Image forming apparatus, method, and program

Abstract

To provide a technique for ensuring the reproducibility of the gradation of a print image compared to a document image regardless of the basis weight of a document conveyed to a reading position by using au automatic document conveying unit.SOLUTION: An image forming apparatus comprises: image reading means that reads an image of a document conveyed on a predetermined reading position to acquire an image signal; acquisition means that acquires basis weight information indicating the basis weight of the document; correction means that acquires gradation correction information according to the basis weight of the document on the basis of the basis weight information, and corrects the image signal by using the acquired gradation correction information; and forming means that forms an image on a sheet on the basis of the corrected image signal.SELECTED DRAWING: Figure 12

Description

[Technical field]

[0001] The present disclosure relates to an image forming apparatus equipped with an automatic document transport unit. [Background technology]

[0002] In image forming devices such as MFPs (Multi-Functional Peripherals) that have multiple functions such as printing, copying, and facsimile, tone correction processing is performed to correct the tone characteristics of the image forming device in order to stabilize the quality of images formed on paper (see, for example, JP 2007-272112 A (Patent Document 1)).

[0003] In this gradation correction process, a test image that combines gradation patterns is formed on paper to create a test pattern. This test pattern is then read by an image reading unit attached to the image forming device, and gradation correction data used for gradation correction of the image signal is generated based on the read result.

[0004] During printing, image processing including tone correction using the tone correction data is performed on the image signal generated by reading the image of the document, thereby generating image data on which the toner image is based. A print image is formed based on the generated image data. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2007-272112 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the image reading unit reads the document transported to a predetermined reading position by the automatic document transport unit to form an image, the gradation characteristics of the image signal corresponding to the image of the document may vary depending on the basis weight of the document. In some cases, when the basis weight of the document is small, the density of the image signal tends to be denser than the density of the document image. Conversely, when the basis weight of the document is large, the density of the image signal tends to be thinner than the density of the document image. One of the reasons why the gradation characteristics of the image signal vary depending on the basis weight of the document is that when the document transported to the reading position is read, the amount of reflected light of the light irradiated to the reading position of the document differs depending on the basis weight of the document.

[0007] Such variations in the gradation characteristics of the image signal cause variations in the gradation characteristics of the print image formed based on the image data generated by image processing of the image signal, which may result in a decrease in the gradation reproducibility of the print image relative to the original image, depending on the basis weight of the original.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a technology for ensuring the gradation reproducibility of a print image relative to an original image, regardless of the basis weight of the original transported to a reading position using an automatic original transport unit. [Means for solving the problem]

[0009] The image forming apparatus according to the present disclosure includes an image reading means for reading an image of a document transported over a predetermined reading position and acquiring an image signal, an acquisition means for acquiring basis weight information indicating the basis weight of the document, a correction means for acquiring gradation correction information corresponding to the basis weight of the document based on the basis weight information and correcting the image signal using the acquired gradation correction information, and a formation means for forming an image on a sheet based on the corrected image signal.

[0010] In the above disclosure, the image forming apparatus further includes a storage unit that stores a plurality of gradation correction information pieces created for each basis weight. The correction unit selects gradation correction information pieces corresponding to the basis weight of the document from the plurality of gradation correction information pieces stored in the storage unit. The correction unit corrects the image signal using the selected gradation correction information.

[0011] In the above disclosure, the image forming apparatus further includes a creating unit that creates a plurality of pieces of gradation correction information. When creating the plurality of pieces of gradation correction information, the creating unit forms a plurality of test patterns having different basis weights. The image reading unit reads the image of each test pattern conveyed above the reading position to obtain a test pattern signal. The creating unit creates gradation correction information for each test pattern based on the density of the test pattern signal obtained by the image reading unit and the density of the image of the test pattern.

[0012] In the above disclosure, the image forming apparatus further includes a communication unit that allows the image forming apparatus to communicate with an external device. The correction unit receives a plurality of pieces of gradation correction information created for each basis weight from the external device via the communication unit. The correction unit selects gradation correction information corresponding to the basis weight of the document from the received plurality of pieces of gradation correction information. The correction unit corrects the image signal using the selected gradation correction information.

[0013] In the above disclosure, the tone correction information includes a tone correction table that indicates the correspondence relationship between the density of an image signal obtained from a document and the density of an image formed on a sheet.

[0014] In the above disclosure, the obtaining means includes a detecting means for detecting the basis weight of the document conveyed to the reading position.

[0015] In the above disclosure, the obtaining means includes a setting means for receiving a setting of the basis weight of the document from a user.

[0016] In the above disclosure, the image forming apparatus further includes a storage unit that stores the image signal obtained by the image reading unit. The image reading unit stores the basis weight information obtained by the image reading unit in the storage unit in association with the image signal.

[0017] In the above disclosure, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of gradation correction information, the correction means selects gradation correction information corresponding to the basis weight closest to the basis weight of the document, and corrects the image signal using the selected gradation correction information.

[0018] In the above disclosure, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of gradation correction information, the correction means creates gradation correction information corresponding to the basis weight of the document by interpolating gradation correction information corresponding to a basis weight larger than the basis weight of the document and gradation correction information corresponding to a basis weight smaller than the basis weight of the document. The correction means corrects the image signal using the created gradation correction information.

[0019] The method disclosed herein is a computer-implemented method, and includes the steps of reading an image of a document transported over a predetermined reading position of an image forming device to obtain an image signal, obtaining basis weight information indicating the basis weight of the document, obtaining gradation correction information corresponding to the basis weight of the document based on the basis weight information, correcting the image signal using the obtained gradation correction information, and forming an image on a sheet based on the corrected image signal.

[0020] The program of the present disclosure, executed by a computer, causes the computer to execute the steps of reading an image of a document transported over a predetermined reading position of an image forming device and acquiring an image signal, acquiring basis weight information indicating the basis weight of the document, acquiring gradation correction information corresponding to the basis weight of the document based on the basis weight information, correcting the image signal using the acquired gradation correction information, and forming an image on a sheet based on the corrected image signal. Effect of the Invention

[0021] According to the present disclosure, by correcting the image signal read from the image of the original using gradation correction information corresponding to the basis weight of the original transported to a specified reading position, it is possible to ensure gradation reproducibility of the print image relative to the original image even if fluctuations occur in the gradation characteristics of the image signal due to the basis weight of the original. [Brief description of the drawings]

[0022] [Figure 1] 1 is a perspective view showing the appearance of an MPF ​​that is an embodiment of an image forming apparatus according to the present disclosure. [Diagram 2] FIG. 2 is a diagram illustrating an internal configuration of an MPF. [Diagram 3] FIG. 2 is a diagram illustrating a hardware configuration of an MFP. [Figure 4] 4 is a diagram for explaining a flow of image data generation processing in an image processing unit. FIG. [Diagram 5] FIG. 4 is a diagram illustrating an example of a tone correction table. [Figure 6] FIG. 13 is a diagram illustrating an example of a test pattern. [Figure 7] 1 is a flowchart showing a procedure of a general tone correction process. [Figure 8] FIG. 1 is a diagram illustrating a printing operation in a typical image forming apparatus. [Figure 9] 4 is a flowchart showing a procedure of a tone correction process according to the present embodiment. [Figure 10] 5A to 5C are diagrams illustrating a tone correction process according to the present embodiment. [Figure 11] 11A and 11B are diagrams illustrating a procedure for creating a tone correction table. [Figure 12] 5A to 5C are diagrams illustrating a printing operation in the image forming apparatus according to the present embodiment. [Figure 13] 4 is a flowchart showing a procedure of a printing operation according to the present embodiment. [Figure 14] FIG. 4 is a diagram illustrating an example of a display of an operation panel. [Figure 15] 11A and 11B are diagrams illustrating a method for acquiring a tone correction table. [Figure 16] 13 is a flowchart showing a procedure of a printing operation according to a first modified example of the present embodiment. [Figure 17] 13 is a flowchart showing a procedure of a printing operation according to a second modified example of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] An embodiment of an image forming apparatus will be described below with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, the description thereof will not be repeated.

[0024] In this embodiment, an MFP (Multi-Functional Peripheral) is exemplified as an image forming apparatus, but the present embodiment is not limited to such a multi-function peripheral, and can also be applied to, for example, a printer, a copier, or the like.

