JP6201557B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that performs image formation by controlling light emission of a beam in accordance with output data by PWM.

  By repeating the operation of scanning the light beam in the first direction to form an image for one line on the image carrier, while relatively moving the image carrier and the light beam in the direction orthogonal to the first direction, 2 is performed. There is an image forming apparatus that performs printing by forming a two-dimensional image on an image carrier and then revealing the two-dimensional image with toner and transferring it to a recording paper.

  In the above-described image forming apparatus, the light beam is ON / OFF controlled according to a PWM (Pulse Width Modulation) modulation signal created based on the image data. The light beam emits light for a time corresponding to the pulse width (pulse on period) of each pulse of the PWM modulation signal.

  However, the time during which the laser diode actually emits the light beam is shorter than the pulse width input to the drive circuit due to the pulse response characteristics of the laser diode and its drive circuit. Therefore, in the case of a pixel in which the pulse of the PWM modulation signal is an isolated pulse with a short pulse width, the laser light emission time is shortened at a high rate by the above response characteristics with respect to the pulse width. There is a case where the toner does not emit light sufficiently and the toner does not adhere well on the image carrier.

  For example, in Patent Document 1, when there is an isolated pulse with a short pulse width, there is a technique for performing correction to increase the pulse width of the pulse so that the actual light emission time of the light beam is equal to the pulse width. It is disclosed (see Patent Document 1).

  18A shows a PWM modulation signal including a pulse having a short pulse width, and FIG. 18B shows a PWM modulation signal whose pulse width is corrected to be long by the method of Patent Document 1. By increasing the pulse width, the emission time of the light beam is increased, so that the toner can be reliably applied.

JP 2005-193589 A

  According to the method described in Patent Document 1, even for a pixel that is an isolated pulse with a short pulse width such that the pulse of the PWM modulation signal does not overlap with the toner, the toner corresponding to the pixel is corrected by correcting the pulse width to be long. An image can be formed at that pixel location.

  However, since the PWM modulation signal is normally generated in synchronization with a predetermined clock signal, the pulse width can be adjusted only in units of one clock, and the pulse width cannot be finely corrected. As a result, the pulse width becomes longer than the necessary correction amount, and there are cases where more toner is applied than the toner amount for the original pulse width. For example, in the case of performing multi-gradation expression with area gradation, it is important to reproduce the designated gradation by making the toner amount more accurate than the accuracy of the pixel position. The described method is not preferred.

  The present invention is intended to solve the above-mentioned problem, and even for a pixel in which the pulse of the PWM modulation signal becomes an isolated pulse having a short pulse width, the density of the pixel is more accurately reproduced on the image carrier. An object of the present invention is to provide an image forming apparatus that can perform the above-described process.

  The gist of the present invention for achieving the object lies in the inventions of the following items.

[1] The operation of scanning the laser beam in the first direction to form an image for one line on the image carrier is performed by relatively moving the image carrier and the laser beam in a direction orthogonal to the first direction. An image forming unit that repeatedly forms a two-dimensional image on the image carrier,
A PWM modulation signal generator for generating a PWM modulation signal for on / off control of the laser beam based on image data;
When a second pixel having a halftone density exists next to a first pixel having a halftone having a predetermined density or less in the same line in the first direction, all or part of the density of the first pixel A PWM modulation signal in which a pulse corresponding to the density of the first pixel after being moved to the second pixel and a pulse corresponding to the density of the second pixel after being moved is continued is the PWM A correction unit for generating the modulation signal generation unit;
I have a,
The PWM modulation signal generation unit includes an output memory that divides a period of one pixel into a plurality of sections and stores output data indicating ON / OFF of a pulse in each section for one line, and is stored in the output memory. Generating the PWM modulation signal based on the output data being
The image forming apparatus , wherein the correction unit changes the output data stored in the output memory .

  In the above invention, the image forming apparatus generates a PWM modulation signal based on the image data, controls the laser beam on / off according to the PWM modulation signal, and scans the laser beam in the first direction for one line. The two-dimensional image is formed on the image carrier by repeatedly performing the operation of forming the image on the image carrier while relatively moving the image carrier and the laser beam in the direction orthogonal to the first direction. When a second pixel having a halftone density exists next to the first pixel having a halftone having a predetermined density or less in the same line in the first direction, that is, a pulse of the PWM modulation signal corresponding to the first pixel is generated. When there is an isolated pulse and there is a second halftone pixel next to it, all or part of the density of the first pixel is moved to the second pixel, and the second pixel after the movement is moved. A PWM modulation signal in which a pulse corresponding to the density of one pixel and a pulse corresponding to the density of the second pixel after being moved are generated is generated. Thereby, it is possible to prevent the generation of an isolated pulse in which the density is lost during image formation, and to improve density reproducibility.

  When a low-density first pixel and a halftone second pixel are continuous, the pulse is turned off between a short pulse corresponding to the first pixel and a pulse corresponding to the second pixel (a pulse which is not 100% ON). Since the period occurs, the short pulse of the first pixel is isolated and the toner image corresponding to the first pixel is not formed on the image carrier. Therefore, all or part of the density of the first pixel is moved to the second pixel.

  For example, if the on time of the pulse corresponding to the first pixel is less than or equal to the off time of the pulse corresponding to the second pixel, the density of the first pixel can be moved to the second pixel, and if all are moved, The pulse corresponding to the first pixel disappears, and the density of the first pixel and the second pixel is reproduced on the image carrier as the second pixel having the total density, and becomes a pulse of one continuous second pixel. When the ON time of the pulse corresponding to the first pixel exceeds the OFF time of the pulse corresponding to the second pixel, the density of a part of the first pixel is moved to the second pixel. For example, if the density of the second pixel is set to 100% by the movement of the density, the pulse corresponding to the remaining density of the first pixel is moved to the second pixel side so that the pulse corresponding to the first pixel is sent to the second pixel. It is possible to continue the pulses corresponding to the above, and to prevent the generation of isolated pulses.

If the second pixel is all white, even if the density of the first pixel is moved to the second pixel, only an isolated pulse is generated at the position of the second pixel. On the other hand, when the second pixel has a density of 100%, the density of the first pixel cannot be moved to the second pixel. Therefore, the density of the first pixel is moved to the second pixel only when a second halftone pixel exists next to the first pixel.
In the above invention, the density of the first pixel is moved to the second pixel by changing the output data for one line stored in the output memory. If the output data is changed when the density of the first pixel is moved to the second pixel, the pulse ON / OFF timing is directly changed, and the pulse corresponding to the density of the first pixel after the movement and the second The pulse corresponding to the pixel density can be made one continuous pulse.

[2] The image forming apparatus according to [1], wherein the density of the first pixel is moved to the second pixel to the maximum within a range where the density of the second pixel does not exceed 100%.

