Image forming apparatus, method for controlling image forming apparatus, and storage medium

Abstract

To provide an image forming apparatus capable of more suitably achieving patchless color correction in real time.SOLUTION: An image forming apparatus 1 according to the present disclosure includes a control unit 10 that, during a print job, performs color clustering processing on read image data obtained by reading a print image to acquire color cluster information, and compares the color cluster information with reference color cluster information created from the read image data obtained at an initial stage of the print job, to adjust input image data or an image forming condition for printing at a next time point.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to an image forming apparatus, a control method for an image forming apparatus, and a control program for an image forming apparatus. [Background technology]

[0002] Conventionally, the mainstream of color image forming devices (such as copiers, printers, and facsimiles) that use electrophotographic process technology is the intermediate transfer method, which uses an intermediate transfer body such as an intermediate transfer belt. The intermediate transfer method involves transferring each color toner image (C, M, Y, K, etc.) formed on a photosensitive drum to the intermediate transfer body, overlaying the four color toner images on the intermediate transfer body, and then transferring them to paper.

[0003] Such image forming devices have the problem that the quality of the output image (image output onto paper) changes due to deterioration over time of the photosensitive drum, developer, etc., and the environment around the device (fluctuations in temperature and humidity), etc. Specifically, a phenomenon occurs in which the color information (e.g., gradation, color, etc.) of the input image data is not faithfully reproduced in the output image (also known as color reproducibility).

[0004] Therefore, conventional image forming apparatuses perform calibration to stably reproduce the color information of input image data in an output image. Calibration involves, for example, detecting the color information of the output image transferred to paper using a color sensor or the like installed in the paper transport path, and generating gradation correction data based on the detection results. Using this gradation correction data, it is possible to provide feedback to the input image data and the image formation conditions of the image forming unit (e.g., charging potential, development potential, exposure amount, etc.). [Prior art documents] [Non-patent literature]

[0005] [Non-Patent Document 1] Dan Pelleg, et al. "X-means: Extending K-means with Efficient Estimation of the Number of Clusters", in ICML'00:Proceedings of the Seventeenth International Conference on Machine Learning, June 2000, Pages 727 - 734, ("URL: https: / / dl.acm.org / doi / 10.5555 / 645529.657808") [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-134281 Summary of the Invention [Problem to be solved by the invention]

[0007] Conventionally, in this type of image forming apparatus, test printing of test patches is carried out, and calibration is carried out based on the color information of the output image formed at that time.

[0008] However, this method requires other jobs to be interrupted in order to perform test printing of the test patch, which causes a problem of reduced productivity.

[0009] In addition, the colors used in the patch images are limited to a limited range, such as cyan, magenta, yellow, and black, and do not necessarily match the colors used in the actual printed matter. Therefore, such a method may not be able to capture the color changes of the various colors used in the actual printed matter. Another problem with such a method is that it is not possible to capture the real-time color changes that occur when the actual printed matter is being printed.

[0010] Against this background, patchless color correction technology is being considered, which performs calibration during a normal print job based on the color information of input image data that is actually instructed to be printed and the color information of the output image.

[0011] For example, the applicant of the present application has investigated a method for comparing input image data for image formation with scanned image data for output on a pixel-by-pixel basis during a normal print job, and monitoring the color difference at corresponding pixel positions between the input image data and the scanned image data. That is, with this method, calibration is performed based on the color difference detected between the two. For details of this method, please refer to Patent Document 1.

[0012] This method eliminates the need to form patch images on paper, reducing paper waste and preventing productivity declines. It also makes it possible to capture real-time color changes that occur during the actual printing process.

[0013] However, during actual printing, the position and orientation of the paper reflected in the scanned image data change in various ways. Therefore, it is difficult to completely identify the corresponding pixels between the input image data and the scanned image data. Therefore, this method faces the problem of difficulty in accurately detecting color changes in the output image, which may lead to erroneous correction.

[0014] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide an image forming apparatus, a control method for an image forming apparatus, and a control program for an image forming apparatus that can more suitably achieve real-time patchless color correction. [Means for solving the problem]

[0015] The main invention that solves the above-mentioned problems is: An image forming apparatus capable of performing continuous printing, The printer includes a control unit that, during a print job, performs color clustering processing on read image data obtained by reading a print image to obtain color cluster information, and compares the obtained color cluster information with reference color cluster information created from the read image data obtained at the beginning of the print job, thereby adjusting input image data or image forming conditions when printing is performed next. It is an image forming apparatus.

[0016] In other respects, A control method for an image forming apparatus capable of performing continuous printing, comprising: During a print job, color cluster information is obtained by performing color clustering processing on the read image data obtained by reading the print image, and by comparing the obtained color cluster information with reference color cluster information created from the read image data obtained at the beginning of the print job, the input image data or image forming conditions are adjusted when printing is performed next. It is a control method.