[0025] In this embodiment, a sheet-shaped recording medium made of a material on which an image is formed is collectively referred to as a "sheet." In this embodiment, a case where the material of the sheet is "paper" is described, but the sheet may be made of a material other than paper. For example, the sheet may include a recording medium made of a resin material or a textile material.

[0026] [1. Overview of MFP configuration] Fig. 1 is a perspective view showing the external appearance of an MPF ​​1 which is an embodiment of an image forming apparatus according to the present disclosure. Fig. 2 is a diagram showing a schematic internal configuration of the MPF 1. The following mainly describes the configuration related to image formation by printing with the MPF 1.

[0027] As shown in FIGS. 1 and 2, the MPF 1 includes an image reading unit 3, paper feed trays 4A to 4D, a transfer unit 5, a fixing unit 6, a paper discharge tray 7, a conveying device 8, and an operation panel 9.

[0028] The image reading unit 3 reads an image from the original P1. The image reading unit 3 is provided on the upper part of the device body 2 of the MFP 1. The image reading unit 3 includes a scanner unit 31 and an automatic document feeder (ADF: Auto Document Feeder) 32 provided on the upper part of the scanner unit 31. The scanner unit 31 reads an image from the original P1. The ADF 32 causes the scanner unit 31 to transport the original P1 one sheet at a time. The image reading unit 3 will be described in detail later.

[0029] The paper feed trays 4A to 4D store paper P2, which is a sheet. Each of the paper feed trays 4A to 4D is configured to be able to supply paper P2 to a transport path. The MFP 1 may have a single or multiple paper feed trays. In the following description, the paper feed trays 4A to 4D may be collectively referred to as "paper feed tray 4."

[0030] The transfer unit 5 transfers the toner image onto the paper P2. The fixing unit 6 fixes the toner image transferred by the transfer unit 5 onto the paper P2. The paper output tray 7 receives the paper P2 on which the image has been fixed by the fixing unit 6.

[0031] The paper discharge tray 7 is provided above the transfer unit 5. The paper feed tray 4 is provided below the transfer unit 5. The paper P2 supplied from the paper feed tray 4 is conveyed upward to the transfer unit 5, where an image is transferred onto the paper P2. Furthermore, the image is fixed onto the paper P2 by the fixing unit 6, and then the paper P2 is discharged onto the paper discharge tray 7.

[0032] The operation panel 9 accepts user operations on the MFP 1. The operation panel 9 is provided on the front of the device body 2. The operation panel 9 is, for example, a touch panel display in which a touch sensor and a display 9A are integrally configured. The operation panel 9 may be configured with hardware buttons arranged thereon. By operating the keys while looking at the display screen of the operation panel 9, the user can perform setting operations for a function selected from various functions of the MFP 1 and instruct the MFP 1 to execute the selected function.

[0033] Next, the internal structure of the device main body 2 will be described with reference to FIG.

[0034] In the image reading section 3, the scanner section 31 includes a document table 33, a light source section 34, image sensors 35A and 35B, an imaging lens 36, and a group of mirrors 37.

[0035] The document table 33 has a platen glass (not shown) on the upper surface side. The light source unit 34 irradiates light onto the document P1. The image sensor 35A photoelectrically converts the reflected light from the document P1 into image data. The imaging lens 36 forms an image of the reflected light on the image sensor 35A. The mirror group 37 sequentially reflects the reflected light from the document P1 and makes it incident on the imaging lens 36. The light source unit 34, the image sensor 35A, the imaging lens 36, and the mirror group 37 are provided inside the document table 33. The light source unit 34 and the mirror group 37 are configured to be movable in the left-right direction relative to the document table 33.

[0036] An ADF 32 is provided on the upper surface side of the scanner unit 31. The ADF 32 can be opened and closed relative to the document table 33, and has a document placement tray 38, a document discharge tray 39, and a document transport mechanism 40. The ADF 32 covers the document P1 on the platen glass of the document table 33, thereby allowing the document P1 to be in close contact with the platen glass.

[0037] In the image reading unit 3, when reading an original P1 on the platen glass of the original table 33, light is irradiated onto the original P1 from a light source unit 34 moving in the right direction (sub-scanning direction). The light reflected from the original P1 is reflected in sequence by a group of mirrors 37 that also moves in the right direction like the light source unit 34, enters an imaging lens 36, and forms an image on an image sensor 35A. The image sensor 35A performs photoelectric conversion for each pixel according to the intensity of the incident light, and generates an image signal (RGB signal) corresponding to the image of the original P1. This image signal is analog data of the reflectance of the three colors R (Red), G (Green), and B (Blue).

[0038] On the other hand, when the image sensor 35A reads the original P1 placed on the original placement tray 38, the original P1 is transported to the reading position by an original transport mechanism 40 composed of a plurality of rollers and the like. The light source unit 34 and the mirror group 37 of the scanner unit 31 are fixed at predetermined positions inside the original table 33. The light source unit 34 irradiates the original P1 at the reading position, and the reflected light is imaged on the image sensor 35A via the mirror group 37 and the imaging lens 36. The image sensor 35A then converts the reflected light into an image signal (RGB signal) corresponding to the image of the original P1. The original P1 is then discharged to the original discharge tray 39.

[0039] An image sensor 35B and a basis weight sensor 30 are provided inside the ADF 32. The image sensor 35B is configured to read the back side of the document P1 placed on the document placement tray 38. The image sensor 35B is, for example, a contact image sensor (CIS). The image sensor 35B irradiates light onto the back side of the document P1, and performs photoelectric conversion of image data of the light reflected from the back side to generate an image signal corresponding to the image of the back side of the document P1.

[0040] The image sensor 35B is disposed downstream in the transport direction of the original P1 from the position where the light source unit 34 and the group of mirrors 37 are disposed. As a result, after the front side of the original P1 is read by the image sensor 35A, the back side of the original P1 is read by the image sensor 35B.

[0041] The basis weight sensor 30 detects the basis weight (g / m 2 The basis weight sensor 30 is, for example, an optical sensor, and detects the basis weight of the document P1 from the transmittance when light is applied to the document P1. The basis weight sensor 30 corresponds to one embodiment of the "detecting means".

[0042] The transfer unit 5 transfers the toner image onto the paper P2. The transfer unit 5 includes a plurality of image forming units 51, an exposure unit 52, an intermediate transfer belt 53, a plurality of primary transfer rollers 54, a drive roller 55, a driven roller 56, a secondary transfer roller 57, and a cleaner unit 58. The plurality of image forming units 51 generate toner images of the respective colors of C (Cyan), M (Magenta), Y (Yellow), and K (Black). The exposure unit 52 is provided below the plurality of image forming units 51. The intermediate transfer belt 53 abuts against the plurality of image forming units 51 arranged in the horizontal direction, so that the toner images of the respective colors are transferred from the image forming units 51 to the intermediate transfer belt 53. Each of the plurality of primary transfer rollers 54 is provided at a position facing the upper side of the image forming unit 51 of the corresponding color so as to sandwich the image forming unit 51 of each color and the intermediate transfer belt 53. The drive roller 55 rotates the intermediate transfer belt 53. The driven roller 56 rotates as the rotation of the drive roller 55 is transmitted through the intermediate transfer belt 53. The secondary transfer roller 57 is disposed at a position facing the drive roller 55 with the intermediate transfer belt 53 in between. The cleaner unit 58 is disposed at a position facing the driven roller 56 with the intermediate transfer belt 53 in between.

[0043] The image forming unit 51 includes a photoconductor drum 61, a charger 62, a developing unit 63, and a cleaner unit 64. The photoconductor drum 61 abuts against the outer peripheral surface of the intermediate transfer belt 53. The charger 62 charges the outer peripheral surface of the photoconductor drum 61 by corona discharge. The developing unit 63 attaches the toner, which has been stirred and charged, to the outer peripheral surface of the photoconductor drum 61. The cleaner unit 64 removes the toner remaining on the outer peripheral surface of the photoconductor drum 61 after the toner image is transferred to the intermediate transfer belt 53. The photoconductor drum 61 is installed at a position facing the primary transfer roller 54 across the intermediate transfer belt 53, and rotates in a clockwise direction in FIG. 2. Around the photoconductor drum 61, the primary transfer roller 54, the cleaner unit 64, the charger 62, and the developing unit 63 are arranged in order along the rotation direction of the photoconductor drum 61.

