Information processing apparatus, printing system, control method of printing system, and program

Abstract

To achieve both of the quality maintenance of printed matter and the suppression of the productivity reduction of a printing device by performing the density correction processing at an appropriate timing based on a state of the printing device.SOLUTION: An inspection result of an already printed sheet output from a printing device is accumulated, and when a color defect in which the target color is not reproduced, continuously occurs more than a predetermined number of times at a position not overlapping with other defects, the printing device is made to perform the density correction processing.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a control technique for density correction in a printing apparatus.

Background Art

[0002] Printed matter output from a printing apparatus may have so-called printing defects such as dirt and color bleeding. Since such printing defects deteriorate the quality of the printed matter, it is required to inspect for the presence or absence of printing defects. And visual inspection in which an inspector visually inspects for the presence or absence of printing defects requires a lot of time and cost, so techniques for automatically performing inspection without relying on visual inspection have been proposed. On the other hand, in a printing apparatus, density correction processing for maintaining color reproducibility is appropriately necessary, but during that time, the printing job must be stopped, so there is a desire to reduce its execution frequency as much as possible. In this regard, in an in-line type printing system in which an inspection apparatus and a printing apparatus are connected and printing output can be performed while automatically inspecting, the inspection apparatus also instructs the printing apparatus to execute density correction processing. For example, Patent Document 1 discloses a method of controlling the type and execution timing of density correction processing based on the inspection threshold (severity of inspection criteria) for printing defects in an inspection apparatus.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the technology of the above Patent Document 1, when strict inspection criteria are set, regardless of the state of the printing apparatus, density correction processing involving downtime (i.e., productivity decreases) is periodically executed. That is, in the case of the method of Patent Document 1, there is a possibility that density correction processing that is inherently unnecessary from the state of the printing apparatus is executed, which is insufficient from the viewpoint of improving productivity.

Means for Solving the Problems

[0005] An information processing apparatus according to the present disclosure is an information processing apparatus that inspects printed matter, and includes an acquisition unit that acquires a read image obtained by reading a printed sheet output from a printing apparatus and a reference image that serves as a reference in an inspection of the read image, and based on the acquired read image and the reference image, Printing defect a detection unit that detects The printing defect for the plurality of the printed sheets and an instruction unit that instructs the printing apparatus to execute density correction processing based on the detection result of has, and the printing defect includes the color abnormality in which the target color is not reproduced in the read image and other abnormalities other than the color abnormality, when the color abnormality continuously occurs at a position where it does not overlap with the other abnormality, the instructing means instructs the printing apparatus to execute the density correction process which is characterized in that.

Effects of the Invention

[0006] According to the technology of the present disclosure, density correction processing can be executed at an appropriate timing based on the state of the printing apparatus. Thereby, it becomes possible to achieve both maintenance of the quality of printed matter and suppression of a decrease in productivity of the printing apparatus.

Brief Description of the Drawings

[0007]

Figure 1

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Best Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments do not limit the present invention, and not all combinations of features described in each embodiment are essential. Note that the same reference numerals will be used to describe the same configurations.

[0009] [Embodiment 1] <Configuration of the Printing System> First, with reference to FIG. 1, a configuration example of the entire printing system according to this embodiment will be described. The printing system according to this embodiment includes an inspection apparatus 100, a printing server 180, and a printing apparatus 190. The printing server 180 has a function of generating a printing job for causing the printing apparatus 190 to execute a printing process and inputting it to the printing apparatus 190. The printing server 180 also has a function of receiving a generation request for a printing job, document data to be printed, etc. from an external apparatus (not shown) communicably connected via a network.

[0010] ≪Outline of the Printing Apparatus≫ The printing device 190 has a printing function of forming an image on a recording medium such as paper (hereinafter referred to as "sheet"). The printing methods performed by the printing device 190 include an offset method, an electrophotographic method, an inkjet method, etc. In this embodiment, the electrophotographic method will be described as an example, but it is not limited thereto. The printing device 190 has a CPU 197, a RAM 198, a ROM 199, a paper feeding unit 191, a scanner unit 193, a print unit 194, an image processing unit 195, and an inspection device I / F (interface) 196 inside. The user sets the sheet in the paper feeding unit 191 in advance. When a printing job is input, the printing device 190 generates printing image data obtained by performing printing image processing, which will be described later, in the image processing unit 195. Thereafter, while transporting the sheet set in the paper feeding unit 191 along the transport path 192, the printing device 190 forms an image on its front or both sides with the print unit 194 and transports it to the inspection device 100. The CPU 197 is a processor that controls the whole inside of the printing device 190. The RAM 199 functions as the main memory, work area, etc. of the CPU 197. The ROM 198 stores a group of programs executed by the CPU 197. Also, the printing device 190 performs density correction processing to keep the color reproducibility of the print unit 194 constant according to an instruction from the UI panel (not shown) of the printing device 190 or an instruction from the inspection device 100 described later. By this density correction processing, the correction LUT used in the gamma correction processing of the image processing unit 195 described later is updated.

