JP6189698B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to image quality adjustment processing related to an image forming apparatus, and more particularly to a technique for improving adjustment accuracy in the image quality adjustment processing.

  2. Description of the Related Art Conventionally, a technique for adjusting image quality based on an output result of a predetermined test pattern is known in order to maintain image forming characteristics (so-called developer charging characteristics, gamma characteristics, etc.) in an image forming apparatus in an optimal state. (For example, refer to Patent Document 1).

JP 2008-288722 A

  However, according to the above prior art, the density of the test pattern printed during the image adjustment process is greatly influenced by the surface property of the sheet on which the test pattern is printed. Therefore, as shown in FIG. If the value is fixed according to commonly used plain paper, as shown in FIG. 5 (B), the adjustment density target value is set to the sheet for a sheet printed with a low density (for example, medium quality paper). As shown in FIG. 5C, the adjustment density target value exceeds the maximum density value printed on the sheet in a sheet printed with a high density (for example, glossy paper) as shown in FIG. 5C. Therefore, there is a problem that the original characteristics of the sheet cannot be utilized.

  The present invention has been made in view of such circumstances, and an object thereof is to provide an image processing apparatus, an image forming apparatus, and an image processing method capable of adjusting image quality suitable for each sheet. is there.

An image processing apparatus according to the present invention reads a test pattern image formed on a sheet by a sensor and performs a predetermined image quality adjustment process based on the read information. The test pattern is a patch having the highest density. Including a plurality of patches, and the sensor includes a patch density measurement unit that measures the density of the plurality of patches, and includes a target value calculation unit that calculates a target value of density with respect to an input value of the plurality of patches, The target value calculation unit sets the target value of the high density portion to be proportional to the input value with the highest density patch density value as the maximum target value, and sets the target value of the low density portion as The target value between the low density portion and the high density portion is smoothly interpolated so as not to cause gradation skipping while keeping the fixed value set in advance.

An image forming apparatus according to the present invention includes any one of the above-described image processing apparatuses and an image forming unit that forms an image processed by the image processing apparatus on a sheet.

An image forming apparatus according to the present invention includes a paper feed unit capable of setting a paper type of a stored sheet, and a test pattern image formed on a sheet of a predetermined paper type set in the paper feed unit. When the storage unit that stores the measurement value measured by the patch density measuring unit and the paper feeding unit is selected as the supply source of the target sheet for image adjustment processing, the paper type of the target sheet is estimated as the predetermined paper type A measurement value comparison unit that compares the measurement value measured by the patch density measurement unit with the test pattern image formed on the target sheet and the measurement value stored in the storage unit, and the image processing parts, when two measurements by the measurement value comparison unit is significantly different from the determination, the paper type of the target sheet that warning to the effect is not a predetermined paper type.

An image processing method according to the present invention reads a test pattern image formed on a sheet by a sensor, performs predetermined image quality adjustment processing based on the read information, and includes a plurality of patches including a patch having the highest density. Forming a test pattern having: a step of measuring the density of the plurality of patches read by the sensor; a target value of a high density portion; and an input value with the highest density patch density value as a maximum target value. The target value for the low density part remains at a preset fixed value, and the target value between the low density part and the high density part is set to a gradation. including a step of flying is smoothly interpolated so as not to generate, the.

  According to the present invention, the image processing apparatus can appropriately adjust the density of an image while taking advantage of the maximum density characteristic unique to the sheet.

  According to the present invention, the image processing apparatus can appropriately adjust the density of an image without being affected by the low density characteristic unique to the sheet.

1 is a longitudinal sectional view illustrating an internal configuration example of an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram illustrating a configuration example of a control system of the image forming apparatus according to the embodiment. FIG. It is a flowchart which shows the procedure of the image process by an image process part. It is a flowchart which shows the procedure of a gradation correction process. It is a schematic diagram which shows the gradation correction result of a prior art. It is a schematic diagram which shows the gradation correction result (1st Embodiment) of this invention. It is a schematic diagram which shows the gradation correction result (2nd Embodiment) of this invention. It is a flowchart which shows the procedure of the gradation correction process which concerns on 3rd Embodiment of this invention.

