Image forming apparatus

Abstract

To provide an image formation apparatus in which a user can perform an operation at the calibration without confusion.SOLUTION: An image formation apparatus comprises: a printer 300 which creates a test chart by forming a test pattern used in the calibration on a sheet; a document scanner 215 which reads the test chart in any of a first reading mode and a second reading mode; an ADF 220 on which the test chart is set in the first reading mode; a document table 102 on which the test chart is set in the second reading mode; and a CPU which makes the document scanner 215 read the test chart when the test chart is set on the instructed device after the device to be set with the test chart is instructed, and performs the calibration on the basis of the reading result of the test chart by the document scanner 215.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus having a calibration function.

Background Art

[0002] An electrophotographic image forming apparatus forms an image on a sheet by the following image forming process. First, the image forming apparatus uniformly charges the surface of a photoreceptor. The image forming apparatus irradiates the surface of the photoreceptor uniformly charged on the surface based on an image signal, thereby forming an electrostatic latent image on the surface of the photoreceptor. The image forming apparatus forms a developer image on the surface of the photoreceptor by developing the electrostatic latent image with a developer such as toner. The image forming apparatus transfers and fixes this developer image onto a sheet, thereby forming an image on the sheet. When forming a color image, the image forming apparatus individually forms developer images of a plurality of colors and superimposes them to generate a color image.

[0003] The density and color tone of an image formed by such an image forming apparatus on a sheet vary due to various factors. For example, the density of an image formed by the image forming apparatus changes due to changes in environmental conditions such as temperature and humidity, or due to changes over time in the components of the image forming apparatus. Therefore, the image forming apparatus performs calibration to control the density of the image to a target density. In calibration, a test chart on which a test pattern for detecting image density is formed on a sheet is used. By reading the test pattern of the test chart with an image reading device, the image density of the test pattern is obtained. Image forming conditions such as parameters for adjusting the image density are adjusted so that this image density becomes the target density. By correcting the image signal with such parameters, stable density and gradation characteristics are ensured even when changes in environmental conditions or changes over time in components occur. The image forming apparatus described in Patent Document 1 uses an automatic document feeder (ADF) to convey a test chart in order to read the test chart. Thereby, the work load of the user when performing calibration is reduced.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2007-329929 [Overview of the project] [Problems that the invention aims to solve]

[0005] In addition to the ADF (Automatic Document Feeder), the image reader can also read test patterns from a test chart placed on the document glass. Therefore, users may be unsure whether to use the ADF or the document glass during calibration.

[0006] This invention has been made in view of the above problems, and its main objective is to provide an image forming apparatus that allows users to perform calibration operations without confusion. [Means for solving the problem]

[0007] The image forming apparatus of the present invention is The image forming means for forming an image on a sheet; a paper feed cassette provided vertically below the image forming means and containing sheets transported to the image forming means; a document transport means provided vertically above the image forming means and comprising a platen on which a sheet is placed; a tray on which a sheet is placed and for transporting the sheet placed on the tray; a lamp provided on the document transport means; an image sensor that reads the sheet placed on the platen and the sheet transported by the document transport means; an operation unit equipped with a display unit for the user to input instructions; a detection means for detecting the presence or absence of a sheet on the tray; and when reading a test image formed on a sheet using the image sensor and adjusting the image density based on the reading result, the image The system includes a forming means for forming the test image, and a control means for controlling the density of the image formed by the image forming means based on the reading result of the test image by the image sensor. The lamp lights up when the detection means detects that there is a sheet on the tray. When adjusting the image density, the control means displays a selection screen on the display unit for selecting whether to place the sheet with the test image on it on the tray or on the platen. The control means uses the lamp to indicate that the tray has been selected as the placement destination from the selection screen. When the tray is selected as the placement destination, the lamp lights up. When the platen is selected as the placement destination, the lamp does not light up. It is characterized by the following: [Effects of the Invention]

[0008] According to the present invention, users will be able to perform calibration operations without any confusion. [Brief explanation of the drawing]

[0009] [Figure 1] Diagram showing the configuration of an image forming apparatus. [Figure 2] Diagram illustrating the reader image processing unit. [Figure 3] Diagram illustrating the printer control unit. [Figure 4] Diagram illustrating a document scanner. [Figure 5] External perspective view of the ADF. [Figure 6] Internal configuration diagram of the ADF. [Figure 7] 4th period chart. [Figure 8] A flowchart illustrating the gradation correction process. [Figure 9] An example diagram of a test chart. [Figure 10] (a) and (b) are illustrative diagrams of screens displayed on a display. [Figure 11] A flowchart illustrating the gradation correction process. [Figure 12] (a) and (b) are illustrative diagrams of screens displayed on a display. [Modes for carrying out the invention]

[0010] Embodiments of the present invention will be described below with reference to the figures.

