Recording device, control method for recording device, and program

Abstract

The present invention provides a recording device and a control method thereof that achieve head shading (HS) correction, which corrects density unevenness to an appropriate amount according to the type of recording paper, while suppressing an increase in workload. [Solution] In the image processing unit of the recording device, the HS correction table creation unit creates a correction table for the conversion paper based on first read image data obtained by reading a test chart recorded on a reference paper, which is a first type of recording paper; second read image data obtained by reading a test chart recorded on a conversion paper, which is a second type of recording paper; and third read image data obtained by reading a test chart recorded on the reference paper. The HS correction processing unit then performs HS correction by referring to the correction table.

Description

Technical Field

[0001] The present disclosure relates to a recording apparatus, a control method for the recording apparatus, and a program, and more particularly to a technique for head shading correction.

Background Art

[0002] As an image recording apparatus for recording an arbitrary image on a paper surface, an inkjet recording apparatus that records an image on a recording paper using a recording head including a plurality of recording elements (also referred to as nozzles) is widely used.

[0003] One of the factors that prevent obtaining a high-quality image by inkjet recording is density unevenness of an image caused by variations in ejection characteristics of recording elements. In an inkjet recording apparatus including a plurality of recording elements, density unevenness may occur in a recorded image due to variations in ejection characteristics of each recording element. Such variations in ejection characteristics are classified into variations in landing positions of ink and variations in ejection amounts, and factors such as variations in heat generation amounts of heating heaters that heat ink and variations in nozzle diameters are cited. Further, a difference in the amount of ink ejected from each recording element also occurs due to variations in heat generation amounts of heating heaters due to aging and variations in viscosity of ink due to differences in use environments.

[0004] As a method for reducing the influence of variations in ejection characteristics of recording elements, head shading correction (HS correction) is known. HS correction refers to reading a test chart printed on a paper using a recording head and correcting image data corresponding to each nozzle by image processing so as to reduce density unevenness. The ejection characteristics of each recording element are not constant and change depending on the ejection history of each recording element. Therefore, in order to maintain the effect of reducing density unevenness, it is necessary to periodically execute HS correction.

[0005] Incidentally, the density characteristics of recorded images generally differ depending on the type of recording paper used. More specifically, differences in the surface properties and the chromaticity of the paper itself can lead to variations in density unevenness on the paper and average density gradation characteristics. Therefore, it is necessary to perform HS correction according to the type of recording paper used.

[0006] However, interrupting the print job to perform HS correction for each type of recording paper presents a problem in that productivity decreases. To address this problem, Patent Document 1 discloses a method for performing HS correction on multiple types of recording paper based on readings from a test chart printed on one type of recording paper. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2002-160353 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] However, Patent Document 1 corrects for differences in density gradation characteristics depending on the type of recording paper, but does not take into account differences in density unevenness characteristics. In other words, by using an HS correction table for each target paper, it is possible to achieve the target density value for each paper type in terms of the average density value for each gradation, but it was not possible to adequately correct the differences in density unevenness between paper types. Furthermore, Patent Document 1 requires the creation of a correction table for each type of recording paper, which necessitates printing and reading a test chart for each type, thus increasing the workload for the user.

[0009] Therefore, in view of the above issues, this disclosure aims to realize head shading correction that performs density unevenness correction with an appropriate correction amount according to the type of recording paper, while suppressing an increase in workload. [Means for solving the problem]

[0010] One embodiment of the present disclosure is a recording device comprising: a recording head having a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle; a correction table creation means for creating a correction table for reducing the chromaticity difference of an image recorded by the plurality of nozzle groups, the correction table creation means for creating the correction table for the conversion paper based on a first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper; a second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper; and a third read image data obtained by reading a test chart recorded by the recording head on the reference paper which is a reference paper; and a head shading correction means for performing head shading correction on image data to be recorded on the conversion paper using the correction table. [Effects of the Invention]

[0011] According to this disclosure, it is possible to achieve head shading correction that performs density unevenness correction with an appropriate correction amount according to the type of recording paper, while suppressing an increase in workload. [Brief explanation of the drawing]

[0012] [Figure 1] Block diagram showing the hardware configuration of the recording device in the first embodiment. [Figure 2] A schematic diagram showing the general configuration of the recording device in the first embodiment. [Figure 3] Block diagram showing the configuration of the image processing unit in the first embodiment. [Figure 4] Diagram showing the HS correction table [Figure 5] Flowchart of the conversion reading acquisition process in the first embodiment [Figure 6] Figure showing a test chart used for HS correction [Figure 7] Flowchart of user image printing process in the first embodiment [Figure 8] Flowchart of HS correction table creation process (S710) in the first embodiment [Figure 9] Flowchart of HS correction table creation process (S803, etc.) in the first embodiment [Figure 10] Schematic diagram for explaining correction amount calculation [Figure 11] Block diagram showing the configuration of the image processing unit in the second embodiment [Figure 12] Flowchart of conversion characteristic acquisition process in the second embodiment [Figure 13] Flowchart of user image printing process in the second embodiment [Figure 14] Flowchart of HS correction table creation process in the second embodiment [Figure 15] Figure showing conversion characteristics[[ID=We]]

Mode for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present disclosure will be described with reference to the drawings. In the embodiments described below, specific descriptions may be made for sufficient explanation, but this is merely an example showing technically preferable examples and is not intended to limit the scope of the present disclosure more than necessary. For example, dimensions, materials, shapes, and relative arrangements of components described in the following embodiments are not intended to limit the scope of the present disclosure only to those, unless otherwise specified.

[0014] [First Embodiment] [Hardware Configuration of the Recording Device] FIG. 1 is a diagram showing the hardware configuration of the recording apparatus 10 in the present embodiment. The recording apparatus 10 includes a CPU 100, a RAM 101, a ROM 102, an operation unit 103, a display unit 104, a storage device 105, an image processing unit 106, an image recording unit 107, an image reading unit (image acquisition unit) 108, an I / F (interface) unit 109, a paper feeding unit 110, and a bus 111.

[0015] The CPU 100 controls the operation of the entire recording apparatus 10 using the input data and the computer programs stored in the RAM 101 and the ROM 102. In the following, a mode in which the CPU 100 controls the entire recording apparatus 10 will be described, but this is an example, and as another mode, for example, a plurality of hardware may share the processing to control the entire recording apparatus 10.

[0016] In the RAM 101, data such as computer programs and data read from the storage device 105 and data received from the outside via the I / F unit 109 are temporarily stored. The RAM 101 is used as a storage area when the CPU 100 executes various processes, and is also used as a storage area when the image processing unit 106 executes image processing. In the ROM 102, setting parameters for setting each unit in the recording apparatus 10, a boot program, and the like are stored.

[0017] The operation unit 103 includes an input device such as a keyboard and a mouse, and receives an operation (instruction) by an operator such as a general user. Thereby, the operator can input various instructions to the CPU 100. The display unit 104 is a display device such as a CRT (Cathode Ray Tube) or a liquid crystal screen, and can display the processing result by the CPU 100 as an image, characters, or the like. When the display unit 104 is a touch panel capable of detecting a touch operation, the display unit 104 may function as a part of the operation unit 103.

[0018] The storage device 105 is a large-capacity information storage device, such as a hard disk drive. The storage device 105 stores computer programs and data that allow the OS (operating system) and CPU 100 to execute various processes. It also stores temporary data created by the processing of each part (for example, input / output image data and threshold matrices used by the image processing unit 106). The computer programs and data stored in the storage device 105 are read as appropriate according to the control of the CPU 100, loaded into RAM 101, and become the target of processing by the CPU 100.

[0019] The image processing unit 106 is implemented as a processor capable of executing computer programs or as a dedicated image processing circuit, and performs various image processing operations to convert the image data input for printing into data (recorded data) that can be output by the image recording unit 107 described later. Alternatively, instead of providing a dedicated processor for the image processing unit 106, the CPU 100 may be configured to perform various image processing operations as the image processing unit 106.

