Patent Grant
12140880
The present invention relates to an image-forming apparatus, a correction chart, and a method.
As a type of electrophotographic image-forming apparatus, an apparatus that uses a solid-state exposure method is commonly known, in which a latent image is formed by exposing a photosensitive drum with light emitted by LEDs (e.g., organic EL elements) instead of laser light. An exposure head of this type of apparatus includes a light-emitting element set that includes a plurality of light-emitting elements arranged parallel with an axial direction of the photosensitive drum, and a rod lens array that focuses light from the light-emitting element set on a surface of the photosensitive drum. Japanese Patent Laid-Open No. 2018-1679 discloses a method in an image-forming apparatus that uses the solid-state exposure method for correcting, based on a result of reading a test chart, an unevenness (unevenness in light amount) in an image due to a light amount difference between a plurality of light-emitting chips each having a light-emitting element set.
However, with the correction method disclosed by Japanese Patent Laid-Open No. 2018-1679, recognition accuracy of sections included in the test chart that correspond to the light-emitting chips might be insufficient, resulting in inability to favorably correct the unevenness in light amount. Factors that cause an unevenness in light amount may include not only an error per light-emitting chip, but also an error in lenses in the lens array and individual differences between circuits within a single light-emitting chip. To capture a position of such a local unevenness with high accuracy to correct the unevenness, it is important to be capable of precisely recognizing which part of the chart corresponds to which part of each chip in the exposure head.
In view of the foregoing issue, the present invention aims to provide an improved mechanism for correcting an unevenness in light amount in an image.
According to an aspect, there is provided an image-forming apparatus including: an image-forming unit including a photosensitive member and an exposure head configured to expose the photosensitive member with light in accordance with image data; a generating unit configured to cause the image-forming unit to form an image of a correction chart, and generate correction data for correcting an unevenness in light amount of the exposure head using a read image of the correction chart obtained by optically reading the formed image; and a correction unit configured to correct the image data input to the image-forming unit based on the correction data generated by the generating unit. The exposure head includes a plurality of light-emitting chips located at different positions in a first direction parallel with an axial direction of the photosensitive member, each of the plurality of light-emitting chips including an array of a plurality of light-emitting elements arranged at least in the first direction. The correction chart includes: a plurality of regions arranged in a second direction perpendicular to the first direction and having different gradations, at least one first reference mark located on one side of the plurality of regions in the second direction and indicating a boundary between adjoining light-emitting chips among the plurality of light-emitting chips, and at least one second reference mark located on the other side of the plurality of regions in the second direction and indicating the boundary between adjoining light-emitting chips among the plurality of light-emitting chips. The generating unit is configured to determine partial regions respectively formed by the plurality of light-emitting chips within the plurality of regions based on positions of the first reference mark and the corresponding second reference mark in the read image of the correction chart, and generate the correction data based on a result of measuring a density in each of the determined partial regions.
Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).
Hereinafter, embodiments will be described in detail with reference to the attached drawings. Note, the following embodiments are not intended to limit the scope of the claimed invention. Multiple features are described in the embodiments, but limitation is not made to an invention that requires all such features, and multiple such features may be combined as appropriate. Furthermore, in the attached drawings, the same reference numerals are given to the same or similar configurations, and redundant description thereof is omitted.
The image-making unit 103 includes image-forming units 101a, 101b, 101c, and 101d. The image-forming units 101a, 101b, 101c, and 101d form toner images in black, yellow, magenta, and cyan, respectively. The image-forming units 101a, 101b, 101c and 101d have the same configuration, and are also referred to collectively as image-forming units 101 below. A photosensitive member 102 of each image-forming unit 101 is driven to rotate in the clockwise direction in the figure during image formation. A charger 107 electrically charges a corresponding photosensitive member 102. An exposure head 106 exposes a corresponding photosensitive member 102 with light in accordance with image data to form an electrostatic latent image on a surface of the photosensitive member 102. A developer 108 develops the electrostatic latent image on the surface of the photosensitive member 102 with toner to form a toner image. The toner image formed on the surface of the photosensitive member 102 is transferred to a sheet that is being transported on a transfer belt 111. A color image containing four color components, namely, black, yellow, magenta, and cyan, can be formed by transferring the toner images of the four photosensitive members 102 to the sheet in a superimposed manner.
