Image forming apparatus

Abstract

The present invention relates to an image forming apparatus. An image forming apparatus includes at least one processor configured to generate second image data corresponding to each of a plurality of light emitting elements based on first image data, the second image information indicating whether to cause each of the plurality of light emitting elements to emit light, and to change first image data indicating that a light emitting element is to emit light to second image data indicating that the light emitting element is not to emit light based on correction information, and a circuit unit configured to supply a current to each of the plurality of light emitting elements based on the second image data.

Description

Technical Field

[0001] This invention relates to an image forming apparatus for an electrophotographic method. Background Technology

[0002] An image forming apparatus in an electrophotographic method forms an electrostatic latent image on a photosensitive member by exposing it to a photosensitive member driven to rotate, and forms an image by developing the electrostatic latent image using a toner. Note that the direction parallel to the rotation axis of the photosensitive member is called the main scanning direction. Japanese Patent Publication No. 2018-1679 discloses an image forming apparatus in which multiple chips including multiple light-emitting elements are arranged in the main scanning direction, and the image forming apparatus exposes a line in the main scanning direction. Japanese Patent Publication No. 2018-1679 discloses a configuration for correcting density inhomogeneities caused by the difference in light intensity between two chips adjacent to each other in the main scanning direction.

[0003] However, differences in light intensity can occur not only between chips but also between multiple light-emitting elements within a chip. Therefore, correcting only the differences in light intensity between chips still leaves the possibility of uneven concentration in the formed image. In other words, uneven concentration occurs in the image formed using the configuration described in Japanese Patent Publication No. 2018-1679. Summary of the Invention

[0004] According to one aspect of the present invention, an image forming apparatus includes: a photosensitive member driven to rotate; an exposure head including a plurality of light-emitting chips placed at different positions along a rotation axis of the photosensitive member, each of the plurality of light-emitting chips including a plurality of light-emitting elements placed at different positions along the rotation axis of the photosensitive member, a digital-to-analog converter outputting a voltage corresponding to a set value as a digital value, and a circuit unit supplying current to the plurality of light-emitting elements based on the voltage output from the digital-to-analog converter; and at least one processor, wherein the at least one processor is configured to generate second image data corresponding to each of the plurality of light-emitting elements based on first image data, the second image data indicating whether each of the plurality of light-emitting elements is to emit light, and to change the first image data indicating that the light-emitting element should emit light to the second image data indicating that the light-emitting element should not emit light based on correction information, and the circuit unit supplying current to each of the plurality of light-emitting elements based on the second image data.

[0005] Other features of the invention will become clear from the following description of exemplary embodiments with reference to the accompanying drawings. Attached Figure Description

[0006] Figure 1 This is a configuration diagram of an image forming apparatus according to an embodiment.

[0007] Figure 2A and Figure 2B This is a diagram showing the exposure head and photosensitive component according to an embodiment.

[0008] Figure 3A and Figure 3B This is a diagram showing the printed circuit board of the exposure head according to an embodiment.

[0009] Figure 4 This is a diagram illustrating the configuration of light-emitting elements inside a light-emitting chip according to an embodiment.

[0010] Figure 5 This is a plan view of the light-emitting chip according to an embodiment.

[0011] Figure 6 This is a cross-sectional view of the light-emitting chip according to an embodiment.

[0012] Figure 7 This is a diagram showing spots on a photosensitive element according to an embodiment.

[0013] Figure 8 This is a diagram illustrating the configuration for controlling each light-emitting chip according to an embodiment.

[0014] Figure 9 This is a block diagram of the interior of the light-emitting chip according to an embodiment.

[0015] Figure 10 This is a block diagram of the light quantity correction unit according to an embodiment.

[0016] Figures 11A to 11D This is a diagram illustrating the processing in the light quantity correction unit according to an embodiment.

[0017] Figure 12 This is a diagram showing the light quantity correction chart according to an embodiment.

[0018] Figure 13 This is a diagram illustrating the process for generating correction information according to an embodiment.

[0019] Figure 14 This is a diagram illustrating the process for generating correction information according to an embodiment.

[0020] Figure 15A and Figure 15B This is a diagram illustrating the process for generating correction information according to an embodiment. Detailed Implementation

[0021] The embodiments are described in detail below with reference to the accompanying drawings. Note that the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but the invention is not limited to requiring all such features, and multiple such features can be appropriately combined. Furthermore, in the drawings, the same reference numerals are given for the same or similar configurations, and redundant descriptions thereof are omitted.

[0022] Figure 1 This is a schematic configuration diagram of the image forming apparatus according to this embodiment. The reading unit 100 optically reads the original placed on the table and generates image data indicating the reading result. The image creation unit 103 forms an image on the sheet, for example, based on the image data generated by the reading unit 100 or based on image data received from an external device via a network.

[0023] Image creation unit 103 includes image forming units 101a, 101b, 101c, and 101d. Image forming units 101a, 101b, 101c, and 101d form black, yellow, magenta, and cyan toner images, respectively. The configurations of image forming units 101a, 101b, 101c, and 101d are similar to each other; hereinafter, they are collectively referred to as image forming unit 101. During image formation, the photosensitive element 102 of image forming unit 101 rotates clockwise as shown in the figure. A charge 107 charges the photosensitive element 102. An exposure head 106 exposes the photosensitive element 102 according to image data and forms an electrostatic latent image on the photosensitive element 102. A developer 108 develops the electrostatic latent image on the photosensitive element 102 using toner. The toner image on the photosensitive element 102 is transferred to a sheet conveyed on a transfer belt 111. Note that colors different from black, yellow, magenta, and cyan can be reproduced by transferring toner images on each photosensitive element 102 in a manner that overlaps toner images with each other.