[0044] The intermediate transfer belt 53 is composed of, for example, an endless belt member having electrical conductivity. The intermediate transfer belt 53 is wound around the driving roller 55 and the driven roller 56 without slack, and rotates in the counterclockwise direction in FIG. 2 in accordance with the rotation of the driving roller 55. A secondary transfer roller 57, a cleaner unit 58, and image forming units 51 for each of the CMYK colors are arranged around the intermediate transfer belt 53 in the rotation direction of the intermediate transfer belt 53 in that order.

[0045] The fixing unit 6 fixes the toner image transferred to the paper P2. The fixing unit 6 includes a heating roller 59 and a pressure roller 60. The heating roller 59 has a halogen lamp or the like that applies heat to fix the toner image on the paper P2. The pressure roller 60 presses the paper P2 by clamping it together with the heating roller 59. The heating roller 59 may have a surface that is heated by generating an eddy current on its surface by electromagnetic induction.

[0046] Each of the paper feed trays 4A to 4D is connected to the paper feed path R1. The transport device 8 that transports the paper P2 includes a feed roller 81, a paper feed roller pair 82, a transport roller pair 83, and a skew correction roller 84. The feed roller 81 feeds the paper P2 stored in the paper feed tray 4 from the top layer to the paper feed path R1. The paper feed roller pair 82 further sends the fed paper P2 to the paper feed path R1. The transport roller pair 83 transports the paper P2 fed by the paper feed roller pair 82 vertically on the main transport path R0. The skew correction roller 84 is disposed downstream of the transport roller pair 83 on the main transport path R0 and transports the paper P2 toward the transfer unit 5. The paper feed tray 4 is provided with a paper feed sensor 80 for detecting the paper P2 fed from the paper feed tray 4.

[0047] The main transport path R0 is a main transport path for the paper P2 in the image formation (printing) process. The paper feed path R1 is provided for each paper feed tray 4 and merges with the main transport path R0. The paper P2 stored in the paper feed tray 4 is sent out one sheet at a time, starting from the top, to the paper feed path R1 by the rotational drive of the delivery roller 81 corresponding to the paper feed tray 4, and then sent out toward the main transport path R0 by a paper feed roller pair 82.

[0048] In the main transport path R0, the paper P2 transported from the paper feed roller pair 82 is transported toward the skew correction roller 84 by the rotational drive of the transport roller pair 83. The skew correction roller 84 transports the paper P2 to the transfer unit 5 in synchronization with the formation timing of the toner image in the transfer unit 5 so that the toner image can be properly transferred to the paper P2 in the transfer unit 5.

[0049] A pair of paper discharge rollers 91 is disposed at the end, which is the most downstream portion, of the main transport path R0. The pair of paper discharge rollers 91 are driven to rotate, thereby discharging the printed paper P2 onto the paper discharge tray 7. In the main transport path R0, below the pair of paper discharge rollers 91 (upstream in the transport direction), a paper discharge sensor 90 is provided that detects the end of the paper P2 to confirm that the paper P2 has been properly discharged onto the paper discharge tray 7.

[0050] [2. Hardware configuration] Fig. 3 is a diagram showing the hardware configuration of the MFP 1. As shown in Fig. 3, the MFP 1 includes a main body controller 10. The main body controller 10 controls each part of the MFP 1. This causes various operations in the MFP 1 (such as printing on paper P2 and reading an image from an original P1) to be performed.

[0051] The main body control unit 10 has a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an image processing unit 104, an image memory 105, a communication I / F (Interface) 106, and an HDD (Hard Disc Drive) 107.

[0052] The CPU 101 executes various calculation processes and controls. The ROM 102 stores control programs and the like. The RAM 103 temporarily stores calculation data. The image processing unit 104 generates image data that is the basis of the toner image formed by the transfer unit 5. The image memory 105 temporarily stores the image signal generated by the image reading unit 3 and the image data obtained by the image processing unit 104. The image processing unit 104 may be configured as a dedicated processor circuit that constitutes an image processing engine, or may be configured as a combination of an image processing program executed by the CPU 101 and a circuit.

[0053] The communication I / F 106 includes a wireless communication I / F 108 and a circuit such as a NIC (Network Interface Card) for controlling communication between the MFP 1 and an external device. The communication I / F 106 controls communication between the MFP 1 and a terminal 200 that can be operated by a user, such as a personal computer, via an external network 110. The network 110 includes various networks such as a LAN (Local Area Network) and the Internet. The wireless communication I / F 108 controls wireless communication between the MFP 1 and a portable terminal 300 that can be operated by a user.

[0054] The MFP 1 further includes an image reading control unit 113, an exposure control unit 114, a transfer control unit 115, a fixing control unit 116, and a transport control unit 118. The image reading control unit 113 controls the image reading unit 3 in accordance with a signal provided from the main body control unit 10. The exposure control unit 114 controls the exposure unit 52 in accordance with a signal provided from the main body control unit 10. The fixing control unit 116 controls the fixing unit 6 in accordance with a signal provided from the main body control unit 10. The transport control unit 118 drives and rotates the delivery roller 81, roller pairs 82, 83, 91, and skew correction roller 84 in the transport device 8 in accordance with a signal provided from the main body control unit 10.

[0055] The exposure section 52, transfer section 5, fixing section 6, transport device 8, and the exposure control section 114, transfer control section 115, fixing control section 116, and transport control section 118 that control them constitute an imaging unit 117 that forms an image (print image) on paper P2. A sensor unit 900 including various sensors that MFP1 has is connected to the main body control section 10. The CPU 101 detects the state of each section of the MFP1 based on a signal from the sensor unit 900.

[0056] [3. Printing Operation] Next, the printing operation by the MFP 1 will be described.

[0057] When the MFP 1 receives an instruction to perform a printing operation via the operation panel 9, the CPU 101 in the main body control unit 10 reads out a control program for the printing operation from the ROM 102 and executes it, thereby starting the control operation for the printing operation.

[0058] Specifically, the CPU 101 controls the image reading unit 3 through the image reading control unit 113 to read the original P1 on the platen glass of the document table 33 or the original P1 placed on the document placement tray 38. The CPU 101 stores in the image memory 105 an image signal read from the original P1 by the image reading unit 3.

[0059] The image processing unit 104 generates image data for forming a toner image of each color of C, M, Y, and K based on the image signal stored in the image memory 105. The CPU 101 outputs the generated image data to the imaging unit 117. The image processing unit 104 will be described in detail later.

[0060] The CPU 101 controls the driving of the transport device 8 through the transport control unit 118, thereby feeding the topmost sheet of paper P2 from the paper feed tray 4 and sending it to the main transport path R0. Furthermore, the CPU 101 provides control signals to the exposure control unit 114 and the transfer control unit 115, and controls the driving of the exposure unit 52 and the transfer unit 5, in order to transfer the toner image to the sheet of paper P2 sent to the main transport path R0.

[0061] The exposure control unit 114 drives light emitting elements in the exposure unit 52 based on image data for each of the C, M, Y, and K colors to form electrostatic latent images on the photoconductor drums 61 for each of the C, M, Y, and K colors. That is, the transfer control unit 115 drives the transfer unit 5, so that the exposure unit 52 irradiates the surface of the photoconductor drum 61 charged by the charger 62 in the image forming units 51 for each of the C, M, Y, and K colors with laser light, and electrostatic latent images corresponding to the image data for each of the C, M, Y, and K colors are formed.

[0062] Toner charged by the developing unit 63 is transferred to the surface of the photoreceptor drum 61 on which this electrostatic latent image is formed, and a toner image is formed on the photoreceptor drum 61, which serves as a first image carrier. The toner image carried on the surface of the photoreceptor drum 61 is then transferred to the intermediate transfer belt 53 by the electrostatic force of the primary transfer roller 54, and a toner image in which the colors C, M, Y, and K are superimposed is formed on the surface of the intermediate transfer belt 53, which serves as a second image carrier. At this time, untransferred toner remaining on the photoreceptor drum 61 after the toner image has been transferred to the intermediate transfer belt 53 is scraped off by the cleaner unit 64 and removed from the photoreceptor drum 61.

