Image forming apparatus and image forming method

Abstract

To provide an image forming apparatus having a charging voltage source and a developing voltage source common to a plurality of image forming parts and capable of obtaining a high-quality image excellent in readability of characters and lines.SOLUTION: An image forming apparatus includes a changing unit that changes a gradation value of input image data from a first gradation value to a second gradation value, a processing unit that performs edge enhancement filter processing on the image data after the processing by the changing unit and performs halftone processing on the image data after the edge enhancement filter processing, and a plurality of image forming units corresponding to toner colors.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus and the like. [Background technology]

[0002] In an image forming apparatus having a common charging voltage source and developing voltage source for a plurality of image forming units, an image forming apparatus is known that performs image density control by applying different exposure conditions to each image forming unit (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-174903 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the image forming apparatus having the above configuration, it is difficult to obtain a high-quality image with excellent readability of characters and lines simply by changing the exposure conditions.

[0005] One of the objects of the present disclosure is to provide an image forming apparatus that has a common charging voltage source and developing voltage source for multiple image forming units, and that is capable of obtaining high-quality images with excellent readability of characters and lines. [Means for solving the problem]

[0006] In order to solve the above problem, the image forming apparatus of the present disclosure comprises a modification unit that modifies the gradation value of input image data from a first gradation value to a second gradation value, a processing unit that performs edge enhancement filter processing on the image data after processing by the modification unit and performs halftone processing on the image data after edge enhancement filter processing, and a plurality of image forming units corresponding to toner colors, wherein the plurality of image forming units form an image using a common development bias set by a specific high density correction processing based on the image data after processing by the processing unit.

[0007] In addition, the image forming method according to the present disclosure includes a modification step of modifying the gradation value of input image data from a first gradation value to a second gradation value, a processing step of performing edge enhancement filter processing on the image data after the modification step and halftone processing on the image data after the edge enhancement filter processing, and an image forming step of forming an image using a plurality of image forming units corresponding to toner colors, wherein the image forming step is characterized in that an image is formed using a common development bias set by a specific high-density correction processing based on the image data after processing in the processing step. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide an image forming apparatus that has a common charging voltage source and developing voltage source for multiple image forming units, and that is capable of obtaining high-quality images with excellent readability of characters and lines. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a front cross-sectional view illustrating the overall configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a diagram illustrating the configuration of a developing unit according to the first embodiment. [Figure 3] FIG. 1 is a diagram illustrating a hardware configuration of an image forming apparatus according to a first embodiment. [Figure 4]FIG. 2 is a diagram illustrating the functional configuration of the image forming apparatus according to the first embodiment. [Figure 5] FIG. 10 is a diagram illustrating a method for calculating the amount of halftoning. [Figure 6] FIG. 2 is a diagram illustrating the overall processing flow according to the first embodiment. [Figure 7] 1 is a flowchart illustrating a processing flow according to the first embodiment. [Figure 8] 1 is a flowchart illustrating a processing flow according to the first embodiment. [Figure 9] 3A to 3C are diagrams illustrating examples of edge enhancement filters according to the first embodiment. [Figure 10] FIG. 2 is a diagram illustrating an example of operation according to the first embodiment. [Figure 11] FIG. 2 is a diagram illustrating an example of operation according to the first embodiment. [Figure 12] FIG. 2 is a diagram illustrating an example of operation according to the first embodiment. [Figure 13] FIG. 10 is a diagram illustrating the functional configuration of an image forming apparatus according to a second embodiment. [Figure 14] 10 is a flowchart illustrating a processing flow according to the third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the following embodiments are examples for explaining the present disclosure, and the technical content of the description set forth in the claims is not limited to the following description.

[0011] [1 First Embodiment] [1.1 Overall structure] 1 is a front cross-sectional view illustrating the overall configuration of a multifunction peripheral 10 as an image forming apparatus according to a first embodiment. The multifunction peripheral 10 includes a main body 100 that houses various components involved in image formation, such as an image forming unit 106, and an image reading unit 120 that is provided above the main body 100 and is capable of generating image data based on a scanned document. The multifunction peripheral 10 is an example of an image forming apparatus that is capable of outputting the image data generated by the image reading unit 120 as a printed matter.

[0012] Inside the main body 100, an image forming unit 106 and a fixing unit 31 are provided along a paper transport path S (indicated by a two-dot chain line in the drawing) that starts at the paper feed cassette 80 and ends at the paper discharge tray 90.

[0013] The paper feed cassette 80 is configured as a box-shaped member that can store stacks of paper, and is detachably attached to the bottom of the multifunction device 10. A pickup roller 81 is provided at the top of the paper feed cassette 80 to pick up the stored paper one sheet at a time from the top and feed it to the paper transport path S.

[0014] The paper discharge tray 90 is formed by utilizing the outer casing of the main body 100, and collects paper sheets on which images have been formed (printed) face down, with the printed surface facing downward.

[0015] Paper transport path S is made up of multiple transport rollers 11a-11d, registration rollers 12, transport path switching means (not shown), etc. Transport rollers 11a-11d are small rollers that promote and assist transport of paper, and pinch and transport paper as they rotate. Registration roller 12 corrects skew of paper on paper transport path S, and transports the paper to transfer unit 6 (secondary transfer roller 65) at a timing that aligns the leading edge of the toner image formed on the surface of a photosensitive drum serving as an image carrier with the leading edge of the paper.

[0016] For example, in the case of single-sided printing in the forward direction relative to the paper transport path S, the paper fed from the paper feed cassette 80 is transported through the transport rollers 11a, the registration rollers 12, the transfer unit 6 (secondary transfer roller 65), and the fixing unit 31, and is then discharged to the paper output tray 90 by the transport rollers 11b. In contrast, in the case of double-sided printing, which includes transport in the reverse direction relative to the paper transport path S, when the leading edge of the paper reaches the transport rollers 11b, the transport rollers 11b rotate in the reverse direction and guide the paper to the paper transport path S formed by the transport rollers 11c and 11d. After passing the transport rollers 11d, the transport path is switched by a transport path switching means (not shown), and the paper is transported to the transfer unit 6 with the print side inverted. After the toner image has been transferred to the reverse side of the initial print side in the transfer unit 6, the paper passes through the fixing unit 31 and is then discharged to the paper output tray 90 by the transport rollers 11b.