[0017] In other respects, A control program for an image forming apparatus capable of performing continuous printing, On the computer, This is a control program that, during a print job, performs color clustering processing on the read image data obtained by reading the print image to obtain color cluster information, and compares this with reference color cluster information created from the read image data obtained at the beginning of the print job, thereby performing processing to adjust the input image data or image formation conditions when printing is performed next. [Effects of the Invention]

[0018] According to the image forming apparatus of the present invention, it is possible to more suitably realize real-time patchless color correction. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a diagram illustrating an overall configuration of an image forming apparatus. [Figure 2] FIG. 1 is a diagram showing the configuration of a control system of an image forming apparatus. [Figure 3] FIG. 1 is a diagram illustrating the processing of a clustering processing unit, a label creation unit, and a correction unit. [Figure 4] FIG. 1 is a diagram illustrating the processing of a clustering processing unit, a label creation unit, and a correction unit. [Figure 5] FIG. 1 is a diagram illustrating the processing of a clustering processing unit, a label creation unit, and a correction unit. [Figure 6] FIG. 1 is a diagram illustrating the processing of a clustering processing unit, a label creation unit, and a correction unit. [Figure 7] FIG. 10 is a diagram showing an example of an operation flow of a control unit; [Figure 8] FIG. 10 is a diagram illustrating the processing of the label creating unit according to Modification 1. [Figure 9] FIG. 10 is a diagram showing an example of an operation flow of a control unit according to Modification 1. [Figure 10] FIG. 10 is a diagram illustrating the processing of the label creating unit according to Modification 2. [Figure 11] FIG. 10 is a diagram showing an example of an operation flow of a control unit according to Modification 2. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0021] [Configuration example of image forming device] First, the overall configuration of an image forming apparatus according to one embodiment of the present invention (hereinafter referred to as "image forming apparatus 1") will be described. Note that the image forming apparatus 1 according to this embodiment is applied to copiers, printers, etc.

[0022] Fig. 1 is a diagram showing a schematic overall configuration of an image forming apparatus 1. Fig. 2 is a diagram showing the configuration of a control system of the image forming apparatus 1.

[0023] The image forming apparatus 1 forms a color image on a sheet of paper by electrophotography based on input image data obtained by reading an image from an original or input image data received from an external device.

[0024] In this embodiment, paper is shown as an example of a recording medium on which an image is formed by the image forming apparatus 1. However, various media can be used as the recording medium, such as paper such as plain paper or coated paper, as well as fabric or sheet-like resin.

[0025] The image forming device 1 is configured to include a control unit 10, an operation unit 11, a display unit 12, a document reading unit 13, an image forming unit 14, a conveying unit 15, a memory unit 17, an interface unit 18, an image processing unit 19, and an image reading unit 20.

[0026] The control unit 10 is configured to include a CPU, a ROM, a RAM, etc. The CPU of the control unit 10 reads a program corresponding to the processing content from the ROM, loads it into the RAM, and in cooperation with the loaded program, performs centralized control of the operation of each block of the image forming apparatus 1. At this time, various data stored in the storage unit 17 is referenced. The storage unit 17 is configured, for example, with a non-volatile semiconductor memory or a hard disk drive. However, it goes without saying that each function of the control unit 10 is not limited to software processing, but can also be realized by a dedicated hardware circuit.

[0027] In this embodiment, the control unit 10 functions as a clustering processing unit 10a, a label creating unit 10b, and a correcting unit 10c of the present invention. Details of these functions will be described later.

[0028] The control unit 10 is configured to be able to send and receive various data (for example, image data) via the IF unit 18 to and from an external device (for example, a personal computer) connected to a communication network such as a LAN or WAN.

[0029] The operation unit 11 includes, for example, a touch panel and various operation buttons, and outputs an operation signal to the control unit 10 based on an operation by a user.

[0030] The display unit 12 is configured by, for example, an LCD, and displays various screens in accordance with instructions of a display signal input from the control unit 10.

[0031] The document reading unit 13 includes, for example, an ADF (automatic document feeder), a scanner, etc., and outputs image data obtained by reading an image of a document to the control unit 10.

[0032] Image forming unit 14 forms an image on paper supplied from conveying unit 15 based on image data that has been image processed by image processing unit 19. Image forming unit 14 is configured to include photosensitive drums 141Y, 141M, 141C, and 141K corresponding to the colors yellow (Y), magenta (M), cyan (C), and black (K), an intermediate transfer belt 142, a secondary transfer roller 143, a fixing unit 144, and the like.

[0033] After being uniformly charged, the photoconductor drum 141Y is scanned and exposed by a laser beam based on yellow image data, forming an electrostatic latent image. Yellow toner is then attached to the electrostatic latent image on the photoconductor drum 141Y, and development is performed. Photoconductor drums 141M, 141C, and 141K are similar to photoconductor drum 141Y except for the colors they handle, and therefore will not be described here.

