JP2010234684A - Image processor, image forming apparatus, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To simply suppress decrease of the reproducibility of an image caused by a positional gap of a focal point of an exposure means to the surface of a photoreceptor. <P>SOLUTION: The image forming apparatus forms an image by sticking a toner to an electrostatic latent image formed on the surface of the photo-sensitive drum by the LED head that exposes the surface of the photo-sensitive drum by a plurality of LEDs on the basis of binary image data. When it is determined that the position of the focal point of the LED head is not normal in the apparatus (S104: YES), the binary image data are generated using a dither matrix for abnormalities, which has a threshold value set so that a low-density image is expressed dark and a high-density image is expressed light (S106). <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, and a program.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms an electrostatic latent image by charging after charging the surface of a photoreceptor, and forming an image by attaching toner to the formed electrostatic latent image has been widely used. In such an image forming apparatus, as a means for exposing the surface of the photoreceptor, a type having a plurality of LEDs (hereinafter referred to as “LED head”) is known in addition to a type that scans a laser beam. Yes.

  For example, in Patent Document 1, a test pattern is printed on a sheet of paper in order to suppress light emission unevenness of an LED head (LPH) included in the image forming apparatus, the density of the test pattern is read from the sheet, and based on the read density distribution. A configuration for correcting the amount of light of the LED is shown. Specifically, when correcting the light amount, the positional relationship between the density data and the LED is determined by detecting and correcting the inclination of the test pattern based on the deviation of the two markers formed in the test pattern. The light amount is corrected with accuracy.

JP 2004-188665 A

  By the way, in an image forming apparatus provided with an LED head, the positional relationship between the LED head and the photosensitive member due to various factors such as a positional deviation at the time of assembling the LED head, a positional deviation that occurs after the assembling, variation in member accuracy, and member deterioration It is conceivable that there will be a gap. When the optical path length from the LED to the surface of the photoconductor changes due to such a positional shift, the focus position of the LED shifts from the surface of the photoconductor, and the light from the LED does not converge on the surface of the photoconductor. As a result, there is a problem that the electrostatic latent image is not properly formed and the reproducibility of the image is lowered.

  Although it is conceivable to provide the image forming apparatus with an adjustment mechanism for finely adjusting the positional relationship so that such positional deviation between the LED head and the photosensitive member can be eliminated, this is a specialized adjustment operation. Therefore, it cannot be easily performed by the user.

  In addition, in the above-mentioned patent document 1, in view of the problem that the test pattern is printed on the paper in a tilted state due to the LED head being inclined, both ends of the test pattern in the sub-scanning direction. Describes a configuration in which a marker is formed and the inclination of the test pattern is corrected based on the deviation in the main scanning direction. However, the configuration described in Patent Document 1 corrects the inclination in order to normally read the test pattern, and cannot eliminate the decrease in image reproducibility. In the first place, since the LED head moves relatively in the sub-scanning direction due to the rotation of the photosensitive member, the position of each LED in the main scanning direction does not change even if the LED head is tilted, and is formed at both ends in the sub-scanning direction. Since the marked marker is not shifted in the main scanning direction, this method cannot even detect the inclination of the LED head.

The present invention has been made in view of these problems, and an image processing apparatus and an image forming apparatus that can easily suppress a reduction in image reproducibility caused by a positional deviation of the focal point of an exposure unit with respect to the surface of a photoreceptor. An object is to provide an apparatus and a program.

  In order to achieve the above object, an image processing apparatus according to a first aspect of the present invention performs processing for generating binary image data used in an image forming apparatus. Specifically, an image is formed by attaching a developer to an electrostatic latent image formed on the surface of the photoreceptor by an exposure unit that exposes the surface of the photoreceptor with a plurality of light emitting elements based on binary image data. The forming apparatus is a target.

  The image processing apparatus includes a determination unit that determines whether or not the focus position of the exposure unit is normal, and a selection that selects a dither matrix used to generate binary image data from a plurality of types of dither matrices. Means. More specifically, the selection means, when the determination means determines that the position of the focus of the exposure means is not normal, the low-density image is expressed darker than when it is determined to be normal. An abnormal dither matrix having a threshold set so that a high-density image is expressed lightly is selected.

According to such an image processing apparatus, it is possible to easily suppress a decrease in image reproducibility due to a positional shift of the focus of the exposure unit with respect to the surface of the photosensitive member.
That is, when the focus position of the exposure means is not normal (deviation), the density of the low density image is lighter than normal, and conversely, the density of the high density image is higher than normal. The inventor of the present invention has found such a concentration characteristic.

  Specifically, a low-density image is represented by isolated dots, but the isolated dots are not properly formed when the position of the focus of the exposure unit is deviated. The concentration is lowered. On the contrary, a high density image is expressed by isolating the dotless portion, but the dotless portion is crushed due to factors such as the scattering of the developer, so that the density is higher than that in the normal state.

  Therefore, in the image processing apparatus according to the present invention, when it is determined that the focus position of the exposure unit is not normal, the threshold value is set so that the low density image is expressed deeply and the high density image is expressed lightly. Binary image data is generated using the set abnormal dither matrix. For this reason, the above-described density characteristic in a state where the focus position of the exposure unit is shifted can be relaxed.

  Specifically, for example, in the image processing apparatus according to claim 2, when the determination unit determines that the focus position of the exposure unit is normal by the determination unit, the selection unit has the lowest threshold value and the highest threshold value. When a normal dither matrix in which each threshold is isolated is selected and it is determined that the threshold is not normal, a plurality of the lowest threshold and the highest threshold are arranged side by side. Select the dither matrix for abnormalities.

  According to such an image processing apparatus, by generating binary image data using the abnormal dither matrix, an isolated dot of a low density image or a non-dot portion of a high density image in the binary image data can be obtained. It can be larger than normal. For this reason, the above-described density characteristic in a state where the focus position of the exposure unit is shifted can be relaxed.

By the way, as an image forming apparatus, there is also known an apparatus that includes a plurality of sets of photoconductors and exposure units, and forms color images by superimposing different color developer images formed in each set. On the premise of such an image forming apparatus, the image processing apparatus of the present invention can be configured as described in claims 3 and 4, for example.

  That is, in the image processing apparatus according to claim 3, the determination unit determines whether or not the position of the focus of the exposure unit is normal for each set, and the selection unit independently calculates the dither matrix for each set. select. According to such an image processing apparatus, a dither matrix suitable for each set can be selected.

  In the image processing apparatus according to the fourth aspect, the determination unit determines whether or not the focus position of the exposure unit is normal for each set. In this image processing apparatus, when there is at least one set in which the position of the focus of the exposure unit is determined to be not normal by the determination unit, the light emitting elements of the set of exposure units determined to be normal Adjusting means for adjusting the control amount to make the position of the focal point a pseudo-normal state is provided, and the selecting means selects the abnormal dither matrix for all sets.

According to such an image processing apparatus, it is possible to appropriately represent a color image even when a group in which the focus position of the exposure unit is normal and a group in which the focus position is not normal are mixed.
In other words, if there are a mixture of normal and non-normal pairs of exposure means, the expression of the developer image formed for each group will vary, and a color image obtained by superimposing these will be appropriate. The problem of not being expressed can arise.