  In the above invention, the density of the first pixel is moved to the second pixel at the maximum within a range where the density of the second pixel does not exceed 100%. If (the density of the first pixel + the density of the second pixel) ≦ 100%, the entire density of the first pixel is moved to the second pixel. If (the density of the first pixel + the density of the second pixel)> 100%, the density of the second pixel is moved by moving the density of the first pixel to the second pixel by (100% −the density of the second pixel). Set to 100%.

[3] The image forming apparatus according to [1] or [2], wherein the first pixel is a pixel having a density that does not have a density when the image is formed alone.

  In the above invention, the pixels having a predetermined density are pixels that do not have a density on the resulting recording paper or image carrier when an image is formed alone. Note that if an image is formed for a certain pixel alone, there are no surrounding pixels, so the pulse corresponding to the pixel becomes an isolated pulse. That is, the predetermined density is such a density that no density is produced on the recording paper or the image carrier when the image is formed with the pulse isolated.

[4] The correcting unit, when the second pixel adjacent to the first pixel in the same line in the first direction does not exist, the first pixel, it toward you perpendicular to the first direction Any one of [1] to [3], wherein if there is a third pixel having a halftone density adjacent to the first pixel, the density of the first pixel is moved to the third pixel. The image forming apparatus described.

  In the above invention, when there is no second pixel having a halftone density adjacent to the first pixel in the same line in the first direction, the isolated pulse is moved by moving the density of the first pixel to the adjacent pixel. It becomes impossible to prevent the occurrence of the. Therefore, in this case, it is checked whether or not there is a third pixel having a halftone density adjacent to the second direction orthogonal to the first direction of the first pixel. If there is, the density of the first pixel is determined. Is moved to the third pixel. As a result, even when pixels of halftone density are not adjacent in the scanning direction, the density is lost during image formation by moving the density of the first pixel to the third pixel of the adjacent line. It is possible to improve the reproducibility of the density by preventing the generation of such isolated pulses.

[ 5 ] The image forming unit scans a plurality of lines of laser beams aligned in a direction orthogonal to the first direction in the first direction, and simultaneously forms the images of the plurality of lines on the image carrier. And
The PWM modulation signal generating section, the output memory for storing one line of the output data with includes the plurality of lines, respectively corresponding to the plurality of lines on the basis of the output data stored in the output memory Generating the PWM modulation signal;
The correction unit stores the output data corresponding to the first pixel stored in the output memory corresponding to the line including the first pixel and the output memory corresponding to the line including the third pixel. The image forming apparatus according to [4], wherein the density of the first pixel is moved to the third pixel by changing output data corresponding to the third pixel.

  In the above invention, the image forming unit is a so-called multi-beam type in which a plurality of adjacent lines are simultaneously formed with a plurality of laser beams, and the PWM modulation signal generating unit correspondingly corresponds to the number of laser beams. Equipped with output memory for minutes. By changing the output data stored in the output memory for the plurality of lines, the density of the first pixel is moved to the third pixel of the adjacent line.

[ 6 ] The image forming apparatus according to any one of [1] to [ 5 ], wherein the first pixel is a pixel in a photographic region.

  In the above invention, density movement is performed when the first pixel is in the photographic region. In the photographic region, halftone pixels are likely to be generated, and gradation expression by area gradation is performed.

  According to the image forming apparatus of the present invention, the density of a pixel can be more accurately reproduced on the image carrier even for a pixel in which the pulse of the PWM modulation signal becomes an isolated pulse with a short pulse width.

1 is a block diagram showing an electrical schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a mechanical schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram illustrating a state where an electrostatic latent image is formed on a photosensitive drum by a printer unit. It is a figure which shows the PWM modulation | alteration signal after correct | amending the density | concentration to the adjacent pixel in the same line, and correcting so that an isolated pulse may disappear. It is a figure which shows the PWM modulation signal after moving the density | concentration to the pixel of an adjacent line, and correcting so that an isolated pulse may disappear. It is a figure which correct | amends output data so that the density | concentration of an isolated pulse pixel may be moved to a 2nd pixel. It is a figure which correct | amends output data so that the density | concentration of an isolated pulse pixel may be shifted to a 3rd pixel. It is a figure which correct | amends output data so that a 2nd pixel may transfer a density | concentration from the adjacent pulse pixel of both sides. It is a figure which correct | amends output data so that the side which approaches a pulse within the pixel unit period of an isolated pulse pixel may be changed. It is a figure which correct | amends output data so that the density of an isolated pulse pixel may be shifted to a 2nd pixel, without bringing a pulse. It is a figure which correct | amends output data so that a part of density | concentration of an isolated pulse pixel may be moved to a 2nd pixel. It is a block diagram which shows schematic structure of an image process part. It is a block diagram which shows schematic structure of a pulse width modulation block. It is a flowchart which shows the process performed by a pulse width modulation block. It is a flowchart which shows the process which correct | amends output data. It is a figure which shows the process which moves the density | concentration of an isolated pulse pixel to a 2nd pixel on image data. It is a figure which shows the process which moves the density | concentration of an isolated pulse pixel to a 3rd pixel on image data. It is a figure which shows the correction method of the isolated point by the conventional method.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an electrical schematic configuration of an image forming apparatus 10 according to an embodiment of the present invention, and FIG. 2 shows a mechanical schematic configuration of the image forming apparatus 10. The image forming apparatus 10 is a copy job that optically reads a document and prints a duplicate image on a recording sheet, a scan job that saves image data of the read document as a file, or transmits the image data to an external device, and a PC ( This is a so-called multi-function machine having a function of executing a job such as a print job for printing an image related to data sent from a personal computer on a recording sheet and outputting the image.

  Also, the image forming apparatus 10. A PWM modulation signal for controlling on / off of the laser beam (light beam) is generated based on the image data, and on / off of the laser beam is controlled based on the PWM modulation signal. Then, the operation of scanning the on / off-controlled laser beam in the first direction (main scanning direction) to form an image for one line on the image carrier is performed in a direction orthogonal to the first direction ( A two-dimensional image is formed on the image carrier by repeatedly moving the image carrier and the laser beam relative to each other in the sub-scanning direction, and then the two-dimensional image is visualized with toner and recorded on the recording paper. Printing is performed by transferring to

  The image forming apparatus 10 includes a CPU (Central Processing Unit) 11 that controls the operation of the image forming apparatus 10, a ROM (Read Only Memory) 12 connected to the CPU 11, a RAM (Random Access Memory) 13, and a nonvolatile memory. A memory 14, a hard disk device 15, a display unit 16, an operation unit 17, a network I / F unit 18, a scanner unit 19, an image processing unit 20, a printer unit 21, and a facsimile communication unit 22 are provided. Configured.

