axis represents the correction amount and the horizontal axis represents the pixel position in the main scanning direction.

In FIG. 5A, P1, P2, ... Pn indicate points (transfer points) shifted by one pixel in the sub-scanning direction due to the above-mentioned bending characteristics. The pixel position of the transfer point in the main scanning direction may be referred to as a "transfer position" or a "correction position". FIG. 5B shows a direction in which the scanning line to the next transfer point is shifted (shifted) at each transfer point P1, P2, ... Pn. There are an upward direction and a downward direction in the shift direction at the transfer point. For example, the transfer point P2 is a point at which a line shift of one pixel should be performed upward until the next transfer point P3. Therefore, the transfer direction in P2 is upward (↑). Similarly, at P3, the transfer direction is upward (↑) until the next transfer point P4. Then, the transfer direction at the transfer point P4 is downward (↓) unlike the direction up to that point. Subsequently, the flow of processing in the image processing unit 108 during the printing process will be described.

FIG. 7 is a flowchart illustrating a processing flow in the image processing unit 108 according to the first embodiment. Here, a series of processes of the image processing unit 108 is achieved by reading a computer-executable program describing the procedure shown below from the ROM in the memory 102 onto the RAM, and then the CPU 101 executing the program. It shall be. However, the present invention is not limited to this, and the image processing unit 108 may be realized by hardware such as an ASIC (application specific integrated circuit).

Upon receiving the print instruction, in S701, the CPU 101 first acquires the data of the drawing bitmap and the attribute bitmap generated by the RIP unit 107. Next, proceeding to S702, the CPU 101 functions as a color conversion unit 201, and the color space (here, RGB) of each pixel of the drawing bitmap is converted into a color space (here, RGB) corresponding to the printer unit 105 by using a color conversion LUT or a matrix calculation. Here, it is converted to CMYK). Then, the process proceeds to S703, and the CPU 101 functions as a halftone processing unit 202, and selects a dither matrix according to the attribute information of each pixel of the attribute bitmap. For example, a high-line dither matrix is selected for character attributes and line attributes, and a low-line dither matrix is selected for graphic attributes and image attributes. Further, the CPU 101 performs halftone processing for each pixel of the drawing bitmap using the selected dither matrix. As a result, bitmap data (halftone image data) in which each multi-valued pixel value of the drawing bitmap is converted into a binary value is generated. The details of the dither matrix used in the first embodiment will be described later. Then, the process proceeds to S704, and the CPU 101 functions as the phase transfer unit 203, performs the above-mentioned phase transfer process on the binary bitmap data after the halftone process, and corrects the bending of the scanning line of the laser beam. The binary bitmap data in which the bending of the scanning line is corrected is sent to the printer unit 105 for printing processing.

Next, the dither matrix used in the first embodiment and its effects will be described in detail with reference to FIGS. 6, 8A, 8B, 9, 10, 11, and 12.

8A and 8B are diagrams showing an example of the dither matrix according to the first embodiment.

The dither matrix 800 of FIG. 8A is composed of four cells 801, 802, 803, and 804, each of which forms one halftone dot. Here, the size of one cell is 6 vertical × 12 horizontal. In addition, in FIG. 8A and FIG. 8B, common parts are indicated by the same reference numbers.

FIG. 9 is a diagram showing an example of the growth order of the cells constituting the dither matrix according to the first embodiment.

900 in FIG. 9A shows the growth order of cells, and cells 801 to 804 in FIGS. 8A and 8B are each less than the total number of cells after multiplying the growth order 900 by an integer by the total number of cells. By adding different values, each cell is configured to have a different threshold while having the same growth order. Further, each threshold value is normalized so as to be less than the maximum value of the input pixel value according to the input pixel value of the image data input to the halftone processing unit 202.

In the first embodiment, since the maximum value of the input pixel value of the image data input to the halftone processing unit 202 is "255", each threshold value is normalized to a value of 0 to 254. Cells in which the thresholds contained in the cells are arranged in the same order and have different thresholds are generally called a submatrix. The cells 801-804 are arranged so that the halftone dots have a predetermined periodicity at a predetermined angle. This net point period can be represented by two vectors, the first vector 805 of FIGS. 8A and 8B has components of 6 in the main scanning direction and -6 in the sub-scanning direction, and the second vector 806 has the main scanning direction. It has 6 components in the sub-scanning direction and 6 components in the sub-scanning direction. The dither matrix 800 represented by these two vectors forms halftone dots of 141 lines and 45 degrees at a resolution of 1200 dpi. The cell growth order 900 is set in two consecutive growth orders so as to be line-symmetrical with respect to the chain line 901 in the sub-scanning direction.