[0020] The image recording unit 107 records an image on a recording medium such as recording paper using a recording material such as ink, based on recording data received directly from the image processing unit 106 or via the RAM 101 or storage device 105. Details of the image recording unit 107 will be described later.

[0021] The image reading unit 108 acquires image data of the image recorded on the recording medium by the image recording unit 107, and specifically, it is an image sensor (line sensor or area sensor) for capturing the recorded image. Details of the image reading unit 108 will be described later.

[0022] The I / F unit 109 functions as an interface for connecting the recording device 10 to external devices. The I / F unit 109 also functions as an interface for exchanging data with communication devices using infrared communication, wireless LAN, etc., and as an interface for connecting to the internet. Through the I / F unit 109, the recording device 10 can exchange data, such as input images, with external devices. Data exchange refers to the transmission or reception of data.

[0023] The paper feed unit 110 is a device for storing recording paper used for printing. Recording media such as recording paper of a specified size are fed from the selected paper cassette to the image recording unit 107. Details of the paper feed unit 110 will be described later.

[0024] Each of the aforementioned components is connected to the bus 111, and data can be exchanged via the bus 111. In the above-described configuration, an example was explained in which each component within the recording device 10 is connected via the bus 111. However, it is also possible for one of the multiple components (for example, the image recording unit 107) to be implemented as an external device of the recording device 10 and connected via the I / F unit 109.

[0025] <Hardware configuration of the image recording unit and image acquisition unit> Figure 2(a) is a schematic diagram showing the image recording unit 107 and image reading unit 108 shown in Figure 1.

[0026] In this embodiment, the image recording unit 107 refers to a unit comprising an inkjet recording head, platen, etc., which records an image by ejecting ink from a nozzle onto recording paper.

[0027] As shown in Figure 2(a), the image recording unit 107 is equipped with multiple recording heads, namely recording heads 201 to 204 corresponding to black (K), cyan (C), magenta (M), and yellow (Y). Each of the recording heads 201 to 204 is a so-called full-line type, in which multiple nozzles for ejecting ink are arranged in a predetermined direction within a range corresponding to the width of the recording paper 206. As shown in Figure 2(a), the width direction of the recording paper 206 is defined as the x-direction, and the transport direction of the recording paper 206 is defined as the y-direction. These coordinate axes will be used as needed in the following explanation.

[0028] Figure 2(b) is a schematic diagram of the recording head 201 corresponding to black (K) as viewed from the nozzle side. As shown in Figure 2(b), the recording head 201 is composed of multiple chip modules 201-1 to 201-5, each of which is connected to an independent circuit board. The recording heads 202 to 204 corresponding to cyan (C), magenta (M), and yellow (Y) have a similar structure to the recording head 201.

[0029] Figure 2(c) shows chip module 201-1, one of the multiple chip modules shown in Figure 2(b), viewed from the nozzle side. As shown in Figure 2(c), chip module 201-1 has multiple nozzles. In the example shown in Figure 2(c), chip module 201-1 has 16 nozzles. The nozzle arrangement resolution for each ink color nozzle row is 1200 dpi.

[0030] Furthermore, regarding the nozzle arrangement in the recording head 201, which is composed of multiple chip modules, it is sufficient that an image can be recorded using multiple nozzle groups arranged in a predetermined first direction intersecting the y direction. Each nozzle group of the multiple nozzle groups includes at least one nozzle arranged in a predetermined second direction intersecting the y direction. In this specification, the "predetermined first direction" and the "predetermined second direction" are described as being the x direction orthogonal to the y direction, but these directions are not limited to the x direction. One of the "predetermined first direction" and the "predetermined second direction" may be a direction slightly inclined from the x direction (for example, about 5 degrees). To give an example of the aforementioned "nozzle group," for example, the nozzle from the left in the upper row of Figure 2(c) can be the first nozzle group, and the nozzle from the left in the lower row can be the second nozzle group. In this case, it can be said that 16 nozzle groups, each containing one nozzle, are arranged so as to intersect the transport direction. Alternatively, the two nozzles from the left in the upper row of Figure 2(c) and the two nozzles from the left in the lower row, totaling four nozzles, can be grouped together as the first nozzle group. In this case, the four nozzle groups, each containing four nozzles, are arranged so as to intersect with the conveying direction.

[0031] For example, if the nozzle arrangement has a resolution of 2400 dpi in the x-direction, a chip module can be used that records images in units of 1200 dpi in multiple areas in the x-direction on the recording medium using two adjacent nozzles in the x-direction. Alternatively, if the nozzle arrangement has multiple rows of nozzles in the y-direction with a resolution of 1200 dpi in the x-direction, a chip module can be used that records images in units of 1200 dpi in multiple areas in the x-direction on the recording medium using multiple nozzles in the y-direction. Note that chip modules 201-2 to 201-5 have the same structure as chip module 201-1.

[0032] Furthermore, the image recording unit 107 is connected to a paper feeding unit 110, which has multiple paper feed cassettes 211 to 214 as shown in Figure 2(d). Hereafter, unless otherwise specified, each of the paper feed cassettes 211 to 214 will be referred to as the paper feeding stage.

[0033] When the user instructs the printer to print, one paper feed cassette is selected from among several paper feed cassettes, and the recording medium is fed from the selected paper feed cassette to the image recording unit 107.

[0034] The transport roller 205 (and other rollers not shown) rotates due to the driving force of a motor (not shown), transporting the recording paper 206 in the direction indicated by arrow 207 in Figure 2(a). While the recording paper 206 is being transported, ink is ejected from each of the recording heads 201 to 204 according to the recording data, and one raster image corresponding to the nozzle row of each recording head is sequentially recorded. In this way, by repeating the ink ejection operation from each recording head to the transported recording paper 206, an image for one page can be recorded.

[0035] The image reading unit 108 is positioned downstream of the recording heads 201-204 in the transport direction of the recording paper 206. The recording paper 206, on which images have been recorded by the recording heads 201-204, is transported so as to pass below the image reading unit 108.

[0036] The image reading unit 108 acquires two-dimensional RGB image data by sequentially capturing images of the transported recording paper 206, and stores the acquired RGB image data in the storage device 105. In this embodiment, the resolution of this RGB image data is 600 dpi. The resolution is arbitrary, and the resolution may differ between the x and y directions, for example, 1200 dpi in the x direction and 600 dpi in the y direction.

[0037] <Configuration of the image processing unit> The configuration of the image processing unit 106 shown in Figure 1 will be explained below with reference to Figure 3. The image processing unit 106 includes an image input unit 301, a gamma correction processing unit 302, an HS correction processing unit 303, an HT processing unit 304, a conversion reading value storage unit 305, a reference reading value storage unit 306, an HS correction table creation unit 307, and a paper type-specific HS correction table storage unit 308. Note that "HS" is an abbreviation for head shading.

[0038] Image data corresponding to the ink colors used in the image recording unit 107 is input to the image input unit 301. In this embodiment, 8-bit CMYK image data is input for each ink color. If the input image data to the image processing unit 106 is RGB image data, the RGB image data is converted to CMYK image data by a color conversion means (not shown) preceding the image input unit 301 before being input to the image input unit 301. A known LUT (lookup table) process can be used for the color conversion process.

[0039] The gamma correction processing unit 302 performs gamma correction on the CMYK color signal image data. Gamma correction is a process that corrects the average density gradation characteristics of printed materials by correcting each ink color. The gamma correction processing uses a known one-dimensional LUT process.