  The CPU 11 is based on an OS (Operating System) program, on which middleware and application programs are executed.

  Various programs are stored in the ROM 12, and each function of the image forming apparatus 10 such as job execution is realized by the CPU 11 executing processes according to these programs.

  The RAM 13 is used as a work memory for temporarily storing various data when the CPU 11 executes a program, an image memory for storing image data, and the like.

  The nonvolatile memory 14 is a rewritable memory (flash memory) that can retain memory even when the power is turned off. The nonvolatile memory 14 stores device-specific information and various setting information.

  The hard disk device 15 is a large-capacity nonvolatile storage device, and stores an OS program, various application programs, print data, image data, a job history, and the like.

  The display unit 16 is composed of a liquid crystal display (LCD) and the like, and has a function of displaying contents related to various operations and settings. The operation unit 17 has a function of accepting various operations such as job input from the user and setting change.

  The operation unit 17 includes a touch panel that is provided on the screen of the display unit 16 and detects a pressed coordinate position, and includes a numeric keypad, a character input key, a start key, and the like outside the screen.

  The network I / F unit 18 communicates with other external devices connected through a network such as a LAN (Local Area Network).

  The scanner unit 19 performs a function of optically reading a document and acquiring image data. The scanner unit 19 sequentially moves, for example, a light source that irradiates light on a document, a line image sensor that receives the reflected light for one line in the width direction, and a reading position in units of lines in the length direction of the document. An optical path composed of a lens, a mirror, and the like for guiding the reflected light from the document to the line image sensor to form an image, a conversion unit for converting the analog image signal output from the line image sensor into digital image data, etc. It is prepared for.

  The facsimile communication unit 22 controls operations related to facsimile transmission and reception.

  The image processing unit 20 generates the above-described PWM modulation signal corresponding to the image to be printed in addition to processing such as image enlargement / reduction and rotation, and outputs the PWM modulation signal to the printer unit 20. The image processing unit 20 corresponds to the PWM modulation signal generation unit described in the claims.

  The printer unit 21 will be described with reference to FIG. The printer unit 21 functions to form an image on a recording sheet based on the PWM modulation signal sent from the image processing unit 20.

  The printer unit 21 includes an endless annular intermediate transfer belt 31 and yellow (Y), magenta (M), cyan (C), and black (K) for forming a single color toner image on the intermediate transfer belt 31. A tandem type comprising four image forming units 32Y, 32M, 32C, and 32K for each color, a paper feeding unit that feeds transfer paper, a transport unit that transports the fed transfer paper, and a fixing device 35. An image forming apparatus is configured as a so-called color laser printer that forms an image by an electrophotographic process.

  The image forming units 32Y, 32M, 32C, and 32K have the same structure although the colors of the toners used are different. Each of the image forming units 32Y, 32M, 32C, and 32K has a cylindrical photosensitive drum 54 (see FIGS. 2 and 3) as an image carrier on which an electrostatic latent image is formed, and is charged around the periphery. An apparatus, a developing device, a transfer device, a cleaning device, and the like are arranged and provided. A laser unit 33 including a laser diode (50, 51), a rotary polygon mirror 52, and various lenses 53 is provided.

  When image formation is performed, a two-dimensional electrostatic latent image is formed on a photosensitive drum 54 (see FIG. 3) uniformly charged by a charging device with a laser beam that is turned on / off according to a PWM modulation signal. .

  FIG. 3 shows how the laser unit 33 forms an electrostatic latent image on the photosensitive drum 54. The laser unit 33 includes a laser diode (laser diode 50 and laser diode 51) that emits a laser beam, a rotary polygon mirror 52, and various lenses 53. The laser beam emitted from the laser diode (laser diode 50, laser diode 51) enters the rotary polygon mirror 52.

  The rotating polygonal mirror 52 rotates at a constant angular velocity in the direction of arrow A (see FIG. 3), and with this rotation, the incident laser beam is reflected as a deflected beam that continuously changes its angle. The laser beam that has become a deflected beam passes through various lenses 53 including an fΘ lens and a cylindrical lens. The laser beams that have passed through the various lenses 53 are scanned at a constant speed in the direction of arrow B (main scanning direction) on a photosensitive drum 54 as an image carrier. As a result, an image for one line is formed on the photosensitive drum 54 in the main scanning direction. This operation of forming an image for one line is repeated by rotating the photosensitive drum 54 in the direction (sub-scanning direction) as shown by an arrow C in the figure while relatively moving the position where the laser beam strikes. A two-dimensional electrostatic latent image is formed on the photosensitive drum 54.

  In the embodiment of the present invention, the laser unit 33 includes two laser diodes (laser diode 50 and laser diode 51). The two laser beams are scanned in parallel, and two adjacent lines are electrostatically charged. A latent image is formed on the photosensitive drum 54 at the same time. Hereinafter, the laser beam emitted from the laser diode 50 is referred to as beam 1 and the laser beam emitted from the laser diode 51 is referred to as beam 2.

  Returning to FIG. 2, the description will be continued. After the electrostatic latent image is formed, the phenomenon device visualizes the electrostatic latent image with toner. The toner image formed on the surface of the photosensitive drum 54 is transferred to the intermediate transfer belt at a location where it contacts the intermediate transfer belt 31.

  The intermediate transfer belt 31 is wound around a plurality of rollers so as to circulate. In the process of rotation, the images (toner images) of each color are sequentially transferred from the image forming units 32Y, 32M, 32C, and 32K. The image is transferred so as to be superimposed on the belt 31, and a full-color image is synthesized. This color image is transferred from the intermediate transfer belt 31 to the recording paper at the secondary transfer position D. Further, the toner remaining on the intermediate transfer belt 31 is removed by a cleaning device 34 provided downstream of the secondary transfer position D. The fixing device 35 is provided at a position downstream of the secondary transfer position D on the conveyance path of the conveyance unit, and fixes the transferred toner image on the recording paper. As a result, an image is formed on the recording paper.

  Next, the PWM modulation signal will be described.

  FIG. 4 shows an example of a PWM modulation signal generated by the image processing unit 20 of the image forming apparatus according to the present embodiment. The PWM modulation signal is generated in synchronization with a predetermined clock. In the PWM modulation signal according to the embodiment of the present invention, four clocks are set as a time for one pixel (referred to as a pixel unit period), and the pulse width (period in which the pulse is turned on) in the pixel unit period is set to one clock unit. By changing the density, the density of each pixel can be shown in five levels (0%, 25%, 50%, 75%, 100%).

