Image forming apparatus, image forming method, and program

Abstract

To provide an image forming apparatus, an image forming method, and a program that can reduce the downtime of the image forming apparatus and the cost of consumable items.SOLUTION: The image forming apparatus comprises: a printing unit that forms an input image; a reading unit that scans the image formed by the printing unit; and a color conversion table updating unit that, on the basis of the combination of color information of a read image obtained by reading, with the reading unit, an image printed from the input image and color information of the input image, updates a color conversion table including values that are converted from a color space of the input image into a color space of the read image.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In a technology for stabilizing color variations in an image formed by an image forming device, a color conversion table that links the colors of the print document with the colors of the read image is created in advance, making it possible to calculate the amount of correction required to correct color variations in the read image in subsequent prints.

[0003] Patent Document 1 discloses a configuration for reducing the number of color charts required to generate a color conversion table, with the aim of reducing the cost of generating the color conversion table. Patent Document 2 discloses a configuration for achieving color stabilization using Jacobi, which can be obtained from a color conversion table, with the aim of achieving color stability in printing. Summary of the Invention [Problem to be solved by the invention]

[0004] However, although the color conversion table creation method has been devised to reduce the number of patches and printed sheets, it is necessary to print a dedicated chart in advance, making it difficult to reduce downtime.

[0005] The present invention has been made in consideration of the above, and aims to provide an image forming apparatus, an image forming method, and a program that can reduce downtime of the image forming apparatus and costs for consumables. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the object, the present invention comprises a printing unit that forms an input image, a reading unit that scans the image formed by the printing unit, and a color conversion table update unit that updates a color conversion table containing values ​​for converting from the color space of the input image to the color space of the read image based on a combination of color information of the read image read by the reading unit from an image printed from the input image and color information of the input image. [Effects of the Invention]

[0007] The present invention provides an advantage in that it is possible to reduce downtime of an image forming apparatus and costs for consumables. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the overall configuration of an image forming system according to the present embodiment. [Figure 2] FIG. 2 is a diagram illustrating an example of a hardware configuration of a DFE according to the present embodiment. [Figure 3] FIG. 3 is a diagram illustrating an example of a functional configuration of the image forming system according to the present embodiment. [Figure 4] FIG. 4 is a flowchart showing an example of the flow of a print job in the image forming system according to the present embodiment. [Figure 5] FIG. 5 is a diagram for explaining an example of a sky color conversion table in the image forming system according to the present embodiment. [Figure 6] FIG. 6 is a diagram for explaining an example of calibration in the image forming system according to the present embodiment. [Figure 7] FIG. 7 is a diagram for explaining an example of calibration in the image forming system according to the present embodiment. [Figure 8] FIG. 8 is a diagram for explaining an example of a color conversion table in the image forming system according to the present embodiment. [Figure 9]FIG. 9 is a diagram for explaining an example of a message display process in the image forming system according to the present embodiment. [Figure 10] FIG. 10 is a diagram for explaining an example of calibration in the image forming system according to the present embodiment. [Figure 11] FIG. 11 is a diagram for explaining an example of a UI for checking colors that have been updated from the initial values ​​in elements of the color conversion table in the image forming system according to this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an image forming apparatus, an image forming method, and an image forming system to which a program is applied will be described in detail below with reference to the accompanying drawings.

[0010] 1 is a diagram showing an example of the overall configuration of an image forming system according to the present embodiment. As shown in FIG. 1, the image forming system 100 according to the present embodiment includes a client PC (Personal Computer) 101, a DFE (Digital Front End) 102, an image forming device 103, a management server 104, and a reading device 105.

[0011] The client PC 101 creates a print job that the user wants to print, and transmits the print job to the DFE 102 or the management server 104. The client PC 101 is equipped with a display unit such as a liquid crystal display, and input devices such as a mouse and keyboard.

[0012] The DFE 102 receives a print job from the client PC 101 or the management server 104 , creates drawing data using a RIP engine based on the received print job, and transmits the drawing data to the image forming apparatus 103 .