[0011] <Overview of the inspection device> The inspection device 100 is an information processing device that inspects printed matter output from the printing device 190 for the presence or absence of printing defects. In this specification, a series of processes for inspecting the presence or absence of printing defects is referred to as "inspection processing", and the process of detecting printing defects corresponding to one or more inspection items included in the inspection processing is referred to as "defect detection processing (or simply detection processing)". The inspection device 100 includes a CPU 101, a RAM 102, a ROM 103, a main storage device 104, and an image reading device 105 inside. In addition, the inspection device 100 includes a printing device 19 I / F (interface) 106, a general-purpose I / F (interface) 107, a UI (user interface) panel 108, and a main bus 109. Furthermore, the inspection device 100 includes a conveyance path 110 for conveying a sheet (printed sheet) printed by the printing device 190, a paper discharge tray 111 for printed sheets that have passed the inspection, and a paper discharge tray 112 for printed sheets that have failed the inspection. Note that the classification of inspection results does not necessarily have to be limited to two types, qualified and unqualified, and may be classified in more detail.

[0012] The CPU 101 is a processor that controls the entire inspection device 100. The RAM 102 functions as the main memory, work area, etc. of the CPU 101. The ROM 103 stores a group of programs executed by the CPU 101. The main storage device 104 stores applications executed by the CPU 101, data used for image processing, etc. The image reading device (scanner) 105 can read one side or both sides of a printed sheet output from the printing device 190 on the conveyance path 110 and acquire it as read image data. Specifically, the image reading device 105 uses one or more reading sensors provided near the conveyance path 110 to read one side or both sides of the conveyed printed sheet. The reading sensor may be provided only on one side, or may be provided on both the front side and the back side of the printed sheet to read both sides simultaneously. When provided only on one side, after reading one side, the front and back of the printed sheet may be reversed using a double-sided conveyance path (not shown) in the conveyance path 110 and the other side may be read by the reading sensor again.

[0013] The printing device I / F 106 is connected to the printing device 190 via the inspection device I / F 196, synchronizes the processing timing of the printed sheet with the printing device 190, and communicates the operating status of each other. The execution instruction for the density correction process for the printing device 190, which will be described later, is also given via this printing device I / F 106. The general-purpose I / F 107 is a serial bus interface such as USB or IEEE1394, and allows the user to take out data such as logs or import some data into the inspection device 100. The UI panel 108 is, for example, a liquid crystal display (display unit), functions as a user interface of the inspection device 100, and performs screen displays for the current status and various settings. Also, with the touch panel function, it is possible to detect user operations on the buttons on the display screen and receive instructions from the user.

[0014] The main bus 109 connects each part of the inspection device 100 to each other. Each part within the inspection device 100 can be operated according to an instruction from the CPU 101 through the main bus 109. For example, the conveyance path 110 can be moved in synchronization with the conveyance path 192 of the printing device 190, or it can be switched which of the paper discharge tray 111 for qualified products and the paper discharge tray 112 for unqualified products to send the printed sheet according to the inspection result. Also, the inspection device 100 may be provided with a GPU specialized for image processing in addition to the CPU 101.

[0015] The inspection apparatus 100 according to this embodiment reads a printed sheet conveyed from the printing apparatus 190 with the image reading device 105, and based on the obtained read image data, executes the inspection process described below. As a result of the inspection process, if no printing defect is detected from the printed sheet, the printed sheet is conveyed to the paper discharge tray 111 for acceptable products, and if any printing defect is detected, it is conveyed to the paper discharge tray 112 for unacceptable products. Further, based on the result of the inspection process, the printing apparatus 190 is instructed to execute density correction processing. In this way, the inspection apparatus 100 collects only the printed sheets with confirmed quality as the products for delivery in the paper discharge tray 111, and controls the execution timing of the density correction processing so that color reproducibility is maintained in the printing apparatus 190.

[0016] <Functional Configuration of Inspection Apparatus> Next, the functions mainly related to the inspection process of the inspection apparatus 100 according to this embodiment will be described. FIG. 2 is a block diagram showing various functions for realizing the inspection process. As shown in FIG. 2, the inspection apparatus 100 includes an image acquisition unit 201, an inspection item setting unit 202, a parameter setting unit 203, a detection processing unit 204, a density correction instruction unit 205, and a result output unit 206.