  Hereinafter, an image processing apparatus, an image forming apparatus, and an image processing method according to the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.

<First Embodiment>
FIG. 1 is a longitudinal sectional view showing an example of the internal configuration of the image forming apparatus according to the present embodiment. The image forming apparatus 1 of the present embodiment has a print function for forming multicolor and single color images on sheets such as copy paper and OHP (Over Head Projector) film based on the acquired image data. The image forming apparatus 1 also has a function of receiving image data such as characters, graphics, and photographs from an external information processing apparatus in a page description language format, and generating printable print execution data (image data).

  At the bottom of the image forming apparatus 1 of the present embodiment, a drawer-type paper feed cassette (first paper feed unit) 20 having a tray for storing sheets (recording paper) used for image formation is disposed. Yes. The paper feed cassette 20 can be opened by the user pulling it toward the front side, and sheets can be replenished with the tray open. Further, a manual feed tray (second paper feed unit) 26 on which a small amount of sheets is placed is provided on the right side surface of the image forming apparatus 1 in FIG. 1, and the sheets placed on the manual feed tray 26 are also provided. An image is formed by being taken into the image forming apparatus 1.

  An exposure unit 11 is provided above the paper feed cassette 20. In the upper part of the exposure unit 11, in order to form a multicolor image using each color of black (BK), cyan (C), magenta (M), and yellow (Y), developing units 12a, 12b, 12c, 12d, photosensitive drums 13a, 13b, 13c, 13d, cleaner units 14a, 14b, 14c, 14d, chargers 15a, 15b, 15c, 15d, and the like.

  The symbols a, b, c, and d attached to each symbol are described so as to correspond to, for example, each color of black (BK), cyan (C), magenta (M), and yellow (Y). In the following, except for the case where a member corresponding to a specific color is specified and described, the members provided for each color are collected together into a developing device 12, a photosensitive drum 13, a cleaner unit 14, and a charger. It is described as 15.

  As the chargers 15a to 15d, roller-type chargers configured to come into contact with the corresponding photosensitive drums 13a to 13d are used, and the surfaces of the photosensitive drums 13a to 13d are uniformly set to a predetermined potential. To charge. A configuration using a brush-type charger or a charger-type charger may be used instead of the roller-type charger. For example, the chargers 15a to 15d respectively charge the surfaces of the corresponding photosensitive drums 13a to 13d with a negative polarity.

  The exposure unit 11 is configured by a laser scanning unit (LSU) including a laser irradiation unit that irradiates laser light and a reflection mirror, and laser light emitted from the laser irradiation unit is irradiated onto the photosensitive drums 13a to 13d. As shown, a polygon mirror and a reflecting mirror are provided. In addition to the LSU, the exposure unit 11 may be a writing head in which light emitting elements such as EL (Electro Luminescence) and LED (Light Emitting Diode) are arranged in an array.

  The exposure unit 11 emits a laser beam based on the print execution data, irradiates the surface of the photosensitive drums 13a to 13d charged by the chargers 15a to 15d with the laser beam, and negative charges on the photosensitive drums 13a to 13d. Remove. As a result, electrostatic latent images corresponding to print execution data (image data) are formed on the photosensitive drums 13a to 13d.

  Each of the developing devices 12a to 12d stores toners (developers) of black, cyan, magenta, and yellow, and the stored toner is charged to a negative polarity, and this toner is charged to the photosensitive drum 13a. It supplies with respect to the electrostatic latent image formed in the surface of -13d. The negatively charged toner is adsorbed on the surface of the photoconductive drums 13a to 13d where the negative charge is removed by the laser beam, so that the developing devices 12 are respectively on the corresponding photoconductive drums 13. A toner image in which the electrostatic latent image is visualized is formed.

