JP2012071483A - Image recording system and image recording method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the occurrence of streak unevenness caused by continuous overcorrection or insufficient correction.SOLUTION: An image recording system 1 is configured as follows. Regarding each discharge port of a recording module 211, the average and standard deviation of correction coefficients which are calculated a plurality of times are calculated as statistical correction coefficients with respect to a gradation value. Normal random numbers based on the average and standard deviation are calculated as random correction coefficients by which an appearance probability is determined on the basis of the statistical correction coefficients. Subsequently, the ink discharge amount from each discharge port is determined on the basis of the gradation values of pixels corresponding to each discharge port in original image data and the random correction coefficients of each discharge port. In a period during which ink discharge from each discharge port is executed, a step for determining the ink discharge amount is repeated by calculating the random correction coefficients. By this, it is possible to suppress the generation of a state that pixels having density larger (or smaller) than the gradation values of the original image data continuously appear in a scanning direction. Namely, it is possible to suppress the generation of streak unevenness caused by continuous overcorrection or insufficient correction.

Description

  The present invention relates to an image recording apparatus and an image recording method for recording an image on an object.

  When recording a multi-tone (that is, continuous tone) original image on various objects, dots of a certain size irregularly arranged (the smallest recordable pixel unit, also called a micro dot). ) Is used, an FM (Frequency Modulated) screen in which gradation expression is realized. In particular, an FM screen is often used in an image recording apparatus having a relatively low dot recording resolution, such as an ink jet printer.

  In recent years, in an image recording apparatus that discharges minute droplets from a head and records an image on an object, the droplets have been miniaturized, thereby reducing graininess in the recorded image. ing. However, since the weight of the droplet is reduced, the droplet is easily affected by the surrounding air current, and the relative landing position of the droplet with respect to the discharge port (the actual formation position of the dot on the object) is not good. May become stable. In addition, depending on the processing accuracy of the head, the ejection direction of droplets from a plurality of ejection ports may vary. In such a case, streaky unevenness extending in the scanning direction of the head (also referred to as banding unevenness, hereinafter referred to as “streaky unevenness”) in a portion where an area having a substantially uniform density is expressed in the recorded image. ) May occur, and in an FM screen in which dots are irregularly and uniformly dispersed, streak irregularity is usually noticeable.

  In Patent Document 1, in order to suppress unevenness caused by variations in the discharge amount of micro droplets from a plurality of discharge ports, a predetermined test pattern is printed and the density of a region corresponding to each of the plurality of discharge ports Is disclosed, and a threshold matrix for halftoning the original image data is corrected based on the difference between the measured density and the target density.

JP 2007-196472 A

  By the way, in the correction method of patent document 1, when the cause of a nonuniformity is a processing error etc. of a discharge outlet and there is reproducibility of a nonuniformity when printing the same pattern in multiple times, the nonuniformity is suppressed. Is possible. However, when the density of the recorded image is not stable due to the influence of the airflow near the discharge port, the temperature change of the ink, the variation in the conveyance speed of the printing target, and the like, streak unevenness with low reproducibility occurs. In the correction method, there is a risk of streak irregularity due to continuous overcorrection or insufficient correction.

  The present invention has been made in view of the above problems, and an object thereof is to suppress the occurrence of streaks due to continuous overcorrection or insufficient correction.

  The invention according to claim 1 is an image recording apparatus for recording an image on an object, and ejects ink droplets from a plurality of ejection openings arranged in a predetermined arrangement direction toward the object. An ejection unit, a moving mechanism that moves the object relative to the ejection unit in a scanning direction that intersects the arrangement direction, and the ejection unit in synchronization with the relative movement of the object in the scanning direction. A main body control unit that records an image on the object by controlling ink ejection from the object, a scanner that reads an image on the object, and correction of ink ejection amounts from the plurality of ejection ports A correction unit that obtains a statistical correction coefficient that is input, and based on the input original image data of the multi-tone original image and the statistical correction coefficient of the plurality of ejection ports, Of ink from the nozzle When the image is recorded on the object and the correction unit obtains the statistical correction coefficient of the plurality of discharge ports, a1) the main body control unit controls the discharge unit and the moving mechanism. By controlling, a set of three or more test drawing regions can be obtained by moving the object once in the scanning direction while ejecting ink from the plurality of ejection ports corresponding to one input gradation value. A step of recording a test image in a test drawing region group, a2) a step of reading each test image of the test drawing region group by the scanner, and a3) a correction unit based on an output from the scanner In each test image, an average density that is an average of the density of a plurality of pixels corresponding to each of the plurality of ejection openings is obtained, and a difference between the average density and a reference density corresponding to the input gradation value is obtained. A step of obtaining a correction coefficient to be corrected for each of the ejection openings; a4) a correction coefficient for all the test images in the test drawing region group as a statistical correction coefficient for the input gradation value for each of the ejection openings by the correction unit; A step of obtaining an average correction coefficient that is an average of the above and a variation value indicating a variation of the correction coefficient in all the test images; and a5) changing the input gradation value to another gradation value and performing the a1) process to By repeating the step a4), a step of obtaining a relationship between the gradation value and the statistical correction coefficient of each discharge port is performed. In recording an image on the object, the correction unit performs b1). Based on the gradation value of one pixel corresponding to each of the ejection openings in the original image data, and the relationship between the gradation value obtained in the step a5) and the statistical correction coefficient of each of the ejection openings. And b2) obtaining a random correction coefficient whose appearance probability is determined based on the statistical correction coefficient of each discharge port for each of the discharge ports; b3 ) A step of determining a discharge amount from each discharge port based on a gradation value of a pixel corresponding to each discharge port in the original image data and the random correction coefficient of each discharge port; b4) While ink is ejected from each of the ejection ports, the steps b1) to b3) are repeated.

