JP2016178557A - Image processing apparatus, correction method and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing apparatus, a correction method and a program that can improve precision of correction for a density defect.SOLUTION: An image processing apparatus comprises: a read image acquisition part 401 which acquires a read image by reading printed matter including a first region where no color information is printed, a second region where color information for printing density defect detection is printed, and a third region where color information to be used to generate color conversion information is printed; a first detection part 403 which detects a read density defect place on the read image using a first corresponding region as a region on a read image corresponding to the first region; a first correction part 405 which corrects the detected read density defect place on the read region so as to generate a first correction image; a second detection part 407 which detects the printing density defect place on the first correction image using a second corresponding region as a region on the first correction image corresponding to the second region; and a second correction part 409 which corrects the detected printing density defect place on the first correction image so as to generate a second correction image.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image processing apparatus, a correction method, and a program.

  2. Description of the Related Art Conventionally, a technique for generating a color profile used for color conversion from CMYK to different color spaces such as RGB, or color conversion (calibration) for suppressing color fluctuations due to machine differences or environments.

  In general, color profiles are generated by printing, reading, and measuring colors in color charts with multiple color patches. Color information before and after processing It is performed by associating with.

  By the way, when printing a color chart, a print density defect such as print unevenness may occur, or when a printed color chart is read, a read density defect such as read unevenness may occur. If a color profile is generated by using a color chart in which a print density defect has occurred or a read image of a color chart in which a read density defect has occurred as it is, the accuracy of color conversion is significantly deteriorated.

  For this reason, for example, in Patent Document 1, a color patch and a patch for detecting color unevenness are alternately arranged on the color chart, and after reading the color chart, the density of the patch for detecting color unevenness is uniform. A technique for eliminating the influence of color unevenness by performing correction processing on a read image of a color chart is disclosed.

  However, in the conventional technology as described above, since the print density defect that occurred in the printing stage and the read density defect that occurred in the reading stage are corrected together, the correction accuracy tends to be low.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an image processing apparatus, a correction method, and a program capable of improving the accuracy of correction for density defects.

  In order to solve the above-described problems and achieve the object, an image processing apparatus according to an aspect of the present invention has a first area where color information is not printed, and color information for detecting a print density defect is printed. A read image acquisition unit that acquires a read image obtained by reading a printed matter including a second area and a third area on which color information used to generate color conversion information is printed; and the first area corresponding to the first area A first detection unit configured to detect, on the read image, a read density defective portion that is a density defective portion generated in the read image by using a first corresponding region that is a region on the read image; The read density defect portion thus corrected is corrected on the read image to generate a first correction image, and the first correction image corresponding to the second area is the first correction image. Using the corresponding area of 2 occurs in the printed matter at the time of printing A second detection unit for detecting a print density defect portion, which is a density defect portion, on the first correction image; and correcting the detected print density defect portion on the first correction image; A second correction unit that generates a corrected image.

  According to the present invention, it is possible to improve the accuracy of correction for density defects.

FIG. 1 is a schematic diagram illustrating an example of a printed matter inspection system according to the present embodiment. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the printed matter inspection apparatus according to the present embodiment. FIG. 3 is a block diagram illustrating an example of the configuration of the printing apparatus and the printed matter inspection apparatus according to the present embodiment. FIG. 4 is a diagram illustrating an example of the RIP image of the color chart of the present embodiment. FIG. 5 is a block diagram illustrating an example of the configuration of the generation unit of the present embodiment. FIG. 6 is an explanatory diagram of an example of streak (line) detection by the first detection unit of the present embodiment. FIG. 7 is an explanatory diagram of an example of unevenness detection by the first detection unit of the present embodiment. FIG. 8 is a diagram illustrating an example of a target density selection screen according to the present embodiment. FIG. 9 is an explanatory diagram of an example of the color measurement method of the present embodiment. FIG. 10 is a flowchart illustrating an example of a flow of color profile generation processing performed in the printed matter inspection system according to the present embodiment. FIG. 11 is a flowchart illustrating an example of the flow of the process of step S105 in the flowchart of FIG. FIG. 12 is a flowchart showing a detailed example of the processing of steps S203 and S205 in the flowchart of FIG. FIG. 13 is a flowchart illustrating an example of the flow of the procedure of the image inspection process performed in the printed matter inspection system of the present embodiment. FIG. 14 is a flowchart illustrating an example of the flow of the process of step S411 in the flowchart of FIG. FIG. 15 is a flowchart illustrating an example of the flow of the process of step S413 in the flowchart of FIG. FIG. 16 is an explanatory diagram illustrating an example of a correction method according to the second modification. FIG. 17 is an explanatory diagram of an example of a color chart of the third modification.

  Hereinafter, embodiments of an image processing apparatus, a correction method, and a program according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic diagram illustrating an example of a printed matter inspection system 1 according to the present embodiment. As illustrated in FIG. 1, the printed matter inspection system 1 includes a printing device 100, a printed matter inspection device 200 (an example of an image processing device), and a stacker 300.

  The printing apparatus 100 includes an operation panel 101, photosensitive drums 103Y, 103M, 103C, and 103K, a transfer belt 105, a secondary transfer roller 107, a paper feeding unit 109, a conveyance roller pair 111, and a fixing roller 113. , And an inversion path 115.

  The operation panel 101 is an operation display unit that performs various operation inputs to the printing apparatus 100 and displays various screens.

  Each of the photosensitive drums 103Y, 103M, 103C, and 103K forms a toner image by performing an image forming process (charging process, exposure process, developing process, transfer process, and cleaning process), and the formed toner image. Is transferred to the transfer belt 105. In this embodiment, a yellow toner image is formed on the photoreceptor drum 103Y, a magenta toner image is formed on the photoreceptor drum 103M, a cyan toner image is formed on the photoreceptor drum 103C, and the photoreceptor drum 103K is formed. Although a black toner image is formed, the present invention is not limited to this.

  The transfer belt 105 conveys the toner image (full color toner image) transferred from the photosensitive drums 103Y, 103M, 103C, and 103K to the secondary transfer position of the secondary transfer roller 107. In this embodiment, a yellow toner image is first transferred to the transfer belt 105, and then a magenta toner image, a cyan toner image, and a black toner image are sequentially superimposed and transferred. However, the present invention is not limited to this. Is not to be done.

  The paper feeding unit 109 stores a plurality of recording papers, and feeds the recording papers.

