JP6236799B2 - Color measuring device, image forming apparatus, color measuring method and program - Google Patents

Description

  The present invention relates to a color measurement device, an image forming apparatus, a color measurement method, and a program.

  In an image forming apparatus such as a printer, processing called color management is performed in order to improve output reproducibility with respect to input by suppressing variations in output due to device-specific characteristics. Color management improves the reproducibility of an output image by performing color conversion between a standard color space and a device-dependent color based on a device profile (ICC profile) that describes device-specific characteristics. When generating or modifying a device profile, an image forming apparatus actually forms a test pattern in which color charts (patches) of a large number of reference colors are arranged on a recording medium, and applies to each patch included in the test pattern. Perform colorimetry.

  A spectrocolorimeter is widely used as a color measuring device for measuring the color of a patch. Since the spectral colorimeter can obtain spectral reflectance for each wavelength, it can perform highly accurate color measurement. However, since the spectrocolorimeter is an expensive device, it is desired to perform high-precision colorimetry using a cheaper device.

  An example of a method for realizing high-precision colorimetry at low cost is to image a colorimetric object as a subject using an imaging device, and convert the RGB value of the subject obtained by the imaging to a color value in a standard color space. . For example, Patent Document 1 uses a two-dimensional image sensor to simultaneously capture a color measurement target patch and a reference chart including a plurality of patches whose colorimetric values are known in advance, and obtain a measurement obtained by imaging. A technique for calculating a colorimetric value of a color measurement target patch based on the RGB value of the color target patch and the RGB value of the patch included in the reference chart is described.

  In the technique described in Patent Document 1, the two-dimensional image sensor is attached to a carriage on which a recording head is mounted. When performing color measurement of the patch, the carriage is stopped at a position where the two-dimensional image sensor faces the patch, the patch is imaged by the two-dimensional image sensor, and the patch is detected based on the obtained image data. Colorimetric values are calculated. For this reason, in order to perform color measurement on a large number of patches included in the test pattern, there is a problem that the movement and stop of the carriage are repeated for each patch, and it takes time for color measurement.

  The present invention has been made in view of the above, and an object of the present invention is to provide a color measuring device, an image forming apparatus, a color measuring method, and a program capable of performing patch colorimetry in a short time.

In order to solve the above-mentioned problems and achieve the object, the present invention provides a two-dimensional image sensor that captures an image while moving on a recording medium on which a patch is formed, and outputs a plurality of frames of image data. A selection unit that excludes image data having a predetermined number or more of pixel values close to the stored RGB values of the recording medium from a plurality of frames of image data output from a three-dimensional image sensor, and selects image data obtained by capturing the patch And a calculation unit that calculates a colorimetric value of the patch based on the image data selected by the selection unit.

  According to the present invention, it is possible to perform patch colorimetry in a short time.

FIG. 1 is a perspective view illustrating the inside of the image forming apparatus. FIG. 2 is a top view showing an internal mechanical configuration of the image forming apparatus. FIG. 3 is a diagram for explaining an arrangement example of the recording heads mounted on the carriage. FIG. 4A is a longitudinal sectional view of the colorimetric camera (a sectional view taken along line X1-X1 in FIG. 4-2). FIG. 4B is a top view of the colorimetric camera as seen through. FIG. 4-3 is a plan view of the bottom surface of the housing as viewed from the X2 direction in FIG. 4-1. FIG. 5 is a diagram illustrating a specific example of the reference chart. FIG. 6 is a block diagram illustrating a schematic configuration of a control mechanism of the image forming apparatus. FIG. 7 is a block diagram illustrating a configuration example of the control mechanism of the colorimetric camera. FIG. 8 is a timing chart for explaining the operation of the two-dimensional image sensor. FIG. 9 is an explanatory diagram illustrating image data selected by the selection unit. FIG. 10 is an explanatory diagram for explaining that the number of dots of a patch formed by halftone printing increases by using image data of a wide area in the patch for colorimetry. FIG. 11 is an explanatory diagram for explaining that the influence of an abnormal portion whose color changes locally in a patch is mitigated by using image data of a wide area in the patch for colorimetry. FIG. 12 is an explanatory diagram for explaining processing by the averaging processing unit. FIG. 13 is a diagram illustrating an example of a test pattern formed on a recording medium. FIG. 14 is a diagram for explaining processing for obtaining a reference colorimetric value and a reference RGB value and processing for generating a reference value linear transformation matrix. FIG. 15 is a diagram illustrating an example of the initial reference RGB values. FIG. 16 is a diagram for explaining the outline of the color measurement process. FIG. 17 is a diagram for describing processing for generating a linear conversion matrix between reference RGB. FIG. 18 is a diagram illustrating the relationship between the initial reference RGB value and the colorimetric reference RGB value. FIG. 19 is a diagram for explaining basic colorimetry processing. FIG. 20 is a diagram for explaining basic colorimetry processing. FIG. 21 is a diagram illustrating a schematic configuration of a color measurement system.

  Exemplary embodiments of a color measurement device, an image forming apparatus, a color measurement method, and a program according to the present invention will be described below in detail with reference to the accompanying drawings.

