JP2014176981A - Calibration method and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to perform calibration of output density easily without using a spectroscopy chromatometer.SOLUTION: A calibration method of the embodiment is a calibration method performed by an image formation device which indicates density of an image to be formed on a recording medium by an image point area, and includes a printing process in which a chart image of a preset stipulated density is formed on the recording medium, an acquiring process which a picked-up image is acquired by expanding each image pint included in the chart image formed in a distinguishable manner, an area calculation process in which an area of each image point included in the chart image is calculated based on the acquired picked-up image, a deviation amount calculation process in which the deviation amount between the image point area to be formed at the stipulated density and the calculated image point area is calculated, and a calibration process in which correlation information indicating a correlation relationship of an energy amount applied to the image forming part for each density upon forming the image on the recording medium is calibrated based on the calculated deviation amount.

Description

  Embodiments described herein relate generally to a calibration method and an image forming apparatus.

  Conventionally, in an image forming apparatus that prints C (cyan), M (magenta), Y (yellow), and Bk (black) on a medium such as paper, color reproduction that faithfully reproduces color tones in C, M, Y, and Bk Therefore, output density calibration is performed by measuring a printed chart image with a spectrocolorimeter.

JP 2005-318433 A

  However, in the above-described prior art, it is necessary to use an expensive spectrocolorimeter when calibrating the output density.

  In order to solve the above-described problem, a calibration method according to an embodiment is a calibration method executed by an image forming apparatus that expresses the density of an image formed on a print medium by the area of a dot, and has a preset specified density. A printing process for forming a chart image on the print medium, an acquisition process for acquiring a captured image obtained by enlarging and individually identifying individual image points included in the formed chart image, and the acquired captured image Based on the area calculation step of calculating the area of each image dot included in the chart image, and the amount of deviation between the area of the image dot to be formed at the specified density and the area of the calculated image dot A calibration for calibrating correlation information indicating a correlation between energy amounts applied to the image forming unit for each density at the time of image formation on the print medium based on the calculated shift amount calculation step and the calculated shift amount. Craft And, including the.

  The image forming apparatus according to the embodiment is an image forming apparatus that expresses the density of an image to be formed on a print medium by an area of a dot, and is a printing unit that forms a chart image having a preset specified density on the print medium. And an acquisition means for acquiring a picked-up image obtained by enlarging each image point included in the formed chart image in an identifiable manner, and an individual included in the chart image based on the acquired picked-up image An area calculating means for calculating the area of the image dots, a deviation amount calculating means for calculating an amount of deviation between the area of the image dots to be formed at the specified density and the area of the calculated image dots, and the calculated Calibration means for calibrating correlation information indicating the correlation of the amount of energy applied to the image forming unit for each density when forming an image on the print medium based on the amount of deviation.

FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus according to the embodiment. FIG. 3 is a schematic diagram schematically showing the configuration of the printing apparatus. FIG. 4 is a schematic diagram illustrating an example of a print medium after printing. FIG. 5 is a schematic diagram showing the configuration of the intermediate transfer ribbon. FIG. 6 is a block diagram schematically showing a control system of the printing apparatus. FIG. 7 is a side view schematically showing the transfer operation from the intermediate transfer ribbon to the printing surface of the printing medium. FIG. 8 is a diagram showing an outline of the entire printing process. FIG. 9 is a schematic diagram for explaining area gradation printing by driving a thermal head. FIG. 10 is a schematic diagram illustrating an example of a density-gradation table and a pulse number-gradation table. FIG. 11 is a schematic diagram illustrating an example of a gradation-density graph, a pulse number-density graph, and a gradation-pulse number graph. FIG. 12 is a flowchart illustrating an example of the calibration process. FIG. 13 is a schematic diagram illustrating the area of the image dots for each gradation. FIG. 14 is a schematic diagram illustrating an example of a chart image for calibration. FIG. 15 is a flowchart illustrating an example of a calibration process according to the first modification. FIG. 16 is a flowchart illustrating an example of a calibration process according to the second modification.

  Hereinafter, a calibration method and an image forming apparatus according to an embodiment will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 100 according to the embodiment. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 100. As shown in FIGS. 1 and 2, the image forming apparatus 100 includes a printing apparatus 1, a printing control apparatus 101, and an input / output apparatus 102. When the density (gradation) of the image formed on the print medium is calibrated, the image acquisition device 103 is connected via a communication interface (not shown) such as a USB (Universal Serial Bus), and the printing device 1 In this configuration, a captured image obtained by capturing the formed chart image is acquired from the image acquisition device 103.