  For example, if the pixel density is 75%, a pulse having a pulse width corresponding to 3 clocks in a 4-clock pixel unit period (pulse with a duty ratio of 75%) is generated, and the pixel density is 50%. If there is, a pulse having a pulse width corresponding to two clocks in a pixel unit period of 4 clocks (a pulse having a duty ratio of 50%) is generated, and if the pixel density is 25%, the pixel unit period of 4 clocks Among them, a pulse having a pulse width corresponding to one clock (a pulse having a duty ratio of 25%) is generated. If the pixel density is 0%, all pulses in the 4-clock pixel unit period are off (duty ratio 0%), and if the pixel density is 100%, the entire period of the 4-clock pixel unit period ( Pulse having a pulse width of 4 clocks) (pulse with a duty ratio of 100%) is generated.

  The vertical dotted line in the figure indicates the boundary of the pixel unit period. In the embodiment of the present invention, the PWM modulation signal of each pixel is generated so as to bring a pulse (on period) to the end point of the pixel unit period. In the figure, the time direction is from left to right, and the pulse (on period) of each pixel appears right justified within the pixel unit period of that pixel.

  FIG. 4A shows an example of a PWM modulation signal that performs on / off control of the clock and the beam 1. In the PWM modulation signal, when there is a period in which the pulse is turned off before and after a short pulse corresponding to a halftone pixel (first pixel) having a predetermined density or less, the short pulse of the first pixel is isolated. This isolated short pulse is called an isolated pulse. For example, when a halftone pixel is adjacent to a low-density first pixel on the same line (hereinafter, a halftone pixel adjacent to the first pixel on the same line is referred to as a second pixel), the first A pulse corresponding to the first pixel is generated between a short pulse corresponding to the pixel and a pulse corresponding to the second pixel (pulse which is 100% on or not 0% on in the pixel unit period). Becomes an isolated pulse.

  In FIG. 4A, the pulse surrounded by the ellipse is an isolated pulse. Note that a pixel corresponding to an isolated pulse is referred to as an isolated pulse pixel.

  Note that a pixel having a predetermined density (a pixel serving as the first pixel) is a pixel having no density on the resulting recording paper or image carrier when an image is formed alone. When an image is formed on a single pixel, the pulse corresponding to the pixel is an isolated pulse because there are no surrounding pixels. The isolated pulse pixel, which is a pixel having a density equal to or lower than a predetermined density, does not generate a density on the recording paper or the image carrier when an image is formed.

  When an isolated pulse is generated in the PWM modulation signal, a toner image corresponding to the isolated pulse pixel is not formed on the image carrier. Therefore, the image forming apparatus 10 of the present invention moves all or part of the density of the first pixel to the second pixel, specifically, moves the pulse of the isolated pulse pixel to the adjacent second pixel, Correction is performed so that the pulse corresponding to the isolated pulse pixel and the pulse corresponding to the second pixel become one continuous pulse so that the isolated pulse is not generated in the PWM modulation signal.

  4A shows a PWM modulation signal in which an isolated pulse is generated, and FIG. 4B shows a PWM modulation signal corrected so that the isolated pulse of the PWM modulation signal in FIG. 4A does not appear. .

  In the embodiment of the present invention, the correction target is an isolated pulse pixel having a pulse width corresponding to a density of 25% or less. In FIG. 4A, the pulse corresponding to the first pixel has a pulse width corresponding to a density of 25% (pulse width corresponding to one clock), and the pulse corresponding to the second pixel has a pulse width corresponding to a density of 75%. (Pulse width for 3 clocks). The image forming apparatus 10 shifts the density from the isolated pulse pixel to the second pixel when preventing the generation of the isolated pulse.

  FIG. 4B shows a PWM modulation signal in which the density of the first pixel which is an isolated pulse pixel is shifted to the second pixel. The total density of the first pixel is transferred to the second pixel, the density of the first pixel is 0%, and the density of the second pixel is 100%. Since the density of the first pixel, which is an isolated pulse pixel, is entirely transferred to the adjacent second pixel, the pulse of the first pixel disappears (no isolated pulse is generated). The pulse of the second pixel whose density is moved from the first pixel becomes one continuous pulse corresponding to the total density of the density of the first pixel before movement and the density of the second pixel before movement. Thereby, the density of the first pixel and the second pixel, which were isolated pulse pixels, is reproduced on the image carrier as the second pixel having the total density.

  In FIG. 4, correction is performed so that the density is moved from the first pixel, which is an isolated pulse pixel, to the second pixel. However, when a halftone pixel is not adjacent to the isolated pulse pixel on the same line, that is, the second pixel is May not be next door. In that case, a halftone pixel (hereinafter referred to as a third pixel) exists on the line adjacent to the line including the isolated pulse pixel at the same position in the main scanning direction as the isolated pulse pixel. For example, correction may be performed so that the density of the isolated pulse pixel is transferred to the third pixel.

  FIG. 5 shows a PWM modulation signal corresponding to the beam 1 and a PWM modulation signal corresponding to the beam 2. The PWM modulation signal corresponding to the beam 1 includes an isolated pulse, and the PWM modulation signal corresponding to the beam 2 includes a pulse corresponding to the third pixel.

  FIG. 5A shows a PWM modulation signal in which an isolated pulse is generated. In FIG. 5A, the density of the first pixel which is an isolated pulse pixel is 25% (the isolated pulse has a pulse width corresponding to one clock). In addition, the third pixel in the line adjacent to the first pixel at the same position in the main scanning direction as the first pixel has a density of 75% (the pulse corresponding to the third pixel has a pulse width corresponding to 3 clocks). Yes. When preventing the generation of an isolated pulse, the image forming apparatus 10 moves the density of the first pixel, which is an isolated pulse pixel, to the third pixel of the adjacent line.

  FIG. 5B shows a PWM modulation signal when the density of the first pixel, which is an isolated pulse pixel, is shifted to the third halftone pixel at the same main scanning position on the adjacent line. The total density of the first pixel is transferred to the third pixel, the density of the first pixel is 0%, and the density of the third pixel is 100%. Since the density of the first pixel, which is an isolated pulse pixel, is entirely transferred to the third pixel, there is no pulse corresponding to the first pixel (no isolated pulse is generated). The pulse of the third pixel whose density has been moved from the first pixel is one continuous pulse corresponding to the total density of the density of the first pixel before movement and the density of the third pixel before movement. Thereby, the density of the first pixel and the third pixel, which were isolated pulse pixels, is reproduced on the image carrier as the third pixel having the total density.

  The PWM modulation signal is generated based on output data indicating the on / off timing of the pulse in the pixel unit period for each pixel. Further, the correction for moving the density of the isolated pulse pixel is performed on the output data.

  Next, the configuration of the output data and the correction method will be described with reference to FIGS. The output data is digital data composed of “1” and “0”. “1” corresponds to turning on the pulse, and “0” corresponds to turning off the pulse. One bit of output data corresponds to one clock, and instructs on / off of a pulse during one clock. Output data for one pixel is represented by four consecutive bits.