[0034] The toner images of each color formed on the photosensitive drums 141Y, 141M, 141C, and 141K are transferred one after another (primary transfer) onto the rotating intermediate transfer belt 142. That is, a color toner image in which the toner images of four colors are superimposed is formed on the intermediate transfer belt 142. The color toner images on the intermediate transfer belt 142 are transferred all at once onto a sheet of paper by the secondary transfer roller 143 (secondary transfer).

[0035] The fixing unit 144 includes a heating roller that heats the paper onto which the color toner image has been transferred, and a pressure roller that pressurizes the paper, and fixes the color toner image to the paper by applying heat and pressure.

[0036] The transport unit 15 includes a paper feed unit, a paper discharge unit, a transport path unit, etc. The three paper feed trays TT1 to TT3 that make up the paper feed unit store sheets of paper classified based on basis weight, size, etc., according to preset types. The transport path unit includes a plurality of transport roller pairs, such as registration roller pairs.

[0037] The sheets of paper stored in the paper feed trays TT1 to TT3 are fed one by one from the top, and are transported by a transport path to the image forming unit 14. Then, in the image forming unit 14, the toner images on the intermediate transfer belt 142 are secondarily transferred all at once onto one side of the sheets of paper, and a fixing process is performed in the fixing unit 144. Then, the sheets of paper on which the images have been formed are discharged outside the apparatus by the paper discharge unit.

[0038] The storage unit 17 is a non-volatile storage device such as a HDD or semiconductor memory that stores various data such as image data. The storage unit 17 also stores reference color cluster information (see FIG. 4) created by the control unit 10 based on the color cluster information of the scanned image data obtained at the beginning of a print job.

[0039] The interface unit 18 (IF unit) receives image data input from an external device.

[0040] The image processing unit 19 performs the necessary image processing on input image data obtained by reading an image from a document using the document reading unit 13, and on input image data input from an external device, and sends the processed image data to the image forming unit 14. Image processing includes gradation processing, halftone processing, color conversion processing, etc. Gradation processing is a process of converting the gradation values ​​of each pixel of the input image data into corrected gradation values ​​so that the density characteristics of the image formed on paper match the target density characteristics. Halftone processing includes error diffusion processing and screen processing using ordered dithering. Color conversion processing is a process of converting each RGB gradation value into each CMYK gradation value.

[0041] The image reading unit 20 is configured to include, for example, an image sensor (e.g., a CCD), an optical system, a light source, etc. The image reading unit 20 is disposed, for example, downstream of the image forming unit 14, and photographs the top side of the paper being transported by the transport unit 15. The image reading unit 20 is disposed in a line along the width direction of the paper. For example, the image reading unit 20 photographs the paper at each position while the paper is being transported from the upstream side to the downstream side, thereby photographing the entire paper. Then, the images photographed by the image reading unit 20 at each position are superimposed to generate read image data of the entire paper (i.e., the entire output image).

[0042] For example, the image reading unit 20 acquires the read image data of the printed matter every time a printed matter (i.e., a sheet of paper after an image is formed) is produced by the image forming unit 14. Then, the image reading unit 20 sequentially sends the read image data of the printed matter to the control unit 10.

[0043] For example, the image reading unit 20 detects color information (e.g., RGB values) of the output image for each pixel area over the entire area of ​​the output image formed on paper. Note that the spot size of the pixel area detected by the image reading unit 20 corresponds to the area of ​​one pixel, for example.

[0044] <Detailed configuration of the control unit 10> The detailed configuration of the control unit 10 will be described below with reference to FIGS.

[0045] In this embodiment, calibration will be described for a print job in which the same image is printed consecutively on different sheets of paper, such as in advertising printing.

[0046] As described above, the conventional technique of detecting color changes in an output image (meaning an image formed on paper) using patch images cannot capture color changes in the various colors used in actual printed matter. Furthermore, such a technique cannot capture real-time color changes that occur when an actual printed matter is being printed.

[0047] Therefore, the image forming apparatus 1 according to this embodiment uses the scanned image data of the printed matter itself to detect color changes in the output image. That is, the image forming apparatus 1 according to this embodiment is configured to detect color changes that appear in the scanned image data while the printed matter is being continuously printed during a print job in real time, and sequentially correct the input image data or the image forming conditions of the image forming unit 14.

[0048] However, the method of directly detecting color changes in the scanned image data of each printed item is not a suitable method due to the difficulty of aligning different scanned image data on a pixel-by-pixel basis, etc. This is because the position and orientation of the paper reflected in the scanned image data changes in various ways during actual printing.

[0049] Therefore, in the image forming apparatus 1 according to this embodiment, color clustering processing is performed on the scanned image data of each printed matter to obtain color cluster information, and color changes that appear in the scanned image data during continuous printing of printed matter are detected by tracking the color cluster information. In a situation where the same image is continuously printed on different sheets of paper, the color cluster information obtained from the scanned image data of each printed matter will basically be the same. Therefore, by adopting a method for tracking color cluster information, it is possible to capture color changes in the colors actually used in the printed matter and perform calibration without aligning different scanned image data on a pixel-by-pixel basis.