[0063] The transfer control unit 115 operates the skew correction roller 84 in accordance with the timing at which the toner image is transferred to the intermediate transfer belt 53. At this time, the toner image transferred to the intermediate transfer belt 53 moves to a transfer position where it abuts against the secondary transfer roller 57 as the intermediate transfer belt 53 rotates by the drive roller 55 and the driven roller 56, and is transferred to the paper P2 that has been transported to the transfer position on the main transport path R0. Untransferred toner remaining on the intermediate transfer belt 53 after the toner image has been transferred to the paper P2 is scraped off by the cleaner unit 58 and removed from the intermediate transfer belt 53.

[0064] The paper P2 onto which the toner image has been transferred at the contact position with the secondary transfer roller 57 is pressurized by the heating roller 59 and pressure roller 60, and the unfixed toner image is fixed to the paper surface. Then, the paper P2 after the toner image has been fixed (after single-sided printing) is transported to the paper discharge roller pair 91, which discharges the paper onto the paper discharge tray 7. At this time, the paper discharge sensor 90 detects the rear end of the paper P2, and provides the detection result to the main body control unit 10. This enables the main body control unit 10 to confirm that the paper P2 has been normally discharged onto the paper discharge tray 7.

[0065] [4. Image data generation processing] Fig. 4 is a diagram for explaining the flow of image data generation processing in the image processing unit 104 shown in Fig. 3. As shown in Fig. 4, the image processing unit 104 includes an A / D conversion unit 140, a shading correction unit 142, a LOG (Laplacian Of Gaussian) conversion unit 144, a color conversion unit 146, and a gamma correction unit 148.

[0066] The A / D conversion unit 140 receives an image signal (RGB signal) read from the original P1 by the image reading unit 3. The image signal is analog data of the reflectance of the three colors R, G, and B. The A / D conversion unit 140 converts the image signal into a multi-value digital image signal.

[0067] The shading correction unit 142 performs a predetermined shading correction on the A / D converted image signal. This shading correction is a process for eliminating uneven illumination of the light source unit 34 in the scanner unit 31 and uneven sensitivity of the image sensors 35A and 35B.

[0068] The LOG conversion unit 144 converts the image signal that has been subjected to the shading correction into density data. The color conversion unit 146 converts the image signal that has been converted into the density data into an image signal consisting of CMYK signals.

[0069] Gamma correction unit 148 performs gamma correction (tone correction) on the image signal consisting of CMYK signals. Gamma correction is a process of converting the image signal so that the tone characteristics of MFP1 become ideal characteristics. A tone correction table prepared in advance is used for gamma correction. The tone correction table is also called a "gamma lookup table." Image data including the gamma-corrected image signal is output by CPU 101 to imaging unit 117, and a printing operation is performed in imaging unit 117.

[0070] Fig. 5 is a diagram showing an example of a tone correction table. The horizontal axis of Fig. 5 indicates the density (input signal) of the image signal used in image formation, and the vertical axis of Fig. 5 indicates the density (output signal) of the print image formed on paper P2. The vertical axis corresponds to the density of the image to be printed on paper P2.

[0071] The gradation correction table corresponds to one embodiment of "gradation correction information" indicating the correspondence relationship between the density of an image signal input to the image processing unit 104 and the density of image data output from the image processing unit 104 and used for image formation. The gradation correction table is made up of gradation correction curves 201-204 for each of the colors C, M, Y, and K.

[0072] The tone correction table is created based on the original tone characteristics to which gamma correction has not been applied and ideal tone characteristics. In the ideal tone characteristics, the density of the input image signal and the density of the output image data have a linear relationship. If this linear relationship is maintained, ideal tone reproducibility can be obtained. However, in reality, due to fluctuations in the charging characteristics of the toner, the photosensitive characteristics of the photosensitive drum, and temperature and humidity, the density of the input image signal and the density of the output image data have a nonlinear relationship. Therefore, the density of the printer image printed on the paper P2 changes significantly for each density (tone value) with respect to the density of the input image signal.

[0073] Therefore, a tone correction table is created by correcting the original tone characteristics so that the relationship between the density of the input image signal and the density of the output image data becomes an ideal tone characteristic. As shown in Fig. 5, in the tone correction table, the density of the input image signal and the density of the image data have a nonlinear relationship.

[0074] When an image signal is given as an input signal to the image processing unit 104, the gamma correction unit 148 corrects the image signal using the tone correction table, thereby converting the original tone characteristics into ideal tone characteristics. This makes it possible to maintain the density of the image formed on the paper P2 based on the input image signal at a target value.

[0075] However, since the gradation characteristics of the MFP1 vary depending on aging and the usage environment, the quality of the formed image (image quality) is likely to become unstable. In order to stabilize the image quality, it is necessary to update the gradation correction table in accordance with the variation in the gradation characteristics of the MFP1. Therefore, the MFP1 executes a gradation correction process for correcting the gradation characteristics of the MFP1. In one aspect, when an instruction to execute the gradation correction process is received from the operation panel 9, the CPU 101 starts the gradation correction process.

[0076] [5. Tone correction processing] A test pattern is used in the gradation correction process. FIG. 6 is a diagram showing an example of the test pattern. As shown in FIG. 6, the test pattern has gradation patterns of the colors C, M, Y, and K. The gradation pattern of each color is composed of a plurality of patches (for example, nine patches) having different densities. For example, in the gradation pattern of C, the patch with patch number 1 has the lowest density, and the density increases stepwise, with the patch with patch number 9 having the highest density. The gradation patterns of M, Y, and K are similar. The test pattern is formed by printing the gradation patterns of C, M, Y, and K on paper P2.

[0077] Fig. 7 is a flow chart showing the procedure of a general gradation correction process. As shown in Fig. 7, first, a test pattern shown in Fig. 6 is created in step ST100. In step ST100, an image processing unit 104 generates image data based on a test pattern signal which is an image signal for forming the test pattern. At this time, a gamma correction unit 148 of the image processing unit 104 performs gamma correction on the test pattern signal provided by the CPU 101 using the gradation correction table shown in Fig. 5. The gamma-corrected test pattern signal is stored in an image memory 105.

[0078] The test pattern signal stored in the image memory 105 is read by the CPU 101 and applied to the imaging unit 117. By executing the above-mentioned printing operation in the imaging unit 117, gradation patterns of the colors C, M, Y, and K are printed on the paper P2 being transported on the transport path, and the test pattern shown in FIG.

[0079] When the test pattern is created, in step ST200, the test pattern is read by image reading unit 3. In step ST200, CPU 101 instructs the user to place the test pattern on the platen glass of document table 33. In one aspect, CPU 101 causes display 9A of operation panel 9 to display a message instructing the user to place the test pattern on the platen glass of document table 33.

[0080] The user places a test pattern on the platen glass of the document table 33 in accordance with the message, and then issues an instruction to read the test pattern via the operation panel 9. Upon receiving this reading instruction, the scanner unit 31 of the image reading unit 3 reads the test pattern on the platen glass and generates a reading signal that is the reading result.

[0081] When the read signal of the test pattern is generated, a gradation correction table is created by using the read signal in step ST300. In step ST300, CPU 101 first creates gradation curves for each of the colors C, M, Y, and K based on the relationship between the image density of the test pattern obtained from the read signal and the image density of the test pattern signal read from image memory 105. Next, CPU 101 creates a gradation correction table by determining gradation correction curves 201 to 204 (FIG. 5) for correcting deviations from an ideal gradation curve based on the created gradation curve. CPU 101 updates the gradation correction table by setting the created gradation correction table in gamma correction unit 148.

[0082] [6. Issues with General Image Forming Devices] Next, a problem with a typical image forming apparatus will be described with reference to FIG.