[0017] The image acquisition unit 201 acquires an image pair of a read image to be inspected (hereinafter referred to as an "inspection image") obtained by reading a printed sheet stored in the RAM 102 or the main storage device 104 and a reference image corresponding thereto. Here, the reference image is an image serving as a reference for comparison with the inspection image. The reference image can be obtained, for example, by reading a printed sheet (sample sheet) that the user has confirmed to be printed normally with the image reading device 105. The reference image is stored in advance in the RAM 102 or the main storage device 104 of the inspection apparatus 100 before the start of the inspection process. Note that, for example, the image acquisition unit 201 may be configured to acquire the reference image held in the printing server 180 or the printing apparatus 190. When acquiring the reference image from an external device of the inspection apparatus 100, the image acquisition unit 201 may send an acquisition request to the external device and acquire the reference image as a response thereto.

[0018] The inspection item setting unit 202 and the parameter setting unit 203 set inspection items to be detected in the inspection process and processing parameters corresponding to each inspection item based on user selection via the UI panel 108 or the like. The detection processing unit 204 uses the processing parameters set by the parameter setting unit 203 to execute a defect detection process according to the inspection items set by the inspection item setting unit 202. The result output unit 206 outputs the inspection result of the defect detection process by the detection processing unit 204 to the UI panel 108 and / or an external device (not shown). The density correction instruction unit 205 creates history information of the inspection results and determines whether density fluctuations are continuously occurring from the history information. Then, when it is inferred that density fluctuations are continuously occurring, the density correction process is instructed to be executed on the printing device 190.

[0019] <Image processing for printing> Next, the image processing for printing performed by the printing device 190 will be described with reference to FIG. 3. FIG. 3 is a block diagram showing the internal configuration of the image processing unit 195 of the printing device 190. The image processing unit 195 includes a color processing unit 301, a gamma correction unit 302, and a halftone processing unit 303. And each of these units is realized, for example, by the CPU 197 reading out a program stored in the ROM 198 and executing it in the RAM 199.

[0020] When a print job is input from the print server 180, first, the CPU 197 analyzes the PDL data included in the print job to generate bitmap-formatted image data and passes it to the image processing unit 195. This bitmap-formatted image data is an image in which the color value of each pixel is represented in, for example, an 8-bit RGB color space (hereinafter referred to as an "RGB image"). Therefore, in the image processing unit 195, first, color conversion processing is performed by the color processing unit 301 to convert the RGB image into an image represented by four colors of CMYK corresponding to the toner color materials (hereinafter referred to as a "CMYK image"). As a result, an image in which each pixel has a color value in the RGB color space is converted into an image in which each pixel has a color value in the CMYK color space. Next, gamma correction processing is performed for each color of CMYK by the gamma correction unit 302. The gamma correction processing is a process of correcting the density value of each color plate of the CMYK image using a correction LUT that associates an input density value and an output density value so as to obtain an appropriate tone expression according to the gamma characteristics of the print unit 194. The correction LUT is prepared in advance, and the gamma correction unit 302 reads the correction LUT from the RAM 199 and executes gamma correction. Finally, in the halftone processing unit 303, halftone processing is performed for each color of CMYK on the CMYK image that has been gamma-corrected. As a result, it is converted into halftone image data that can be processed by the print unit 194. The halftone image data for each color plate thus obtained is sent to the print unit 194 and printed out.

[0021] <Inspection Process> Next, the procedure of the inspection process performed by the inspection apparatus 100 according to the present embodiment will be described. FIG. 4 is a flowchart showing the flow of the inspection process, and S401 is executed in units of print jobs, and S402 and subsequent steps are executed in units of pages (sheet units). Hereinafter, a case where a print job for mass-printing a document consisting of one page is input will be described as an example. A series of processes shown in the flowchart of FIG. 4 are realized, for example, by the CPU 101 reading a program stored in the ROM 103 into the RAM 102 and executing it. In the following description, the symbol "S" means a step.