[0040] The HS correction processing unit 303 refers to the HS correction table stored in the paper type-specific HS correction table storage unit 308 and performs HS correction processing on the CMYK color signal image data. Here, HS correction processing is a process that corrects density unevenness in printed materials caused by variations in the ejection characteristics of the recording heads 201 to 204, by correcting each region. The HS correction table stored in the paper type-specific HS correction table storage unit 308 exists for each CMYK color, and in this embodiment, an HS correction table for the four CMYK colors is prepared for each paper type that can be recorded by the recording device 10. Thus, in this embodiment, the gamma correction processing unit 302 that performs gradation correction and the HS correction processing unit 303 that performs density unevenness correction are separated.

[0041] Figure 4 shows an example of the HS correction table 400 in this embodiment. The input signal value 401 is an 8-bit signal value corresponding to the signal value of any one color in the CMYK image. The nozzle group number 402 is a number associated with each nozzle group of the recording head.

[0042] As shown in Figure 4, the HS correction table 400 is a table that stores the correction amount for each nozzle group number for each input signal value. The HS correction processing unit 303 corrects the signal value using the input signal value corresponding to the signal value of each color in the CMYK image data corresponding to the type of paper being recorded, and the correction value identified by the nozzle group number. Specifically, for each pixel of the color signal image data, the pixel value of the pixel of interest and the corresponding nozzle group number are acquired. Then, by referring to the HS correction table 400 and using the acquired pixel value and nozzle group number, the correction value is identified and acquired, and this acquired correction value is used instead of the signal value.

[0043] Furthermore, linear interpolation is performed when referencing the table. For example, in Figure 4, when the input signal value is 8 and the nozzle group number is 0, the correction value 14 is obtained by linear interpolation between "the value for input value 0 and nozzle group number 0" (correction value 0) and "the value for input value 16 and nozzle group number 0" (correction value 28). In addition, nearest neighbor interpolation may be performed when referencing the nozzle group number. For example, in Figure 4, when the nozzle group numbers are from 5 to 12, the table for nozzle group number 8 is obtained.

[0044] The HS correction table 400 is created by the HS correction table creation unit 307. Details of the HS correction table creation process will be described later.

[0045] Returning to the explanation of Figure 3, the HT processing unit 304 performs HT processing (quantization processing) on ​​the image data after HS correction processing. "HT" is an abbreviation for halftone. In this embodiment, 8-bit image data for each color is converted into 1-bit HT image data for each color. A known dithering method is used for HT processing. Note that the HT processing method is arbitrary, and methods such as error diffusion can also be applied.

[0046] The image recording unit 107 receives HT image data as recording data and records an image on the recording paper 206 by ejecting ink from the recording heads 201 to 204 based on the received HT image data.

[0047] The image reading unit 108 acquires image data recorded on the printed material by capturing an image of the printed material. If the printed material is a test chart as described later, the image reading unit 108 sends the image data acquired by capturing an image to the conversion reading value storage unit 305 or the reference reading value storage unit 306.

[0048] Here, the conversion reading value is a reading value acquired only once, such as when registering new media, and the conversion reading value storage unit 305 stores reading values ​​for multiple paper types.

[0049] Furthermore, the reference reading is a reading that is updated at a predetermined timing, and the reference reading storage unit 306 stores the reading of one type of paper. The paper type used to acquire or store the reference reading is one of the multiple paper types used to acquire or store the conversion reading.

[0050] In the following, the type of paper used to obtain conversion readings will be referred to as "conversion paper," and the type of paper used to obtain reference readings will be referred to as "reference paper."

[0051] The conversion reading value storage unit 305 stores the reading values ​​read by the image reading unit 108 when the conversion reading value acquisition flow described later is executed, linked to the type of paper used for the printed document.

[0052] The reference reading value storage unit 306 stores the reading values ​​read by the image reading unit 108 when the reference reading value acquisition flow described later is executed, linked to the type of paper used for the printed material.

[0053] In this embodiment, we will describe an example in which the image data acquired by imaging with the image reading unit 108 (image data in which each pixel constituting the image has a pixel value, and this image data is referred to as read image data) is stored as the read value. However, the data format of the read value is not limited as long as the data can retain information on the density characteristics of each nozzle group on the recording paper acquired from the read image data.

[0054] The HS correction table creation unit 307 creates an HS correction table according to the type of recording paper. First, it refers to the readings stored in the conversion reading value storage unit 305 and calculates the conversion characteristics from the reference paper to the conversion paper. Based on these conversion characteristics and the reference readings updated with the latest ejection characteristics, it creates an HS correction table for the conversion paper. Therefore, even if the ejection characteristics change over time, it is possible to update the HS correction table for the conversion paper to a state corresponding to the latest ejection characteristics by remeasuring only the reference paper. Details of the HS correction table creation process will be described later.

[0055] The paper type-specific HS correction table storage unit 308 stores an HS correction table for each created recording sheet, linked to the paper type information of the recording sheet.

[0056] <Flowchart for obtaining conversion readings> The following describes the process for obtaining conversion readings in this embodiment (this process will be referred to as the conversion reading acquisition process) using Figure 5. Figure 5 is a flowchart of the conversion reading acquisition process in this embodiment.

[0057] The acquisition of conversion readings is performed at any time instructed by the user, or at the start of a print job, and conversion readings for multiple paper types are obtained within a predetermined period during which the ejection characteristics of the nozzle group can be considered equivalent. In this embodiment, the user instructs the acquisition of conversion readings by operating the operation unit 103.

[0058] First, the user inputs or sets information about the paper type to be measured for conversion readings from among the paper types set in the paper feed tray via the operation unit 103 to the recording device 10, and starts acquiring conversion readings. Then, in step S501, the CPU 100 acquires information about the paper type to be measured for conversion readings. Note that when acquiring conversion readings, all paper types set in the paper feed tray may be acquired as paper types to be measured for conversion readings. Also, when acquiring conversion readings at the start of a print job, all paper types used in the print job may be acquired as paper types to be measured for conversion readings. Hereafter, "step S~" will be abbreviated as "S~".

[0059] In S502, the image input unit 301 acquires image data of a test chart for acquiring conversion readings from the storage device 105. Figure 6 shows an example of a test chart. The test chart 600 includes unevenness acquisition patches 601 to 609 of a uniform input signal value S(t) with 9 grayscale levels. t is the grayscale number, and in the example in Figure 6, there are 9 grayscale levels from t=1 to 9, but it is not limited to this and can be any number of grayscale levels. The test chart 600 also includes markers 610a to 610j for associating the nozzle group positions on the recording head with the positions of the unevenness acquisition patches. As shown in Figure 6, the markers in this example are composed of multiple straight lines extending in the y direction, and each of these multiple straight lines is formed at a predetermined interval in the x direction.

[0060] Returning to the explanation of Figure 5, in S503, the HT processing unit 304 performs HT processing on the image data acquired in S502.

[0061] In S504, the paper feed unit 110 feeds recording paper of the paper type for which conversion readings are to be measured from the paper feed cassette to the image recording unit 107. Subsequently, the image recording unit 107 records an image on the fed recording paper based on the image data (i.e., recording data) after HT processing in S503.

[0062] In S505, the CPU 100 acquires read image data by using the image reading unit 108 to capture an image of the test chart recorded in S504. The read image data acquired in this step is image data in two-dimensional bitmap format.

[0063] In S506, the CPU 100 stores the read image data acquired in S505 in the conversion read value storage unit 305, linking it with the recorded paper type information.

[0064] In S507, the CPU 100 determines whether it has obtained conversion readings for all paper types for which conversion readings should be measured. If the result of this step is YES, the conversion reading acquisition flow is terminated. On the other hand, if the result of this step is NO, the process returns to S504. In this case, the paper type for which conversion readings are measured is set to one for which conversion readings have not yet been measured, and the process from S504 is repeated.

[0065] <Printing user images> The following describes the printing process for an image specified by the user (referred to as the user image) using Figure 7(a). Figure 7(a) is a flowchart of the user image printing process in this embodiment. This flow is triggered when a print job is submitted to the recording device 10 by the user via the operation unit 103.