  Around the photosensitive drums 13a to 13d, in addition to the developing units 12a to 12d and the charging units 15a to 15d, a toner image visualized on the surface of the photosensitive drums 13a to 13d is transferred to a sheet and then the photosensitive member. Cleaner units 14a-14d for collecting and removing toner remaining on the surfaces of the drums 13a-13d are provided.

  The image forming apparatus 1 according to the present embodiment is configured to transfer toner images on the photosensitive drums 13a to 13d onto a sheet by an intermediate transfer method, and an intermediate transfer belt unit is provided above the photosensitive drums 13a to 13d. 18 is provided. The intermediate transfer belt unit 18 includes an intermediate transfer belt 17, an intermediate transfer belt driving roller 171, an intermediate transfer belt driven roller 172, intermediate transfer rollers 16a, 16b, 16c, and 16d, an intermediate transfer belt cleaning unit 19, and the like. The intermediate transfer belt unit 18 includes an intermediate transfer belt tension mechanism (not shown) that maintains the tension state of the intermediate transfer belt 17. Hereinafter, the intermediate transfer rollers 16a, 16b, 16c, and 16d are collectively referred to as an intermediate transfer roller 16.

  The intermediate transfer belt drive roller 171, the intermediate transfer belt tension mechanism, the intermediate transfer rollers 16 a to 16 d, the intermediate transfer belt driven roller 172, etc. stretch the intermediate transfer belt 17, and intermediate transfer is performed by the driving force of the intermediate transfer belt drive roller 171. The belt 17 is configured to rotate in the direction indicated by the arrow in the figure. The intermediate transfer rollers 16a to 16d are rotatably supported by an intermediate transfer roller mounting portion provided in the intermediate transfer belt tension mechanism. Further, the intermediate transfer rollers 16a to 16d are connected to a power supply unit (not shown) of the intermediate transfer belt tension mechanism, and the intermediate transfer belt 17 is brought into contact with the intermediate transfer belt 17 by a charging potential from the power supply unit. Charge to a predetermined potential (transfer bias). As a result, the toner images transferred from the photosensitive drums 13 a to 13 d are attracted to the intermediate transfer belt 17.

  The intermediate transfer belt 17 is formed in an endless shape using, for example, a film having a thickness of about 1100 μm to 1150 μm, and the surface thereof is provided in contact with each of the photosensitive drums 13 a to 13 d. A color toner image (multicolor toner image) is formed on the intermediate transfer belt 17 by sequentially superimposing and transferring the respective color toner images formed on the photosensitive drums 13a to 13d onto the intermediate transfer belt 17. Is done.

  Transfer of the toner image from the photosensitive drums 13 a to 13 d to the intermediate transfer belt 17 is performed by intermediate transfer rollers 16 a to 16 d that are in contact with the back side of the intermediate transfer belt 17. To the intermediate transfer rollers 16a to 16d, a high voltage transfer bias, that is, a high voltage having a polarity (+) opposite to the charging polarity (−) of the toner is applied to transfer the toner image. The intermediate transfer rollers 16a to 16d are rollers whose base is a metal (for example, stainless steel) shaft having a diameter of 18 to 110 mm and whose surface is covered with a conductive elastic material (for example, EPDM, foamed urethane, etc.). . The intermediate transfer rollers 16 a to 16 d can uniformly apply a high voltage to the intermediate transfer belt 17 by the conductive elastic material. In the present embodiment, a roller-shaped electrode is used as the transfer electrode, but a brush-shaped electrode can also be used.

  As described above, the toner images visualized in accordance with the respective colors on the respective photosensitive drums 13a to 13d are stacked on the intermediate transfer belt 17, and an image for printing is formed on the intermediate transfer belt 17 by a multicolor toner image. It is reproduced. The multicolor toner image thus transferred onto the intermediate transfer belt 17 is transferred onto the sheet by the transfer roller 21 disposed at the contact position between the sheet and the intermediate transfer belt 17 by the rotation of the intermediate transfer belt 17. .