[0050] In the image forming apparatus 1 according to this embodiment, the clustering processing unit 10a, the label creating unit 10b, and the correcting unit 10c of the control unit 10 realize such calibration.

[0051] 3 to 6 are diagrams for explaining the processing of the clustering processing unit 10a, the label creating unit 10b, and the correcting unit 10c.

[0052] The clustering processing unit 10a performs color clustering processing on the scanned image data of each printed matter that is sequentially created during a print job, and acquires color cluster information of the scanned image data. Note that Fig. 4 shows a schematic diagram of the transition of color cluster information of the scanned image data of each printed matter that is obtained during a print job.

[0053] Color clustering is a process of clustering each pixel constituting scanned image data in a predetermined color space, as shown in Fig. 3. Specifically, it can be realized by mapping each pixel in the predetermined color space, and then dividing the predetermined color space into regions by classifying similar colors into the same cluster using thresholds such as Euclidean distance or Mahalanobis distance. That is, color clustering acquires color cluster information for each cluster, including the color value of the center position (i.e., center of gravity position) of the color cluster and information on the number of pixels included in the color cluster.

[0054] The clustering processing unit 10a, for example, performs color clustering on each pixel constituting the read image data, extracts two or more representative colors (here, seven colors) in descending order of cluster size, and acquires color cluster information for the read image data. In this embodiment, the clustering processing unit 10a acquires color cluster information for each of the seven representative color clusters, including the color value of the center position of the color cluster (here, the center of gravity position) and information on the number of pixels included in the color cluster.

[0055] In this embodiment, the clustering processing unit 10a first converts the pixel data (RGB values) of each pixel of the scanned image data into pixel values ​​in a four-dimensional CMYK color space. Then, the clustering processing unit 10a performs color clustering of each pixel constituting the scanned image data using the X-means algorithm. The execution conditions of the clustering process are the same for each scanned image data of each printed matter.

[0056] Clustering using the X-means algorithm itself is well known, so a detailed description will be omitted here. The X-means algorithm has the advantage that it can automatically determine the optimal number of clusters using sequential repetition of the K-means algorithm and a division stopping criterion based on the Bayes Information Criterion. For details of the X-means algorithm, see, for example, Non-Patent Document 1.

[0057] The color clustering method used by the clustering processing unit 10a may be any known method. For example, instead of the X-means algorithm, a K-means algorithm or a Gaussian mixture model algorithm may be used.

[0058] As a pre-processing step for the clustering process, the clustering processing unit 10a preferably performs image compression and gradation reduction on the scanned image data to the extent that the image features of the scanned image data are preserved, thereby enabling the clustering process to converge quickly.

[0059] Through the processing of the clustering processing unit 10a, color cluster information of the scanned image data of each printed matter is acquired sequentially during the print job. However, from the viewpoint of reducing the processing load, the clustering processing unit 10a may perform clustering processing on the scanned image data of each printed matter at intervals of several copies.

[0060] The label creation unit 10b creates reference color cluster information (i.e., a label to be used as a reference) based on the color cluster information of the read image data obtained at the beginning of the print job, and stores it in the storage unit 17. For example, the label creation unit 10b stores the color cluster information of the read image data of the first printed matter of the print job in the storage unit 17 as the reference color cluster information.

[0061] The "reference color cluster information" serves as a reference for detecting color changes that may occur in the output image during a print job due to changes in the characteristics of the image forming unit 14, etc. In other words, color changes in the output image are detected by comparing the reference color cluster information with the color cluster information of the currently acquired scanned image data. Note that hereinafter, the "reference color cluster information" is also referred to as a "label."

[0062] However, the label creation unit 10b may store color cluster information obtained from scanned image data of the several copies of printed matter in a print job as reference color cluster information in the storage unit 17. Alternatively, the label creation unit 10b may store color cluster information obtained by averaging multiple scanned image data obtained at the beginning of a print job as reference color cluster information in the storage unit 17. This is because there are cases where more preferable colors are reproduced in an output image after the operation of the image forming unit 14 has stabilized. Alternatively, the label creation unit 10b may obtain scanned image data and create reference color cluster information by performing test printing at the beginning of a print job.

[0063] The correction unit 10c compares the color cluster information of the read image data acquired at each point in time during the print job with the reference color cluster information stored in the storage unit 17. Then, based on the color change, it identifies the correction value to be applied to the image forming unit 14 or input image data at the next point in time. That is, the correction unit 10c uses the reference color cluster information created by the label creation unit 10b at the beginning of the print job as a reference, and tracks the temporal color change in the color cluster information of the read image data acquired thereafter (i.e., each printed material generated thereafter).