[0013] The image forming device 103 forms an image based on the drawing data received from the DFE 102 .

[0014] The management server 104 manages print jobs received from the client PC 101. Furthermore, the management server 104 transmits print jobs to the DFE in response to a request from the DFE .

[0015] The reading device 105 reads an image formed by the image forming device 103 and transmits the image to the DFE 102. The reading device 105 may be externally connected to the image forming device 103 or may be an in-line sensor or the like that is present inside the image forming device 103. The reading device 105 transmits colorimetric data such as RGB images, Lab, and CMYK densities to the DFE 102.

[0016] 2 is a diagram showing an example of the hardware configuration of a DFE according to this embodiment. A CPU 201 uses a RAM 203 as a work area and executes a program stored in a ROM 202. A HDD / SSD 204 is used as a storage unit and stores preset setting values. Information stored in the HDD / SSD 204 may be read by the CPU 201 and used when executing a program.

[0017] The I / F 205 is an interface that enables communication between the DFE 102, the client PC 101, the image forming apparatus 103, and the management server 104. The image processing unit 206 generates drawing data (RIP image) that is RIP-processed print data that can be drawn by the image forming apparatus 103. The image processing unit 206 also has a gradation correction unit that corrects engine fluctuations, and a detection unit that generates paper characteristic information, detects defective images, and corrects color fluctuations over time during printing.

[0018] 3 is a diagram showing an example of the functional configuration of the image forming system according to this embodiment. In this embodiment, the image forming system includes a color conversion processing unit 206a, a gradation correction unit 206b, a print processing unit 206c, a color fluctuation detection unit 206d, a reading processing unit 206e, and a color conversion table management unit 206f, as shown in FIG.

[0019] The color conversion processing unit 206a performs predetermined color conversion processing using a RIP engine or the like on the color information (CMYK values, RGB values, etc.) of the input image data, and converts it into image data (RIP image) in CMYK format or the like that is suitable for the print processing unit 206c. The color conversion processing unit 206a corresponds to the function of the DFE 102.

[0020] The gradation correction unit 106b corrects the image data converted by the color conversion processing unit 206a based on the calibration correction gamma and color correction information received from the color fluctuation detection unit 206d. The gradation correction unit 206b corresponds to a function possessed by the DFE 102.

[0021] The print processing unit 206c forms an image based on the image data after gradation correction received from the gradation correction unit 206b. In other words, the print processing unit 206c is an example of a printing unit that forms an input image from a user. The print processing unit 206c corresponds to a function of the image forming apparatus 103.

[0022] The reading processing unit 206e reads the image (printed image) formed by the print processing unit 206c in RGB format. In other words, the reading processing unit 206e is an example of a reading unit that scans the image formed by the print processing unit 206c. The reading processing unit 206e also transmits the read image (read image) to the color variation detection unit 206d and the color conversion table management unit 206f. The reading processing unit 206e corresponds to the function of the reading device 105.

[0023] The color variation detection unit 206d detects whether an abnormal image or color variation occurs in real time during job printing. When the color variation detection unit 206d detects an abnormal image, it notifies the client PC 101, and when a color variation occurs, it generates color correction information and feeds it back to the gradation correction unit 106b. The color variation detection unit 206d corresponds to a function possessed by the image processing unit 206.

[0024] When detecting color variations, the color variation detection unit 206d uses the RIP image created by the color conversion processing unit 206a, the read image read by the reading processing unit 206e, and the color conversion table notified by the color conversion table management unit 206f. The color variation detection unit 206d converts the RIP image into an image of the same format as the read image by referring to the color conversion table, and compares it with the read image to detect color variations. The color variation detection unit 206d corresponds to a function possessed by the image processing unit 206.