[0011] (Image forming apparatus) Figure 1 is a diagram of the configuration of the image forming apparatus according to this embodiment. The image forming apparatus 100 comprises a reader 200, which is an image reading device that reads an image from a document (sheet), a printer 300 that forms an image on the sheet, and an operation unit 400. The reader 200 comprises a document scanner 215 and an automatic document feeder (hereinafter referred to as "ADF") 220. The document scanner 215 is mounted on the printer 300, and the ADF 220 is mounted on the document scanner 215. The reader 200 reads the image printed on the document 101 and transmits an image signal representing the read image to the printer 300. The printer 300 can perform image forming processing on the sheet based on the image signal acquired from the reader 200. The operation unit 400 is a user interface and includes input and output devices. The input devices include, for example, various key buttons such as input keys, numeric keypads, start keys, stop keys, and touch panels. User instruction information is input via the operation unit 400. Output devices include, for example, displays and speakers.

[0012] The reader 200 reads the document fed from the document tray 501 of the ADF 220 or the document 101 placed on the document table 102 provided on the ADF 220 side of the document scanner 215. The document table 102 is a transmissive member such as a plate-shaped glass. The document scanner 215 includes a reader image processing unit 108 inside. The reader image processing unit 108 converts the electrical signal generated by reading the document 101 into an image signal and transmits it to the printer 300.

[0013] The document scanner 215 includes a reference white plate 106 on the document table 102. The reader 200 reads the reference white plate 106 before reading the document 101 to perform so-called shading correction. The document scanner 215 includes a first mirror unit 104a, a second mirror unit 104b, a lens 115, and an image sensor 105. The first mirror unit 104a has a light source 103. The first mirror unit and the second mirror unit 104b are movable in the direction of arrow K1. When reading the document 101 on the document table 102, the first mirror unit 104a irradiates the document 101 with light from the light source 103 while moving in the direction of arrow K1. The reflected light by the document 101 is received by the image sensor 105. The image sensor 105 is a reading sensor that includes a plurality of photoelectric conversion elements (light receiving elements) having RGB filters and converts the reflected light into an electrical signal one line at a time. A CCD sensor or a CMOS sensor can be used for the image sensor 105. The reader image processing unit 108 acquires an electrical signal from the image sensor 105 and converts this electrical signal into an image signal (luminance signal). Details of the document scanner 215 will be described later.

[0014] The printer 300 includes a printer control unit 109 inside. The printer control unit 109 acquires an image signal (luminance signal) from the reader image processing unit 108 of the document scanner 215. The printer control unit 109 forms an image on the sheet based on the acquired image signal. The printer 300 includes an image forming unit 120, 130, 140, 150, an exposure device 110, a transfer belt 111, and a fixing device 114 for image formation.

[0015] The image forming units 120, 130, 140, and 150 only differ in the colors of the images they form, and perform the same operations with the same configurations. The image forming unit 120 forms a yellow (Y) image. The image forming unit 130 forms a magenta (M) image. The image forming unit 140 forms a cyan (C) image. The image forming unit 150 forms a black (K) image. Here, the configuration of the image forming unit 120 will be described, and the descriptions of the configurations of the other image forming units 130, 140, and 150 will be omitted.

[0016] The image forming unit 120 includes a photosensitive drum 121, a charger 122, a developer 123, a transfer blade 124, and a surface potentiometer 125. The photosensitive drum 121 is a drum-shaped photoreceptor having a photosensitive layer on its surface. The photosensitive drum 121 rotates in the clockwise direction in the figure. The charger 122 uniformly charges the surface of the rotating photosensitive drum 121 to a predetermined potential. The surface of the charged photosensitive drum 121 is scanned with a laser beam by the exposure unit 110, thereby forming an electrostatic latent image on the surface. The developer 123 develops the electrostatic latent image with a developer (e.g., toner) of the corresponding color (here, yellow), and forms a toner image on the surface of the photosensitive drum 121.

[0017] Note that the exposure unit 110 is controlled by the printer control unit 109 to irradiate the photosensitive drum 121 with a laser beam. The exposure unit 110 scans the photosensitive drum 121 in the Y direction. Therefore, the Y direction becomes the main scanning direction. The printer control unit 109 modulates the laser beam emitted from the exposure unit 110 with a PWM (Pulse Width Modulation) signal based on the image signal.

[0018] The transfer blade 124 is disposed with the transfer belt 111 sandwiched therebetween and the photosensitive drum 121. The transfer belt 111 conveys the sheet fed from the paper feed cassette 152. The transfer blade 124 transfers the toner image formed on the photosensitive drum 121 to the sheet conveyed by the transfer belt 111 by performing discharge. Thereby, a yellow toner image is formed on the sheet.