[0064] At this time, the correction unit 10c determines the correspondence between each cluster of the color cluster information of the read image data acquired at each time point and each cluster of the color cluster information of the reference color cluster information, for example, based on the following cluster approximation criteria (see Figure 5). (1) The distance between the color values ​​of the center positions of the color clusters is less than a predetermined distance (e.g., 10). (2) The difference in the number of pixels included in the color clusters is less than a predetermined number (for example, 50).

[0065] Basically, each cluster of color cluster information created from the same original image should satisfy these two conditions. Therefore, if these two conditions are satisfied, the correction unit 10c considers both to be the same cluster (i.e., the same color region). Then, based on the above cluster approximation criteria, the correction unit 10c identifies the correspondence between the reference color cluster information (color value at the center position of the color cluster) and the color cluster information (color value at the center position of the color cluster) for each of the seven representative colors of the color cluster information.

[0066] However, the cluster approximation criteria can be changed as appropriate as long as the identity of the clusters can be determined.

[0067] Next, the correction unit 10c calculates the difference between the reference color cluster information (color value at the center of the color cluster) and the color cluster information (color value at the center of the color cluster) for each of the seven representative colors of the color cluster information, and uses the difference value as the correction value to be added to the input image data (see FIG. 6).

[0068] The correction unit 10c then applies gradation correction by the calculated correction value to pixels that correspond to the seven representative colors among the pixels that make up the input image data. Figure 6 shows a state in which, for a certain representative color, the color value (0,8,32,0) of the cluster center in the currently acquired color cluster information has changed by (0,-3,-17,0) from the color value (0,5,15,0) of the cluster center in the reference color cluster information. In this case, the correction unit 10c applies gradation correction by (0,-3,-17,0) to pixels that correspond to the representative color among the pixels that make up the input image data.

[0069] Here, it is preferable that the correction unit 10c performs color clustering processing on the input image data in advance, similar to that performed by the clustering processing unit 10a, to obtain color cluster information of the input image data and store it in the storage unit 17. This makes it possible to identify, among the pixels constituting the input image data, pixels corresponding to each of the seven representative colors to be corrected.

[0070] In this embodiment, the correction unit 10c corrects input image data, but instead of the input image data, the correction unit 10c may correct the image forming conditions of the image forming unit 14. As is well known, similar gradation correction is possible by correcting the image forming conditions of the image forming unit 14 (for example, charging potential, development potential, exposure amount, etc.).

[0071] Fig. 7 is a diagram showing an example of the operation flow of the control unit 10 according to this embodiment. The flowchart shown in Fig. 7 shows the process executed by the control unit 10 in accordance with a computer program when executing a print job, for example. Note that here, a print job in which the same image is printed sequentially on a predetermined number of sheets of paper will be described.

[0072] In step S1, the control unit 10 causes the image forming unit 14 to form an image on a sheet based on input image data set in the print job.

[0073] In step S2, the control unit 10 causes the image reading unit 20 to read the output image formed on the paper, and acquires read image data.

[0074] In step S3, the control unit 10 performs color clustering processing on the read image data and acquires color cluster information.

[0075] In step S4, the control unit 10 determines whether or not reference color cluster information is stored in the storage unit 17. If reference color cluster information is stored in the storage unit 17 (step S4: YES), the control unit 10 proceeds to step S6. On the other hand, if reference color cluster information is not stored in the storage unit 17 (step S4: NO), the control unit 10 proceeds to step S5.

[0076] In step S5, the control unit 10 creates reference color cluster information based on the color cluster information obtained in step S3, and stores the reference color cluster information in the storage unit 17.

[0077] In step S6, the control unit 10 compares the reference color cluster information stored in the memory unit 17 with the color cluster information of the currently obtained read image data, and calculates a color change of the color cluster information of the currently obtained read image data from the reference color cluster information. Note that the color cluster information of the currently obtained read image data here means the color cluster information obtained in step S3 in the current loop processing.

[0078] In step S6, the control unit 10 calculates, for example, a difference value between the reference color cluster information (color value at the center position of the color cluster) and the color cluster information (color value at the center position of the color cluster) for each of the seven representative colors of the currently obtained color cluster information. The difference value is the color change value from the reference color cluster information of the currently obtained color cluster information.

[0079] In step S7, the control unit 10 uses the color change calculated in step S6 as a correction value and performs correction processing on the input image data for printing at the next point in time (i.e., step S1 of the next loop).

[0080] In step S7, the control unit 10 applies gradation correction by the calculated correction value to, for example, pixels corresponding to the seven representative colors among the pixels constituting the input image data. Here, it is assumed that the control unit 10 has previously performed a color clustering process similar to step S3 on the input image data, obtained color cluster information of the input image data, and stored it in the storage unit 17.

[0081] In step S8, the control unit 10 determines whether the print job (for example, printing a predetermined number of sheets) has ended. If the print job has ended (step S8: YES), the control unit 10 ends the series of steps. On the other hand, if the print job has not ended (step S8: NO), the control unit 10 returns to step S1 and executes printing again using the input image data corrected in step S7. This process is then repeated until the print job is completed.