[0025] The color conversion table management unit 206f generates and updates a color conversion table (LUT) that associates the color information (e.g., CMYK values) of the RIP image created by the color conversion processing unit 206a with the color information (e.g., RGB values) of the scanned image based on the RIP image created by the color conversion processing unit 206a and the scanned image read by the read processing unit 206e. The color conversion table is a table containing values ​​(e.g., RGB values ​​and CMYK values) used to convert the color space of the RIP image to the color space of the scanned image acquired by the read processing unit 206e. In other words, the color conversion table management unit 206f is an example of a color conversion table update unit that updates the color conversion table based on the combination of the scanned image read by the read processing unit 206e and the RIP image (an example of an input image). This eliminates the need to print a dedicated chart when creating a color conversion table, thereby reducing downtime and consumable costs for the image forming apparatus 103. The color conversion table management unit 206f corresponds to a function of the image processing unit 206.

[0026] The color conversion table management unit 206f updates the value of the color conversion table when the value (output) of the color conversion table corresponding to the combination of the color information of the scanned image and the color information of the RIP image is null (Nan). Furthermore, when referring to a null value among the values ​​of the color conversion table, the color conversion table management unit 206f may refer to a provisional value by performing interpolation processing based on the non-null values ​​among the values ​​of the color conversion table.

[0027] Furthermore, the color conversion table management unit 206f is an example of a display control unit that, when referencing a null value in the color conversion table, displays a message on the display unit of the client PC 101 indicating that the color conversion table is unavailable (for example, a message indicating that color stabilization cannot be performed). The color conversion table management unit 206f may also display the percentage of null values ​​in the color conversion table on the display unit of the client PC 101. The color conversion table management unit 206f also visualizes colors that correspond to null values ​​in the color conversion table. For example, the color conversion table management unit 206f may display colors that correspond to null values ​​in the color conversion table on the display unit of the client PC 101.

[0028] FIG. 4 is a flowchart showing an example of the flow of a print job in the image forming system according to the present embodiment. FIG. 5 is a diagram illustrating an example of an empty color conversion table in the image forming system according to the present embodiment. FIGS. 6 and 7 are diagrams illustrating an example of calibration in the image forming system according to the present embodiment. In FIG. 7, the vertical axis represents the input of the calibration chart, and the horizontal axis represents the density of the calibration chart. FIG. 8 is a diagram illustrating an example of a color conversion table in the image forming system according to the present embodiment. FIG. 9 is a diagram illustrating an example of message display processing in the image forming system according to the present embodiment. FIG. 10 is a diagram illustrating an example of calibration in the image forming system according to the present embodiment. In FIG. 10, the vertical axis represents the output (tone-corrected image), and the horizontal axis represents the input (RIP image).

[0029] First, the user registers paper characteristic information for the paper they want to use for printing from client PC 101 to DFE 102 (step S1001). Here, registering paper characteristic information includes not only adding new paper characteristic information for the paper they want to use, but also updating paper characteristic information for paper that has already been registered. In this case, the user inputs paper characteristic information such as paper size, thickness, color, type, etc. into client PC 101.

[0030] The DFE 102 assigns a unique paper ID to each paper sheet and stores it as paper characteristic information. The DFE 102 notifies the image processing unit 206 of the paper sheet ID.

[0031] The image processing unit 206 checks whether a color conversion table associated with the paper ID notified by the DFE 102 has already been generated (step S1002).

[0032] If a color conversion table associated with the paper ID has not been generated, the image processing unit 106 generates a new color conversion table (empty color conversion table) and associates it with the paper ID notified by the DFE 102 (step S1003).

[0033] The format of the empty color conversion table is an LUT that can reference the colors of the scanned image from the colors of the RIP image, and all values ​​(elements) that make up the LUT are initial values. As an example, if the colors of the RIP image are in CMYK format with a domain of 0 to 100, the colors of the scanned image are in RGB format with a domain of 0 to 255, and the CMYK interval of the LUT is 10, then the CMYK-RGB combinations can be 11 to the fourth power. Note that the color space and domain of the RIP image, the color space and domain of the scanned image, and the CMYK interval of the LUT are merely examples; other color spaces and values ​​are also acceptable. The following explanation will be based on the above example. If the initial RGB values ​​are set to Nan, the image of the empty color conversion table that is generated will be as shown in Figure 5.