[0083] Fig. 8 shows a printing operation in a typical image forming apparatus. In Fig. 8, a printing operation is performed for each of three types of originals P1A to P1C. The originals P1A to P1C have the same image formed thereon, but have different basis weights. The basis weight of the original P1A is 50 (g / m 2 ), and the basis weight of manuscript P1B is 80 (g / m 2 ), and the basis weight of manuscript P1C is 150 (g / m 2 ) The basis weight of the document P1A is the smallest, and the basis weight of the document P1C is the largest.

[0084] Original documents P1A to P1C are placed on an original placement tray 38 of the ADF 32. Each of original documents P1A to P1C is transported to the scanner unit 31 by the ADF 32. An image sensor 35A of the scanner unit 31 reads an image from each of original documents P1A to P1C. The image sensor 35A generates an image signal corresponding to each of original documents P1A to P1C.

[0085] 8 shows read images I1A to I1B based on image signals generated by scanner unit 31. Read image I1A is a read image generated by reading document P1A. Read image I1B is a read image generated by reading document P1B. Read image I1C is a read image generated by reading document P1C.

[0086] Comparing the scanned images I1A to I1C, it is found that the scanned images have different gradation characteristics even though the same image has been scanned. In the example of Fig. 8, the scanned image I1A has the highest density, and the scanned image I1C has the lowest density. In this way, the difference in the basis weight of the document causes a variation in the gradation characteristics of the scanned images generated by scanning the document.

[0087] One reason why the gradation characteristics of the read image vary depending on the basis weight of the document is that when the scanner unit 31 reads the document transported to a specified reading position by the ADF 32, the amount of light reflected from the document differs depending on the basis weight of the document.

[0088] The image processing unit 104 generates image data based on image signals corresponding to each of the read images I1A to I1C. At this time, the gamma correction unit 148 performs gamma correction on each image signal using the gradation correction table shown in Fig. 5. The imaging unit 117 executes a printing operation based on the generated image data to form a print image on the paper P2.

[0089] 8, print image I2A is a print image formed based on read image I1A. Print image I2B is a print image formed based on read image I1B. Print image I2C is a print image formed based on read image I1C. By performing gamma correction on read images I1A to I1C in image processing unit 104, each of print images I2A to I2C has good gradation reproducibility for the read images.

[0090] On the other hand, when comparing the originals P1A to P1C with the print images I2C to I2C, it is found that the gradation characteristics of the originals are not consistent with the gradation characteristics of the print images. In detail, in the original P1A with the smallest basis weight, the read image I1A has a high density, and therefore the print image I2A also has a high density. Since the print image I2A has a higher density than the original P1A, color loss occurs, making it difficult to reproduce the density difference in the high density area. On the other hand, in the original P1C with the largest basis weight, the read image I1C has a low density, and therefore the print image I2C also has a low density. Since the print image I2C has a lower density than the original P1C, color loss occurs, and the reproducibility of the low density image is reduced.

[0091] When reading original P1 using ADF32 in this manner, a problem may occur in which the gradation characteristics of the read image vary depending on the basis weight of the original, and this causes the gradation characteristics of the print image formed after gamma correction of the read image to also vary.

[0092] In order to solve such problems, the technical idea of ​​the image forming apparatus according to the present disclosure is to perform gamma correction (tone correction) on an image signal read from a document by using a tone correction table corresponding to the basis weight of the document. Hereinafter, an embodiment of the technical idea according to the present disclosure will be described.

[0093] 7. Tone Correction Process According to the Present Embodiment Fig. 9 is a flowchart showing the procedure of the tone correction process according to the present embodiment, and Fig. 10 is a diagram for explaining the tone correction process according to the present embodiment.

[0094] As shown in Fig. 9, first, in step ST10, the test pattern shown in Fig. 6 is created for each basis weight of the document. In step ST10, multiple test patterns are created using multiple sheets of paper P2 with different basis weights. The type of basis weight of the paper P2 can be set in consideration of the type of basis weight of the document.

[0095] In step ST10, similarly to step ST100 in Fig. 7, the image processing unit 104 first generates image data based on a test pattern signal, which is an image signal for forming a test pattern. At this time, the gamma correction unit 148 performs gamma correction on the test pattern signal provided by the CPU 101 using a tone correction table that it has in advance. As this tone correction table, the tone correction table (Fig. 5) created in the tone correction process shown in Fig. 7 can be used. When updating the tone correction table, the tone correction table before the update can be used.

[0096] The gamma-corrected test pattern signal is provided to the imaging unit 117 by the CPU 101. The imaging unit 117 prints gradation patterns (FIG. 6) of the colors C, M, Y, and K on each of a plurality of sheets of paper P2 having different basis weights, thereby forming a plurality of test patterns.

[0097] The test patterns have different basis weights. 2 Test pattern TPA using paper P2 with a basis weight of 80 (g / m 2 Test pattern TPB using paper P2 with a basis weight of 150 (g / m 2 6.) Test pattern TPC using paper P2. Each test pattern has the gradation patterns of the colors C, M, Y, and K shown in FIG.

[0098] Next, in step ST20, a plurality of test patterns are read by image reading unit 3. In step ST20, CPU 101 instructs the user to place a plurality of test patterns on document placement tray 38 of ADF 32. In one aspect, CPU 101 causes display 9A of operation panel 9 to display a message instructing the user to place the test patterns on document placement tray 38.

[0099] The user places multiple test patterns on document placement tray 38 in accordance with the message, and then issues an instruction to read the multiple test patterns via operation panel 9. Upon receiving this reading instruction, ADF 32 conveys the multiple test patterns one by one to scanner unit 31. Scanner unit 31 sequentially reads the multiple test patterns and generates a read signal for each test pattern.

[0100] In step ST30, in accordance with the reading operation of the multiple test patterns in step ST20, the basis weight sensor 30 detects the basis weight of each test pattern transported by the document transport mechanism 40. Basis weight information indicating the detected basis weight is associated with the read signal for each test pattern.

[0101] 10 shows scanned images I11A to I11C based on the read signal of the test pattern generated by the scanner unit 31. The scanned image I11A is a scanned image of the test pattern TPA (basis weight 50 g / m 2 The scanned image I11B is a scanned image generated by scanning a test pattern TPB (grammage 80 g / m 2 The scanned image I11C is a scanned image generated by scanning a test pattern TPC (grammage 150 g / m 2 ) is read and generated. As described above, by reading the test pattern using the ADF 32, the gradation characteristics of the read image vary according to the basis weight of the test pattern.

[0102] Next, a gradation correction table is created in step ST40. In step ST40, a gradation correction table is created for each test pattern (i.e., for each basis weight). Fig. 11 is a diagram for explaining the procedure for creating a gradation correction table. Fig. 11 representatively shows the procedure for creating a gradation correction table corresponding to the test pattern TPA.

[0103] Figures 11(a)-(d) show data on the reflectance of the three colors R, G, and B, which are the read signals of test pattern TPA, and the reflectance of the common parts of the three colors R, G, and B. Figure 11(a) is a graph showing the relationship between the density of the C (cyan) gradation pattern and the reflectance of R (red). The horizontal axis of the graph is the patch number in the C gradation pattern, and the vertical axis is the reflectance of R. As the patch number increases, the density of C increases. And as the density of C increases, the reflectance of R decreases.

[0104] FIG. 11(b) is a graph showing the relationship between the density of the M (Magenta) gradation pattern and the reflectance of G (Green). The horizontal axis of the graph is the patch number in the M gradation pattern, and the vertical axis is the reflectance of G. FIG. 11(c) is a graph showing the relationship between the density of the Y (Yellow) gradation pattern and the reflectance of B (Blue). The horizontal axis of the graph is the patch number in the Y gradation pattern, and the vertical axis is the reflectance of B. FIG. 11(d) is a graph showing the relationship between the density of the K (Black) gradation pattern and the reflectance of the common part of RGB. The horizontal axis of the graph is the patch number in the K gradation pattern, and the vertical axis is the reflectance of the common part of RGB.