  The vertical dotted lines in FIGS. 6 to 11 indicate the boundaries of the pixel unit period. In the embodiment of the present invention, the output data is converted into a PWM modulation signal in synchronization with the clock in order from the left bit in the figure. For example, if the output data (four bits) of a certain pixel is 0001, a pulse that is off for 1 to 3 clocks in the pixel unit period and is on only for the 4th clock is generated for this pixel. That is, a PWM modulation signal corresponding to a pixel having a density of 25% is generated from this output data.

  Similarly, if the output data is 0011, a pulse (a PWM modulation signal corresponding to a pixel having a density of 50%) is generated between 1 clock and 2 clocks and between 3 clocks and 4 clocks. If the output data is 0111, a pulse (PWM modulation signal corresponding to a pixel having a density of 75%) is generated in which one clock is off and two to four clocks are on. If the output data is 1111, a pulse (PWM modulation signal corresponding to a pixel having a density of 100%) is generated in which all periods of 1 clock and 4 clocks are on.

  FIG. 6 exemplifies 16-bit output data corresponding to four pixels A to D that are continuously imaged by the beam 1.

  In FIG. 6, the density of the pixel A is 0% (0000), the density of the pixel B is 0% (0000), the density of the pixel C is 25% (0001), and the density of the pixel D is 75% (0111). When a PWM modulation signal is generated from this output data, the pulse corresponding to the pixel C becomes an isolated pulse (the pixel C is an isolated pulse pixel). The pixel D corresponds to a second halftone pixel adjacent to the isolated pulse pixel. That is, the PWM modulation signal generated from the output data of the pixel C is like the first pixel in FIG. 4A, and the PWM modulation signal generated from the output data of the pixel D is the second pixel in FIG. become that way.

  In the correction of output data, “1” data of the pixel C is transferred to the pixel D, so that the density of the pixel C is transferred to the pixel D. No isolated pulse is generated in the PWM modulation signal generated from the corrected output data. The PWM modulation signals generated from the corrected output data of the pixel C and the pixel D are as shown in the first pixel and the second pixel in FIG.

  Next, a case where the density of the isolated pulse pixel is shifted to the third pixel will be described. FIG. 7 shows 16-bit output data corresponding to pixels E to H corresponding to pixels E to H that are continuously imaged by beam 1 and 16 bits corresponding to pixels I to L that are continuously imaged by beam 2. The output data for minutes.

  The line from pixel I to pixel L is a line adjacent to pixel E to pixel H, and pixel E and pixel I, pixel F and pixel J, pixel G and pixel K, pixel H and pixel L are in the main scanning direction. Pixels at the same position.

  In FIG. 7, the density of the pixel E is 0% (0000), the density of the pixel F is 0% (0000), the density of the pixel G is 25% (0001), and the density of the pixel H is 0% (0000). When a PWM modulation signal is generated from this output data, the pulse corresponding to the pixel G becomes an isolated pulse (the pixel G is an isolated pulse pixel). That is, the PWM modulation signal generated from the output data of the pixels E to H becomes the PWM modulation signal of the beam 1 in FIG. Pixel G corresponds to the first pixel. Since the pixels F and H adjacent to the pixel G are not halftone pixels, they do not correspond to the second pixel.

  In FIG. 7, the density of the pixel I is 0% (0000), the density of the pixel J is 0% (0000), the density of the pixel K is 75% (0111), and the density of the pixel L is 0% (0000). Yes. Since the positions of the pixel G and the pixel K in the main scanning direction are the same position, the pixel K corresponds to the third pixel. That is, the PWM modulation signal generated from the output data of the pixels I to L becomes the PWM modulation signal of the beam 2 in FIG.

  In the correction of the output data, the “1” data of the pixel G is transferred to the pixel K, so that the density of the pixel G is transferred to the pixel K. No isolated pulse is generated in the PWM modulation signal generated from the corrected output data. The PWM modulation signal generated from the corrected output data of the pixels E to H becomes like the PWM modulation signal of the beam 1 in FIG. 5B, and the PWM generated from the corrected output data of the pixels I to L. The modulation signal is like the PWM modulation signal of the beam 2 in FIG.

  8 to 11 below show other specific examples in the correction of output data.

(Pattern 1)
FIG. 8 illustrates a case where the density of two isolated pulse pixels is shifted to the second pixel when there are two isolated pulse pixels across the second pixel. FIG. 8 shows output data for 20 bits corresponding to five consecutive pixels (pixel A to pixel E) formed by the beam 1.

  In FIG. 8, the density of the pixel A is 0% (0000), the density of the pixel B is 25% (0001), the density of the pixel C is 50% (0011), the density of the pixel D is 25% (0001), and the pixel E The pixel B and the pixel D each correspond to an isolated pulse pixel, and the pixel C corresponds to a second halftone pixel adjacent to the isolated pulse pixel.

  In the correction of the output data, “1” data of the pixels B and D is transferred to the pixel C. After the correction, all the densities of the isolated pulse pixels B and D are transferred to the pixel C to 0%, and the density of the pixel C is 100%. Since all the densities of the isolated pulse pixels B and D are moved to the pixel C, no isolated pulse is generated in the PWM modulation signal generated from the corrected output data. In the PWM modulation signal, the pulses corresponding to the pixel B, the pixel D, and the pixel C before correction become one continuous pulse corresponding to the pixel C after correction. The densities of the pixel B, the pixel D, and the pixel C are reproduced on the image carrier as the pixel C having the total density.

(Pattern 2)
In FIG. 9, a method for preventing the generation of an isolated pulse without shifting the density of the isolated pulse pixel to another pixel will be described. FIG. 9 shows 16-bit output data corresponding to four consecutive pixels (pixel A to pixel D) formed by the beam 1.

  In FIG. 9, the density of the pixel A is 100% (1111), the density of the pixel B is 25% (0001), the density of the pixel C is 0% (0000), and the density of the pixel D is 0% (0000). When a PWM modulation signal is generated from this output data, the pulse corresponding to the pixel B becomes an isolated pulse (the pixel B is an isolated pulse pixel).

  Further, the pixels A and C adjacent to the pixel B, which is an isolated pulse pixel, do not correspond to the second pixel because they are not halftone pixels. Therefore, there is no pixel to which the density of the pixel B is moved.

  When a pixel A having a density of 100% is adjacent to an isolated pulse pixel, if the pulse of the pixel B is brought close to the pulse of the pixel A, these can be made one continuous pulse. Therefore, the output data is corrected so that such a PWM modulation signal is generated. Specifically, correction is performed so that the data “1” corresponding to the isolated pulse pixel is brought to the start point of the pixel unit period. In the figure, the data “1” is changed from right justification to left justification within the pixel unit period. Thereby, in the PWM modulation signal, the pulse of the pixel B and the pulse of the pixel A become one continuous pulse, so that the generation of an isolated pulse can be prevented.