The transport unit 105 controls feed and transport of sheets. Specifically, the transport unit 105 feeds a sheet from a unit designated from among internal storage units 109a and 109b, an external storage unit 109c, and a manual feed unit 109d to a transport path in the image-forming apparatus 1. The fed sheet is transported to a registration roller 110. The registration roller 110 transfers the sheet onto the transfer belt 111 at an appropriate timing such that the toner image of each photosensitive member 102 is transferred to the sheet. As mentioned above, the toner images are transferred to the sheet while the sheet is transported on the transfer belt 111. The fixing unit 104 fixes the toner images to the sheet by heating and pressurizing the sheet to which the toner images have been transferred. After the toner images have been fixed, the sheet is discharged to outside the image-forming apparatus 1 by a discharge roller 112. An optical sensor 113 is located at a position facing the transfer belt 111. The optical sensor 113 is used to detect a misalignment (color misalignment) between color components in a test image formed on the transfer belt 111 by the image-forming units 101. If a color misalignment is detected, the image-forming positions of the image-forming units 101a, 101b, 101c, and 101d are corrected so as to compensate for the detected color misalignment under the control of a later-described image controller 800.
Although an example in which the toner image is directly transferred from each photosensitive member 102 to the sheet on the transfer belt 111 has been described here, the toner image may alternatively be transferred indirectly from each photosensitive member 102 to the sheet via an intermediate transfer member. Further, although an example of forming a color image using toner of multiple colors has been described here, the technology according to the present disclosure is also applicable to an image-forming apparatus that forms a monochrome image using toner of a single color.
The light-emitting element array in each light-emitting chip 400 is a two-dimensional array consisting of N columns (N is an integer of 2 or more) in the axial direction D1 and M rows (M is an integer of 2 or more) in the circumferential direction D2. In an illustrative embodiment, N may be 748 and M may be 4; in this case, each light-emitting chip 400 has a total of 2992 (=748×4) light-emitting elements 602. In the entire light-emitting element set 201 that includes 20 light-emitting chips 400, 14960 light-emitting elements are arranged in the axial direction D1. The pitch of light-emitting elements 602 adjoining in the axial direction D1 may be approximately 21.16 μm in correspondence with a resolution of 1200 dpi. In this case, the length of the entire light-emitting element set 201 in the axial direction D1 is approximately 316 mm (maximum width of a formable image), and the length of each light-emitting chip 400 in the axial direction D1 is approximately 15.8 mm. The M light-emitting elements in the respective columns are shifted from each other in the axial direction D1 at a pitch of about 5 μm, which corresponds to a resolution of 4800 dpi, and arranged in a staircase pattern.
In the present embodiment, the light-emitting elements 602 are configured as organic electro-luminescence (EL) elements. For example, an organic EL film can be used as the light-emitting layer 506. In another embodiment, the light-emitting elements 602 may be configured as inorganic EL elements by using an inorganic EL film as the light-emitting layer 506. Generally, the light-emitting element 602 may be any type of light-emitting diodes (LEDs).
The upper electrode 508 is constituted by a transparent electrode made of indium tin oxide (ITO) or the like so as to allow the emission wavelength of the light-emitting layer 506 to be transmitted. In the example in
Although one continuous light-emitting layer 506 is formed in
While the use of organic EL elements as the light-emitting elements 602 facilitates downsizing and cost reduction of the apparatus, there are cases where the amount of light that can be emitted by a single organic EL element is insufficient to form an image with a desired density. The present embodiment adopts a multiple exposure technique to subject each pixel region (spot region) on the photosensitive member 102 to multiple exposure by causing the plurality of light-emitting elements 602 arranged in the circumferential direction of the photosensitive member 102 to successively emit light.
Due to four light-emitting elements in each column being arranged in a staircase pattern as in the example in
In the following description, a spot region in which a spot of an electrostatic latent image is formed as a result of multiple exposure performed with light emitted by M light-emitting elements 602 is referred to as an “exposed dot”, and a spot region in which no spot is formed due to no light-emitting element 602 emitting light is referred to as a “non-exposed dot”.