  The printing apparatus 1 performs density control by area gradation that represents the density of C (cyan), M (magenta), Y (yellow), and Bk (black) images formed on a print medium by the area of a dot (dot). To perform desired color image printing. The print control apparatus 101 is a PC (Personal Computer), a controller, or the like provided with a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The CPU stores a program stored in the ROM. The operation of the image forming apparatus 100 is controlled by developing it in the RAM and executing it sequentially. The print control apparatus 101 has functions as a calibration chart printing unit 1011, a print data correction unit 1012, and a calibration data calculation unit 1013 (details will be described later) when the CPU executes a program. The input / output device 102 is a touch panel type liquid crystal display that also serves as a data display and an input device, and receives an operation input from a user and displays a screen to the user.

  The image acquisition device 103 includes a digital lens including an optical lens for magnifying and a solid-state imaging device such as a complementary metal oxide semiconductor (COMS) / charge coupled device (CCD) image sensor that captures an image magnified by the optical lens. It is a microscope. The image acquisition device 103 may be a portable digital microscope that can be brought in during a print calibration operation for calibrating the density of an image formed on a print medium, and is a print control device via a communication interface such as a USB. 101 is connected and the captured image data is output to the print control apparatus 101.

  In addition, it is assumed that the magnified shooting in the image acquisition device 103 has a magnification that can identify individual image points included in the chart image. Specifically, the magnification may be such that the fluctuation of the area of the image point in the area gradation can be detected by the solid-state imaging device. For example, if the area of the image dot is changed by the number of pulses, the fluctuation Any magnification that can be identified by the number of pixels of the image data when the amount of fluctuation of the area of the image point for one pulse that minimizes the amount is captured by the solid-state imaging device may be used.

  FIG. 3 is a schematic diagram schematically showing the configuration of the printing apparatus 1. The printing apparatus 1 simultaneously prints (records) a multi-tone image such as a face image and a binary image such as a character on a printing medium P such as a personal authentication card, a passbook, or a bank passbook at a financial institution. The protective film is formed simultaneously.

  In FIG. 3, a printing apparatus 1 includes a printing unit 2 that functions as a printing unit that forms an image on a printing medium P using a fusion thermal transfer method, and a transfer unit that functions as a transfer unit provided below the printing unit 2. 3.

  The printing unit 2 includes a line-type thermal head 4 in which a plurality of heating elements are arranged in a line, a platen roller 5 disposed opposite to the thermal head 4, and the like. Between the thermal head 4 and the platen roller 5, for example, a transparent ink layer mainly composed of a colorless or flame-colored transparent resin that functions as a black ink layer and an adhesive layer is formed on one surface of the film-like substrate. Sequentially provided ink ribbons 6 are interposed.

  The platen roller 5 functions as a supply means for supplying an intermediate transfer ribbon 7 having an image receiving layer capable of transferring ink of the ink layer from the ink ribbon 6 on one surface of the film-like substrate at a predetermined speed.

  One end of the ink ribbon 6 is wound around the delivery shaft 8, and the other end is wound around the winding shaft 9. At least one of the delivery shaft 8 and the winding shaft 9 can be driven independently in both forward and reverse directions. A midway portion of the ink ribbon 6 delivered from the delivery shaft 8 is stretched around the guide shafts 10 and 11.

  The transfer unit 3 includes a heat roller 12 as a transfer roller, a backup roller 13 disposed opposite to the heat roller 12, and the like. The heat roller 12 includes a heater 12a for heating and a cut surface 12b in which a part of the circumference is cut out. An intermediate transfer ribbon 7 that functions as an intermediate transfer medium is interposed between the heat roller 12 and the backup roller 13.

  The intermediate transfer ribbon 7 is included in the printing medium P, and has one end wound around a feed shaft 14 provided on the upper side of the printing unit 2 and the other end side wound on the lower side of the printing unit 2. It is wound around the shaft 15. At least one of the delivery shaft 14 and the take-up shaft 15 can be driven independently in both forward and reverse directions. The delivery shaft 14 and the take-up shaft 15 function as supply means for supplying the intermediate transfer ribbon 7 toward the printing unit 2. The intermediate portion of the intermediate transfer ribbon 7 fed from the feed shaft 14 is stretched over the guide shafts 16 to 18 and is stretched over the tension roller 19 to be maintained at a substantially constant tension.

