JP2023141875A - Image forming apparatus, correction chart, and generation method of correction information - Google Patents

Abstract

To provide a technique to suppress density unevenness of a formed image.SOLUTION: A image forming apparatus has: a reading unit which reads an image; an exposure head that includes a plurality of current sources being arranged at different positions in a main scanning direction and supplying current according to a setting value, and a group composed of a plurality of light emission elements to which current is supplied from each of the current sources; an image forming unit which develops an electrostatic latent image on a photoreceptor according to image data to form an image; a correction unit which corrects the image data so as to correct light quantity unevenness of the exposure head; and a generation unit which generates correction information by the correction unit. The correction unit corrects a difference in light emission quantity between the groups of the plurality of light emission elements on the basis of a first correction value, corrects a difference in light emission quantity between subgroups of the light emission elements in the group of the plurality of light emission elements on the basis of a second correction value, and corrects a difference in spot size by light emission for each of the plurality of light emission elements on the basis of a third correction value. The generation unit generates the first correction value, the second correction value and the third correction value on the basis of a read correction chart.SELECTED DRAWING: Figure 12

Description

This invention relates to an electrophotographic printer.

In electrophotographic printers, a method is generally known in which a photoreceptor drum is exposed to light using an exposure head using an LED, an organic EL, or the like as a light source to form a latent image on the surface of the photoreceptor drum. This type of exposure head includes a row of light emitting elements arranged in the longitudinal direction of a photoreceptor drum, and a rod lens array that forms an image of light from the row of light emitting elements on the photoreceptor drum. Patent Document 1 discloses a technique for correcting density unevenness due to a difference in light amount between two adjacent chips in the main scanning direction using a configuration in which exposure is performed using an exposure head in which a plurality of such light emitting elements are arranged.

JP 2018-1679 Publication

However, in addition to the unevenness of each light-emitting chip, the unevenness of light amount includes unevenness of light amount caused by other factors, such as unevenness of light amount caused by local fluctuations of the lens and unevenness of light amount generated within the light-emitting chip. In particular, variations in the amount of light due to individual differences in the circuits inside the light emitting chip are easily visible because the density changes abruptly. If the change is steep, even if the unevenness of the light amount of the exposure head is corrected, the position to be corrected may shift, resulting in image streaks. Furthermore, when performing correction processing in accordance with the position where the light amount of the light emitting chip changes, there is a problem that the correction position does not match with light amount fluctuations caused by other lenses. As described above, the unevenness of the light amount of the exposure head is caused by multiple factors, and it is sometimes not possible to correct it by correcting the density difference between adjacent chips.

The present invention has been made in view of the above-mentioned conventional example, and an object of the present invention is to improve image quality by suppressing unevenness in light amount caused by complex factors.

The image forming apparatus according to the present invention includes:
a reading means for reading an image formed on the sheet;
An exposure head including a plurality of light emitting chips arranged at different positions in a main scanning direction, each of the plurality of light emitting chips having a plurality of current sources that supply current according to a set value, and a plurality of current sources that supply a current according to a set value. and a group of a plurality of light emitting elements, each of which is supplied with current;
an image forming unit that develops an electrostatic latent image on a photoreceptor according to image data to form an image on the photoreceptor, and forms an image corresponding to the electrostatic latent image on a sheet;
a correction means for correcting the image data in order to correct unevenness in light amount of the exposure head;
generating means for generating correction information by the correction means,
The correction means corrects the difference in light emission amount between the groups of the plurality of light emitting elements based on a first correction value, and corrects the difference in the amount of light emitted by the light emitting elements in the group of the plurality of light emitting elements based on the second correction value. correcting a difference in light emission amount between subgroups, correcting a difference in spot size due to light emission of each of the plurality of light emitting elements based on a third correction value,
The generating means generates the first correction value, the second correction value, and the third correction value based on an image read by the reading means from a predetermined correction chart formed by the image forming means. It is characterized by generating and saving.

According to the present invention, it is possible to improve image quality by suppressing light intensity unevenness caused by complex factors.

FIG. 1 is a configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a diagram illustrating an exposure head and a photoreceptor, according to one embodiment. FIG. 2 is a diagram illustrating a printed circuit board of an exposure head, according to one embodiment. FIG. 2 is an explanatory diagram of the arrangement of light emitting elements within a light emitting chip, according to one embodiment. FIG. 2 is a top view of a light emitting chip, according to one embodiment. FIG. 2 is a cross-sectional view of a light emitting chip, according to one embodiment. FIG. 2 is a diagram illustrating spots on a photoreceptor, according to one embodiment. FIG. 3 is a control configuration diagram of each light emitting chip according to one embodiment. FIG. 2 is a block diagram within a light emitting chip, according to one embodiment. FIG. 3 is a block diagram of a light amount correction unit according to an embodiment. FIG. 4 is an explanatory diagram of processing in a light amount correction unit according to an embodiment. FIG. 7 is a diagram showing a light amount correction chart according to one embodiment. FIG. 4 is an explanatory diagram of correction information generation processing according to an embodiment. FIG. 4 is an explanatory diagram of correction information generation processing according to an embodiment. FIG. 4 is an explanatory diagram of correction information generation processing according to an embodiment. 7 is a flowchart of correction information generation processing according to one embodiment.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the claimed invention. Although a plurality of features are described in the embodiments, not all of these features are essential to the invention, and the plurality of features may be arbitrarily combined. Furthermore, in the accompanying drawings, the same or similar components are designated by the same reference numerals, and redundant description will be omitted.

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to this embodiment. The reading unit 100 optically reads a document placed on a document table and generates image data representing an image on the surface of the document. The image forming unit 103 forms an image on a sheet, for example, based on image data read by the reading unit 100 or based on image data received via a network.

The image forming section 103 includes image forming sections 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 the image forming units 101a, 101b, 101c, and 101d are similar, and hereinafter, they will also be collectively referred to as image forming units 101. The photoreceptor 102 of the image forming unit 101 is rotated clockwise in the figure during image formation. The charger 107 charges the photoreceptor 102. The exposure head 106 exposes the photoreceptor 102 to light according to image data, and forms an electrostatic latent image on the photoreceptor 102. A developing device 108 develops the electrostatic latent image on the photoreceptor 102 with toner. The toner image on the photoreceptor 102 is transferred onto a sheet conveyed on a transfer belt 111. Note that by overlapping and transferring the toner images on each photoreceptor 102, colors different from black, yellow, magenta, and cyan can be reproduced.

The conveyance unit 105 controls sheet feeding and conveyance. Specifically, the conveyance unit 105 feeds the sheet from a designated unit among the internal storage units 109a and 109b, the external storage unit 109c, and the manual feed unit 109d to the conveyance path of the image forming apparatus. The fed sheet is conveyed to registration rollers 110. The registration roller 110 conveys the sheet onto the transfer belt 111 at a predetermined timing so that the toner image on each photoreceptor 102 is transferred onto the sheet. As described above, a toner image is transferred to the sheet while being conveyed on the transfer belt 111. The fixing unit 104 fixes the toner image onto the sheet by heating and pressing the sheet onto which the toner image has been transferred. After the toner image is fixed, the sheet is discharged to the outside of the image forming apparatus by a discharge roller 112. Note that an optical sensor 113 is arranged at a position facing the transfer belt 111. The optical sensor 113 detects a test chart formed on the transfer belt 111 by the image forming unit 101 for measuring the amount of color misregistration. Based on the detection results of the test chart, a control unit (not shown) performs color shift correction control.