FIG. 10 is a diagram showing an example of halftone dots formed by using the dither matrix 800 shown in FIG. 8A.

FIG. 10A shows binary bitmap data (1200 dpi) obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “27” using the dither matrix 800, and then performing phase transfer processing. Is shown. In FIG. 10A, the broken line 1001 is a transfer point at which a line shift of one pixel should be performed in the upward direction in the sub-scanning direction (see transfer point P3 in FIG. 5B). It can be seen that the halftone dots in the second region are shifted upward by one pixel (1 line) in the sub-scanning direction with respect to the transfer point indicated by the broken line 1001. Then, in the first region, a plurality of on-pixels are periodically gathered at halftone dots 1002, and in the second region, a plurality of on-pixels are periodically gathered, and one pixel is formed in the sub-scanning direction from the halftone dots 1002. The offset halftone dots 1003 are lined up. As the input pixel value of these halftone dots 1002 and 1003 increases, the area ratio is increased while increasing the area ratio from the center of the halftone dots toward the outside to grow the halftone dots.

Then, FIG. 10B shows binary bitmap data in which a drawing bitmap having all input pixel values of “31” is subjected to halftone processing using the dither matrix 800 and then phase transfer processing is performed. 1200 dpi) is shown. As described above, in FIG. 10B, it can be seen that the input pixel values are larger than those in FIG. 10A, and the halftone dots 1002 and 1005, which are one pixel thicker than the halftone dots 1002 and 1003, are periodically arranged. ..

FIG. 6 is an enlarged view of a part of the binary bitmap data of FIGS. 10A and 10B.

FIG. 6A is an enlarged view of a part of the binary bitmap data of FIG. 10A. Halftone dots 1002 expose 4 pixels of the A laser and 4 pixels of the on pixel of the B laser in the first region. Similarly, at the halftone dot 1003, the A laser exposes 4 pixels and the B laser exposes 4 pixels of the on-pixel in the second region. Since there are two halftone dots 1002 and 1003 in the first region and the second region of FIG. 6 (A), respectively, in the first region and the second region of FIG. 6 (A), the A laser has 8 pixels. The B laser will expose the same number of on-pixels of 8 pixels.

On the other hand, FIG. 6B is an enlarged view of a part of the binary bitmap data of FIG. 10B, and corresponds to the case where the input pixel value is larger than that of FIG. 6A. In FIG. 6B, halftone dots 1004 expose 4 pixels of A laser and 5 pixels of B laser in the first region, and halftone dots 1005 have 5 pixels of A laser and 5 pixels of B laser in the second region. The on-pixel of 4 pixels is exposed. That is, since there are two halftone dots 1004 and 1005 in the first region and the second region in FIG. 6B, respectively, in the first region in FIG. 6B, the A laser has 10 pixels and the B laser has 10 pixels. Exposes 8 on-pixels, and in the second region, the A laser exposes 8 pixels and the B laser exposes 10 on-pixels.

At this time, if there is a difference in the amount of laser beam between the A laser and the B laser, the number of on-pixels exposed by each laser is switched between the first region and the second region. Therefore, different halftone dots are formed on the recording medium in the first region and the second region with the transfer point as the boundary. As a result, when the dither matrix 800 of FIG. 8A is used, the first region and the second region are reproduced with different densities and colors in the input pixel values of FIG. 10 (B).

The dither matrix 810 of FIG. 8B contains four cells 801, 804, 811 and 812, each forming one halftone dot. The dither matrix 810 has the same number of cells as the dither matrix 800, but the threshold values included in the cells 811 and 812 are interchanged with respect to the cells 801 and 804 in the order of continuous growth in the sub-scanning direction. The growth order of the cells is shown in the growth order 902 of FIG. 9 (B). FIG. 9B is a diagram showing the growth order 902 of cells 811 and 812, and it can be seen that the growth order 900 of FIG. 9A is line-symmetrically replaced with respect to the chain line 903. As described above, the growth order 900 is set to have two consecutive growth orders so as to be line symmetric with respect to the chain line 901. Therefore, the growth order 902 is also line symmetric with respect to the chain line 903. Two consecutive growth orders are set so that

Since the arrangement of cells 801, 804, 811, and 812 in FIG. 8B is the same as the arrangement of cells 801 to 804 in the dither matrix 800 of FIG. 8A, the dither matrix 810 of FIG. Form halftone dots of degree. However, in FIG. 8B, cells 801 and 811 and cells 804 and 812 are arranged alternately with respect to the main scanning direction.