[0034] Next, the user performs calibration on the registered paper (step S1004). In the calibration, a calibration chart consisting of gradation patches of 0 to 100% gradation is printed as shown in Fig. 6, the patches printed on the paper are read, and the information is sent to the gradation correction unit 206b.

[0035] The gradation correction unit 206b generates a corrected gamma (calibration correction gamma) based on the measured colorimetric data (calibration chart measurement values) and target data (calibration target), as shown in Fig. 7. From the next time onwards, when a print job is executed on this paper, the gradation correction unit 206b uses the generated calibration correction gamma for the printed image. The color conversion table management unit 206f is notified of the relationship value (calibration target) between input and density when the calibration correction gamma is applied.

[0036] The color conversion table management unit 206f updates the color conversion table based on the calibration target notified by the DFE 102 (step S1005). From the calibration target, it is possible to extract the CMYK values ​​of the original image (RIP image), which is the input of the color conversion table, and the RGB values ​​of the scanned image, which is the output of the color conversion table. For example, in the case of the single-color calibration chart shown in FIG. 6, the corresponding RGB values ​​can be referenced for single colors of CMYK. The color conversion table management unit 206f reflects the referenced values ​​in the color conversion table, as shown in FIG. 8. The color conversion table management unit 206f does not update values ​​for CMYK that cannot be referenced.

[0037] Next, the user executes a print job (step S1006). The executed print job is notified to the DFE 102.

[0038] The color conversion processing unit 206a performs RIP on the image to be printed and converts it into a printable format (RIP image). The color conversion processing unit 206a notifies the gradation correction unit 206b, color fluctuation detection unit 206d, and color conversion table management unit 206f of the RIP image. The gradation correction unit 206b performs gradation correction on the RIP image based on the calibration correction gamma and color correction information notified by the color fluctuation detection unit 206d, and notifies the print processing unit 206c. The print processing unit 206c forms the notified RIP image (i.e., prints one page of the image) (step S1007).

[0039] The reading processing unit 206e scans the formed image (step S1008) and notifies the color variation detection unit 206d and the color conversion table management unit 206f of the scanned image in RGB format.

[0040] The color conversion table management unit 206f extracts the CMYK values ​​of the RIP image and the RGB values ​​of the scanned image for matching areas where coordinates match between the RIP image and the scanned image, and creates a list of correspondences (step S1009). The matching areas handled here may be rectangular areas rather than single pixels to minimize the effects of noise. The CMYK and RGB values ​​may be average values ​​of the pixels within the rectangular area. Ideally, a rectangular area would consist of only pixels with the same CMYK values. However, it is rare to be able to detect a rectangular area consisting of only identical pixels in an actual printed image. Therefore, the condition for a rectangular area is that it consists of pixels with similar CMYK values. Examples of conditions for determining pixels with similar CMYK values ​​include checking that the difference between the maximum and minimum CMYK values ​​of the pixels within the rectangular area is less than a threshold, or checking that no edges exist within the rectangular area by detecting edges in the RIP image using an edge detection filter or the like. The associated combinations of CMYK and RGB values ​​are compiled into a list and retained until the processing of step S1010 is completed.

[0041] The color conversion table management unit 206f refers to the list created in step S1009 and updates the values ​​(outputs) that make up the color conversion table and that are set to Nan (initial value) (step S1010). After updating the color conversion table, the color conversion table management unit 206f notifies the color fluctuation detection unit 206d of the color conversion table.

[0042] Specifically, for CMYK values ​​for which the output RGB is Nan, the color conversion table management unit 206f extracts values ​​for which the output is determined in a rectangular area or color conversion table with close CMYK values ​​from the list, and performs interpolation processing based on these to update the output. An example of the interpolation processing performed here is tetrahedral interpolation. Steps (1) to (5) are shown below. Here, the output RGB values ​​will be explained assuming that the target CMYK values ​​to be updated are CMYK=(10,20,0,0).