  The transport roller pair 111 transports the recording paper fed by the paper feed unit 109 in the direction of arrow s on the transport path a.

  The secondary transfer roller 107 collectively transfers the full-color toner image conveyed by the transfer belt 105 onto the recording paper conveyed by the conveyance roller pair 111 at the secondary transfer position.

  The fixing roller 113 fixes the full color toner image on the recording paper by heating and pressing the recording paper on which the full color toner image is transferred.

  In the case of single-sided printing, the printing apparatus 100 discharges a printed matter, which is a recording sheet on which a full-color toner image is fixed, to the printed matter inspection apparatus 200. On the other hand, in the case of double-sided printing, the printing apparatus 100 sends the recording paper on which the full-color toner image is fixed to the reverse path 115.

  The reverse path 115 reverses the front and back surfaces of the recording paper by switching back the fed recording paper and conveys it in the direction of the arrow t. The recording paper conveyed by the reverse path 115 is re-conveyed by the conveying roller pair 111, the full-color toner image is transferred to the surface opposite to the previous one by the secondary transfer roller 107, fixed by the fixing roller 113, and printed. The paper is discharged to the printed product inspection apparatus 200.

  The printed matter inspection apparatus 200 includes reading units 201A and 201B and an operation panel 211.

  The operation panel 211 is an operation display unit that performs various operation inputs to the printed material inspection apparatus 200 and displays various screens. Note that the operation panel 211 may be omitted. In this case, the operation panel 101 may also serve as the operation panel 211, or an externally connected PC (Personal Computer) may serve as the operation panel 211.

  The reading unit 201A optically reads one surface of the printed material discharged from the printing apparatus 100, and the reading unit 201B optically reads the other surface of the printed material discharged from the printing device 100. The reading units 201A and 201B can be realized by, for example, a line scanner. Then, the printed matter inspection apparatus 200 discharges the printed matter that has been read to the stacker 300.

  The stacker 300 includes a tray 301. The stacker 300 stacks the printed material discharged by the printed material inspection apparatus 200 on the tray 301.

  FIG. 2 is a block diagram illustrating an example of a hardware configuration of the printed matter inspection apparatus 200 according to the present embodiment. As shown in FIG. 2, the printed matter inspection apparatus 200 has a configuration in which a controller 910 and an engine unit (Engine) 960 are connected by a PCI bus. The controller 910 is a controller that controls the overall control, drawing, communication, and input from the operation display unit 920 of the printed matter inspection apparatus 200. The engine unit 960 is an engine that can be connected to the PCI bus, and is, for example, a scanner engine such as a scanner. The engine unit 960 includes an image processing part such as error diffusion and gamma conversion in addition to the engine part.

  The controller 910 includes a CPU (Central Processing Unit) 911, a North Bridge (NB) 913, a system memory (MEM-P) 912, a South Bridge (SB) 914, a local memory (MEM-C) 917, and an ASIC. (Application Specific Integrated Circuit) 916 and a hard disk drive (HDD) 918 are provided, and the North Bridge (NB) 913 and the ASIC 916 are connected by an AGP (Accelerated Graphics Port) bus 915. The MEM-P 912 further includes a ROM 912a and a RAM 912b.

  The CPU 911 performs overall control of the printed matter inspection apparatus 200, has a chip set including the NB 913, the MEM-P 912, and the SB 914, and is connected to other devices via the chip set.

  The NB 913 is a bridge for connecting the CPU 911 to the MEM-P 912, SB 914, and the AGP bus 915, and includes a memory controller that controls reading and writing to the MEM-P 912, a PCI master, and an AGP target.

  The MEM-P 912 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, a memory for drawing printers, and the like, and includes a ROM 912a and a RAM 912b. The ROM 912a is a read-only memory used as a memory for storing programs and data, and the RAM 912b is a writable and readable memory used as a program / data development memory, a printer drawing memory, and the like.

  The SB 914 is a bridge for connecting the NB 913 to a PCI device and a peripheral device. The SB 914 is connected to the NB 913 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 916 is an IC (Integrated Circuit) for image processing having hardware elements for image processing, and has a role of a bridge for connecting the AGP bus 915, the PCI bus, the HDD 918, and the MEM-C 917, respectively. The ASIC 916 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 916, a memory controller that controls the MEM-C 917, and a plurality of DMACs (Direct Memory) that perform image data rotation by hardware logic and the like. Access Controller) and a PCI unit that performs data transfer between the engine unit 960 via the PCI bus. The ASIC 916 is connected to a USB 940 and an IEEE 1394 (the Institute of Electrical and Electronics Engineers 1394) interface (I / F) 950 via a PCI bus. The operation display unit 920 is directly connected to the ASIC 916.

  The MEM-C 917 is a local memory used as a copy image buffer and a code buffer, and the HDD 918 is a storage for storing image data, programs, font data, and forms.

  The AGP bus 915 is a bus interface for a graphics accelerator card proposed for speeding up graphics processing. The AGP bus 915 speeds up the graphics accelerator card by directly accessing the MEM-P 912 with high throughput. It is.

  FIG. 3 is a block diagram illustrating an example of the configuration of the printing apparatus 100 and the printed matter inspection apparatus 200 according to the present embodiment. As illustrated in FIG. 3, the printing apparatus 100 includes a RIP (Raster Image Processor) unit 121, a print control unit 123, and a printing unit 125. The printed matter inspection apparatus 200 includes a reading unit 201, a generation unit 203, a storage unit 205, a master image generation unit 207 (an example of a color conversion unit), and an inspection unit 209. In this embodiment, it is assumed that the printing apparatus 100 and the printed material inspection apparatus 200 are connected by a local interface such as USB (Universal Serial Bus) or PCIe (Peripheral Component Interconnect Express). The connection form between the apparatus 100 and the printed matter inspection apparatus 200 is not limited to this.

  The RIP unit 121 and the printer control unit 123 may be realized by causing a processing device such as a CPU (Central Processing Unit) to execute a program, that is, by software, or by hardware such as an IC or an ASIC. Alternatively, software and hardware may be used in combination. The printing unit 125 is realized by, for example, the photosensitive drums 103Y, 103M, 103C, and 103K, the transfer belt 105, the secondary transfer roller 107, and the fixing roller 113, but is not limited thereto. As described above, in this embodiment, an image is printed by an electrophotographic method, but the present invention is not limited to this, and an image may be printed by an inkjet method.