  In addition, the transfer unit 3 includes conveyance roller pairs 20 and 21. The conveyance roller pair 20 is disposed upstream of the heat roller 12 in the conveyance direction. Further, the transport roller pair 21 is disposed downstream of the heat roller 12 in the transport direction.

  The transport roller pairs 20 and 21 transport the print medium P inserted from the print medium intake port 22 along the transport path 23 to a predetermined transfer position by the heat roller 12. That is, the transport roller pairs 20 and 21 transport the print medium P so that the transfer start position on the print surface of the print medium P is aligned with the transfer position by the heat roller 12.

  Furthermore, the transfer unit 3 includes sensors S1 and S2 that function as detection means arranged along the supply path of the intermediate transfer ribbon 7. The sensors S1 and S2 optically detect a bar mark arranged outside the effective area of the intermediate transfer ribbon 7, and output a detection signal thereof.

  In addition, the transfer unit 3 includes sensors S3 and S4 that function as detection means arranged along the conveyance path 23 of the print medium P. The sensors S3 and S4 optically detect the presence / absence of the print medium P inserted from the print medium intake port 22, and output the detection signal.

  FIG. 4 is a schematic diagram illustrating an example of the print medium P after printing. In FIG. 4, a multi-tone image (for example, a face image of the owner of the print medium P) 32 and a binary image (characters such as personal information) 33 such as characters are displayed in a printable area 31 on the print medium P. While being printed, a transparent protective layer is formed on the entire printing surface.

  FIG. 5 is a schematic diagram showing the configuration of the intermediate transfer ribbon 7. As shown in FIG. 5, the intermediate transfer ribbon 7 is configured, for example, by sequentially laminating a transparent protective layer 42 and an image receiving layer 43 on which an image is formed on one surface of a base layer (film-like substrate) 41. ing. In order to facilitate peeling from the base layer 41, a structure in which a peeling layer is provided between the base layer 41 and the protective layer 42 may be used.

  FIG. 6 is a block diagram schematically showing a control system of the printing apparatus 1. In FIG. 6, a CPU 51 functioning as a control means for controlling the entire apparatus stores a control program for controlling the entire apparatus, or at least a multi-tone image 32 and a binary image developed into bitmap data. A memory unit 52 that stores print data 33 and an interface unit 53 that receives print data necessary for printing from an external device such as a host computer (print control apparatus 101) are connected. Print data received via the interface unit 53 is temporarily stored in the memory unit 52.

  The CPU 51 includes a thermal head control circuit 54, a printing unit conveyance control circuit 55, a heater temperature control circuit 56, a heat roller rotation control circuit 57, a transfer unit conveyance control circuit 58, a printing medium conveyance control circuit 59, and a sensor input. A circuit 60 or the like is connected.

  The thermal head control circuit 54 controls the printing operation of the thermal head 4 based on the print data. The printing unit conveyance control circuit 55 controls driving of the delivery shaft 8 and the winding shaft 9 that function as a conveyance mechanism in the printing unit 2. The heater temperature control circuit 56 controls the heater 12a in the heat roller 12 so as to maintain the heat roller 12 at a predetermined temperature.

  The heat roller rotation control circuit 57 controls the rotation driving of the heat roller 12. That is, the heat roller rotation control circuit 57 aligns the transfer start position with respect to the printing surface of the print medium P and the transfer position of the predetermined information printed on the intermediate transfer ribbon 7 by the heat roller 12, in a state where the heat roller 12 is aligned. After the edge portion of the cut surface 12b is brought into contact with the transfer start position, the heat roller 12 is rotated in a predetermined direction to transfer the predetermined information on the intermediate transfer ribbon 7 to the printable area 31 of the print medium P. .

  The transfer unit conveyance control circuit 58 controls driving of the platen roller 5, the feed shaft 14, and the winding shaft 15 that function as a conveyance mechanism in the transfer unit 3. The print medium conveyance control circuit 59 controls the driving of the conveyance roller pairs 20 and 21 that function as a conveyance mechanism, takes the print medium P from the print medium intake port 22, conveys it to a predetermined transfer position, and completes the transfer. The printed print medium P is discharged from the print medium intake port 22.

  The sensor input circuit 60 detects the bar mark of the intermediate transfer ribbon 7 based on the output signals from the sensors S1 and S2. The sensor input circuit 60 detects the presence or absence of the print medium P based on output signals from the sensors S3 and S4.