An image data generation unit 801 performs image processing on image data received from the reading unit 100 or an external device, and generates image data in a binary bitmap format for performing control to turn on and off light emission by the light-emitting elements 602 of the light-emitting chips 400 on the printed circuit board 202. Image processing here may include, for example, raster transformation and halftoning (e.g., dithering). Image data after being subjected to halftoning is a set of bits indicating, for a position of each of pixels constituting an image to be formed, whether or not to cause corresponding M light-emitting elements 602 to emit light. If a bit for a certain pixel position indicates “emission”, a corresponding spot region on the surface of the photosensitive member 102 will be an exposed dot. If this bit indicates “non-emission”, the corresponding spot region will be a non-exposed dot. The image data generation unit 801 outputs the generated image data to the light amount correction unit 802.
The light amount correction unit 802 performs correction processing on the image data input from the image data generation unit 801 to correct an unevenness in light amount of the exposure head 106 based on correction data generated by the CPU 811. The light amount correction unit 802 then outputs the corrected image data to the chip data conversion unit 803. The correction of an unevenness in light amount performed by the light amount correction unit 802 will be described in more detail later.
The chip data conversion unit 803 reads pixel values within a corresponding read range in the image data input from the light amount correction unit 802 in each line period identified by the line synchronization signal Lsync, and sends the image data indicating the read pixel values over the data signal line 807. The image data DATA is, for example, a sequence of pixel values corresponding to the respective light-emitting elements 602 of twenty light-emitting chips 400. The chip data conversion unit 803 designates which light-emitting chip 400 is to receive each portion of the image data DATA, by means of the chip select signal CS. The chip data conversion unit 803 generates the clock signal CLK and supplies the generated signal to the light-emitting chips 400 in order to achieve synchronization of timings of transmitting and receiving individual signal values with the light-emitting chips 400.
The synchronization signal generating unit 804 determines delimitation of a line of the image data, generates the line synchronization signal Lsync, and supplies the generated line synchronization signal Lsync to the synchronization signal line 808.
A storage unit 810 on the printed circuit board 202 is a memory or a register that stores control data for controlling light emission performed by the light-emitting chips 400. As will be described later, the control data stored in the storage unit 810 may include, for example, setting values related to an amount of supplied current and later-described correction data.
The light-emitting chips 400 drive light-emitting elements 602 in each line period identified by the line synchronization signal Lsync in accordance with the image data after correction of light amounts input from the chip data conversion unit 803. For example, if the chip select signal CS indicates a data reception timing for a certain light-emitting chip 400, this light-emitting chip 400 receives a portion of the image data DATA that is directed thereto via the data signal line 807. Each light-emitting chip 400 then drives light-emitting elements 602 in a light-emitting element array of M rows and N columns in accordance with the pixel values included in the received image data.
The CPU 811 controls the entire image-forming apparatus 1. For example, the CPU 811 controls generation of the aforementioned image data, light amount correction, generation of the line synchronization signal, and transmission of the image data to the printed circuit board 202. In the present embodiment, the CPU 811 also executes calibration using a correction chart in response to an instruction given via a user interface. Specifically, the CPU 811 causes the image-forming units 101 to form an image of the correction chart on a sheet. After the sheet with the image of the correction chart formed thereon has been set on the reading unit 100, the CPU 811 causes the reading unit 100 to optically read the image of the correction chart on the sheet. The CPU 811 then generates correction data for correcting an unevenness in light amount of the exposure head 106 using the read image of the correction chart that is obtained as a result of the reading. Accordingly, in the present embodiment, the CPU 811 functions as a generating unit that generates the correction data. An example of the correction data that may be generated by the CPU 811 will be described in more detail later.