2(A) and 2(B) show the photoreceptor 102 and the exposure head 106. FIG. 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 rod lens array 203, and a housing 204 that attaches the rod lens array 203 to the printed circuit board 202. The rod lens array 203 focuses the light emitted by the light emitting element group 201 onto the photoreceptor 102 to form an imaging spot (hereinafter simply referred to as a spot) of a predetermined size on the photoreceptor 102 .

3(A) and 3(B) show the printed circuit board 202. FIG. Note that FIG. 3(A) shows the surface on which the connector 305 is mounted, and FIG. 3(B) shows the surface on which the light emitting element group 201 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 two rows in a staggered manner along the main scanning direction. More specifically, the light emitting chips 400-(2k-1) (k is an integer from 1 to 10) are arranged in a line along the main scanning direction, and the light emitting chips 400-2k are arranged in a row along the main scanning direction. are arranged in a line. The positions of the row of light emitting chips 400-(2k-1) and the row of light emitting chips 400-2k in the sub-scanning direction orthogonal to the main scanning direction are different. In the following description, the light emitting chips 400-1 to 400-20 are also collectively referred to as the light emitting chips 400. Further, the light emitting chip 400-(2k-1) is expressed as an odd-numbered column of light-emitting chips 400, and the light-emitting chip 400-2k is expressed as an even-numbered column of light-emitting chips 400. Each light emitting chip 400 has a plurality of light emitting elements. Each light emitting chip 400 on the printed circuit board 202 is connected to an image controller 800 (FIG. 8), which is a control unit, via a connector 305.

FIG. 4 is an explanatory diagram of the arrangement of the light emitting chip 400. The light emitting chip 400 includes four sets of 748 light emitting elements 602 arranged along the main scanning direction. Each set of light emitting elements 602 is arranged side by side in the sub-scanning direction. The pitch between adjacent light emitting elements 602 in the main scanning direction is approximately 21.16 μm, which corresponds to a resolution of 1200 dpi. Therefore, the length of one set of 748 light emitting elements in the main scanning direction is approximately 15.8 mm. Note that each set is shifted in the main scanning direction by approximately 5 μm corresponding to a resolution of 4800 dpi. Furthermore, the light-emitting chips 400 in even-numbered columns and the light-emitting chips 400 in odd-numbered columns are arranged so as to overlap in the main scanning direction. The distance Ly between the light-emitting elements 602 of the light-emitting chips 400 in even-numbered rows and the light-emitting elements 602 of the light-emitting chips 400 in odd-numbered rows is, for example, about 105 μm.

FIG. 5 is a plan view of the light emitting chip 400. The light emitting chip 400 includes a light emitting section 404 including a plurality of light emitting elements 602. The light emitting section 404 is formed on the light emitting substrate 402. Further, the light emitting board 402 is provided with a circuit section 406 for controlling the light emitting section 404. A line for communicating with the image controller 800 is connected to the pad 408 .

FIG. 6 shows a part of the cross section taken along line AA in FIG. A plurality of lower electrodes 504 are formed on the light emitting substrate 402 . The lower electrode 504 is provided for one light emitting element 602, and a gap of length dx is provided between two adjacent lower electrodes 504. A light emitting layer 506 is provided on the lower electrode 504, and an upper electrode 508 is provided on the light emitting layer 506. The upper electrode 508 is one common electrode for the plurality of lower electrodes 504. When a predetermined voltage is applied between the lower electrode 504 and the upper electrode 508, a current flows from the lower electrode 504 to the upper electrode 508, causing the light emitting layer 506 to emit light. That is, the light emitting layer 506 corresponding to the region where the lower electrode 504 is provided emits light. Note that although the light emitting element 350 in the following description corresponds to the lower electrode 504, the light emitting element may correspond to a light emitting layer, for example.

By increasing the length dx with respect to the length dz between the lower electrode 504 and the upper electrode 508, leakage current between adjacent lower electrodes 504 can be suppressed, and erroneous light emission of adjacent light emitting elements 602 can be suppressed. I can do it.

For example, an organic EL film can be used for the light emitting layer 506. Further, an inorganic EL film can be used for the light emitting layer 506. The upper electrode 508 is made of, for example, a transparent electrode such as indium tin oxide (ITO) so as to transmit the emission wavelength of the light emitting layer 506. Note that in this embodiment, the entire upper electrode 508 transmits the emission wavelength of the light emitting layer 506, but the entire upper electrode 508 does not need to transmit the emission wavelength. Specifically, it is sufficient that the region from which light is emitted from each light emitting element 602 (corresponding to the lower electrode 504) transmits the emission wavelength.

Note that in this embodiment, one light emitting layer 506 is provided for the lower electrode 504 provided in the light emitting chip 400-i (i is an integer from 1 to 20). That is, the light emitting layer 506 is common to all the lower electrodes 504 provided in the light emitting chip 400-i, but this is not the case. For example, a first plurality of lower electrodes 504 among the plurality of lower electrodes 504 provided on the light emitting chip 400-i are covered with the first light emitting layer 506, and a first plurality of lower electrodes 504 among the plurality of lower electrodes 504 provided on the light emitting chip 400-i are A configuration may be adopted in which the second plurality of lower electrodes 504 are covered with the second light emitting layer 506. Further, the light emitting layer 506 may be individually provided for each of the plurality of lower electrodes 504 provided in the light emitting chip 400-i.

Note that although this embodiment has described a configuration in which an organic EL (Electro-Luminescence) is used as a mechanism for emitting light, an LED (Light Emitting Diode) may be used as a light emitting element. When an LED is used as a light emitting element, the light emitting element 350 corresponds to one LED.

As explained using FIG. 4, one light emitting chip 400 has four sets of a plurality of light emitting elements 602 arranged along the main scanning direction, and one set of the plurality of light emitting elements 602 is arranged in the sub scanning direction. is shifted by 5 μm in the main scanning direction with respect to the other set. When exposing one line of the photoreceptor 102, the light emission timings of the four sets are controlled so that the corresponding line of the photoreceptor 102 is exposed. Therefore, as shown in FIG. 7, four sets of four light emitting elements 602 having substantially the same position in the main scanning direction expose the photoreceptor 102 at positions shifted by 5 μm. In this way, by overlapping the spots of each light emitting element 602 with each other, a smooth electrostatic latent image is formed. Note that in this embodiment, the number of sets is four, but the number of sets can be two or more.