  Next, the overall basic operation of the printing apparatus 1 will be briefly described. First, in the printing unit 2, drive control is performed on the surface of the image receiving layer 43 of the intermediate transfer ribbon 7 to which the transparent protective layer 42 has been applied in advance, based on the print data developed in the bitmap data stored in the memory unit 52. The multi-tone image 32 and the binary image 33 are simultaneously printed by the thermal head 4 and the ink ribbon 6. At this time, in order to control the printing position of the intermediate transfer ribbon 7, the bar mark of the intermediate transfer ribbon 7 fed out from the feed shaft 14 is detected by the sensor S1, thereby printing at a predetermined position.

  The image printing method is a method in which the printing pitch is printed at the pitch between the heating elements of the thermal head 4 in both the arrangement direction of the heating elements of the thermal head 4 and the direction orthogonal to the arrangement direction of the heating elements. The pitch is the pitch between the heating elements of the thermal head 4 in both the arrangement direction of the heating elements of the thermal head 4 and the direction orthogonal to the arrangement direction of the heating elements, and even-numbered pixels and odd-numbered pixels are arranged for each print line. Any method of alternately forming and printing may be used.

  Since the speed of the intermediate transfer ribbon 7 is determined mainly by the platen roller 5, the platen roller 5 is accurately driven by combining, for example, a five-phase stepping motor with a speed reduction mechanism. Further, there is a feature that an image to be printed is a reverse image.

  Next, in the printing unit 2, a colorless or flame color that functions as an adhesive layer by the thermal head 4 and the ink ribbon 6 on the surface of the image receiving layer 43 on which the multi-tone image and the two-tone image of the intermediate transfer ribbon 7 are printed. A transparent ink layer mainly composed of a transparent resin is transferred.

  Next, in the transfer unit 3, the printing surface of the intermediate transfer ribbon 7 printed by the printing unit 2 (the surface on which the transparent ink layer as the adhesive layer is transferred on the surface of the image receiving layer 43) and the printing surface of the printing medium P. Are superposed on each other and pressed and heated by the heat roller 12 to simultaneously transfer the print image (image receiving layer 43) and the protective layer 42 through the transparent ink layer. At this time, the alignment between the intermediate transfer ribbon 7 and the print medium P is performed as follows.

(1) After the corresponding transfer area of the intermediate transfer ribbon 7 has been printed, the intermediate transfer ribbon 7 is wound in the direction of the heat roller 12, and the position of the intermediate transfer ribbon 7 is grasped by the sensor S2 in the middle of the path. Thereafter, the amount of movement of the intermediate transfer ribbon 7 relative to the position of the heat roller 12 is determined.
(2) The print medium P is taken from the print medium take-in port 22 and conveyed to a predetermined position with respect to the heat roller 12.
(3) The intermediate transfer ribbon 7 and the printing surface of the printing medium P, which have been positioned relative to each other, are brought together with the rotation of the heat roller 12, and are pressed and heated, whereby transfer through the transparent ink layer is performed. .

  The print medium P thus transferred is discharged again from the print medium intake port 22 toward the operator. In this example, the heat roller 12 is driven at an accurate speed by a DC servo motor or a stepping motor, and a pressure generated by a coil spring is applied to the freely rotatable backup roller 13. .

  FIG. 7 is a side view schematically showing the transfer operation from the intermediate transfer ribbon 7 to the printing surface of the printing medium P. As shown in FIG. 7, the images (multi-tone image 32 and binary image 33) printed by the protective layer 42, the image receiving layer 43, and the thermal head 4 of the intermediate transfer ribbon 7 by the pressure and heating operation by the heat roller 12. And the transparent ink layer (adhesive layer) 45 transferred by the thermal head 4 is transferred to the printing surface of the printing medium P.

  In this example (FIG. 7), the base layer 41 of the intermediate transfer ribbon 7 is peeled immediately after passing through the heat roller 12, but the peeling guide (guide shaft 18) is attached to the heat roller 12 as shown in FIG. It is also possible to change the peeling parameter from the base layer 41 by disposing the intermediate transfer ribbon 7 at a position away from the base layer 41 and cooling the intermediate transfer ribbon 7 after being heated by the heat roller 12 to the guide shaft 18. .