  In this regard, in the image processing apparatus according to claim 4, when there is at least one group in which the focus position of the exposure unit is determined to be not normal, the exposure unit of the group determined to be normal is determined. The focus position is set to a pseudo-normal state, and an abnormal dither matrix is selected for all sets. Therefore, a color image can be appropriately expressed.

  In particular, in the image processing apparatus according to claim 5, the adjustment means indicates that the density measurement result of the density patch representing the density at a plurality of levels formed by the image forming apparatus is lower than the density when the low density patch is normal. Until the focus position of the exposure means is determined to be normal by the determination means until the thin and high density patch has a density characteristic higher than the normal density. Repeat control amount adjustment.

According to such an image processing apparatus, it is possible to appropriately reproduce a state where the focus position of the exposure unit is not normal by adjusting the control amount of the light emitting element.
The image processing apparatus of the present invention can be a constituent element of an image forming apparatus, for example, as described in claim 6. That is, in the image forming apparatus according to claim 6, the developer is applied to the electrostatic latent image formed on the surface of the photoconductor by an exposure unit that exposes the surface of the photoconductor with a plurality of light emitting elements based on the binary image data. An image is formed by adhering to the image processing apparatus, and includes the image processing apparatus according to any one of claims 1 to 5.

  Further, according to the program described in claim 7, it is possible to cause the computer to function as the image processing apparatus according to claim 1, thereby obtaining the above-described effects.

1 is a side sectional view showing a schematic configuration of an image forming apparatus according to an embodiment. FIG. 3 is a side cross-sectional view illustrating an open state of a top cover of the image forming apparatus according to the embodiment. It is explanatory drawing about the structure of an internal sensor. 1 is a block diagram illustrating an electrical configuration of an image forming apparatus according to an embodiment. It is explanatory drawing about the shift | offset | difference of the positional relationship of a LED head and a photosensitive drum. It is explanatory drawing about the influence which the shift | offset | difference of the positional relationship of a LED head and a photosensitive drum has on an image. It is a graph which shows the relationship between input density and output density. It is explanatory drawing of the dither matrix for normality. It is explanatory drawing of the dither matrix for abnormalities. It is explanatory drawing about the voltage change of the surface of a photosensitive drum. It is explanatory drawing of a density patch. It is a flowchart of the matrix selection process of 1st Embodiment. It is a flowchart of a printing process. It is explanatory drawing of the image for visual confirmation. It is an enlarged view of a low density part confirmation image. It is an enlarged view of a high density part confirmation image. It is a flowchart of the matrix selection process of 2nd Embodiment. It is a flowchart of the matrix selection process of 3rd Embodiment. FIG. 6 is an explanatory diagram of an image in a state where toner in a state with a positional deviation and toner in a state without a positional deviation are mixed. It is a flowchart of the matrix selection process of 4th Embodiment.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. First Embodiment]
First, the first embodiment will be described.

[1-1. overall structure]
FIG. 1 is a side sectional view showing a schematic configuration of an image forming apparatus 1 according to the first embodiment. In the following description, the left side in FIG. 1 is the front, and the near side in FIG. 1 is the right.

  The image forming apparatus 1 is a direct transfer tandem type color printer, and includes a substantially box-shaped housing 2 as shown in FIG. A front cover 3 is provided on the front surface of the housing 2. A paper discharge tray 5A on which paper 4 as a recording medium after image formation is stacked is formed on the upper surface of the housing 2, and the paper discharge tray 5A is provided integrally so that the image forming apparatus 1 is located upward. The top cover 5 is provided so as to be openable and closable around the upper rear end of the image forming apparatus 1 (see FIG. 2). By opening the top cover 5, an image forming unit 30 and a belt unit 20 to be described later can be drawn upward from the inside of the housing 2.

  A paper feed tray 7 that accommodates paper 4 for forming an image is attached to the lower portion of the housing 2 so as to be able to be drawn forward. A pressure plate (not shown) that can be tilted so as to stack and support the paper 4 and lift the front end side of the paper 4 is provided in the paper feed tray 7. Further, a paper feed roller 11 that conveys the paper 4 is provided at a position above the front end of the paper feed tray 7, and a paper that is conveyed by the paper feed roller 11 on the downstream side in the paper conveyance direction by the paper feed roller 11. A separation roller 12 and a separation pad 13 are provided for separating the four pieces one by one.

  The uppermost sheet 4 in the sheet feeding tray 7 is separated one by one by the separation roller 12 and further conveyed while being sandwiched between a paper dust removing roller 14 and a counter roller 15, and a pair of registration rollers 16, Sent between 17. The registration rollers 16 and 17 send the paper 4 onto the rear belt unit 20 at a predetermined timing.

The belt unit 20 is attachable to and detachable from the housing 2, and the conveyor belt 2 is installed horizontally between a belt driving roller 21 and a tension roller 22 that are spaced apart from each other in the front-rear direction.
3 (so-called transfer conveyance belt). The transport belt 23 is an endless belt made of a resin material such as polycarbonate, and the paper placed on the upper surface thereof is circulated in the clockwise direction in FIG. 1 when the rear belt drive roller 21 is rotationally driven. 4 is conveyed backward.

  Inside the conveyance belt 23, four transfer rollers 24 arranged to face each photosensitive drum 31 included in the image forming unit 30 to be described later are arranged at regular intervals in the front-rear direction, and a transfer corresponding to each photosensitive drum 31. The conveyance belt 23 is sandwiched between the rollers 24. When transferring a toner image, which will be described later, a transfer bias is applied between the transfer roller 24 and the photosensitive drum 31, and a predetermined amount of transfer current is applied.

  The image forming unit 30 is paired with four LED heads 40 that expose the surface of the photosensitive drum 31, and corresponds to each color of black (K), yellow (Y), magenta (M), and cyan (C) from the front. The image forming unit 30 and the LED head 40 are arranged in series along the conveyance direction of the paper 4. The LED head 40 includes a plurality of LEDs arranged in a line along the main scanning direction (left-right direction), and a lens (optical system) that collects irradiation light from the LEDs on the surface of the photosensitive drum 31.

  Each image forming unit 30 includes a photosensitive drum 31, a toner storage chamber 33, a developing roller 35, and the like. The photosensitive drum 31 includes a grounded metal drum main body, and is configured by covering the surface layer with a positively chargeable photosensitive layer. The surface of the photosensitive drum 31 is uniformly positively charged by a charging wire (not shown) at the time of rotation, and then exposed to a plurality of LEDs arranged in a row at the lower end of the LED head 40, so that the sheet 4 is exposed. An electrostatic latent image corresponding to the image to be formed is formed.