[0019] Similarly, a magenta toner image is formed on the photosensitive drum 131 of the image forming unit 130, a cyan toner image is formed on the photosensitive drum 141 of the image forming unit 140, and a black toner image is formed on the photosensitive drum 151 of the image forming unit 150. The magenta toner image formed on the photosensitive drum 131 is transferred so as to be superimposed on the yellow toner image on the sheet. The cyan toner image formed on the photosensitive drum 141 is transferred so as to be superimposed on the yellow and magenta toner images on the sheet. The black toner image formed on the photosensitive drum 151 is transferred so as to be superimposed on the yellow, magenta, and cyan toner images on the sheet. By superimposing and transferring the toner images of each color, a full-color toner image is formed on the sheet.

[0020] The sheet on which the full-color toner image has been formed is transported to the fuser 114 by the transfer belt 111. The fuser 114 fixes the transferred toner image to the sheet. The fuser 114 fixes the toner image to the sheet by, for example, heating, melting, and pressurizing the toner image. As a result, an image is formed on the sheet. The sheet with the formed image is discharged from the printer 300.

[0021] Furthermore, the surface potential meters 125, 135, 145, and 155 of each image forming unit 120, 130, 140, and 150 measure the surface potential of the photosensitive drums 121, 131, 141, and 151. The contrast potential is adjusted according to the measurement results from the surface potential meters 125, 135, 145, and 155.

[0022] In this embodiment, the ADF220 is equipped with a lamp 156. The document scanner 215 is equipped with a lamp 157. The ADF220 is equipped with a sensor for detecting the presence or absence of a sheet in the document tray 501. The lamp 156 of the ADF220 lights up when the sensor's detection result indicates that a sheet has been placed in the document tray 501. The lamp 156 turns off when the sensor's detection result indicates that no sheet has been placed in the document tray 501. The lamps 156 and 157 light up during calibration when the test chart used for calibration is placed (set). In this embodiment, the lamp 156 lights up during calibration regardless of the sensor's detection result.

[0023] (Reader image processing unit) Figure 2 is an explanatory diagram of the reader image processing unit 108. The reader image processing unit 108 comprises an AFE (Analog Front End) circuit board 201 and a reader controller circuit board 210. The AFE circuit board 201 comprises an analog image processing unit 202 and an A / D conversion unit 203. The reader controller circuit board 210 comprises a shading processing unit 212 and a CPU (Central Processing Unit) 211. The CPU 211 controls the operation of the reader 200 by executing a predetermined computer program.

[0024] The reader image processing unit 108 acquires the electrical signal output from the image sensor 105 using the AFE circuit board 201. The electrical signal is, for example, an analog signal corresponding to the amount of light received by the image sensor 105. The AFE circuit board 201 performs analog processing such as gain adjustment using the analog image processing unit 202. The electrical signal after analog processing is converted into a digital signal by the A / D conversion unit 203.

[0025] The shading processing unit 212 of the reader controller circuit board 210 acquires the digital signal generated by the A / D conversion unit 203. The shading processing unit 212 performs shading correction on the digital signal under the control of the CPU 211 and generates an image signal. The image signal is transmitted to the printer control unit 109. The image signal includes R (red), G (green), and B (blue) luminance information.

[0026] (Printer control unit) Figure 3 is an explanatory diagram of the printer control unit 109. The printer control unit 109 is controlled by the CPU 301. The CPU 301 is the main control unit that controls the operation of the image forming apparatus 100 and performs image forming processing on the sheet by executing a control program stored in the memory 302. The memory 302 is either ROM (Read Only Memory) or RAM (Random Access Memory) and stores the control program and various data. The CPU 301 and memory 302 are provided in the printer 300.

[0027] The printer control unit 109 acquires image signals from the reader 200 or server 500, etc. The server 500 is an external device provided separately from the printer 300 and connected to the printer 300 via a network such as a LAN (Local Area Network). The image signal is represented by 8 bits for each of the R, G, and B grayscale levels. The printer control unit 109 includes a color processing unit 303, a grayscale control unit 311, a dithering processing unit 307, a PWM unit 308, and a laser driver 309. The printer control unit 109 converts the R, G, and B image signals into PWM signals to control the emission of light from the semiconductor laser 310 provided in the exposure unit 110.

[0028] The R, G, and B image signals are input to the color processing unit 303. The color processing unit 303 performs image processing and color processing on the input image signals so that the desired output result (image) can be obtained if the output characteristics of the printer 300 are ideal. The color processing unit 303 expands the number of gradations of the image signal from 8 bits to 10 bits for improved accuracy. The color processing unit 303 is equipped with a lookup table called LUTid 304. LUTid 304 is a luminance-density conversion table that converts the luminance information contained in the image signal into density information. The color processing unit 303 uses LUTid 304 to convert the luminance information of each R, G, and B image signal into density information of the yellow (Y), magenta (M), cyan (C), and black (K) image signals. The Y, M, C, and K image signals are input to the gradation control unit 311.