[0022] In S401, the inspection item setting unit 202 and the parameter setting unit 203 respectively set the inspection items to be implemented and the processing parameters corresponding thereto based on user input via a UI screen (not shown) or the like. Examples of the types of inspection items include dot (spot) defects, linear (streak) defects, color defects where the target color cannot be reproduced, and image unevenness. If the user does not select any inspection items, the inspection item setting unit 202 may set the items that are predefined as default inspection items. The parameter setting unit 203 sets, as the processing parameters corresponding to the inspection items selected by the user, for example, the type and size of the filter used in the filtering process, the threshold value used in the binarization process, and the like. FIG. 5(a) shows the characteristics of a filter for emphasizing dot defects, and FIG. 5(b) shows the characteristics of a filter for emphasizing linear defects. For example, when the inspection item is a dot defect, by reducing the shape of the filter in FIG. 5(a), dot defects of a smaller size are emphasized and are more easily detected. Also, if the threshold value for the binarization process is reduced, even a smaller difference value (contrast value) or color difference value will exceed the threshold value, and it will be more easily detected as a defect. In this way, the size of the filter, the threshold value during the binarization process, and the like are set as processing parameters.

[0023] Next, in S402, the image acquisition unit 201 acquires the data of the reference image pre-registered by scanning a sample sheet or the like from the RAM 102 or the main storage device 104. In the subsequent S403, the image acquisition unit 201 acquires the data of the inspection image obtained by reading the printed sheet conveyed from the printing device 190 from the RAM 102. Note that the configuration may be such that the data of the inspection image pre-read by the image reading device 105 and held in the main storage device 104 is acquired.

[0024] Next, in S404, the detection processing unit 204 determines the inspection items to be executed from among the inspection items set in S401. If there is no priority order in the execution order of the inspection items, it may be determined in an arbitrary order, such as the selected order. In the subsequent S405, the detection processing unit 204 executes the defect detection process for the determined inspection items. Details of the defect detection process will be described later. Then, in S406, it is determined whether the defect detection process for all the inspection items set in S401 has been completed. If the defect detection process for all the inspection items has been completed, the process proceeds to S407. On the other hand, if not completed, the process returns to S404 to determine the next inspection item to be executed and the defect detection process continues.

[0025] In S407, the result output unit 206 generates a UI screen showing the results for all the inspection items set in S401 and displays it on the UI panel 108. Note that the display destination of the results is arbitrary, and for example, it may be displayed on the display of an external device such as a PC communicably connected via a network. Figures 6(a) and (b) are examples of UI screens showing inspection results. In the image display area 601 of the UI screen 600 shown in Figure 6(a), three types of defects 602 to 604 detected from the inspection image are displayed together with the respective character strings "color defect", "dot-like defect", and "linear defect" indicating the corresponding inspection items. Further, the coordinate information 605 to 607 indicating the positions of the three types of defects 602 to 604 in the inspection image is also displayed. The UI screen 600' shown in Figure 6(b) is an example when the color defect 602 and the linear defect 604' are detected overlapping. Here, an example is shown where one dot-like defect, one linear defect, and one color defect are each detected. Of course, a plurality of these defects may be detected, and if detected, all of them will be displayed. Also, the UI screens 600 and 600' have buttons 608 to 610 for adjusting the processing parameters for each inspection item. For example, when the button 609 corresponding to the "dot-like defect" is pressed, the processing parameters for detecting the dot-like defect can be adjusted. When these adjustment buttons are selected, it may be possible to transition (or pop up and display) to a UI screen for parameter adjustment and allow the user to adjust the processing parameters.

[0026] In the next S408, the density correction instruction unit 205 determines the necessity of density correction processing based on the results of defect detection processing corresponding to all the inspection items set in S401. Then, when it is determined that density correction processing is necessary, the printing apparatus 190 is instructed to execute density correction processing. Details of the density correction necessity determination processing will be described later.

[0027] Then, in S409, it is determined whether the inspection of all the printed sheets related to the input printing job has been completed. If the inspection of all the printed sheets related to the printing job has been completed, this process ends. On the other hand, if there are unprocessed printed sheets, the process returns to S403 to obtain the next inspection image and the process continues.

[0028] The above is the general flow of the inspection process. In this embodiment, the case of mass-printing a document composed of only one page has been described as an example, but it is similarly applicable to the case of mass-printing a document composed of a plurality of pages, for example. In this case, if necessary, the process may return to S402 to obtain a reference image corresponding to the inspection image.

[0029] <Defect Detection Processing> Next, with reference to the flowchart of FIG. 7, details of the defect detection processing executed by the detection processing unit 204 in S405 will be described.

[0030] First, in S701, alignment between the reference image and the inspection image is performed using a general alignment method. As a general alignment method, for example, there is a method of extracting feature points and performing projective transformation or affine transformation so that the sum of the Euclidean distances of the extracted feature points becomes minimum. Subsequently, in S702, the processing is branched depending on whether the inspection item to be executed is a color defect. If the inspection item other than the color defect is the execution target, the process proceeds to S703, and if the color defect is the execution target, the process proceeds to S704.