  At this time, the intermediate transfer belt 17 and the transfer roller 21 are pressed against each other at a predetermined nip, and a voltage for transferring the multicolor toner image onto the sheet, that is, the charging polarity (−) of the toner is applied to the transfer roller 21. Is applied with a high voltage of reverse polarity (+). Here, in order to constantly obtain a nip between the intermediate transfer belt 17 and the transfer roller 21, either the transfer roller 21 or the intermediate transfer belt drive roller 171 is made of a hard material such as metal, and the other is It is made of a soft material such as elastic rubber or foamable resin.

  Further, the toner attached to the intermediate transfer belt 17 by the contact with the photosensitive drums 13a to 13d as described above, or the toner remaining on the intermediate transfer belt 17 without being transferred onto the sheet by the transfer roller 21, Since it causes toner color mixing in the next step, it is removed and collected by the intermediate transfer belt cleaning unit 19 provided in the vicinity of the intermediate transfer belt driven roller 172. The intermediate transfer belt cleaning unit 19 is provided with a cleaning blade as a cleaning member that comes into contact with the intermediate transfer belt 17, and the portion where the cleaning blade comes into contact with the intermediate transfer belt 17 starts from the back side of the intermediate transfer belt 17. It is supported by a driven roller 172.

  The sheet feeding cassette 20 and the manual feed tray 26 have pickup rollers 28a and 28b in the vicinity of the leading end portions of the stacked sheets, and the sheets separated and fed one by one by the pickup rollers 28a and 28b are as follows. The toner is supplied into the image forming apparatus 1 through the transport path S. A plurality of conveyance rollers 27 for promoting and assisting conveyance of the sheet are provided at appropriate positions on the conveyance path S, and are separately fed by the pickup rollers 28a and 28b and conveyed to the conveyance roller 27. The sheet is conveyed through the conveyance path S by the conveyance roller 27 to the registration roller 23.

  The registration roller 23 is provided below the transfer roller 21 and the intermediate transfer belt driving roller 171 described above. The registration roller 23 temporarily holds the sheet conveyed from the paper feed cassette 20 or the manual feed tray 26, and the sheet is transferred to the transfer roller 21 at a timing when the leading edge of the sheet and the leading edge of the toner image on the intermediate transfer belt 17 are aligned. The toner image on the intermediate transfer belt 17 is transferred onto the sheet by being conveyed.

  The sheet onto which the toner image has been transferred is conveyed substantially vertically and reaches a fixing unit 22 provided on the upper side of the transfer roller 21. The fixing unit 22 includes a heat roller 24, a pressure roller 25, and the like, and controls the heater (not shown) based on a detection value from a temperature detector (not shown) to set the heat roller 24 to a predetermined fixing temperature. Keep on. Further, the fixing unit 22 rotates the sheet on which the multicolor toner image is transferred between the heat roller 24 and the pressure roller 25 and heat-fixes the multicolor toner image on the sheet by the heat of the heat roller 24. The multicolor toner image transferred to the sheet is melted, mixed, and pressed to be thermally fixed on the sheet.

  The sheet on which the multicolor toner image is thermally fixed is discharged from the fixing unit 22 by a conveyance roller provided near the exit of the fixing unit 22.

  In the case of a single-side printing request, the sheet that has passed through the fixing unit 22 is discharged face-down onto a discharge tray 30 provided on the upper surface of the image forming apparatus 1 through a discharge roller 29. In the case of double-sided printing request, the sheet that has passed through the fixing unit 22 is once chucked by the paper discharge roller 29, and then guided to the double-sided document transport path S 1 by the reverse rotation of the paper discharge roller 29. Is again conveyed to the registration roller 23. Then, after the toner image is transferred and thermally fixed on the back side, the sheet is discharged onto the discharge tray 30 by the discharge roller 29.