  A second aspect of the present invention is the image recording apparatus according to the first aspect, wherein the variation value obtained in the step a4) is a standard correction coefficient for all the test images in the test drawing region group. Deviation.

  Invention of Claim 3 is an image recording apparatus of Claim 2, Comprising: The said random correction coefficient calculated | required by the said b2) process is the said average correction coefficient calculated | required by the said b1) process, And a normal random number having a normal probability distribution obtained based on the standard deviation.

  A fourth aspect of the present invention is the image recording apparatus according to any one of the first to third aspects, wherein the step b3) is a gradation value of a pixel corresponding to each of the ejection openings in the original image data. Are corrected based on the random correction coefficient of each discharge port to generate corrected image data, and a step of determining a discharge amount from each discharge port based on the corrected image data.

  A fifth aspect of the present invention is the image recording apparatus according to any one of the first to third aspects, wherein a threshold value matrix for halftoning the original image is stored in a storage unit, and the b3 ) Correcting a threshold value corresponding to each discharge port of the threshold value matrix based on the random correction coefficient of each discharge port to generate a correction threshold value matrix; and a plurality of the original image data Generating halftone image data in which the original image is halftoned by comparing gradation values and a plurality of threshold values included in the correction threshold value matrix at corresponding pixel positions; and the halftone image And a step of determining a discharge amount from each discharge port based on the data.

  A sixth aspect of the present invention is the image recording apparatus according to any one of the first to fifth aspects, wherein the supply unit holds a plurality of objects and sequentially supplies the plurality of objects to the moving mechanism. Is further provided.

  According to a seventh aspect of the present invention, there is provided an ejection unit that ejects micro droplets of ink toward a target from a plurality of ejection ports arranged in a predetermined arrangement direction, and the target in a scanning direction that intersects the arrangement direction. A moving mechanism for moving an object relative to the ejection unit, and controlling the ejection of ink from the ejection unit in synchronization with the relative movement of the object in the scanning direction. An image recording apparatus comprising: a main body control unit that records an image; a scanner that reads an image on the object; and a correction unit that obtains a statistical correction coefficient used for correcting the amount of ink ejected from the plurality of ejection ports. In the method of recording an image on the object, a) a step of obtaining a statistical correction coefficient, b) input original image data of a multi-tone original image, and step a) Statistical correction factor determined by And a step of recording an image on the object by controlling a discharge amount of ink from the plurality of discharge ports by the main body control unit, and the step a) includes a1) the main body control. By controlling the ejection unit and the moving mechanism by a unit, the object is moved once in the scanning direction while ejecting ink from the plurality of ejection ports corresponding to one input gradation value. A step of recording a test image in a test drawing region group which is a set of three or more test drawing regions, a2) a step of reading each test image of the test drawing region group by the scanner, and a3) the correction unit Based on the output from the scanner, in each test image, an average density that is an average of the density of a plurality of pixels corresponding to each ejection port of the plurality of ejection ports is obtained, and the average density and the A step of obtaining a correction coefficient for correcting the difference from the reference density corresponding to the force gradation value for each of the ejection openings; a4) as a statistical correction coefficient for the input gradation value for each of the ejection openings by the correction unit; A step of obtaining an average correction coefficient that is an average of correction coefficients in all test images in the test drawing region group and a variation value indicating a variation in correction coefficients in all the test images; And determining the relationship between the gradation value and the statistical correction coefficient of each discharge port by repeating the steps a1) to a4). B1) The gradation value of one pixel corresponding to each ejection port in the original image data, and the relationship between the gradation value obtained in the step a5) and the statistical correction coefficient of each ejection port. Based on Obtaining a statistical correction coefficient for each of the ejection openings; b2) obtaining a random correction coefficient whose appearance probability is determined based on the statistical correction coefficient of each of the ejection openings for each of the ejection openings; b3) Determining a discharge amount from each discharge port based on a gradation value of a pixel corresponding to each discharge port in the original image data and the random correction coefficient of each discharge port; b4) A step of repeating the step b1) to the step b3) while ink is ejected from each ejection port.

  In the present invention, it is possible to suppress the occurrence of streak unevenness due to continuous overcorrection or insufficient correction.

1 is a diagram illustrating a configuration of an image recording apparatus according to an embodiment. It is a bottom view of a recording module. It is a block diagram which shows the function structure of an image recording device. It is a figure which shows original image data and a threshold value matrix. It is a figure which shows the flow of recording of an image. It is a figure which shows the flow of recording of an image. It is a figure which shows a test image. It is a figure which shows an average density | concentration. It is a figure which shows an image. It is a figure which shows an image. It is a figure which shows an image.

  FIG. 1 is a diagram showing a configuration of an inkjet image recording apparatus 1 according to an embodiment of the present invention. The image recording apparatus 1 is a color printer that records a plurality of color component images on a printing paper 9 as an object. The image recording apparatus 1 is a sheet format image recording apparatus that sequentially records images on a plurality of printing papers 9.

  The image recording apparatus 1 includes a head 21 that is a discharge unit that discharges ink droplets from a plurality of discharge ports toward the printing paper 9, and the printing paper 9 relative to the head 21 in the X direction in FIG. 1. A moving mechanism 22 that moves to the moving mechanism 22, a supply unit 23 that sequentially holds the plurality of printing papers 9 and supplies the plurality of printing papers 9 to the moving mechanism 22, a scanner 24 that reads an image on the printing paper 9, and double-sided printing. A reversing mechanism 25 for reversing the printing paper 9, a collecting unit 26 for collecting the printing paper 9 on which an image is recorded, and a control unit for controlling these configurations are provided. In the image recording apparatus 1, the ejection of ink from the head 21 is controlled by a main body control unit (described later) in the control unit in synchronization with the relative movement of the printing paper 9 in the X direction. An image is recorded. In the following description, the X direction is referred to as “scanning direction”.