[0024] The conveying unit 105 controls the feeding and transport of the sheet. Specifically, the conveying unit 105 feeds the sheet from designated units among the internal storage units 109a and 109b, the external storage unit 109c, and the manual feeding unit 109d to the transport path in the image forming apparatus. The fed sheet is then conveyed to the registration roller 110. The registration roller 110 conveys the sheet onto the transfer belt 111 at predetermined timings, so that the toner image on each photosensitive element 102 is transferred to the sheet. As previously described, the toner image is transferred to the sheet while it is being transported on the transfer belt 111. The fixing unit 104 applies heat and pressure to the sheet with the transferred toner image, thereby fixing the toner image onto the sheet. After the toner image is fixed, the sheet is discharged from the image forming apparatus by the discharge roller 112. Note that the optical sensor 113 is positioned facing the transfer belt 111. Optical sensor 113 detects a test chart formed by image forming unit 101 on transfer belt 111 to measure the amount of color registration misalignment. A control unit (not shown in the figures) performs color registration misalignment correction control based on the detection results of the test chart.

[0025] Figure 2A and Figure 2B The image shows a photosensitive element 102 and an exposure head 106. The exposure head 106 includes a light-emitting element group 201, a printed circuit board 202 on which the light-emitting element group 201 is mounted, a cylindrical lens array 203, and a housing 204 for attaching the cylindrical lens array 203 to the printed circuit board 202. The cylindrical lens array 203 collects light emitted by the light-emitting element group 201 on the photosensitive element 102, forming an imaging spot (hereinafter referred to as a spot) of a predetermined size on the photosensitive element 102.

[0026] Figure 3A and Figure 3B This indicates printed circuit board 202. Note that... Figure 3A This indicates that the surface on which connector 305 is mounted is... Figure 3BThis refers to the surface on which the light-emitting element group 201 is mounted (the surface opposite to the surface on which the connector 305 is mounted). In this embodiment, the light-emitting element group 201 includes 20 light-emitting chips 400-1 to 400-20. The light-emitting chips 400-1 to 400-20 are arranged in a two-row zigzag pattern along the main scanning direction. More specifically, the light-emitting chips 400-(2k-1) (where k is an integer from 1 to 10) are arranged in rows along the main scanning direction, and the light-emitting chips 400-2k are also arranged in rows along the main scanning direction. The position of the row of light-emitting chips 400-(2k-1) in the sub-scanning direction is different from the position of the row of light-emitting chips 400-2k in the sub-scanning direction. Note that the sub-scanning direction corresponds to the rotation direction of the photosensitive member 102. Furthermore, the sub-scanning direction is perpendicular to the main scanning direction. In the following description, the light-emitting chips 400-1 to 400-20 are also collectively referred to as light-emitting chips 400. Furthermore, the light-emitting chips 400-(2k-1) are referred to as the odd-numbered rows of light-emitting chips 400, and the light-emitting chips 400-2k are referred to as the even-numbered rows of light-emitting chips 400. Each light-emitting chip 400 includes multiple light-emitting elements. Each light-emitting chip 400 on the printed circuit board 202 is connected via connector 305 to the image controller 800, which serves as a control unit. Figure 8 ).

[0027] Figure 4 This diagram illustrates the configuration of the light-emitting chip 400. In the light-emitting chip 400, four sets of light-emitting elements 602 are arranged in the sub-scanning direction, each set comprising 748 light-emitting elements arranged along the main scan direction. The spacing between adjacent light-emitting elements 602 in the main scan direction is approximately 21.16 μm, corresponding to a resolution of 1200 dpi. Therefore, the length of the 748 light-emitting elements in one set in the main scan direction is approximately 15.8 mm. Note that these sets are positioned such that they are offset from each other in the main scan direction by approximately 5 μm, corresponding to a resolution of 4800 dpi. Furthermore, the light-emitting chips 400 in even-numbered rows and those in odd-numbered rows are positioned such that they overlap in the main scan direction. The spacing Ly between the light-emitting elements 602 in the even-numbered rows and those in the odd-numbered rows is, for example, approximately 105 μm.

[0028] Figure 5 This is a plan view of the light-emitting chip 400. The light-emitting chip 400 has a light-emitting unit 404 including a plurality of light-emitting elements 602. The light-emitting unit 404 is formed on the light-emitting substrate 402. Furthermore, a circuit unit 406 for controlling the light-emitting unit 404 is disposed on the light-emitting substrate 402. Lines for communicating with the image controller 800 are connected to pads 408.

[0029] Figure 6 Indicates along Figure 5 The image shows a portion of a cross-section taken by line AA. Multiple lower electrodes 504 are formed on the light-emitting substrate 402. A gap of length dx exists between two adjacent lower electrodes 504. A light-emitting layer 506 is disposed on the lower electrodes 504, and an upper electrode 508 is disposed on the light-emitting layer 506. The upper electrode 508 is a shared electrode corresponding to the multiple lower electrodes 504. When a predetermined voltage is applied between the lower electrodes 504 and the upper electrode 508, current flows from the lower electrodes 504 to the upper electrode 508, thereby causing the light-emitting layer 506 to emit light. That is, each lower electrode 504 is correspondingly disposed to a light-emitting element 602. By making the length dx large relative to the length dz between the lower electrodes 504 and the upper electrode 508, leakage current between adjacent lower electrodes 504 can be suppressed, and erroneous emission of adjacent light-emitting elements 602 can be suppressed.

[0030] For example, an organic EL film can be used as the light-emitting layer 506. Alternatively, an inorganic EL film can be used as the light-emitting layer 506. The upper electrode 508 is constructed, for example, of a transparent electrode such as indium tin oxide (ITO), allowing the emission wavelength of the light-emitting layer 506 to be transmitted. Note that although the entire upper electrode 508 allows the emission wavelength of the light-emitting layer 506 to be transmitted in this embodiment, it is not necessary for the entire upper electrode 508 to allow the emission wavelength to be transmitted. Specifically, it is sufficient for the emission wavelength to be transmitted through the area from the light beam emitted by the individual light-emitting elements 602 (corresponding to the lower electrode 504).

[0031] If used Figure 4 As described, a light-emitting chip 400 includes a plurality of light-emitting elements 602 arranged in four sets along the main scanning direction, and one set of elements adjacent to each other in the sub-scanning direction is offset by 5 μm from the other set in the main scanning direction. When exposing a line of the photosensitive element 102, the timing of the light emission of the four sets is controlled such that the line of the photosensitive element 102 is exposed. Therefore, as... Figure 7 As shown, four light-emitting elements 602 located at substantially the same position in the main scanning direction in four sets expose the photosensitive member 102 at positions offset from each other by 5 μm. In this way, a smooth electrostatic latent image is formed because the spots formed by the individual light-emitting elements 602 overlap each other. Note that although the number of sets is four in this embodiment, the number of sets can be two or more.