[0029] The gradation control unit 311 includes an UCR (Under Color Remove) unit 305 and a lookup table LUTa 306. The gradation control unit 311 performs gradation correction of the Y, M, C, and K image signals so that the desired output result (image) can be obtained in accordance with the actual output characteristics of the printer 300. The UCR unit 305 limits the sum of the image signal levels by regulating the integrated value of the image signal at each pixel. If the sum exceeds a specified value, the UCR unit 305 performs undercolor removal processing (UCR) by replacing a predetermined amount of C, M, and Y image signals with a K image signal, thereby reducing the sum of the image signal levels. The regulation of the sum of the image signal levels is performed to optimize the operation of the printer 300 by regulating the amount of toner applied when the printer 300 forms an image. Optimizing the operation of the printer 300 in this embodiment means preventing image defects and the like that occur when the amount of toner applied exceeds a specified value. LUTa306 is a 10-bit conversion table for correcting density characteristics, and is used, for example, to change the gamma characteristics of the printer 300. In this embodiment, LUTa is used as an example to describe the image formation conditions adjusted by calibration. The Y, M, C, and K image signals after gradation correction are input to the dithering processing unit 307.

[0030] The dithering unit 307 performs dithering on the 10-bit Y, M, C, and K image signals after gradation correction, converting them into 4-bit signals through intermediate tone processing (dithering). The PWM unit 308 performs pulse width modulation on the dithered signal to generate a PWM signal, which is the control signal for the exposure unit 110. The PWM signal is input to the laser driver 309. The laser driver 309 controls the emission of the semiconductor laser 310 according to the PWM signal.

[0031] (Document scanner) Figure 4 is an explanatory diagram of the document scanner 215. As described above, the document scanner 215 includes a first mirror unit 104a, a second mirror unit 104b, a lens 115, and an image sensor 105 within its housing. The document scanner 215 also includes a motor 116 and a home position sensor 412. The first mirror unit 104a includes a light source 103 and a first mirror 107a. The second mirror unit 104b includes a second mirror 107b and a third mirror 107c. The first mirror unit 104a and the second mirror unit 104b are driven by the motor 116 and move in the direction of K1 in Figure 1. The document scanner 215 with this configuration starts operating when image reading is instructed by the operation unit 400.

[0032] The document scanner 215 can perform image scanning in two modes: a first scanning mode in which it reads the original document 101 transported by the ADF 220, and a second scanning mode in which it reads the original document 101 placed on the document glass 102. The first scanning mode is sometimes called "swiping" or "ADF scanning." The second scanning mode is sometimes called "fixed scanning" or "document glass scanning."

[0033] Regardless of whether the reading mode is the first or second reading mode, the operation of the document scanner 215 to read the image is the same. When image reading starts, the document scanner 215 uses the motor 116 to move the first mirror unit 104a and the second mirror unit 104b to the home position, which is the detection position of the home position sensor 412. Then, the document scanner 215 turns on the light source 103 and irradiates light onto the reading surface (the side on which the image is printed) of the original document 101. The first mirror 107a, the second mirror 107b, and the third mirror 107c deflect the reflected light (image light) irradiated onto the original document 101 and guide it to the lens 115. The lens 115 forms an image of the image light on the light-receiving surface of the image sensor 105. The image sensor 105 generates an electrical signal based on the image light.

[0034] As described above, the first mirror unit 104a and the second mirror unit 104b are driven by the same motor 116 and move in the direction of arrow K1. By applying a movable pulley, the speed V at which the first mirror unit 104a moves is set to half the speed at which the second mirror unit 104b moves (V / 2). As the first mirror unit 104a and the second mirror unit 104b move, they illuminate the original document 101 with light, thereby reading an image of the entire surface of the original document 101.

[0035] (ADF) Figure 5 is an external perspective view of the ADF220. Figure 6 is an internal configuration diagram of the ADF220. The ADF220 includes a document stacking section 601, a document feeding section 614, a document transport section 615, and a document reversing section 608.

[0036] The document loading unit 601 has a document tray 501. The document tray 501 can hold one or more documents 101 on its loading surface. The document tray 501 functions as a paper feed unit. The document loading unit 601 is provided with a document indicator 503 that lights up when a document 101 is loaded onto the document tray 501. For this purpose, a document detection sensor (not shown) that detects a document placed on the document tray 501 is positioned between the pickup roller 602 (described later) and the paper feed roller 603. The documents 101 loaded onto the document tray 501 are transported one by one onto the document table 102 by the document feed unit 614, pass over the document table 102, and are discharged into the output tray 617 by the document inversion unit 608.