[0017] The image forming unit 106, which is provided along the paper transport path S, includes, in order from upstream in the movement direction of the intermediate transfer belt 61, a yellow image forming unit 106Y, a magenta image forming unit 106M, a cyan image forming unit 106C, and a black image forming unit 106K. Here, the image data handled by the multifunction peripheral 10 corresponds to a color image using the colors yellow (Y), magenta (M), cyan (C), and black (K). Therefore, the yellow image forming unit 106Y, the magenta image forming unit 106M, the cyan image forming unit 106C, and the black image forming unit 106K each include a photosensitive drum 3 (3Y, 3M, 3C, 3K), a cleaning unit 4 (4Y, 4M, 4C, 4K), a developing unit 5 (5Y, 5M, 5C, 5K), and a charging unit 7 (7Y, 7M, 7C, 7K). The photosensitive drums 3 (3Y, 3M, 3C, 3K), cleaning units 4 (4Y, 4M, 4C, 4K), developing units 5 (5Y, 5M, 5C, 5K), and charging units 7 (7Y, 7M, 7C, 7K) may have the same configuration for each toner color. Therefore, unless otherwise specified, they will be simply referred to as the image forming unit 106, photosensitive drums 3, cleaning units 4, developing units 5, and charging units 7.

[0018] In addition, the charging units 7 (7Y, 7M, 7C, 7K) included in each of the yellow image forming unit 106Y, magenta image forming unit 106M, cyan image forming unit 106C, and black image forming unit 106K according to the present disclosure are supplied with the same charging voltage from a common charging voltage source, and similarly, the developing units 5 (5Y, 5M, 5C, 5K) are supplied with the same developing bias from a common developing voltage source.

[0019] The exposure unit 1 exposes the charged photosensitive drum 3 to light in accordance with image data input from an external source or image data generated by reading a document with the image reading unit 120, thereby forming an electrostatic latent image on the surface of the photosensitive drum 3 in accordance with the image data. Such an exposure unit 1 can be configured, for example, as an LED unit having a light-emitting element such as an LED (light emitting diode) element and a lens array, or as a laser scanning unit having a laser emitter and a reflecting mirror. The exposure unit 1 is positioned so that irradiation light based on the image data (indicated by a dashed dotted line in the figure) forms an image on the surface of the photosensitive drum 3. Note that the exposure unit 1 exposes the surface of the photosensitive drum 3, which is charged to, for example, -600 V, thereby charging the exposed portion (electrostatic latent image portion) to a charging voltage of -150 V.

[0020] The photosensitive drum 3 is an image carrier that forms an electrostatic latent image corresponding to image data for each toner color. The photosensitive drum 3 can be formed, for example, as a cylindrical image carrier with a photosensitive layer formed on the surface of a conductive support. The photosensitive drum 3 is configured to be rotatable around the axis of the conductive support by a driving force supplied from a driving source (e.g., a motor) not shown. The photosensitive layer can be made of a material that exhibits conductivity when exposed to light, such as amorphous silicon, selenium, selenium alloy, cadmium sulfide, zinc oxide, or an organic optical semiconductor. Note that an endless photosensitive belt can also be used as the image carrier instead of the photosensitive drum 3.

[0021] The cleaning unit 4 is a cleaning unit that collects post-transfer residual toner remaining on the surface of the photosensitive drum 3 after development and transfer. The cleaning unit 4 includes a cleaning blade 41 that faces the photosensitive drum 3. The cleaning blade 41 collects the post-transfer residual toner by scraping it off the surface of the photosensitive drum 3.

[0022] The developing unit 5 develops the electrostatic latent images formed on the respective photosensitive drums 3 with toner of four colors, yellow (Y), magenta (M), cyan (C), and black (K), to form toner images. The developing unit 5 develops the electrostatic latent images using toner of each color supplied from toner cartridges 500 (500(Y), 500(M), 500(C), 500(K)) mounted above the image forming unit 21. The configuration of the developing unit 5 according to the first embodiment will be described later.

[0023] The transfer unit 6 transfers the toner image formed on the surface of the photosensitive drum 3 onto a transfer material such as paper. The transfer unit 6 includes an endless intermediate transfer belt 61, an intermediate transfer belt drive roller 62, an intermediate transfer belt driven roller 63, a primary transfer roller 64, a secondary transfer roller 65, and an intermediate transfer belt cleaning unit 66.

[0024] The intermediate transfer belt 61 is stretched over an intermediate transfer belt drive roller 62, which rotates by a driving force supplied from a drive source (not shown), and an intermediate transfer belt driven roller 63, which is driven to rotate by the driving force of the intermediate transfer belt 61. Primary transfer rollers 64 are provided at positions facing each photosensitive drum 3 across the intermediate transfer belt 61. A primary transfer bias is applied to the primary transfer rollers 64 to transfer the toner images formed on the surfaces of the photosensitive drums 3 onto the intermediate transfer belt 61. The intermediate transfer belt 61 primarily transfers the toner images corresponding to each toner color sequentially while driving from the photosensitive drum (3Y) corresponding to yellow to the photosensitive drum (3K).

[0025] The secondary transfer roller 65 is provided so as to be in pressure contact with the intermediate transfer belt drive roller 62 via the intermediate transfer belt 61. A secondary transfer bias is applied to the secondary transfer roller 65 to secondarily transfer the toner image that has been primarily transferred onto the intermediate transfer belt 61 onto the paper transported along the paper transport path S.