  The reading unit 201 includes reading units 201A and 201B, and can be realized by the engine unit 960, for example. The generation unit 203, the master image generation unit 207, and the inspection unit 209 can be realized by, for example, the CPU 911, the system memory 912, the ASIC 916, the operation display unit 920, and the like. The storage unit 205 can be realized by the system memory 912, for example.

  In the following, the operations of the printing apparatus 100 and the printed matter inspection apparatus 200 will be described first with respect to the generation operation of a color profile (an example of color conversion information) used for color conversion to a different color space, and then the generated color An image inspection operation using the master image after performing color conversion of the master image using the profile will be described. In the present embodiment, a color profile for color conversion from the CMYK color space to the RGB color space will be described as an example of the color profile. However, the present invention is not limited to this.

  First, a color profile generation operation will be described. In this embodiment, the CMYK value of the color patch on the RIP image of the color chart and the RGB value of the read image of the color chart obtained by reading the printed matter on which the RIP image of the color chart is read are measured, and for each color patch, A color profile is generated by associating CMYK values with RGB values.

  The RIP unit 121 performs RIP processing on the print data of the color chart, and generates a RIP image (bitmap image) of the color chart. The color chart print data may be stored in advance by the printing apparatus 100 or may be acquired from the printing apparatus 100.

  In this embodiment, the RIP image of the color chart is CMYK RIP image data, and each pixel of each RIP image data of C (Cyan), M (Magenta), Y (Yellow), and K (Black) is 1 bit. Although it is 600 dpi, it is not limited to this.

  Note that the RIP image of the color chart of the present embodiment includes a first area where no color information is arranged, a second area where color information for detecting print density defects is arranged, and colors used for generating a color profile. It includes a third area where information is arranged. A print density defect is a density defect that occurs during printing, and includes unevenness and streaks (lines). Specifically, the first area is arranged so that there are areas constituting the first area in the vertical and horizontal directions of the RIP image of the color chart, and the second area is the vertical direction and the In the horizontal direction, at least the section of the third area and the area constituting the second area exist.

  FIG. 4 is a diagram illustrating an example of the RIP image of the color chart of the present embodiment. In the example shown in FIG. 4, the marker 501 is arranged in four places in the RIP image of the color chart, and is used to generate a color profile in the third area 502 that is an area inside the four markers 501. Color patches are arranged in a grid pattern. The four markers 501 serve as a reference for grasping the third region 502, and one of the markers 501 has a different pattern from the other in order to grasp the direction of the third region 502.

  A second region 503 is arranged on the outer periphery of the third region 502. Therefore, the second area 503 is arranged so that at least the section of the third area 502 and the area constituting the second area 503 exist in both the vertical direction and the horizontal direction of the RIP image of the color chart. ing. Since the second area 503 is an area for detecting a print density defect, in this embodiment, the second area 503 is preferably composed of a uniform color of mixed colors of all CMYK colors such as gray. However, the present invention is not limited to this. Absent.

  The outer periphery of the second area 503 is all the first area 504. Therefore, the first area 504 is arranged so that there are areas constituting the first area in both the vertical direction and the horizontal direction of the RIP image of the color chart. The first area 504 is an area for detecting a reading density defect, and no color information is arranged. The reading density defect is a density defect occurring at the time of reading, and includes unevenness and streaks (lines).

  The print control unit 123 transmits the color chart RIP image generated by the RIP unit 121 to the printed matter inspection apparatus 200 and also to the printing unit 125.

  The printing unit 125 executes a printing process such as an image forming process, prints a print image based on the RIP image of the color chart on a recording sheet, and generates a printed matter of the color chart.

  The reading unit 201 reads the color chart printed matter generated by the printing apparatus 100 and generates a read image of the color chart (hereinafter simply referred to as “read image”). Specifically, the reading unit 201 optically reads the print image from the printed material on which the print image based on the RIP image of the color chart is printed, and generates a read image. In the present embodiment, the read image is RGB image data, and each pixel of the R, G, and B image data is 8-bit 200 dpi. However, the present invention is not limited to this.

  The generation unit 203 generates a color profile using the color chart RIP image transmitted from the printing apparatus 100 and the read image generated by the reading unit 201, and stores the color profile in the storage unit 205.

  FIG. 5 is a block diagram illustrating an example of the configuration of the generation unit 203 of this embodiment. As illustrated in FIG. 5, the generation unit 203 includes a read image acquisition unit 401, a first detection unit 403, a first correction unit 405, a second detection unit 407, and a second correction unit 409. , A RIP image acquisition unit 411 and a color conversion information generation unit 413.

  The read image acquisition unit 401 acquires the read image generated by the reading unit 201. That is, the read image acquisition unit 401 prints the first area where the color information is not printed, the second area where the color information for detecting the print density defect is printed, and the color information used for generating the color profile. A read image obtained by reading the printed material including the third area is obtained.

  The first detection unit 403 uses the first corresponding area, which is an area on the read image corresponding to the first area, to read a read density defect portion that is a density defect portion generated in the read image at the time of reading. Detect above. The first area is an area in which color information is not printed and a print density defect does not occur, but a read density defect may occur. For this reason, it is possible to detect a density defect due to a reading density defect alone from the first corresponding region.

  Specifically, the first detection unit 403 detects a defective reading density portion based on at least one of density variation and variation in the first corresponding region in the sub-scanning direction of the read image. This is because the reading density defect often occurs in parallel with the arrangement of CCD (Charge Coupled Device) image sensors of the reading unit 201, that is, in the sub-scanning direction of the read image.

  For example, the first detection unit 403 divides the read image into a plurality of first sections in the sub-scanning direction of the read image, and the first correspondence included in the first section for each first section. A first average density which is an average density of the partial area of the area is calculated. Note that the first detection unit 403 calculates, for each first section, the density distribution of the partial area of the first corresponding area included in the first section, and excludes outliers of the density distribution. The average density of 1 may be calculated. In this way, even if an image defect such as dirt occurs, this influence can be eliminated.

  Then, the first detection unit 403 obtains the fluctuation of the first average density of the adjacent first section in the order of the sub-scanning direction, and the first average density with respect to the previous first section as a reading density defect portion. The first section in which the fluctuation of the number exceeds the first threshold is detected. Accordingly, it is possible to detect the first section in which a streak (line) is generated by reading the read image. Note that the value of the first threshold value may be set in accordance with how much stripe (line) is detected.