  In addition to the above-described configuration, the image forming apparatus 1 includes, for example, a paper feed cassette that can store a plurality of types of sheets having different sizes, a large-capacity paper feed cassette that can store thousands of sheets, and a plurality of paper discharge cassettes. It is also possible to provide a paper tray and a transport mechanism for transporting the image-formed sheet to each paper discharge tray, and it is also possible to adopt a configuration in which these can be retrofitted as an optional function.

  FIG. 2 is a block diagram illustrating a configuration example of a control system of the image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 2, a RAM (Random Access Memory) 3, an HDD (Hard Disk Drive) 4, an operation panel 5, a network controller 6, an image processing unit 7, and an image forming unit 8. Etc. The units included in the image forming apparatus 1 are connected to each other via a bus. The image processing unit 7 performs an operation as an image processing apparatus according to the present invention.

  The CPU 2 controls the operation of the above-described hardware units connected via the bus, and executes various software functions according to a control program stored in the HDD 4.

  The HDD 4 is a large-capacity memory device, and stores in advance a control program for the CPU 2 to control each hardware unit as described above. The RAM 3 is a volatile semiconductor memory, and temporarily stores data generated during execution of the control program by the CPU 2. The CPU 2 reads the control program stored in the HDD 4 into the RAM 3 and sequentially executes it, thereby causing the image forming apparatus 1 to operate as the image processing apparatus and the image forming apparatus of the present invention.

  Further, the HDD 4 receives a print job received from an external device via the network controller 6, print execution data obtained by developing the print job (data to be printed), and predetermined image processing performed by the image processing unit 7. Store data etc. Data stored in the HDD 4 (data to be processed) is read to the image processing unit 7 or the image forming unit 8 at a timing instructed by the CPU 2.

  Further, the HDD 4 stores various data used for image processing by the image processing unit 7 (for example, the correction amount of the gradation correction processing result used for halftone processing).

  The operation panel 5 includes an operation unit having various operation buttons for receiving operation instructions from the user, and a display unit such as an LED display or a liquid crystal display that displays information to be notified to the user. . In addition, you may comprise the operation panel 5 with the touchscreen which can input by touching a display screen.

  The network controller 6 is a communication interface for communicating with an information processing apparatus such as an external personal computer via a communication line, and transmits / receives data to / from the external information processing apparatus. The external information processing apparatus transmits page description language format data (print job), and the network controller 6 receives the print job transmitted from the external information processing apparatus. The network controller 6 transfers the received print job to the HDD 4 or the image processing unit 7. The image processing unit 7 develops the transferred print job to generate print execution data, and transfers the generated print execution data to the HDD 4. The HDD 4 stores the print job transferred from the network controller 6 and the print execution data transferred from the image processing unit 7 in units of pages, for example.

  The image processing unit 7 performs a process of expanding the print job received by the network controller 6 and generating print execution data. Also, the color conversion process, the gradation correction process, the halftone process, and the like are performed on the print execution data. Various image processes are executed. In particular, the image processing unit 7 of the present embodiment calculates a target value for image quality adjustment processing in the image processing unit 7 in order to perform halftone processing using the correction amount of the image quality adjustment processing result according to the sheet characteristics. A target value calculation unit (not shown) is provided. Details of processing performed by the image processing unit 7 will be described later. The image processing unit 7 outputs the image-processed data (image data) to the HDD 4.

  The image processing unit 7 may be a software function realized by the CPU 2 executing a control program for executing predetermined image processing, or may be realized by a dedicated hardware circuit.

  The image forming unit 8 is an image forming unit that includes the units illustrated in FIG. 1 and forms an image based on data to be printed on a sheet.

  In addition to the above-described configuration, the image forming apparatus 1 also includes a density sensor 9, a temperature / humidity sensor 10, and the like as information acquisition means used for color calibration performed to improve color reproducibility by the image forming unit 8. Also good.

  The image forming apparatus 1 having the above-described configuration generates print execution data by the image processing unit 7 from a print job received from an external information processing apparatus via the network controller 6, and displays an image based on the generated print execution data. It forms on a sheet | seat by the formation part 8. FIG.