  Here, print data representing an image to be formed on the paper 4 (image for printing) is transmitted from, for example, an external personal computer. Then, the image forming apparatus 1 according to the present embodiment converts print data (256-gradation image data expressed in the RGB color system in this embodiment) transmitted from the outside into a CMYK table corresponding to the toner color. A color conversion process for converting to color image data is performed. Further, binarization processing is performed to binarize the image data after color conversion processing (256-level CMYK data) and generate binary image data of each color of CMYK. In this binarization processing, for each pixel of the image represented by the image data, an input level (0 to 255) that is the pixel value and a threshold value of a dither matrix (1 to 255) prepared in advance are set. If the input level is greater than or equal to the threshold value, the dot at that location is turned on, and if the input level is less than the threshold value, the dot at that location is turned off. Based on the binary image data of each color generated in this way, an image represented by the binary image data is formed as an electrostatic latent image on the surface of the photosensitive drum 31 by the LED head 40 corresponding to each color.

  In the toner storage chamber 33, positively chargeable nonmagnetic one-component toners of CMYK colors are stored as developers. The toner stored in the toner storage chamber 33 is positively frictionally charged by the rotation of the developing roller 35 or the like, and is carried on the developing roller 35 as a thin layer having a constant thickness. Next, the electrostatic latent toner formed on the surface of the photosensitive drum 31 when the positively charged toner carried on the developing roller 35 comes into contact with the photosensitive drum 31 by the rotation of the developing roller 35. Supplied to the image. As a result, the electrostatic latent image on the photosensitive drum 31 is visualized, and a toner image (a visible image formed by the toner) in which toner is attached only to the exposed portion is carried on the surface of the photosensitive drum 31. The

  Thereafter, the toner image carried on the surface of each photosensitive drum 31 is sequentially applied to the paper 4 by the transfer current when the paper 4 conveyed by the conveyance belt 23 passes between the photosensitive drum 31 and the transfer roller 24. Transcribed. The paper 4 on which the color image is formed by transferring the toner images of the respective colors in this manner is then conveyed to the fixing device 50.

  The fixing device 50 is disposed behind the conveyance belt 23 in the housing 2. The fixing device 50 includes a heating roller 51 that is rotationally driven with a heat source such as a halogen lamp, and a pressure roller 52 that is disposed below the heating roller 51 so as to face the heating roller 51 and is driven to rotate. It has. In the fixing device 50, the toner image (color image) is fixed to the paper 4 by heating the paper 4 on which the toner image of each color is transferred while being nipped and conveyed by the heating roller 51 and the pressure roller 52. . The sheet 4 on which the toner image is fixed is further conveyed by a conveying roller 53 disposed obliquely above and behind the fixing device 50, and is discharged by the discharge roller 54 provided on the upper portion of the housing 2. It is discharged onto the tray 5A.

  In addition, an internal sensor 60 is provided at a position facing the surface of the conveyor belt 23 obliquely below the belt driving roller 21. As will be described in detail later, the internal sensor 60 detects the density patch P and the like when the density patch P (see FIG. 3) and the like are formed on the transport belt 23 by the image forming unit 30. Further, a well-known belt cleaner 99 for erasing density patches P and the like formed on the surface of the conveyor belt 23 abuts on the lower surface of the conveyor belt 23 installed between the belt driving roller 21 and the tension roller 22. ing.

  As shown in FIG. 2, the top cover 5 rotates around a shaft 5 </ b> B disposed at the rear end thereof in the left-right direction (that is, the direction orthogonal to the moving direction of the conveyor belt 23). The four LED heads 40 are slidably connected to the lower surface via connection links (not shown). Therefore, by opening the top cover 5, each LED head 40 can be separated from the photosensitive drum 31 as shown in FIG. 2, and by closing the top cover 5, each LED head as shown in FIG. 40 can be disposed at a position facing the photosensitive drum 31.

  As shown in FIG. 3A, the internal sensor 60 is provided in the vicinity of one end portion of the conveyor belt 23 in the left-right direction so as to face the lower surface of the conveyor belt 23 folded back by the belt driving roller 21. Yes. Note that the internal sensor 60 may be disposed opposite to the conveyor belt 23 that is curved along the surface of the belt driving roller 21 as shown in FIG.

[1-2. Electrical configuration]
Next, the electrical configuration of the image forming apparatus 1 will be described with reference to the block diagram of FIG. In addition, illustration and description are abbreviate | omitted about a structure with little relation with the characteristic part of this invention.

As shown in FIG. 1, the image forming apparatus 1 includes a control unit 70, an operation unit 71, a display unit 72, a communication unit 73, and a storage unit 74 in addition to the LED head 40 and the internal sensor 60 described above.
The control unit 70 is a computer that comprehensively controls each unit of the image forming apparatus 1 and includes a CPU, a ROM, a RAM, and the like. The CPU executes a matrix selection process (FIG. 12), a printing process (FIG. 13), and the like, which will be described later, according to a program stored in the ROM.

The operation unit 71 is an input device for inputting a command by an external operation from a user, and includes various operation buttons.
The display unit 72 is an output device for displaying various information as an image that can be visually recognized by the user, and a small liquid crystal display is used.

The communication unit 73 is an interface for performing data communication with an external device (in this embodiment, the personal computer 80).
The storage unit 74 is a nonvolatile storage device that can rewrite stored data, and a flash memory is used in this embodiment. The storage unit 74 stores a normal dither matrix and an abnormal dither matrix, which will be described later.

[1-3. Overview of processing]
Next, an outline of processing executed by the image forming apparatus 1 of the first embodiment will be described.
In the image forming apparatus 1, the LED head 40 and the photosensitive drum 31 are caused by various factors such as a position shift when the LED head 40 is assembled, a position shift caused by opening and closing the top cover 5, a variation in member accuracy, a member deterioration, and the like. It is conceivable that there is a deviation in the positional relationship between

  5A and 5B show a normal state in which the positional relationship between the LED head 40 and the photosensitive drum 31 is not displaced (hereinafter referred to as “the state without positional displacement”) viewed from the front and above. It is a schematic diagram. On the other hand, FIGS. 5C and 5D show a state in which the positional relationship between the LED head 40 and the photosensitive drum 31 is shifted (hereinafter referred to as “the state with positional shift”) as viewed from the front and above. It is a schematic diagram.

  When there is a positional deviation, the optical path lengths L1 and L2 (FIG. 5C) from the LED disposed at the lower end of the LED head 40 to the surface of the photosensitive drum 31 are normal optical paths when there is no positional deviation. It may be different from the length L0 (FIG. 5A). When the optical path length changes in this way, the focus of the LED is deviated from the surface of the photosensitive drum 31, and the light from the LED does not converge on the surface of the photosensitive drum 31, so that the electrostatic latent image is not properly formed. . Specifically, the voltage change on the surface of the photosensitive drum 31 becomes dull, and the toner does not adhere correctly or adheres to a location outside the target.

  6A to 6D are enlarged views of images printed with only black toner. Among these, FIG. 6A is an enlarged image of a light portion (low-density image) of the image without a positional shift, and FIG. 6B is a light portion of the image with a positional shift. It is an enlarged image. On the other hand, FIG. 6C is an enlarged image of a dark portion (high-density image) of an image without a positional shift, and FIG. 6D is an enlarged image of the dark portion with a positional shift.