The D/A 901 performs digital-to-analog conversion on a digital value indicating a setting value of the reference current, which is set by the CPU 811, and outputs an analog signal having a voltage corresponding to the setting value to the reference current sources 902. The setting value of the reference current is stored in advance in the aforementioned storage unit 810, read by the CPU 811, and output to the D/A 901. Each of the reference current sources 902-1 to 902-5 supplies a reference current corresponding to the voltage of the analog signal input from the D/A 901 to a corresponding group of the light-emitting elements 602. Note that the number of reference current sources 902 provided in each light-emitting chip 400 is not limited to the above example, and may be any number depending on wiring length in the chip or the driving capability of the reference current sources 902.
<5-1. Factors of Unevenness in Light Amount>
Examples of factors that cause an unevenness in light amount in the image-forming apparatus employing a solid-state exposure method may include the following items:
Optical errors due to manufacturing variations of lenses can occur at any position on a light-emitting chip 400 in the longitudinal direction (axial direction of the photosensitive member 102), and cause a local unevenness in light amount. Errors in the amount of supplied current due to individual differences of the current sources can occur per group of light-emitting elements 602 that are supplied with a current from the reference current sources 902. Note that errors in the amount of supplied current are not necessarily uniform even within one group since the current loss on a circuit can differ depending on the positions of the light-emitting elements 602. Fluctuations in spot size affect density characteristics relative to the gradation value of the image to be reproduced. Specifically, as the spot size enlarges on an imaging plane of light from the exposure head 106, the density of a printed image in a low gradation range becomes lower relative to an equivalent gradation value due to an insufficient light amount. Meanwhile, if the spot size enlarges, the density of a printed image in a high gradation range becomes higher relative to an equivalent gradation value due to clipping between adjoining spots. Fluctuations in spot size are primarily caused by variations during manufacturing of the exposure head 106. In the following description, an imaging spot with an enlarged size is referred to as an abnormal spot. An abnormal spot causes a local unevenness in density in the longitudinal direction of the exposure head 106. Note that the terms “unevenness in light amount” and “unevenness in density” may be used interchangeably herein, since the density of each spot in a formed image correlates with the light amount during exposure by corresponding light-emitting elements.
<5-2. Basic Correction Method>
Possible methods for correcting an unevenness in light amount include adjusting the amount of current supplied from the reference current sources 902 to the light-emitting chips 400, and correcting input image data so as to vary the local areal gradation. The present embodiment adopts both methods. The two correction methods may be combined in various manners; for example, it is conceivable to correct a coarse unevenness in light amount between the light-emitting chips 400 using the former method, and correct a fine unevenness in light amount within each light-emitting chip 400 using the latter method.
The former method may be performed by rewriting the setting value regarding the amount of supplied current within the control data stored in the storage unit 810. For example, the unevenness in light amount between the light-emitting chips 400 may be measured in an inspection phase after assembly of a product, without using a later-described correction chart 200. For example, the light amount from each light-emitting element 602 is measured in a state where all light-emitting elements 602 emit light, and a light-emitting element 602 with the lowest measured value is selected per light-emitting chip 400. Then, a setting value (later-described adjustment target value T) related to the amount of current supplied to each light-emitting chip 400 is determined such that the amount of light from each selected light-emitting element 602 becomes a target light amount that is constant over the light-emitting chips 400. The determined setting value is written into the storage unit 810 of each light-emitting chip 400. During subsequent image formation in the image-forming apparatus 1, differences in the light amount between the light-emitting chips 400 are generally eliminated, and the unevenness in light amount within each light-emitting chip 400 can be corrected using the latter method.
The latter method, which allows for fine correction of an unevenness in light amount, will be described below with reference to
If a pixel at the same position as a pixel to be changed that is selected in the correction matrix IM2 indicates an exposed dot in the small image IM1, the light amount correction unit 802 changes this pixel to a non-exposed dot (i.e., inverts the pixel value).
Here, assuming that the light amount is to be increased or decreased by a large proportion, it would be necessary to select a large number of pixels to be changed and to change the pixel values thereof. However, such changes would have a risk of disrupting dot shapes in an image to be reproduced and degrading image quality. In the present embodiment, a coarse unevenness in light amount between the light-emitting chips 400 is corrected by adjusting the amount of supplied current, and only the remaining unevenness in light amount is corrected by changing the areal gradation, as mentioned above. Thus, the proportion by which the light amount is to be increased or decreased using the latter method is kept relatively small. Accordingly, it is possible to prevent degradation of image quality due to a collapse of dot shapes.