  The correction of the pattern 2 is performed with priority over the correction of shifting the density of the isolated pulse pixel to the third pixel. The correction for shifting the density of the isolated pulse pixel to the third pixel is executed when the correction of the pattern 2 is impossible.

(Pattern 3)
A case where an isolated pulse pixel, a second halftone pixel, and a pixel having a density of 100% are arranged in order on the same line will be described. FIG. 10 shows 16-bit output data corresponding to four consecutive pixels (pixel A to pixel D) formed by the beam 1.

  In FIG. 10, the density of the pixel A is 0% (0000), the density of the pixel B is 25% (0001), the density of the pixel C is 50% (0011), and the density of the pixel D is 100% (1111). When a PWM modulation signal is generated from this output data, the pulse corresponding to the pixel B becomes an isolated pulse (the pixel B is an isolated pulse pixel). Pixel C corresponds to the second pixel.

  In FIG. 10, since the density of the pixel D adjacent to the right side of the pixel C is 100%, the pulse of the pixel C and the pixel D becomes one continuous pulse in the PWM modulation signal.

  When correction is made so that the data of “1” is brought close to the start point of the pixel unit period in the output data array corresponding to the pixel C, one pulse in which the pulses of the pixel B and the pixel C are continuous with the PWM modulation signal. And the generation of isolated pulses can be prevented. However, in FIG. 10, since the pulse of the pixel C and the pixel D is originally a continuous pulse in the PWM modulation signal, the correction of bringing the data “1” corresponding to the pixel C to the start point of the pixel unit period is performed. If done, pixel C will not be able to maintain the continuity of the pulses of pixel D.

  Therefore, in the correction of the output data, the “1” data of the pixel B is moved to the pixel C, so that the density of the pixel B is moved to the pixel C. As a result, no isolated pulse is generated in the PWM modulation signal generated from the corrected output data. Further, the continuity of the pulses of the pixel C and the pixel D is maintained.

(Pattern 4)
A case where a part of the density of the isolated pulse pixel is transferred will be described. FIG. 11 shows 16-bit output data corresponding to four consecutive pixels (pixel A to pixel D) formed by the beam 1. In FIG. 11, a pulse having a pulse width corresponding to a concentration of 50% or less is an isolated pulse.

  In FIG. 11, the density of the pixel A is 0% (0000), the density of the pixel B is 50% (0011), the density of the pixel C is 75% (0111), and the density of the pixel D is 100% (1111). When a PWM modulation signal is generated from this output data, the pulse corresponding to the pixel B becomes an isolated pulse (the pixel B is an isolated pulse pixel). Pixel C corresponds to the second pixel.

  In FIG. 11, the pulse of the pixel C and the pixel D becomes one continuous pulse by the PWM modulation signal as in FIG. 10, and therefore, the correction for bringing the data “1” corresponding to the pixel C to the start point of the pixel unit period. When this is performed, the pixel C cannot maintain the continuity of the pulse of the pixel D.

  In addition, since the on time of the pulse corresponding to the isolated pulse pixel (pixel B) exceeds the off time of the pulse corresponding to the second pixel (pixel C), the entire density of the pixel B cannot be transferred to the pixel C.

  In the correction of the output data in FIG. 11, the density of a part of the isolated pulse pixel (pixel B) is moved to the second pixel (pixel C). Specifically, the data “1” is moved to one pixel C. Further, the data “1” corresponding to the remaining density of the isolated pulse pixel is brought to the end point of the pixel unit period. Thereby, the pulse corresponding to the isolated pulse pixel (pixel B) can be continued to the pulse corresponding to the second pixel (pixel C), and the generation of the isolated pulse can be prevented.

  As described above, in the embodiment of the present invention, when the density is transferred from the first pixel to the second pixel, the maximum density is moved within a range where the density of the second pixel does not exceed 100%. Further, when the density of the isolated pulse pixel remains after the density shift (when it is not 0%), data “1” corresponding to the remaining density of the isolated pulse pixel is used as a pixel unit period corresponding to the isolated pulse pixel. In this, the pixel unit period side corresponding to the second pixel is approached.

  Next, details of the image processing unit 20 will be described. FIG. 12 shows a schematic configuration of the image processing unit 20. The image processing unit 20 includes an image processing block 60, a line buffer 61 corresponding to each color of Y, M, C, and K, and a pulse width modulation block 70.

  The image processing block 60 performs image processing such as screen processing on the image indicated by the image data to be printed. Further, output data to be transmitted to the line buffer 61 of each color Y, M, C, and K is created from the image data after the image processing.

  Each line buffer 61 has a line buffer for holding output data for controlling on / off of the beam 1 and a line buffer for holding output data for controlling on / off of the beam 2. The output data held in each line buffer 61 is input to the pulse width modulation block 70 corresponding to the same color.

  Each pulse width modulation block 70 takes in output data from the line buffer 61. Then, when the isolated output pixel exists in the fetched output data, the output data is corrected. The pulse width modulation block 70 captures output data for every two beams (beam 1 and beam 2) and simultaneously performs correction processing. The pulse width modulation block 70 generates a PWM modulation signal from the corrected output data and outputs the PWM modulation signal to the printer unit 21. The pulse width modulation block 70 corresponds to a correction unit and a PWM modulation signal generation unit described in the claims.

  FIG. 13 shows a schematic configuration of the pulse width modulation block 70. The pulse width modulation block 70 includes a control unit 71, a processing unit 72, a setting register unit 73, an input data register 74, and an output data register 75.

  The input data register 74 includes a beam 1 register and a beam 2 register, and takes in output data from the line buffer 61 and holds it.

  The processing unit 72 corrects the output data held in the input data register 74. The output data is corrected to prevent the generation of isolated pulse pixels and sent to the output data register 75.

  The output data register 75 has a register for beam 1 and a register for beam 2 and holds the output data corrected by the processing unit 72 and generates a PWM modulation signal based on the held output data. And output to the printer unit 21.

  The control unit 71 monitors whether or not output data is held in the input data register 74 and whether or not there is a free area in the output data register 75, and transmits an instruction to correct the output data to the processing unit 72. .

  The setting register unit 73 holds information on images to be printed. Based on this information, the CPU 11 recognizes whether or not an isolated pulse pixel is present in the photographic area and the size of the image (one page) to be printed, and whether or not a necessary amount of PWM modulation signal has been generated. Is determined.

  FIG. 14 shows processing performed in each pulse width modulation block 70.

  First, it waits until each input data register 74 for beam 1 and beam 2 becomes empty (step S101; No). The input data registers 74 for beam 1 and beam 2 output a Request signal when they become empty.