  As shown in these figures, in the light portion of the image, isolated dots that are clearly formed in a state without misalignment (FIG. 6A) are correctly formed in a state with misalignment (FIG. 6B). It becomes a state of being blurred without being. On the other hand, in the dark part of the image, the dot-free (blank) portion that is clearly formed in the state without misalignment (FIG. 6C), and the toner in the state with misalignment (FIG. 6D). Crushing occurs due to factors such as scattering.

  Therefore, as shown in FIG. 7, the output density (measured density of the actually formed toner image) with respect to the input density (density based on the binary image data) is not misaligned when there is misalignment (dotted line). Compared to the above state (solid line), the density characteristic of the light part decreases and the density of the dark part increases conversely (hereinafter referred to as “position shift characteristic”).

  Therefore, the image forming apparatus 1 according to the present embodiment determines whether the focus position of the LED head 40 is normal (whether the position is not misaligned or is not misaligned). The determination is made for each of the LED head 40 and the photosensitive drum 31 (for each color of CMYK). Based on the determination result, a dither matrix used for generating binary image data is independently selected for each color of CMYK from two types of dither matrices.

Specifically, when it is determined that the focus position of the LED head 40 is not normal, a low-density image is expressed deeper and higher than the normal dither matrix selected when it is determined normal. An abnormal dither matrix having a threshold value set so that an image of density is expressed lightly is selected.

  The normal dither matrix used in this embodiment has a size of 24 × 24 as shown in FIG. 8A, and one or more threshold values “1” to “255” are arranged. , 0 to 255 gradations (256 gradations) corresponding to each input level are expressed by a plurality of halftone dots.

  In this normal dither matrix, at least the lowest threshold value “1” and the highest threshold value “255” are arranged in isolation. That is, in the state of the input level “1”, the dot is turned on only at the location of the threshold “1”, and in the state of the input level “254”, the dot is turned off only at the location of the threshold “255”. The threshold value is set so that a dot or a non-dot (blank) portion is formed in an isolated size with a size of one dot.

  Specifically, in the present embodiment, as shown in FIG. 8B, dots (halftone dots) at threshold values “1” to “15” formed in the state of the input level “15”, As shown in FIG. 8C, the non-dotted portions of the threshold values “241” to “255” formed in the state of the input level “240” are all isolated by the size of one dot. The threshold is set so as to be formed.

  On the other hand, the abnormal dither matrix used in the present embodiment is also 24 × 24 size as shown in FIG. 9A, and one or more threshold values “1” to “255” are arranged. This corresponds to the normal dither matrix (FIG. 8A). However, the abnormal dither matrix is different from the normal dither matrix in that at least the lowest threshold value “1” and the highest threshold value “255” are arranged side by side in the horizontal direction. Different.

  Specifically, in the present embodiment, as shown in FIG. 9B, dots (halftone dots) at threshold values “1” to “16” formed in the state of the input level “16”, As shown in FIG. 9C, the non-dotted portions of the threshold values “240” to “255” formed in the state of the input level “239” are all formed in the size of two dots. The threshold is set so that Conversely, in the abnormal dither matrix, the threshold value is set so that the dot or no-dot portion is not arranged so as to be isolated in the size of one dot unlike the normal dither matrix.

  FIG. 10A is a graph showing the voltage change on the surface of the photosensitive drum 31 when an isolated dot for one dot is arranged (the vertical axis is voltage and the horizontal axis is the position in the main scanning direction). A boundary line (a straight line indicated by a broken line) along the horizontal axis is a boundary line as a measure of whether or not a large amount of toner adheres, and the higher the boundary line, the easier the toner adheres. As shown in this graph, the voltage change in the state with misalignment (curve indicated by the dotted line) is more gradual than the voltage change in the state without misalignment (curve indicated by the solid line). Since the exceeding part becomes small, it is difficult for the toner to adhere.

  FIG. 10B is a graph showing a change in voltage when two dots are continuously arranged in the horizontal direction in a state where there is a positional deviation. As shown in this graph, the voltage change for one dot (curve indicated by a dotted line) is added by two, resulting in a voltage change indicated by a two-dot chain line, and the portion beyond the boundary line is increased, so that the toner easily adheres. .

FIG. 10C is a graph showing a voltage change when a dotless portion is continuously arranged in the horizontal direction by two dots. As shown in this graph, the voltage change in the state of misalignment (
The curve (shown by the dotted line) has a gradual peak and wider skirt compared to the voltage change (curve shown by the solid line) without any misalignment, so the voltage also changes in the blank area, and the toner is applied to this area. A small amount of toner tends to adhere (toner scatters easily). When toner adheres, the collapse occurs as described above. Therefore, the threshold value is set in the abnormal dither matrix so that the dark space is formed larger than the normal dither matrix.

  Here, the determination of whether there is no misalignment or a misalignment is made based on whether the measurement result of the density patch P has misregistration characteristics. Specifically, at the timing when the power of the image forming apparatus 1 is turned on, as shown in FIG. 3A, at one end in the left-right direction of the conveyor belt 23, a plurality of stages of CMYK colors (in this example, A toner image representing the density of the five levels is formed as a density patch P, and the density of the formed density patch P is measured by the internal sensor 60.

  Note that the determination timing is merely an example, and other timing may be used. In particular, in the image forming apparatus 1 of the present embodiment, the LED head 40 is swingably connected to the lower surface of the top cover 5 as described above, and the position of the LED head 40 is shifted by opening and closing the top cover 5. Since there is a possibility, it is also effective to set the timing at which the top cover 5 is closed instead of (or at the same time as) the timing when the power is turned on. Moreover, it is good also as the timing instruct | indicated by the user.

  As shown in FIG. 11A, the density patch P represents a solid image of each color of CMYK in five levels of density of 20%, 40%, 60%, 80%, and 100%. This is binarized with a dither matrix for density patches shown in (B). The binarized dot arrangement pattern for each density is as shown in FIGS. 11C to 11G. For example, if the density patch P has a density of 20%, “1” in FIG. A pattern in which toner adheres to a portion is arranged in a pattern corresponding to the size of the density patch P.

  Then, when the measurement result of the density patch P has the position shift characteristic, it is determined that there is a position shift. Specifically, for each color of CMYK, each measurement result of five levels of density is linearly interpolated to obtain a measurement density line (dotted line shown in FIG. 7) based on the measurement result. Then, the integration of the difference between this measured density line and a normal density line (solid line shown in FIG. 7 and stored in advance as a judgment reference value) based on the density without misalignment (in the normal state). Based on the value, it is determined whether or not it has misalignment characteristics.

  For example, the integrated value of the value obtained by subtracting the “value on the measured density line” from the “value on the normal density line” in the range of the input density less than 50% with the input density of 50% as a boundary (in other words, the normal density line From the “value on the measured density line” to the “normal density line” in the range where the input density is 50% or more. When the condition that the integral value (in other words, the area of the region formed between the measurement density line and the normal density line) is less than or equal to the second determination reference value is satisfied, It determines with having a position shift characteristic. By determining with the integral value in this way, even when there are some variations in the measurement results, it is possible to detect the misregistration characteristics based on the overall tendency.