  The moving mechanism 22 is arranged in the scanning direction and connected to a motor (not shown), two belt rollers 222, a belt 223 hung on the two belt rollers 222, and a plurality of tables attached on the belt 223. 221 and a linear motor mechanism 224. In the moving mechanism 22, the belt roller 222 rotates counterclockwise, so that the table 221 moves at a high speed along the orbit. At the time of recording an image, the table 221 holding one printing sheet 9 is detached from the belt 223 and is moved in the scanning direction with high accuracy by the linear motor mechanism 224. When the image recording is completed, the table 221 is attached to the belt 223 again.

  The head 21 is disposed on the (−X) side of the pre-processing module 212, four recording modules 211 that respectively eject black, cyan, magenta, and yellow ink, and the pre-processing module 212 and each recording module 211. Five heaters 213 are provided. The preprocessing module 212 applies a transparent pretreatment agent to the printing paper 9 before the image is recorded. The heater 213 dries the ink ejected onto the printing paper 9 by blowing hot air onto the printing paper 9.

  The pre-processing module 212, the four recording modules 211, and the five heaters 213 are arranged in the scanning direction, and the above-described scanner is disposed between the recording module 211 and the heater 213 positioned closest to the (−X) side. 24 is arranged. The scanner 24 includes a line-shaped CCD camera, and reads an image recorded on the printing paper 9 passing below.

  FIG. 2 is a bottom view of the recording module 211. On the bottom surface of the recording module 211, a plurality of ejection openings 210 are formed, each ejecting fine ink droplets toward the printing paper 9 (in the (−Z) direction in FIG. 1). The plurality of ejection openings 210 are arranged at a constant pitch in a predetermined arrangement direction that intersects the scanning direction on a plane parallel to the printing paper 9 (that is, a plane parallel to the XY plane). In the present embodiment, the plurality of ejection openings 210 are arranged in the Y direction perpendicular to the scanning direction. Actually, more ejection ports 210 are provided in the recording module 211 than shown in FIG. In the recording module 211, ejection of minute droplets from the ejection port 210 is realized by a piezoelectric element, but a recording module that ejects minute droplets by another method may be employed.

  The pre-processing module 212 and each recording module 211 are provided over the entire printing area on the printing paper 9 in the Y direction (here, over the entire Y direction of the printing paper 9), and the moving mechanism 22. The printing paper 9 is moved relative to the head 21 by one time (that is, the printing paper 9 moves in the (−X) direction and passes below the head 21 once), and the image on the printing paper 9 is displayed. Is completed (so-called one-pass printing is performed).

  FIG. 3 is a block diagram showing a functional configuration of the image recording apparatus 1. The control unit 3 includes a calculation unit 4 that performs various calculations, and a main body control unit 10 that controls each component such as the head 21 and the moving mechanism 22. The arithmetic unit 4 stores image data of a color image input from the outside (that is, image data in which each pixel has gradation values of a plurality of color components, hereinafter referred to as “original image data”). A memory 41, a plurality of matrix storage units 42 (also referred to as SPM (Screen Pattern Memory)), each of which stores a threshold matrix for a plurality of color components, and a comparison for comparing the original image data and the threshold matrix for each color component A comparator 43 (halftoning circuit), and a correction unit 45 for obtaining a statistical correction coefficient used for correcting the ejection amount of ink from the plurality of ejection ports 210 of each recording module 211. The comparison unit that compares the original image data and the threshold matrix may be realized by software. In addition, the main body control unit 10 controls the movement control unit 102 that controls the relative movement of the printing paper 9 with respect to the head 21 by the movement mechanism 22 and the plurality of ejection ports 210 of the head 21 in synchronization with the relative movement of the printing paper 9. A discharge control unit 101 that controls the discharge of the ink.

  Next, details of the operation of the image recording apparatus 1 for recording an image will be described. In the image recording apparatus 1, color original image data is input from an external computer and stored in the image memory 41 of the calculation unit 4. Actually, an image is recorded on the basis of the corrected image data obtained by correcting the original image data. To facilitate understanding of the operation of the image recording apparatus 1, first, an image based on the original image data is assumed. The flow of image recording when the above recording is performed will be described. Thereafter, generation of corrected image data and recording of an image based on the corrected image data will be described.

  FIG. 4 is a diagram abstractly showing the original image data 70 and the threshold matrix 710. In each of the original image data 70 and the threshold matrix 710, a row direction corresponding to the scanning direction (shown as an x direction in FIG. 4) and a column direction perpendicular to the row direction (shown as a y direction in FIG. 4). A plurality of pixels or a plurality of elements are arranged. In the following description, the original image data is expressed in a gradation range from 0 to 255. Further, in the case of simply meaning a level in the gradation range, each gradation value is referred to as a gradation level in distinction from a gradation value that is a pixel value (pixel value) in image data.

  When the original image data 70 is stored in the image memory 41 (see FIG. 3), the original image data 70 is compared with the threshold value matrix 710 for each color component, whereby a multi-gradation image (exposure) indicated by the original image data is obtained. Color halftone image data (in fact, an image represented by an FM screen when recorded on the printing paper 9) is generated. Is done. In the following description, not only the process of recording the halftone image representing the original image on the printing paper 9 based on the original image but also the process of generating the halftone image data from the original image data 70 is halftoned. Call.