As described above, the exposure head 106 of this embodiment has 20 light emitting chips 400 arranged in two rows in a staggered manner along the main scanning direction, and each light emitting chip 400 has a zigzag pattern along the main scanning direction. It has four sets of a plurality of light emitting elements 602 arranged in the same manner. Each set is arranged along the sub-scanning direction, and the position of one of the adjacent sets in the main-scanning direction is shifted by 5 μm for a resolution of 4800 dpi with respect to the position of the other set in the main-scanning direction. Ru. When looking at the entire exposure head 106, the positions of the plurality of light emitting elements 602 in the main scanning direction are different. Note that although the positions of the plurality of light emitting elements 602 in the sub-scanning direction are not the same, the light emission timing of each light emitting element 602 is adjusted so that the same line of the photoreceptor 102 is exposed. Therefore, spots by each of the plurality of light emitting elements 602 can be formed on the photoreceptor 102 at intervals of about 5 μm on one line in the main scanning direction. In the following description, the position where each of the plurality of light emitting elements 602 forms a spot will be referred to as a "dot". Furthermore, when the light emitting element 602 emits light at a dot position, the dot is referred to as an "exposed dot", and when the light emitting element 602 does not emit light at the dot position, the dot is referred to as a "non-exposed dot". write.

FIG. 8 shows a control configuration of each light emitting chip 400 by the image controller 800. Image data indicating the gradation value of each pixel of an image to be formed is input to the image data generation unit 801. The image data generation unit 801 performs dithering processing (halftone processing) on the image data at a resolution instructed by the CPU 811, and outputs the processed image data to the light amount correction unit 802. The image data after halftone processing indicates whether each dot forming the image is an exposed dot or a non-exposed dot. In other words, the image data after halftone processing indicates whether or not the light emitting element 602 corresponding to each dot emits light. The light amount correction unit 802 performs light amount correction on the image data based on the correction information, and outputs the image data after the light amount correction to the chip data conversion unit 803. A synchronization signal generation unit 804 generates a line synchronization signal (Lsync) 808. The line synchronization signal 808 is used to determine the data portion of the image data that corresponds to one line in the main scanning direction on the photoreceptor 102. The chip data converter 803 transmits one line of image data (DATA) 807 to each light emitting chip 400 in synchronization with a line synchronization signal 808 . Note that a chip select signal (CS) 805 indicates which light emitting chip 400 the image data 807 is addressed to. Additionally, the chip data converter 803 transmits a clock signal (CLK) 806 to each light emitting chip 400.

Correction information, which will be described later, is stored in the storage section 810 of the printed circuit board 202. Note that each block shown in FIG. 8 is configured to be able to exchange various information by transmitting and receiving a control signal (CTL) 809. When each light emitting chip 400 receives image data 807 from the chip data converter 803, it performs a light emitting operation according to the received image data 807 at the input timing of the next line synchronization signal 808.

FIG. 9 is a block diagram of the light emitting chip 400. A digital-to-analog converter (D/A) 901 outputs an analog voltage according to a digital value that is a set value set by the CPU 811. The digital value is indicated in the correction information, and the CPU 811 determines the digital value to be set for the D/A 901 of each light emitting chip 400 by reading out the correction information stored in the storage unit 810. The light emitting elements 602 of the light emitting chip 400 are grouped into a plurality of blocks in the main scanning direction. Each group is provided with one corresponding reference current source 902. In FIG. 9, the light emitting elements 602 are grouped into five groups, and therefore the light emitting chip 400 has reference current sources 902-1 to 902-5 corresponding to each group. Reference current sources 902-1 to 902-5 output a reference current according to an output value output by D/A 901, that is, an analog voltage, to each light emitting element 602 of a corresponding group. In this way, the D/A 901 functions as a current control unit that controls the reference current to the light emitting element 602. The amount of light emitted by the light emitting element 602 is controlled based on the reference current output by the corresponding reference current source 902.

FIG. 10 is a block diagram of the light amount correction section 802. The light amount correction value A, the light amount correction value B, and the spot correction value C are indicated in the correction information. The CPU 811 reads out the correction information stored in the storage section 810 and notifies the light amount correction value A, the light amount correction value B, and the spot correction value C to the light amount correction section 802. The light amount correction unit 802 corrects the binarized image data input from the image data generation unit 801 based on the light amount correction value A, the light amount correction value B, and the spot correction value C, respectively.

The light amount correction value A is a correction value for correcting the difference in light amount between groups of light emitting chips 400. In this embodiment, since the light emitting elements 602 in one light emitting chip 400 are grouped into five, five light intensity correction values A are set for one light emitting chip 400. One group, that is, one reference current source 902, is associated with one light amount correction value A. That is, the light amount correction value A is a correction value that is set for each group of light emitting chips that share the reference current source 902, and has a value that reduces the light amount as described later.

The light amount correction value B is a correction value for correcting the difference in light amount between the light emitting elements 602 within the group. Although details will be described later, in this embodiment, four light amount correction values B are associated with one group of one light emitting chip 400. For example, a plurality of light emitting elements 602 that emit light using a reference current from one reference current source 902 are subgrouped into four subgroups according to their positions in the main scanning direction. Note that the light emitting elements 602 included in one subgroup form a spot continuously in the main scanning direction. Then, one light amount correction value B is associated with one subgroup. That is, the light amount correction value B is a correction value that is set for each subgroup within the group of light emitting chips that share the reference current source 902, and has a value that reduces the light amount.

The spot correction value C is a value indicating the amount of deviation of the spot from the reference value (hereinafter referred to as the amount of spot deviation) for correcting the difference in light amount due to the enlargement of the spot by the light emitting element 602 in the main scanning direction. The spot correction value C is set for each light emitting element 602 whose spot becomes enlarged. Note that the light emitting element 602 for which the spot correction value C is not set is interpreted as having a spot correction value C of 0. Although details will be described later, the effect when the spot produced by the light emitting element 602 enlarges in the main scanning direction differs depending on the gradation. Specifically, when the gradation is high, the density increases as the spot enlarges in the main scanning direction. Therefore, if the spot for forming a portion with a high gradation value is enlarged in the main scanning direction, the light amount is reduced. On the other hand, when the gradation is low, the density becomes low because the spot becomes enlarged in the main scanning direction. Therefore, if the spot for forming a portion with a low gradation value is enlarged in the main scanning direction, the amount of light is increased. Note that the absolute value of the increase/decrease in the amount of light increases as the amount of spot shift increases.

Correction information including the light amount correction value A, the light amount correction value B, and the spot correction value C is stored in the storage unit 810 before shipping. Further, the CPU 811 can obtain the light amount correction value A, the light amount correction value B, and the spot correction value C using a method described later, and can update the correction information stored in the storage unit 810.

The image data dithered by the image data generation unit 801 is input to the gradation determination unit 1105 and the image correction unit 1109. As described above, the image data indicates whether or not each light emitting element 602 is caused to emit light when exposing each line of the photoreceptor 102 in the main scanning direction. That is, in this embodiment, the image data generation unit 801 performs binary dither processing to generate image data composed of binary pixels corresponding to each light emitting element.