[0026] The intermediate transfer belt cleaning unit 66 is a cleaning unit that collects residual toner remaining on the intermediate transfer belt 61. The intermediate transfer belt cleaning unit 66 includes a belt cleaning blade 661 that contacts the intermediate transfer belt 61 with a predetermined pressure. The belt cleaning blade 661 collects the residual toner by scraping it off the intermediate transfer belt 61.

[0027] The charging unit 7 charges the surface of the photosensitive drum 3 to a predetermined potential. As the charging unit 7, for example, a corona discharge device, a brush-type charging device, a roller-type charging device, an ion generating device, or the like can be used.

[0028] Fixing unit 31 includes heat roller 311 and pressure roller 312. Fixing unit 31 is located downstream of the paper transport path from the secondary transfer position formed by secondary transfer roller 65 and intermediate transfer belt drive roller 62. Heat roller 311 is temperature controlled to maintain a predetermined fixing temperature. When paper with a transferred toner image passes through the nip formed by heat roller 311 and pressure roller 312 that have reached the fixing temperature, heat and pressure are applied, and the toner image on the paper is thermally fixed.

[0029] Image reading unit 120, which is provided above main body 100, includes document table 121 made of a transparent material such as transparent glass. Above document table 121, there is provided document pressing cover 122 which can be opened and closed in the direction of arrow M in the figure via a hinge or the like (not shown). A document feed tray 123 is attached to the top of document pressing cover 122, and an automatic document feeder 125 is provided inside it to transport documents set in document feed tray 123 to document reading unit 124.

[0030] The document reading unit 124 includes a light source, multiple reflecting mirrors, an imaging lens, a line sensor with a light receiving element, and the like. The document reading unit 124 focuses light emitted from the light source and reflected from the reading surface of the document onto the imaging lens using multiple reflecting mirrors. The reflected light focused by the imaging lens forms an image on the light receiving element of the line sensor. The line sensor detects the luminance and chromaticity of the reflected light that forms an image on the light receiving element, and generates image data based on the image of the reading surface of the document. Note that, for example, a CCD (Charge Coupled Device), a CIS (Contact Image Sensor), or the like can be used as the line sensor.

[0031] [1.2 Development section configuration] Next, the developing unit 5 will be described. FIG. 2 is a front cross-sectional view illustrating the configuration of the developing unit 5. Note that FIG. 2 is an enlarged view of the developing unit 5 (for example, the developing unit 5Y for yellow toner color) and its surrounding area in FIG. 1. The configurations of the photosensitive drum 3, cleaning unit 4, and charging unit 7 are the same as those described in FIG. 1, so their description will be omitted here. Also, the reference symbols (Y, M, C, K) used to identify the components corresponding to each toner color will be omitted.

[0032] In this disclosure, a two-component developer (developer DE) consisting of a mixture of toner T and carrier CA is used to develop the toner image. Here, non-magnetic toner can be used as the toner T, and magnetic materials such as iron powder and ferrite can be used as the carrier CA.

[0033] The developing unit 5 develops the electrostatic latent image formed on the surface of the photosensitive drum 3 by supplying toner T to the electrostatic latent image. The developing unit 5 includes stirring members 51a and 51b, a developing roller 52, a doctor blade 54, a developer amount detection unit 55, and the like, and each of these members is held in a predetermined arrangement by a housing 57.

[0034] Inside housing 57, there is provided developer tank 53, which is a developer container that contains developer DE containing toner T. Developer tank 53 contains a two-component developer (developer DE) consisting of toner T and carrier CA, and the toner T contained in the developer DE is supplied to photosensitive drum 3 via developing roller 52.

[0035] The stirring members 51a and 51b may be configured as, for example, auger screws each having a cylindrical rotating shaft with a spiral blade provided on the outer circumferential surface thereof. The stirring members 51a and 51b mix and stir the toner T and carrier CA while rotating in the direction of the arrow in the figure, thereby charging the toner T and circulating the developer DE in a predetermined direction inside the developer tank 53.

[0036] The developing roller 52 is provided above the agitating member 51b and serves as a developer carrier that rotates in the direction of the arrow (counterclockwise) in the figure to supply the developer DE to the photosensitive drum 3. The developing roller 52 is configured as a magnetic roller. The developer DE mixed and rubbed by the agitating members 51a and 51b in the developer tank 53 is attracted to the developing roller 52 in a brush-like manner by the magnetic force of the developing roller 52 and then rotates and transported to the photosensitive drum 3. When the developer layer on the developing roller 52 comes into contact with the electrostatic latent image formed on the photosensitive drum 3, the toner T of the developer DE adheres to the electrostatic latent image, and the electrostatic latent image on the surface of the photosensitive drum 3 is developed into a toner image. At this time, a predetermined developing voltage (developing bias) is applied to the developing roller 52 so that the surface of the developing roller 52 is at a predetermined potential. The developing bias is applied so that the toner T of the developer DE carried on the surface of the developing roller 52 moves smoothly toward the electrostatic latent image on the surface of the photosensitive drum 3.

[0037] The doctor blade 54 is provided so as to form a predetermined gap between itself and the surface of the developing roller 52. The doctor blade 54 is formed as a plate-like member extending in the same axial direction as the axial direction of the developing roller 52. The doctor blade 54 regulates the thickness of the developer DE layer on the surface of the developing roller 52 to a predetermined layer thickness.

[0038] The developer amount detection unit 55 is a sensor that detects the amount of the developer DE in the developer tank 53. The developer amount detection unit 55 can be a transmission type or reflection type optical sensor, a magnetic permeability sensor, a mechanical sensor, or the like.

[0039] [1.3 Hardware Configuration] Next, the hardware configuration of the multifunction peripheral 10 according to the first embodiment will be described with reference to Fig. 3. Note that the same components as those previously described will be assigned the same reference numerals, and the description thereof may be omitted.