  FIG. 6 is an explanatory diagram of an example of streak (line) detection by the first detection unit 403 of the present embodiment. The read image in which the streak (line) 601 is generated and the first average density of the read image are illustrated. A correspondence with the density distribution 611 is shown.

  In the example shown in FIG. 6, the x direction (x coordinate) is the sub-scanning direction of the read image, and the y direction (y coordinate) is the main scanning direction of the read image. In the example shown in FIG. 6, the width of the first section is 3 pixels in the x direction. That is, the first section is a rectangle having a width of 3 pixels, a length, and a read image short side length. A density distribution 611 represents the first average density in each first section as a line graph. The width of the line (line) 601 is assumed to be 1.2 pixels in the x direction.

  In the example illustrated in FIG. 6, the first average density in the first section in which the streak (line) 601 is generated is significantly smaller than the first average density in the other first sections. For this reason, when the difference of the first average density of the adjacent first sections in the order of the x direction (the order of the x coordinate is small), the first section where the streak (line) 601 is generated is Since the difference in the first average density with respect to the previous first interval exceeds the first threshold, it is possible to detect the first interval in which streaks (lines) are generated by reading the read image.

  Further, the first detection unit 403 obtains a variation in the first average density of the plurality of first sections, and the difference between the first target density and the first average density based on the variation sets the second threshold value. The first section that exceeds is detected. Accordingly, it is possible to detect the first section in which unevenness is caused by reading the read image. Note that the value of the second threshold value may be set according to how much unevenness is detected.

  The first target density is determined by the user when the variation of the first average density of the plurality of first sections exceeds the third threshold, and the first target density is plural when the variation does not exceed the third threshold. The mode value of the first average density of the first interval of Note that the value of the third threshold value may be set according to how much unevenness is detected.

  FIG. 7 is an explanatory diagram of an example of unevenness detection by the first detection unit 403 of the present embodiment, and shows the correspondence between a read image in which unevenness occurs and the density distribution 621 of the first average density of the read image. Show.

  In the example shown in FIG. 7, the x direction (x coordinate) is the sub-scanning direction of the read image, and the y direction (y coordinate) is the main scanning direction of the read image. In the example shown in FIG. 7, the width of the first section is 3 pixels in the x direction. That is, the first section is a rectangle having a width of 3 pixels, a length, and a read image short side length. A first average density distribution 621 is a line graph representing the first average density of each first section.

  Since the detection of unevenness is performed based on the difference between the first target density (density in which the unevenness does not occur in the read image) that is the density after correction and the first average density, first, the first target density is determined. decide. The first detection unit 403 obtains the variance and mode value of the density distribution 621 of the first average density and compares it with the third threshold value.

  When the dispersion of the density distribution 621 exceeds the third threshold value, it is expected that there is unevenness that occupies a wide area of the read image. In this case, since it is difficult to automatically determine the first target density, the user selects it. Specifically, the first detection unit 403 displays a target density selection screen on the operation panel 211 and determines the first target density based on a user input from the operation panel 211.

  FIG. 8 is a diagram illustrating an example of a target density selection screen according to the present embodiment. In the example shown in FIG. 8, the target density selection screen shows the correspondence between the read image and the density distribution of the first average density of the read image as shown in FIG. 7, and the first target density candidate. A plurality of target candidate densities 651 and an operation button 652 for selecting the first target density are arranged. Examples of the target candidate density 651 include an inflection point of the density distribution 621 and a local maximum value of a histogram obtained by counting the number of first sections corresponding to the first target density for each first target density.

  Then, the first detection unit 403 sets the target candidate density 651 selected by the user with the operation button 652 as the first target density. In addition, when the read image is inappropriate or there is no appropriate option, the user can re-generate or cancel the color profile by selecting cancel with the operation button 652.

  On the other hand, when the variance of the density distribution 621 does not exceed the third threshold, the first detection unit 403 sets the mode value of the density distribution 621 as the first target density.

  Then, the first detection unit 403 obtains a difference between the first average density and the first target density in the first interval for each first interval, and the obtained difference exceeds the second threshold value. By detecting one section, it is possible to detect the first section in which unevenness is caused by reading the read image.

  The first correction unit 405 corrects the read density defect portion detected by the first detection unit 403 on the read image, and generates a first correction image.

  Specifically, when the first detection unit 403 detects a first section in which a streak (line) is generated, the first correction unit 405 sets the detected first section to the previous first Correct to the interval. For example, in the case of the example illustrated in FIG. 6, the first correction unit 405 determines the first section in which the streak (line) 601 detected by the first detection unit 403 is generated as 1 of the first section. Replace with the previous first interval. That is, the first correction unit 405 copies the first section immediately before the first section to the first section in which the streak (line) 601 is generated.

  In addition, when the first detection unit 403 detects the first section in which the unevenness is generated, the first correction unit 405 corrects the detected density of the first section to the first target density. For example, the first correction unit 405 corrects the detected density of each pixel in the first section to the first target density using Expression (1).

  P ′ = P × (T / A) (1)

  Here, P ′ is the corrected pixel value, P is the corrected pixel value, T is the target density, and A is the first average density in the first section to be corrected.

  However, the correction method to the first target density is not limited to the above formula (1), and any correction method may be used as long as an equivalent effect can be obtained.

  The second detection unit 407 uses the second corresponding area that is the area on the first corrected image corresponding to the second area, and print density that is a density defect portion that has occurred in the printed matter of the color chart during printing. A defective portion is detected on the first corrected image. The second area is an area in which color information is printed, and there is a possibility that a print density defect may occur, and a read density defect may also occur. However, in the first corrected image, since the reading density defect is corrected by the first correction unit 405, the density defect due to the printing density defect alone can be detected from the second corresponding region.

  Specifically, the second detection unit 407 detects a defective print density portion based on at least one of density variation and variation in the second corresponding area in the sub-scanning direction of the printed matter of the color chart in the read image. To detect. This is because a print density defect often occurs in the transport direction of a printed image, that is, in the sub-scanning direction of the printed matter of the color chart. Note that the printing density defect detection method by the second detection unit 407 is the same as the reading density defect detection method by the first detection unit 403.

  For example, the second detection unit 407 divides the first correction image into a plurality of second sections in the sub-scanning direction of the printed matter of the color chart in the first correction image. A second average density that is an average density of the partial areas of the second corresponding area included in the second section is calculated. The second detection unit 407 calculates, for each second section, the density distribution of the partial region of the second corresponding area included in the second section, and excludes outliers of the density distribution. An average density of 2 may be calculated. In this way, even if an image defect such as dirt occurs, this influence can be eliminated.