  When halftoning the original image data 70, as shown in FIG. 4, the entire area indicated by the original image data 70 is divided into a plurality of areas having the same size, and a repetitive area serving as a halftoning unit. 71 is set. Each matrix storage unit 42 has a storage area corresponding to one repetitive area 71, and stores a threshold matrix 710 by setting a threshold at each address (coordinate) of this storage area. Conceptually, each repetition area 71 of the original image data 70 and the threshold matrix 710 of each color component are superimposed, and the gradation value (pixel value) of the color component of each pixel in the repetition area 71 and the threshold matrix 710 are overlapped. By comparing with the corresponding threshold value, it is determined whether or not to record (form the dot of the color) at the position of the pixel on the printing paper 9.

  Actually, the gradation value of one pixel of the original image data 70 is read from the image memory 41 for each color component based on the address signal from the address generator included in the comparator 43 of FIG. On the other hand, the address generator also generates an address signal indicating a position in the repetitive area 71 corresponding to the pixel in the original image data 70, specifies one threshold value in the threshold value matrix 710 for each color component, and stores it from the matrix storage unit 42. Read out. Then, the gradation value from the image memory 41 and the threshold value from the matrix storage unit 42 are compared for each color component by the comparator 43, so that the position of the pixel in the binary output image data of each color component ( Address) gradation value is determined. Therefore, when focusing on one color component, in the multi-tone original image data 70 shown in FIG. 4, for example, the tone value “ 1 ”(that is, a dot is placed), and the gradation value“ 0 ”is assigned to the remaining pixels (that is, no dot is placed), and the binary output image data is a halftone of the color component. Generated as image data.

  As described above, the calculation unit 4 in FIG. 3 uses the comparator 43 to match pixel positions (threshold values) that the plurality of gradation values that the input original image data has and the plurality of threshold values that the threshold value matrix 710 has. The half-tone image data for generating half-tone image data for halftoning the original image (that is, recording the half-tone image representing the original image on the printing paper 9) is compared in the matrix 710 (element positions). It is a tone image data generation unit. The calculation unit 4 can also be regarded as a halftone image data generation device.

  In the image recording apparatus 1 of FIG. 1, each recording module 211 of the head 21 is controlled by the ejection control unit 101 of the main body control unit 10 according to the halftone image data. Further, in the main body control unit 10, the movement control unit 102 also controls the moving speed and the moving amount of the printing paper 9 by the moving mechanism 22.

  In the image recording apparatus 1, when halftone image data (portion) of a portion (for example, a plurality of (+ y) side repeating areas 71) first recorded in the original image data 70 is generated for each color. The movement control unit 102 drives the movement mechanism 22 to start the movement of the printing paper 9. In parallel with the halftoning process (halftone image data generating process), the print paper 9 is output from the plurality of ejection openings 210 in each recording module 211 in synchronization with the relative movement in the scanning direction with respect to the head 21. Ink ejection is controlled by the ejection control unit 101.

  Here, since the halftone image data is data for recording an image on the printing paper 9, it can be considered that a plurality of pixels of the halftone image data are set and arranged on the printing paper 9. In the ejection control unit 101, the half corresponding to the ejection position (that is, the dot formation position) of each ejection port 210 on the printing paper 9 in synchronization with the relative movement of the head 21 serving as the dot formation unit with respect to the printing paper 9. When the tone value of the tone image data is “1”, a dot is formed at the ejection position. When the gradation value of the halftone image data is “0”, a dot is formed at the ejection position. Not. In this way, with respect to each of black, cyan, magenta, and yellow, a plurality of ejection positions on the printing paper 9 respectively corresponding to the plurality of ejection openings 210 are moved relative to the printing paper 9 while a plurality of ejection positions are moved. Based on halftone image data that is a comparison result between the gradation value of the original image data 70 at the discharge position and the corresponding threshold value of the threshold value matrix 710 for halftoning the original image, Ink ejection is controlled (that is, the amount of ink ejected from each ejection port 210 is determined).

  In the image recording apparatus 1, for black, cyan, magenta, and yellow, an operation of generating halftone image data and recording an image according to the halftone image data is performed in parallel, and a color original image is printed on the printing paper 9. A color halftone image representing the above is recorded.

  Actually, in the image recording apparatus 1, the ejection amount from each ejection port 210 is determined based on the corrected image data obtained by correcting the original image data, not the original image data, and the color halftone image is printed on the printing paper 9. Is recorded. Hereinafter, generation of corrected image data based on the original image data and recording of an image based on the corrected image data will be described with reference to FIG. A and FIG. A description will be given along B. Hereinafter, generation of corrected image data and recording of an image regarding ink of one color will be described, but the same applies to generation of corrected image data and recording of an image regarding ink of other colors.

  First, by controlling the head 21 and the moving mechanism 22 by the main body control unit 10, one input gradation value (in this embodiment, while the printing paper 9 is moved once in the scanning direction by a predetermined distance). , The ink is ejected from the plurality of ejection openings 210 corresponding to the maximum gradation value “255” (10% gradation value), and as shown in FIG. 6, a strip having a predetermined width in the scanning direction. A test image 93a, which is a tint image, is recorded in the test image area 92a (step S11).

  Subsequently, the input gradation value is changed to another gradation value (a gradation value of 20% of the maximum gradation value) (steps S12 and S13). Then, returning to step S11, similarly to the test image 93a, after the test image 93b, which is a tint image, is recorded in the test image area 92b adjacent to the (+ x) side of the test image area 92a, the input gradation value is maximized. The tone value is changed to another tone value that is 10% larger than the tone value (steps S11 to S13). In the image recording apparatus 1, the input gradation value is increased by 10% of the maximum gradation value and steps S11 to S13 are repeated until the test image 93j whose input gradation value is the maximum gradation value is recorded. As a result, test images 93a to 93j are recorded in ten test image areas 92a to 92j arranged in the x direction on the printing paper 9.