[0031] In S703 when performing inspections other than color defects, an image showing the difference between the reference image and the inspection image (hereinafter referred to as the "difference image") is generated. Here, the difference image can be obtained by converting the reference image and the inspection image, each pixel of which has density values in the RGB three channels, into one channel, comparing the pixel values for each corresponding pixel, and obtaining the difference value for each pixel. In the subsequent S704, filter processing for emphasizing a specific defect shape is performed on the difference image generated in S703.

[0032] In S705 when performing color defect inspections, an image showing the color difference between the reference image and the inspection image (hereinafter referred to as the "color difference image") is generated. Here, the color difference image can be obtained by converting the reference image and the inspection image, in which the color of each pixel is represented in the RGB color space, into the L * a * b * color space and obtaining the color difference ΔE76, which is the Euclidean distance in the L * a * b * color space for each pixel. Note that the color difference ΔE76 can be obtained by, for example, taking the pixel value in the L * a * b * color space of the reference image as (L * 1,a * 1,b * 1), the pixel value of the inspection image as (L * 2,a * 2,b * 2), and using the following formula (1).

[0033]

Equation

[0034] Normally, when the value of ΔE obtained by the above formula (1) is about "2 - 3", it is said that the difference can be seen when comparing two colors separately. Note that here ΔE76 is used to evaluate the color difference, but it goes without saying that the index for evaluating the color difference is not limited to this.

[0035] In the next S706, binarization processing is performed on the difference image filtered in S704 or the color difference image generated in S705. Specifically, for each pixel value (difference value or color difference value), if it is greater than or equal to the threshold value, a value "1" indicating the presence of a defect is assigned, and if it is less than the threshold value, a value "0" indicating the absence of a defect is assigned. This process is performed on a pixel-by-pixel basis to generate a binary image in which each pixel has a value of "1" or "0".

[0036] Subsequently, in S707, it is determined whether there is a pixel having a pixel value of "1" among the pixels constituting the binary image generated by the binarization processing. As a result of the determination, if it exists, the process proceeds to S708, and if it does not exist, the process proceeds to S709.

[0037] In S708, as information on the detection result, information indicating that a defect has been detected (specifically, information associating the type of inspection item and the position coordinates of the detected defect location) is stored in the RAM102. When the information regarding the detected defect is stored, this process ends and returns to the flow of FIG. 4. Also, in S709, it is determined that there is no defect corresponding to the inspection item in the inspection image, and information indicating no defect is stored in the RAM102 as information on the detection result, and then the process returns to the flow of FIG. 4.

[0038] The above is the content of the defect detection process according to this embodiment.

[0039] <Density correction necessity determination process> Next, with reference to the flowchart of FIG. 8, the details of the density correction necessity determination process executed by the density correction instruction unit 205 in S408 will be described.

[0040] In S801, the information of the detection result stored in S708 or S709 of the above-described defect detection process is read from the RAM 102. Then, in S802 to S804, the process is allocated based on the read detection result information. First, in S802, it is determined whether the acquired detection result information includes information indicating that a color defect has been detected. If it is included, the process proceeds to S803; if not, the process proceeds to S805. Then, in S803 when the information indicating that a color defect has been detected is included, it is determined whether the acquired detection result information further includes information indicating that a defect other than the color defect has been detected. If it is included, the process proceeds to S804; if not (when no defect has been detected), the process proceeds to S806. Then, in S804 when both a color defect and a defect other than the color defect have been detected, if the color defect and the defect other than the color defect overlap, the process proceeds to S805; if not, the process proceeds to S806. In this embodiment, defects other than color defects correspond to dot-like defects and line-like defects. For determining whether a color defect and other defects overlap, for example, coordinate information indicating the position of each defect is used. Alternatively, a flag indicating the fact may be assigned to the pixels determined as defect pixels in the defect detection process, and when the flag is set for both the color defect and other defects for the pixels at the same position, it may be determined that both defects overlap.

[0041] In S805, it is determined that there is no density variation in the printing apparatus 190, and a value indicating "no density variation" is added to the history information that accumulates the results of density variation determination, and the history information update process is performed. Here, the reason for determining that there is no density variation is that when other defects overlap with color defects, the color defects can be regarded as being affected by the other defects. Also, in S806, it is determined that there is density variation in the printing apparatus 190, and a value indicating "there is density variation" is added to the above-mentioned history information, and the history information update process is performed. FIGS. 9(a) and 9(b) are diagrams for explaining how the table as the above-mentioned history information is updated. FIG. 9(a) is the table before update, and FIG. 9(b) is the table after update. In the update process, a new result value of density variation determination is inserted into the row of "No1", and each result value before update is sequentially sent to the lower row, and the result value stored in the row of "No20" before update is deleted. Note that although the determination results for 20 pages are accumulated in the tables of FIGS. 9(a) and 9(b), the number of pages to be retained as history information is arbitrary and is not limited to 20 pages. It is sufficient if there is an information amount sufficient to determine whether it is necessary to cause the printing apparatus 190 to execute density correction processing.