[0032] As described above, the exposure head 106 according to this embodiment includes 20 light-emitting chips 400 arranged in a two-row zigzag pattern along the main scanning direction, and each light-emitting chip 400 includes a plurality of light-emitting elements 602 arranged in four sets along the main scanning direction. These sets are arranged along the sub-scanning direction, and the position of one set in the main scanning direction is offset from the position of the other set in the main scanning direction by 5 μm corresponding to a resolution of 4800 dpi. Throughout the exposure head 106, the respective positions of the plurality of light-emitting elements 602 in the main scanning direction are different from each other. Note that although the positions of the plurality of light-emitting elements 602 are different in the sub-scanning direction, the emission timing of each light-emitting element 602 is adjusted so that the same line of the photosensitive member 102 is exposed. Therefore, spots formed by the plurality of light-emitting elements 602 can be formed on the photosensitive member 102 along the main scanning direction at intervals of approximately 5 μm. In the following description, the positions where the plurality of light-emitting elements 602 form spots are referred to as "dots". Furthermore, when the light-emitting element 602 emits light at a point, that point is called the "exposure point"; when the light-emitting element 602 does not emit light at a point, that point is called the "non-exposure point".

[0033] Figure 8 The image controller 800 controls the configuration of each light-emitting chip 400. Image data indicating the tonal values ​​of each pixel in the image to be formed is input to the image data generation unit 801. The image data generation unit 801 performs dithering processing (half-tone processing) on ​​the image data according to the resolution specified by the CPU 811, and outputs the processed image data to the light intensity correction unit 802. The half-tone processed image data indicates whether each point constituting the image is an exposed point or an unexposed point. In other words, the half-tone processed image data indicates whether the light-emitting element 602 corresponding to each point emits light. The light intensity correction unit 802 performs light intensity correction on the image data based on correction information, and outputs the light intensity corrected image data to the chip data conversion unit 803. The synchronization signal generation unit 804 generates a line synchronization signal (Lsync) 808. The line synchronization signal 808 is used to determine the data portion corresponding to a line of the photosensitive element 102 in the main scanning direction from the image data. The chip data conversion unit 803 synchronously sends image data (DATA) 807 corresponding to one line to each light-emitting chip 400 in conjunction with the line synchronization signal 808. Note that the chip select signal (CS) 805 indicates which light-emitting chip 400 the image data 807 is addressed to. In addition, the chip data conversion unit 803 sends a clock signal (CLK) 806 to each light-emitting chip 400.

[0034] The correction information, described later, is stored in storage unit 810 of printed circuit board 202. Note that... Figure 8 The blocks shown are configured to exchange various types of information via the transmission and reception of control signals (CTL) 809. When image data 807 is received from the chip data conversion unit 803, each light-emitting chip 400 performs a light-emitting action according to the received image data 807 at the input timing of the next line synchronization signal 808.

[0035] Figure 9 This is a block diagram of the light-emitting chip 400. The digital-to-analog converter (D / A) 901 outputs an analog voltage corresponding to a digital value, which is a setpoint set by the CPU 811. This digital value is indicated by calibration information; the CPU 811 determines the digital value to be set for the D / A 901 in each light-emitting chip 400 by reading the calibration information stored in the storage unit 810. The light-emitting elements 602 in the light-emitting chip 400 are grouped into multiple blocks in the main scan direction. Each group is provided with a corresponding reference current source 902. Figure 9 In this design, the light-emitting elements 602 are grouped into five groups, and therefore the light-emitting chip 400 includes reference current sources 902-1 to 902-5 corresponding to these groups. Reference current sources 902-1 to 902-5 output a reference current to each light-emitting element 602 in its corresponding group, corresponding to the output value (i.e., analog voltage) from the D / A 901. In this way, the D / A 901 serves as a current control unit for controlling the reference current to the light-emitting elements 602. The amount of light emitted by the light-emitting elements 602 is controlled based on the reference current output from the corresponding reference current source 902.

[0036] Figure 10 This is a block diagram of the light intensity correction unit 802. The correction information indicates light intensity correction value A, light intensity correction value B, and spot correction value C. The CPU 811 reads the correction information stored in the storage unit 810 and notifies the light intensity correction unit 802 of the light intensity correction value A, light intensity correction value B, and spot correction value C.

[0037] The light intensity correction value A is a correction value used to correct the light intensity difference between groups of light-emitting chips 400. In this embodiment, since the light-emitting elements 602 inside a light-emitting chip 400 are grouped into five groups, five light intensity correction values ​​A are set for a single light-emitting chip 400. One group (that is, one reference current source 902) is associated with one light intensity correction value A.

[0038] The light intensity correction value B is a correction value used to correct the light intensity difference between the light-emitting elements 602 within a group. Although details will be described later, in this embodiment, four light intensity correction values ​​B are associated with one group of a light-emitting chip 400. For example, based on their position in the main scanning direction, a plurality of light-emitting elements 602 emitting light based on a reference current from a reference current source 902 are regrouped into four subgroups. Note that the light-emitting elements 602 contained in a subgroup form a continuous spot in the main scanning direction. Then, one light intensity correction value B is associated with one subgroup.

[0039] The spot correction value C is a value designed to correct for the difference in light intensity attributable to the expansion of the spots formed by the light-emitting elements 602 in the main scanning direction and to indicate the amount of displacement of the spots from a reference value (hereinafter referred to as spot displacement). The spot correction value C is set for each light-emitting element 602 that forms the expanded spots. Note that light-emitting elements 602 for which no spot correction value C is set are interpreted as having a spot correction value C of 0. Although details will be described later, the effect varies depending on the hue when spots formed by the light-emitting elements 602 expand in the main scanning direction. Specifically, in the case of high hue, the concentration increases as the spots expand in the main scanning direction. Therefore, when spots used to form portions with high hue values ​​expand in the main scanning direction, the light intensity decreases. On the other hand, in the case of low hue, the concentration decreases as the spots expand in the main scanning direction. Therefore, when spots used to form portions with low hue values ​​expand in the main scanning direction, the light intensity increases. Note that the absolute value of the increase or decrease in light intensity increases with the increase of the spot displacement.