[0105] CPU 101 creates gradation curves for each of the colors C, M, Y, and K by converting the reflectance data shown in FIGS. 11(a) to (d) into density data. The gradation curves for each color represent the relationship between the image density of the test pattern TPA obtained from the read signal of the test pattern TPA and the image density of the test pattern signal read from the image memory 105. Based on the created gradation curves, CPU 101 calculates gradation correction curves 201 to 204 for correcting deviations from the ideal gradation curves. FIG. 11(e) shows gradation correction curve 201 for C, FIG. 11(f) shows gradation correction curve 202 for M, FIG. 11(g) shows gradation correction curve 203 for Y, and FIG. 11(h) shows gradation correction curve 204 for K. In this way, test pattern TPA (basis weight 50 g / m 2 ) is generated.

[0106] In step ST40, a test pattern TPB (basis weight 80 g / m 2 A gradation correction table LUTB is created corresponding to the test pattern TPC (grammage 150g / m 2 ) is generated. The generated tone correction tables LUTA to LUTC are associated with the basis weight information of the corresponding test patterns and stored in HDD 107. Each of the tone correction tables LUTA to LUTC includes a graph and / or a polynomial function representing the tone correction curves 201 to 204.

[0107] 8. Printing Operation According to the Present Invention Fig. 12 is a diagram illustrating a printing operation in an image forming apparatus according to the present embodiment. In Fig. 12, a printing operation is performed for each of the same three types of documents P1A to P1C as in Fig. 8. That is, documents P1A to P1C have the same image formed thereon, but have different basis weights. The basis weight of document P1A is 50 (g / m 2 ), and the basis weight of manuscript P1B is 80 (g / m 2 ), and the basis weight of manuscript P1C is 150 (g / m 2 ).

[0108] The originals P1A to P1C are placed on an original placement tray 38 of the ADF 32. Each of the originals P1A to P1C is transported to the scanner unit 31 by the ADF 32. The image sensor 35A of the scanner unit 31 reads an image from each of the originals P1A to P1C. The image sensor 35A generates an image signal corresponding to each of the originals P1A to P1C. The basis weight sensor 30 detects the basis weight of each original transported by the original transport mechanism 40. Basis weight information indicating the detected basis weight is linked to an image signal for each original. The image signals corresponding to the originals P1A to P1C are stored in an image memory 105.

[0109] 12 shows read images I1A-I1B based on image signals generated by scanner unit 31. Read image I1A is a read image generated by reading original document P1A. Read image I1B is a read image generated by reading original document P1B. Read image I1C is a read image generated by reading original document P1C. As described in FIG. 8, read image I1A of original document P1A, which has the smallest basis weight, has the highest density, and read image I1C of original document P1C, which has the largest basis weight, has the lowest density.

[0110] Image processing unit 104 generates image data based on image signals corresponding to each of read images I1A to I1C. At this time, gamma correction unit 148 reads out a gradation correction table corresponding to the basis weight of the document from HDD 107 based on the basis weight information linked to the image signal for each document. Then, image processing unit 104 performs gamma correction on the image signal using the read out gradation correction table.

[0111] In the example of FIG. 12, the document P1A has a basis weight of 50 (g / m 2 ), so the basis weight is 50 (g / m 2 ) is read out. Then, using the gradation correction table LUTA, gamma correction is performed on the image signal corresponding to the original P1A.

[0112] The manuscript P1B has a basis weight of 80 (g / m 2 ), so the basis weight is 80 (g / m 2 ) is read out. Then, the tone correction table LUTB is used to perform gamma correction on the image signal corresponding to the original P1B.

[0113] The manuscript P1C has a basis weight of 150 (g / m 2 ), so the basis weight is 150 (g / m 2) is read out. Then, the tone correction table LUTC is used to perform gamma correction on the image signal corresponding to the original P1C.

[0114] The imaging unit 117 forms a print image on the paper P2 by executing a printing operation based on the generated image data for each of the documents P1A to P1C. In Fig. 12, the print image I2A is a print image formed based on the read image I1A. The print image I2B is a print image formed based on the read image I1B. The print image I2C is a print image formed based on the read image I1C.

[0115] In the image processing unit 104, gamma correction is performed on the read image of the original using a gradation correction table that matches the basis weight of the original. As a result, good gradation reproducibility for the originals P1A to P1C can be obtained in the print images I2A to I2C, even though the gradation characteristics of the read image vary depending on the basis weight of the original.

[0116] [9. Printing Operation Flowchart] 13 is a flowchart showing the procedure of the printing operation according to the present embodiment. This flowchart is realized by CPU 101 executing a control program for the printing operation.

[0117] As shown in FIG. 13, the CPU 101 first determines whether or not the original P1 is placed on the original placement tray 38 of the ADF 32 based on a signal from the sensor unit 900 (step S01).

[0118] If the document P1 is placed on the document placement tray 38 (YES in S01), the CPU 101 then determines whether or not the user has turned on a print operation start button provided on the operation panel 9 (step S02). Note that the instruction to start the print operation can be given by an external terminal, in addition to operating the start button provided on the operation panel 9.

[0119] When the start button is turned on (YES in S02), CPU 101 starts reading of document P1 by image reading unit 3 by sending a control signal to image reading control unit 113. When reading is instructed, ADF 32 first transports document P1 placed on document placement tray 38 one sheet at a time to scanner unit 31 (step S03). When document P1 is transported to the reading position by document transport mechanism 40, basis weight sensor 30 detects the basis weight of document P1. CPU 101 acquires basis weight information relating to the basis weight of document P1 based on a signal from basis weight sensor 30 (step S04).

[0120] The scanner unit 31 reads an image from the document P1 transported to a predetermined reading position (step S05). The image reading unit 3 associates the basis weight information of the document P1 with an image signal corresponding to the image of the document P1, and stores the image in the image memory 105.

[0121] Every time an image is read from one sheet of document P1, CPU 101 determines whether or not the next document P1 is present on document placement tray 38 based on a signal from sensor unit 900 (step S07). If the next document P1 is present on document placement tray 38, CPU 101 returns to step S03, reads the next document P1, obtains basis weight information of the document P1, and stores the obtained basis weight information in image memory 105 while linking it to an image signal.

[0122] If there is no next document P1 on the document loading tray 38, i.e., if all documents P1 have been read by the scanner unit 31 (when S07 is judged as YES), the CPU 101 executes a printing process to form an image on paper P2 based on the image signal stored in the image memory 105.

[0123] In the printing process, the image processing unit 104 reads out the image signal of the first original P1 from the image memory 105 (step S08). The read-out image signal is linked to the basis weight information of the first original P1. The image processing unit 104 generates image data based on the read-out image signal, as shown in FIG. 4. At this time, the image processing unit 104 selects a tone correction table corresponding to the basis weight of the first original P1 from among a plurality of tone correction tables stored in the HDD 107, based on the basis weight information (step S09).

[0124] The image processing unit 104 performs gamma correction on the image signal using the selected tone correction table. The imaging unit 117 executes a printing operation based on the image data generated by the image processing unit 104, thereby forming a print image on the paper P2 (step S10).

[0125] When a print image is formed for the first original P1, the CPU 101 determines whether or not an image signal remains in the image memory 105 based on a signal from the sensor unit 900 (step S11). If an image signal remains in the image memory 105 (YES determination in S11), the process returns to step S08, and the image signal of the next original P1 is read out from the image memory 105. Then, image data is generated by performing gamma correction on the image signal using a tone correction table corresponding to the basis weight of the next original P1. A print operation is performed based on the image data, and a print image is formed on the paper P2.

[0126] When print images have been formed for all image signals stored in image memory 105 and it is determined that no image signals remain in image memory 105 (NO in S11), CPU 101 ends the printing process.

[0127] [10. Basis weight information of manuscript] In the above-described embodiment, a configuration was described in which the basis weight information of the original P1 is obtained by detecting the basis weight of the original P1 using the basis weight sensor 30 provided inside the ADF 32. However, the basis weight information of the original P1 may also be obtained by a user operation on the operation panel 9 or from an external terminal.

[0128] 14 is a diagram showing an example of the display 9A of the operation panel 9. The CPU 101 causes the display 9A to display a UI (User Interface) screen for receiving user settings related to the basis weight of the document P1, and acquires basis weight information of the document P1 based on a user operation on the screen.

[0129] 14, when the user operates an icon 502 on a menu screen 500, a setting screen 504 for setting the basis weight of the original P1 is displayed on the display 9A. A plurality of icons 506 corresponding to a plurality of basis weights are provided on the setting screen 504. The number of icons 506 can be set to any number within the range of basis weights of originals that can be read by the image reading unit 3.