The gradation determination unit 1105 determines the gradation value of the pixel based on the input image data and notifies the gradation-by-gradation correction unit 1106. The gradation-by-gradation correction unit 1106 has a correction table for each gradation. Note that the correction table is included in the correction information. The correction table is a table showing reference light amount correction values for each gradation. Note that a positive value of the reference light amount correction value indicates that the amount of light is increased, and a negative value of the reference light amount correction value indicates that the amount of light is decreased. As described above, the effect when the spot enlarges in the main scanning direction differs depending on the gradation. For example, the gradation determination unit 1105 classifies the gradation of the pixel of interest into three types: low gradation, middle gradation, and high gradation based on the pixel of interest and its surrounding pixels using a first threshold and a second threshold. shall be taken as a thing. The pixels input to the gradation determination unit 1105 are pixels that have been dithered, and are, for example, binarized in this embodiment. Therefore, the original density of the pixel of interest is expressed as the average density including its surrounding pixels. Therefore, the gradation determination unit 1105 classifies the gradation of the pixel of interest based on, for example, the pixel of interest and its surrounding pixels. The range of peripheral pixels may be, for example, comparable to the dither matrix. Alternatively, it may be about 3×3 pixels centered on the pixel of interest. Furthermore, if the pixel value of interest is corrected based on the surrounding pixel values before correction, there is a risk that the correction will be excessive. Therefore, the corrected pixel may be fed back to the gradation determination unit 1105, and the gradation of the pixel of interest may be classified based on the values of the corrected surrounding pixels. Note that the first threshold is larger than the second threshold, a gradation value larger than the first threshold is a high gradation, a gradation value smaller than the second threshold is a low gradation, and a gradation value greater than the second threshold and the first A gradation value below the threshold is a middle gradation. The reference light amount correction value indicated by the correction table is a positive value at a low gradation, a negative value at a high gradation, and 0 at a middle gradation. In other words, the negative reference light amount correction value is 0 at low and middle gradations, and the positive reference light amount correction value is 0 at high and middle gradations.

The gradation-by-gradation correction unit 1106 converts the standard light amount correction value of the gradation of the pixel notified from the gradation determination unit 1105 into the amount of spot deviation indicated by the spot correction value C of the light emitting element 602 that forms the dots constituting the pixel. The light amount correction value D of the dot is determined by correcting the dot based on the following. As an example, the gradation-by-gradation correction unit 1106 holds coefficient information indicating the correspondence between the spot deviation amount (that is, the correction value C) and the coefficient, and stores the reference light amount of the gradation notified from the gradation determination unit 1105. A light amount correction value D is obtained by multiplying the correction value by a coefficient corresponding to the spot shift amount. The correspondence between the spot deviation amount (that is, the spot correction value C) and the coefficient may be experimentally determined in advance for each spot size, for example, and maintained. Note that the light amount correction value D of a dot formed by a light emitting element 602 to which a spot correction value C is not set, that is, a light emitting element 602 whose spot correction value C is 0, is always 0. The gradation-by-gradation correction unit 1106 outputs data indicating the light amount correction value D of each dot making up the image to the image correction unit 1109.

The calculation unit 1107 calculates the light amount correction value E of each light emitting element 602 arranged at different positions in the main scanning direction based on the light amount correction value A and the light amount correction value B. The light amount correction value E of the light emitting element 602 is the sum of the light amount correction value A of the group to which the light emitting element 602 belongs and the light amount 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 a negative value, and is a positive value. It has no value. That is, the value of the sum is a value indicating that the amount of light is to be left unchanged or decreased, and is not a value indicating that the amount of light is to be increased. The light amount correction value E is also a correction value for the light amount of each dot on one line in the main scanning direction formed by the light emitting elements 602 arranged at different positions in the main scanning direction. The calculation unit 1107 outputs the light amount correction value E of each dot in one line in the main scanning direction to the image correction unit 1109.

The image correction unit 1109 inputs data indicating the light intensity correction value D of each dot constituting the image, first data indicating the light intensity correction value D of the dot that increases the light intensity, and light intensity correction value D of the dot that decreases the light intensity. The second data shown in FIG. Furthermore, the image correction unit 1109 generates third data indicating the light amount correction value E of each dot constituting the image, based on the light amount correction value E of each dot in one line in the main scanning direction. Then, the image correction unit 1109 adds the absolute value of the light amount correction value D and the absolute value of the light amount correction value E of the same dot of the second data and the third data, and corrects the total light amount of each dot constituting the image. Fourth data indicating the value is generated. The total light amount correction value of each dot indicated by the fourth data indicates that the amount of decrease in light amount is 0 or more, and is hereinafter referred to as subtraction data. On the other hand, the light amount correction value D of each dot indicated by the first data indicates that the amount of increase in light amount is 0 or more, and is hereinafter referred to as addition data. The image correction unit 1109 corrects image data based on the subtraction data and addition data. In this embodiment, the image correction unit 1109 performs image correction in units of partial images of a predetermined size that are part of the image to be formed. In this example, the size of the partial image is 10×10 pixels (100 pixels in total). FIG. 11A shows an example of a partial image of a 10×10 pixel portion of an image formed by image data before correction. In FIG. 11(A), one square indicates one pixel. Note that the shaded pixels indicate pixels to which toner adheres, and the white pixels indicate pixels to which toner does not adhere. Note that since the density of the formed image has a value that corresponds to the amount of light from the light emitting element, the light amount correction can also be referred to as density correction.

In this embodiment, it is assumed that one pixel is formed by one continuous dot in each of the main scanning direction and the sub-scanning direction. FIG. 11(B) shows an example of the 10×10 image data of FIG. 11(A). Hereinafter, the light emitting elements 602 corresponding to the ten dots in the main scanning direction in FIG. 11(B) will be referred to as light emitting elements #1 to #10. The Kth square (K is an integer from 1 to 10) from the left side of FIG. 11(B) indicates a dot (spot) caused by light emitting element #K. Specifically, the shaded cells indicate that the exposed dots, that is, the light emitting element #K are to be caused to emit light, and the white cells are the non-exposed dots, that is, that the light emitting element #K is not to be caused to emit light. Note that the vertical direction in FIG. 11(B) corresponds to the position in the sub-scanning direction. For example, light emitting element #1 is shown to emit light at the first to fourth, seventh, and eighth dot formation positions among the ten dot formation positions in the sub-scanning direction. FIG. 11B can be regarded as indicating whether each of the 10×10 dots forming one pixel is an exposed dot or a non-exposed dot.

In the following, the dots (spots) shown in FIGS. 11(B) to 11(D) are identified by numbers in the main scanning direction and the sub-scanning direction. In the main scanning direction, the leftmost dot is numbered 1, and the rightmost dot is numbered 10. The numbers in the sub-scanning direction are 1 for the uppermost dot and 10 for the lowermost dot. For example, the second dot in the main scanning direction and the third dot in the sub-scanning direction is expressed as (2, 3).