[0042] In S807, with reference to the history information of density variation determination updated in S805 or S806, it is determined whether "there is density variation" is continuously recorded a predetermined number of times or more starting from "No1". As a result of the determination, if "there is density variation" is continuously recorded a predetermined number of times or more, the process proceeds to S808; otherwise, S808 is skipped and the process proceeds to S809. Here, assuming that the predetermined number of times is set to 3, when the table in FIG. 9(a) becomes the state of the table in FIG. 9(b), the process proceeds to S808. On the other hand, when the value of "No1" in the updated table is "there is density variation" but is not continuous for a predetermined number of times or more, or when the value of "No1" is "no density variation", the process proceeds to S809.

[0043] In S808, first, the execution of the inspection process in the inspection apparatus 100 is stopped. Then, via the printing apparatus I / F 106 and the inspection apparatus I / F 196, the printing apparatus 190 is instructed to execute density correction processing. Upon receiving this instruction, the printing apparatus 190 stops the execution of the input printing job and immediately executes density correction processing. Specifically, first, the print unit 194 outputs a prescribed chart image. Next, the output result is read by the scanner unit 193 to obtain the density characteristics of the print unit 194. Then, the output density value of the correction LUT used in the gamma correction process is corrected so that desired density characteristics are obtained. After completing the density correction processing, the printing apparatus 190 notifies the inspection apparatus 100 to that effect and resumes the execution of the stopped printing job.

[0044] In S809, it is a check process to determine whether there is a notification from the printing apparatus 190 that the density correction processing has been completed. When a notification that the density correction processing has been completed is received, the process proceeds to S810. Then, in S810, the inspection process is resumed. After resumption, the process returns to the flow of FIG. 4.

[0045] The above is the content of the density correction necessity determination process. Thereby, it becomes possible to cause the printing apparatus 190 to execute density correction processing only when color defects that can be expected to be improved by the density correction processing occur continuously in a portion that does not overlap with other defects. Note that, in the present embodiment, the output result of the chart image is read by the scanner unit 193 of the printing apparatus 190 to correct the correction LUT, but the present invention is not limited thereto. For example, a density sensor, a spectroscopic sensor, an RGB sensor, or the like may be provided near the conveyance path 192 of the printing apparatus 190, and the correction LUT may be corrected using the measured value. Alternatively, the output result of the chart image may be read by the image reading apparatus 105 of the inspection apparatus 100 to correct the correction LUT.

[0046] <Modification Example> Next, as a modified example, a mode will be described in which a state where density fluctuations at a level not reaching "color defect" occur is detected, and the printing apparatus 190 is caused to perform density correction processing preventively before the occurrence of "color defect". Since the flow of the inspection process shown in the flowchart of FIG. 4 is the same, the description thereof will be omitted, and the following will focus on the differences from the above-described embodiment.

[0047] ≪Defect Detection Processing≫ FIG. 10 is a flowchart showing details of the defect detection processing according to this modified example. Here, a state where density fluctuations at a predetermined level not reaching "color defect" in the inspection level related to user selection occur will be referred to as "quasi-color defect". Also, the detection of "quasi-color defect" may be automatically performed as an incidental process, for example, when "color defect" is set as an inspection item. Alternatively, the user may be able to select whether to detect "quasi-color defect" via a UI screen (not shown). Hereinafter, the description will focus on the differences from the flowchart of FIG. 7 of Embodiment 1.

[0048] First, in S1001, similar to S701, alignment between the reference image and the inspection image is performed using a general alignment method. Subsequently, in S1002, the processing is branched depending on whether the inspection item to be executed is a color defect or a quasi-color defect. If the inspection item to be executed is other than a color defect or a quasi-color defect, the process proceeds to S1003, and if the inspection item to be executed is a color defect or a quasi-color defect, the process proceeds to S1004.

[0049] In S1003, similar to S703, a difference image showing the difference between the reference image and the inspection image is generated. In the subsequent S1004, filter processing for emphasizing a specific defect shape is performed on the difference image generated in S1003. Also, in S1005, similar to S705, a color difference image showing the color difference between the reference image and the inspection image is generated.