[0040] Prior to shipment, correction information, including light intensity correction value A, light intensity correction value B, and spot correction value C, is stored in storage unit 810. Furthermore, CPU 811 can update the correction information stored in storage unit 810 by obtaining light intensity correction value A, light intensity correction value B, and spot correction value C using a method described later.

[0041] Image data that has undergone color dithering in the image data generation unit 801 is input to the tone determination unit 1105 and the image correction unit 1109. As mentioned above, this image data indicates whether each light-emitting element 602 should emit light when the photosensitive member 102 is exposed along each line in the main scanning direction.

[0042] The tone determination unit 1105 determines the tone value of a pixel based on the input image data and notifies the tone-by-tone correction unit 1106. The tone-by-tone correction unit 1106 includes a tone-by-tone correction table. Note that the correction table is included in the correction information. The correction table is a table indicating a reference light intensity correction value based on each tone. Note that a reference light intensity correction value with a positive value indicates an increase in light intensity, while a reference light intensity correction value with a negative value indicates a decrease in light intensity. As previously mentioned, when a spot expands in the main scanning direction, its effect varies according to the tone. For example, assume that the tone is classified into three types, namely low tone, medium tone, and high tone, using a first threshold and a second threshold. Note that the first threshold is greater than the second threshold, tone values ​​greater than the first threshold represent high tone, tone values ​​less than the second threshold represent low tone, and tone values ​​greater than or equal to the second threshold and less than or equal to the first threshold represent medium tone. The reference light intensity correction value indicated by the correction table has a positive value for low tone, a negative value for high tone, and 0 for medium tone. In other words, a negative reference light intensity correction value is 0 for low and mid tones, while a positive reference light intensity correction value is 0 for high and mid tones.

[0043] The tone-by-tone correction unit 1106 corrects the reference light intensity correction value of the pixel's tone, as notified by the tone determination unit 1105, based on the speckle displacement amount indicated by the speckle correction value C of the light-emitting element 602 forming the point constituting the pixel, thereby obtaining the light intensity correction value D of that point. As an example, the tone-by-tone correction unit 1106 stores coefficient information indicating the correspondence between the speckle displacement amount and the coefficient, and obtains the light intensity correction value D by multiplying the reference light intensity correction value of the tone notified by the tone determination unit 1105 by the coefficient corresponding to the speckle displacement amount. Note that the light intensity correction value D of points formed by light-emitting elements 602 that have not been set with a speckle correction value C (that is, light-emitting elements 602 with a speckle correction value C of 0) is always 0. The tone-by-tone correction unit 1106 outputs data indicating the light intensity correction values ​​D of each point constituting the image to the image correction unit 1109.

[0044] Based on the light intensity correction value A and the light intensity correction value B, the calculation unit 1107 obtains the light intensity correction value E of each light-emitting element 602 placed at different positions in the main scanning direction. The light intensity correction value E of the light-emitting element 602 is the sum of the light intensity correction value A of the group to which the light-emitting element 602 belongs and the light intensity correction value B of the subgroup to which the light-emitting element 602 belongs. Although details will be described later, the sum of the light intensity correction value A of the group to which the light-emitting element 602 belongs and the light intensity correction value B of the subgroup to which the light-emitting element 602 belongs is 0 or negative, and does not become positive. That is, the value of the sum indicates whether the light intensity should remain the same or decrease, and does not become a value indicating that the light intensity should increase. The light intensity correction value E is also the light intensity correction value of each point on a line in the main scanning direction formed by the light-emitting elements 602 placed at different positions in the main scanning direction. The calculation unit 1107 outputs the light intensity correction value E of each point on a line in the main scanning direction to the image correction unit 1109.

[0045] The image correction unit 1109 divides the data indicating the light quantity correction value D of each point constituting the image into first data indicating the light quantity correction value D for points used to increase light quantity and second data indicating the light quantity correction value D for points used to decrease light quantity. Furthermore, based on the light quantity correction value E of each point along a line in the main scanning direction, the image correction unit 1109 generates third data indicating the light quantity correction value E of each point constituting the image. Then, the image correction unit 1109 adds the absolute value of the light quantity correction value D in the second data to the absolute value of the light quantity correction value E of the same point in the third data, thereby generating fourth data indicating the total light quantity correction value of each point constituting the image. The total light quantity correction value of each point indicated by the fourth data indicates a decrease in light quantity of 0 or greater, and is hereinafter referred to as subtraction data. On the other hand, the light quantity correction value D of each point indicated by the first data indicates an increase in light quantity of 0 or greater, and is hereinafter referred to as addition data. The image correction unit 1109 corrects the image data based on the subtraction data and the addition data. In this embodiment, the image correction unit 1109 performs image correction on a unit of a portion of an image of a predetermined size, which is a part of the image to be formed. In this example, it is assumed that the size of the portion of the image is 10×10 pixels (100 pixels in total). Figure 11A This is an example representing a portion of the image, specifically a 10×10 pixel section corresponding to an image formed from pre-corrected image data. Figure 11A In this context, a cell represents a pixel. Note that shaded pixels represent pixels to which toner is applied, while white pixels represent pixels to which no toner is applied.

[0046] In this embodiment, it is assumed that a pixel is formed by 10 consecutive points in both the main scanning direction and the sub-scanning direction. Figure 11BIndicates the use of forming Figure 11A An example of image data for one pixel. The following forms... Figure 11B The ten light-emitting elements 602 in the main scanning direction of one pixel are referred to as light-emitting elements #1 to #10. Figure 11B In the diagram, the Kth cell from the left (where K is an integer from 1 to 10) represents the point (spot) formed by the light-emitting element #K. Specifically, shaded cells indicate exposed points, or indicate that the light-emitting element #K should emit light, while white cells indicate unexposed points, or indicate that the light-emitting element #K should not emit light. Note that... Figure 11B The up and down directions in the diagram correspond to the positions in the sub-scanning direction. According to the diagram, for example, the light-emitting element #1 emits light at the first to fourth, seventh, and eighth positions among the 10 points formed in the sub-scanning direction. Figure 11B It can be viewed as indicating whether each of the 10×10 points that form a pixel is an exposed point or an unexposed point.