The image correction unit 1109 has a threshold matrix table for subtraction and a threshold matrix table for addition. The threshold value matrix table is a table showing threshold values for 10×10 pixels, that is, 10×10 dots, on which image correction is performed. The image correction unit 1109 compares the absolute value of the total light intensity correction value of the dots corresponding to the partial image among the dots of the image indicated by the subtraction data with the threshold value of the corresponding dot indicated by the threshold value matrix table for subtraction. do. Then, the image correction unit 1109 determines a first change dot for a dot for which the absolute value of the total light amount correction value exceeds the threshold value of the threshold value matrix table for subtraction.

FIG. 11C shows an example of the determination result based on the subtraction threshold matrix table for the one-pixel portion corresponding to FIG. 11B. In FIG. 11C, the dots at positions (4, 2), (7, 5), (2, 8), and (8, 10) are determined to be the first changed dots. When the first changed dot is an exposed dot, the image correction unit 1109 changes the first changed dot to a non-exposed dot. On the other hand, if the first changed dot is a non-exposed dot, the image correction unit 1109 leaves the first changed dot as a non-exposed dot. Therefore, the image correction unit 1109 corrects the image data of FIG. 11(B) as shown in FIG. 11(D). The dot at position (4, 2) in FIG. 11(B) is originally a non-exposed dot, and therefore remains a non-exposed dot even after correction. On the other hand, the dots at positions (7, 5), (2, 8), and (8, 10) have been corrected from exposed dots to non-exposed dots.

Similarly, the image correction unit 1109 uses the addition data and the threshold value matrix table for addition to perform the second changed dot determination. When the second changed dot is a non-exposed dot, the image correction unit 1109 changes the second changed dot to an exposed dot. On the other hand, when the second changed dot is an exposed dot, the image correction unit 1109 leaves the second changed dot as an exposed dot. When the same dot is selected as the first changed dot and the second changed dot, the image correction unit 1109 does not change the exposure/non-exposure of the dot and leaves it in the state indicated by the original image data. Note that a threshold matrix table having high spatial frequency characteristics used in the generally known blue noise mask method can be used.

The same threshold matrix table (10×10 dots in this example) is used repeatedly in the main scanning direction and the sub-scanning direction. However, since the subtraction data and addition data to be compared are for the entire image and are not repeated at any period, it is possible to suppress the occurrence of image defects at processing boundaries. Note that in the threshold value matrix table, the threshold values are set so that the intervals between the first changed dots and the intervals between the second changed dots are not uniform. Moire can be prevented from occurring by making the intervals between the first modified dots and the intervals between the second modified dots uneven.

Furthermore, by making the correction resolution sufficiently fine with respect to the pixel size of the original image data, it becomes possible to correct the amount of light with high precision. Furthermore, by performing the light amount correction before the chip data conversion unit 803 divides the image data of each light emitting chip 400, image defects occur at the boundaries of the light emitting chips 400 compared to a configuration in which the light amount correction is performed after the division. You can refrain from doing that.

In this manner, in this embodiment, the exposure/non-exposure of dots obtained by dividing one pixel indicated by image data is corrected in units of partial images of a predetermined area (10×10 pixels in this example). With this configuration, it is possible to perform simple and highly accurate correction compared to performing light amount correction using a complicated analog circuit. In addition, the occurrence of image defects is prevented by correcting the light amount based on the light amount correction value of each light emitting element 602 that forms a spot continuously in the main scanning direction, that is, the light amount correction value at each consecutive position in the main scanning direction. be able to.

In this embodiment, variations in the light amount of each light emitting element 602 in the main scanning direction are corrected in two stages. First, as a first-stage correction, the variation in the amount of light between the light emitting chips 400 is corrected by adjusting the digital value set in the D/A 901 of the light emitting chips 400. In order to determine the digital value to be set in the D/A 901 of each light-emitting chip 400, all the light-emitting elements 602 in the light-emitting chip 400 are turned on and the light amount value of each light-emitting element 602 in the light-emitting chip 400 is measured. Then, a digital value to be set in the D/A 901 is determined so that the light amount of the light emitting element 602 with the lowest light amount in the light emitting chip 400 becomes the target light amount. Therefore, the amount of light from all the light emitting elements 602 in the light emitting chip 400 exceeds the target amount of light. Therefore, as described above, the light amount correction value E of each light emitting element is a value indicating that the light amount is left unchanged or reduced. By performing the first stage of light amount correction using the digital value set in the D/A 901, the amount of correction in the light amount correction unit 802 can be reduced, and therefore, deterioration of image quality due to image data correction can be suppressed.

The second stage of correction is correction of light amount fluctuations within the light emitting chip 400, and is executed by the light amount correction unit 802 correcting the image data as described above. The light intensity correction value A, light intensity correction value B, and spot correction value C used by the light intensity correction unit 802 and the digital values input to the D/A 901 of each light emitting chip 400 described above are the measurement results in the assembly and adjustment process of the exposure head 106. Generated based on. Each generated correction value is stored in the storage unit 810 as correction information. The CPU 811 reads out the correction information, sets the light amount correction value A, the light amount correction value B, and the spot correction value C in the light amount correction unit 802, and also sets a digital value in the D/A 901 of each light emitting chip 400.

Note that the spot correction value C indicates the amount of deviation of the spot from the reference value (spot deviation amount). To measure the spot correction value C, each of the light emitting elements 602 is caused to emit light individually. Then, the spot size is measured by reading the spot with a CCD camera, the amount of change from the reference value is measured, and the occurrence position, that is, the relationship with the light emitting element 602 is set as the spot correction value C.

●Generation of correction information Note that the correction information may be generated within the image forming apparatus. FIG. 12 shows a light amount correction chart which is a measurement image formed on a sheet to generate correction information. The light amount correction chart is formed by the image forming apparatus in response to a user's instruction to perform light amount unevenness adjustment. The user causes the reading unit 100 to read the sheet on which the light amount correction chart is formed. Thereby, the CPU 811 obtains chart data that is the reading result by the reading unit 100. The chart data is data indicating the density distribution in the main scanning direction for each of the plurality of gradation images 2101 to 2106. Note that although the correction information generation process is executed by the CPU 811, for example, it may be executed by another information processing apparatus if there is image data obtained by reading a correction chart formed by an image forming apparatus.

The light amount correction chart includes a plurality of gradation images 2101 to 2106 that are band-shaped in the main scanning direction, and reference marks 2111-1 to 2119-19 and 2112-1 to 2112- placed above and below the gradation images 2101 to 2106. 19. Each reference mark is a marker image for specifying the position of each light emitting chip 400, and is formed by light emission from the light emitting element 602 at the end of each light emitting chip 400 in the main scanning direction. For example, the reference mark 2111-2 is formed by light emission from the four light emitting elements 602 at the right end of the light emitting chip 400-2 and the four light emitting elements 602 at the left end of the light emitting chip 400-3. The CPU 811 determines each reference mark based on the chart data. Then, the CPU 811 determines the light emitting chips 400-1 to 400- for each of the gradation images 2101 to 2106 by a line connecting the reference mark 2111-p (p is an integer from 1 to 19) and the reference mark 2112-p. 20 is determined. For example, region B1 in FIG. 12 is determined to be formed by light emitting chip 400-2. It is determined that the left end in FIG. 12 is formed by the light emitting chip 400-1, and the right end in FIG. 12 is determined to be formed by the light emitting chip 400-20.