[0037] The document feeding unit 614 includes a pickup roller 602, a feed roller 603, and a pair of registration rollers 604, which are provided along the transport path of the document 101. The pickup roller 602 is a rotatable and vertically movable roller. When feeding, the pickup roller 602 descends and makes contact with the topmost document in the stack of documents loaded in the document tray 501. At this time, the middle plate on which the stack of documents in the document tray 501 is placed rises, pressing the stack of documents against the feed roller 603. After the pickup roller 602 has made contact with the topmost document, the pickup roller 602 and the feed roller 603 rotate in the CW (Clock Wise) direction in the figure and begin transporting the documents.

[0038] The pickup roller 602 and the paper feed roller 603 feed the original document 101 one sheet at a time using a friction separation method. For example, the second and subsequent original documents that are about to be fed together with the top original document by the pickup roller 602 are stopped by friction pieces and remain in the original document stacking section 601. The original documents being transported one sheet at a time are detected by a separation sensor (not shown) located downstream of the paper feed roller 603 in the direction of document transport. The paper feed roller 603 transports the original document 101 that has been transported by the pickup roller 602 to the registration roller pair 604.

[0039] The registration roller pair 604 is stopped when the leading edge of the document 101 reaches it. The feed roller 603 continues to transport the document 101 even after the leading edge of the document 101 collides with the registration roller pair 604. This causes the document 101 to form a loop. The formation of the loop corrects the skew of the document 101 relative to the transport direction. After the skew correction, the registration roller pair 604 starts rotating and transports the document 101 to the document transport unit 615.

[0040] The document transport unit 615 comprises a transport belt 605, a drive roller 606, a driven roller 607, and a plurality of pressure rollers 616. The document transport unit 615 transports the document 101 using the transport belt 605. The transport belt 605 is stretched over the drive roller 606 and the driven roller 607. Furthermore, the transport belt 605 is pressed toward the document table 102 by the pressure rollers 616. The transport belt 605 transports the document 101 that has entered between the transport belt 605 and the document table 102 by frictional force. As a result, the document 101 is transported on the document table 102.

[0041] When the document 101 reaches a predetermined position on the document tray 102, the transport belt 605 stops. While the document 101 is stopped, the document scanner 215 reads the image. After the image is read, the transport belt 605 transports the document 101 to the document inversion unit 608. If there is a subsequent document, the subsequent document is transported by the transport belt 605 to a predetermined position in the same way as the preceding document, stops, and its image is read. While the subsequent document is being read, the preceding document is inverted by the document inversion unit 608 and discharged into the output tray 617.

[0042] The document reversal unit 608 includes a reversal roller 609, a transport roller pair 610, a reversal flapper 611, a paper discharge flapper 613, and a reversal roller 612. The reversal roller 609 and the transport roller pair 610 are driven by a drive motor (not shown). This drive motor is capable of forward and reverse rotation. By using a separate drive motor from the document transport unit 615, the document reversal unit 608 can operate independently of the document transport unit 615.

[0043] The document 101, transported by the transport belt 605 of the document transport unit 615, is picked up by the inversion flapper 611 and transported to the inversion roller 609 when it enters the document inversion unit 608. The inversion flapper 611 restricts the document's movement near the document entrance of the document inversion unit 608 and, under the control of a solenoid (not shown), takes the position shown and picks up the document. The document 101 is held between the inversion roller 609, which rotates in the CCW (Counter Clock Wise) direction, and the opposing inversion roller 612, and transported to the transport roller pair 610. When the rear end of the document 101 passes the paper discharge flapper 613, the paper discharge flapper 613 rotates in the CW direction. The inversion roller 609 also rotates in the CW direction. As a result, the document 101 is transported in a switchback direction and discharged into the paper discharge tray 617 of the paper discharge stacking unit 320.

[0044] (Calibration operation) This embodiment describes the case where the image forming apparatus 100, which can operate in a first reading mode (ADF reading) and a second reading mode (plate glass reading) during calibration, is set to ADF reading by default. When performing calibration, the image forming apparatus 100 outputs a test chart with a test pattern formed on a sheet, and then lights up the lamp 156 of the ADF 220. This allows the user to confirm where to set the test chart, reducing confusion during processing and alleviating the workload.

[0045] Calibration to obtain the desired density and gradation characteristics is performed by controlling the LUTa306, a correction circuit that performs gamma correction. Figure 7 is a four-part chart illustrating how the image signal is converted to correct the gradation characteristics.