[0047] Next, we will use the serial numbers in the main scanning direction and the sub-scanning direction for identification. Figures 11B to 11D The points (spots) shown are numbered as follows: In the main scan direction, the leftmost point is represented by 1, and the rightmost point by 10. In the sub-scan direction, the topmost point is represented by 1, and the bottommost point by 10. Furthermore, for example, a point that is second in the main scan direction and third in the sub-scan direction is represented by (2,3).

[0048] Image correction unit 1109 includes a threshold matrix table for subtraction and a threshold matrix table for addition. The threshold matrix table indicates the thresholds for 10×10 pixels, or 100×100 points, for image correction. Image correction unit 1109 compares the absolute value of the total light intensity correction value for a point corresponding to a portion of the image indicated by the subtraction data with the corresponding threshold indicated by the threshold matrix table for subtraction. Then, image correction unit 1109 determines the point whose absolute value of the total light intensity correction value exceeds the threshold in the threshold matrix table for subtraction as the first change point.

[0049] Figure 11C Indicates about and corresponding Figure 11B An example of the result determined using a threshold matrix table for subtraction, representing a portion of a pixel. Figure 11C In the image, points at positions (4,2), (7,5), (2,8), and (8,10) are identified as first change points. If the first change point is an exposed point, the image correction unit 1109 changes it to an unexposed point. Conversely, if the first change point is an unexposed point, the image correction unit 1109 retains it as an unexposed point. Therefore, as... Figure 11DAs shown, the image correction unit 1109 corrects... Figure 11B Image data. Figure 11B The point at position (4,2) was initially an unexposed point, and therefore remains an unexposed point after correction. On the other hand, the points at positions (7,5), (2,8), and (8,10) have been corrected from exposed points to unexposed points.

[0050] The image correction unit 1109 similarly uses the addition data and a threshold matrix table for addition to determine the second change point. If the second change point is an unexposed point, the image correction unit 1109 changes it to an exposed point. Conversely, if the second change point is an exposed point, the image correction unit 1109 retains it as an exposed point. When the same point is selected as both the first and second change points, the image correction unit 1109 does not change the exposure / unexposed state of that point and retains it in the state indicated by the original image data. Note that a table with high spatial frequency characteristics used in the well-known blue noise mask method can be used as the threshold matrix table.

[0051] Regarding the threshold matrix table (100×100 points in this example), the same table is used repeatedly in both the main and sub-scanning directions. However, since the subtraction and addition data to be compared correspond to the entire image and are not data repeated within a single cycle, image defects at processing boundaries can be suppressed. Note that the thresholds in the threshold matrix table are set such that the intervals between the first and second change points are non-uniform. By making the intervals between the first and second change points non-uniform, moiré fringes can be prevented.

[0052] Furthermore, by using a correction resolution that is sufficiently high relative to the pixel size of the original image data, the light intensity can be corrected with high precision. Additionally, by correcting the light intensity before the chip data conversion unit 803 performs segmentation into image data for each light-emitting chip 400, compared to a configuration where the light intensity is corrected after segmentation, the occurrence of image defects at the boundaries of the light-emitting chips 400 can be suppressed.

[0053] As described above, according to this embodiment, the exposure / unexposure of a point obtained by segmenting a pixel in the image data is corrected on a unit basis, using a portion of the image of a predetermined region (10×10 pixels in this example). With this configuration, a simple and highly accurate correction can be performed compared to correction of light intensity using complex analog circuitry. Furthermore, by correcting the light intensity based on the light intensity correction values ​​of each light-emitting element 602 that continuously forms spots in the main scanning direction (that is, the light intensity correction values ​​at each continuous position in the main scanning direction), image defects can be prevented. Additionally, by correcting the light intensity on a unit basis, obtained by segmenting a pixel, the light intensity can be corrected with high precision.

[0054] In this embodiment, the light intensity fluctuation of the light-emitting elements 602 in the main scanning direction is corrected in two steps. First, as a first step of correction, the light intensity fluctuation between the light-emitting chips 400 is corrected by adjusting the digital value set in the D / A 901 of the light-emitting chip 400. To determine the digital value to be set in the D / A 901 of each light-emitting chip 400, all light-emitting elements 602 inside the light-emitting chip 400 are made to emit light, and the light intensity value of each light-emitting element 602 in the light-emitting chip 400 is measured. Then, the digital value to be set in the D / A 901 is determined such that the smallest light intensity among the light-emitting elements 602 inside the light-emitting chip 400 is used as the target light intensity. In this way, the light intensity of all light-emitting elements 602 inside the light-emitting chip 400 is equal to or greater than the target light intensity. Therefore, as mentioned above, the light intensity correction value E of each light-emitting element is a value indicating whether the light intensity should remain the same or be reduced. By correcting the light amount in the first step using the digital value set in D / A 901, the correction amount in the light amount correction unit 802 can be reduced, and as a result, the degradation of image quality caused by the correction of image data can be suppressed.

[0055] The correction in the second step is the correction of light intensity fluctuations within the light-emitting chip 400, and is performed by the light intensity correction unit 802 to correct the image data in the manner described above. The light intensity correction values ​​A, B, and C used by the light intensity correction unit 802, as well as the aforementioned digital values ​​input to the D / A 901 of each light-emitting chip 400, are generated based on measurement results during the assembly and adjustment process of the exposure head 106, and are stored as correction information in the storage unit 810. The CPU 811 reads the correction information, sets the light intensity correction values ​​A, B, and C in the light intensity correction unit 802, and further sets the digital values ​​in the D / A 901 of each light-emitting chip 400.

[0056] Note that the spot correction value C indicates the amount of displacement of the spot from the reference value (spot displacement). To measure the spot correction value C, each of the light-emitting elements 602 is made to emit light individually. The spot size is then measured by reading the spots using a CCD camera, the amount of change from the reference value is measured, and the relationship with the position of appearance (i.e., the light-emitting element 602) is used as the spot correction value C.