[0082] 7 shows an example in which calibration (here, correction of input image data) is performed each time one copy of a printed material is produced. However, the frequency at which calibration is performed can be changed as appropriate. The control unit 10 may perform calibration, for example, at intervals of several minutes.

[0083] [effect] As described above, the image forming apparatus according to this embodiment During a print job, a control unit performs color clustering processing on the read image data obtained by reading the print image to obtain color cluster information, and compares the obtained color cluster information with reference color cluster information created from the read image data obtained at the beginning of the print job, thereby adjusting the input image data or image formation conditions when printing is performed next.

[0084] Therefore, the image forming apparatus according to this embodiment can detect color changes occurring in each color in the output image in real time and calculate correction values ​​to be applied to the image forming unit or input image data when printing is next performed, thereby preventing color changes from occurring in the image formed on the recording medium during a print job.

[0085] In particular, the image forming apparatus according to this embodiment is configured to capture color changes occurring in each color in the output image based on color cluster information of the scanned image data, which is useful in that it can calculate appropriate correction values ​​while avoiding the difficulty of identifying the correspondence between each pixel position between the input image data and the scanned image data.

[0086] Furthermore, the image forming apparatus according to this embodiment can capture color changes that occur in each color in an actual printed matter, thereby maintaining high color reproducibility.

[0087] Furthermore, when implementing the image forming apparatus according to this embodiment, it is also possible to consider a method of creating reference color cluster information based on input image data and comparing it with the color cluster information of the read image data acquired at each point during the printing job.

[0088] However, due to the influence of the dither pattern used in image formation and the unique characteristics of each image forming device, the color values ​​of the scanned image data of the output image actually printed on paper do not completely match the color values ​​of the input image data. In addition, if the output image actually printed on paper is not used as a reference, the color tone of the output image that the user initially judged as the ideal color may not be the same as the color tone of the input image. It may change due to calibration.

[0089] From this perspective, it is preferable that the reference color cluster information be created based on the read image data of an output image that is actually printed on paper, as in the image forming apparatus according to this embodiment.

[0090] (Variation 1) In the above embodiment, the same image is continuously printed on different sheets of paper in a print job.

[0091] In this regard, some print jobs create multiple printouts consisting of multiple pages, each containing different images. For example, this may be the case when creating multiple copies of a printout consisting of m pages. In this case, the print job first prints the first, second, ..., mth page in order for the first copy of the printout. Then, the print job prints the first, second, ..., mth page in order for the second copy of the printout. Then, the print job prints the first, second, ..., mth page in order for the Nth copy of the printout.

[0092] In this case, when performing the above calibration, the label creating unit 10b needs to create reference color cluster information for each of the first, second, through m-th pages.

[0093] FIG. 8 is a diagram for explaining the processing of the label creating unit 10b according to the first modification.

[0094] 8, the label creation unit 10b needs to create reference color cluster information for each of the images on page m. Therefore, the label creation unit 10b according to this modification determines, based on a predetermined label determination criterion set in advance, whether the original image of the color cluster information of the currently acquired scanned image data is identical to the original image of the reference color cluster information stored in the storage unit 17. If the two are different, the label creation unit 10b stores the color cluster information of the currently acquired scanned image data in the storage unit 17 as new reference color cluster information for a different original image.

[0095] As a result, the label creation unit 10b sequentially creates reference color cluster information for each of the first, second, through mth pages, and stores the reference color cluster information for each of the first, second, through mth pages in the memory unit 17.

[0096] A specific label determination criterion can be any criterion that can determine the similarity between both pieces of color cluster information, for example, whether the seven representative colors included in both pieces of color cluster information are the same.

[0097] That is, for example, the label creation unit 10b first identifies the correspondence between each cluster of the color cluster information of the read image data acquired at each time point and each cluster of the color cluster information of the reference color cluster information based on the cluster approximation criterion described above. Then, if the seven representative colors included in both sets of color cluster information are the same, the label creation unit 10b considers the original image of the color cluster information of the read image data acquired at the current time to be the same as the original image of the reference color cluster information stored in the storage unit 17. On the other hand, if the seven representative colors included in both sets of color cluster information are not the same, the label creation unit 10b considers the original image of the color cluster information of the read image data acquired at the current time to be different from the original image of the reference color cluster information stored in the storage unit 17.

[0098] In this modified example, the reference color cluster information to be compared with the color cluster information of the read image data acquired at each point during the print job must be from the same original image.

[0099] Therefore, based on the label determination criteria, the label creation unit 10b reads out, from the storage unit 17, reference color cluster information created based on the same original image as the original image of the color cluster information of the currently acquired read image data, and passes it to the correction unit 10c as a reference object.