[0130] The user can set the basis weight of the document P1 by operating any one of the icons 506. For example, the basis weight is set to 80 (g / m 2 ), the document P1 has a basis weight of 80 g / m 2 The CPU 101 acquires this set basis weight as basis weight information, and stores it in the image memory 105 in association with the image signal of the original P1.

[0131] [11. Gradation correction table] In the above-described embodiment, a configuration has been described in which a gradation correction table for each basis weight is created by performing gradation correction processing using a plurality of test patterns having different basis weights, but a configuration in which a gradation correction table for each basis weight is received from an external device may also be used.

[0132] 15, for example, CPU 101 can obtain a gradation correction table for each basis weight by communicating between MPF ​​1 and terminal 200 such as a personal computer via network 110. Alternatively, CPU 101 can obtain a gradation correction table for each basis weight by wirelessly communicating between MPF ​​1 and portable terminal 300. Note that multiple gradation correction tables can be received in advance before starting a printing operation and stored in HDD 107. Alternatively, communication can be performed with terminal 200 during a printing operation, and a gradation correction table corresponding to the basis weight of document P1 can be received from terminal 200.

[0133] [12. Variations of Printing Operation] (First Modification) Fig. 16 is a flowchart showing the procedure of a printing operation according to a first modified example of the present embodiment. The flowchart shown in Fig. 16 is obtained by adding the processes of steps S12 to S14 to the flowchart shown in Fig. 13.

[0134] 13, gamma correction unit 148 of image processing unit 104 selects a gradation correction table corresponding to the grammage of original P1 from among a plurality of gradation correction tables stored in HDD 107 based on the grammage information of original P1. At this time, image processing unit 104 determines whether or not there is a gradation correction table matching the grammage of original P1 among the plurality of gradation correction tables stored in HDD 107 (step S12).

[0135] If there is a gradation correction table with a basis weight that matches the basis weight of the original P1, S12 is judged as YES. In this case, the image processing unit 104 performs gamma correction on the image signal of the original P1 using the gradation correction table with a basis weight that matches the basis weight of the original P1. The imaging unit 117 forms a print image on the paper P2 by executing a printing operation based on the image data generated by the image processing unit 104 (step S13).

[0136] On the other hand, if there is no tone correction table with a basis weight matching the basis weight of the original P1 among the plurality of tone correction tables, S12 is judged as NO. In this case, the image processing unit 104 proceeds to step S14 and selects a tone correction table corresponding to a basis weight closest to the basis weight of the original P1 from among the plurality of tone correction tables. Then, the image processing unit 104 performs gamma correction on the image signal of the original P1 using the selected tone correction table. The imaging unit 117 forms a print image on the paper P2 by executing a printing operation based on the image data generated by the image processing unit 104 (step S14).

[0137] According to the first modified example, even if there is no tone correction table that matches the basis weight of the original P1, the image signal of the original P1 can be corrected using a tone correction table that corresponds to the basis weight of the original P1.

[0138] (Second Modification) Fig. 17 is a flowchart showing the procedure of a printing operation according to the second modified example of the present embodiment. The flowchart shown in Fig. 17 is obtained by adding the processes of steps S12 to S17 to the flowchart shown in Fig. 13.

[0139] 13, gamma correction unit 148 of image processing unit 104 selects a gradation correction table corresponding to the grammage of original P1 from among the plurality of gradation correction tables stored in HDD 107 based on the grammage information of original P1. At this time, image processing unit 104 determines whether or not there is a gradation correction table matching the grammage of original P1 among the plurality of gradation correction tables stored in HDD 107 (step S12).

[0140] If there is a gradation correction table with a basis weight that matches the basis weight of the original P1, S12 is judged as YES. In this case, the image processing unit 104 performs gamma correction on the image signal of the original P1 using the gradation correction table with a basis weight that matches the basis weight of the original P1. The imaging unit 117 forms a print image on the paper P2 by executing a printing operation based on the image data generated by the image processing unit 104 (step S13).

[0141] On the other hand, if there is no gradation correction table with a basis weight matching that of the document P1 among the plurality of gradation correction tables, S12 is judged as NO. In this case, the image processing unit 104 proceeds to step S15 and selects a gradation correction table corresponding to a basis weight higher than that of the document P1 (i.e., a basis weight larger than that of the document P1) from among the plurality of gradation correction tables. Also, the image processing unit 104 selects a gradation correction table corresponding to a basis weight lower than that of the document P1 (i.e., a basis weight smaller than that of the document P1) from among the plurality of gradation correction tables.

[0142] Next, the image processor 104 creates a gradation correction table corresponding to the basis weight of the document P1 based on the two gradation correction tables selected in S15 (step S16). In S16, the image processor 104 creates a gradation correction table corresponding to the basis weight of the document P1 by interpolating between the two gradation correction tables.

[0143] For example, if the basis weight of the document P1 is s (g / m 2 ) and the gradation correction table that matches the grammage is not stored in the HDD 107. In this case, the image processing unit 104 selects the gradation correction table that matches the grammage m (g / m) from among a plurality of gradation correction tables. 2 ) and the first gradation correction table corresponding to the basis weight n (g / m 2 ), where n <s<mである。

[0144] Here, in the gradation correction curves of each color included in the first gradation correction table, the density of the printer image relative to the density (x) of the image signal used in image formation is represented by a polynomial function f(x) of x. Also, in the gradation correction curves of each color included in the second gradation correction table, the density of the printer image relative to the density (x) of the image signal used in image formation is represented by a polynomial function g(x) of x.

[0145] In the tone correction curves of each color included in the tone correction table corresponding to the basis weight of the document P1, the density of the printer image relative to the density (x) of the image signal used in image formation is expressed by a polynomial function h(x) of x. The polynomial function h(x) can be calculated by linearly interpolating the polynomial function f(x) and the polynomial function g(x). The polynomial function h(x) can be expressed by the following equation (1). h(x)={(sn)f(x)+(ms)×g(x)} / (mn)...(1) The image processing unit 104 performs gamma correction on the image signal of the document P1 using the created gradation correction table. The imaging unit 117 executes a printing operation based on the image data generated by the image processing unit 104, thereby forming a print image on the paper P2 (step S17).

[0146] According to the second modification, even if there is no tone correction table that matches the basis weight of the original P1, the image signal of the original P1 can be corrected using a tone correction table that corresponds to the basis weight of the original P1.

[0147] [13. Program] An application program including a program for executing the printing operations shown in Figs. 13, 16, and 17 can be recorded on a computer-readable storage medium such as external storage medium 120 that is attached to MFP1 as a computer having a processor, and provided as a program product. Alternatively, the program can be provided by recording it on a recording medium such as HDD 107 built into the computer. The program can also be provided by downloading via network 110 or wireless communication. The program can be executed by one or more processors such as CPU 101, or by a combination of a processor and a circuit such as an Application Specific Integrated Circuit (ASIC) or a Field-Programmable Gate Array (FPGA).

[0148] [14. Advantages] According to this embodiment, when a print image is formed on a sheet based on an image signal obtained by reading an image of an original P1 conveyed on a predetermined reading position in the image reading unit 3, gamma correction (tone correction) is performed on the image signal using tone correction information (tone correction table) according to the basis weight of the original P1. As a result, even if the tone characteristics of the image read by the image reading unit 3 vary according to the basis weight of the original, good tone reproducibility for the original can be obtained in the print image formed on the sheet.

[0149] [Note] The above-described embodiment and modified examples include the following technical ideas.

[0150] [Configuration 1] an image reading means for reading an image of a document conveyed on a predetermined reading position and acquiring an image signal; an acquisition means for acquiring basis weight information indicating a basis weight of the document; a correction means for acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; and forming means for forming an image on a sheet based on the corrected image signal.

[0151] [Configuration 2] Further, a storage means for storing a plurality of pieces of gradation correction information created for each basis weight is provided, The correction means is selecting tone correction information corresponding to the basis weight of the document from the plurality of tone correction information stored in the storage means based on the basis weight information; 2. The image forming apparatus according to configuration 1, wherein the image signal is corrected using the selected gradation correction information.