FIG. 11 is a diagram showing an example of binary bitmap data in which different input pixel values are subjected to halftone processing and then phase transfer processing using the dither matrix 810 of FIG. 8B. Here, an example of arranging halftone dots in two predetermined regions (first and second regions) located before and after the transfer point 1101 in the main scanning direction is shown.

FIG. 11A shows binary bitmap data obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “27” using the dither matrix 810 of FIG. 8B, and then performing phase transfer processing. It is a figure which shows (1200 dpi).

In FIG. 11A, the broken line 1101 is a transfer point at which a line shift of one pixel should be performed in the upward direction in the sub-scanning direction (see transfer point P3 in FIG. 5B). It can be seen that the halftone dots in the second region are shifted upward by one pixel (one line) in the sub-scanning direction with the transfer point 1101 as a boundary. Then, in the first region, a plurality of on-pixels are periodically gathered at halftone dots 1102, and in the second region, a plurality of on-pixels are periodically gathered, and one pixel is periodically gathered in the sub-scanning direction from the halftone dots 1102. The offset halftone dots 1103 are lined up. These halftone dots 1102 and 1103 are the same as the above-mentioned halftone dots 1002 and 1003 in FIG. 10 (A).

FIG. 11B shows binary bitmap data obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “31” using the dither matrix 810 of FIG. 8B, and then performing phase transfer processing. It is a figure which shows (1200 dpi). As described above, in FIG. 11B, halftone dots 1104 and 1105, 1106, 1107, which have a larger input pixel value than FIG. 11A and are one pixel thicker than halftone dots 1102 and 1103, are arranged periodically. You can see that there is.

Further, FIG. 11C shows binary bits obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “35” using the dither matrix 810 of FIG. 8B, and then performing phase transfer processing. It is a figure which shows the map data (1200 dpi). Since the input pixel value in FIG. 11C is larger than that in FIG. 11B, the halftone dots 1108 and 1109 that are one pixel thicker than the halftone dots 1104, 1105, 1106, and 1107 in FIG. 11B are periodically generated. You can see that they are lined up.

In FIG. 11B, two types of halftone dots 1104 and 1105 exist in the first region, and two types of halftone dots 1106 and 1107 also exist in the second region. On the other hand, in FIG. 11C, there is only one type of halftone dot 1108 in the first region and one type of halftone dot 1109 in the second region. That is, when the dither matrix 810 of FIG. 8B according to the first embodiment is used, one kind of halftone dots are provided in each of the first region and the second region for a certain input pixel value, and two halftone dots are used for each region for a larger input pixel value. For input pixel values with larger types of line-symmetrical halftone dots, the existence of one type of halftone dots in each region is repeated.

FIG. 12 is an enlarged view of a part of the binary bitmap data of FIGS. 11A and 11B.

In FIG. 12A, the number of on-pixels exposed by the A laser and the B laser does not change between the first region and the second region as in FIG. 6A. On the other hand, in FIG. 12B in which the input pixel value is large, the A laser exposes 5 pixels and the B laser exposes 4 pixels on the halftone dots 1104 in the first region. Further, the A laser exposes 4 pixels and the B laser exposes 5 pixels on the halftone dots 1106 in the second region. When only halftone dots 1104 are present in the first region, and when there is a difference in the amount of laser beam between the A laser and the B laser, the same problem as that of the dither matrix 800 described above occurs. However, there are halftone dots 1105 inverted in the sub-scanning direction with respect to halftone dots 1104 in the first region, and halftone dots 1107 in the second region. Therefore, in the first region, both the A laser and the B laser expose 9 pixels, and in the second region, both the A laser and the B laser expose 9 pixels on-pixel. In this way, since the A laser and the B laser both emit light the same number of times in the first region and the second region, the above-mentioned problem does not occur even if there is a difference in the amount of laser beam between the A laser and the B laser.

In the first embodiment, at 1200 dpi, the first vector has 6 components in the main scanning direction and -6 components in the sub scanning direction, and the second vector has 6 components in the main scanning direction and 6 components in the sub scanning direction. , 141 lines and 45 degrees of the dither matrix have been described as an example, but the present invention is not limited to this.