[0040] The control unit 101 controls the entire multifunction peripheral 10. The control unit 101 realizes various functions by reading and executing various programs stored in a storage device (for example, the storage 108, the ROM 110, etc.). The control unit 101 may be realized by one or more control devices / arithmetic units (CPUs (Central Processing Units), SoCs (System on Chips)). The control unit 101 may also be configured by a control circuit.

[0041] The display unit 102 displays various types of information to the user, etc. The display unit 102 can be configured by a display device such as an LCD (Liquid Crystal Display) or an organic EL (Electro-Luminescence) display, for example.

[0042] The operation input unit 103 accepts information input from a user or the like. The operation input unit 103 can be configured with hard keys (for example, a numeric keypad), buttons, etc. The operation input unit 103 can be configured as a touch panel that allows input via the display unit 102. In this case, the input method of the touch panel can be a general method such as a resistive film method, an infrared method, an electromagnetic induction method, or a capacitance method.

[0043] The communication unit 104 is a communication interface for communicating with other devices. For example, the communication unit 104 may be a network interface connectable to a wireless LAN or a network interface connectable to Ethernet (registered trademark) via a wired connection. The communication unit 104 may also be a communication device connectable to a mobile communication network such as LTE / 4G / 5G / 6G.

[0044] The image processing unit 105 is composed of a control device / arithmetic unit capable of executing a program, a dedicated image processing circuit, etc., and analyzes the input image data and performs gradation change, edge emphasis filter processing, halftone processing, etc. on the image data to generate (output) image data to be output by the image forming unit 106. The functions realized by the image processing unit 105 will be described with reference to FIG. 4.

[0045] The density adjustment unit 107 functions as a density adjustment mechanism that is configured with a control device / arithmetic unit capable of executing a program, a dedicated density adjustment circuit, etc. The density adjustment unit 107 adjusts the density of the toner image developed on the photosensitive drum 3. The functions realized by the density adjustment unit 107 will be described with reference to FIG. 4.

[0046] Storage 108 is a non-volatile storage device capable of storing programs and data. Storage 108 may be configured with a storage device such as a hard disk drive (HDD) or a solid state drive (SSD). Storage 108 may also be a universal serial bus (USB) memory or the like connectable to a connection terminal (not shown), or may be a storage area provided on a cloud (not shown) connected via a network NW.

[0047] The storage 108 according to the present disclosure has at least a setting value memory area 1081 for storing various setting values ​​for operating the multifunction device 10, a target density memory area 1083 for storing target densities set for each toner color, and a halftone processing amount memory area 1085 for storing detected toner density values ​​and halftone processing amounts in association with each other.

[0048] RAM (Random Access Memory) 109 is the main memory that is mainly used by the control unit 101 when executing processing. RAM 109 is a rewritable memory that temporarily stores programs read from storage 108 or ROM 110, and data including the results of processing execution.

[0049] The ROM (Read Only Memory) 110 is a non-volatile memory that can retain programs and data even when the power is turned off.

[0050] The power supply unit 111 includes a power supply device (not shown), such as a DC power supply, an AC power supply, or a high-voltage power supply, and supplies predetermined power to the photosensitive drum 3, cleaning unit 4, developing unit 5, transfer unit 6, charging unit 7, etc. Note that the power supply unit 111 according to the present disclosure supplies power to the photosensitive drum 3, cleaning unit 4, developing unit 5, transfer unit 6, and charging unit 7 constituting each of the yellow image forming unit 106Y, magenta image forming unit 106M, cyan image forming unit 106C, and black image forming unit 106K, based on control by a power supply control unit 1071 described in the next figure. In particular, the power supply unit 111 according to the present disclosure is configured to supply the same developing bias from a common developing voltage source to the developing unit 5 of each image forming unit 106, and to supply the same charging voltage from a common charging voltage source to the charging unit 7.

[0051] [1.4 Functional Configuration] Next, the functional configuration of the multifunction peripheral 10 will be described with reference to Fig. 4. Fig. 4 is a block diagram illustrating the functional configuration of the multifunction peripheral 10, particularly the functions realized by the image processing unit 105 and density adjustment unit 107.

[0052] The image processing unit 105 includes, as functional units, an image data analysis unit 1051, a gradation modification unit 1053, an edge enhancement filter processing unit 1055, and a halftone processing unit 1057. Note that some or all of the functional processing units included in the image processing unit 105 may be configured with electronic circuits.

[0053] When executing a print job, the image data analysis unit 1051 analyzes (interprets) the image data of the print job and renders it into bitmap data. The image data analysis unit 1051 may also be configured to draw objects included in the image data and generate intermediate code. The generated intermediate code can also contain tag information such as the object's type (image / text / graphics, etc.) as object attributes, edge / non-edge information representing the edge of the object, and information on conversion from RGB color signals to YMCK signals for each pixel or for each set of pixels of the bitmap data. If the input image data is in bitmap format, the image data analysis unit 1051 may omit the processing described above.

[0054] The gradation change unit 1053 is a functional unit that changes the gradation value of the object included in the image data from a first gradation value (256 gradations (0 to 255) if the density gradation expression width is 8 bits) to a second gradation value (255 gradations (0 to 254)) based on the analysis results by the image data analysis unit 1051.

[0055] The edge enhancement filter processing unit 1055 is a functional unit that performs edge enhancement filter processing on image data (object) whose gradation value has been changed from a first gradation value to a second gradation value. At this time, the edge enhancement filter processing unit 1055 sets a first maximum value that can be set for density gradation as the maximum density gradation value of the edge portion ("255" if the density gradation expression width is 8 bits), and sets a second maximum value ("254" if the density gradation expression width is 8 bits) obtained by subtracting a predetermined value from the first maximum value as the maximum density gradation value of the non-edge portion.

[0056] The halftone processing unit 1057 is a functional unit that performs halftone processing on image data after edge enhancement filtering. Here, an example of calculating the amount of halftone processing according to the present disclosure will be described with reference to FIG.