[0100] The process of the correction unit 10c is the same as that described in the above embodiment. That is, the correction unit 10c compares the color cluster information of the scanned image data acquired at each time point with the reference color cluster information specified as a reference target by the label creation unit 10b. Then, based on the color change, it determines the correction value to be applied to the image forming unit 14 or input image data when printing is performed next time point.

[0101] FIG. 9 is a diagram showing an example of an operation flow of the control unit 10 according to this modification.

[0102] The flowchart in Fig. 9 differs from the flowchart in Fig. 7 only in the process of step S4a. In this modification, in step S4a, the control unit 10 performs label determination on the color cluster information of the read image data acquired at each time point.

[0103] As described above, label determination is a determination of the identity of an original image using the label determination criterion. That is, in step S4a, the control unit 10 uses the label determination criterion to search the storage unit 17 for reference color cluster information created from an original image that is identical to the color cluster information of the scanned image data acquired at each time point.

[0104] Then, if the corresponding reference color cluster information exists in the memory unit 17 (step S4a: YES), the control unit 10 uses the reference color cluster information to calculate the color change of the color cluster information of the currently acquired read image data (step S6).

[0105] On the other hand, if the control unit 10 does not have the corresponding reference color cluster information in the memory unit 17 (step S4a: NO), the control unit 10 adds the color cluster information of the read image data acquired at that time to the memory unit 17 as new reference color cluster information (step S5a).

[0106] As described above, the method of this modified example allows the image forming apparatus 1 to perform calibration appropriately during a print job, even when creating printed material having different images for each page.

[0107] (Variation 2) In the above embodiment, when color correction is performed on input image data, the same color correction is performed on the entire area of ​​the input image data.

[0108] In this regard, color unevenness may occur in only a part of the image due to changes in the characteristics of the image forming unit 14. Such color unevenness may occur, for example, along the main scanning direction or the sub-scanning direction. In such cases, it is preferable to perform color correction on the input image data for each image region.

[0109] From this perspective, the control unit 10 according to this modification employs a configuration that enables color correction of input image data to be performed for each image region of the input image data.

[0110] Fig. 10 is a diagram illustrating the processing of the label creation unit 10b according to Modification 2. Fig. 10 shows an example in which the scanned image data is divided into three image areas R1, R2, and R3 along the sub-scanning direction, and reference sub-color cluster information is created for each image area.

[0111] The clustering processing unit 10a in this modified example acquires color cluster information for the entire read image data, and then further divides the read image data into multiple image areas, performs color clustering processing for each image area, and acquires sub-color cluster information for the read image data for each image area.

[0112] Furthermore, the label creation unit 10b according to this modified example creates reference color cluster information for the entire scanned image data in a print job, and then stores the sub-color cluster information for each image area of ​​the scanned image data in the memory unit 17 as sub-reference color cluster information.

[0113] Here, the reference color cluster information of the entire scanned image data is used to determine whether the original images are the same for a print job in which different images exist on each page, as described above.The sub-reference color cluster information for each image area of ​​the scanned image data is used as reference information for performing correction for each image area.

[0114] The correction unit 10c according to this modification also compares the sub-color cluster information of the currently acquired scanned image data with the sub-reference color cluster information for each image region, and then calculates, based on the color change, a correction value to be applied to the image forming unit 14 or input image data when printing is next performed for each image region.

[0115] In this modified example, the algorithms for the color clustering process for each image region and the correction process for each image region are the same as those used when performing the process on the entire image.

[0116] FIG. 11 is a diagram showing an example of an operation flow of the control unit according to this modification.

[0117] The flowchart in FIG. 11 differs from the flowchart in FIG. 7 only in the processes of steps S3b, S5b, S6b, and S7b.

[0118] In step S3b, the control unit 10 performs color clustering processing on the read image data acquired at that time point, and acquires color cluster information of the read image data, similar to step S3 in Fig. 7. At this time, the control unit 10 further divides the read image data acquired at each time point into multiple image regions, performs color clustering processing on each image region, and acquires sub-color cluster information of the read image data for each image region.

[0119] In step S4, the control unit 10 determines whether or not reference color cluster information is stored in the storage unit 17. If reference color cluster information is stored in the storage unit 17 (step S4: YES), the control unit 10 proceeds to step S6b. On the other hand, if reference color cluster information is not stored in the storage unit 17 (step S4: NO), the control unit 10 proceeds to step S5b.

[0120] In step S5b, the control unit 10 creates reference color cluster information and sub-reference color cluster information based on the color cluster information obtained in step S3b, and stores them in the storage unit 17.

[0121] In step S6b, the control unit 10 compares the sub-reference color cluster information stored in the storage unit 17 with the sub-color cluster information of the currently obtained read image data, and calculates a color change of the color cluster information of the currently obtained read image data from the reference color cluster information. Note that the sub-color cluster information of the currently obtained read image data here means the sub-color cluster information obtained in step S3b in the current loop processing.