  Note that the value of the output density relative to the input density may deviate due to secular changes (such as changes over time or changes due to the operation amount), but it is normal for the output density to change in the overall increase direction. . Therefore, a change in output density due to a secular change and a change in output density due to a positional deviation of the LED head 40 can be distinguished based on characteristics of how the output density is shifted.

[1-4. Specific processing procedure]
Next, a specific processing procedure executed by the control unit 70 to realize the above-described processing will be described.

First, matrix selection processing executed by the control unit 70 when the power of the image forming apparatus 1 is turned on will be described with reference to the flowchart of FIG.
When the matrix selection process is started, the control unit 70 first performs a process for forming the density patch P (FIG. 11A) on the transport belt 23 in S101.

Subsequently, in S102, a process for measuring the density of the density patch P formed on the transport belt 23 in S101 by the internal sensor 60 is performed.
Subsequently, in S103, one unprocessed color (a color that has not been processed in S105 or S106 to be described later and is specified in S108 to be described later) is selected from the four CMYK colors, and the color is selected. Analyze the measurement results for color. Specifically, as described above, a calculation process is performed in which the measurement result is linearly interpolated to obtain an integral value.

Subsequently, in S104, it is determined whether or not the measurement result of the density patch P has a positional deviation characteristic.
If it is determined in S104 that the position deviation characteristic is not present, the process proceeds to S105, and a dither matrix (hereinafter referred to as “used dither matrix”) used for binarization processing (S203 described later) is normally used. Set to dither matrix. Thereafter, the process proceeds to S107.

  On the other hand, if it is determined in S104 that the position deviation characteristic is present, the process proceeds to S106, and the use dither matrix is set to the abnormal dither matrix. Thereafter, the process proceeds to S107.

In S107, it is determined whether or not the processing has been completed for all four colors of CMYK.
If it is determined in S107 that the processing has not been completed for all four colors (there is an unprocessed color), the process proceeds to S108, and the process target color is set to the next color (the unprocessed color). Change to one of them). Thereafter, the process returns to S103.

On the other hand, if it is determined in S107 that the process has been completed for all four colors, the matrix selection process is terminated.
Next, a printing process executed by the control unit 70 in response to receiving a print command for an image represented by print data (256 gradation RGB data) will be described with reference to a flowchart of FIG.

  When starting the printing process, the control unit 70 first acquires unprocessed pixel data for one pixel from pixel data (RGB values) that are data in pixel units constituting an image represented by the print data in S201. To do.

Subsequently, in S202, pixel data is converted into CMYK values of 256 gradations by executing color conversion processing using the used color profile.
Subsequently, in S203, the binarization process is executed using the set use dither matrix (the dither matrix set in the process of S105 or S106 described above).

Subsequently, in S204, it is determined whether or not the processing has been completed for all the pixels constituting the image represented by the print data.
If it is determined in S204 that the processing has not been completed for all pixels (there are unprocessed pixels), the process returns to S201.

  On the other hand, if it is determined in S204 that the processing has been completed for all the pixels, the process proceeds to S205, and print processing is executed based on the binary image data generated by the binarization processing. Thereafter, the printing process is terminated.

[1-5. effect]
As described above, in the image forming apparatus 1 according to the first embodiment, when it is determined that the focus position of the LED head 40 is not normal, the low density image is expressed darkly and the high density image is thin. Binary image data is generated using the abnormal dither matrix in which threshold values are set so as to be expressed (S106, S203). In the binary image data generated using the abnormal dither matrix, the isolated dots of the low density image and the non-dot portions of the high density image are larger than normal, so that the misregistration characteristics can be relaxed. As a result, it is possible to easily suppress a decrease in image reproducibility due to the focal position shift of the LED head 40.

  In addition, the abnormality dither matrix used in the first embodiment has one or more threshold values “1” to “255” arranged similarly to the normal dither matrix (threshold values are continuous). Therefore, gradation (256 gradations) corresponding to each input level from 0 to 255 can be expressed. Accordingly, it is possible to suppress a decrease in image reproducibility without impairing the gradation of print data.

  Further, in the image forming apparatus 1 of the first embodiment, it is determined for each color whether or not the focus position of the LED head 40 is normal, and the used dither matrix is selected independently for each color. Therefore (S103 to S108), a dither matrix suitable for each color can be selected.

  In particular, in the image forming apparatus 1 according to the first embodiment, the matrix selection process is executed when the power of the image forming apparatus 1 is turned on. It is possible to prevent the normal dither matrix from being used for a long time.

[1-6. Correspondence with Claims]
In the first embodiment, the photosensitive drum 31 corresponds to a photosensitive member, and the LED head 40 corresponds to an exposure unit (LED is a light emitting element). The control unit 70 that executes the processes of S103 to S108 corresponds to an image processing apparatus. In particular, the control unit 70 that executes the processes of S103 and S104 is a determination unit, and the control unit 70 that executes the processes of S105 and S106. Each corresponds to a selection means.

[2. Second Embodiment]
Next, a second embodiment will be described.
[2-1. overall structure]
The image forming apparatus 1 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in the contents of matrix selection processing executed by the control unit 70. In addition, since the basic configuration is the same as that of the first embodiment, the same reference numerals are used for the common parts and the description thereof is omitted, and differences will be mainly described.

[2-2. Overview of processing]
An outline of processing executed in the image forming apparatus 1 of the second embodiment will be described.
The image forming apparatus 1 according to the second embodiment is different from the image forming apparatus 1 according to the first embodiment in a determination method for determining which of the state without misalignment and the state with misalignment. In other words, in the image forming apparatus 1 according to the first embodiment, the determination as to which of the no-shift state and the mis-position state is made depends on whether the measurement result of the density patch P has a mis-position characteristic. Like to do.

  On the other hand, in the image forming apparatus 1 of the second embodiment, the user is allowed to determine which of the state without displacement and the state with displacement. Specifically, a visual confirmation image 100 (FIG. 14) for allowing the user to visually recognize the misregistration characteristics is printed on the paper 4, and an instruction (determination result) input from the user based on the visual confirmation image 100 is used. Then, it is determined whether or not there is a positional deviation.

  As shown in FIG. 14, the visual confirmation image 100 includes low-density image confirmation images 110 </ b> C, 110 </ b> M, 110 </ b> Y, and 110 </ b> K for each color of CMYK for visually confirming the printed state of the low-density image, and the printed state of the high-density image. For high density portion confirmation images 120C, 120M, 120Y, and 120K for each color of CMYK. Note that the four low-density portion confirmation images 110C, 110M, 110Y, and 110K are all the same image, and are different only in color. The same applies to the high-density portion confirmation images 120C, 120M, 120Y, and 120K.

FIG. 15 is an enlarged view of the low density portion confirmation image 110K. In addition, although the low density part confirmation image 110K of black is illustrated here, the same applies to other colors.
In the low-concentration portion confirmation image 110K, four confirmation marks 111 each having four visual dots 112 arranged in a square frame 113 are arranged vertically and horizontally (16 in total). The size of the visual dot 112 in the mark 111 differs depending on the arrangement position of the confirmation mark 111.