  FIG. 8 is a diagram showing an outline of the entire printing process. As shown in FIG. 8, first, image information is printed on an intermediate transfer medium (intermediate transfer ribbon 7). More specifically, printing is performed on the intermediate transfer medium in the order of the print colors cyan (C), magenta (M), and yellow (Y), and the multi-tone image 32 of the print medium P is printed. Next, a binary image 33 is printed with black (Bk) on the intermediate transfer medium, and then, transparent ink that functions as an adhesive layer is formed on the printed information in order to ensure adhesion with the intermediate transfer medium. Print on the surface of the transfer medium. Subsequently, the intermediate transfer medium is pressed against the print medium P while applying heat, whereby the intermediate transfer medium is transferred to the print medium P, and the print medium P is completed.

  FIG. 9 is a schematic diagram for explaining area gradation printing by driving the thermal head 4. In the printing apparatus 1, heat is generated by selectively energizing each heating element of the thermal head 4, and thermal transfer printing is performed by melting the ink on the ink ribbon 6. At this time, as shown in FIG. 9, one set of a non-energized portion (non-shaded portion) and a energized portion (shaded portion) is defined as one pulse, and an arbitrary print density can be obtained by changing the number of pulses. That is, area gradation printing is reproduced. In the example of FIG. 9, for example, when the intermediate density is printed, 3 pulses are energized, and when the highest density is printed, 6 pulses are energized.

  Next, density control during area gradation printing in the printing apparatus 1 will be described. In the printing of the printing medium P in the printing apparatus 1, the printing density of each color of C, M, Y, and Bk is the amount of energy applied to the ink ribbon 6 for each density when an image is formed on the printing medium P (for example, The correlation information indicating the correlation of the number of pulses) is defined by being divided into an arbitrary number of gradations. Specifically, in order to control printing density, the correspondence between the number of pulses and the gradation described above is held in the memory unit 52 in the form of a table, for example.

  FIG. 10 is a schematic diagram illustrating an example of a density-gradation table and a pulse number-gradation table. As shown in FIG. 10, in this embodiment, it is assumed that the memory unit 52 holds a table of density and pulse number for 256 gradation levels (density C0 to C255 and pulse number P0 to P255) of each color. . Here, the subscripts C, M, Y, and BK in the densities C0 to C255 and the pulse numbers P0 to P255 indicate the colors C, M, Y, and Bk, respectively.

  The correlation information indicating the correlation of the amount of energy (for example, the number of pulses) applied to the ink ribbon 6 for each density at the time of image formation on the print medium P includes density-gradation, pulse, in addition to the table format described above. It is good also as a coefficient of the function which shows the number-gradation correlation. For example, the coefficients of the third order, second order, first order, and constant terms when the density-gradation and pulse number-gradation correlations are approximated as a cubic function may be held in the memory unit 52.

  When printing on the print medium P, energization is performed with a pulse corresponding to the density of the dot in the print data by referring to a table (or a coefficient in the function format) held in the memory unit 52 under the control of the CPU 51. As a result, an image is formed at a desired print density.

  In printing by area gradation, the printing density is uniquely determined by the area ratio of the printed dots and the density of the color material contained in the ink. Therefore, in this embodiment, the density is in the form of an area ratio. Shall have.

  FIG. 11 is a schematic diagram illustrating an example of a gradation-density graph, a pulse number-density graph, and a gradation-pulse number graph. As shown in FIG. 11, the relationship between gradation and density (area ratio) is ideally linear in 1 to 255 gradations. Similarly, the relationship between the number of pulses and the density and the relationship between the gradation and the number of pulses are also linear.

  Next, the calibration process of the printing apparatus 1 performed under the control of the printing control apparatus 101 will be described in detail. FIG. 12 is a flowchart illustrating an example of the calibration process.

  In the calibration in the present embodiment, first, an operator (user) forms a chart image for confirmation on the print medium P by the printing apparatus 1 in order to confirm the state of the printing apparatus 1 to be calibrated. Specifically, as shown in FIG. 12, when processing is started by an operation instruction of the input / output device 102 (for example, an instruction to start calibration processing), the calibration chart printing unit 1011 stores in advance in a memory (ROM) or the like. The recorded calibration data is read, and a color chart (chart image) with a specified density patch is printed on the print medium P (S11).