  The test images 93a to 93j recorded in the test image areas 92a to 92j on the printing paper 9 are sequentially read by the scanner 24 and sent to the calculation unit 4 of the control unit 3 (step S14). In the calculation unit 4, a plurality of pixels corresponding to the respective ejection ports 210 in the test image 93 a (that is, the ejection ports 210 in the test image area 92 a) based on the output from the scanner 24 by the correction unit 45 illustrated in FIG. 3. The average density Ave (10%, i), which is the average of the density of a plurality of pixels arranged in the x direction at the corresponding y direction position, is obtained. 10% in parentheses indicates an input tone value in the test image 93a, and i indicates a number for distinguishing each ejection port 210 from the other. The same applies to the following correction coefficient Coeff and statistical correction coefficient Coeff_sta for the number i of the discharge port 210.

  FIG. 7 is a diagram showing the average density Ave (10%, i) of each ejection port 210. The horizontal axis in FIG. 7 indicates the position of each discharge port 210 in the Y direction (that is, the number i of the discharge port 210), and the vertical axis indicates the average density Ave (10%, i). In addition, a two-dot chain line in FIG. 7 indicates Ave_total (10%) that is an average value of the average density Ave (10%, i) of all the discharge ports 210. In this embodiment, Ave_total (10%) is set as a reference density corresponding to the input gradation value of the test image 93a, and the difference between the average density Ave (10%, i) and the reference density Ave_total (10%) is corrected. The correction coefficient Coeff (10%, i) is obtained for each ejection port 210 using Equation (1) using the maximum gradation value “255”.

(Equation 1)
Coeff (10%, i) = 255 / (255 + Ave (10%, i) −Ave_total (10%))

  In the correction unit 45, based on the output from the scanner 24, similar to the test image 93a, the average densities Ave (20%, i) to Ave (100%, i) is obtained, reference concentrations Ave_total (20%) to Ave_total (100%) are obtained, and correction coefficients Coeff (20%, i) to Coeff (100%, i) of each ejection port 210 are obtained. (Step S15).

  In the image recording apparatus 1, Steps S <b> 11 to S <b> 15 are performed on a plurality (10 in the present embodiment) of the printing paper 9, and the average of the discharge ports 210 for the test images 93 a to 93 j of the printing paper 9. Concentrations Ave (10%, i) to Ave (100%, i) are obtained, reference concentrations Ave_total (10%) to Ave_total (100%) are obtained, and a correction coefficient Coeff (10%) for each discharge port 210 is obtained. , I) to Coeff (100%, i) are obtained (step S16).

  Subsequently, the correction unit 45 causes the test image area 92a (hereinafter referred to as the test image area 92a) of the ten printing sheets 9 to be used as the statistical correction coefficient Coeff_sta (10%, i) for the input tone value corresponding to the test image 93a. A set of these test image areas 92a is referred to as “test image area group 92a”). Average correction coefficient μ (10%, i), which is an average of correction coefficients Coeff (10%, i) in all test images 93a, Then, the standard deviation σ (10%, i) of the correction coefficient Coeff (10%, i) in all the test images 93a in the test image region group 92a is obtained. Similar to the test image 93a, the correction unit 45 obtains statistical correction coefficients Coeff_sta (20%, i) to Coeff_sta (100%, i) for the input tone values corresponding to the test images 93b to 93j (step S17). . The statistical correction coefficients Coeff_sta (20%, i) to Coeff_sta (100%, i) are respectively the same as the statistical correction coefficients Coeff_sta (10%, i), and the average correction coefficients μ (20%, i) to μ (100%). , I) and standard deviation σ (20%, i) to σ (100%, i).

  The correction unit 45 associates the input gradation values corresponding to the test images 93a to 93j with the statistical correction coefficients Coeff_sta (10%, i) to Coeff_sta (100%, i) of each ejection port 210, thereby tones the gradation. The relationship between the value and the statistical correction coefficient Coeff_sta of each discharge port 210 is determined (step S18).

  In the image recording apparatus 1, it is not always necessary to record the test image 93 a (the same applies to the test images 93 b to 93 j) on ten printing sheets 9, and the test image 93 a has three or more test image areas. What is necessary is just to be recorded in the test image area group 92a which is a set of 92a. For example, one test image area 92a may be provided on each of three or more printing sheets 9, and three or more test image areas 92a may be separated from each other on one printing sheet that is a roll paper. Or you may provide continuously. Further, the test image need not be recorded for each of the 10 input gradation values, and by recording each of the plurality of input gradation values, the gradation value and the statistical correction coefficient Coeff_sta of each ejection port 210 are recorded. The relationship is determined.

  In the image recording apparatus 1, the above-described steps S <b> 11 to S <b> 18 are not necessarily performed in the order described above in determining the statistical correction coefficient Coeff_sta for the plurality of ejection ports 210. In the image recording apparatus 1, a set of three or more test image areas is obtained by relatively moving the printing paper 9 once in the scanning direction while ejecting ink from the plurality of ejection openings 210 corresponding to one input gradation value. The step of recording the test image in the test image region group, the step of reading each test image of the test image region group, the average density Ave corresponding to each ejection port 210 and the correction coefficient Coeff of each ejection port 210 in each test image The relationship between the gradation value and the statistical correction coefficient Coeff_sta of each discharge port 210 is determined by repeating the process of determining and the process of determining the statistical correction coefficient Coeff_sta for each discharge port 210 while changing the input gradation value. If so, the operation may be performed in a procedure different from steps S11 to S18.

  As described above, while the main body control unit 10 controls the head 21, the moving mechanism 22, and the scanner 24, the correction unit 45 obtains the statistical correction coefficient Coeff_sta of the plurality of ejection ports 210, and the gradation value and each ejection port 210. When the relationship with the statistical correction coefficient Coeff_sta is determined, the main body control unit 10 sets a plurality of values based on the input original image data of the multi-tone original image and the statistical correction coefficients Coeff of the plurality of ejection ports 210. By controlling the amount of ink discharged from the discharge port 210, a color halftone image representing a color original image is recorded on the printing paper 9.