  Below, the process which the image process part 7 performs is demonstrated. FIG. 3 is a flowchart showing a procedure of image processing by the image processing unit 7. Here, various image processes performed on print execution data obtained by the image processing unit 7 developing a print job received via the network controller 6 will be described. The print job is, for example, print processing from a user's PC (Personal Computer). The image processing unit 7 of the image forming apparatus 1 generates print execution data such as CMYK (C: cyan, M: magenta, Y: yellow, K: black) data or BK (monochrome) data based on a print job. To do. The print execution data is expressed by, for example, 256 gradations, and the pixel value (gradation value) of each pixel takes any value from 0 to 255.

  The image processing unit 7 determines whether or not the print execution data to be processed is RGB data (step S1). If the print execution data is RGB data (step S1: YES), color conversion is performed on the print execution data. Processing is performed (step S2), and CMYK (C: cyan, M: magenta, Y: yellow, K: black) data is generated. In the color conversion process, RGB data is converted into a complementary color CMY color space to generate CMY data, K data is generated from the CMY data, and new CMY data is subtracted from the original CMY data. Is a process for generating

  On the other hand, when the print execution data to be processed is not RGB data (step S1: NO), the image processing unit 7 skips the process of step S2 and does not perform the color conversion process. The color conversion process is performed based on the color table of the ICC profile, for example, by a color management module mounted on firmware (not shown) included in the image forming apparatus 1.

  The image processing unit 7 performs gradation correction processing on the print execution data (step S3). As a result, the spatial frequency characteristics of the print execution data (image data) are corrected, and blurring or graininess deterioration of the output image can be prevented. If the print execution data is CMYK data, the image processing unit 7 performs gradation correction processing for each color component.

  Next, the image processing unit 7 performs halftone processing using a dither matrix pattern on the print execution data subjected to gradation correction processing (step S4). Details of the halftone process will be described later. The halftone process is also performed for each color component if the print execution data is CMYK data.

  The image processing unit 7 temporarily stores the print execution data subjected to the halftone processing in the HDD 4 or the RAM 3, reads it at a predetermined timing for image formation, outputs it to the image forming unit 8, and forms an image in the image forming unit 8. (Step S5).

  Next, the control operation of the gradation correction operation of the image forming apparatus according to the present embodiment will be described with reference to the flowchart of FIG.

  When the gradation correction operation starts, first, a patch image is created by the image forming unit 8 (step S11). The patch image includes a CMYK monochromatic halftone patch and a highest density patch, and a paper white patch for measuring the background of paper on which nothing is printed. The halftone patch includes several gradations.

  Next, each patch of the created patch image is read by the density sensor 9 (step S12). At this time, as long as the density can be measured, the sensor is not limited to the sensor, and the image forming apparatus may be provided, or may be read by a scanner as another apparatus or by visual observation. Although not shown in FIG. 1, the density sensor 9 is disposed on the downstream side of the fixing unit 22 on the transport path S. For example, the sheet discharge roller 29 can be disposed at a discharge port through which the sheet is discharged onto the sheet discharge tray 30. The density read by the density sensor 9 is compared with the intermediate gradation characteristic of the target value (step S13), and the gradation correction amount is calculated so that the intermediate gradation characteristic of the image forming apparatus approaches the target value (step S14). .

  In the present invention, using the result of reading the density of each patch in step S12, the halftone gradation characteristic of the target value to be compared in step S13 is calculated.

  FIGS. 5A to 5C are schematic diagrams of conventional halftone characteristics of target values. The target value is a fixed value recorded in advance in the image processing unit 7, and is normally set to a value that is effective for general paper types as shown in FIG. However, as shown in Fig. 5 (B), when the paper type such as glossy paper is printed darker than the general paper type, the target value should be able to be output due to the fixed value. The image density is suppressed by image processing. As shown in FIG. 5C, when the paper type such as medium-quality paper is printed with a lighter density than a general paper type, the target value is a fixed value, and all of the input values exceeding a certain value are used. The maximum density is output, and the gradation in the high density portion is lost.