  FIG. 13 is a schematic diagram illustrating the area of the image dots for each gradation. FIG. 14 is a schematic diagram illustrating an example of a chart image for calibration. For each color (C, M, Y, Bk), chart images having different specified gradations (densitys) in the order of G1, G2, and G3 are printed on the print medium P. At the time of calibration, since the density is not always shifted uniformly throughout, the chart image of different gradations is measured and used for calibration to improve accuracy. Actually, it is preferable to print a chart image for performing measurement of two or more gradations including low gradation and high gradation (for example, G1 and G3). Further, as shown in FIG. 14, in S11, a chart image in which density patches of a prescribed density (gradation) are arranged for each color of C, M, Y, and Bk may be printed on one print medium P. Alternatively, printing may be performed on the print medium P for each color and each gradation.

  Next, the worker photographs each patch (density patch) in the color chart printed in S11 with the image acquisition device 103 (S12). The print control apparatus 101 captures a captured image (image that is captured in an identifiable manner on each image point included in the image data captured by the image acquisition apparatus 103 in S12, that is, the chart image formed on the print medium P). Data).

  More specifically, for each color of C, M, Y, and Bk, the screen is displayed on the input / output device 102 so that the density patches are imaged in the order of G1, G2, and G3. Imaging is performed by the acquisition device 103. Accordingly, the print control apparatus 101 sequentially acquires, from the image acquisition apparatus 103, the density patch image data captured in the order of G1, G2, and G3 for each color of C, M, Y, and Bk. The acquired image data is stored in a temporary memory (RAM).

  Next, the calibration data calculation unit 1013 calculates the ink area ratio (area of the image dots) in the captured patch (S13). Specifically, the calibration data calculation unit 1013 uses image data obtained by imaging with the image acquisition device 103 as a threshold value set in advance to identify a portion on which an image dot is printed and a blank page portion. Convert to value. Then, the calibration data calculation unit 1013 calculates the ink area ratio by counting the number of pixels in the portion where the image dots are printed.

  Next, the calibration data calculation unit 1013 calculates a deviation amount between the calculated ink area ratio and the prescribed area ratio that should be printed (S14). Specifically, the ink area ratio for each patch in the color chart printed in S11 is recorded in advance in a memory or the like, and the calibration data calculation unit 1013 includes the ink area ratio recorded in advance in the memory and the image. The difference between the ink area ratio in the image data obtained by imaging with the acquisition device 103, that is, the ink area ratio actually printed on the print medium P is calculated.

  Next, the calibration data calculation unit 1013 calculates calibration data for calibrating the number of pulses corresponding to the deviation amount calculated in S14 (S15). Specifically, the calibration data calculation unit 1013 converts the deviation amount of the ink area ratio into a gradation deviation amount, and calculates the number of pulses (energy amount) corresponding to the gradation deviation amount as the gradation-pulse number. Calibration data is calculated based on conversion data recorded in a memory such as a graph (FIG. 11).

  The calibration data is calculated by sequentially reading out the image data from the temporary memory for the gradations corresponding to the density patches of G1, G2, and G3 for each color of C, M, Y, and Bk. For this reason, for C (cyan), for example, calibration data for G1, G2, and G3 gradations are sequentially calculated. The calibration data other than the gradation corresponding to the density patches of G1, G2, and G3 are calculated based on the shift amounts interpolated by linear interpolation based on the shift amounts of G1, G2, and G3. Thereby, calibration data for calibrating the pulse number-gradation table (see FIG. 10) for C, M, Y, and Bk is calculated.

  It should be noted that the calibration data in S15 indicates that the deviation calculated in S14 is more than a specified threshold value set in a memory or the like (the actual ink area ratio is wider than the preset ink area ratio by a specified threshold value or more). If the deviation amount calculated in S14 does not deviate by more than a predetermined threshold value, it is not necessary to calibrate.

  Next, the print data correction unit 1012 stores the calibration data calculated in S15 in the memory unit 52 of the printing apparatus 1 (S16). Specifically, the print data correction unit 1012 is based on the calibration data calculated in S15, and the number of pulses of each color of C, M, Y, and Bk recorded in the memory unit 52 of the printing apparatus 1 minus the floor. The key table (see FIG. 10) is corrected. The correction of the pulse number-gradation table may be performed by notifying the calculated calibration data to the printing apparatus 1 together with the control command and storing it in the memory unit 52 under the control of the CPU 51 of the printing apparatus 1. , Output (display) the calibration data calculated in S15 to the input / output device 102, etc., receive data input from the operator from the input / output device 102, and notify the printing device 1 of the data input together with the control command. Alternatively, the data may be stored in the memory unit 52.