[0122] In step S7b, the control unit 10 performs a correction process on the input image data using the color change for each image area calculated in step S6b as a correction value for printing at the next point in time (i.e., step S1 of the next loop).

[0123] In performing step S7b, it is desirable that the control unit 10, for example, performs color clustering processing similar to that performed in step S3b on the input image data in advance, obtains sub-color cluster information of the input image data for each image region, and stores the information in the storage unit 17. This enables the control unit 10 to perform correction processing on the input image data for each image region.

[0124] As described above, the method of this modified example enables the image forming apparatus 1 to perform appropriate calibration so as to remove color unevenness that occurs during a print job.

[0125] In the above description, reference color cluster information for the entire scanned image data and sub-reference color cluster information for each image area of ​​the scanned image data are stored in the storage unit 17. However, in a configuration where label determination for each page is not required, as in the above embodiment, only sub-reference color cluster information for each image area of ​​the scanned image data may be stored in the storage unit 17. In this case, the clustering processing unit 10a only needs to perform clustering processing for each image area of ​​the scanned image data.

[0126] As a further modification, the following configuration may be added.

[0127] That is, the control unit 10 may compare the color cluster information of the first image region with the color cluster information of the second image region in the color cluster information obtained for each image region at each point in time, and monitor whether or not there is a difference in the color information of the same representative color. With this configuration, it is possible to continuously monitor, for example, the occurrence of color unevenness along the main scanning direction or the sub-scanning direction.

[0128] (Other embodiments) For example, in the above embodiment, reference color cluster information is created and stored in the storage unit 17 for each print job.

[0129] However, when implementing the image forming apparatus according to the present disclosure, the reference color cluster information that has been created may be stored and held in the storage unit 17. The reference color cluster information may then be made available for use in subsequent print jobs.

[0130] Although the above embodiment only describes the case where the image forming apparatus according to the present disclosure is applied to an electrophotographic image forming apparatus, the image forming apparatus according to the present disclosure can also be applied to image forming apparatuses of other image forming methods, such as an inkjet image forming apparatus.

[0131] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above. [Industrial Applicability]

[0132] According to the image forming apparatus of the present invention, it is possible to more suitably realize real-time patchless color correction. [Explanation of symbols]

[0133] 1. Image forming device 10 Control Unit 10a Clustering processing section 10b Label Creation Department 10c correction section 11 Control section 12 Display section 13 Document reading unit 14 Image forming unit 15 Conveying section 17 Memory section 18 IF section (interface section) 19 Image processing section 20 Image reading unit

Claims

1. An image forming apparatus capable of performing continuous printing, The printer includes a control unit that, during a print job, performs color clustering processing on read image data obtained by reading a print image to obtain color cluster information, and compares the obtained color cluster information with reference color cluster information created from the read image data obtained at the beginning of the print job, thereby adjusting input image data or image forming conditions when printing is performed next. Image forming device.

2. The color cluster information is information including, for a cluster of two or more representative colors extracted when the color clustering process is performed, the color value of the cluster center and the number of pixels included in the cluster. The image forming apparatus according to claim 1 .

3. The control unit specifies the correction value for each of the two or more representative colors of the color cluster information, and performs gradation correction on pixels in the input image data that correspond to the two or more representative colors based on the correction value. The image forming apparatus according to claim 2 .

4. The control unit determines whether the original image of the acquired color cluster information and the original image of the reference color cluster information are identical in accordance with a predetermined label determination criterion, and if they are different, stores the acquired color cluster information in a storage unit as new reference color cluster information relating to a different original image. The image forming apparatus according to claim 1 .

5. The control unit reads out the reference color cluster information created based on the same original image as the original image of the acquired read image data from the storage unit based on the predetermined label determination criterion, and refers to the reference color cluster information as a comparison target. The image forming apparatus according to claim 4 .

6. The control unit divides the read image data into a plurality of image areas, performs the color clustering process for each of the image areas, acquires the color cluster information for each of the image areas, and compares the color cluster information with the reference color cluster information for each of the image areas, thereby adjusting the input image data or the image forming conditions when printing is performed next. The image forming apparatus according to claim 1 .

7. The control unit performs image compression and gradation reduction of the read image data as preprocessing of the color clustering process. The image forming apparatus according to claim 1 .

8. A control method for an image forming apparatus capable of performing continuous printing, comprising: During a print job, color cluster information is obtained by performing color clustering processing on the read image data obtained by reading the print image, and by comparing the obtained color cluster information with reference color cluster information created from the read image data obtained at the beginning of the print job, the input image data or image forming conditions are adjusted when printing is performed next. Control method.

9. A control program for an image forming apparatus capable of performing continuous printing, On the computer, A control program that, during a print job, performs color clustering processing on read image data obtained by reading a print image to obtain color cluster information, and compares this with reference color cluster information created from the read image data obtained at the beginning of the print job, thereby performing processing to adjust the input image data or image formation conditions when printing is performed next.

Images