  Specifically, in recording an image on the printing paper 9, first, the gradation value of one pixel corresponding to each ejection port 210 in the original image data and the gradation value obtained in step S18. And the statistical correction coefficient Coeff_sta of each discharge port 210, the correction unit 45 obtains the statistical correction coefficient Coeff_sta (that is, the average correction coefficient μ and the standard deviation σ) of each discharge port 210 (step S19).

  Subsequently, a random correction coefficient Coeff_rdm whose appearance probability is determined based on the statistical correction coefficient Coeff_sta of each discharge port 210 is obtained for each discharge port 210 by the correction unit 45 (step S20). In the present embodiment, the random correction coefficient Coeff_rdm is a normal random number having a normal probability distribution obtained based on the average correction coefficient μ and the standard deviation σ obtained in step S19.

  Next, the correction unit 45 corrects the gradation value of one pixel corresponding to each ejection port 210 in the original image data based on the random correction coefficient Coeff_rdm to obtain a corrected gradation value. The correction gradation value is a product of the gradation value of the pixel and the random correction coefficient Coeff_rdm. Then, the ejection amount of ink from the ejection port 210 at the position corresponding to the one pixel is determined based on the correction gradation value, and the ejection amount of ink is ejected toward the printing paper 9 (step S21). ).

  In the image recording apparatus 1, while the printing paper 9 is moved in the scanning direction by the moving mechanism 22 and the recording module 211 is controlled by the ejection control unit 101, while ink is ejected from each ejection port 210, Steps S19 to S21 are repeated for one pixel corresponding to each ejection port 210 at each position in the scanning direction (step S22). Thereby, for a plurality of pixels corresponding to each ejection port 210 (that is, a plurality of pixels arranged in the scanning direction), determination of the correction gradation value and determination of the ejection amount based on the correction gradation value are sequentially performed. Is called. In other words, by repeating Step S21, the corrected image data is corrected by correcting the gradation values of a plurality of pixels corresponding to each ejection port 210 in the original image data based on the random correction coefficient Coeff_rdm of each ejection port 210. The generating step and the step of determining the discharge amount from each discharge port 210 based on the corrected image data are performed in parallel.

  As described above, in the present embodiment, the random correction coefficient Coeff_rdm is obtained for each pixel corresponding to each ejection port 210 to determine the ink ejection amount. Preferably, the determination of the ink ejection amount corresponding to each of 10 or less pixels is one random correction coefficient Coeff_rdm (for example, one random number obtained when recording the first pixel among the plurality of pixels). Correction coefficient Coeff_rdm) may be performed. In other words, in step S21, the amount of ink discharged to one or more pixels corresponding to each ejection port 210 is determined by the random correction coefficient of each ejection port 210 and the one or more pixels in the original image data. It is determined based on the gradation value.

  By the way, in the correction method disclosed in Japanese Patent Application Laid-Open No. 2007-196472, in order to correct the threshold value matrix, a test pattern is printed and the density of a region corresponding to each ejection port is measured. In the test pattern recording, due to non-stationary causes such as the influence of the air flow near the ejection port, the temperature change of the ink, the variation in the conveyance speed of the printing paper, and the like, as in the image 95a shown in FIG. When the density of the band-like region 96 parallel to the vertical direction in FIG. 8 becomes larger than that during normal image recording, if the threshold value matrix is corrected based on the image 95a, the actual image Unless the unsteady state occurs at the time of recording, the correction for the region 96 becomes excessive. Therefore, when printing is performed based on the corrected threshold value matrix, the density of the region 96 becomes smaller than the gradation value of the corresponding region of the original image data, as in the image 95b shown in FIG. The region 96 is recognized by the observer as streak irregularity. 8 and 9, the width of the region 96 is equal to the width of one pixel (the same applies to FIG. 10).

  On the other hand, in the image recording apparatus 1 according to this embodiment, as described above, steps S11 to S18 are performed, and the gradation value and the statistical correction coefficient Coeff_sta (the average correction coefficient μ and the standard deviation of each discharge port 210) are performed. σ) is determined, and in steps S19 to S22, the discharge from each discharge port 210 is based on the relationship and the random correction coefficient of each discharge port 210 obtained from the gradation value of the pixel in the original image data. Since the amount is determined, as in the image 97 shown in FIG. 10, the density of each pixel in the region 96 appears with respect to the gradation value of the corresponding pixel in the original image data, but the level of the original image data. It is possible to prevent a plurality of pixels having a density that is substantially (or smaller) than the tone value from appearing continuously in the scanning direction. Thereby, it is possible to suppress (or prevent) the region 96 from being recognized by the observer as streak unevenness due to continuous overcorrection or insufficient correction.

  As described above, the image recording apparatus 1 can suppress the occurrence of streak unevenness due to an unsteady cause. Therefore, the printing state and the standby state are frequently repeated, thereby causing unsteady variation in the discharge amount. It is particularly suitable for sheet-type recording devices that tend to occur. The image recording apparatus 1 can easily record a corrected image based on corrected image data obtained by correcting original image data with a random correction coefficient.

  In step S21, it is not always necessary to determine the ejection amount of ink from each ejection port 210 based on the corrected image data. The gradation value of the pixel corresponding to each ejection port 210 in the original image data, and each As long as the ejection amount of ink from each ejection port 210 is determined based on the random correction coefficient of the ejection port 210, the ejection amount of each ejection port 210 may be determined by other methods.