<Mechanical configuration of image forming apparatus>
First, the mechanical configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIGS. 1 to 3. FIG. 1 is a perspective view illustrating the inside of the image forming apparatus 100 according to the present embodiment. FIG. 2 is a top view illustrating the internal mechanical configuration of the image forming apparatus 100 according to the present embodiment. FIG. 6 is a diagram for explaining an arrangement example of the recording head 6 mounted on the carriage 5.

  As shown in FIG. 1, the image forming apparatus 100 according to the present embodiment reciprocates in the main scanning direction (arrow A direction in the figure) and is intermittently conveyed in the sub-scanning direction (arrow B direction in the figure). A carriage (support) 5 for forming an image on the recording medium P is provided. The carriage 5 is supported by a main guide rod 3 extending along the main scanning direction. The carriage 5 is provided with a connecting piece 5a. The connecting piece 5 a engages with the sub guide member 4 provided in parallel with the main guide rod 3 to stabilize the posture of the carriage 5.

  As shown in FIG. 2, the carriage 5 includes a recording head 6y that discharges yellow (Y) ink, a recording head 6m that discharges magenta (M) ink, a recording head 6c that discharges cyan (C) ink, and black. (Bk) A plurality of recording heads 6k that discharge ink (hereinafter, the recording heads 6y, 6m, 6c, and 6k are collectively referred to as recording heads 6) are mounted. The recording head 6 is supported by the carriage 5 such that the ejection surface (nozzle surface) faces downward (recording medium P side).

  A cartridge 7, which is an ink supply body for supplying ink to the recording head 6, is not mounted on the carriage 5 and is disposed at a predetermined position in the image forming apparatus 100. The cartridge 7 and the recording head 6 are connected by a pipe (not shown), and ink is supplied from the cartridge 7 to the recording head 6 through this pipe.

  The carriage 5 is connected to a timing belt 11 stretched between a driving pulley 9 and a driven pulley 10. The drive pulley 9 is rotated by driving the main scanning motor 8. The driven pulley 10 has a mechanism for adjusting the distance to the driving pulley 9 and has a role of applying a predetermined tension to the timing belt 11. The carriage 5 reciprocates in the main scanning direction when the timing belt 11 is fed by driving the main scanning motor 8. The movement of the carriage 5 in the main scanning direction is controlled based on an encoder value obtained when the encoder sensor 13 provided on the carriage 5 detects a mark on the encoder sheet 14 as shown in FIG.

  Further, the image forming apparatus 100 according to the present embodiment includes a maintaining mechanism 15 for maintaining the reliability of the recording head 6. The maintenance mechanism 15 performs cleaning and capping of the ejection surface of the recording head 6 and discharging unnecessary ink from the recording head 6.

  As shown in FIG. 2, a platen 16 is provided at a position facing the ejection surface of the recording head 6. The platen 16 is for supporting the recording medium P when ink is ejected from the recording head 6 onto the recording medium P. The image forming apparatus 100 according to the present embodiment is a wide-width machine in which the moving distance of the carriage 5 in the main scanning direction is long. For this reason, the platen 16 is configured by connecting a plurality of plate-like members in the main scanning direction (movement direction of the carriage 5). The recording medium P is sandwiched between transport rollers driven by a sub scanning motor (not shown), and is intermittently transported on the platen 16 in the sub scanning direction.

  The recording head 6 includes a plurality of nozzle arrays, and forms an image on the recording medium P by ejecting ink from the nozzle arrays onto the recording medium P transported on the platen 16. In this embodiment, in order to secure a large width of an image that can be formed on the recording medium P by one scan of the carriage 5, as shown in FIG. 3, the upstream recording head 6 and the downstream recording head are provided on the carriage 5. The head 6 is mounted. Further, the recording head 6k that discharges black ink is mounted on the carriage 5 as many times as the recording heads 6y, 6m, and 6c that discharge color ink. The recording heads 6y and 6m are arranged separately on the left and right. This is because the color stacking order is adjusted by the reciprocating operation of the carriage 5 so that the color does not change between the forward path and the return path. The arrangement of the recording heads 6 shown in FIG. 3 is an example, and the arrangement is not limited to the arrangement shown in FIG.

  Each of the above-described constituent elements constituting the image forming apparatus 100 according to the present embodiment is disposed inside the exterior body 1. The exterior body 1 is provided with a cover member 2 that can be opened and closed. At the time of maintenance of the image forming apparatus 100 or when a jam occurs, the cover member 2 can be opened to perform work on each component provided inside the exterior body 1.

  The image forming apparatus 100 according to the present embodiment intermittently conveys the recording medium P in the sub scanning direction, and moves the carriage 5 in the main scanning direction while the conveyance of the recording medium P in the sub scanning direction is stopped. Then, ink is ejected from the nozzle row of the recording head 6 mounted on the carriage 5 onto the recording medium P on the platen 16 to form an image on the recording medium P.