[0046] Quadrant I represents the reading characteristics of the reader 200, which converts the document density, representing the density of the image formed on the document, into a density signal. Note that the characteristics of converting document density to a density signal may differ depending on the reading mode (ADF reading, document glass reading). Quadrant II represents the conversion characteristics of the grayscale control unit 311 (LUTa306), which converts the density signal into a laser output signal representing the amount of light of the laser beam output from the semiconductor laser 310. Quadrant III represents the recording characteristics of the printer 300, which converts the laser output signal into an output density representing the density of the image formed on the sheet. Quadrant IV represents the relationship between the document density and the recording density of the image formed on the sheet. This relationship represents the overall grayscale reproduction characteristics of the image forming apparatus 100.

[0047] In this embodiment, the printer 300 compensates for the non-linear recording characteristics of the printer 300 in the third quadrant by the conversion characteristics of the gradation control unit 311 in the second quadrant, in order to make the gradation characteristics of the fourth quadrant linear. LUTa 306 is created by swapping the input and output of the characteristics of the third quadrant obtained when a test chart is created without processing by the gradation control unit 311. In this embodiment, the number of output gradations is 256 (8 bits), but since the gradation control unit 311 processes a 10-bit digital signal, the gradation control unit 311 has 1024 gradations.

[0048] (Tone correction) Tone correction is performed when the density and color reproduction accuracy of the image formed by the printer 300 deteriorates. Tone correction is performed by reading a tone correction test chart formed by the printer 300 with the reader 200, and creating a LUTa to correct the density characteristics (γ characteristics) based on the reading results.

[0049] Figure 8 is a flowchart representing the tone correction process. Figure 9 is an example of a test chart used for tone correction. Figure 10 is an example of the screen displayed on the display of the operation unit 400 during the tone correction process.

[0050] The CPU 301 creates a test chart for gradation correction, as illustrated in Figure 9, using the printer 300 (S1). A sheet of a predetermined size is pre-loaded into the paper cassette of the printer 300. The CPU 301 displays a guidance screen, as illustrated in Figure 10(a), on the display of the operation unit 400. The guidance screen displays the message "Printing to perform calibration" and a "Print" button to instruct the creation of the test chart. When the "Print" button is pressed on the operation unit 400, the CPU 301 sends a density signal of the image signal (test pattern) for creating the test chart to the color processing unit 303. The density signal processed by the color processing unit 303 is sent to the dithering processing unit 307 via the gradation control unit 311. At this time, the LUTa 306 is not used. In other words, the density signal YMCK output from the UCR unit 305 bypasses the LUTa 306 and is input to the dithering processing unit 307. In this way, a test pattern corresponding to the concentration signal YMCK, which bypasses LUTa306, is printed on the sheet, and a test chart is created.

[0051] As shown in Figure 9, test charts 801a and 801b each contain a test pattern consisting of 10 gradations for each color, Y, M, C, and K. The 10-gradation test pattern is formed, for example, by density signals of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, and 100% for each color. The dithering unit 307 can apply multiple halftone processing. For example, the dithering unit 307 has low-line screens (160 lpi (lines per inch) to 180 lpi) and high-line screens (250 lpi to 300 lpi). Test chart 801a is a test chart to which a low-line screen is applied. Test chart 801b is a test chart to which a high-line screen is applied. Note that gradation images may be created with a low-line screen, and line images such as characters may be created with a high-line screen. If the gradation characteristics differ significantly depending on the screen ruling, it is preferable to set the gradation level according to the screen ruling. If the printer 300 has the capability to form images with three or more different screen rulings, there may also be three or more types of test charts. For the sake of explanation, here we assume that there is one test chart formed when performing gradation correction.

[0052] The CPU 301, which created the test chart, turns on the lamp of the device on which the test chart is to be placed (S2). In this embodiment, since ADF reading is set by default, the CPU 301 turns on the lamp 156 of the ADF 220. If platen scanning is used, the CPU 301 turns on the lamp 157 of the document scanner 215. The CPU 301 instructs the user to place the test chart on the device by turning on the lamp. The user places the test chart on the instructed device (location).

[0053] If the ADF220 does not have a lamp 156, the CPU 301 may illuminate the document indicator 503 to instruct the user to set the test chart. In addition to illuminating lamps 156 and 157, the CPU 301 may also instruct the user to set the test chart using sound. Naturally, the illumination of lamps 156 and 157 and sound may be used in combination.

[0054] Lamps 156 and 157 may be set to a specific blinking pattern during calibration, such as continuous illumination, blinking, or illumination in a pattern different from the normal one. The colors of lamps 156 and 157 may be different during calibration and during normal operation. In addition, increasing the light intensity of lamps 156 and 157 can improve user recognition.