  For example, in the image recording apparatus 1, the threshold value corresponding to each discharge port 210 of the threshold value matrix is corrected based on the random correction coefficient Coeff_rdm of each discharge port 210 (specifically, the threshold value is divided by the random correction coefficient Coeff_rdm). ) To generate a correction threshold value matrix, and a plurality of gradation values included in the original image data and a plurality of threshold values included in the correction threshold value matrix are compared at pixel positions corresponding to each other by the comparator 43. Halftone image data obtained by halftoning an image may be generated. Based on the halftone image data, the ejection amount of ink from each ejection port 210 is determined, and the ejection amount of ink is ejected toward the printing paper 9. As described above, by generating the correction threshold value matrix, it is not necessary to correct the original image data. Therefore, it is possible to quickly record a plurality of types of original images.

  As mentioned above, although embodiment of this invention has been described, this invention is not limited to the said embodiment, A various change is possible.

  In step S17, as the statistical correction coefficient Coeff_sta, the average correction coefficient μ, which is the average of the correction coefficients Coeff in all test images in the test image area group of ten printing papers 9, and the correction in all test images in the test image area group. A standard deviation σ of the coefficient Coeff is obtained. The standard deviation σ is one of the variation values indicating the variation of the correction coefficient Coeff in all the test images in the test image region group. In the statistical correction coefficient Coeff_sta, other variation values are used instead of the standard deviation σ. Also good. In step S20, a random correction coefficient Coeff_rdm other than a normal random number having a normal probability distribution may be obtained. For example, the maximum value and the minimum value of the correction coefficient Coeff are obtained as the variation value of the correction coefficient Coeff, and the uniform random number uniformly distributed between the maximum value and the minimum value of the correction coefficient Coeff as the random correction coefficient Coeff_rdm. May be required. However, in the image recording apparatus 1, the standard deviation σ is used as the variation value of the correction coefficient Coeff, and the normal random number is used as the random correction coefficient Coeff_rdm, so that the ink discharge amount from each discharge port 210 is easily determined. can do.

  In step S15, the reference density for obtaining the correction coefficient of each ejection port 210 does not necessarily need to be the average value Ave_total of the average density Ave of all the ejection ports 210, for example, the average density Ave of all the ejection ports 210. It may be a minimum value. Further, an appropriately set density may be input as the reference density.

  In the image recording apparatus 1, the image may be recorded by moving the head 21 in the scanning direction while the printing paper 9 is fixed. Further, if the test images 93a to 93j are recorded by one-pass printing, a halftone image obtained by halftoning the original image may be recorded by, for example, interless printing.

  In the above embodiment, the corrected image data and the threshold value matrix are compared to generate binary halftone image data. In the image recording apparatus 1, different amounts of fine liquid droplets are discharged from each discharge port. When a plurality of sizes of dots can be formed, a halftone image expressed with three or more values may be generated. For example, when the image recording apparatus 1 can form three types of dots of the minimum S size, the intermediate M size, and the maximum L size, the threshold matrix for S size and the threshold matrix for M size , And a threshold matrix for L size is prepared, and a halftone image of quaternary expression is generated.

  In the image recording apparatus, first, a gradation value “1” is provisionally given to pixels whose gradation value of the corrected image data is larger than the corresponding threshold value of the threshold matrix for S size, and gradation is applied to the remaining pixels. The value “0” is assigned. Subsequently, the gradation value of the pixel whose gradation value of the corrected image data is larger than the corresponding threshold value of the threshold matrix for M size is changed to “2”. At this time, the gradation values of the remaining pixels are not changed. Thereafter, the gradation value of the pixel whose gradation value of the corrected image data is larger than the corresponding threshold value of the threshold matrix for L size is changed to “3”. Also at this time, the gradation values of the remaining pixels are not changed. As a result, a quaternary halftone image is generated, no dot is formed at the position of the gradation value “0”, and the positions of the gradation values “1”, “2”, and “3” are respectively S size, M size and L size dots are formed.

  Further, in the image recording apparatus, similarly to the above, the S size threshold matrix, the M size threshold matrix, and the L size threshold matrix are respectively corrected to generate three correction threshold value matrices. May be sequentially compared to generate a quaternary halftone image.

  The image recording apparatus 1 may record an image on another object other than the printing paper 9 such as a plastic film. When an image is recorded on a plastic film or the like, for example, an ultraviolet curable ink is used as the ink ejected from the recording module 211, and an irradiation unit that irradiates the ink on the object with ultraviolet rays instead of the heater 213. Provided.

  The configurations in the above-described embodiments and modifications may be combined as appropriate as long as they do not contradict each other.

DESCRIPTION OF SYMBOLS 1 Image recording device 9 Printing paper 10 Main body control part 22 Movement mechanism 23 Supply part 24 Scanner 42 Matrix memory | storage part 45 Correction | amendment part 70 Original image data 92a-92j Test image area 93a-93j Test image 97 Image 210 Ejection port 211 Recording module 710 Threshold matrix S11-S22 steps

Claims (7)