The set of gradation images 2101 and 2102 is a band-shaped area of uniform density formed by image data of the same gradation value. However, when forming the gradation image 2102, the CPU 811 changes the digital value set to the D/A 901 of each light emitting chip 400 to the digital value set to the D/A 901 of each light emitting chip 400 when forming the gradation image 2101. Lower the value by a predetermined ratio. Therefore, the density of the gradation image 2102 is lower than the density of the gradation image 2101. The same applies to the set of gradation images 2103 and 2104 and the set of gradation images 2105 and 2106. Note that the tone values indicated by the image data used to form the set of tone images 2101 and 2102, the set of tone images 2103 and 2104, and the set of tone images 2105 and 2106 are different. Specifically, the gradation value indicated by the image data when forming the set of gradation images 2101 and 2102 is made the highest, and the gradation value indicated by the image data when forming the set of gradation images 2105 and 2106 is set to the highest. to the lowest. Note that the density of the gradation image 2102 is higher than the density of the gradation image 2103, and the density of the gradation image 2104 is higher than the density of the gradation image 2105. In this way, the correction chart includes a plurality of band-shaped regions of uniform density arranged in parallel in the sub-scanning direction of the image forming apparatus and whose longitudinal direction is the main-scanning direction. Furthermore, it includes a reference mark corresponding to the position of the light emitting chip arranged along the main scanning direction. Here, the correction chart includes a plurality of sets of band-shaped areas formed with different densities, with one set being at least two band-shaped areas corresponding to image data of the same density. However, in at least two band-shaped areas included in one set, the setting values of the D/A 901 are different values, for example, a first setting value and a second setting value. Although this set value is common to each group in this example, it does not necessarily have to be common, and it is sufficient if there is a difference within one group. Note that the correction chart in FIG. 12 includes reference marks in order to specify the range in the image corresponding to each light emitting chip. However, if the device that generates the correction information knows in advance the range corresponding to the light emitting chip in the image, the reference mark does not necessarily have to be included.

Next, a method of converting chart data read by the reading unit 100 into light amount data will be described using FIGS. 13 and 16. When the CPU 811 reads the correction chart (S1601), it identifies the section corresponding to the light emitting chip based on the reference mark (S1602), and converts the density distribution of the correction chart into a light amount distribution (S1603). For this purpose, the CPU 811 obtains average densities 2101_D to 2106_D for each of the gradation images 2101 to 2016 by averaging the read densities at each position in the main scanning direction. FIG. 13 shows the relationship between the digital values set in the D/A 901 when forming each of the gradation images 2101 to 2106 and the average densities 2101_D to 2106_D. The CPU 811 calculates the amount of change k1 in the digital value with respect to the change in density for the set of gradation images 2101 and 2102. Specifically, the CPU 811 calculates the amount of change k1 by dividing the difference between the digital values set in the D/A 901 when forming the gradation images 2101 and 2102 by the difference between the average density 2101_D and the average density 2102_D. demand. Similarly, the CPU 811 determines an amount of change k2 for the set of gradation images 2103 and 2104, and an amount of change k3 for the set of gradation images 2104 and 21054.

The CPU 811 calculates the light amount distribution in the main scanning direction of the gradation image 2101 by multiplying the density at each position in the main scanning direction of the gradation image 2101 determined based on the chart data by the slope k1. Similarly, the CPU 811 determines the light amount distribution in the main scanning direction for the gradation image 2103 and the gradation image 2105 as well. Note that instead of changing the digital value set in the D/A 901, it is also possible to adopt a configuration in which the light amount distribution is determined by changing the gradation of image data for forming the gradation images 2101 and 2102. By multiplying the density distribution by the ratio of the set value to the density (set value/density), the density distribution in the main scanning direction is converted to a distribution of digital values (ie, set values) set in the D/A 901. In this embodiment, this value is called the light amount. This amount of light is obtained by converting the density into a set value, and the distribution does not change even if the value changes.

In this embodiment, the CPU 811 calculates a digital value to be set in the D/A 901, a light amount correction value A, and a light amount correction value B based on the light amount distribution of the gradation image 2103, which is an image in an intermediate density region (S1604 ~S1606). Further, the CPU 811 calculates a spot correction value C based on the light amount distribution of the gradation image 2101 in the high density area and the gradation image 2105 in the low density area (S1607). Below, using FIG. 14, a method for obtaining the digital value to be set in the D/A 901, the light amount correction value A, and the light amount correction value B will be described.

FIG. 14 shows the light amount distribution of the gradation image 2103. Note that FIG. 14 shows only a portion corresponding to one light emitting chip 400. Which part of the gradation image 2103 is formed by which light emitting chip 400 can be determined by the reference mark, as described using FIG. 12. The CPU 811 determines a digital value to be set in the D/A 901 for each light emitting chip, that is, for each group, so that the lowest light amount in FIG. 14 becomes the target light amount T (target value). Specifically, by increasing the digital value set in the D/A 901 when forming the gradation image 2103 by the digital value corresponding to the value obtained by subtracting the lowest light amount in FIG. determines the digital value to be set in the D/A 901. The determined digital value is stored in a non-volatile storage medium as a new setting value. The saved setting values are set as digital values input to the D/A 901 of the corresponding group during image formation. That is, a bias is added to the digital value input to the D/A 901 of each group so that the lowest light amount of that group is set as the target light amount.

The light amount 2301 in FIG. 14 is the light amount at a predetermined position within the range where dots are formed by the plurality of light emitting elements 602 in the group corresponding to the reference current source 902-1. Similarly, the amounts of light 2302 to 2305 are the amounts of light at predetermined positions within the range where dots are formed by the plurality of light emitting elements 602 in the group corresponding to the reference current sources 902-2 to 902-5, respectively. For example, the CPU 811 sets the difference between the light amount 2301 and the lowest light amount in FIG. 14 as the light amount correction value A associated with the reference current source 902-1. Note that, as described above, the lowest light amount in FIG. 14 becomes the target light amount T depending on the digital value set in the D/A 901. That is, the amount of light in FIG. 14 becomes equal to or greater than the target value of the amount of light depending on the digital value set in the D/A 901. The CPU 811 similarly obtains the light amount correction values A associated with the reference current sources 902-2 to 902-5. The predetermined position within the range in which dots are formed by the light-emitting elements 602 may be, for example, the edge or center of the range, or the average of the entire range may be used as the amount of light at the predetermined position. Note that the light amount correction value A is a value obtained by subtracting the light amount at a predetermined position of each group from the lowest light amount within the range of each group, and its sign is negative.