[0066] In S701, the CPU 100 acquires one or more print jobs submitted by the user. Users can submit not only jobs that print on a single type of paper, so-called single jobs, but also jobs that sequentially switch between multiple types of paper set in the paper feed tray, so-called mixed jobs. If there are any types of paper used in a print job for which the acquisition of conversion readings has not been completed, the display unit 104 may be used to notify the user of this fact. This allows the user to perform the conversion reading acquisition process as needed.

[0067] In S702, the CPU 100 determines whether or not to update the reference reading in the recording device 10. Specifically, it compares the count value Cnt of the update counter with a predetermined threshold Th and determines whether Cnt > Th is satisfied. If the result of this step is YES, it is determined that updating the reference reading is necessary, and the process proceeds to S703. On the other hand, if the result of this step is NO (in other words, if Cnt ≤ Th is satisfied), it is determined that updating the reference reading is unnecessary, and the process proceeds to S706.

[0068] Here, the update counter is a counter for determining the timing of updating the reference reading data, and is used to update the reference reading data after a predetermined period has elapsed during which the ejection characteristics of the nozzle group change. In this embodiment, it counts the cumulative number of printed pages. Alternatively, it may count the cumulative printing time. The threshold Th can also be changed as appropriate by the user via the operation unit 103.

[0069] In S703, the CPU 100 executes a process to acquire a reference reading (this process is referred to as the reference reading acquisition process). The flow of the reference reading acquisition process is explained using Figure 7(b). Figure 7(b) is a detailed flowchart of the reference reading acquisition process in S703.

[0070] In S7031, the CPU 100 acquires information about the paper type for which the reference reading is to be measured. The paper type for which the reference reading is to be measured is set by the user. Alternatively, the user may specify the paper type for which the reference reading is to be measured in advance via the operation unit 103, or the paper type of the recording paper to be used for the next print job may be set in the print job. It is preferable that the paper type for which the reference reading is to be measured is selected from among the paper types for which conversion readings have already been acquired.

[0071] In step S7032, the image input unit 301 acquires image data of a test chart for acquiring reference readings from the storage device 105. This image data is stored in the storage device 105 and is the same image data as the test chart for acquiring readings shown in Figure 6.

[0072] In S7033, the HT processing unit 304 performs HT processing on the image data acquired in S7032.

[0073] In S7034, the paper feed unit 110 feeds the reference paper from the paper feed cassette, which is set with the paper type used to measure the reference reading, to the image recording unit 107. Subsequently, the image recording unit 107 records an image on the fed reference paper based on the HT image acquired in S7033.

[0074] In step S7035, the CPU 100 uses the image reading unit 108 to capture an image of the recorded test chart. The image data acquired by the imaging in this step is two-dimensional read image data.

[0075] In S7036, the CPU 100 stores the read image data acquired in S7035 in the reference reading value storage unit 306, linked to the information of the recorded paper type, and then terminates the reference reading value acquisition process.

[0076] Returning to the explanation of Figure 7(a), in S704, CPU100 resets the update counter's count value Cnt to zero.

[0077] In S705, the CPU 100 deletes all HS correction tables for each type of recording paper stored in the paper type HS correction table storage unit 308.

[0078] The processes from S703 to S705 described above complete the updating of the reference readings to accommodate the latest ejection characteristics and the deletion of the old HS correction tables for each paper type that were created before the update and corresponded to the old ejection characteristics.

[0079] In S706, CPU100 increments the update counter.

[0080] In S707, the image input unit 301 acquires print image data included in the print job.

[0081] In S708, the gamma correction processing unit 302 performs gamma correction processing on the print image data acquired in S707.

[0082] In S709, the HS correction processing unit 303 determines whether it is necessary to create an HS correction table. Specifically, it checks whether an HS correction table corresponding to the type of paper to be used for the next print job has already been created, and if not, it determines that it is necessary to create one. If the result of this step is YES, the process proceeds to S710. On the other hand, if the result of this step is NO, the process proceeds to S711.

[0083] In S710, CPU100 executes the process of creating an HS correction table for each paper type (this process is referred to as the HS correction table creation process). Details of the HS correction table creation process will be described later.

[0084] In S711, the HS correction processing unit 303 retrieves the HS correction table corresponding to the paper type to be recorded from the paper type HS correction tables stored in the paper type HS correction table storage unit 308, and performs HS correction processing by referring to the retrieved HS correction table.

[0085] In S712, the HT processing unit 304 performs HT processing on the image data after the HS correction processing in S711.

[0086] In S713, the paper feed unit 110 feeds the recording paper to be used for printing from the paper feed cassette into the image recording unit 107. Subsequently, the image recording unit 107 records an image on the recording paper based on the image data (i.e., recording data) after the HT processing in S712.

[0087] In S714, the CPU 100 determines whether all print jobs have ended. If the determination result in this step is YES, the user image printing flow ends. On the other hand, if the determination result in this step is NO, it returns to S702, and for the print jobs that have not yet ended, the processing from S702 is repeatedly executed.

[0088] Through the processing from S701 to S714 described above, the image specified by the user can be printed.

[0089] <HS correction table creation process in S710> In this embodiment, it is checked whether an HS correction table corresponding to the type of recording paper to be used for the next print in the print job has been created. If not created, in S710 of FIG. 7(a), the HS correction table creation unit 307 creates an HS correction table. Hereinafter, the HS correction table creation process in S710 will be described using FIG. 8. FIG. 8 is a flowchart of the HS correction table creation process. Note that the following processing is executed for each ink color.

[0090] In S801, the HS correction table creation unit 307 acquires, as the information of the first paper type, the information of the paper type associated with the reference reading value stored in the reference reading value storage unit 306. <00​​​​​​​​​​​

[0094] In S805, the HS correction table creation unit 307 acquires the read image data stored in association with the second paper type from the conversion read value storage unit 305 as the second read image data.

[0095] In S806, the HS correction table creation unit 307 creates a second HS correction table based on the second read image data. The creation process in this step is the same as in S803, and the details will be described later.

[0096] In step S807, the HS correction table creation unit 307 derives the conversion characteristics based on the first HS correction table and the second HS correction table. Details of the conversion characteristics derivation process in this step will be described later.

[0097] In S808, the HS correction table creation unit 307 creates a third HS correction table based on the read image data (referred to as the third read image data) stored in the reference read value storage unit 306. The creation process in this step is the same as in S803, and the details will be described later.

[0098] In S809, the HS correction table creation unit 307 creates a fourth HS correction table by converting the third HS correction table created in S808 based on the conversion characteristics acquired in S807. The conversion method in this step will be described later.

[0099] In S810, the HS correction table creation unit 307 links the created fourth HS correction table to the second paper type and stores it in the paper type-specific HS correction table storage unit 308.

[0100] Based on the processing steps S801 to S810 described above, an HS correction table can be created according to the type of paper used for printing in the print job, based on the updated reference readings.

[0101] <HS Correction Table Creation Process in S803, S806, and S808> Hereinafter, the HS correction table creation process in S803, S806, and S808 will be described using FIG. 9. FIG. 9 is a flowchart of the HS correction table creation process in S803, S806, or S808. The main body of each step in this flowchart is the HS correction table creation unit 307.

[0102] In S901, a non-uniformity acquisition patch image is extracted from the read image data, and for a plurality of pixels having the same x-direction position that constitute the extracted non-uniformity acquisition patch image, the average in the conveyance direction (y direction) is taken to derive a line profile (which is one-dimensional data). In the derivation of the line profile, among the RGB image signals of the read image data, a color signal that can obtain sufficient contrast is selected and used according to the ink color. Note that, according to the ink color, a weighted average signal value of the RGB image signals may be used.