  Specifically, the horizontal width of the visual dot 112 in the confirmation mark 111 arranged in the leftmost column (“× 1” column) is one dot, and the horizontal width is shifted every time the column is shifted to the right. It increases by one dot, and in the rightmost column (“× 4” column), the horizontal width becomes four dots. Similarly, the vertical width of the visual dot 112 in the confirmation mark 111 arranged in the uppermost row (“× 1” row) is one dot, and the vertical width every time the row is shifted downward. Increases by one dot, and the vertical width of the bottom row (“× 4” row) is four dots. That is, 16 patterns of confirmation marks 111 are arranged in which the size of the visual dot 112 is one dot each vertically and horizontally and four dots vertically and horizontally.

  The square frame 113 in each confirmation mark 111 has slits 114 formed at the center positions of the four sides, and the width (vertical width or horizontal width) of the slit 114 is the vertical width of the visual dot 112 or It corresponds to the width.

  On the other hand, FIG. 16 is an enlarged view of the high density portion confirmation image 120K. Since the high density portion confirmation image 120K is simply a reverse of the low density portion confirmation image 110K, a detailed description thereof will be omitted.

  Based on such 16 patterns of confirmation marks 111, it is possible to determine the formation state of isolated dots in a low-density image and the formation state of no-dot (blank) portion in a high-density image relatively visually. For example, let the user determine how large the isolated dot and no-dot portion can be seen, and if both the isolated dot and no-dot portion cannot be confirmed with a size of 2 dots × 2 dots, determine that the position is shifted. It becomes possible.

[2-3. Specific processing procedure]
Next, matrix selection processing executed by the control unit 70 instead of the matrix selection processing (FIG. 12) of the first embodiment will be described with reference to the flowchart of FIG. This matrix selection processing is executed at an arbitrary timing specified by the user (for example, triggered by an operation for selecting printing of the visual confirmation image from the menu displayed on the display unit 72).

When starting the matrix selection process, the control unit 70 first performs a process of printing the visual confirmation image 100 on the paper 4 in S301.
Subsequently, in S <b> 302, a determination result input screen that prompts the user to input the determination result of the visual confirmation image 100 (input operation on the operation unit 71) is displayed on the display unit 72. Specifically, a visual determination result (“deviation” or “no deviation”) is sequentially input for each color of CMYK, and an uninput color (the processing of S304 or S305 described later is performed). The second and subsequent times are specified in S307, which will be described later.) One is selected, and input of a determination result for that color is prompted.

Subsequently, in S303, it is determined whether or not the determination result input by the user on the determination result input screen displayed on the display unit 72 in S302 is “with deviation”.
If it is determined in S303 that the determination result is not “difference”, the process proceeds to S304, and the use dither matrix is set to the normal dither matrix. Thereafter, the process proceeds to S306.

  On the other hand, if it is determined in S303 that the determination result is “There is a deviation”, the process proceeds to S305, and the use dither matrix is set to the abnormal dither matrix. Thereafter, the process proceeds to S306.

In S306, it is determined whether determination results have been input for all four colors of CMYK.
If it is determined in S306 that determination results have not been input for all four colors (there is an uninput color), the process proceeds to S307 and the input color is changed to the next color (the uninput color). Change to one of them). Thereafter, the process returns to S302.

On the other hand, if it is determined in S306 that determination results have been input for all four colors, the matrix selection process is terminated.
[2-4. effect]
According to the image forming apparatus 1 of the second embodiment described above, the same effects as those of the image forming apparatus 1 of the first embodiment can be obtained. In particular, in the image forming apparatus 1 according to the second embodiment, since the user is determined to determine whether there is misalignment or not, misjudgment may occur even when misalignment characteristics occur accidentally due to other factors. Can be prevented.

[2-5. Correspondence with Claims]
In the second embodiment, the control unit 70 that executes the processes of S302 to S307 corresponds to the image processing apparatus. In particular, the control unit 70 that executes the processes of S302 and S303 performs the determination unit and the processes of S304 and S305. The control unit 70 to be executed corresponds to the selection unit.

[3. Third Embodiment]
Next, a third embodiment will be described.
[3-1. overall structure]
The image forming apparatus 1 according to the third embodiment is different from the image forming apparatus 1 according to the first embodiment in the contents of matrix selection processing executed by the control unit 70. In addition, since the basic configuration is the same as that of the first embodiment, the same reference numerals are used for the common parts and the description thereof is omitted, and differences will be mainly described.

[3-2. Overview of processing]
An overview of processing executed by the image forming apparatus 1 according to the third embodiment will be described.
The image forming apparatus 1 according to the third embodiment is different from the image forming apparatus 1 according to the first embodiment in a determination method for determining which of the state without misalignment and the state with misalignment. In other words, in the image forming apparatus 1 according to the first embodiment, the determination as to which of the no-shift state and the mis-position state is made depends on whether the measurement result of the density patch P has a mis-position characteristic. Like to do.

  On the other hand, in the image forming apparatus 1 according to the third embodiment, when the measurement result of the density patch P has the misregistration characteristic, the visual confirmation image 100 is printed on the paper 4, and the visual confirmation image 100 is printed by the user. And make the judgment result input. That is, a determination method that combines the determination method of the first embodiment and the determination method of the second embodiment is employed.

[3-3. Specific processing procedure]
Next, matrix selection processing executed by the control unit 70 instead of the matrix selection processing (FIG. 12) of the first embodiment will be described with reference to the flowchart of FIG. This matrix selection process is executed when the power of the image forming apparatus 1 is turned on, as in the first embodiment.

When the matrix selection process is started, the control unit 70 first performs a process for forming the density patch P (FIG. 11A) on the transport belt 23 in S401.
Subsequently, in S402, processing for measuring the density of the density patch P formed on the conveyance belt 23 in S401 by the internal sensor 60 is performed.

Subsequently, in S403, the measurement result for each color of CMYK is analyzed. Specifically, as described above, a calculation process is performed in which the measurement result is linearly interpolated to obtain an integral value.
Subsequently, in S404, it is determined whether or not a color having a misregistration characteristic exists in the measurement result of the density patch P of each color of CMYK.

  If it is determined in S404 that there is no color having misregistration characteristics, the process proceeds to S412 and the use dither matrix is set as the normal dither matrix for all four CMYK colors. Thereafter, the matrix selection process is terminated.

On the other hand, if it is determined in S404 that there is at least one color having misregistration characteristics,
The process proceeds to S405. Subsequent processing (S405 to S411) is the same as the matrix selection processing (S301 to S307) of the second embodiment, and thus description thereof is omitted.

[3-4. effect]
According to the image forming apparatus 1 of the third embodiment described above, the same effects as those of the image forming apparatus 1 of the first embodiment can be obtained. In particular, in the image forming apparatus 1 according to the third embodiment, the matrix selection process is executed when the power of the image forming apparatus 1 is turned on. It is possible to prevent the normal dither matrix from being used for a long time. In addition, since the user is surely determined whether or not there is misalignment, misjudgment can be prevented even when misalignment characteristics occur accidentally due to other factors. .