  Then, the second detection unit 407 obtains the variation in the second average density in the adjacent second section in the order of the sub-scanning direction, and determines the second average density for the previous second section as the print density defect portion. The second interval in which the fluctuation of the second value exceeds the fourth threshold is detected. As a result, it is possible to detect the second section in which a streak (line) is generated by printing the printed matter of the color chart. Note that the value of the fourth threshold value may be set in accordance with how much stripe (line) is detected.

  In addition, the second detection unit 407 obtains the variation in the second average density of the plurality of second sections, and the difference between the second target density and the second average density based on the variation sets the fifth threshold value. A second interval that exceeds is detected. Thereby, the 2nd area in which the nonuniformity has arisen by printing of the printed matter of a color chart is detectable. Note that the value of the fifth threshold may be set according to how much unevenness is detected.

  The second target density is determined by the user when the variation in the second average density of the plurality of second sections exceeds the sixth threshold, and the second target density is determined when the variation does not exceed the sixth threshold. The mode value of the second average density of the second interval of the second interval may be used. Note that the value of the sixth threshold value may be set according to how much unevenness is detected. A specific method for determining the second target density is the same as the method for determining the first target density, and thus description thereof is omitted.

  The second correction unit 409 corrects the print density defect portion detected by the second detection unit 407 on the first correction image, and generates a second correction image.

  Specifically, when the second detection unit 405 detects the second section in which the streak (line) is generated, the second correction unit 409 uses the detected second section as the previous second. Correct to the interval. Note that a specific method of correcting a line (line) is the same as that of the first correction unit 405, and thus the description thereof is omitted.

  In addition, when the second detection unit 407 detects the second section in which the unevenness is generated, the second correction unit 409 corrects the detected density of the second section to the second target density. Note that a specific unevenness correction method is the same as that of the first correction unit 405, and thus the description thereof is omitted.

  The RIP image acquisition unit 411 acquires the RIP image of the color chart transmitted from the printing apparatus 100. In the present embodiment, the RIP image acquisition unit 411 converts the resolution of the acquired RIP image of the color chart from 600 dpi to 200 dpi and reduces the size in order to smooth halftone dots and increase the processing speed. The RIP image of the color chart has not been printed or read, and therefore no density defect has occurred, so the density defect is not corrected.

  The color conversion information generation unit 413 generates a color profile using a third corresponding area that is an area on the second corrected image corresponding to the third area. Specifically, the color conversion information generation unit 413 obtains RGB colorimetric values by measuring the color patches on the third corresponding area of the second corrected image, and also obtains the RIP image of the RIP image of the color chart. CMYK colorimetric values are obtained by measuring the color patches in the area 3.

  Note that the color conversion information generation unit 413 specifies the position of the color patch based on the marker 501, and acquires an average of color measurement range pixel values of a certain size on the color patch as a color measurement value. The average value is obtained in order to cancel errors in printing and reading such as noise. In the case of the example illustrated in FIG. 9, the color conversion information generation unit 413 acquires an average of pixel values in the color measurement range 661 out of the color patches 662 as a color measurement value.

  The color conversion information generation unit 413 generates a color profile for color conversion from the CMYK color space to the RGB color space by associating the acquired RGB colorimetric values with the CMYK colorimetric values, and the storage unit 205. To remember.

  Next, an image inspection operation using a master image that has been color-converted using a color profile will be described.

  The RIP unit 121 receives print data from an external device such as a host device, performs RIP processing on the received print data, and generates a RIP image. In the present embodiment, the print data includes data described in a page description language (PDL) such as PostScript (registered trademark), image data in a TIFF (Tagged Image File Format) format, and the like. However, the present invention is not limited to this.

  In this embodiment, the RIP image is CMYK RIP image data, and each pixel of the RIP image data of C (Cyan), M (Magenta), Y (Yellow), and K (Black) is 1 bit at 600 dpi. It shall be, but is not limited to this.

  The print control unit 123 transmits the RIP image generated by the RIP unit 121 to the printed matter inspection apparatus 200 and also to the printing unit 125. Further, the print control unit 123 uses the inspection result transmitted (feedback) from the printed material inspection apparatus 200 to specify, for example, the discharge destination of the printed material that has not passed the quality inspection for the stacker 300 or the quality inspection. The printed material that does not pass is marked, or the printing unit 125 is instructed to perform replacement printing.

  The printing unit 125 executes a print processing process such as an image forming process, prints a print image based on the RIP image on a recording sheet, and generates a printed matter.

  The reading unit 201 reads the printed matter generated by the printing unit 125 and generates an inspection image. Specifically, the reading unit 201 optically reads the print image from the printed material on which the print image based on the RIP image is printed, and generates an inspection image. In the present embodiment, the inspection image is RGB image data, and each pixel of the R, G, and B image data has an 8-bit 200 dpi, but is not limited thereto.

  The master image generation unit 207 acquires the RIP image transmitted from the printing apparatus 100 and generates a master image based on the RIP image. Specifically, the master image generation unit 207 converts the acquired RIP image from 1 bit of each CMYK pixel to 8 bits of each CMYK pixel, converts the resolution from 600 dpi to 200 dpi, and stores it in the storage unit 205 by the color profile generation operation. Using the color profile for color conversion from the CMYK color space to the RGB color space, color conversion is performed from 8 bits of CMYK pixels to 8 bits of RGB to obtain a master image. Then, the master image generation unit 207 sets a reference point in the master image. The reference point is a feature point that serves as a reference for aligning the master image and the read image during image inspection.

  The inspection unit 209 compares the inspection image generated by the reading unit 201 with the master image generated by the master image generation unit 207, and inspects the quality of the printed matter generated by the printing apparatus 100. Specifically, the inspection unit 209 aligns the inspection image and the master image, compares the inspection image and the master image in units of pixels, generates a difference image composed of pixel value difference values, Based on the magnitude relationship between the value and the threshold value, the printed matter generated by the printing apparatus 100 is inspected for defects. For example, a location having a large difference value (pixel group) or a location having a large difference area (pixel group) becomes a defect. Then, the inspection unit 209 stores the inspection result such as the position and type of the defect, the inspection image, and the master image in association with each other and transmits (feeds back) them to the printing apparatus 100.