  When the Request signal is output from the input data registers 74 for the beam 1 and the beam 2 (step S101; Yes), the line buffers 61 for the beam 1 and the beam 2 that have received the request signal receive the enable signal and output data. Is output. Output data is output for one line in order from the head of the line. The input data register 74 captures and holds this output data (step S102).

  Each input data register 74 for beam 1 and beam 2 outputs a ready signal 1 to the control unit 71 when holding output data for one line. Each of the output data registers 75 of the beam 1 and the beam 2 outputs a Request signal to the processing unit 72 when an empty area for one line is secured. Upon receiving the Request signal, the processing unit 72 sends a Ready signal 2 to the control unit 71.

  When the control unit 71 receives both the Ready signal 1 and the Ready signal 2 (step S103; Yes, step S104; Yes), the control unit 71 outputs a Start signal to the processing unit 72. That is, in steps S103 and S104, the process waits until both the Ready signal 1 and the Ready signal 2 are prepared. When the input data register 74 has data and the output data register 75 has a space, both the Ready signal 1 and the Ready signal 2 are prepared.

  Receiving the Start signal, the processing unit 72 takes out the output data held in the input data register 74 and performs correction to prevent the above-described isolated pulse from occurring (step S105). That is, when an isolated pulse pixel exists in the output data, the isolated pulse is prevented from being generated by shifting the density of the isolated pulse pixel to the second pixel, the third pixel, or the like. This correction is executed only when the isolated pulse pixel is a pixel in the photographic area.

  Thereafter, the processing unit 72 sends the corrected output data to the output data register 75, and the output data register 75 holds the corrected output data. Then, a PWM modulation signal is generated from the output data held in the output data register 75 in synchronization with the clock signal, and is output to the printer unit 21 (step S106). The output data register 75 includes output data registers for the beam 1 and the beam 2, and outputs PWM modulation signals for two lines at the same time.

  The processing unit 72 sends output data to the output data register 75, counts the number of processed lines that are converted into PWM modulation signals and output to the printer unit 21, and is stored in the setting register unit 73. Until processing for the number of lines of the image to be printed is completed (step S107; No), the processing returns to step S101 and continues. Then, when the processing for the number of lines is completed (step S107; Yes), this processing is terminated.

  FIG. 15 shows the correction process performed in step S105 of FIG.

  First, output data to be corrected is checked (step S201). In this check, whether or not there is an isolated pulse pixel is checked, and if there is an isolated pulse pixel, the density of surrounding pixels is checked.

  If there is no isolated pulse pixel (step S202; No), no correction is performed (step S209), and this process ends.

  If there is an isolated pulse pixel (step S202; Yes) and there is a halftone pixel (second pixel) next to it (step S203; Yes), an output is performed so that the density of the isolated pulse pixel is transferred to the second pixel. The data is corrected (step S206), and this process ends. In the embodiment of the present invention, when there are second pixels on both sides of an isolated pulse pixel, the density of the isolated pulse pixel is preferentially transferred to the right adjacent pixel (or the left adjacent pixel). Note that the density is shifted to the maximum in a range where the density of the second pixel does not exceed 100%. If the density remains in the isolated pulse pixel even if the density is moved until the density of the second pixel reaches 100%, a pulse (on the pixel unit period side corresponding to the second pixel within the pixel unit period of the isolated pulse pixel ( (1 data) is corrected.

  If there is no second pixel (step S203; No), and a pixel with the density of 100% is adjacent to the isolated pulse pixel (step S204; Yes), it is within the pixel unit period of the isolated pulse pixel. In step S207, the correction is performed so that the data of “1” is brought closer to the pixel having the density of 100% (step S207), and this process is terminated.

  A pixel with 100% density is not adjacent to the isolated pulse pixel on the same line (step S204; No), and the third pixel is in the same main scanning direction position as the isolated pulse pixel and adjacent to the isolated pulse pixel. If there is (step S205; Yes), the output data is corrected so that the density of the isolated pulse pixel is shifted to the third pixel (step S208), and this process is terminated.

  If there is no third pixel (step S205; No), the correction is impossible and the correction is not performed (step S209), and this process is terminated.

  As described above, when there is an isolated pulse pixel in the output data, the image forming apparatus 10 according to the embodiment of the present invention is a pixel of the halftone density (second pixel) on the same line as the isolated pulse pixel. The isolated pulse pixel density is shifted to (pixel), and the pulse corresponding to the isolated pulse pixel and the second pixel is made one continuous pulse by the PWM modulation signal to prevent the generation of the isolated pulse. If the second pixel does not exist, the density of the isolated pulse pixel is transferred to a halftone density pixel (third pixel) on the line adjacent to the isolated pulse pixel and at the same position in the scanning direction. Prevents the generation of isolated pulses. As a result, even for a pixel in which the pulse of the PWM modulation signal becomes an isolated pulse, the density of the pixel can be accurately reproduced on the image carrier.

  Instead of correcting the output data to prevent the generation of isolated pulses, the density of isolated pulse pixels may be moved on the image data to be printed to prevent the generation of isolated pulses. Processing for shifting the density of isolated pulse pixels on image data will be described with reference to FIGS.

  FIG. 16 shows how the density is transferred from the isolated pulse pixel to the second pixel on the image data. FIG. 16 shows pixels A to E that are continuously arranged on the same line in the main scanning direction. In the figure, the density of each pixel is expressed in five levels from 0 to 4, where density 0 is 0%, density 1 is 25%, density 2 is 50%, density 3 is 75%, and density 4 is 100%. Note that when creating output data based on the density of each pixel, as shown in FIGS. 6 to 11, it is created so that data of “1” is brought to the end point of the pixel unit period.

  When the density of 25% or less is set as the density of the isolated pulse pixel, if the density of the pixel adjacent to the right side of the density 1 pixel is not 100% (density 4), the density 1 pixel becomes an isolated pulse pixel. . In FIG. 16, the density of pixel A is 0%, the density of pixel B is 25%, the density of pixel C is 75%, the density of pixel D is 0%, and the density of pixel E is 0%. Corresponds to an isolated pulse pixel, and pixel C corresponds to a second halftone pixel adjacent thereto.

  In the correction of image data, the density of the pixel B is set to 0% by shifting the density of the pixel B to the pixel C. In the corrected image data, the pixel B has a density of 0% and the pixel C has a density of 100%. If output data is created based on the corrected image data and a PWM modulation signal is generated from the output data, no isolated pulse is generated in the PWM modulation signal.

  When the output data is created based on the density of each pixel, if the data is created so that the data of “1” is brought to the end point of the pixel unit period, the density of the first pixel is set to the next. Even in the case where the density remains in the first pixel even if it is moved to the second pixel as much as possible, the pulse of the PWM modulation signal corresponding to the first pixel after the movement can be obtained simply by moving the density on the image data. The pulse of the PWM modulation signal corresponding to the second pixel after movement becomes one continuous pulse.