[0103] In this embodiment, nine line profiles corresponding to the non-uniformity acquisition patches 601 to 609 are obtained. The line profiles obtained here represent the chromaticity values on the recording paper for each region in the x direction, and it is preferable to convert them into data of density values or lightness values using a predetermined conversion function from the signal values of the read image data and then use them. Hereinafter, the description will be made assuming that the line profiles are density value data.

[0104] In S902, the position of the read image is associated with the nozzle group number. Specifically, the markers 610a to 610j in FIG. 6 are detected from the read image, and the marker positions are associated with the nozzle group numbers corresponding to the relevant markers.

[0105] In S903, a correction target value for each of the nine line profiles is obtained. In this embodiment, the average value of the line profile for each gradation (which is the average value of the pixel values of the pixels arranged in the x direction) is used as the correction target value.

[0106] In S904, initialize the target nozzle group number. In this embodiment, since the nozzle group at the left end of the recording head is set as nozzle group number 0, initialize the target nozzle group number to 0.

[0107] In S905, for each gradation (t) of the test chart, calculate the correction amount in the target nozzle group. Details of the correction amount calculation process for each nozzle group in this step will be described later.

[0108] In S906, determine whether the correction amount has been calculated for all nozzle groups. If the determination result in this step is YES, that is, when the calculation of the correction amount for all nozzle groups is completed, end the HS correction table creation process. On the other hand, if the determination result in this step is NO, that is, when there is a nozzle group for which the correction amount has not been calculated, advance the target nozzle group number by one and return to S905.

[0109] <Correction amount calculation process for each nozzle group in S905> Hereinafter, the correction amount calculation process for each nozzle group in S905 will be described using FIG. 10.

[0110] In S905, for each input signal value S(t) of the test chart, calculate the correction amount in the target nozzle group. Here, t is the gradation number, and in this embodiment, as shown in FIG. 6, t = 1 to 9. To calculate the correction value in the input signal value S(t), use the values of the line profiles of the gradation (t) in the target nozzle group and the gradations (t - 1, t + 1) before and after the target nozzle group. Therefore, in this embodiment, for the first gradation without a previous gradation and the ninth gradation without a subsequent gradation, the correction amount is not calculated. However, for the ninth gradation, virtual data for the tenth gradation may be created by extrapolation based on the density values of the eighth and ninth gradations, and the correction amount may be calculated.

[0111] Figure 10(a) shows the density characteristics of two different nozzle groups (first nozzle group: 1011, second nozzle group: 1012) and the correction target value (1010) obtained in S903 in the line profile derived from the first read image data. Figure 10(b) shows the density characteristics of two different nozzle groups (first nozzle group: 1021, second nozzle group: 1022) and the correction target value (1020) obtained in S903 in the line profile derived from the second read image data. Figure 10(c) shows the density characteristics of two different nozzle groups (first nozzle group: 1031, second nozzle group: 1032) and the correction target value (1030) obtained in S903 in the line profile derived from the third read image data.

[0112] In Figures 10(a) to (c), the vertical axis represents the density value, and the horizontal axis represents the input signal value of the test chart's grayscale. Furthermore, in Figures 10(a) to (c), the input signal value S(t) used to calculate the correction value, as well as the input signal values ​​S(t-1) and S(t+1) for the grayscales before and after it, are shown, out of the nine grayscale levels.

[0113] The concentration values ​​in the acquired line profiles differ for each nozzle group's discharge characteristics. For example, in a nozzle group with a high discharge rate, the curve connecting the plots shifts upward (towards a darker direction). On the other hand, in a nozzle group with a low discharge rate, the curve connecting the plots shifts downward (towards a brighter direction).

[0114] Furthermore, the density characteristics of the recorded image generally differ depending on the type of recording paper used. More specifically, the surface properties and the chromaticity of the paper itself differ, resulting in differences in density variation with respect to the amount of paper ejected (density unevenness characteristics) and average density variation with respect to the number of ejected particles (density gradation characteristics).

[0115] The first read image data for conversion (see Figure 10(a)) and the second read image data for conversion (see Figure 10(b)) are acquired at approximately the same time. Therefore, the ejection characteristics of the nozzle group are the same when the first read image data is acquired and when the second read image data is acquired, but the type of recording paper is different. Consequently, the change in density (density unevenness characteristics) and the average change in density with respect to the number of ejected shots (gradation) (density gradation characteristics) differ between the first nozzle group and the second nozzle group.

[0116] On the other hand, the third read image data for reference (see Figure 10(c)) is acquired at a different timing than the aforementioned approximately identical timing, specifically after a predetermined number of prints have been made based on the count value of the update counter. Therefore, although the type of recording paper is the same when the third read image data is acquired and when the first read image data for conversion (see Figure 10(a)) is acquired, the ejection characteristics of the nozzle group are different. In this example, when the first read image data for conversion is acquired, the recording density by the first nozzle group is greater than the correction target value, and the recording density by the second nozzle group is less than the correction target value. This state changes when the third read image data for reference is acquired, so that the recording density by the first nozzle group is less than the correction target value, and the recording density by the second nozzle group is greater than the correction target value.

[0117] The following example illustrates how to create the first HS correction table HS1(S,n) using Figure 10(a). Here, S represents the input signal value and n represents the nozzle group number.

[0118] First, obtain the correction target value Tgt(S(t)) corresponding to the input signal value S(t).

[0119] For the first nozzle group, the input signal value S11 is obtained by referring to the density characteristic 1011 to achieve the correction target value. Then, D11, which is the difference between S11 and S(t), is obtained as the correction value HS(S, 1) for the first nozzle group to correct (reduce) the chromaticity difference between the correction target value and the density value of the first nozzle group. Linear interpolation is performed when referring to the density characteristic.

[0120] In the case of the second nozzle group, an input signal value S12 for realizing the corrected target value is obtained by referring to the density characteristic 1012. Then, a difference D12 between S12 and S(t) is obtained as a correction value HS(S, 2) of the second nozzle group for correcting (reducing) the chromaticity difference between the corrected target value and the density value of the second nozzle group. By repeatedly executing the above processing for the input signal value S(t) of each gradation and each nozzle group n, the first HS correction table HS1(S, n) can be obtained.

[0121] Regarding the second HS correction table HS2(S, n) and the third HS correction table HS3(S, n), they can be obtained based on the line profile derived from the respective read image data and the corrected target value, in the same manner as the first HS correction table HS1(S, n).

[0122] <Derivation process of conversion characteristics in S807> Hereinafter, the acquisition process of the conversion characteristics in S807 will be described using FIGS. 10(a) and 10(b).

[0123] In S807, conversion characteristics are obtained based on the first HS correction table HS1 and the second HS correction table HS2. As described above, since the first read image data for conversion and the second read image data for conversion are acquired at substantially the same timing, the ejection characteristics of the nozzle group are the same at the time of acquiring the first read image data and at the time of acquiring the second read image data, and the types of recording paper are different. Although the ejection characteristics are the same, the types of recording paper are different, so the density change (density unevenness characteristic) of the first nozzle group and the second nozzle group and the average density change (density gradation characteristic) with respect to the ejection number (gradation) are different. Therefore, as tables for correcting density unevenness, two types of tables, specifically, the first HS correction table HS1(S, n) and the second HS correction table HS2(S, n), are prepared. Different correction amounts are held in the first HS correction table HS1(S, n) and the second HS correction table HS2(S, n).

[0124] The correction amount for each recording paper is determined depending on density characteristics (density unevenness characteristics, density gradation characteristics). At this time, if the ejection characteristics for each nozzle group are the same, it can be said that the ratio of the correction amounts between paper types is substantially constant regardless of the nozzle group. Specifically, when the ratio of the correction amount for the first nozzle group, (S11 - S(t)) / (S21 - S(t)), is defined as R(1), and the ratio of the correction amount for the second nozzle group, (S12 - S(t)) / (S22 - S(t)), is defined as R(2), then R(1) ≈ R(2). In the present embodiment, the average value Rave of the ratio of the correction amounts between paper types calculated for each nozzle group is obtained as the conversion characteristic of the correction amount. By obtaining this for each input signal value S(t) of each gradation, as shown in (Equation 1), the conversion characteristic T12(S(t)) of the correction amount between paper types that does not depend on the state of the ejection characteristics can be obtained. The conversion characteristic T12(S(t)) is a value for each input signal value.