Although an example in which the size of the small image is 10×10 pixels has been described here, the present embodiment is not limited to this example. For example, when a pixel to be changed is selected in accordance with the blue noise mask method, setting the size of the small image to a larger size, namely 128×128 pixels or 256×256 pixels can spread the spatial frequency more randomly and significantly suppress interference moiré.
<5-3. Configuration Example of Correction Chart>
To effectively correct an unevenness in light amount as mentioned above, it is important to capture with high accuracy a local position at which the unevenness is occurring and to precisely determine at which position in the axial direction and to what degree the light amount is to be increased or decreased. In the present embodiment, the image-forming apparatus 1 uses a correction chart 200 such as that shown in
Referring to
The correction chart 200 includes at least one first reference mark, namely first reference marks 2111-1 to 2111-19 located on one side (upper side in the figure) of the band-shaped regions 2101 to 2106 in the circumferential direction D2. In addition, the correction chart 200 includes at least one second reference mark, namely second reference marks 2112-1 to 2112-19 located on the other side (lower side in the figure) of the band-shaped regions 2101 to 2106 in the circumferential direction D2. The first reference marks 2111-1 to 2111-19 represent the boundaries of adjoining light-emitting chips among the plurality of light-emitting chips 400. The second reference marks 2112-1 to 2112-19 also represent those boundaries. When the correction data is generated based on the read image of the correction chart 200, the CPU 811 determines a representative position of a first reference mark 2111-p and a representative position of a corresponding second reference mark 2112-p (p=1, 2, . . . , 19) in the read image. The representative position here may be, for example, a centroid, one of the vertices, or the position of an end point in the axial direction D1 of each reference mark, depending on the mark shape. The CPU 811 then determines partial regions respectively formed by the light-emitting chips 400-1 to 400-20 within each of the band-shaped regions 2101 to 2106, using line segments connecting the determined representative positions (shown as dashed lines in the figure) as boundary lines. The CPU 811 measures the density in each of the thus-determined partial regions, and generates later-described correction data based on the measurement results.
The first reference marks 2111-1 to 2111-19 and the second reference marks 2112-1 to 2112-19 may be formed by effective light-emitting elements at least at one end of each light-emitting chip 400 in the axial direction D1 emitting light. For example, the first reference mark 2111-1 and the second reference mark 2112-1 may be formed as a result of four effective light-emitting elements 602 at the right end of the light-emitting chip 400-1 emitting light. The first reference mark 2111-2 and the second reference mark 2112-2 may be formed as a result of four effective light-emitting elements 602 at the right end of the light-emitting chip 400-2 emitting light. When specific light-emitting elements 602 adjoining a boundary between chips are driven to form a pair of the first reference mark 2111-p and the second reference mark 2112-p, a line segment connecting the representative positions of these reference marks substantially coincides with the boundary. For example, six partial regions between dashed lines 2113-1 and 2113-2 in the figure are image regions formed by the light-emitting chip 400-2.
For example, the CPU 811 causes the image-forming unit 101 to form an image of the correction chart 200 on a sheet in response to an instruction to execute calibration given via a user interface. A user or an engineer sets, on the reading unit 100, the sheet with the image of the correction chart 200 formed thereon and gives an instruction to read the image. The reading unit 100 optically reads the image of the correction chart 200 and outputs the read image to the CPU 811. The read image serves as input to generation of the correction data for correcting the unevenness in light amount. There is a possibility that, during this reading operation, a tilted read image is obtained due to skewing of the sheet. In the present embodiment, the correction chart 200 has six band-shaped regions 2101 to 2106. Thus, the effect of skewing of the sheet is more significant than in the case where only a single or a few band-shaped regions are present. If the correction chart 200 has only either the first reference marks 2111 or the second reference marks 2112, it is difficult to precisely determine in a tilted read image the boundaries between the light-emitting chips. However, in the present embodiment, the correction chart 200 has both the first reference marks 2111 and the second reference marks 2112. This enables the CPU 811 to precisely determine the boundaries between the light-emitting chips based on the positions of those reference marks and appropriately extract the respective partial regions from the read image.