  FIG. 6 is a schematic diagram of the intermediate gradation characteristics of the target value according to the present embodiment. In step S12, the maximum density of each color is read by the density sensor, and this is used as the maximum density target value to calculate the halftone characteristics of the density target value so as to be proportional to the input value. As a result, as shown in FIG. 6A, even when the density of a paper type such as glossy paper is printed higher than that of a general paper type, the target value varies depending on the maximum density, so that the density that can be originally obtained is set. Printing can be performed without being suppressed by image processing. In addition, as shown in FIG. 6B, even when the density of a paper type such as medium quality paper is printed lower than that of a general paper type, the maximum density is output because the target value varies depending on the maximum density. Only the maximum input value is used, and printing can be performed without losing the gradation of the high density portion.

<Second Embodiment>
FIG. 7 is a schematic diagram of the intermediate gradation characteristics of the target value in consideration of the characteristics of the low density portion. When printing is performed with a paper type such as glossy paper having a higher density than a general paper type, the low density portion takes a fixed target value as in FIG. 5, and the high density portion as in FIG. 6A. In step S12, the maximum density of each color is read by the density sensor 9, which is used as the maximum density target value, and the intermediate gradation characteristics of the density target value are calculated so as to be proportional to the input value. The portion between the low density and the high density is smoothly interpolated so that gradation skip does not occur. Interpolation may be performed by a linear function, or an exponential function, a power function, a spline curve, or the like may be used.

  Even in a paper whose maximum density is higher than that of a general paper type, when it is better that the low density portion has halftone characteristics similar to that of a general paper type, the target as in this embodiment is used. The value is preferred.

  Whether the target value described in the first embodiment (see FIG. 6) or the target value described in the present embodiment is adopted may be selected by the user according to the application. It may be fixed to an appropriate person.

<Third Embodiment>
In some cases, the image forming apparatus includes a paper feeding unit that can set the paper type of a sheet to be stored. For example, in the image forming apparatus 1 of FIG. 1, the manual feed tray 26 (second paper feeding unit) is set as a tray dedicated to glossy paper.

  In the present embodiment, assuming such a case, the density sensor 9 of the patch image formed on a sheet of a predetermined paper type (glossy paper in the above example) set in the manual feed tray 26 in the HDD 4 is used. The measured value is stored. The data stored may be only the latest measured value.

  In this embodiment, in addition to the function of the target value calculation unit, the image processing unit 7 glosses the paper type of the target sheet when the manual feed tray 26 is selected as the supply source of the target sheet for image adjustment processing. It also functions as a measurement value comparison unit that compares the measured value estimated by the density sensor 9 and the measured value stored in the HDD 4 with the test pattern image estimated on the paper and formed on the target sheet.

  Next, the control operation of the gradation correction operation of the image forming apparatus according to the present embodiment will be described with reference to the flowchart of FIG.

  When the user selects the manual feed tray 26 as the supply source of the gradation correction target sheet through the operation panel 5 and starts the gradation correction operation, the image processing unit 7 moves the gradation correction target sheet to the manual feed tray. It is estimated to be a predetermined paper type specified in 26 (step S21).

  Then, a patch image is created by the image forming unit 8 in the same manner as in step S11 of FIG. 4 (step S22). Next, each patch of the patch image created in the same manner as step S12 in FIG. 4 is read by the density sensor 9 (step S23).

  Next, the image processing unit 7 reads out the density value of each patch measured for the sheet of the target paper type and the density value of each patch measured for the sheet of the predetermined paper type stored in the HDD 4 to the RAM 3. And determine whether or not the measurement results are significantly different (step S24). As a result of the determination, if the measurement result for the target paper type and the measurement result for the registered paper type are significantly different (step S24: YES), the image processing unit 7 determines that the target sheet paper type is a predetermined paper type through the operation panel 5. A warning to that effect is issued (step S25).