Further, the dither matrix according to the first embodiment is configured by combining four cells, but the present invention is not limited to this. For example, 8 or 16 cells may be combined, and half of the cells may be arranged in a growth order that is line-symmetrical with respect to the remaining half of the cells.

The dither matrix used in the first embodiment has two values, but it goes without saying that a multi-value dither matrix may be used as long as the above-mentioned two growth orders are combined. Further, the laser scanner used in the first embodiment has been described as drawing using two lasers, but the drawing is not limited to this, and it goes without saying that a plurality of lasers other than two, such as four lasers, may be used. ..

As described above, according to the first embodiment, in a plurality of cells constituting the dither matrix, a dither matrix in which the cell growth order is line-symmetrically inverted in the sub-scanning direction is used. As a result, even when there is a difference in the amount of light of the laser beams of a plurality of lasers, it is possible to form the same halftone dots in the first region and the second region with the transfer point as the boundary, and the same halftone dots are obtained in all regions. It is possible to reproduce various densities and colors.

[Embodiment 2]
In the first embodiment described above, in the halftone processing unit 202, two consecutive growth orders are set so as to be line-symmetrical in the sub-scanning direction, and two different growth orders that are line-symmetrically inverted in the sub-scanning direction. The case of using a dither matrix in which the cells of the above cells are combined has been described.

On the other hand, in the second embodiment, a case where a dither matrix of cells in which two consecutive growth orders are set so as to be point-symmetrical will be described. In the second embodiment, only the configuration of the dither matrix used by the halftone processing unit 202 is different from that of the first embodiment. Therefore, the same parts as those in the first embodiment are assigned the same number, the description thereof is omitted, and the different parts are different. Only will be described below.

The dither matrix used in the second embodiment and its effects will be described in detail with reference to FIGS. 13A, 13B, 14, 15, and 16.

13A and 13B are diagrams showing an example of the dither matrix according to the second embodiment.

The dither matrix 1300 of FIG. 13A is composed of four cells 1301, 1302, 1303, and 1304, each of which forms one halftone dot. The parts common to FIGS. 13A and 13B are indicated by the same reference numbers.

FIG. 14 is a diagram showing an example of the growth order of the cells constituting the dither matrix according to the second embodiment.

FIG. 14A shows the cell growth order 1400. The cells of cells 1301 to 1304 in FIG. 13A are different for each cell even though they have the same growth order by multiplying the growth order 1400 by an integer by the total number of cells and then adding different values less than the total number of cells to each. It is configured to have a threshold. Further, each threshold value is normalized so as to be less than the maximum value of the input pixel value according to the input pixel value of the image data input to the halftone processing unit 202.

In the second embodiment, since the maximum value of the input pixel value of the image data input to the halftone processing unit 202 is "255", it is normalized to a value of 0 to 254. The halftone dot period of the second embodiment is the same as that of the first embodiment, and a halftone dot of 141 lines and 45 degrees is formed at a resolution of 1200 dpi. The cell growth order 1400 is set so that two consecutive growth orders are point-symmetrical. Since the halftone dots are formed so that on-pixels are gathered, a point 1401 as a reference for point symmetry is set between the two lowest growth orders.

Using the dither matrix 1300 shown in FIG. 13A, the binary bitmap data when the input pixel values are “27” and “31” is the same as in FIGS. 10 (A) and 10 (B). Is omitted. When the dither matrix 1300 is used in this way, when there is a difference in the amount of laser beam between the two lasers, and if the input pixel values are different, there is an on-pixel difference between the first region and the second region. Area is reproduced with different densities and colors.

On the other hand, in the case of the dither matrix 1310 of FIG. 13B, it is composed of four cells 1301, 1302, 1311, and 1312, each of which forms one halftone dot. The dither matrix 1310 has the same number of cells as the dither matrix 1300, but the thresholds included in the cells 1311 and 1312 are arranged symmetrically with respect to the cells 1301 and 1302 with respect to the reference point. ..

The cell growth order 1402 shown in FIG. 14 (B) indicates the growth order of cells 1311 and 1312, and the growth center 1403 is the growth center 1401 of the cell growth order 1400 shown in FIG. 9 (A). The same is true. Comparing FIG. 14 (B) and FIG. 14 (A), in FIG. 14 (B), for example, the threshold values 0, 1, 2, 3, 4 and 5 (consecutive even numbers and odd numbers) are interchanged. Understand. Since the arrangement of cells 1301, 1302, 1311, and 1312 is the same as that of the dither matrix 1300, the dither matrix 1310 in FIG. 13B forms halftone dots of 141 lines and 45 degrees at a resolution of 1200 dpi.