  FIG. 17 shows how the isolated pulse is prevented from being generated by shifting the density from the isolated pulse pixel to the third pixel on the image data.

  FIG. 17 shows image data of a part of two main scanning direction lines (first line and second line) adjacent in the sub-scanning direction. The pixels F to J are continuously arranged on the first line, and the pixels K to O are continuously arranged on the second line at the same position in the main scanning direction. As in FIG. 16, the density of each pixel is expressed in five levels from 0 to 4. Further, when generating output data based on the density of each pixel, as shown in FIGS. 6 to 11, it is generated so that “1” data is brought to the end point of the pixel unit period.

  Pixel F and pixel K, pixel G and pixel L, pixel H and pixel M, pixel I and pixel N, and pixel J and pixel O are pixels at the same position in the main scanning direction.

  When the density of 25% or less is the density of the isolated pulse pixel, the density of the pixel F to pixel J is 0% for the pixel F, 25% for the pixel G, 0% for the pixel H, 0% for the pixel I, J is 0%, and the pixel G corresponds to an isolated pulse pixel. However, since both the pixels F and H adjacent to the pixel G in the first line have a density of 0%, the isolated pulse pixel is not eliminated even if the density is moved to these pixels F and H. The density of the pixels K to O is 0% for the pixel K, 50% for the pixel L, 0% for the pixel M, 0% for the pixel N, and 0% for the pixel O. The pixel L is the third pixel. Applicable.

  Therefore, in the correction of the image data, the density of the pixel G is moved to the pixel L and the density of the pixel G is set to 0%. In the corrected image data, the density of the pixel G is 0% and the density of the pixel L is 75%. Thus, if output data is created based on the corrected image data and a PWM modulation signal is generated from the output data, no isolated pulse is generated in the PWM modulation signal.

  When the density of the isolated pulse pixel is shifted on the image data, the CPU 11 may perform correction for shifting the density, for example. In this case, the CPU 11 corresponds to the correction unit described in the claims.

  The embodiment of the present invention has been described with reference to the drawings. However, the specific configuration is not limited to that shown in the embodiment, and there are changes and additions within the scope of the present invention. Are also included in the present invention.

  In the embodiment of the present invention, in the output data, the density of one pixel is indicated by 4-bit data (“1” and “0” data), but the number of bits for one pixel is not limited to this. Further, although the pixel density has been described in five stages of 0%, 25%, 50%, 75%, and 100%, the number of stages is not limited to this.

  In the embodiment of the present invention, the density of 25% or less (50% or less only in FIG. 11) is the density of the isolated pulse pixel, but the density of the isolated pulse pixel is not limited to this. What is necessary is just to set suitably according to the characteristic of image formation. The density of the isolated pulse pixel corresponds to the predetermined density described in the claims.

  In the embodiment of the present invention, the image forming apparatus 10 includes two laser diodes, but the number of laser diodes is not limited thereto. One is acceptable. More numbers may be provided.

  In the embodiment of the present invention, when generating output data from image data, data “1” is arranged at the end point of the pixel unit period, but data “1” is arranged at the start point. It may be.

  In the embodiment of the present invention, if the isolated pulse pixel is a pixel in the photographic region, correction is performed to shift the density of the isolated pulse pixel. However, the correction is performed even if the isolated pulse pixel is a pixel outside the photographic region. May be.

DESCRIPTION OF SYMBOLS 10 ... Image forming apparatus 11 ... CPU
12 ... ROM
13 ... RAM
DESCRIPTION OF SYMBOLS 14 ... Nonvolatile memory 15 ... Hard disk apparatus 16 ... Display part 17 ... Operation part 18 ... Network I / F part 19 ... Scanner part 20 ... Image processing part 21 ... Printer part 22 ... Facsimile communication part 31 ... Intermediate transfer belt 32 (32Y, 32M, 32C, 32K) ... image forming unit 33 ... laser unit 34 ... cleaning device 35 ... fixing device 50 ... laser diode 51 ... laser diode 52 ... rotating polygon mirror 53 ... various lenses 54 ... photosensitive drum 60 ... image processing block 61 ... line buffer 70 ... pulse width modulation block 71 ... control unit 72 ... processing unit 73 ... setting register unit 74 ... input data register 75 ... output data register A ... arrow B ... arrow C ... arrow D ... two-dimensional transfer position

Claims (6)

The operation of scanning the laser beam in the first direction to form an image for one line on the image carrier is repeatedly performed while relatively moving the image carrier and the laser beam in a direction perpendicular to the first direction. An image forming unit for forming a two-dimensional image on the image carrier,
A PWM modulation signal generator for generating a PWM modulation signal for on / off control of the laser beam based on image data;
When a second pixel having a halftone density exists next to a first pixel having a halftone having a predetermined density or less in the same line in the first direction, all or part of the density of the first pixel A PWM modulation signal in which a pulse corresponding to the density of the first pixel after being moved to the second pixel and a pulse corresponding to the density of the second pixel after being moved is continued is the PWM A correction unit for generating the modulation signal generation unit;
I have a,
The PWM modulation signal generation unit includes an output memory that divides a period of one pixel into a plurality of sections and stores output data indicating ON / OFF of a pulse in each section for one line, and is stored in the output memory. Generating the PWM modulation signal based on the output data being
The image forming apparatus , wherein the correction unit changes the output data stored in the output memory . The image forming apparatus according to claim 1, wherein the density of the first pixel is moved to the second pixel to the maximum within a range where the density of the second pixel does not exceed 100%. The image forming apparatus according to claim 1, wherein the first pixel is a pixel having a density that does not have a density in a resultant product when an image is formed independently. Wherein the correction unit, when the second pixel adjacent to the first pixel in the same line in the first direction does not exist, the first pixel, adjacent in the direction orthogonal to the first direction The image forming apparatus according to any one of claims 1 to 3, wherein if there is a third pixel having a halftone density, the density of the first pixel is moved to the third pixel. . The image forming unit scans a plurality of lines of laser beams aligned in a direction orthogonal to the first direction in the first direction, and simultaneously forms the images of the plurality of lines on the image carrier,
The PWM modulation signal generating section, the output memory for storing one line of the output data with includes the plurality of lines, respectively corresponding to the plurality of lines on the basis of the output data stored in the output memory Generating the PWM modulation signal;
The correction unit stores the output data corresponding to the first pixel stored in the output memory corresponding to the line including the first pixel and the output memory corresponding to the line including the third pixel. The image forming apparatus according to claim 4, wherein the density of the first pixel is moved to the third pixel by changing output data corresponding to the third pixel. The first pixel, the image forming apparatus according to any one of claims 1 to 5, characterized in that a pixel of the photograph area.

Images