[0057] 5(a), patch images 1, 2, 3, and 4 are printed on a transfer material such as paper or intermediate transfer belt 61, and the toner density of the patch images is measured. Note that patch images 1, 2, 3, and 4 are images adjusted so that the toner density increases in the order from patch image 1 to patch image 4.

[0058] The amount of halftoning processing for each toner concentration is set in advance, and the correlation between the toner concentration and the amount of halftoning processing shown in FIG. 5B is stored, for example, in the halftoning processing amount storage area 1085 of the storage 108.

[0059] The amount of halftoning at the target density can be calculated by linearly interpolating the color measurement results of the patch image from the density-halftoning amount graph shown in Fig. 5(c). For example, if the target density is 1.4, the amount of halftoning can be calculated as "700" from the density-halftoning amount graph shown in Fig. 5(c).

[0060] 4, the density adjusting unit 107 adjusts the toner density, for example, when the device is started up or when the image forming unit 106 (image forming unit) is replaced. The density adjusting unit 107 includes a power supply control unit 1071, a density correcting unit 1073, and a low-density toner specifying unit 1075 as functional units.

[0061] The power supply control unit 1071 is a functional unit that controls the power output of the power supply unit 111 to adjust the density of the toner image formed on the photosensitive drum 3. Based on instructions from the density correction unit 1073, the power supply control unit 1071 controls the power supply unit 111 to supply the same developing bias from a common developing voltage source to the developing units 5 (5Y, 5M, 5C, 5K) included in each of the image forming units 106, namely, the yellow image forming unit 106Y, the magenta image forming unit 106M, the cyan image forming unit 106C, and the black image forming unit 106K. Note that when the surface potential of the photosensitive drum 3 is adjusted to a constant level, the power supply control unit 1071 may adjust the density by changing only the developing bias as an adjustment of the effective developing potential.

[0062] The density correction unit 1073 is a functional unit that comprehensively controls processes related to density correction. The density correction unit 1073 forms (prints) patch images for each toner color in cooperation with the power supply control unit 1071 based on a common development bias identified by a low-density toner identification unit 1075 (described later). The density correction unit 1073 then calculates the amount of processing for halftone processing based on the measurement results of the toner density (second density value) of the patch image.

[0063] During high-density correction processing, low-density toner specifying unit 1075 calculates a developing bias (second developing bias) for outputting a preset target density for each toner color from the measurement results of the toner density (first density value) of a patch image formed for each toner color with the same predetermined developing bias (first developing bias) supplied from a common developing voltage power supply and the first developing bias. Then, low-density toner specifying unit 1075 determines the toner color with the largest difference (differential developing potential: first adjustment potential) between the second developing bias and the first developing bias required to raise the density to the target density for each toner color as the low-density toner, and specifies image forming unit 106 for that toner color as the reference image forming unit.

[0064] [1.5 Overall processing flow] Next, a description will be given of the flow of processing according to the first embodiment. First, the overall flow of processing according to the first embodiment will be described with reference to FIG.

[0065] In the first embodiment, high density correction is performed by first forming a patch image for each toner color based on a predetermined development bias (for example, a set value before high density correction) and measuring the toner density (first density value) of the patch image (FIG. 6(a)). Then, based on the measurement results of the toner density of the patch image, low density toner specifying unit 1075 calculates the differential development potential (ΔE in the figure) required to obtain (increase) the target density set for each toner color, and specifies image forming unit 106 for the toner color with the largest differential development potential as the reference image forming unit.

[0066] 6(a), if the toner color with the largest differential development potential is yellow (Y), the density correction unit 1073 adjusts the densities of toner colors other than yellow (Y) (magenta (M), cyan (C), and black (K)) based on the development bias for making the toner density of the patch image formed by the yellow image forming unit 106Y specified as the reference image forming unit satisfy the target density. Note that the development bias (first development bias + differential development potential) determined so that the low-density toner used in the reference image forming unit satisfies (ensures) the target density is referred to as the reference development bias.

[0067] 6(b) shows the results of forming patch images of toner colors other than yellow (Y), including yellow (Y), based on the common developing bias for the yellow image forming unit 106Y specified as the reference image forming unit, and measuring the toner densities (second density values) of the patch images. In the first embodiment, patch images of the other toner colors are formed based on the developing bias (common developing bias) for the yellow image forming unit 106Y specified as the reference image forming unit, so the densities of the other toner colors are higher than the target density.

[0068] However, for other toner colors that exhibit toner densities higher than the target density due to density adjustment based on the common development bias, it is necessary to reduce the toner density to the target density by performing image quality processing such as halftone processing on the image data (object) (for example, Figure 6(c)).

[0069] However, when image density is reduced by image quality processing such as halftone processing, jagged edges of objects made of toner (color) other than low-density toner occur, and for example, if the object is a text object, problems arise such as reduced readability of the text and lines.

[0070] Regarding improving the readability of characters and lines, prior art techniques such as those disclosed in Japanese Patent Application Laid-Open No. 2006-262204 and Japanese Patent Application Laid-Open No. 2006-340144 are known. However, in these prior art techniques, the processing of edge portions is highly demanding and a high-performance circuit configuration is required to achieve this processing, making it difficult to improve the readability of characters and lines with a simplified device configuration that is designed to achieve low cost.

[0071] In the first embodiment, even if the image density is reduced by image quality processing such as halftone processing, the gradation value of the input image data is changed from a first gradation value to a second gradation value, edge enhancement filter processing is performed on the image data whose gradation value has been changed, and halftone processing is performed on the image data after the edge enhancement filter processing, thereby improving the readability of characters and lines of objects related to toners (colors) other than low-density toner.

[0072] [1.6 Processing flow for density adjustment] 7 is a flowchart illustrating the flow of processing by the density adjustment unit 107 according to the first embodiment. The processing illustrated in FIG. 7 is executed by the density adjustment unit 107 (power supply control unit 1071, density correction unit 1073, and low-density toner identification unit 1075).