  As a result of the determination, if the measurement result for the target paper type and the measurement result for the registered paper type do not differ greatly (step S24: NO), the image processing unit 7 reads the density sensor 9 in the same manner as in step S13 in FIG. Compared with the intermediate gradation characteristic of the target value (step S26), the gradation correction amount is calculated so that the intermediate gradation characteristic of the image forming apparatus approaches the target value in the same manner as in step S14 of FIG. (Step S27).

  According to the present embodiment, when a sheet of a paper type different from the paper type registered in the manual feed tray 26 is mistakenly set in the manual feed tray 26, the user can be made aware of an error when the image quality adjustment process is executed. It becomes possible. Also, if the paper type has different paper quality on the front and back sides, it functions even if the front and back sides are wrong.

  In this embodiment, the case where the manual feed tray 26 (second paper feed unit) is used as a paper feed unit dedicated to a predetermined paper type has been described. However, the paper feed cassette 20 (first paper feed unit) The paper type may be specified on the other side, or both the paper feed cassette 20 and the manual feed tray 26 may be used as dedicated paper feed units for different paper types.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus 2 ... CPU
3 ... RAM
4 ... HDD
DESCRIPTION OF SYMBOLS 5 ... Operation panel 6 ... Network controller 7 ... Image processing part 8 ... Image forming part 9 ... Density sensor 11 ... Exposure unit 12a, 12b, 12c, 12d ... Developing device 13a, 13b, 13c, 13d ... Photoconductor drum 14a, 14b , 14c, 14d ... cleaner units 15a, 15b, 15c, 15d ... chargers 16a, 16b, 16c, 16d ... intermediate transfer roller 17 ... intermediate transfer belt 18 ... intermediate transfer belt unit 19 ... intermediate transfer belt cleaning unit 20 ... paper feed Cassette (first paper feeder)
DESCRIPTION OF SYMBOLS 21 ... Transfer roller 22 ... Fixing unit 23 ... Registration roller 24 ... Heat roller 25 ... Pressure roller 26 ... Manual feed tray 27 ... Conveyance roller 28a, 28b ... Pick-up roller 29 ... Paper discharge roller 30 ... Paper discharge tray 31 ... Conveyance roller 171 ... Intermediate transfer belt drive roller 172 ... Intermediate transfer belt driven roller

Claims (2)

An image processing apparatus that reads a test pattern image formed on a sheet with a sensor and performs a predetermined image quality adjustment process based on the read information. The test pattern image includes a plurality of patches including a patch having the highest density. a, the sensor will have a patch density measurement means for measuring the concentration of said plurality of patches, and the image processing apparatus,
An image forming unit that forms an image processed by the image processing apparatus on a sheet;
A paper feeder capable of setting the paper type of the stored sheet;
A storage unit for storing a measurement value obtained by measuring the test pattern image formed on the sheet of a predetermined paper type set in the sheet feeding unit by the patch density measuring unit;
When the paper supply unit is selected as a supply source of a target sheet for image adjustment processing, the paper type of the target sheet is estimated as the predetermined paper type, and a test pattern image formed on the target sheet is used as the patch. A measurement value comparison unit that compares the measurement value measured by the concentration measurement unit with the measurement value stored in the storage unit;
With
The image processing apparatus includes a target value calculation unit that calculates a target value of density for an input value of the plurality of patches, and the target value calculation unit uses the patch density value of the highest density as a target calculation value,
The image processing apparatus warns that the paper type of the target sheet is not the predetermined paper type when the measured value comparison unit determines that the two measured values are greatly different . The target value calculator is
The target value of the high density part is set so as to be proportional to the input value with the patch density value of the highest density as the maximum target value,
Keep the target value for the low concentration part as a fixed value set in advance.
The image forming apparatus according to claim 1, wherein a target value between the low density portion and the high density portion is smoothly interpolated so as not to cause a gradation skip.