[0055] The CPU 301, having instructed the CPU 301 to place the test chart, reads the test chart using the reader 200 (S3). After instructing the CPU 301 to place the test chart, it displays an input screen for reading the test chart on the display of the operation unit 400. Figure 10(b) illustrates such an input screen. The input screen displays the message "Please place the test chart in the ADF to read it," and a "Read" button to instruct the reading. When the "Read" button is pressed by the operation unit 400, the CPU 301 starts transporting the test chart using the ADF 220 and reads the test chart using the document scanner 215.

[0056] The CPU 301 acquires the density signal of the test pattern based on the reading result (luminance signal) (S4). The CPU 301 converts the luminance signal into a density signal using the LUTid 304 of the color processing unit 303. This provides a density signal for each of the 10 grayscale images.

[0057] The CPU 301 creates LUTa (S5) based on the density signal used to generate the test pattern and the density signal obtained from the reading of the test chart. The CPU 301 stores the created LUTa in memory 302. At this stage, the CPU 301 can obtain the recording characteristics of the printer 300 shown in quadrant III of Figure 7. The CPU 301 determines the LUTa of the printer 300 by swapping the input and output in these recording characteristics and sets it in the gradation control unit 311. There is insufficient data to calculate LUTa. Ideally, 256 gradations are needed, but only 10 gradation patches have been formed. Therefore, the CPU 301 creates the necessary data by interpolating the missing data. Through this calibration, a gradation characteristic that is linear with respect to the target density can be achieved. The gradation correction process is performed in this manner.

[0058] In this embodiment, the image forming apparatus 100, which is capable of both ADF reading and document glass reading, reduces user confusion by instructing the user on where to set the test chart. This allows the image forming apparatus 100 to perform calibration with reduced user workload.

[0059] (modified version) This section describes gradation correction when the user can select between ADF reading and document glass reading. Figure 11 is a flowchart showing the gradation correction process in this case. Figure 12 is an example of the screen displayed on the control unit 400 display during the gradation correction process. In this example, test charts are created using different test patterns for ADF reading and document glass reading.

[0060] When grayscale correction is performed based on user instruction information, the CPU 301 displays the guidance screen shown in Figure 12(a) on the display of the operation unit 400 to allow the user to select a reading method (S11). The guidance screen shown in Figure 12(a) displays a message prompting the user to select a reading method and buttons that allow the user to select either ADF reading or document glass reading. The user selects either ADF reading or document glass reading from this guidance screen. The CPU 301 functions as a selection means for selecting a reading mode based on user instruction information input from the operation unit 400.

[0061] If ADF reading is selected (S11: ADF), the CPU 301 starts lighting the lamp 156 of the ADF 220 (S12). Furthermore, the CPU 301 displays the guidance screen exemplified in Figure 12(b) on the display of the operation unit 400. The guidance screen exemplified in Figure 12(b) is the same as the guidance screen shown in Figure 10(a).

[0062] Next, when the user presses the button to start printing on the guidance screen in Figure 12(b), the CPU 301 controls the printer 300 to print a test pattern for ADF reading onto a sheet (S13). When the test chart created by the ADF reading test pattern is output from the printer 300, the CPU 301 displays a button on the display of the operation unit 400 to start reading the test chart. At this time, since the lamp 156 is lit, the user can recognize that the test chart should be placed on the document tray 501 of the ADF 220. Furthermore, guidance prompting the user to place the test chart on the document tray 501 of the ADF 220 may be displayed on the display of the operation unit 400.

[0063] When the user presses the button to start scanning, the CPU 301 controls the ADF 220 to transport the test chart on the document tray 501 to the scanning position and scans the test chart (S14). After the user presses the button to start scanning, the CPU 301 stops the illumination of the lamp 156 on the ADF 220. Next, the CPU 301 acquires the density signal of the test pattern based on the scanning result (luminance signal) (S15). The CPU 301 converts the acquired luminance signal into a density signal based on the LUTid 304 of the color processing unit 303. This gives a density signal for each of the 10 grayscale images. The CPU 301 creates a LUTa based on the density signal used to generate the test pattern and the density signal obtained from the scanning result of the test chart (S16), and terminates the grayscale correction process.

[0064] If platen scanning is selected in the S11 process (S11: platen), the CPU 301 starts lighting the lamp 157 of the document scanner 215 (S17). Furthermore, the CPU 301 displays the guidance screen illustrated in Figure 12(b) on the display of the operation unit 400. The guidance screen illustrated in Figure 12(b) is the same as the guidance screen shown in Figure 10(a).