  FIG. 10 is a flowchart illustrating an example of a flow of a color profile generation process performed in the printed matter inspection system 1 according to the present embodiment.

  First, the RIP unit 121 generates a color chart RIP image, and the printing unit 125 prints a print image based on the color chart RIP image on a recording sheet to generate a color chart printed matter (step S101).

  Subsequently, the reading unit 201 reads the color chart printed matter generated by the printing apparatus 100 to generate a read image, and the read image acquisition unit 401 acquires the read image (step S103).

  Subsequently, the first detection unit 403, the first correction unit 405, the second detection unit 407, and the second correction unit 409 perform reading density defect and print density defect correction processing on the read image ( Step S105).

  Subsequently, the color conversion information generation unit 413 measures the color patches on the read image (second corrected image) that has been subjected to the correction process, and obtains RGB colorimetric values (step S107).

  On the other hand, the RIP image acquisition unit 411 acquires the RIP image of the color chart transmitted from the printing apparatus 100 (step S109), converts the resolution from 600 dpi to 200 dpi, and reduces it (step S111).

  Subsequently, the color conversion information generation unit 413 measures the color patch on the RIP image on which the resolution conversion process has been performed, and obtains CMYK colorimetric values (step S113).

  Note that either the processing from step S103 to S107 or the processing from step S109 to S113 may be performed first or may be performed in parallel.

  Subsequently, the color conversion information generation unit 413 generates a color profile for color conversion from the CMYK color space to the RGB color space by associating the acquired RGB colorimetric values with the CMYK colorimetric values, and stores them. The data is stored in the unit 205 (step S115).

  FIG. 11 is a flowchart illustrating an example of the flow of the process of step S105 in the flowchart of FIG.

  First, the first detection unit 403 identifies a first corresponding area that is an area on the read image corresponding to the first area (step S201), and uses the identified first corresponding area to read density. A defective part is detected on the read image (step S203).

  Subsequently, the first correction unit 405 corrects the reading density defect portion detected by the first detection unit 403 on the read image to generate a first correction image (step S205).

  Subsequently, the second detection unit 407 specifies a second corresponding area that is an area on the first corrected image corresponding to the second area (step S207), and uses the specified second corresponding area. Then, the defective print density portion is detected on the first corrected image (step S209).

  Subsequently, the second correction unit 409 corrects the print density defect portion detected by the second detection unit 407 on the first correction image, and generates a second correction image (step S211).

  FIG. 12 is a flowchart showing a detailed example of the processing of steps S203 and S205 in the flowchart of FIG.

  First, the first detection unit 403 divides the read image into a plurality of first sections in the sub-scanning direction of the read image (step S301), and each first section is included in the first section. A first average density which is an average density of the partial area of the first corresponding area is calculated (step S303).

  Subsequently, the first detection unit 403 obtains a first average density difference between adjacent first sections in the order of the sub-scanning direction, and a magnitude relationship between the first average density difference and the first threshold value. Is determined (step S305).

  When the difference in the first average density exceeds the first threshold (Yes in step S305), the first detection unit 403 detects the first section in which the streak (line) is generated, and performs the first correction The unit 405 corrects the detected first section to the previous first section (step S307). Note that, in the case of No in step S305, the process of step S307 is not performed.

  Subsequently, the first detection unit 403 obtains the variance and mode value of the density distribution of the first average density (step S309), and compares the variance with the third threshold value (step S311).

  When the variance exceeds the third threshold (Yes in step S311), the first detection unit 403 displays a target density selection screen on the operation panel 211, and the first target based on the user selection from the operation panel 211. The density is determined (steps S313 and S315).

  On the other hand, in the case of No in step S311, the first detection unit 403 determines the dispersion and mode value of the density distribution of the first average density as the first target density (step S315).

  Subsequently, for each first section, the first detection unit 403 obtains a difference between the first average density and the first target density in the first section, and calculates the difference and the second threshold value. Is determined (step S317).

  When the difference between the first average density and the first target density exceeds the second threshold (Yes in step S317), the first detection unit 403 detects the first section in which unevenness occurs, The first correction unit 405 corrects the detected density of the first section to the first target density (step S319). Note that, in the case of No in step S317, the process of step S319 is not performed.

  FIG. 13 is a flowchart illustrating an example of the flow of the procedure of the image inspection process performed in the printed matter inspection system 1 of the present embodiment.

  First, the RIP unit 121 receives print data from an external device such as a host device, performs RIP processing on the received print data, and generates a RIP image (step S401).

  Subsequently, the printing unit 125 prints a print image based on the RIP image on a recording sheet to generate a printed material (steps S403 and S405).

  Subsequently, the reading unit 201 reads the printed matter generated by the printing unit 125 and generates an inspection image (step S409).

  On the other hand, the master image generation unit 207 acquires the RIP image transmitted from the printing apparatus 100, and generates a master image based on the RIP image (step S411).

  Note that either the processing of steps S403 to S409 and the processing of step S411 may be performed first or in parallel.

  Subsequently, the inspection unit 209 compares the inspection image generated by the reading unit 201 with the master image generated by the master image generation unit 207, and inspects the quality of the printed matter generated by the printing apparatus 100 (Step S109). In step S413, the inspection result such as the position and type of the defect is transmitted (feedback) to the printing apparatus 100 (step S415).

  FIG. 14 is a flowchart illustrating an example of the flow of the process of step S411 in the flowchart of FIG.

  First, the master image generation unit 207 converts the acquired RIP image from CMYK pixel 1 bit to CMYK pixel 8 bit (step S501).

  Subsequently, the master image generation unit 207 converts the resolution of the acquired RIP image from 600 dpi to 200 dpi (step S503).

  Subsequently, the master image generation unit 207 uses the acquired RIP image and the color profile for color conversion from the CMYK color space to the RGB color space stored in the storage unit 205 by the color profile generation operation, to each CMYK pixel 8 bits. To RGB each pixel is converted into 8 bits (step S505) to obtain a master image.

  Subsequently, the master image generation unit 207 sets a reference point in the master image (step S507).

  FIG. 15 is a flowchart illustrating an example of the flow of the process of step S413 in the flowchart of FIG.

  First, the inspection unit 209 acquires the inspection image generated by the reading unit 201 and the master image generated by the master image generation unit 207 (step S601).

  Subsequently, the inspection unit 209 aligns the acquired inspection image and the master image (step S603).

  Subsequently, the inspection unit 209 compares the aligned inspection image with the master image in units of pixels and generates a difference image composed of pixel value difference values (step S605).