[0043] (1) Extract up to four values ​​from the color conversion table that are close to the target and whose output has already been determined. (2) Extract up to four rectangular areas from the list whose difference between the target and each CMYK plate is 10 or less (0≦C≦20, 10≦M≦30, 0≦Y≦10, 0≦K≦10). At this time, make sure that the total number of extractions in (1) and (2) is four. (3) Check that the target is contained within the tetrahedron with the extracted four points as vertices. If it is not contained within, repeat steps (1) and (2). If it is not possible to extract four points that contain the target even after repeating the specified number of times, skip updating this target. (4) Tetrahedron interpolation is performed on a tetrahedron with the extracted four points as vertices. (5) Update the calculated RGB values ​​as the target output.

[0044] The color variation detection unit 206d calculates the amount of color variation of the formed image based on the RIP image, the scanned image, and the color conversion table (step S1011). The specific method for calculating the amount of color variation is the same as that in Patent Document 2. Patent Document 2 uses a Jacobian matrix when calculating the amount of color variation, and this Jacobian matrix can be calculated from the color conversion table. For example, the Jacobian matrix J(v) for the input value v=(c, m, y, k) is given by the following equation (1).

number

number

number

[0045] Depending on the state of the color conversion table, elements necessary for calculating the Jacobian matrix may remain as Nan, which may make it impossible to calculate the amount of color variation. In this case, a message to the effect that color stabilization cannot be performed is displayed on the UI to notify the user (see Figure 9). One possible method of notifying the user is to add this to the print status message (Ready, Printing, etc.) (see Figure 9).

[0046] The color variation detection unit 206d notifies the gradation correction unit 206b of color correction information calculated from the amount of color variation (step S1012). The color correction information is a correction gamma generated to suppress color variation, similar to the calibration in step S1004. As shown in FIG. 10, the gradation correction unit 206b reflects the correction gamma (color correction information) obtained by multiplying the calibration correction gamma generated by the calibration and the correction gamma generated from the amount of color variation in subsequent image formation.

[0047] DFE102 checks whether printing of all pages of the print job has been completed (i.e., whether there are any images remaining that have not been formed), and if there are (step S1013: No), it forms the next image (step S1007); if there are no images remaining, it ends the process.

[0048] FIG. 11 is a diagram illustrating an example of a UI for checking colors that have been updated from their initial values ​​in elements of a color conversion table in an image forming system according to this embodiment. In this embodiment, a pop-up displaying the valid range of the color conversion table is called from a screen for checking the settings of paper characteristic information. In the pop-up shown in FIG. 11, the color conversion table management unit 206f displays the percentage of values ​​(elements) that make up the color conversion table that have been updated from Nan as the color information acquisition rate. The color conversion table management unit 206f also visualizes, on a chromaticity diagram, the colors that have been updated from Nan in the elements that make up the color conversion table.

[0049] In this way, according to the image forming system of this embodiment, the creation of a color conversion table does not require printing of a dedicated chart, thereby reducing downtime of the image forming apparatus 103 and the cost of consumables.

[0050] The program executed by image forming system 100 of this embodiment is provided in a state where it is pre-installed in a ROM or the like. The program executed by image forming system 100 of this embodiment may be provided by being recorded in an installable or executable file format on a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk).

[0051] Furthermore, the program executed by image forming system 100 of the present embodiment may be stored on a computer connected to a network such as the Internet and provided by being downloaded via the network. Also, the program executed by image forming system 100 of the present embodiment may be provided or distributed via a network such as the Internet.

[0052] The program executed by the image forming system 100 of this embodiment has a modular structure including the above-mentioned units (color conversion processing unit 206a, gradation correction unit 206b, color fluctuation detection unit 206d, and color conversion table management unit 206f), and in actual hardware, an example of a processor such as a CPU reads and executes the program from the above-mentioned ROM, thereby loading the above-mentioned units onto the main memory, and the color conversion processing unit 206a, gradation correction unit 206b, color fluctuation detection unit 206d, and color conversion table management unit 206f are generated on the main memory.