[0050] In the next S1006, binarization processing is performed on the difference image filtered in S1004 or the color difference image generated in S1005. At this time, when the inspection item to be executed is a quasi-color defect, the threshold value used is a value obtained by multiplying the threshold value used for color defects by a ratio less than 100% determined in advance. For example, if the threshold value used in the binarization processing for detecting color defects is ΔE76 = 6 and the ratio less than 100% determined in advance is 50%, the threshold value used in the binarization processing for detecting quasi-color defects is ΔE76 = 3.

[0051] The subsequent processing is the same as the flow of FIG. 7 described above. That is, it is determined whether there is a pixel having a pixel value "1" among the pixels constituting the binary image generated by the binarization processing (S1007). If it exists, the process proceeds to S1008, and if it does not exist, the process proceeds to S1009. Then, in S1008, as information on the detection result, information indicating that a defect has been detected is stored in the RAM102, and this process ends. Also, in S1009, it is determined that there is no defect corresponding to the inspection item in the inspection image, and information indicating no defect is stored in the RAM102 as information on the detection result, and this process ends.

[0052] The above is the content of the defect detection process according to this modification example. After the defect detection process for all the set inspection items has ended, the process proceeds to the inspection result display process (No in S406, S407), but it is not necessary to display the result of detection / non-detection of quasi-color defects.

[0053] ≪Density correction necessity determination process≫ FIG. 11 is a flowchart showing the details of the density correction necessity determination process according to this modification example. Hereinafter, the description will be centered on the differences from the flow of FIG. 8 of the first embodiment.

[0054] In S1101, similar to S801, the information of the detection result stored in S1008 or S1009 of the above-described defect detection process is read from the RAM 102. Then, in S1102 to S1104, the process is branched based on the read detection result information. First, in S1102, if the acquired detection result information includes information indicating that a color defect or a quasi-color defect has been detected, the process proceeds to S1103; otherwise, it proceeds to S1105. Then, in S1103 when a color defect or a quasi-color defect has been detected, if the acquired detection result information further includes information indicating that a defect other than the color defect or the quasi-color defect has been detected, the process proceeds to S1104; otherwise (when no defect has been detected), the process proceeds to S1106. Then, in S1104 when both a color defect or a quasi-color defect and other defects have been detected, if the color defect or the quasi-color defect and other defects overlap, the process proceeds to S1105; if they do not overlap, the process proceeds to S1106.

[0055] In S1105, it is determined that no density variation has occurred in the printing apparatus 190, and an update process is performed to add a value indicating "no density variation" to the history information for accumulating the result of the density variation determination.

[0056] The subsequent processing is the same as the flow of FIG. 8 described above. That is, in S1105, it is determined that no density variation has occurred in the printing apparatus 190, and an update process is performed to add a value indicating "no density variation" to the above-described history information. Also, in S1106, it is determined that a density variation has occurred in the printing apparatus 190, and an update process is performed to add a value indicating "density variation present" to the above-described history information. Then, in S1107, the history information of the density variation determination updated in S1105 or S1106 is referred to, and it is determined whether "density variation present" has been continuous from "No1" for a predetermined number of times or more. As a result of the determination, if "density variation present" has been continuous for a predetermined number of times or more, the process proceeds to S1108, where the execution of the inspection process is stopped and an instruction to execute the density correction process for the printing apparatus 190 is given. Then, when a notification indicating that the density correction process has been completed is received from the printing apparatus 190 (Yes in S1109), the inspection process is resumed (S1110).

[0057] The above is the content of the density correction necessity determination process according to this modification example.

[0058] By the above processing, it is possible to detect a "quasi-color defect" in which density fluctuations at a level that do not meet the "color defect" occur, and to cause the printing apparatus 190 to perform density correction processing preventively before the "color defect" occurs.

[0059] As described above, according to this embodiment, it is possible to execute density correction processing at an appropriate timing based on density fluctuations of the printing apparatus, and to preferably suppress color defects while suppressing execution of unnecessary density correction processing.

[0060] <Other Embodiments> The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiment to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. Further, it can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Claims

1. An information processing apparatus for inspecting printed matter, an acquisition means for acquiring a read image obtained by reading a printed sheet output from a printing apparatus and a reference image serving as a reference in an inspection of the read image; a detection means for detecting a printing defect based on the acquired read image and the reference image; an instruction means for instructing the printing apparatus to execute density correction processing based on the detection results of the printing defects for a plurality of the printed sheets; characterized by comprising: the printing defects include the color abnormality in which the target color in the read image is not reproduced and other abnormalities other than the color abnormality; when the color abnormalities occur continuously at positions where they do not overlap with the other abnormalities, the instruction means instructs the printing apparatus to execute the density correction processing An information processing apparatus characterized by the above.