  As described above, in the calibration method according to the embodiment, a chart image having a preset specified density is formed on the print medium P, and each image point included in the formed chart image is enlarged so as to be identifiable. The captured image is acquired, and the area of each image point included in the chart image is calculated based on the acquired captured image. Then, the amount of deviation between the area of the image dots to be formed with the specified density and the calculated area of the image dots is calculated, and for each density at the time of image formation on the print medium P based on the calculated amount of deviation. The correlation information (pulse number-gradation table) indicating the correlation of the energy amount (pulse number) applied to the ink ribbon 6 is calibrated. Therefore, in the calibration method according to the embodiment, it is not necessary to use an expensive spectrocolorimeter when calibrating the output density, and calibration can be performed at a lower cost.

(Modification 1)
Next, Modification 1 of the above-described embodiment will be described. In the first modification, a chart image is formed again based on the calibrated correlation information (pulse number-gradation table), and the deviation amount calculated in S14 based on the chart image is within a prescribed threshold. Check if it exists. Thus, the accuracy of calibration may be increased by performing reconfirmation after calibration.

  FIG. 15 is a flowchart illustrating an example of a calibration process according to the first modification. As shown in FIG. 15, the print control apparatus 101 prints the chart on the print medium P again reflecting the calibration data after S16 (S17). Then, the print control apparatus 101 performs the above-described processing of S12 to S14, and determines whether or not the deviation amount calculated in S14 is within a predetermined threshold (S18). As the threshold value, a density difference (color difference) that allows a human to feel the same color is preset in a memory or the like. Specifically, a density difference within 2.5% is a density difference that humans feel as the same color, and therefore a value for determining that a density difference of 2.5% or more has occurred is a threshold value. Is set as

  If the deviation amount is within the predetermined threshold (S18: YES), the print control apparatus 101 ends the process assuming that the calibration is correctly performed. If the deviation amount is not within the predetermined threshold (S18: NO), the print control apparatus 101 performs the processing of S15 and S16, calibrates with the deviation amount calculated by reconfirmation, and then returns to S17 and performs the calibration. Check again. As a result, the calibration process is repeatedly performed until the deviation amount falls within a predetermined threshold.

(Modification 2)
Next, a second modification of the above-described embodiment will be described. In the second modification, the color of each image point included in the chart image is detected and detected based on the captured image acquired by imaging the print medium P on which the chart image is printed by the image acquisition device 103. An error is output if the selected color is not a preset color. In this way, by checking not only the density expressed by area gradation with C, M, Y, and K inks, but also the ink color, the color change of the ink is also checked at the same time, and more rigorous calibration is performed. It becomes possible.

  FIG. 16 is a flowchart illustrating an example of a calibration process according to the second modification. As shown in FIG. 16, following S11, the image acquisition device 103 is set to a predetermined illumination condition such as illuminance and constant luminance with a white light source (S11a). More specifically, after setting up a black screen so as not to be affected by external light when the image acquisition device 103 is picked up, the illumination conditions may be such that the illuminance and luminance are constant with a white light source. In this way, the C, M, Y, and K ink colors are imaged under the same illumination conditions as the prescribed illumination conditions.

  After S12, the print control apparatus 101 acquires the image data captured by the image acquisition apparatus 103 and applies ink (image dots) to the pixels of the portion where the image dots obtained by binarization are printed. The color is confirmed by the RGB value (S20). Next, the print control apparatus 101 determines whether or not the color of the image point (RGB value) is within a specified range preset in a memory or the like (S21).

  If the color of the image dot is within the specified range (S21: YES), the process proceeds to S13 because the ink color is normal. If the color of the dot is not within the specified range (S21: NO), since the ink color is different from the specified color, the print control apparatus 101 displays ink on the display screen of the input / output device 102. A ribbon replacement request is displayed (error display) (S22).

  Note that the program executed by the print control apparatus 101 of the present embodiment is provided by being incorporated in advance in a ROM or the like. The program executed in the present embodiment is an installable or executable file, and is a computer-readable recording such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disk). You may comprise so that it may record and provide on a medium.

  Furthermore, the program executed in the present embodiment may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. The program executed in the present embodiment may be configured to be provided or distributed via a network such as the Internet.