[0053] In the above embodiment, the image forming apparatus of the present invention is described as being applied to a multifunction peripheral having at least two of the functions of a copy function, a printer function, a scanner function, and a facsimile function, but the present invention can be applied to any image forming apparatus such as a copier, printer, scanner device, or facsimile device.

[0054] For example, aspects of the present invention are as follows. <1> a printing unit for forming an input image; a reading unit that scans the image formed by the printing unit; a color conversion table update unit that updates a color conversion table containing values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from the input image using the reading unit and color information of the input image; An image forming apparatus comprising: <2> the color conversion table update unit updates the value in the color conversion table corresponding to the combination of the color information of the read image and the color information of the input image when the value is empty. <1> 2. The image forming apparatus according to claim 1 . <3> a color conversion table management unit that, when referring to a null value among the values ​​of the color conversion table, refers to a provisional value by performing interpolation processing based on a non-null value among the values ​​of the color conversion table. <1> or <2> 2. The image forming apparatus according to claim 1 . <4> a display control unit that displays a message that the color conversion table is unavailable when a null value is referenced among the values ​​in the color conversion table. <1> from <3> 10. The image forming apparatus according to claim 9, wherein <5> a display control unit that displays the ratio of blank values ​​among the values ​​in the color conversion table; <1> from <4> 10. The image forming apparatus according to claim 9, wherein <6> a display unit that visualizes a color corresponding to a null value among the values ​​of the color conversion table. <1> from <5> 10. The image forming apparatus according to claim 9, wherein <7> An image forming method executed by an image forming apparatus, a printing unit forming an input image; a step in which a reading unit scans an image formed by the printing unit; a step in which a color conversion table update unit updates a color conversion table including values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from the input image using the reading unit and color information of the input image; An image forming method comprising: <8> Computer, a color conversion table update unit that updates a color conversion table containing values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from an input image by a printing unit using a read unit and color information of the input image; A program to function as a [Explanation of symbols]

[0055] 100 Image forming system 101 Client PC 102 DFE 103 Image forming device 104 Management Server 105 Reading device 201 CPU 202 ROM 203 RAM 204 HDD / SSD 205 Interface 206 Image Processing Unit 206a Color conversion processing unit 206b Gradation correction section 206c Print processing unit 206d Color fluctuation detection unit 206e Reading processing unit 206f Color conversion table management unit [Prior art documents] [Patent documents]

[0056] [Patent Document 1] Patent No. 6947060 [Patent Document 2] Japanese Patent Application Publication No. 2019-142221

Claims

1. a printing unit for forming an input image; a reading unit that scans the image formed by the printing unit; a color conversion table update unit that updates a color conversion table containing values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from the input image using the reading unit and color information of the input image; An image forming apparatus comprising:

2. The image forming apparatus according to claim 1 , wherein the color conversion table update unit updates the value in the color conversion table corresponding to a combination of the color information of the read image and the color information of the input image when the value is null.

3. An image forming apparatus as described in claim 1 or 2, further comprising a color conversion table management unit that, when referencing an empty value among the values ​​of the color conversion table, references a provisional value by performing interpolation processing based on a non-empty value among the values ​​of the color conversion table.

4. The image forming apparatus according to claim 1 , further comprising: a display control unit that displays a message indicating that the color conversion table is unavailable when a null value among the values ​​in the color conversion table is referenced.

5. The image forming apparatus according to claim 1 , further comprising a display control unit that displays a ratio of blank values ​​among the values ​​in the color conversion table.

6. The image forming apparatus according to claim 1 , further comprising a display unit that visualizes colors corresponding to null values ​​among the values ​​in the color conversion table.

7. An image forming method executed by an image forming apparatus, a printing unit forming an input image; a step in which a reading unit scans an image formed by the printing unit; a step in which a color conversion table update unit updates a color conversion table including values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from the input image using the reading unit and color information of the input image; An image forming method comprising:

8. Computer, a color conversion table update unit that updates a color conversion table containing values ​​for converting from a color space of the input image to a color space of the read image based on a combination of color information of a read image obtained by reading an image printed from an input image by a printing unit using a read unit and color information of the input image; A program to function as a

Images