  Subsequently, the inspection unit 209 inspects a defect of the printed matter generated by the printing apparatus 100 based on the magnitude relationship between the difference value of the difference image and the threshold value (Step S607).

  Subsequently, the inspection unit 209 stores the inspection result such as the position and type of the defect, the inspection image, and the master image in association with each other (step S609).

  As described above, according to the present embodiment, the print density defect generated in the printing stage and the read density defect generated in the reading stage are separately corrected, so that the accuracy of correction for the density defect can be improved.

(Modification 1)
In the above embodiment, the case of generating a color profile for color conversion from the CMYK color space to the RGB color space has been described as an example. However, the present invention is not limited to this. For example, the color from the CMYK color space to the Lab color space is used. The present invention can also be applied to a case where a color profile for conversion or a color profile for color conversion from the RGB color space to the CMYK color space is generated. Further, the present invention can also be applied to a case where a color profile for color conversion (calibration) for suppressing color variation due to machine difference or environment is generated.

(Modification 2)
In the above embodiment, an example has been described in which a reading density defect portion is detected and corrected based on at least one of density variation and variation in the first corresponding region in the sub-scanning direction of the read image. However, the present invention is not limited, and a defective reading density portion may be detected and corrected in the same manner in the main scanning direction of the read image.

  That is, the first detection unit 403 detects a reading density defect portion based on at least one of density variation and variation in the first corresponding area in the sub-scanning direction and main scanning direction of the read image. May be.

  Similarly, in the above-described embodiment, a print density defect portion is detected and corrected based on at least one of density variation and variation in the second corresponding area in the sub-scanning direction of the printed matter of the color chart in the read image. Although an example has been described, the present invention is not limited to this, and a printing density defect portion may be detected and corrected in the same manner in the main scanning direction of the printed matter of the color chart.

  That is, the second detection unit 407 determines the location of the print density defect based on at least one of the density variation and the variation of the second corresponding area in the sub-scanning direction and the main scanning direction of the printed matter of the color chart in the read image. May be detected.

  In this way, it is possible to further improve the accuracy of correction for density defects.

  In this case, the sub-scanning direction and the main scanning direction may not be corrected separately, but may be corrected collectively. For example, as shown in FIG. 16, the average density of the partial areas A, B, C, and D of the first corresponding area included in the upper, lower, left, and right sides of the correction area 701, the correction area 701, and the partial areas A, B, From the distances from C and D, correction may be performed collectively by calculation such as bilinear interpolation.

(Modification 3)
In the above embodiment, the example in which the third area where the color patch is arranged is one area has been described. However, in order to perform correction with higher accuracy, the third area where the color patch is arranged as shown in FIG. The region may be divided into a plurality of blocks, and correction may be performed for each block.

(Modification 4)
In the above embodiment, the color chart extends over a plurality of pages, and the printed matter of the color chart is composed of a plurality of pages each including a first area, a second area, and a third area. The read image acquisition unit 401 acquires a read image of each of a plurality of pages, and the first detection unit 403 detects a reading density defect portion in each of the plurality of read images, and first of the plurality of read images. The first target density of the read image other than the read image may be set as the first target density of the read image read first.

  Similarly, the first correction unit 405 corrects the detected reading density defect portion on each of the plurality of read images to generate a plurality of first correction images, and the second detection unit 407 includes a plurality of the second detection units 407. In each of the first corrected images, a defective print density is detected, and the second target density of the first corrected image other than the first corrected image read first among the plurality of first corrected images is determined. The second target density of the first corrected image read first may be used.

  In this way, the difference in color between pages can be corrected.

(program)
The program executed by the printed matter inspection apparatus 200 of the above embodiment is a file in an installable format or an executable format, and is a CD-ROM, CD-R, memory card, DVD (Digital Versatile Disk), flexible disk (FD). Or the like stored in a computer-readable storage medium.

  The program executed by the printed matter inspection apparatus 200 of the above embodiment may be provided by storing it on a computer connected to a network such as the Internet and downloading it via the network. You may make it provide or distribute the program run with the printed matter inspection apparatus 200 of the said embodiment via networks, such as the internet. The program executed by the printed matter inspection apparatus 200 of the above embodiment may be provided by being incorporated in advance in a ROM or the like.

  The program executed by the printed matter inspection apparatus 200 according to the embodiment has a module configuration for realizing the above-described units on a computer. As actual hardware, for example, the CPU reads out a program from the ROM to the RAM and executes the program, so that each functional unit is realized on the computer.

DESCRIPTION OF SYMBOLS 1 Printed product inspection system 100 Printing apparatus 101 Operation panel 103Y, 103M, 103C, 103K Photosensitive drum 105 Transfer belt 107 Secondary transfer roller 109 Paper feed part 111 Conveying roller pair 113 Fixing roller 115 Reverse path 121 RIP part 123 Print control part 125 Printing unit 200 Printed matter inspection apparatus 201, 201A, 201B Reading unit 203 Generation unit 205 Storage unit 207 Master image generation unit 209 Inspection unit 211 Operation panel 300 Stacker 301 Tray 401 Read image acquisition unit 403 First detection unit 405 First correction Unit 407 second detection unit 409 second correction unit 411 RIP image acquisition unit 413 color conversion information generation unit 910 controller 911 CPU
912 System memory 912a ROM
912b RAM
913 North Bridge 914 South Bridge 915 AGP Bus 916 ASIC
917 Local memory 918 Hard disk drive 920 Operation display unit 940 USB
950 IEEE1394 interface 960 engine part

Japanese Patent No. 5484085

Claims (19)