[0057] Note that correction information can be generated within the image forming apparatus. Figure 12 This represents a light intensity correction chart, which is a measurement image formed on a sheet to generate correction information. The light intensity correction chart is formed by the image forming apparatus in response to a user-issued command to perform an adjustment for light intensity non-uniformity. The user instructs the reading unit 100 to read the sheet on which the light intensity correction chart has been formed. Therefore, the CPU 811 obtains chart data as a reading result of the reading unit 100. The chart data is data indicating the density distribution in the main scanning direction of each of the plurality of tonal images 2101 to 2106.

[0058] The light intensity correction chart includes multiple hue images 2101 to 2106 arranged in bars along the main scanning direction, and reference marks 2111-1 to 2119-19 and 2112-1 to 2112-19 located above and below the hue images 2101 to 2106. Each reference mark is a marker image used to specify the position of each light-emitting chip 400, and is formed by the emission of light-emitting elements 602 located at the edges of each light-emitting chip 400 in the main scanning direction. For example, reference mark 2111-2 is formed by the emission of four light-emitting elements 602 at the right edge of light-emitting chip 400-2 and four light-emitting elements 602 at the left edge of light-emitting chip 400-3. CPU 811 determines each reference mark based on the chart data. Then, for each of the tone images 2101 to 2106, the CPU 811 determines the regions formed by the light-emitting chips 400-1 to 400-20 respectively by using a line connecting reference marker 2111-p (where p is an integer from 1 to 19) and reference marker 2112-p. For example, determining Figure 12 Region B1 is formed by the light-emitting chip 400-2. Note that... Figure 12 The left edge is formed by the light-emitting chip 400-1, and Figure 12 The right edge is formed by the light-emitting chip 400-20.

[0059] The sets of hue images 2101 and 2102 are formed from image data having the same hue value. However, when forming hue image 2102, the CPU 811 reduces the digital value to be set in the D / A 901 of each light-emitting chip 400 by a predetermined ratio compared to the digital value set in the D / A 901 of each light-emitting chip 400 when forming hue image 2101. This makes the density of hue image 2102 lower than that of hue image 2101. The same applies to the sets of hue images 2103 and 2104, and the sets of hue images 2105 and 2106. Note that the hue values ​​indicated by the image data used to form the sets of hue images 2101 and 2102, the sets of hue images 2103 and 2104, and the sets of hue images 2105 and 2106, respectively, are different from each other. Specifically, the image data used to form the set of tone images 2101 and 2102 is set to indicate the maximum tone value, and the image data used to form the set of tone images 2105 and 2106 is set to indicate the minimum tone value. Note that the density of tone image 2102 is higher than that of tone image 2103, and the density of tone image 2104 is higher than that of tone image 2105.

[0060] Next, use Figure 13 The method described is to convert the graph data read by the reading unit 100 into light intensity data. The CPU 811 obtains the average concentrations 2101_D to 2106_D of the hue images 2101 to 2106 by averaging the concentrations read at various positions in the main scanning direction. Figure 13 This represents the relationship between the digital values ​​set in D / A 901 when forming tone images 2101 to 2106, and the average concentrations 2101_D to 2106_D, respectively. For the set of tone images 2101 and 2102, CPU 811 obtains the change in digital values ​​relative to the concentration change, k1. Specifically, CPU 811 obtains the change k1 by dividing the difference between the digital values ​​set in D / A 901 when forming tone images 2101 and 2102 by the difference between the average concentrations 2101_D and 2102_D. Similarly, CPU 811 obtains the change k2 for the set of tone images 2103 and 2104, and the change k3 for the set of tone images 2104 and 2105.

[0061] CPU 811 obtains the light intensity distribution of tone image 2101 in the main scanning direction by multiplying the concentration of tone image 2101 at various positions in the main scanning direction, determined based on chart data, by the slope k1. Similarly, CPU 811 also obtains the light intensity distribution in the main scanning direction with respect to tone images 2103 and 2105. Note that it is also permissible to use a configuration that obtains the light intensity distribution by changing the hue of the image data used to form tone images 2101 and 2102, rather than changing the digital value set in D / A 901.

[0062] In this embodiment, the CPU 811 obtains the digital value, light intensity correction value A, and light intensity correction value B set in the D / A 901 based on the light intensity distribution of the tone image 2103, which is an image of intermediate density region. Furthermore, the CPU 811 obtains the speckle correction value C based on the light intensity distribution of tone images 2101 and 2105, which are respectively high-density and low-density regions. Hereinafter, using... Figure 14 Describes a method for obtaining the digital values, light quantity correction value A, and light quantity correction value B set in D / A 901.

[0063] Figure 14 This represents the light distribution in the hue image 2103. Note that... Figure 14 This only indicates the portion corresponding to one light-emitting chip 400. (If used...) Figure 12 As described, a reference marker can be used to determine which portion of the tone image 2103 is formed by which light-emitting chip 400. The CPU 811 determines the digital value to be set in the D / A 901, such that... Figure 14 The minimum light intensity in the image is used as the target light intensity T (target value). Specifically, the CPU 811 increases the digital value set in the D / A 901 when forming the tone image 2103 by adding and subtracting the target light intensity T. Figure 14 The digital value corresponding to the minimum light intensity obtained in the D / A 901 is used to determine the digital value to be set in the D / A 901.

[0064] Figure 14 The light intensity 2301 is the light intensity at a predetermined location within the range of the forming points of multiple light-emitting elements 602 within the group corresponding to the reference current source 902-1. Similarly, light intensities 2302 to 2305 are respectively the light intensities at predetermined locations within the range of the forming points of multiple light-emitting elements 602 within the groups corresponding to the reference current sources 902-2 to 902-5. For example, the CPU 811 uses light intensity 2301 and... Figure 14 The difference between the minimum light quantities is used as the light quantity correction value A associated with the reference current source 902-1. Note that, as mentioned earlier, due to the digital value set in D / A 901, therefore... Figure 14The minimum light intensity in the sample is used as the target light intensity T. The CPU 811 also similarly obtains the light intensity correction value A associated with the reference current sources 902-2 to 902-5.