FIG. 15 shows an example of binary bitmap data obtained by performing halftone processing on different input pixel values and then performing phase transfer processing using the dither matrix 1310 of FIG. 13B according to the second embodiment. It is a figure which shows.

FIG. 15A shows binary bitmap data (1200 dpi) obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “27” using a dither matrix 1310, and then performing phase transfer processing. Is shown. In FIG. 15 (A), the broken line 1501 indicates a transfer point at which a line shift of one pixel should be performed in the upward direction in the sub-scanning direction (see transfer point P3 in FIG. 5 (B)). It can be seen that the halftone dots in the second region are shifted upward by one pixel (one line) in the sub-scanning direction with the transfer point 1501 as a boundary. Then, in the first region, a plurality of on-pixels are periodically gathered at halftone dots 1502, and in the second region, a plurality of on-pixels are periodically gathered, and one pixel is periodically gathered in the sub-scanning direction from the halftone dots 1502. The offset halftone dots 1503 are lined up. The halftone dots 1502 and 1503 are the same as the halftone dots 1002 and 1003 in FIG. 10 (A) described above.

FIG. 15B shows binary bitmap data (1200 dpi) obtained by performing halftone processing on a drawing bitmap in which all input pixel values are “31” using a dither matrix 1310, and then performing phase transfer processing. Is shown. As described above, in FIG. 15B, halftone dots 1504 and 1505, 1506, 1507, which have a larger input pixel value than FIG. 15A and are one pixel thicker than halftone dots 1502 and 1503, are arranged periodically. You can see that there is.

Further, FIG. 15C shows binary bitmap data in which a drawing bitmap having all input pixel values of “35” is subjected to halftone processing using the dither matrix 1310 and then phase transfer processing is performed. 1200 dpi) is shown.

As described above, in FIG. 15C, the input pixel values are larger than those in FIG. 15B, and the halftone dots 1508 and 1509, which are one pixel thicker than the halftone dots 1504, 1505, 1506, and 1507, are periodically arranged. I understand. In FIG. 15B, two types of halftone dots 1504 and 1505 existed in the first region, and two types of halftone dots 1506 and 1507 existed in the second region. However, in FIG. 15C, the first region had two types of halftone dots. There is only one type of halftone dot 1508 and one type of halftone dot 1509 in the second region.

As described above, when the dither matrix 1310 according to the second embodiment is used, one kind of halftone dots are used in each of the first and second regions for a certain input pixel value, and two kinds of halftone dots are used for each region for a larger input pixel value. For input pixel values with larger point-symmetric halftone dots, the existence of one type of halftone dots in each region is repeated.

FIG. 16 is an enlarged view of a part of the binary bitmap data of FIGS. 15A and 15B according to the second embodiment.

In FIG. 16A, similarly to FIG. 6A, the number of on-pixels exposed by the A laser and the B laser does not change between the first region and the second region. On the other hand, in FIG. 16B in which the input pixel value is large, the halftone dot 1504 exposes on-pixels of 5 pixels of the A laser and 4 pixels of the B laser in the first region, and the halftone dot 1506 is the A laser in the second region. Exposes 4 pixels and the B laser exposes 5 on-pixels. With only the halftone dots 1504 in the first region, the same problem as the dither matrix 1300 described above occurs when there is a difference in the amount of light of the laser beam between the A laser and the B laser. However, there are halftone dots 1505 that are point-symmetric with respect to halftone dots 1504 in the first region, and halftone dots 1507 are present in the second region. In this way, since halftone dots that are point-symmetrical exist in each of the first region and the second region, the A laser and the B laser both expose 9 on-pixels in the first region, and A in the second region as well. Both the laser and the B laser expose 9 on-pixels. Therefore, even if there is a difference in the amount of light of the laser beam between the A laser and the B laser, the above-mentioned problem does not occur.

In the second embodiment, at 1200 dpi, the first vector has 6 components in the main scanning direction and -6 components in the sub scanning direction, and the second vector has 6 components in the main scanning direction and 6 components in the sub scanning direction. , 141 lines and 45 degrees of the dither matrix have been described as an example, but the present invention is not limited to this.

Further, the dither matrix of the second embodiment is configured by combining four cells, but the present invention is not limited to this. For example, 8 or 16 cells may be combined, and half of the cells may be arranged in a growth order that is point-symmetrical with respect to the remaining half of the cells.