[3-5. Correspondence with Claims]
In the third embodiment, the control unit 70 that executes the processes of S403 to S411 corresponds to an image processing apparatus. In particular, the control unit 70 that executes the processes of S403 to S407 performs the determination unit, and the processes of S408 and S409. The control unit 70 to be executed corresponds to the selection unit.

[4. Fourth Embodiment]
Next, a fourth embodiment will be described.
[4-1. overall structure]
The image forming apparatus 1 according to the fourth embodiment is different from the image forming apparatus 1 according to the first embodiment in the contents of matrix selection processing executed by the control unit 70. In addition, since the basic configuration is the same as that of the first embodiment, the same reference numerals are used for the common parts and the description thereof is omitted, and differences will be mainly described.

[4-2. Overview of processing]
An outline of processing executed in the image forming apparatus 1 according to the fourth embodiment will be described.
The image forming apparatus 1 according to the fourth embodiment is different from the image forming apparatus 1 according to the first embodiment in a method for selecting a use dither matrix. That is, in the image forming apparatus 1 according to the first embodiment, it is determined for each color whether or not the focus position of the LED head 40 is normal, and the use dither matrix is selected independently for each color. .

  On the other hand, in the image forming apparatus 1 of the fourth embodiment, it is determined for each color whether or not the focus position of the LED head 40 is normal, and there is even one color determined to be not normal. First, the LED head 40 of the color determined to be normal is put into a pseudo-normal state. Then, an abnormal dither matrix is selected for all colors.

  This is done for the following reason. That is, the method of using a dedicated dither matrix (abnormality dither matrix) in a state where there is a positional deviation is used when the LED heads 40 of all CMYK four colors are in a state where there is a positional deviation or when printing is performed in a single color. Especially effective. However, if the four LED heads 40 are both misaligned and misaligned, the toner image formed for each color will vary in expression. There may be a problem that the combined color image is not properly expressed.

More specifically, when an abnormal dither matrix is used for a color with a positional deviation, toner adheres, but as shown in FIG. Compared to the voltage change (FIG. 10A) in the case where the minute isolated dots are arranged, the mountain is spread as a whole, so that the toner is fixed throughout the mountain.

  On the other hand, in the color without misalignment, the toner is concentrated and fixed in a narrow range. Therefore, the color with no misalignment is scattered and fixed, and the color without misalignment is fixed. The toner clearly forms dots and fixes them.

  FIG. 19A is an enlarged image showing a state in which the magenta toner with a positional deviation and the black toner without a positional deviation overlap. As shown in this figure, it is conceivable that a dot of a color without displacement (black in this example) becomes conspicuous and the user recognizes it as a pattern.

  Therefore, in the image forming apparatus 1 according to the fourth embodiment, by adjusting parameters that affect the voltage change such as the amount of light, the lighting time, and the bias of the LED head 40 in a color in which there is no positional deviation, Make the voltage change the same as the voltage change. In addition, an abnormal dither matrix is also used for the color without any positional deviation.

[4-3. Specific processing procedure]
Next, matrix selection processing executed by the control unit 70 instead of the matrix selection processing (FIG. 12) of the first embodiment will be described with reference to the flowchart of FIG. This matrix selection process is executed when the power of the image forming apparatus 1 is turned on, as in the first embodiment.

When the matrix selection process is started, the control unit 70 first performs a process for forming the density patch P (FIG. 11A) on the transport belt 23 in S501.
Subsequently, in S502, processing for measuring the density of the density patch P formed on the conveyance belt 23 in S501 by the internal sensor 60 is performed.

In step S503, the measurement result for each color of CMYK is analyzed. Specifically, as described above, a calculation process is performed in which the measurement result is linearly interpolated to obtain an integral value.
Subsequently, in S504, it is determined whether or not there is a color having misregistration characteristics in the measurement result of the density patch P of each color of CMYK.

  If it is determined in S504 that there is no color having misregistration characteristics, the process proceeds to S505, and the use dither matrix is set to the normal dither matrix for all four CMYK colors. Thereafter, the matrix selection process is terminated.

  On the other hand, if it is determined in S504 that there is even one color having misregistration characteristics, the process proceeds to S506, and the color to be processed (process color) is set to black in the subsequent processes (S507 to S511). To do.

Subsequently, in S507, it is determined whether or not the processing color measurement result has a misregistration characteristic.
If it is determined in step S507 that the measurement result of the processed color does not have misregistration characteristics, the process proceeds to step S508, and parameters relating to the voltage change of the LED head 40 of the processed color (light quantity, lighting time, bias, etc.). Is changed by a predetermined amount. Specifically, for example, a method of reducing the voltage applied to the LED or reducing the lighting time (duty ratio) can be mentioned. By reducing the voltage and duty ratio,
Although it is possible to approximate the voltage change in the state without misalignment to the voltage change in the state with misalignment, on the contrary, the voltage change in the state without misalignment It is difficult to bring the voltage close to the voltage change (sharpening the blurred and non-dotted portions).

In step S <b> 509, processing for forming the processing color density patch P on the transport belt 23 is performed.
Subsequently, in S510, processing for measuring the density of the density patch P formed on the conveyance belt 23 in S509 by the internal sensor 60 is performed.

Subsequently, in S511, it is determined whether or not the measurement result of the processed color has a misalignment characteristic.
If it is determined in S511 that the measurement result of the processed color does not have the positional deviation characteristic, the process returns to S508, and if it is determined that the measurement result of the processed color does not have the positional deviation characteristic, the process proceeds to S512. That is, the parameter relating to the voltage change of the LED head 40 is adjusted until the measurement result of the processed color has the position shift characteristic.

On the other hand, if it is determined in S507 that the measurement result of the processed color has the misregistration characteristic, the process proceeds to S512 as it is.
In S512, it is determined whether or not the processing has been completed for all four colors of CMYK.

  If it is determined in S512 that the process has not been completed for all four colors (there is an unprocessed color), the process proceeds to S513, and the process color is changed to the next color (of the unprocessed colors). 1). Thereafter, the process returns to S508.

  On the other hand, if it is determined in S512 that the processing has been completed for all four colors, the process proceeds to S514, and the use dither matrix is set to the abnormal dither matrix for all four CMYK colors. Thereafter, the matrix selection process is terminated.

[4-4. effect]
According to the image forming apparatus 1 of the fourth embodiment described above, the same effects as those of the image forming apparatus 1 of the first embodiment can be obtained.

  In particular, in the image forming apparatus 1 according to the fourth embodiment, when there is at least one of the four LED heads 40 in which the focus position is determined to be not normal, it is determined to be normal. Is set in a pseudo-normal state, and an abnormal dither matrix is selected for all colors. For this reason, even when the focus positions of the four LED heads 40 are normal and the focus positions are not normal, a color image can be appropriately expressed.

  FIG. 19B is an enlarged view showing a state in which the magenta toner in a state where there is misalignment and the black toner in a state where there is no misalignment but which is close to a state where there is a pseudo misalignment overlap. It is an image. As shown in this figure, black is also magenta and the toner is scattered and attached, and dots are formed blurry. Therefore, compared to the state shown in FIG. 19A, black dots are less noticeable. ing.