A first area in which color information is not printed; a second area in which color information for detecting a print density defect is printed; and a third area in which color information used to generate color conversion information is printed. A read image acquisition unit that acquires a read image obtained by reading a printed matter;
Using the first corresponding area that is an area on the read image corresponding to the first area, a read density defect portion that is a density defect portion that has occurred in the read image at the time of reading is detected on the read image. A first detection unit;
A first correction unit for correcting the detected reading density defect portion on the read image and generating a first correction image;
Using the second corresponding area that is the area on the first correction image corresponding to the second area, the first correction is performed on a print density defect portion that is a density defect portion that has occurred in the printed matter during printing. A second detector for detecting on the image;
A second correction unit for correcting the detected print density defect portion on the first correction image and generating a second correction image;
An image processing apparatus comprising: The first region is arranged such that there is a region constituting the first region in the vertical direction and the horizontal direction of the printed matter,
The said 1st detection part detects the said reading density defect location based on at least any one of the fluctuation | variation and dispersion | variation in the density | concentration of the said 1st corresponding area | region in the subscanning direction of the said reading image. Image processing apparatus. The first detection unit divides the read image into a plurality of first sections in the sub-scanning direction of the read image, and the first correspondence included in the first section for each first section. Calculating a first average density of a partial area of the area, and detecting a first section in which a variation in the first average density with respect to the previous first section exceeds a first threshold as the defective reading density portion;
The image processing apparatus according to claim 2, wherein the first correction unit corrects the detected first section to the previous first section. The first detection unit divides the read image into a plurality of first sections in the sub-scanning direction of the read image, and the first correspondence included in the first section for each first section. A first average density of a partial area of the area is calculated, and a first target density and a first average density based on a variation in the first average density of the plurality of first sections are calculated as the defective reading density portion. A first interval in which the difference between the two exceeds a second threshold,
The image processing apparatus according to claim 2, wherein the first correction unit corrects the detected density of the first section to the first target density.   The first target density is determined by a user when a variation in the first average density of the plurality of first sections exceeds a third threshold, and the first average density of the plurality of first sections 5. The image processing apparatus according to claim 4, wherein when the variation of the first density does not exceed the third threshold value, the mode value of the first average density of the plurality of first sections. The printed matter includes a plurality of pages, each page including the first area, the second area, and the third area,
The read image acquisition unit acquires a read image of each of the plurality of pages,
The first detection unit detects the read density defect portion in each of the plurality of read images,
5. The image processing according to claim 4, wherein a first target density of a read image other than the first read image among the plurality of read images is a first target density of the first read image. 6. apparatus.   For each of the first intervals, the first detection unit excludes an outlier of the concentration distribution of the partial region of the first corresponding region included in the first interval, and performs the first average concentration The image processing device according to any one of claims 3 to 6, wherein The second region is arranged such that at least a section of the third region and a region constituting the second region exist in the vertical direction and the horizontal direction,
The second detection unit detects the print density defect portion based on at least one of density variation and variation of the second corresponding region in the sub-scanning direction of the printed matter in the read image. The image processing apparatus according to any one of 2 to 7. The second detection unit divides the first correction image into a plurality of second sections in the sub-scanning direction of the printed matter in the first correction image, and performs the second correction for each second section. The second average density of the partial area of the second corresponding area included in the section is calculated, and the variation of the second average density with respect to the previous second section has a fourth threshold value as the print density defect portion. Detect a second interval that exceeds,
The image processing apparatus according to claim 8, wherein the second correction unit corrects the detected second section to the previous second section. The second detection unit divides the first correction image into a plurality of second sections in the sub-scanning direction of the printed matter in the first correction image, and performs the second correction for each second section. A second average density of a partial area of the second corresponding area included in the section is calculated, and a second density based on the second average density variation of the plurality of second sections is calculated as the print density defect portion. Detecting a second section in which a difference between the target density and the second average density exceeds a fifth threshold;
The image processing apparatus according to claim 8, wherein the second correction unit corrects the detected density of the second section to the second target density.   The second target density is determined by a user when the variation of the second average density of the plurality of second sections exceeds a sixth threshold, and the second target density of the plurality of second sections The image processing apparatus according to claim 10, wherein when the variation of the second density does not exceed the sixth threshold, the mode value of the second average density of the plurality of second sections. The printed matter includes a plurality of pages, each page including the first area, the second area, and the third area,
The read image acquisition unit acquires a read image of each of the plurality of pages,
The first detection unit detects the read density defect portion in each of the plurality of read images,
The first correction unit corrects the detected reading density defect portion on each of the plurality of read images, and generates a plurality of first correction images,
The second detection unit detects the print density defect portion in each of the plurality of first correction images,
The second target density of the first correction image other than the first correction image read first among the plurality of first correction images is the second target density of the first correction image read first. The image processing apparatus according to claim 10, wherein the image processing apparatus has a target density.   The second detection unit excludes outliers of density distributions of partial regions of the second corresponding area included in the second section for each second section, and performs the second average density The image processing apparatus according to any one of claims 9 to 12, which calculates   The first detection unit detects the defective reading density portion based on at least one of density variation and variation of the first corresponding region in the sub-scanning direction and main scanning direction of the read image. Item 8. The image processing apparatus according to Item 1.   The second detection unit detects the print density defect portion based on at least one of a density variation and a variation of the second corresponding area in the sub-scanning direction and the main scanning direction of the printed matter in the read image. The image processing apparatus according to claim 14 for detection.   16. The color conversion information generation unit for generating the color conversion information using a third corresponding area that is an area on the second corrected image corresponding to the third area. The image processing apparatus according to claim 1.   The image processing apparatus according to claim 16, further comprising a color conversion unit that performs color conversion using the color conversion information. A first area in which color information is not printed; a second area in which color information for detecting a print density defect is printed; and a third area in which color information used to generate color conversion information is printed. A read image acquisition step of acquiring a read image obtained by reading a printed matter;
Using the first corresponding area that is an area on the read image corresponding to the first area, a read density defect portion that is a density defect portion that has occurred in the read image at the time of reading is detected on the read image. A detection step;
A correction step of correcting the detected read density defect portion on the read image and generating a first corrected image;
Using the second corresponding area that is the area on the first correction image corresponding to the second area, the first correction is performed on a print density defect portion that is a density defect portion that has occurred in the printed matter during printing. A detection step for detecting on the image;
A correction step of correcting the detected print density defect portion on the first correction image to generate a second correction image;
A correction method including: A first area in which color information is not printed; a second area in which color information for detecting a print density defect is printed; and a third area in which color information used to generate color conversion information is printed. A read image acquisition step of acquiring a read image obtained by reading a printed matter;
Using the first corresponding area that is an area on the read image corresponding to the first area, a read density defect portion that is a density defect portion that has occurred in the read image at the time of reading is detected on the read image. A detection step;
A correction step of correcting the detected read density defect portion on the read image and generating a first corrected image;
Using the second corresponding area that is the area on the first correction image corresponding to the second area, the first correction is performed on a print density defect portion that is a density defect portion that has occurred in the printed matter during printing. A detection step for detecting on the image;
A correction step of correcting the detected print density defect portion on the first correction image to generate a second correction image;
A program that causes a computer to execute.