Further, the CPU 811 determines, for example, the amount of light at four positions within the range where dots are formed by the plurality of light emitting elements 602 in the group corresponding to the reference current source 902-1. Note that the positions for determining the amount of light are each selected from within the range where dots are formed by the plurality of light emitting elements 602 of one subgroup. The CPU 811 sets the difference between each of the four determined light quantities and the light quantity 2301 as a light quantity correction value B associated with each subgroup of the reference current source 902-1. The CPU 811 similarly determines the light amount correction value B associated with the reference current sources 902-2 to 902-5. The amount of light for each subgroup may also be at the edge or center of the range corresponding to the subgroup. Alternatively, the average or representative value of the range may be used as the light amount of the range. For example, if the light emitting elements of each subgroup are arranged consecutively in the main scanning direction, the section divided by the reference mark is further divided into subsections with a length equivalent to the subgroup, and the average light amount within each subsection is The value or the value of the representative point within the sub-interval may be used as the light amount of the sub-group. Note that the light amount correction value B is a value obtained by subtracting the light amount at a predetermined position of each subgroup from the lowest light amount within the range of each group, and its sign is negative.

In this way, the entire light emitting elements 602 within a group are corrected using the light intensity correction value A with the reference current source 902 as a unit, and the light intensity variation between subgroups of the light emitting elements 602 within the group is corrected using the light intensity correction value B. . With this configuration, the light amount correction value B can be expressed with a small number of bits, and the amount of correction information can be reduced. As an example, the light amount correction value A can be represented by 4 bits, and the light amount correction value B, which indicates the light amount fluctuation within the group, that is, the residual component, can be represented by 2 bits.

Next, a method for determining the spot correction value C will be explained. FIG. 15(A) is another example showing the light amount distribution of tone images 2101, 2103, and 2105. Note that in FIG. 15A, the light amounts of each of the gradation images 2101, 2103, and 2105 are normalized and displayed. That is, to explain the gradation image 2101, the value obtained by dividing the amount of light at each position in the main scanning direction of the gradation image 2101 by the average amount of light of the gradation image 2101 is taken as the value of the vertical axis in FIG. The same applies to the gradation images 2103 and 2105. Because of the standardization, the light quantities of the gradation images 2101, 2103, and 2105 have similar values at most positions in the main scanning direction.

However, if the spot produced by the light emitting element 602 changes locally due to manufacturing variations in the exposure head 106, the light amounts of the gradation images 2101, 2103, and 2105 will become different. Specifically, in the case of a gradation image 2105 with a low gradation, if the spot becomes locally large, sufficient emission intensity cannot be obtained and the density becomes low. That is, when converted into light amount, the light amount decreases as shown by reference numeral 2307 in FIG. 15(A). On the other hand, in the case of a high-gradation image 2101, the density increases due to the gaps between adjacent pixels collapsing. That is, when converted into light amount, the light amount increases as shown by reference numeral 2306 in FIG. 15(A). Note that reference numeral 2308 in FIG. 15(A) indicates the light amount of the medium gradation image 2103.

The solid line in FIG. 15(B) shows the density characteristics when there is no variation in the spot, and the dotted line shows the density characteristics when the spot becomes larger than the reference. As shown in FIG. 15B, when the spot becomes larger than the reference, the density increases in the high gradation area and decreases in the low gradation area. Note that the influence in the middle gradation area is small.

The CPU 811 calculates the normalized peak value of the light amount of the gradation image 2101 (reference numeral 2306 in FIG. 15(A)) and the normalized peak value of the light amount of the gradation image 2105 (reference numeral 2307 in FIG. 15(A)). ) to find the peak value difference. The image forming apparatus stores in advance determination information indicating the relationship between the experimentally determined peak value difference and the spot deviation amount (spot size variation). The CPU 811 uses the determination information based on the determined peak value difference to determine the spot correction value C associated with the light emitting element 602 corresponding to the position in the main scanning direction where the normalized light amount is changing. For example, the determination information includes a coefficient for converting the above-mentioned peak value difference into a spot diameter, and the peak value difference is converted into an index value indicating the spot diameter. This value may then be saved as the spot correction value C. Furthermore, if this coefficient is provided for each peak value difference, nonlinear conversion can be handled. At the time of correction, for example, the correction value C, which is the index value of the spot diameter, is multiplied by, for example, a predetermined coefficient and converted into an index value of the amount of light emitted, and the correction may be performed based on this. In this way, the correction value C is determined based on the difference in light amount between the high-density area and the low-density area of the correction chart. Since the difference in light amount is determined based on the density of each area, it can be said that the correction value C is determined based on the density difference between the high density area and the low density area of the correction chart.

Note that the specific values used in the description of this embodiment are merely examples, and the present invention is not limited to the use of these specific values. Alternatively, the light amount may be corrected with high precision by performing the light amount correction in units of dots obtained by dividing one pixel.

As described above, in this embodiment, the light amount fluctuation of each light emitting element 602 in the main scanning direction is corrected in two stages. First, the image controller 800 corrects the difference in light amount between the light emitting chips 400 using a digital value set in the D/A 901 in the light emitting chips 400. Then, the image controller 800 corrects the variation in the light amount of each light emitting element 602 in the light emitting chip 400 by correcting the image data. By correcting the difference in light intensity between the light emitting chips 400 using a digital value set in the D/A 901 in the light emitting chip 400, the amount of image data correction can be reduced, and deterioration in image quality due to image data correction can be suppressed. I can do it. In addition, by correcting the difference in the light amount of the light emitting elements 602 in the light emitting chip 400 by correcting the image data, it is simpler and more accurate than a configuration in which a correction circuit is provided that individually corrects the current flowing in the light emitting elements 602. It can be corrected to

Further, the image data is corrected by using a partial image as a unit and changing exposed dots and non-exposed dots using a threshold matrix having the same size as the partial image. The same threshold matrix is used repeatedly for each partial image that makes up the image. However, since the light amount correction value compared with the threshold matrix is for the entire image and is unrelated to the size of the threshold matrix, it is possible to suppress the occurrence of image defects at the boundaries of partial images. Further, since the exposure dots/non-exposed dots are changed in units of a plurality of dots constituting one pixel, the light amount can be corrected with high precision.

[Other embodiments]
The present invention provides a system or device with a program that implements one or more of the functions of the embodiments described above via a network or a storage medium, and one or more processors in the computer of the system or device reads and executes the program. This can also be achieved by processing. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

The invention is not limited to the embodiments described above, and various changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, the following claims are hereby appended to disclose the scope of the invention.