In addition, in the image forming apparatus 1 according to the fourth embodiment, the adjustment of the control amount of the LED head 40 determined to be normal is repeated until the measurement result of the density patch P has the displacement characteristic. Therefore, the state where the focus position of the LED head 40 is not normal can be appropriately reproduced.

[4-5. Correspondence with Claims]
In the fourth embodiment, the control unit 70 that executes the processes of S503 to S514 corresponds to an image processing apparatus. In particular, the control unit 70 that executes the processes of S503, S504, and S507 is a determination unit, and S505 and S514. The control unit 70 that executes processing corresponds to the selection unit.

[5. Other forms]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  For example, in each of the above embodiments, an abnormal dither matrix in which two dots or no-dot portions are continuously arranged is illustrated, but the present invention is not limited to this and is lower than the normal dither matrix. Any threshold value may be used as long as the density image is expressed darkly and the high density image is expressed lightly.

  Further, in each of the above embodiments, the configuration in which only one type of dither matrix is used as the abnormality dither matrix is illustrated, but the present invention is not limited to this, and a plurality of types of abnormality dither matrices are prepared and used properly. Also good. For example, the abnormality dither matrix exemplified in each of the above embodiments is such that a threshold is set so that a dot or no-dot portion is arranged in a size of 2 dots × 1 dot. For example, a plurality of types of abnormality dither matrices, such as 2 dots.times.2 dots, 3 dots.times.3 dots, etc., having different arrangement sizes of dots and non-dot portions are prepared. In this way, it is possible to select a more appropriate dither matrix depending on the degree of misalignment characteristics.

  Further, in each of the above-described embodiments, examples of the determination method of whether or not there is a positional deviation include a method for determining whether the density measurement result of the density patch P has a positional deviation characteristic, and a method for causing the user to make a determination. The determination method is not limited to these, and various determination methods can be used.

  On the other hand, in each of the above-described embodiments, the image forming apparatus 1 configured to form the density patch P on the transport belt 23 has been exemplified. However, the present invention is not limited thereto, and may be configured to be formed on the intermediate transfer belt. Further, it may be formed on a recording medium such as paper 4.

  In each of the above embodiments, the image forming apparatus 1 that forms a color image using a plurality of LED heads 40 has been exemplified. However, the present invention is not limited to this. For example, an image is formed using only one LED head. It may be an image forming apparatus to be formed.

Furthermore, in each said embodiment, although LED was illustrated as a light emitting element of this invention, it is not limited to this, If it has the same function, it is applicable.
In addition, in each of the above-described embodiments, the case where the image processing apparatus of the present invention is used as a component of the image forming apparatus 1 is illustrated, but the present invention is not limited to this and is separate from the image forming apparatus. Also good. For example, a personal computer in which a printer driver corresponding to the image forming apparatus is installed can be caused to function as the image processing apparatus of the present invention. Specifically, if the configuration is such that the binary image data based on the print data is generated on the personal computer side and the generated binary image data is transmitted from the personal computer to the image forming apparatus, the same as the matrix selection process described above. This process can be executed by a personal computer.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Housing, 4 ... Paper, 5 ... Top cover, 23 ... Conveyor belt, 24 ... Transfer roller, 30 ... Image forming unit, 31 ... Photosensitive drum, 33 ... Toner storage chamber, 35 ... Development Roller, 40 ... LED head, 50 ... fixer, 60 ... internal sensor, 70 ... control unit, 71 ... operation unit, 72 ... display unit, 73 ... communication unit, 74 ... storage unit, 80 ... personal computer, 99 ... belt Cleaner, 100 ... Visual confirmation image, 110C, 110M, 110Y, 110K ... Low density portion confirmation image, 111 ... Confirmation mark, 112 ... Visual dot, 113 ... Frame, 114 ... Slit, 120C, 120M, 120Y, 120K ... High density part confirmation image, P ... density patch

Claims (7)

Used in an image forming apparatus that forms an image by attaching a developer to an electrostatic latent image formed on the surface of the photosensitive member by an exposure unit that exposes the surface of the photosensitive member with a plurality of light emitting elements based on binary image data. An image processing apparatus for performing processing for generating the binary image data to be generated,
Determination means for determining whether the focus position of the exposure means is normal;
Selecting means for selecting a dither matrix used for generating the binary image data from a plurality of types of dither matrices;
With
When the determination unit determines that the focus position of the exposure unit is not normal, the selection unit expresses a low-density image darker than a case where it is determined to be normal and a high density An abnormality dither matrix in which a threshold value is set so that the image of the image is expressed lightly is selected. When the determining unit determines that the position of the focal point of the exposure unit is normal, the selecting unit is for normal use in which each of the lowest threshold value and the highest threshold value is arranged in isolation. A dither matrix is selected, and when it is determined that the condition is not normal, an abnormal dither matrix in which a plurality of the lowest threshold value and the highest threshold value are arranged side by side is selected. The image processing apparatus according to 1. The image forming apparatus includes a plurality of sets of the photosensitive member and the exposure unit, and forms a color image by superimposing developer images of different colors formed in each set,
The determination means determines whether the focus position of the exposure means is normal for each set,
The image processing apparatus according to claim 1, wherein the selection unit selects a dither matrix independently for each set. The image forming apparatus includes a plurality of sets of the photosensitive member and the exposure unit, and forms a color image by superimposing developer images of different colors formed in each set,
The determination means determines whether the focus position of the exposure means is normal for each set,
When there is at least one set in which the position of the focus of the exposure unit is determined to be not normal by the determination unit, the control amount of the light emitting element of the exposure unit of the set determined to be normal is adjusted. The adjustment means for making the position of the focal point pseudo-normal state by
The image processing apparatus according to claim 1, wherein the selection unit selects the abnormal dither matrix for all sets. The adjustment means has a density patch density measurement result representing a plurality of levels of density formed by the image forming apparatus, wherein a low density patch is thinner than a normal density and a high density patch is normal. Adjustment of the control amount of the light emitting element of the set of exposure means determined to be normal by the determination means until it has a density characteristic higher than the density of the exposure means. The image processing apparatus according to claim 4. An image forming apparatus that forms an image by attaching a developer to an electrostatic latent image formed on a surface of a photoconductor by an exposure unit that exposes the surface of the photoconductor with a plurality of light emitting elements based on binary image data. And
An image forming apparatus comprising the image processing apparatus according to any one of claims 1 to 5. Used in an image forming apparatus that forms an image by attaching a developer to an electrostatic latent image formed on the surface of the photosensitive member by an exposure unit that exposes the surface of the photosensitive member with a plurality of light emitting elements based on binary image data. A program for causing a computer to function as an image processing apparatus that performs processing for generating the binary image data,
Determination means for determining whether the focus position of the exposure means is normal;
Selecting means for selecting a dither matrix used for generating the binary image data from a plurality of types of dither matrices;
Function as a computer
When the determination unit determines that the focus position of the exposure unit is not normal, the selection unit expresses a low-density image darker than a case where it is determined to be normal and a high density A program characterized by selecting a dither matrix for abnormalities with a threshold value set so that the image of the image is lightly expressed.