Further, the dither matrix used in the second embodiment is set to two values, but it goes without saying that a multi-value dither matrix may be used as long as the above-mentioned two growth orders are combined.

Further, the laser scanner used in the second embodiment has been described as drawing using two lasers, but the present invention is not limited to this, and it goes without saying that a plurality of lasers other than two, such as four lasers, may be used.

As described above, according to the second embodiment, in a plurality of cells constituting the dither matrix, a dither matrix that is point-symmetric with respect to a point based on the cell growth order is used. As a result, even if there is a difference in the amount of light of the laser beams of a plurality of lasers, it is possible to form the same halftone dots in the first region and the second region with the transfer point as the boundary, and in any region. It is possible to reproduce the same density and color.

(Other embodiments)
The present invention supplies a program that realizes one or more functions of the above-described embodiment to a system or device via a network or storage medium, and one or more processors in the computer of the system or device reads and executes the program. It can also be realized by the processing to be performed. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The present invention is not limited to the above embodiments, and various modifications and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to make the scope of the present invention public, the following claims are attached.

100 ... MFP (multifunction device), 101 ... CPU, 102 ... memory, 108 ... image processing unit, 201 ... color conversion unit, 202 ... halftone processing unit, 203 ... phase transfer unit, 800, 810, 1300, 1301 ... dither Matrix

Claims (10)

It is an image forming device
A halftone processing means for forming halftone image data including a plurality of halftone dots on the input image data using a dither matrix, and
A correction means for correcting the image data so as to correct the bending of the scanning line with respect to the halftone image data formed by the halftone processing means.
It has an image forming means for forming an image based on the image data corrected by the correcting means.
At least one of the plurality of halftone dots included in the halftone image data is formed with halftone dots in the first growth order, and at least the other one of the plurality of halftone dots is relative to the first growth order. An image forming apparatus, characterized in that halftone dots are formed in a second growth order that is symmetrical in the direction in which the correction means corrects the bending of the scanning line. The image forming means forms an image by an electrophotographic method, and each has a plurality of light emitting elements that irradiate different rows in the main scanning direction.
Claim 1 is characterized in that the correction means shifts the halftone image data in the sub-scanning direction according to the bending so as to correct the bending in the main scanning direction irradiated by the plurality of light emitting elements. The image forming apparatus according to. In each of the two predetermined regions located before and after the main scanning direction with respect to the shifted position in the main scanning direction, one type or two are used based on the pixel value of the input image data. The image forming apparatus according to claim 2, wherein there are various types of line-symmetrical halftone dots. The image forming apparatus according to claim 3, wherein the plurality of light emitting elements emit light at the same number of times in the two predetermined regions. The dither matrix has at least a first cell in which a plurality of threshold values are arranged in the first growth order and a second cell in which a plurality of threshold values are arranged in the second growth order, and the second cell. The image forming apparatus according to any one of claims 2 to 4, wherein the growth order is line-symmetrical with respect to the first growth order in a direction for correcting the bending of the scanning line. The dither matrix has at least a first cell in which a plurality of threshold values are arranged in the first growth order and a second cell in which a plurality of threshold values are arranged in the second growth order, and the second cell. The image forming apparatus according to any one of claims 2 to 4, wherein the growth order is point-symmetrical with respect to the first growth order in a direction for correcting the bending of the scanning line. The image forming apparatus according to claim 5 or 6, wherein the first cell and the second cell are alternately arranged in a direction corresponding to the main scanning direction in the dither matrix. Any of claims 5 to 7, wherein the total number of the plurality of cells included in the dither matrix is an even number, and the total number of the first cell and the second cell included in the dither matrix is the same. The image forming apparatus according to item 1. It is an image forming method in an image forming apparatus.
A halftone processing step of forming halftone image data including a plurality of halftone dots on the input image data using a dither matrix, and
A correction step of correcting the image data so as to correct the bending of the scanning line with respect to the halftone image data formed in the halftone processing step, and a correction step of correcting the image data.
It has an image forming step of forming an image based on the image data corrected in the correction step.
At least one of the plurality of halftone dots included in the halftone image data is formed with halftone dots in the first growth order, and at least the other one of the plurality of halftone dots is relative to the first growth order. A method for forming an image, wherein halftone dots are formed in a second growth order that is symmetrical in the direction of correcting the bending of the scanning line in the correction step. A program for causing a computer to function as each means of the image forming apparatus according to any one of claims 1 to 8.

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