[0125] [Number]

[0126] FIG. 15 shows conversion characteristic 1500 as an example of the conversion characteristic in the present embodiment. The input signal value 1501 is an 8-bit signal value corresponding to the input signal value 401 of the HS correction table. Also, the ink color 1502 is the color for which the HS correction table is prepared.

[0127] As shown in FIG. 15, the conversion characteristic 1500 is a table in which the conversion coefficient with respect to the correction amount is held for each input signal value of the HS correction table, and the correction amount is converted using the same correction coefficient for each nozzle group. Note that for the first gradation and the ninth gradation for which the correction amount is not calculated in the present embodiment, the conversion characteristic is set to 1.

[0128] <(Process of converting the third HS correction table to create the fourth HS correction table in S809)> Hereinafter, the process of converting the third HS correction table to create the fourth HS correction table in S809 will be described.

[0129] In S809, a fourth HS correction table is created based on the third HS correction table HS3 and the conversion characteristics of the correction amount. As mentioned above, the third read image data for reference is acquired after a predetermined number of prints have been made based on the count value of the update counter. Therefore, at the time of acquiring the third read image data, the type of recording paper is the same as when acquiring the first read image data for conversion, but the ejection characteristics of the nozzle group are in their most up-to-date state.

[0130] The HS correction table for the first paper type (third HS correction table HS3), calculated based on the discharge characteristics of the latest nozzle group, is converted using the conversion characteristic T12 for the correction amount between the first and second paper types, which is independent of the discharge characteristics.

[0131] This makes it possible to create a fourth HS correction table HS4 for the second paper type that corresponds to the discharge characteristics of the latest nozzle group, as shown in (Equation 2).

[0132]

number

[0133] <Effects of this embodiment> As described above, in this embodiment, the conversion characteristics from the reference paper to the conversion paper are calculated based on the readings stored in the conversion reading storage unit 305. Based on these conversion characteristics and the reference readings updated with the latest ejection characteristics, an HS correction table for the conversion paper is created. Therefore, even if the ejection characteristics change over time, the HS correction table for the conversion paper can be updated to correspond to the latest ejection characteristics by simply remeasuring only the reference paper.

[0134] Thus, according to this embodiment, head shading correction can be achieved to correct density unevenness to an appropriate amount according to the paper type without performing the printing and reading of a test chart of a second paper type corresponding to the latest ejection characteristics.

[0135] <Variation> In the above-described embodiment, an example was explained in which the read image data (pixel values ​​thereof) is stored as the read value, but the system is not limited to this configuration. The converted read value storage unit 305 may also store the data in the form of a line profile derived in S901 (see Figure 9) or an HS correction table derived in the flow shown in Figure 9. When storing the data in the form of a line profile, the line profile is obtained directly from the converted read value storage unit 305, so the processing in S901 is unnecessary.

[0136] Furthermore, when storing the data in the format of an HS correction table, the processes in S802 and S803 become unnecessary, and the first HS correction table can be directly obtained from the conversion reading value storage unit 305. Similarly, the processes in S805 and S806 become unnecessary, and the second HS correction table can be directly obtained from the conversion reading value storage unit 305.

[0137] By storing the data in the format of line profiles or HS correction tables, the amount of memory required for storage can be reduced.

[0138] [Second Embodiment] In the first embodiment, a reference reading value storage unit and a conversion reading value storage unit store the reading value data, and an example was described in which the conversion characteristics between the paper type (reference paper) from which the reference reading value was obtained and the paper type set in the print job are obtained each time. However, obtaining the conversion characteristics each time is computationally burdensome. To address this issue, in this embodiment, the conversion characteristics are obtained and stored in advance. Since it is difficult to obtain the conversion characteristics for all combinations of paper types in advance, an example is described in which the conversion characteristics for converting from one reference HS correction table to an HS correction table for each paper type are obtained and stored in advance.

[0139] In the following, we will focus on explaining the differences from the previously described embodiment, and will omit explanations of similar points as appropriate.

[0140] <Functional Configuration of Image Processing Unit> The configuration of the image processing unit 106 in this embodiment will be described below with reference to Figure 11.

[0141] As shown in Figure 11, the image processing unit 106 includes an image input unit 301, a gamma correction processing unit 302, an HS correction processing unit 303, and an HT processing unit 304. The image processing unit 106 also includes an HS correction table creation unit 1101, a conversion characteristic acquisition unit 1102, and a conversion characteristic storage unit 1103. Furthermore, the image processing unit 106 includes an HS correction table standardization unit 1104, a standard HS correction table storage unit 1105, an HS correction table conversion unit 1106, and a paper type-specific HS correction table storage unit 1107.

[0142] The HS correction table creation unit 1101 creates an HS correction table based on the read image data acquired by the image reading unit 108.

[0143] The conversion characteristics acquisition unit 1102 acquires the conversion characteristics for each paper type relative to a reference HS correction table. Details will be described later.

[0144] The conversion characteristics storage unit 1103 stores the conversion characteristics acquired by the conversion characteristics acquisition unit 1102, linked to the paper type information.

[0145] The HS correction table standardization unit 1104 converts the HS correction tables created for each paper type into a standard HS correction table based on the conversion characteristics. Details will be described later.

[0146] The reference HS correction table storage unit 1105 stores the reference HS correction table acquired by the HS correction table standardization unit 1104. This table is referred to as the reference HS correction table, reference correction table, etc.

[0147] The HS correction table conversion unit 1106 converts the reference HS correction table into a paper type-specific HS correction table based on conversion characteristics. Details will be described later.

[0148] The paper type-specific HS correction table storage unit 1107 stores the HS correction tables for each paper type acquired by the HS correction table conversion unit 1106.

[0149] <Conversion characteristics acquisition process> The process for acquiring the conversion characteristics in this embodiment (referred to as the conversion characteristics acquisition process) will be explained below using Figure 12. Note that steps S502 to S505 in Figure 12 are the same as steps S502 to S505 in Figure 5, so their explanation will be omitted.

[0150] The conversion characteristics acquisition process shown in Figure 12 is executed at any time specified by the user or at the start of a print job.

[0151] First, the user inputs or sets information about the paper types to be used to acquire conversion characteristics from among the paper types set in the paper feed tray via the operation unit 103 to the recording device 10. At this time, two or more paper types are set, and at least one type of paper for which conversion characteristics have already been acquired is set. Then, when the user starts acquiring the conversion readings, in S1201, the CPU 100 acquires information about the paper types to be used to acquire conversion characteristics (information about two or more paper types).

[0152] In S1202, the HS correction table creation unit 1101 creates an HS correction table based on the two-dimensional read image data acquired by the image reading unit 108 (i.e., imaging). The procedure for creating the HS correction table is the same as the flowchart shown in Figure 9, so the explanation is omitted.

[0153] In S1203, the HS correction table creation unit 1101 determines whether an HS correction table has been created for all paper types used to acquire conversion characteristics. If the result of this step is YES, the process proceeds to S1204. On the other hand, if the result of this step is NO, the process returns to S504. In this case, the processing from S504 is executed for paper types for which an HS correction table has not yet been created.