[0065] Furthermore, for example, the CPU 811 determines the light quantity at four locations from the range of points formed by multiple light-emitting elements 602 within a group corresponding to the reference current source 902-1. Note that the location for determining the light quantity is selected from the range of points formed by multiple light-emitting elements 602 within a subgroup. The CPU 811 uses the difference between the four determined light quantities and the light quantity 2301 as the light quantity correction value B associated with each subgroup under the reference current source 902-1. The CPU 811 similarly obtains the light quantity correction values ​​B associated with reference current sources 902-2 to 902-5.

[0066] As described above, a light quantity correction value A based on a reference current source 902 is used to correct the overall light-emitting elements 602 within the group, and a light quantity correction value B is used to correct light quantity fluctuations in the light-emitting elements 602 within the group. With this configuration, the light quantity correction value B can be represented using a small number of bits, and the amount of data for correction information can be reduced. As an example, four bits can be used to represent the light quantity correction value A, and two bits can be used to represent the light quantity correction value B, which indicates fluctuations in light quantity within the group (i.e., residual components).

[0067] Next, the method for obtaining the speckle correction value C is described. Figure 15A This represents the light intensity distribution of tonal images 2101, 2103, and 2105. Note that... Figure 15A This represents the normalized light intensity of each hue image 2101, 2103, and 2105. That is, regarding hue image 2101, the value obtained by dividing the light intensity at each position of hue image 2101 in the main scanning direction by the average light intensity of hue image 2101 is used as the normalized light intensity along the main scanning direction. Figure 15A The value of the vertical axis. The same applies to tonal images 2103 and 2105. As a result of normalization, the light intensity of tonal images 2101, 2103, and 2105 has similar values ​​at most locations along the main scanning direction.

[0068] However, if the spots formed by the light-emitting element 602 change locally due to manufacturing variations in the exposure head 106, the light intensity of the tonal images 2101, 2103, and 2105 begins to change. Specifically, in the case of the tonal image 2105 representing a low tone, if the spots locally enlarge, sufficient luminous intensity cannot be obtained, and the concentration decreases. That is, when converted into light intensity, the light intensity... Figure 15AAs indicated by reference numeral 2307, the intensity decreases. On the other hand, in the case of a high-key tonal image 2101, reducing the gap between adjacent pixels leads to an increase in density. That is, when converted to light intensity, the light intensity is as follows: Figure 15A The reference numeral 2306 is increased as shown in the attached figure. Note that... Figure 15A The reference numeral 2308 in the attached figure indicates the amount of light in the tonal image 2103, which represents the midtones.

[0069] exist Figure 15B In the diagram, solid lines represent concentration characteristics when the spots do not fluctuate, while dashed lines represent concentration characteristics when the spots become larger than the standard. For example... Figure 15B As shown, when the spots become larger than the standard, the concentration increases in the high-tone region and decreases in the low-tone region. Note that the effect is small in the mid-tone region.

[0070] CPU 811 obtains the peak difference, which is the peak value of the normalized light intensity of the tone image 2101. Figure 15A The reference numeral 2306 in the attached figure and the peak value of the normalized light intensity of the hue image 2105 are shown. Figure 15A The difference between the peak difference and the experimentally obtained spot displacement is determined by the determination information, which is stored in advance in the image forming apparatus. By using the determination information based on the obtained peak difference, the CPU 811 obtains the spot correction value C associated with the position of the light-emitting element 602 in the main scanning direction corresponding to the fluctuation of the normalized light amount.

[0071] Note that the specific values ​​used in the description of this embodiment are examples, and the invention is not limited to using these specific values.

[0072] As described above, in this embodiment, fluctuations in the light intensity of each light-emitting element 602 in the main scanning direction are corrected in two steps. First, the image controller 800 corrects the light intensity difference between the light-emitting chips 400 by using a digital value set in the D / A 901 inside the light-emitting chip 400. Then, the image controller 800 corrects the fluctuations in the light intensity of each light-emitting element 602 inside the light-emitting chip 400 by correcting the image data. By using a digital value set in the D / A 901 inside the light-emitting chip 400 to correct the light intensity difference between the light-emitting chips 400, the amount of image data correction can be reduced, and the degradation of image quality caused by image data correction can be suppressed. Similarly, by correcting the light intensity difference between the light-emitting elements 602 inside the light-emitting chip 400 in the same way as correcting the image data, a simpler and more accurate correction can be performed compared to a configuration that provides a correction circuit for correcting the current flowing through each light-emitting element 602 individually. In other words, with the configuration of this embodiment, compared to the case where a correction circuit is provided in the chip to correct the current flowing through each light-emitting element 602 inside the light-emitting chip 400, uneven concentration can be suppressed without increasing the circuit size.

[0073] Furthermore, image data correction is performed on a per-partial-image basis by changing the exposure and non-exposure points using a threshold matrix of the same size as the partial images. The same threshold matrix is ​​reused for each of the partial images constituting the overall image. However, since the intensity correction value compared to the threshold matrix corresponds to the entire image and is independent of the size of the threshold matrix, image defects at the boundaries of the partial images can be suppressed. Additionally, since intensity correction is performed with high precision by changing the exposure / non-exposure points on a per-pixel basis (multiple points), it is possible to perform intensity correction effectively.

[0074] Other embodiments

[0075] Embodiments of the present invention can also be implemented by a computer that reads and executes computer-executable instructions (e.g., one or more programs) recorded on a storage medium (also more fully referred to as a "non-transitory computer-readable storage medium") to perform one or more functions of the above embodiments and / or includes one or more circuits (e.g., application-specific integrated circuits (ASICs)) for performing one or more functions of the above embodiments, and by a method by which the computer of the system or device, for example, reads and executes computer-executable instructions from the storage medium to perform one or more functions of the above embodiments and / or controls one or more circuits to perform one or more functions of the above embodiments. The computer may include one or more processors (e.g., a central processing unit (CPU), a microprocessor unit (MPU)) and may include separate computers or networks of separate processors to read and execute computer-executable instructions. The computer-executable instructions may, for example, be provided to the computer from a network or storage medium. The storage medium may include, for example, a hard disk, random access memory (RAM), read-only memory (ROM), storage devices for distributed computing systems, optical discs (such as CDs, DVDs, or Blu-ray discs). TM One or more of the following: flash memory devices and memory cards.