2. The instruction means creates history information for recording the presence or absence of the color abnormality in units of sheets of the printed sheet, and when the presence of the color abnormality is continuously recorded a predetermined number of times or more in the history information, instructs the printing apparatus to execute the density correction processing. The information processing apparatus according to claim 1, characterized by the above.

3. When the color abnormality and the other abnormality are detected by the detection means, the instruction means records "with density variation" in the history information when the color abnormality occurs at a position where it does not overlap with the other abnormality, records "without density variation" in the history information when the color abnormality occurs at a position where it overlaps with the other abnormality, The information processing apparatus according to claim 2, characterized by the above.

4. The information processing apparatus according to claim 3, characterized in that the other abnormality is a dot-like defect or a line-like defect.

5. The detection means generates a difference image showing the difference between the read image and the reference image, and detects the color abnormality for each pixel from the image showing the difference. The information processing apparatus according to any one of claims 1 to 4, characterized by the above.

6. The color of each pixel of the read image and the reference image is represented in the RGB color space, For the detection of the color abnormality, the detection means converts the color of each pixel represented in the RGB color space into the L*a*b* color space, and detects using a first difference image obtained by evaluating the color difference for each pixel based on the Euclidean distance in the L*a*b* color space. For the other abnormalities, after changing the color of each pixel represented in the RGB three channels, the pixel values are compared for corresponding pixels, and detection is performed using a second difference image obtained by acquiring the difference values generated by the comparison for each pixel. The information processing apparatus according to claim 5, characterized in that.

7. The detection means performs binarization processing using a threshold value on the difference image to detect the color abnormality and the other abnormalities, the information processing apparatus according to claim 5 or 6, characterized in that.

8. The binarization processing is a process of assigning a value indicating that there is a defect if each difference value in the difference image is equal to or greater than the threshold value, and assigning a value indicating that there is no color abnormality if it is less than the threshold value, the information processing apparatus according to claim 7, characterized in that.

9. The detection means further includes setting means for setting the type of the color abnormality detected by the detection means, When the color abnormality is set by the setting means, the detection means further detects a color variation at a predetermined level that does not meet the color abnormality, When the color variations occur continuously at positions that do not overlap with the other abnormalities, the instruction means instructs the printing apparatus to execute the density correction processing. The information processing apparatus according to claim 7 or 8, characterized in that.

10. The detection means performs the binarization processing using, as a threshold value corresponding to the predetermined level, a value obtained by multiplying a value less than 100% predetermined for the threshold value used in the binarization processing for detecting the color abnormality, to detect the color variation, the information processing apparatus according to claim 9, characterized in that.

11. The detection means further includes output means for displaying a UI screen including information associating the type and the occurrence position of the detected color abnormality, The output means does not perform the display for the color variation, The information processing apparatus according to claim 9 or 10, characterized in that.

12. A printing system having a printing apparatus and an inspection apparatus for inspecting printed matter, The inspection apparatus is An acquisition means for acquiring a read image obtained by reading a printed sheet output from the printing apparatus and a reference image serving as a reference in an inspection of the read image; A detection means for detecting a printing defect based on the acquired read image and the reference image; An instruction means for instructing the printing apparatus to execute density correction processing based on the detection results of the printing defects for a plurality of the printed sheets; Comprising; The printing defect includes the color abnormality in which the target color is not reproduced in the read image and other abnormalities other than the color abnormality; When the color abnormality occurs continuously at a position where it does not overlap with the other abnormality, the instruction means instructs the printing apparatus to execute the density correction processing; The printing apparatus executes the density correction processing according to the instruction; A printing system characterized by the above.

13. A control method for a printing system having a printing apparatus and an inspection apparatus for inspecting printed matter, wherein, In the inspection apparatus, Acquire a read image obtained by reading a printed sheet output from the printing apparatus and a reference image serving as a reference in an inspection of the read image, Detect a printing defect based on the acquired read image and the reference image, Based on the detection results of the printing defects for a plurality of the printed sheets, instruct the printing apparatus to execute density correction processing, The printing defect includes the color abnormality in which the target color is not reproduced in the read image and other abnormalities other than the color abnormality, When the color abnormality occurs continuously at a position where it does not overlap with the other abnormality, instruct the printing apparatus to execute the density correction processing, In the printing apparatus, Execute the density correction processing according to the instruction from the inspection apparatus, A control method for a printing system characterized by the above.

14. A program for causing a computer to function as the information processing apparatus according to any one of claims 1 to 11.

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