[0154] In S1204, the conversion characteristic acquisition unit 1102 acquires the conversion characteristics for the second paper type based on the HS correction table for the first paper type for which the conversion characteristics have already been acquired and the HS correction table for the second paper type for which the conversion characteristics have not yet been acquired. In this embodiment, the HS correction table for the first paper type is denoted as the first HS correction table HS1(S, n), and the HS correction table for the second paper type is denoted as the second HS correction table HS2(S, n). The conversion characteristics for the first paper type are denoted as T01, and the conversion characteristics for the second paper type are denoted as T02. Here, the conversion characteristics T01 and T02 are conversion characteristics for converting the reference HS correction table into the HS correction table for the first paper type and the HS correction table for the second paper type. In this embodiment, the conversion characteristic T02 for the second paper type for which the conversion characteristics have not yet been acquired is calculated based on the known conversion characteristic T01.

[0155] The first HS correction table HS1(S, n) and the second HS correction table HS2(S, n) are acquired at approximately the same time. Therefore, the ejection characteristics of the nozzle group are the same when the first read image data is acquired and when the second read image data is acquired, but the type of recording paper is different.

[0156] As mentioned above, although the ejection characteristics are the same, the types of recording paper are different, so the density changes (density unevenness characteristics) of the first nozzle group and the second nozzle group, and the average density changes (density gradation characteristics) with respect to the number of ejections (gradation) are different. For this reason, a first HS correction table HS1 and a second HS correction table HS2 are provided as tables to correct for density unevenness. Different correction amounts are held in the first HS correction table HS1 and the second HS correction table HS2. From these tables, the conversion characteristic T12(S) can be obtained using (Equation 1), as in the first embodiment. Here, the conversion characteristic T12(S) is a conversion characteristic for converting the HS correction table for the first paper type to the HS correction table for the second paper type.

[0157] The conversion characteristic T02(S) to be obtained can be acquired by equation (3) based on the known conversion characteristic T01(S) and the conversion characteristic T12(S) described above.

[0158]

number

[0159] In S1205, the conversion characteristic acquisition unit 1102 stores the acquired conversion characteristic T02(S) in the conversion characteristic storage unit 1103, linked to the second paper type.

[0160] <Printing user images> The user image printing process in this embodiment will be described below using Figure 13(a). Note that processes other than S1301 and S1302 are the same as those in Figure 7(a), and therefore their explanation will be omitted.

[0161] In S702, the CPU 100 determines whether or not the reference reading in the recording device 10 needs to be updated. Specifically, it compares the count value Cnt of the update counter with a predetermined threshold Th and determines whether Cnt > Th is satisfied. If the result of this step is YES, it is determined that the reference reading needs to be updated, and the process proceeds to S1301.

[0162] In S1301, the process of obtaining the reference HS correction table is executed (this process is referred to as the reference HS correction table acquisition process).

[0163] The following describes the process for obtaining the reference HS correction table, using Figure 13(b). Note that steps S13011, S13012, S13013, and S13014 are the same as those in Figure 7(b), and therefore their explanations are omitted.

[0164] In S13011, the CPU 100 acquires information about the paper type for which the reference reading will be measured. The paper type for which the reference reading will be measured is set by the user for the recording device 10 (or recording system). Alternatively, the user may specify the paper type for which the reference reading will be measured in advance via the operation unit 103, or the paper type of the recording paper to be used for the next print job may be set in the print job. It is preferable that the paper type for which the reference reading will be measured be selected from among the paper types for which conversion readings have already been acquired.

[0165] In S13012, the HS correction table creation unit 1101 creates an HS correction table based on the two-dimensional read image data acquired by the image reading unit 108 (i.e., imaging). In this embodiment, the HS correction table created in this step is referred to as the third HS correction table HS3(S, n). The procedure for creating the HS correction table is the same as the flowchart shown in Figure 9, so its explanation is omitted.

[0166] In S13013, the HS correction table standardization unit 1104 obtains the conversion characteristics for the paper type on which the reference reading was measured from the conversion characteristics storage unit 1103. Here, we will explain using the example of measuring the reference reading using the first paper type and obtaining the conversion characteristic T01(S) from the conversion characteristics stored in the conversion characteristics storage unit 1103. Subsequently, the reference HS correction table HSref(S,n) is obtained by converting the third HS correction table HS3(S,n) using the conversion characteristic T01(S) according to equation (4).

[0167]

number

[0168] Furthermore, as the reference HS correction table HSref(S,n), an HS correction table for a specific type of recording paper may be used, or a hypothetical HS correction table in which the standard deviation of the correction amount for each nozzle group has been normalized may be used.

[0169] In S13014, the reference HS correction table HSref(S,n) acquired in S13013 is stored in the reference HS correction table storage unit 1105, and the reference HS correction table acquisition process is terminated.

[0170] Returning to the explanation of Figure 13(a), in S1302, the HS correction table conversion unit 1106 creates an HS correction table corresponding to the paper type by converting the reference HS correction table according to the conversion characteristics for each paper type.

[0171] The HS correction table creation process in S1302 will be explained below using Figure 14. Note that the process shown in Figure 14 is performed for each ink color.

[0172] In S1401, the conversion characteristics stored in the conversion characteristics storage unit 1103 are acquired. The conversion characteristics acquired in this step are those for the type of recording paper to be used for printing in the print job. Here, an example is described in which, based on the print job, printing is performed on the second type of recording paper and the conversion characteristics T2(S) are acquired.

[0173] In S1402, the reference HS correction table HSref(S,n) stored in the reference HS correction table storage unit 1105 is obtained.

[0174] In S1403, the reference HS correction table HSref(S,n) is converted using the conversion characteristic T02(S) according to equation (5) to obtain the HS correction table for the second paper type. The HS correction table obtained in this step is designated as the fourth HS correction table HS4(S,n).

[0175]

number

[0176] In S1404, the fourth HS correction table HS4(S,n) acquired in S1403 is linked to the second paper type and stored in the paper type-specific HS correction table storage unit 1107.

[0177] <Effects of this embodiment> As explained above, according to this embodiment, the computational load can be reduced because the conversion characteristics are acquired and stored in advance. Furthermore, the conversion characteristics for converting from a single reference HS correction table to an HS correction table for each paper type are stored, which eliminates the need to acquire the conversion characteristics for all paper type combinations at the same time, thereby improving convenience.

[0178] <Variation> In the above embodiment, in S709, it was checked whether an HS correction table corresponding to the type of recording paper to be used for the next print job had already been created, and if not, it was determined that an HS correction table needed to be created. However, in the case of recording paper that does not store conversion characteristics, an HS correction table cannot be created. Therefore, in the case of recording paper that does not store conversion characteristics, a test chart may be printed on the recording paper during the execution of the print job to obtain a correction table specific to that recording paper. Alternatively, the conversion characteristics of the recording paper may be obtained by executing a conversion characteristics acquisition process during the execution of the print job.

[0179] Furthermore, in the above-described embodiment, an example was described in which the HS correction table standardization unit 1104 stores a pre-standardized standard HS correction table and converts the standard HS correction table to create an HS correction table for each paper type. However, it is also possible to store a paper type-dependent HS correction table (HS3) before standardization and create an HS correction table (HS4) for each paper type according to (Equation 6) based on the conversion characteristics for standardization (T01) and the conversion characteristics for each paper type (T2).

[0180]

number

[0181] [Other embodiments] In the embodiment described above, the conversion characteristics are set to the average value of the ratio of the correction amounts, but this is not the only option. For example, an approximation function that approximates the correspondence between the correction amounts for each nozzle group, or a lookup table may be used as the conversion characteristics.

[0182] Furthermore, while the above-described embodiment explained an example in which density correction processing (gamma correction processing) and HS correction processing were applied to image data, similar effects can be obtained by applying correction to the threshold matrix used in the dithering method.

[0183] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. It can also be implemented by a circuit (e.g., an ASIC) that implements one or more functions.