Note that if the reading resolution of the reading unit 100 is different from the resolution of the image formed by the exposure head 106, the CPU 811 translates pixel positions in accordance with the ratio between these resolutions to extract the partial regions from the read image of the correction chart 200. For example, if the reading resolution is one-fourth of the resolution of the image formed by the exposure head 106, the resolution difference can be compensated for by multiplying an index of each pixel position in the read image by four (or by performing upsampling by a factor of four).
<5-4. Derivation of Light Amount Distribution>
The CPU 811 extracts the partial regions formed by the light-emitting chips 400 from the read image of the correction chart 200 based on the positions of the reference marks, and measures the density of the image in each extracted partial region.
k=(d1−d2)/(g1−g2)
Similarly, a conversion factor for converting the density difference in the medium gradation range to a difference in the gradation value can be calculated by dividing the difference in the gradation value between the points 223 and 224 by the density difference. A conversion factor for converting the density difference in the low gradation range to a difference of the gradation value can be calculated by dividing the difference in the gradation value between the points 225 and 226 by the density difference.
Further, a light amount distribution in the axial direction in the light-emitting chip 400 can be derived for the high gradation range by multiplying the density at each pixel position measured along the axial direction for the partial regions of the band-shaped region 2101 by the conversion factor k calculated in accordance with the aforementioned equation. In the present embodiment, the CPU 811 derives the light amount distributions for the high gradation range, the medium gradation range, and the low gradation range. The CPU 811 then generates a light amount correction value A and a light amount correction value B, which will be described later, using the light amount distribution in the medium gradation range. The CPU 811 also generates a later-described light amount correction value C using the light amount distributions in the high gradation range and the low gradation range.
Note that the differences in gradation of the image between the band-shaped regions formed on the sheet may be realized by varying the amount of current supplied to the light-emitting elements 602, instead of making the gradation value of the image data of the correction chart different, between the pairs of the band-shaped regions used to calculate the aforementioned conversion factor.
<5-5. Generation of Correction Data>
(1) Fine Correction of Unevenness in Light Amount (Light Amount Correction Value A and Light Amount Correction Value B)
Note that the CPU 811 may also update the target light amount value T so as to minimize the light amount correction values A and B based on the light amount distribution graph 230 derived using the read image of the correction chart 200. For example, the CPU 811 can update the target light amount value T by additionally writing in the storage unit 810 an offset value to be applied to the setting value of the amount of supplied current that is determined during a product inspection phase.
(2) Elimination of Effects of Abnormal Spot (Spot Correction Value C)
The density in partial regions of the band-shaped regions 2103 and 2104 with gradation in the medium gradation range is substantially unaffected by the presence or absence of the abnormal spot. Therefore, the CPU 811 measures an error in light amount per light-emitting element or per light-emitting element group and generates the light amount correction values A and B using the light amount distribution obtained from the results of measuring the density in partial regions of the band-shaped regions 2103 and 2104, as mentioned above. Meanwhile, the light amount distribution in the high gradation range obtained from the results of measuring the density in partial regions of the band-shaped regions 2101 and 2102 and the light amount distribution in the low gradation range obtained from the results of measuring the density in partial regions of the band-shaped regions 2105 and 2106 may be used to detect an abnormal spot. For example, the CPU 811 detects an abnormal spot by examining the maximum value in the light amount distribution in the high gradation range and the minimum value in the light amount distribution in the low gradation range. The CPU 811 then generates, as a spot correction value C, position(s) of the detected abnormal spot(s) and the amount of fluctuation in spot size at each position (a difference from a predetermined reference value; also referred to as a spot shift amount).
(3) Storing and Updating of Correction Data
Initial values of the correction data that includes the above-described light amount correction value A, light amount correction value B, and spot correction value C may be generated in a pre-shipment inspection phase of the product and stored in the storage unit 810 of each light-emitting chip 400. The CPU 811 updates the data stored in the storage unit 810 of each light-emitting chip 400 with the correction data that is generated as a result of calibration executed after the shipment of the product.