[0073] When the process starts, the low density toner identification unit 1075 calculates a development bias (second development bias) for outputting a predetermined target density for each toner color from the measurement results of the toner density (first density value) of the patch image for each toner color formed with a predetermined identical development bias (first development bias) supplied from a common development voltage source and the first development bias (step S10).

[0074] Based on the calculation results in step S10, the low-density toner identification unit 1075 identifies the image forming unit 106 associated with the toner color having the largest difference between the second development bias and the first development bias as the reference image forming unit, and determines the second development bias associated with the reference image forming unit as the common development bias (step S20).

[0075] The density corrector 1073 applies the common developing bias identified in step S20 to forming patch images for the other toner colors (step S30). Based on the applied common developing bias, the density corrector 1073 forms (prints) patch images for each toner color in cooperation with the power supply controller 1071 and measures the toner density (second density value) of the patch image. At this time, the density corrector 1073 stores the bias value of the applied common developing bias in the set value storage area 1081 as the developing bias to be applied when outputting image data related to the print job.

[0076] Then, in order to output all gradations as targeted based on the second density value, the density correction unit 1073 calibrates the halftone processing amount for each toner color using, for example, the calculation method illustrated in FIG. 5, and then ends the process (step S40).

[0077] [1.7 Image processing flow when outputting images] Next, the process from receiving a print job to outputting image data will be described using the flowchart in Fig. 8. The process described in Fig. 5 is executed by the image processing unit 105 (image data analysis unit 1051, gradation change unit 1053, edge enhancement filter processing unit 1055, and halftone processing unit 1057).

[0078] When processing starts, the image data analysis unit 1051 determines whether or not a print job input has been received (step S100). If it is determined that a print job input has been received, the image data analysis unit 1051 analyzes the image data related to the print job (step S100; Yes → step S110). Based on the analysis result by the image data analysis unit 1051, the gradation change unit 1053 changes the gradation value of the image data (object) related to the received print job from a first gradation value (256 gradations (0 to 255) when the density gradation expression width is 8 bits) to a second gradation value (255 gradations (0 to 254)) (step S120). Note that, if it is determined that a print job input has not been received, the image data analysis unit 1051 waits until a print job input is received (step S100; No).

[0079] In step S130, the edge enhancement filter processing unit 1055 performs edge enhancement filter processing on the image data (object) whose gradation value has been changed from the first gradation value to the second gradation value. The edge enhancement filter processing unit 1055 sets a first maximum value that can be set for density gradation as the maximum density gradation value of the edge portion ("255" if the density gradation expression width is 8 bits), and sets a second maximum value obtained by subtracting a predetermined value from the first maximum value ("254" if the density gradation expression width is 8 bits) as the maximum density gradation value of the non-edge portion.

[0080] Next, the halftone processing unit 1057 performs halftone processing on the image data (object) processed by the edge enhancement filter (step S140). At this time, the halftone processing unit 1057 performs halftone processing based on the amount of processing calculated in step S40 of Fig. 7. Note that for each toner density, the density indicating the first maximum value is treated as a special value and is not subject to halftone processing, but the density indicating the second maximum value is subject to halftone processing.

[0081] Finally, the image processing unit 105 outputs the halftone processed image data (object) as a printed matter by supplying a common development bias from a common development voltage source to the multiple image forming units 106 based on the development bias value (common development bias value) stored in the setting value memory area 1081 in step S30 of Figure 7, thereby completing the processing (step S150).

[0082] [1.8 Example of operation] Next, a description will be given of an example of operation according to the first embodiment. Fig. 9 is a diagram illustrating an example of an edge enhancement filter according to the first embodiment.

[0083] The edge enhancement filter according to pattern 1 illustrated in Fig. 9(a) is an example of a 3-row, 3-column edge enhancement filter applicable to the first embodiment, and the edge enhancement filter according to pattern 2 illustrated in Fig. 9(b) is an example of a 5-row, 5-column edge enhancement filter applicable to the first embodiment. The edge enhancement filters illustrated in Fig. 9(a) and Fig. 9(b) are merely examples, and any filter that can enhance the edge portion of image data (object) as an edge enhancement filter can be applied to the present disclosure.

[0084] The upper diagram in Fig. 10(a) corresponds to the processing related to step S120 in Fig. 8, and is a diagram of a portion (area) of pixels of the image data (object) after the gradation value has been changed from the first gradation value (255) to the second gradation value (254) (image data after gradation value change). On the other hand, the lower diagram in Fig. 10(a) represents the 3-row, 3-column edge enhancement filter (pattern 1) exemplified in Fig. 9(a).

[0085] Figure 10(b) shows the image data (object) shown in the upper diagram of Figure 10(a) when the edge enhancement filter shown in the lower diagram of Figure 10(a) is applied to the pixel shown with diagonal lines (sometimes referred to as the pixel of interest).

[0086] For example, if the gradation value of the pixel of interest shown in Fig. 10(a) is 254, after application of the filter shown in the lower part of Fig. 10(a), the calculated gradation value will be 317 as shown in Fig. 10(b). Here, the control unit 11 sets this calculated value to 255, which is the maximum density gradation value of the edge portion (Fig. 10(c)). Note that whether or not the pixel of interest corresponds to an edge portion may be determined by determining that the pixel of interest is an edge portion if the calculated value after application of the edge enhancement filter exceeds a predetermined threshold, or by determining that the pixel of interest is an edge portion based on tag information added when image data (object) is rendered into bitmap data.

[0087] Next, Fig. 11 is a diagram showing a schematic diagram of an overall processing flow according to the first embodiment as an operation example. Here, Fig. 11(1) is a diagram explaining an operation example corresponding to the gradation value change processing of step S120 in Fig. 8. Fig. 11(2) is an operation example corresponding to the edge emphasis filter processing of step S130 in Fig. 8. Fig. 11(3) is an operation example corresponding to the halftone processing of step S140 in Fig. 8.