106: exposure head, 400-1 to 400-20: light emitting chip, 602: light emitting element, 801: image data correction section, 802: light amount correction section, 803: data conversion section, 811: CPU

Claims (11)

An image forming apparatus,
a reading means for reading an image formed on the sheet;
An exposure head including a plurality of light emitting chips arranged at different positions in a main scanning direction, each of the plurality of light emitting chips having a plurality of current sources that supply current according to a set value, and a plurality of current sources that supply a current according to a set value. and a group of a plurality of light emitting elements, each of which is supplied with current;
an image forming unit that develops an electrostatic latent image on a photoreceptor according to image data to form an image on the photoreceptor, and forms an image corresponding to the electrostatic latent image on a sheet;
a correction means for correcting the image data in order to correct unevenness in light amount of the exposure head;
generating means for generating correction information by the correction means,
The correction means corrects the difference in light emission amount between the groups of the plurality of light emitting elements based on a first correction value, and corrects the difference in the amount of light emitted by the light emitting elements in the group of the plurality of light emitting elements based on the second correction value. correcting a difference in light emission amount between subgroups, correcting a difference in spot size due to light emission of each of the plurality of light emitting elements based on a third correction value,
The generating means generates the first correction value, the second correction value, and the third correction value based on an image read by the reading means from a predetermined correction chart formed by the image forming means. An image forming apparatus that generates and stores an image. The image forming apparatus according to claim 1,
The correction chart includes a plurality of areas of uniform density arranged in a sub-scanning direction perpendicular to the main-scanning direction and having a uniform density with the main-scanning direction as the longitudinal direction, and the plurality of areas have the same density and The image data is formed by changing the density of the image data by forming a set of at least two areas formed by the different setting values,
The generating means is
determining a ratio of the set value to the density based on the difference between the density of the area included in the set of areas of the correction chart and the set value;
Obtaining the density for each section corresponding to the group consisting of the plurality of light emitting elements in the region, and generating the first correction value based on the ratio so that the density for each section is set as a target value. ,
For each section, obtain the concentration for each subsection corresponding to the subgroup, and generate the second correction value based on the ratio so that the concentration between the subsections becomes the target value;
The image forming apparatus is characterized in that the third correction value is generated based on a density difference between the regions having different densities at a specific position in the main scanning direction. The image forming apparatus according to claim 2,
The correction chart further includes a reference mark corresponding to a position of each of the plurality of light emitting chips arranged along the main scanning direction,
The image forming apparatus is characterized in that the generating means specifies a section corresponding to the group made up of the plurality of light emitting elements based on the reference mark. The image forming apparatus according to claim 2 or 3,
The concentration for each section is the concentration at a position included in each section,
The image forming apparatus is characterized in that the density for each sub-section is a density at a position included in each of the sub-sections. The image forming apparatus according to claim 4,
The positions included in each of the sections are corresponding positions in each of the sections,
The image forming apparatus is characterized in that positions included in each of the sub-sections are corresponding positions in each of the sub-sections. The image forming apparatus according to claim 4 or 5,
The positions included in each of the sections are the ends or the center of each of the sections,
The image forming apparatus is characterized in that a position included in each of the sub-sections is an end or a center of each of the sub-sections. The image forming apparatus according to claim 2 or 3,
The concentration for each section is the average concentration for each section,
The image forming apparatus is characterized in that the density of each sub-section is an average density of each of the sub-sections. The image forming apparatus according to any one of claims 1 to 7,
The image forming apparatus is characterized in that the generating means further determines the set value so that the amount of light emitted by each of the plurality of light emitting chips is equal to or greater than a target value. A correction chart for correcting light amount unevenness of an image forming apparatus,
The image forming apparatus includes:
a reading means for reading an image formed on the sheet;
An exposure head including a plurality of light emitting chips arranged at different positions in a main scanning direction, each of the plurality of light emitting chips having a plurality of current sources that supply current according to a set value, and a plurality of current sources that supply a current according to a set value. and a group of a plurality of light emitting elements, each of which is supplied with current;
an image forming unit that develops an electrostatic latent image on a photoreceptor according to image data to form an image on the photoreceptor, and forms an image corresponding to the electrostatic latent image on a sheet;
a correction means for correcting the image data in order to correct unevenness in light amount of the exposure head;
generating means for generating correction information by the correction means,
The correction means corrects the difference in light emission amount between the groups of the plurality of light emitting elements based on a first correction value, and corrects the difference in the amount of light emitted by the light emitting elements in the group of the plurality of light emitting elements based on the second correction value. correcting a difference in light emission amount between subgroups, correcting a difference in spot size due to light emission of each of the plurality of light emitting elements based on a third correction value,
The correction chart includes a plurality of regions of uniform density arranged in a sub-scanning direction perpendicular to the main-scanning direction and having a longitudinal direction in the main-scanning direction, and the light-emitting region arranged along the main-scanning direction. a reference mark corresponding to the position of the chip, and the plurality of regions are formed by changing the density of the image data, forming a set of at least two regions formed with the same density and different setting values. Ori,
The generating means is
determining a ratio of the set value to the density based on the difference between the density of the area included in the set of areas of the correction chart and the set value;
obtaining the density for each section divided by the reference mark in the region, and generating the first correction value based on the ratio so that the density within the section is set as a target value;
For each section, obtain the concentration of a subsection corresponding to the subgroup, and generate the second correction value based on the ratio so that the concentration between the subsections becomes the target value;
The correction chart is characterized in that the third correction value is generated based on a density difference between the regions having different densities at a specific position in the main scanning direction. A method for generating correction information for correcting exposure unevenness of an image forming apparatus, the method comprising:
The image forming apparatus includes:
An exposure head including a plurality of light emitting chips arranged at different positions in a main scanning direction, each of the plurality of light emitting chips having a plurality of current sources that supply current according to a set value, and a plurality of current sources that supply a current according to a set value. and a group of a plurality of light emitting elements, each of which is supplied with current;
an image forming unit that develops an electrostatic latent image on a photoreceptor according to image data to form an image on the photoreceptor, and forms an image corresponding to the electrostatic latent image on a sheet;
a correction means for correcting the image data in order to correct unevenness in light amount of the exposure head;
The correction means corrects the difference in light emission amount between the groups of the plurality of light emitting elements based on a first correction value, and corrects the difference in the amount of light emitted by the light emitting elements in the group of the plurality of light emitting elements based on the second correction value. correcting a difference in light emission amount between subgroups, correcting a difference in spot size due to light emission of each of the plurality of light emitting elements based on a third correction value,
In the generation method,
A generating means generates the first correction value, the second correction value, and the third correction value based on an image obtained by reading a predetermined correction chart formed by the image forming means with a reading means. A method for generating correction information, characterized in that the correction information is stored. The method for generating correction information according to claim 10,
The correction chart includes a plurality of areas of uniform density arranged in a sub-scanning direction perpendicular to the main-scanning direction and having a uniform density with the main-scanning direction as the longitudinal direction, and the plurality of areas have the same density and The image data is formed by changing the density of the image data by forming a set of at least two areas formed by the different setting values,
The generating means,
determining a ratio of the set value to the density based on the difference between the density of the area included in the set of areas of the correction chart and the set value;
Obtaining the density for each section corresponding to the group consisting of the plurality of light emitting elements in the region, and generating the first correction value based on the ratio so that the density for each section is set as a target value. ,
For each section, obtain the concentration for each subsection corresponding to the subgroup, and generate the second correction value based on the ratio so that the concentration between the subsections becomes the target value;
A method for generating correction information, characterized in that the third correction value is generated based on a density difference between the regions having different densities at a specific position in the main scanning direction.

Images