Note that the generation of the correction data in the inspection phase need not necessarily be performed using the correction chart 200. For example, the size of an imaging spot of each light-emitting element 602 may be measured by causing the light-emitting elements 602 to discretely emit light, one by one, and receiving the light with a charged coupled device (CCD) camera placed on the imaging plane.
<5-6. Details of Light Amount Correction Unit>
This section will describe a detailed configuration example of the light amount correction unit 802 that corrects image data using the above-described correction data (light amount correction value A, light amount correction value B, and spot correction value C). When the image-forming apparatus 1 executes a job for image formation, the CPU 811 reads the correction data from the storage unit 810 and supplies the read correction data to the light amount correction unit 802. Image data in bitmap format generated by the image data generation unit 801 is input together with the correction data to the light amount correction unit 802.
The light amount correction value A is a correction value for correcting an unevenness in light amount per group of light-emitting elements 602 in each light-emitting chip 400. The light amount correction value A enables correction of an unevenness in light amount caused by errors in the amount of current supplied to the light-emitting elements due to individual differences between the reference current sources 902. The light amount correction value B is a correction value for correcting the remaining component of the unevenness in light amount per light-emitting element in the group. The spot correction value C is a correction value for correcting an unevenness in light amount caused by an abnormal spot. The spot correction value C may indicate position(s) of detected abnormal spot(s) and a spot shift amount at each position. As mentioned above, the effect of the abnormal spot differs depending on the gradation value. In the present embodiment, it is determined whether to decrease or increase the light amount, depending on the gradation value in the image data. The absolute value of the increase/decrease amount is determined based on the spot shift amount.
The gradation determination unit 1105 determines a gradation range at each pixel position based on the input image data. For example, the gradation determination unit 1105 focuses on a patch image that includes a pixel (pixel of interest) at each pixel position and neighboring pixels, and determines whether the gradation of the pixel of interest belongs to the low gradation range, the medium gradation range, or the high gradation range, based on areal gradation (e.g., average pixel value) in the patch image. The size of the patch image may be as large as a dither matrix, or may be about 3×3 pixels, for example. To avoid overcorrection, the gradation determination unit 1105 may determine the gradation range at each pixel position by receiving feedback of the corrected image data, instead of using the image data before correction. For example, if the areal gradation in the patch image is greater than a first threshold, the gradation range of the pixel of interest is classified as the high gradation range. If the areal gradation in the patch image is smaller than or equal to the first threshold and greater than a second threshold (first threshold>second threshold), the gradation range of the pixel of interest is classified as the medium gradation range. If the areal gradation in the patch image is smaller than or equal to the second threshold, the gradation range of the pixel of interest is classified as the low gradation range. The gradation determination unit 1105 notifies the per-gradation correction unit 1106 of the results of determining the gradation range for each pixel position.
The per-gradation correction unit 1106 has a correction table that holds a reference light amount correction value, which is predetermined for each of the high gradation range, the medium gradation range, and the low gradation range. Generally, the reference light amount correction value for the high gradation range indicates a negative light amount correction value, and the sign thereof being negative means that the light amount is to be decreased. The reference light amount correction value for the low gradation range indicates a positive light amount correction value, and the sign thereof being positive means that the light amount is to be increased. The reference light amount correction value for the medium gradation range may be zero. The per-gradation correction unit 1106 obtains, by referencing the correction table, the reference light amount correction value corresponding to the gradation range of which the per-gradation correction unit 1106 was notified by the gradation determination unit 1105 for each of the pixel positions of abnormal spots indicated by the spot correction value C. Next, the per-gradation correction unit 1106 calculates a light amount correction value D based on the obtained reference light amount correction value and the spot shift amount indicated by the spot correction value C. For example, the light amount correction value D may be the product of the reference light amount correction value and a coefficient corresponding to the spot shift amount. To calculate the light amount correction value D, the per-gradation correction unit 1106 may also have a coefficient table or a relationship equation that defines the relationship between the spot shift amount and the coefficient. The per-gradation correction unit 1106 then outputs the calculated light amount correction value D to the image correction unit 1109. Note that the light amount correction value D may be zero for a pixel position where no abnormal spot is detected.