[0088] 11(1), the character object (a) shown to the left of the arrow is an example of the character object "A" included in the image data received as input as a print job. The character object (b) shown to the right of the arrow is an example of the character object "A" after the gradation value of the character object (a) has been changed from a first gradation value (density) of 255 (maximum density) to a second gradation value (density) of 254.

[0089] The character object (b) shown on the left side of the arrow in Fig. 11(2) is the same as the character object (b) shown on the right side of the arrow in Fig. 11(1). The character object (c) shown on the right side of the arrow in Fig. 11(2) is the result of edge enhancement filter processing of the character object (b). The character object (c) shown in Fig. 11(2) is an example in which a gradation value (density) of 255 is set for the edge portion and a gradation value (density) of 254 is set for the non-edge portion, and the edge portion is enhanced.

[0090] The character object (c) shown to the left of the arrow in Fig. 11(3) is the same as the character object (c) shown to the right of the arrow in Fig. 11(2). The character object (d) shown to the right of the arrow in Fig. 11(3) is the result of halftone processing of the character object (c).

[0091] 12A and 12B are diagrams illustrating the results of verification when the first embodiment is applied to input image data (object). FIG. 12A is a diagram showing an example of input image data (object). FIG. 12B is an example of output when image processing according to the first embodiment is not applied to the image data (object) shown in FIG. 12A. FIG. 12C is an example of output when image processing according to the first embodiment is applied to the image data (object) shown in FIG. 12A.

[0092] In Figure 12(b), jagged edges can be seen at the edges of each object (circled areas, etc.), whereas in Figure 12(c), the jagged edges at the edges of each object have been suppressed, resulting in smooth edges.

[0093] As described above, according to the first embodiment, in an image forming apparatus having a common charging voltage source and developing voltage source for multiple image forming units, the readability of high-density characters and lines can be improved for solid images (density) of toner colors, which are difficult to adjust in density, by using simple gradation changes and filter processing such as gradation change, edge emphasis filter processing, and halftone processing.

[0094] [2 Second embodiment] The second embodiment is a form in which it is determined whether or not to perform gradation change, edge emphasis filter processing, etc., and whether or not to perform such change, based on the detection result of high density correction.

[0095] The overall configuration, developing unit, hardware configuration, etc. of the multifunction peripheral 10 according to the second embodiment can be substantially the same as those of the first embodiment, and therefore description thereof will be omitted here.

[0096] [2.1 Functional Configuration] FIG. 13 is a block diagram for explaining the functions realized by the density adjustment unit 207 according to the second embodiment, and is a diagram in which only the functions of the density adjustment unit are extracted from FIG.

[0097] In addition to the functions of the density adjustment unit 107 according to the first embodiment, the density adjustment unit 207 includes a density correction evaluation unit 2071. The density correction evaluation unit 2071 is a functional unit that evaluates, based on the measurement result of the toner density (second density value) of a patch image formed based on the common development bias, whether the second density value is close to the target density and whether the amount of halftone processing is smaller than a predetermined threshold value that has been set in advance.

[0098] Based on the evaluation results by the density correction evaluation unit 2071, the density correction unit 1073 can change the gradation value, change the edge enhancement filter associated with the edge enhancement filter processing, change the amount of halftoning, or omit these processes. Note that, for example, if the gradation value change, edge enhancement filter processing, etc. are omitted and processing that excludes the density that indicates the first maximum value for each toner density from the halftoning process is not performed, the result is the same processing as when halftoning is performed (conventional technology). When the toner density (second density value) is close to the target density, the amount of halftoning is small and the effect of the edge enhancement filter processing is also small. Therefore, by performing processing similar to the conventional technology, it may be possible to reduce toner consumption in the first embodiment.

[0099] As described above, according to the second embodiment, in addition to the effects of the first embodiment, it is possible to reduce the sense of incongruity in low to medium density print areas other than characters and lines, and to optimize toner consumption.

[0100] [3 Third embodiment] In the first embodiment, a case where the toner density of at least one toner color is lower than the target density in the calculation of the differential development potential from the identification of the image forming unit 106 as the reference image forming unit has been described (see, for example, FIG. 6, etc.). In the third embodiment, a case where the toner densities of all toner colors are higher than their respective target densities will be described.

[0101] The overall configuration, developing unit, hardware configuration, functional configuration, etc. of the multifunction peripheral 10 according to the third embodiment can be substantially the same as those of the first embodiment, and therefore description thereof will be omitted here.

[0102] The process flow for density adjustment according to the third embodiment is obtained by adding processes in steps S201 to S205 to the process for identifying low density toner in step S20 in Fig. 7. The process for identifying low density toner according to the third embodiment will be described below with reference to the flowchart in Fig. 14.

[0103] When the low-density toner identification unit 1075 according to the third embodiment starts the process of identifying low-density toner in step S20, it determines whether the toner densities of all toner colors are equal to or greater than their respective target densities based on the measurement results of the toner densities (first density values) of patch images formed for each toner color under predetermined identical development conditions (first development bias) supplied from a common development voltage source to the multiple image forming units 106 (step S201).

[0104] When the low-density toner identification unit 1075 determines that the toner density for at least one toner color is lower than the respective target densities, it determines the toner color with the largest difference (differential development potential: first adjustment potential) between the second development bias and the first development bias required to raise the toner density to the target density for each toner color as the low-density toner, as in the first embodiment, and identifies the image forming unit 106 using that low-density toner as the reference image forming unit (step S201; No → step S203).

[0105] On the other hand, when the low-density toner identification unit 1075 determines that the toner densities for all toner colors are equal to or higher than their respective target densities, it determines the toner color with the smallest difference (differential development potential: second adjustment potential) between the second development bias and the first development bias required to reduce the toner density to the target density for each toner color as the low-density toner, and identifies the image forming unit 106 using that low-density toner as the reference image forming unit (step S201; Yes → step S205).