[0076] Other embodiments

[0077] The embodiments of the present invention can also be implemented by providing software (programs) that perform the functions of the above embodiments to a system or device via a network or various storage media, and the computer or central processing unit (CPU) or microprocessor unit (MPU) of the system or device reads out and executes the program.

[0078] While the invention has been described with reference to exemplary embodiments, it should be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims should be given the broadest interpretation to cover all such variations and equivalent structures and functions.

Claims

1. An image forming apparatus, characterized in that, include: The photosensitive element is driven to rotate; An exposure head includes a plurality of light-emitting chips placed at different positions along the rotation axis of a photosensitive member. Each of the plurality of light-emitting chips includes a plurality of light-emitting elements placed at different positions along the rotation axis of the photosensitive member, a digital-to-analog converter that outputs a voltage corresponding to a set value as a digital value, and a circuit unit that supplies current to the plurality of light-emitting elements based on the voltage output from the digital-to-analog converter. as well as At least one processor, in, The at least one processor is configured to Based on the first image data, second image data corresponding to each of the plurality of light-emitting elements is generated. The second image information indicates whether each of the plurality of light-emitting elements should emit light. Based on the correction information, the first image data indicating that the light-emitting element should emit light is changed to second image data indicating that the light-emitting element should not emit light, and The circuit unit supplies current to each of the plurality of light-emitting elements based on the second image data.

2. The image forming apparatus according to claim 1, wherein, Regarding each of the plurality of points constituting the image, the first image data indicates whether that point is an exposed point to be exposed by illuminating the light-emitting element, or a non-exposed point to be exposed by not illuminating the light-emitting element. The at least one processor is configured to: for each of a plurality of partial images obtained by segmenting the image, based on the correction information, select a first change point from a plurality of first points that are part of the plurality of points and contained in the partial image; and if the first change point is an exposure point, generate second image data by changing the first change point to an exposure point.

3. The image forming apparatus according to claim 2, wherein, The correction information includes first correction information for determining the first light quantity correction value of the plurality of light-emitting elements respectively, and The at least one processor is configured to select a first change point based on a first light intensity correction value of each of the plurality of first light-emitting elements that exposes the plurality of first points contained in the partial image.

4. The image forming apparatus according to claim 3, wherein, The first light intensity correction value for each of the plurality of light-emitting elements does not indicate that the light intensity of each of the plurality of light-emitting elements should be increased.

5. The image forming apparatus according to claim 2, wherein, The at least one processor is configured to: for each of the plurality of partial images, select a second change point from the plurality of first points contained in the partial image based on the correction information; and, if the second change point is an exposure point, generate second image data by changing the second change point to an exposure point.

6. The image forming apparatus according to claim 5, wherein, The at least one processor is configured to keep the first point unchanged if the same first point has already been selected as the first change point and the second change point.

7. The image forming apparatus according to claim 5, wherein, The correction information includes first correction information for determining first light quantity correction values ​​for the plurality of light-emitting elements and second correction information for determining second light quantity correction values ​​for the plurality of light-emitting elements. The at least one processor is configured to: select a first change point based on a first light intensity correction value of each of the plurality of first light-emitting elements that exposes the plurality of first points contained in the partial image; and select a second change point based on a second light intensity correction value of each of the plurality of first light-emitting elements. The first and second light quantity correction values ​​of the light-emitting element are based on the hue values ​​of the pixels, including the points associated with the light-emitting element.

8. The image forming apparatus according to claim 7, wherein, The first light intensity correction value for each of the plurality of light-emitting elements does not indicate an increase in the light intensity of the plurality of light-emitting elements, and the second light intensity correction value for each of the plurality of light-emitting elements does not indicate a decrease in the light intensity of the plurality of light-emitting elements.

9. The image forming apparatus according to claim 8, wherein, The first light quantity correction value for the light-emitting element is the sum of a predetermined first correction value for the light-emitting element and a second correction value based on the hue values ​​of pixels including the points associated with the light-emitting element. The second light quantity correction value for the light-emitting element is a third correction value based on the hue values ​​of the pixels that include the points associated with the light-emitting element.

10. The image forming apparatus according to claim 9, wherein, If the hue value of a pixel, including a point associated with a light-emitting element, is less than a first threshold, the second correction value for the light-emitting element is 0. If the hue value of a pixel, including a point associated with the light-emitting element, is greater than a second threshold, the third correction value for the light-emitting element is 0, and The first threshold is greater than the second threshold.

11. The image forming apparatus according to claim 9, wherein, For a light-emitting element included among the plurality of light-emitting elements and different from the predetermined second light-emitting element, the second correction value is 0, and For a light-emitting element that is included among the plurality of light-emitting elements and is different from the second light-emitting element, the third correction value is 0.

12. The image forming apparatus according to claim 11, wherein, The second light-emitting element is a light-emitting element included in the plurality of light-emitting elements and whose spot size formed on the photosensitive member by emitting light is greater than a reference value.

13. The image forming apparatus according to claim 3, wherein, The at least one processor has a first threshold matrix indicating third thresholds corresponding to the plurality of first points contained in the partial image, and is configured to select a first change point by comparing the third threshold of the first point indicated by the first threshold matrix with a first light quantity correction value of a first light-emitting element that exposes the first point.

14. The image forming apparatus according to claim 13, wherein, The first threshold matrix is ​​set such that the intervals of the first change points selected based on the first light quantity correction value are non-uniform.

15. The image forming apparatus according to claim 7, wherein, The at least one processor has a second threshold matrix indicating fourth thresholds corresponding to the plurality of first points contained in the partial image, and is configured to select a second change point by comparing the fourth threshold of the first point indicated by the second threshold matrix with a second light quantity correction value of a first light-emitting element that exposes the first point.

16. The image forming apparatus according to claim 15, wherein, The second threshold matrix is ​​set such that the intervals of the second variation points selected based on the second light quantity correction value are non-uniform.

17. The image forming apparatus according to claim 2, wherein, The first image data is obtained by performing halftone processing on the third image data regarding the tonal values ​​of the indicator pixels, and The size of the pixel indicated by the third image data is larger than the size of the plurality of points.

Images