The calculation unit 1107 calculates a light amount correction value E for each pixel position based on the light amount correction value A and the light amount correction value B. The light amount correction value E may be the sum of the light amount correction value A determined for the group to which the light-emitting element 602 corresponding to each pixel position belongs and the light amount correction value B determined for this light-emitting element 602. Typically, the light amount correction value E may be zero or a negative value. The calculation unit 1107 outputs the calculated light amount correction unit E to the image correction unit 1109.
The image correction unit 1109 determines a percentage of scaling the light amount at each pixel position based on the light amount correction value D input from the per-gradation correction unit 1106 and the light amount correction value E input from the calculation unit 1107. The image correction unit 1109 then increases or decreases the areal light amount at each pixel position by correcting the image data of a small image around the pixel position in accordance with the method that has been described in detail with reference to
In the present embodiment, an unevenness in light amount is corrected by changing the pixel values in the image data at the stage before data output from the chip data conversion unit 803 to each light-emitting chip 400. Accordingly, the chip data conversion unit 803 can distribute the image data to the light-emitting chips 400 with a common control logic, regardless of the correction of the unevenness in light amount.
Various embodiments of the technology according to the present disclosure have been described in detail above with reference to
In the above embodiment, the first and second reference marks may be formed as a result of effective light-emitting elements at least at one end in the first direction of each light-emitting chip. According to this configuration, an end point of an exposure range of each light-emitting chip (i.e., a boundary position of a partial region to be extracted from the read image) can be directly indicated by the reference marks.
In the above embodiment, the plurality of regions may include at least a region for measuring an error in light amount per light-emitting element or per group of light-emitting elements within each light-emitting chip, and a region for measuring a fluctuation in spot size in an imaging plane of light. These regions may be arranged in the circumferential direction of the photosensitive member, i.e., the transport direction of a sheet on which an image is to be formed. If many regions are thus arranged in the sheet transport direction in the correction chart, there is a concern that the effect of slight skewing of the sheet when the image of the correction chart is read may result in a relatively significant shift of boundary positions. However, in the above embodiment, the reference marks are printed on both sides of the plurality of regions, thus making it possible to precisely determine the boundaries between the light-emitting chips in the read image of the correction chart, even if the sheet skews.
For example, two of the plurality of regions have different gradations belonging to the medium gradation range, and a light amount distribution in the medium gradation range in the first direction of each light-emitting chip may be derived based on the results of measuring the density in partial regions of these two regions. Since the density in the medium gradation range is substantially unaffected by the presence or absence of an enlarged imaging spot, correction data that enables fine correction of an unevenness in light amount can be generated by measuring an error in light amount using the light amount distribution in the medium gradation range. Another two of the plurality of regions may have different gradations belonging to the high gradation range, and yet another two of the regions may have different gradations belonging to the low gradation range. A light amount distribution in the high gradation range and a light amount distribution in the low gradation range in the first direction of each light-emitting chip may be derived based on the results of measuring the density in partial regions of these regions. The light amount distributions in the high gradation range and the low gradation range are likely to be affected by an enlarged imaging spot. Therefore, correction data can be generated that also enables correction of an unevenness in light amount due to an abnormal spot by detecting an abnormal spot using the light amount distributions and measuring a fluctuation in spot size.
Although the above embodiment uses specific numerical values for description, these specific numerical values are examples, and the present invention is not limited to the specific numerical values used in the embodiment. Specifically, the number of light-emitting chips provided on one printed circuit board is not limited to twenty, and may be any number of one or more. The size of the array of the light-emitting elements in each light-emitting chip 400 is not limited to 4 rows×748 columns, and may be any other size. The pitch of the light-emitting elements in the circumferential direction and the pitch thereof in the axial direction are not limited to about 21.16 m and about 5 m, respectively, and may take any other value.
Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of priority from Japanese Patent Application No. 2022-138341, filed on Aug. 31, 2022, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-138341 | Aug 2022 | JP | national |
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| Number | Date | Country | |
|---|---|---|---|
| 20240069463 A1 | Feb 2024 | US |