[0152] [Configuration 3] A creating unit for creating the plurality of pieces of gradation correction information is further provided, When generating the plurality of pieces of gradation correction information, The forming means forms a plurality of test patterns having different basis weights, the image reading means reads images of the plurality of test patterns conveyed above the reading position to obtain test pattern signals; 3. The image forming apparatus according to claim 2, wherein the generating means generates the gradation correction information for each test pattern based on the density of the test pattern signal acquired by the image reading means and the density of the image of the test pattern.

[0153] [Configuration 4] The image forming apparatus further includes a communication unit for communicating with an external device, The correction means is receiving a plurality of pieces of gradation correction information created for each basis weight from the external device via the communication means; selecting tone correction information corresponding to the basis weight of the document from the plurality of pieces of tone correction information received based on the basis weight information; 2. The image forming apparatus according to configuration 1, wherein the image signal is corrected using the selected gradation correction information.

[0154] [Configuration 5] The image forming apparatus according to any one of configurations 1 to 3, wherein the gradation correction information includes a gradation correction table indicating a correspondence relationship between the density of the image signal acquired from the document and the density of the image formed on the sheet.

[0155] [Configuration 6] 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the acquisition unit includes a detection unit that detects a basis weight of the document transported to the reading position.

[0156] [Configuration 7] 6. The image forming apparatus according to any one of configurations 1 to 5, wherein the obtaining means includes a setting means for receiving a setting of a basis weight of the document from a user.

[0157] [Configuration 8] The image reading device further includes a storage unit for storing the image signal obtained by the image reading unit. 8. The image forming apparatus according to claim 6, wherein the image reading means stores the basis weight information acquired by the acquisition means in the storage means in association with the image signal.

[0158] [Configuration 9] The image forming apparatus according to configuration 2 or 4, wherein, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of gradation correction information, the correction means selects gradation correction information corresponding to a basis weight closest to the basis weight of the document, and corrects the image signal using the selected gradation correction information.

[0159] [Configuration 10] The image forming apparatus according to configuration 2 or 4, wherein, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of gradation correction information, the correction means creates gradation correction information corresponding to the basis weight of the document by interpolating gradation correction information corresponding to a basis weight larger than the basis weight of the document and gradation correction information corresponding to a basis weight smaller than the basis weight of the document, and corrects the image signal using the created gradation correction information.

[0160] [Configuration 11] 1. A computer-implemented method comprising: A step of acquiring an image signal by reading an image of a document conveyed on a predetermined reading position of an image forming apparatus; obtaining basis weight information indicating a basis weight of the document; acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; forming an image on a sheet based on the corrected image signal.

[0161] [Configuration 12] A program executed by a computer, The program causes the computer to: A step of acquiring an image signal by reading an image of a document conveyed on a predetermined reading position of an image forming apparatus; obtaining basis weight information indicating a basis weight of the document; acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; and forming an image on a sheet based on the corrected image signal.

[0162] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0163] 1 MFP, 2 device body, 3 image reading unit, 4, 4A to 4D paper feed tray, 5 transfer unit, 6 fixing unit, 7 paper output tray, 8 transport device, 9 operation panel, 9A display, 10 main body control unit, 30 basis weight sensor, 31 scanner unit, 32 ADF, 33 document table, 34 light source unit, 35A, 35B image sensor, 36 imaging lens, 37 mirror group, 38 document placement tray, 39 document output tray, 40 document transport mechanism, 51 imaging unit, 52 exposure unit, 53 intermediate transfer belt, 54 primary transfer roller, 55 drive roller, 56 driven roller, 57 secondary transfer roller, 58, 64 cleaner unit, 59 heating roller, 60 pressure roller, 61 photoconductor drum, 62 charger, 63 developer, 80 paper feed sensor, 81 delivery roller, 82 paper feed roller pair, 83 transport roller pair, 84 skew correction roller, 90 paper discharge sensor, 91 paper discharge roller pair, 101 CPU, 102 ROM, 103 RAM, 104 image processing unit, 105 image memory, 106 communication I / F, 107 HDD, 108 wireless communication I / F, 110 Internet, 113 image reading control unit, 114 exposure control unit, 115 transfer control unit, 116 fixing control unit, 117 imaging unit, 118 transport control unit, 119 memory I / F, 120 external storage medium, 140 A / D conversion unit, 142 shading correction unit, 144 LOG conversion unit, 146 color conversion unit, 148 gamma correction unit, 200, 300 terminal, 201 to 204 gradation correction curve, 500 menu screen, 502, 506 icon, 504 Document weight setting screen, 900 sensor unit, P1, P1A~P1C documents, I1A~I1C, I11A~I11C scanned images, I2A~I2C printed images, LUTA~LUTC tone correction tables, TPA~TPC test patterns.

Claims

1. an image reading means for reading an image of a document conveyed on a predetermined reading position and acquiring an image signal; an acquisition means for acquiring basis weight information indicating a basis weight of the document; a correction means for acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; and forming means for forming an image on a sheet based on the corrected image signal.

2. Further, a storage means for storing a plurality of pieces of gradation correction information created for each basis weight is provided, The correction means is selecting tone correction information corresponding to the basis weight of the document from the plurality of tone correction information stored in the storage means based on the basis weight information; 2. The image forming apparatus according to claim 1, wherein the image signal is corrected using the selected gradation correction information.

3. A creating unit for creating the plurality of pieces of gradation correction information is further provided, When generating the plurality of pieces of gradation correction information, The forming means forms a plurality of test patterns having different basis weights, the image reading means reads images of the plurality of test patterns conveyed above the reading position to obtain test pattern signals; 3. The image forming apparatus according to claim 2, wherein said creating means creates said gradation correction information for each test pattern based on a density of said test pattern signal obtained by said image reading means and a density of an image of said test pattern.

4. The image forming apparatus further includes a communication unit for communicating with an external device, The correction means is receiving a plurality of pieces of gradation correction information created for each basis weight from the external device via the communication means; selecting tone correction information corresponding to the basis weight of the document from the plurality of pieces of tone correction information received based on the basis weight information; 2. The image forming apparatus according to claim 1, wherein the image signal is corrected using the selected gradation correction information.

5. 4. The image forming apparatus according to claim 1, wherein the tone correction information includes a tone correction table indicating a correspondence relationship between the density of the image signal acquired from the document and the density of the image formed on the sheet.

6. The image forming apparatus according to claim 1 , wherein the obtaining unit includes a detecting unit that detects a basis weight of the document transported to the reading position.

7. The image forming apparatus according to claim 1 , wherein the obtaining unit includes a setting unit that receives a setting of the basis weight of the document from a user.

8. The image reading device further includes a storage unit for storing the image signal obtained by the image reading unit.

8. The image forming apparatus according to claim 6, wherein the image reading means stores the basis weight information acquired by the acquisition means in the storage means in association with the image signal.

9. 5. The image forming apparatus according to claim 2, wherein, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of pieces of gradation correction information, the correction means selects gradation correction information corresponding to a basis weight closest to the basis weight of the document, and corrects the image signal using the selected gradation correction information.

10. 5. The image forming apparatus according to claim 2, wherein, when there is no gradation correction information corresponding to the basis weight of the document among the plurality of pieces of gradation correction information, the correction means creates gradation correction information corresponding to the basis weight of the document by interpolating gradation correction information corresponding to a basis weight larger than the basis weight of the document and gradation correction information corresponding to a basis weight smaller than the basis weight of the document, and corrects the image signal using the created gradation correction information.

11. 1. A computer-implemented method comprising: A step of acquiring an image signal by reading an image of a document conveyed on a predetermined reading position of an image forming apparatus; obtaining basis weight information indicating a basis weight of the document; acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; forming an image on a sheet based on the corrected image signal.

12. A program executed by a computer, The program causes the computer to: A step of acquiring an image signal by reading an image of a document conveyed on a predetermined reading position of an image forming apparatus; obtaining basis weight information indicating a basis weight of the document; acquiring tone correction information corresponding to the basis weight of the document based on the basis weight information, and correcting the image signal using the acquired tone correction information; and forming an image on a sheet based on the corrected image signal.

Images