[0106] The density correction unit 1073 according to the third embodiment performs the processes from step S30 onward in FIG. 7 based on the toner color identified as low density toner by the low density toner identification unit 1075.

[0107] As described above, in the third embodiment, even if the toner densities of all toner colors are higher than their respective target densities, it is possible to obtain the same effects as in the first embodiment.

[0108] [4 Variations] The present disclosure is not limited to the above-described embodiments, and various modifications are possible. In other words, embodiments obtained by combining technical means that are appropriately modified within the scope of the present disclosure are also included in the technical scope.

[0109] Although the above-mentioned embodiments are described separately for convenience of explanation, they can be combined to the extent possible. Furthermore, the present invention intends to obtain rights to any of the technologies described in the specification through amendments or divisional applications, etc.

[0110] In addition, the programs that run on each device in each embodiment are programs that control the CPU, etc. (programs that make a computer function) so as to realize the functions of the above-described embodiments. Information handled by these devices is temporarily stored in a temporary storage device (e.g., RAM) during processing, and then stored in various ROMs and HDDs, and is read, modified, and written by the CPU as needed.

[0111] Here, the recording medium for storing the program may be any of semiconductor media (e.g., ROM, non-volatile memory card, etc.), optical recording media / magneto-optical recording media (e.g., DVD (Digital Versatile Disc), CD (Compact Disc), BD (Blu-ray (registered trademark) Disc), etc.), magnetic recording media (e.g., magnetic tape, flexible disk, etc.), etc.

[0112] Furthermore, when distributing the program in the market, the program can be stored in a portable recording medium and distributed, or transferred to a server computer connected via a network such as the Internet. In this case, the storage device of the server device is also included in the present disclosure.

[0113] Furthermore, the above-mentioned data may not be stored within the device, but may be stored in an external device and called up as needed. For example, the data may be stored in a NAS (Network Attached Storage) or on the cloud.

[0114] The scope of the present disclosure is not limited to the configurations explicitly described in the specification, but also includes combinations of the technologies disclosed in the specification. The configurations of the present disclosure for which a patent is sought are set forth in the appended claims, but it is not intended to exclude them from the technical scope on the grounds that they are not set forth in the claims.

[0115] Furthermore, in the above-mentioned specification, the statements "in the case of" and "when" are given as examples and are not intended to limit the configuration to the described contents. The disclosure also includes configurations that are not in these cases or situations, even if they would be obvious to a person skilled in the art, and the applicant intends to obtain rights to them.

[0116] Furthermore, the processes and data flows described in the specification are not limited to the order in which they are described. For example, the patent also discloses configurations in which some processes are deleted or the order is changed, and the patent holder intends to obtain the rights to such configurations.

[0117] Furthermore, although the functions described in the embodiments are executed by each device, they may be realized by one device or may further utilize an external server.

[0118] Furthermore, each functional block or feature of the device used in the above-described embodiments may be implemented or performed by an electrical circuit, for example, an integrated circuit or multiple integrated circuits. The electrical circuit designed to perform the functions described herein may include a general-purpose processor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or a combination thereof. The general-purpose processor may be a microprocessor, or a conventional processor, controller, microcontroller, or state machine. The electrical circuit may be composed of digital circuits or analog circuits. Furthermore, as advances in semiconductor technology emerge that replace current integrated circuits, one or more aspects of the present disclosure may also utilize new integrated circuits based on that technology. [Explanation of symbols]

[0119] 1 Exposure section 3 Photosensitive drum 4 Cleaning Unit 5. Development section 6 Transfer section 7 Charging section 10 Multifunction device 100 Main body 101 Control section 102 Display section 103 Operation input section 104 Communications Department 105 Image processing section 106 Image forming unit 107, 207 Density adjustment section 108 Storage 109 RAM 110 ROM 111 Power supply section 120 Image reading unit 1051 Image Data Analysis Unit 1053 Gradation change section 1055 Edge emphasis filter processing section 1057 Halftone Processing Unit 1071 Power supply control unit 1073 Density correction section 1075 Low density toner specific part 2071 Density Correction Evaluation Unit

Claims

1. a change unit that changes the gradation value of the input image data from a first gradation value to a second gradation value; a processing unit that performs edge enhancement filtering on the image data after the processing by the modification unit, and performs halftone processing on the image data after the edge enhancement filtering; a plurality of image forming units corresponding to toner colors; The plurality of image forming units include: an image forming apparatus that forms an image with a common developing bias set by a specific high density correction process based on the image data processed by the processing section;

2. 2. The image forming apparatus according to claim 1, further comprising a determination unit that determines the common developing bias based on the toner density of patch images formed with a first developing bias in the plurality of image forming units and a target density corresponding to the toner color.

3. 3. The image forming apparatus according to claim 2, further comprising a specifying unit that, when the toner density detected is lower than the target density, calculates a first adjustment potential to ensure the target density and specifies the image forming unit at which the first adjustment potential is maximum.

4. The identification unit 4. The image forming apparatus according to claim 3, wherein, when the toner density lower than the target density is not detected, a second adjustment potential for ensuring the target density is calculated, and the image forming unit for which the second adjustment potential is minimum is identified.

5. The processing unit In the image data, a first maximum value that can be set for density gradation is set as a maximum density gradation value of an edge portion, and a second maximum value obtained by subtracting a predetermined value from the first maximum value is set as a maximum density gradation value of a non-edge portion; 2. The image forming apparatus according to claim 1, wherein the amount of halftone processing for the image data is calculated based on the toner density of the patch image formed with the common development bias and the target density corresponding to the toner color.

6. a changing step of changing the gradation value of the input image data from a first gradation value to a second gradation value; a processing step of performing edge enhancement filtering on the image data after the modifying step, and performing halftone processing on the image data after the edge enhancement filtering; an image forming step of forming images in a plurality of image forming units corresponding to the toner colors; In the image forming step, an image forming method, characterized in that an image is formed with a common developing bias set by a specific high density correction process based on the image data processed by the processing step;

Images