[0184] [Technical Features of This Disclosure] This disclosure includes the following components: (Configuration 1) A recording device comprising: a recording head having a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle; a correction table creation means for creating a correction table for reducing the chromaticity difference of an image recorded by the plurality of nozzle groups, the correction table creation means for creating the correction table for the conversion paper based on a first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper; a second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper; and a third read image data obtained by reading a test chart recorded by the recording head on the reference paper. (Configuration 2) The recording device according to Configuration 1, characterized in that an image is recorded in multiple regions on the recording paper in the second direction by each nozzle group of the multiple nozzle groups. (Configuration 3) The second direction is a direction perpendicular to the first direction. A recording device according to configuration 1 or 2, characterized by the above. (Configuration 4) A recording device according to any one of Configurations 1 to 3, further comprising acquisition means for acquiring image data of an image recorded on recording paper by the recording head. (Configuration 5) A recording device according to any one of Configurations 1 to 4, characterized in that the first read image data and the second read image data are acquired at substantially the same timing in which the discharge characteristics of the plurality of nozzle groups do not change, and the third read image data is acquired at a timing different from the substantially same timing. (Configuration 6) The recording device according to any one of Configurations 1 to 5, characterized in that the third read image data is acquired after a predetermined number of prints have been made. (Configuration 7) The recording device according to any one of Configurations 1 to 6, characterized in that the correction table creation means derives conversion characteristics from the reference paper to the conversion paper based on a first correction table created based on the first read image data and a second correction table created based on the second read image data, creates a third correction table based on the third read image data, and creates a fourth correction table based on the conversion characteristics and the third correction table. (Configuration 8) The recording device according to any one of Configurations 1 to 7, characterized in that the head shading correction means corrects the image data to be recorded on the conversion paper using the fourth correction table. (Configuration 9) The recording device according to any one of Configurations 1 to 8, characterized in that the correction table creation means acquires the conversion characteristics for each input signal value based on the correction value in the first correction table for the same nozzle group in the plurality of nozzle groups and the correction value in the second correction table for the same nozzle group. (Configuration 10) The recording device according to any one of Configurations 1 to 9, characterized in that the test chart includes a patch for acquiring uniformity of input signal values ​​of multiple grayscale levels. (Configuration 11) A recording device according to any one of Configurations 1 to 10, characterized in that a correction value for correcting the chromaticity value recorded on recording paper by the plurality of nozzle groups to approach a predetermined target value is stored in the correction table. (Configuration 12) A recording device according to any one of Configurations 1 to 11, characterized in that, in the correction table, the correction value is stored for each input signal value and for each nozzle group number. (Configuration 13) A recording device according to any one of Configurations 1 to 12, further comprising a gamma correction means for performing gamma correction processing on color signal image data. (Configuration 14) A recording device comprising: a recording head having a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle; a table storage means for storing a reference correction table for a reference paper which is a reference recording paper; a storage means for storing conversion characteristics for each paper type for converting from the reference correction table to a correction table for each paper type; a conversion means for converting the reference correction table to a correction table for the specific paper type based on the conversion characteristics from the reference paper to the conversion paper which is a recording paper of a specific paper type; and a head shading correction means for performing head shading correction on image data to be recorded on the conversion paper using the correction table obtained by the conversion means. (Control method for recording device) A control method for a recording device having a recording head having a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle, comprising: a creation step of creating a correction table for reducing the chromaticity difference of an image recorded by the plurality of nozzle groups, the creation step of creating the correction table for the conversion paper based on a first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper; a second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper; and a correction step of performing head shading correction on image data to be recorded on the conversion paper using the correction table. A program for causing a computer to execute a control method for a recording device having a recording head, the recording head having a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups contains at least one nozzle, the creation step of creating a correction table for reducing the chromaticity difference of an image recorded by the plurality of nozzle groups, the creation step of creating the correction table for the conversion paper based on a first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper, a second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper, and a third read image data obtained by reading a test chart recorded by the recording head on the reference paper, and a correction step of performing head shading correction on image data to be recorded on the conversion paper using the correction table. [Explanation of Symbols]

[0185] 201 Recording head 206 Record Sheet 303 HS Correction Processing Unit 307 HS Correction Table Creation Section

Claims

1. A recording head comprising a plurality of nozzle groups arranged in a second direction intersecting a first direction in which the recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle, A correction table creation means for creating a correction table for reducing the chromaticity difference of images recorded by the plurality of nozzle groups, the means for creating the correction table for the conversion paper based on: first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper; second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper; and third read image data obtained by reading a test chart recorded by the recording head on the reference paper. A head shading correction means that performs head shading correction on the image data to be recorded on the conversion paper using the correction table, Having, A recording device characterized by the following features.

2. Each of the nozzle groups of the plurality of nozzle groups records an image in multiple regions on the recording paper in the second direction. The recording device according to feature 1.

3. The second direction is perpendicular to the first direction. A recording device according to feature 1 or 2.

4. The system further includes acquisition means for acquiring image data of an image recorded on recording paper by the recording head, The recording device according to feature 1.

5. The first read image data and the second read image data are acquired at approximately the same timing in which the discharge characteristics of the plurality of nozzle groups do not change. The third read image data is acquired at a timing different from the substantially same timing. The recording device according to feature 4.

6. The third read image data is acquired after a predetermined number of prints have been made. The recording device according to feature 5.

7. The correction table creation means is Based on the first correction table created based on the first read image data and the second correction table created based on the second read image data, the conversion characteristics from the reference paper to the conversion paper are derived. Based on the aforementioned third read image data, a third correction table is created. A fourth correction table is created based on the conversion characteristics and the third correction table. The recording device according to feature 6.

8. The head shading correction means corrects the image data to be recorded on the conversion paper using the fourth correction table. The recording device according to feature 7.

9. The correction table creation means acquires the conversion characteristics for each input signal value based on the correction values ​​in the first correction table for the same nozzle group in the plurality of nozzle groups and the correction values ​​in the second correction table for the same nozzle group. The recording device according to claim 7 or 8.

10. The aforementioned test chart includes a patch for acquiring uniformity in input signal values ​​across multiple grayscale levels. The recording device according to feature 1.

11. Correction values ​​for adjusting the chromaticity value recorded on the recording paper by the plurality of nozzle groups to approach a predetermined target value are stored in the correction table. A recording device according to claim 1 or 10.

12. In the correction table, the correction value is stored for each input signal value and for each nozzle group number. The recording device according to feature 11.

13. The system further includes a gamma correction means for performing gamma correction processing on color signal image data. A recording device according to feature 1 or 2.

14. A recording head comprising a plurality of nozzle groups arranged in a second direction intersecting a first direction in which the recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle, A table storage means that stores a reference correction table for a reference sheet, which is a standard recording sheet, A storage means stores the conversion characteristics for converting the aforementioned standard correction table into a correction table for each paper type, for each paper type. A conversion means that converts the reference correction table into a correction table for the specific paper type based on the conversion characteristics from the reference paper to the conversion paper which is a specific type of paper. A head shading correction means that performs head shading correction on the image data to be recorded on the conversion paper using the correction table obtained by the conversion means, Having, A recording device characterized by the following features.

15. A recording device having a recording head comprising a plurality of nozzle groups arranged in a second direction intersecting a first direction in which recording paper is transported, wherein each of the plurality of nozzle groups includes at least one nozzle, and a control method for the recording device having the recording head, A creation step for creating a correction table for reducing the chromaticity difference of images recorded by the plurality of nozzle groups, comprising: creating the correction table for the conversion paper based on: first read image data obtained by reading a test chart recorded by the recording head on a reference paper which is a first type of recording paper; second read image data obtained by reading a test chart recorded by the recording head on a conversion paper which is a second type of recording paper; and third read image data obtained by reading a test chart recorded by the recording head on the reference paper. A correction step in which head shading correction is performed on the image data to be recorded on the conversion paper using the correction table, Having, A control method for a recording device, characterized by the following:

16. A program for causing a computer to execute the control method for the recording device described in claim 15.

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