An image recording apparatus for recording an image on an object,
An ejection unit that ejects micro droplets of ink toward a target from a plurality of ejection ports arranged in a predetermined arrangement direction;
A moving mechanism that moves the object relative to the ejection unit in a scanning direction that intersects the arrangement direction;
A main body control unit that records an image on the object by controlling the ejection of ink from the ejection unit in synchronization with the relative movement of the object in the scanning direction;
A scanner for reading an image on the object;
A correction unit for obtaining a statistical correction coefficient used for correcting the ejection amount of ink from the plurality of ejection ports;
With
Based on the input original image data of the multi-tone original image and the statistical correction coefficient of the plurality of ejection ports, the main body control unit controls the ejection amount of ink from the plurality of ejection ports. To record an image on the object,
When the correction unit obtains the statistical correction coefficient of the plurality of discharge ports,
a1) The main body control unit controls the ejection unit and the moving mechanism, thereby ejecting the object 1 in the scanning direction while ejecting ink from the plurality of ejection ports corresponding to one input gradation value. Recording a test image in a test drawing area group, which is a set of three or more test drawing areas, by moving once;
a2) reading each test image of the test drawing area group with the scanner;
a3) Based on the output from the scanner, the correction unit obtains an average density that is an average of the density of a plurality of pixels corresponding to each of the plurality of ejection openings in each test image, and calculates the average Obtaining a correction coefficient for each discharge port for correcting a difference between the density and a reference density corresponding to the input gradation value;
a4) An average correction coefficient that is an average of correction coefficients in all test images of the test drawing region group as a statistical correction coefficient with respect to the input gradation value for each discharge port by the correction unit, and all the test images Obtaining a variation value indicating variation in the correction coefficient in
a5) changing the input tone value to another tone value and repeating the steps a1) to a4) to obtain the relationship between the tone value and the statistical correction coefficient of each discharge port; ,
Is done,
In recording an image on the object, the correction unit
b1) In the original image data, the relationship between the gradation value of one pixel corresponding to each of the ejection openings and the gradation value obtained in the step a5) and the statistical correction coefficient of each of the ejection openings. A step of obtaining a statistical correction coefficient for each of the discharge ports,
b2) obtaining a random correction coefficient for each of the discharge ports, a random correction coefficient whose appearance probability is determined based on the statistical correction coefficient of each of the discharge ports;
b3) determining a discharge amount from each discharge port based on a gradation value of a pixel corresponding to each discharge port in the original image data and the random correction coefficient of each discharge port;
b4) repeating the steps b1) to b3) while the ink is ejected from the ejection ports;
An image recording apparatus. The image recording apparatus according to claim 1,
The image recording apparatus, wherein the variation value obtained in the step a4) is a standard deviation of correction coefficients in all the test images in the test drawing region group. The image recording apparatus according to claim 2,
The random correction coefficient obtained in step b2) is a normal random number having a normal probability distribution obtained based on the average correction coefficient obtained in step b1) and the standard deviation. An image recording apparatus. The image recording apparatus according to any one of claims 1 to 3,
Step b3)
Correcting the gradation value of the pixel corresponding to each of the ejection openings in the original image data based on the random correction coefficient of each of the ejection openings, and generating corrected image data;
Determining a discharge amount from each discharge port based on the corrected image data;
An image recording apparatus comprising: The image recording apparatus according to any one of claims 1 to 3,
A threshold matrix for halftoning the original image is stored in the storage unit,
Step b3)
Correcting a threshold corresponding to each of the discharge ports of the threshold matrix based on the random correction coefficient of each of the discharge ports to generate a correction threshold matrix;
Halftone image data in which the original image is halftoned is generated by comparing a plurality of gradation values of the original image data with a plurality of threshold values of the correction threshold value matrix at corresponding pixel positions. And a process of
Determining a discharge amount from each discharge port based on the halftone image data;
An image recording apparatus comprising: An image recording apparatus according to any one of claims 1 to 5,
An image recording apparatus comprising: a supply unit that holds a plurality of objects and sequentially supplies the plurality of objects to the moving mechanism. A discharge unit that discharges micro droplets of ink toward a target from a plurality of discharge ports arranged in a predetermined arrangement direction; and the target is relative to the discharge unit in a scanning direction that intersects the arrangement direction. A moving mechanism that moves automatically, and a main body control unit that records an image on the object by controlling the ejection of ink from the ejection unit in synchronization with the relative movement of the object in the scanning direction, An image recording apparatus comprising: a scanner that reads an image on the object; and a correction unit that obtains a statistical correction coefficient used for correcting the amount of ink discharged from the plurality of discharge ports. An image recording method for recording,
a) obtaining a statistical correction coefficient;
b) Based on the input original image data of the multi-tone original image and the statistical correction coefficient determined in the step a), the main body control unit discharges ink from the plurality of discharge ports. Recording an image on the object by controlling
With
Step a)
a1) The main body control unit controls the ejection unit and the moving mechanism, thereby ejecting the object 1 in the scanning direction while ejecting ink from the plurality of ejection ports corresponding to one input gradation value. Recording a test image in a test drawing area group, which is a set of three or more test drawing areas, by moving once;
a2) reading each test image of the test drawing area group with the scanner;
a3) Based on the output from the scanner, the correction unit obtains an average density that is an average of the density of a plurality of pixels corresponding to each of the plurality of ejection openings in each test image, and calculates the average Obtaining a correction coefficient for each discharge port for correcting a difference between the density and a reference density corresponding to the input gradation value;
a4) An average correction coefficient that is an average of correction coefficients in all test images of the test drawing region group as a statistical correction coefficient with respect to the input gradation value for each discharge port by the correction unit, and all the test images Obtaining a variation value indicating variation in the correction coefficient in
a5) A step of determining the relationship between the gradation value and the statistical correction coefficient of each discharge port by changing the input gradation value to another gradation value and repeating the steps a1) to a4) When,
With
Step b)
b1) In the original image data, the relationship between the gradation value of one pixel corresponding to each of the ejection openings and the gradation value obtained in the step a5) and the statistical correction coefficient of each of the ejection openings. A step of obtaining a statistical correction coefficient for each of the discharge ports,
b2) obtaining a random correction coefficient for each of the discharge ports, a random correction coefficient whose appearance probability is determined based on the statistical correction coefficient of each of the discharge ports;
b3) determining a discharge amount from each discharge port based on a gradation value of a pixel corresponding to each discharge port in the original image data and the random correction coefficient of each discharge port;
b4) repeating the steps b1) to b3) while the ink is ejected from the ejection ports;
An image recording method comprising:

Images