  The program executed in the present embodiment has a module configuration including the above-described functional configuration. As actual hardware, the CPU (processor) reads the program from the ROM and executes the program, and the functional configuration described above is executed. It is loaded on the main storage device and generated on the main storage device.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Moreover, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, the constituent elements over different embodiments may be appropriately combined.

  DESCRIPTION OF SYMBOLS 1 ... Printing apparatus, 2 ... Printing part, 3 ... Transfer part, 4 ... Thermal head, 5 ... Platen roller, 6 ... Ink ribbon, 7 ... Intermediate transfer ribbon, 8, 14 ... Sending shaft, 9, 15 ... Winding shaft DESCRIPTION OF SYMBOLS 10, 11, 16-18 ... Guide shaft, 12 ... Heat roller, 12a ... Heater, 12b ... Cut surface, 13 ... Backup roller, 19 ... Tension roller, 20, 21 ... Conveyance roller pair, 22 ... Print medium taking-in 23, transport path, 31 ... printable area, 32 ... multi-tone image, 33 ... binary image, 41 ... base layer, 42 ... protective layer, 43 ... image receiving layer, 44 ... image, 45 ... transparent ink layer , 51 ... CPU, 52 ... memory unit, 53 ... interface unit, 54 ... thermal head control circuit, 55 ... printing unit conveyance control circuit, 56 ... heater temperature control circuit, 57 ... heat roller rotation control circuit, 58 ... transfer Transport control circuit 59... Print medium transport control circuit 60 Sensor input circuit 100 Image forming apparatus 101 Print control apparatus 102 Input / output device 103 Image acquisition apparatus 1011 Calibration chart printing unit 1012 ... print data correction unit, 1013 ... calibration data calculation unit, G1 to G3 ... gradation, P ... print medium, S1 to S4 ... sensor

Claims (8)

A calibration method executed by an image forming apparatus that represents the density of an image formed on a print medium by the area of a dot,
A printing step of forming a chart image having a preset predetermined density on the print medium;
An acquisition step of acquiring a captured image obtained by enlarging and identifying each image point included in the formed chart image;
Based on the acquired captured image, an area calculating step for calculating the area of each image point included in the chart image;
A deviation amount calculating step of calculating a deviation amount between the area of the image dots to be formed at the specified density and the calculated area of the image dots;
A calibration step for calibrating correlation information indicating a correlation between the amounts of energy applied to the image forming unit for each density at the time of image formation on the print medium based on the calculated shift amount;
A calibration method comprising: The area calculation step calculates the area of the image point based on pixels corresponding to the image point obtained by binarizing the acquired captured image with a predetermined threshold value.
The calibration method according to claim 1. The image forming unit forms image dots on the print medium for each of cyan, magenta, yellow, and black colors,
The printing step forms the chart image for each of the cyan, magenta, yellow, and black colors,
The calibration step calibrates the correlation information for each of the cyan, magenta, yellow, and black colors based on the shift amount calculated for each of the cyan, magenta, yellow, and black colors.
The calibration method according to claim 1 or 2. The printing step forms a plurality of chart images having different prescribed densities on the print medium,
The calibration step calibrates the correlation information by interpolating a deviation amount having a density different from the density of the plurality of chart images based on a deviation amount calculated for each of the plurality of chart images.
The calibration method according to any one of claims 1 to 3. The image forming unit forms an image on the print medium by a fusion thermal transfer method;
The calibration method as described in any one of Claims 1 thru | or 4. The method further includes a confirmation step of forming the chart image based on the correlation information calibrated in the calibration step, and confirming whether the deviation amount calculated based on the chart image is within a predetermined threshold. ,
The calibration method according to any one of claims 1 to 5. Based on the acquired captured image, a color detection step of detecting the color of each image point included in the chart image;
And an output step of outputting an error when the detected color is not a preset color.
The calibration method according to any one of claims 1 to 6. An image forming apparatus that represents the density of an image formed on a print medium by the area of a dot,
Printing means for forming a chart image having a predetermined density set in advance on the print medium;
An acquisition means for acquiring a captured image obtained by enlarging and individually identifying each image point included in the formed chart image;
Based on the acquired captured image, an area calculating means for calculating the area of each image point included in the chart image;
A deviation amount calculating means for calculating a deviation amount between the area of the dot to be formed at the specified density and the calculated area of the dot;
Calibration means for calibrating correlation information indicating a correlation between energy amounts applied to the image forming unit for each density at the time of image formation on the print medium, based on the calculated deviation amount;
An image forming apparatus comprising:

Images