[0065] Next, when the user presses the button to start printing on the guidance screen in Figure 12(b), the CPU 301 controls the printer 300 to print a test pattern for document scanning onto a sheet (S18). When the test chart created by the document scanning test pattern is output from the printer 300, the CPU 301 displays a button on the display of the operation unit 400 to start reading the test chart. At this time, since the lamp 157 is lit, the user is aware that the test chart should be placed on the document glass 102. Furthermore, guidance prompting the user to place the test chart on the document glass 102 may be displayed on the display of the operation unit 400.

[0066] When the user presses the button to start scanning, the CPU 301 scans the test chart on the document glass 102 (S19). After the user presses the button to start scanning, the CPU 301 stops the illumination of the lamp 157 of the document scanner 215. Next, the CPU 301 acquires the density signal of the test pattern based on the scanning result (luminance signal) (S20). The CPU 301 converts the acquired luminance signal into a density signal based on the LUTid 304 of the color processing unit 303. This gives a density signal for each of the 10 grayscale images. The CPU 301 creates a LUTa based on the density signal used to generate the test pattern and the density signal obtained from the scanning result of the test chart (S21), and terminates the grayscale correction process.

[0067] Furthermore, the timing at which lamp 156 begins to light up is not limited to when ADF reading is selected by the user, but may, for example, be before the test chart is placed on the document tray 501. Similarly, the timing at which lamp 157 begins to light up is not limited to when document glass reading is selected by the user, but may, for example, be before the test chart is placed on the document glass 102. Also, lamps 156 and 157 may remain lit, for example, until LUTa is created.

[0068] If the ADF220 does not have a lamp 156, the CPU301 may illuminate the document indicator 503 to instruct the user to set the test chart. If the document scanner 215 does not have a lamp 157, the CPU301 may illuminate the light source 103 to instruct the user to set the test chart.

[0069] In addition to the illumination of lamps 156 and 157, the CPU 301 may also instruct the device to set the test chart using sound. In this case, for example, the name of the set device and the instruction, such as "Please set it on the document glass" or "Please set it in the ADF," will be output by voice. Naturally, the illumination of lamps 156 and 157 and the sound may be used in combination. Lamps 156 and 157 may be set to a specific blinking pattern during calibration, such as continuous illumination, blinking, or illumination in a pattern different from the normal one. The colors of lamps 156 and 157 may be different during calibration and during normal operation. In addition, increasing the light intensity of lamps 156 and 157 can improve user recognition.

[0070] In this embodiment, the image forming apparatus 100 is capable of both ADF reading and document glass reading, and the user can select between ADF reading and document glass reading. The image forming apparatus 100 reduces user confusion by instructing the user on where to set the test chart according to the user's selection. As a result, the image forming apparatus 100 can perform calibration with reduced user workload.

Claims

1. Image forming means for forming an image on a sheet, A paper feed cassette is provided vertically below the image forming means and contains the sheets that are transported to the image forming means. A reading means comprising: a platen on which a sheet is placed, provided vertically above the image forming means; a tray on which a sheet is placed; a document transport means for transporting the sheet placed on the tray; a lamp provided on the document transport means; and an image sensor that reads the sheet placed on the platen and the sheet transported by the document transport means; An operating unit equipped with a display for the user to input instructions, A detection means for detecting the presence or absence of a sheet on the tray, When reading a test image formed on a sheet using the image sensor and adjusting the image density based on the reading result, The image forming means forms the test image, and the control means controls the density of the image formed by the image forming means based on the reading result of the test image by the image sensor. The lamp lights up when the detection means detects that there is a sheet on the tray. When adjusting the image density, the control means, A selection screen is displayed on the display unit for selecting whether to place the sheet on which the test image is formed on the tray or to place the sheet on which the test image is formed on the platen. After a placement destination is selected from the selection screen, the lamp is controlled to indicate whether the tray has been selected as the aforementioned placement destination. When the tray is selected as the placement destination, the lamp lights up. When the platen is selected as the mounting destination, the lamp does not light up, characterized in that Image forming apparatus.

2. The control means controls the display unit and the lamp to indicate the aforementioned installation location after the installation location has been selected from the selection screen. The display unit is characterized by displaying information indicating the previously selected location. The image forming apparatus according to claim 1.

3. The lamp flashes to indicate that the previously mentioned placement location of the sheet on which the test image is formed is the tray. The image forming apparatus according to claim 1.

4. The test image is characterized by including a first test image which includes a first image having different tonal values, and a second test image which includes a second image which includes different tonal values. The image forming apparatus according to claim 1.

5. The control means includes a grayscale control means that converts the image signal based on conversion conditions. The image forming means forms the image based on the converted image signal. When the first test image is read by the reading means, the control means generates the conversion conditions based on the reading result of the first test image. The control means is characterized in that, when the second test image is read by the reading means, it generates the conversion conditions based on the reading result of the second test image. The image forming apparatus according to claim 4.

Images