  In particular, when adjusting the color of the image forming apparatus 100, ink is actually ejected from the nozzle row of the recording head 6 mounted on the carriage 5 onto the recording medium P on the platen 16, and a large number of patches. A test pattern in which 200 lines are arranged is formed. Then, color measurement is performed on each patch 200 included in the test pattern. Each patch 200 included in the test pattern is an image obtained by outputting a reference color patch from the image forming apparatus 100, and reflects characteristics unique to the image forming apparatus 100. Accordingly, a device profile describing characteristics unique to the image forming apparatus 100 can be generated or corrected using the colorimetric values of the patches 200. Then, by performing color conversion between the standard color space and the device-dependent color based on this device profile, the image forming apparatus 100 can output an image with high reproducibility.

  The image forming apparatus 100 according to the present embodiment includes a colorimetric camera (colorimetric device) 20 for performing colorimetry on each patch 200 included in a test pattern formed on a recording medium P. As shown in FIG. 2, the colorimetric camera 20 is supported by a carriage 5 on which the recording head 6 is mounted. The colorimetric camera 20 picks up an image while moving on the recording medium P on which the test pattern is formed as the carriage 5 moves, and obtains image data (images of a plurality of frames constituting a moving image) obtained by the image pickup. Data), the colorimetric value of the patch 200 is calculated based on the image data obtained by capturing the patch 200.

<Specific example of mechanical configuration of colorimetric camera>
4A to 4C are diagrams illustrating an example of the mechanical configuration of the colorimetric camera 20. FIG. 4A is a longitudinal sectional view of the colorimetric camera 20 (X1- in FIG. 4B). FIG. 4-2 is a top view of the colorimetric camera 20 seen through, and FIG. 4-3 is a plan view of the bottom surface of the housing as viewed from the X2 direction in FIG. 4-1. FIG.

  The colorimetric camera 20 includes a housing 23 configured by combining a frame body 21 and a substrate 22. The frame body 21 is formed in a bottomed cylindrical shape in which one end side which is the upper surface of the housing 23 is opened. The substrate 22 is fastened to the frame body 21 by a fastening member 24 and integrated with the frame body 21 so as to close the open end of the frame body 21 and configure the upper surface of the housing 23.

  The housing 23 is fixed to the carriage 5 so that the bottom surface portion 23a faces the recording medium P on the platen 16 with a predetermined gap d. An opening 25 for enabling the patch 200 formed on the recording medium P to be photographed from the inside of the casing 23 is provided on the bottom surface portion 23 a of the casing 23 facing the recording medium P. The size of the opening 25 is smaller than the size of the patch 200.

  A sensor unit 26 that captures an image is provided inside the housing 23. The sensor unit 26 includes a two-dimensional image sensor 27 such as a CCD sensor or a CMOS sensor, and an imaging lens 28 that forms an optical image in the imaging range of the sensor unit 26 on the sensor surface of the two-dimensional image sensor 27. The two-dimensional image sensor 27 is mounted on, for example, the inner surface (component mounting surface) of the substrate 22 so that the sensor surface faces the bottom surface portion 23 a side of the housing 23. The imaging lens 28 is fixed in a state of being positioned with respect to the two-dimensional image sensor 27 so as to maintain a positional relationship determined according to the optical characteristics thereof.

  A reference chart 400 is disposed on the inner surface of the bottom surface 23a of the housing 23 facing the sensor unit 26 so as to be adjacent to the opening 25 provided in the bottom surface 23a. For example, the reference chart 400 is imaged together with the patch 200 by the sensor unit 26 as a comparison target of the patch 200 to be measured. That is, the sensor unit 26 is arranged on the inner surface side of the bottom surface part 23a of the housing 23 at the same time as imaging the patch 200 outside the housing 23 through the opening 25 provided in the bottom surface part 23a of the housing 23. The reference chart 400 is imaged. Note that the simultaneous imaging here means that one frame of image data including the patch 200 and the reference chart 400 is acquired. That is, even if there is a time difference in data acquisition for each pixel, if image data including the patch 200 and the reference chart 400 is acquired within one frame, the patch 200 and the reference chart 400 are captured simultaneously.

  An illumination light source 29 that illuminates the patch 200 and the reference chart 400 when the sensor unit 26 images the patch 200 and the reference chart 400 at the same time is provided inside the housing 23. As the illumination light source 29, for example, an LED (Light Emitting Diode) is used. In the present embodiment, two LEDs are used as the illumination light source 29. These two LEDs used as the illumination light source 29 are mounted on the inner surface of the substrate 22 together with the two-dimensional image sensor 27 of the sensor unit 26, for example. However, the illumination light source 29 only needs to be disposed at a position where the patch 200 and the reference chart 400 can be illuminated, and does not necessarily have to be directly mounted on the substrate 22. Moreover, in this embodiment, although LED is used as the illumination light source 29, the kind of light source is not limited to LED. For example, an organic EL or the like may be used as the illumination light source 29. When organic EL is used as the illumination light source 29, illumination light close to the spectral distribution of sunlight can be obtained, so that improvement in colorimetric accuracy can be expected.

  Further, in the present embodiment, as shown in FIG. 4B, projection on the bottom surface portion 23a when two LEDs used as the illumination light source 29 are looked down vertically from the substrate 22 side to the bottom surface portion 23a side of the housing 23. These two LEDs are arranged so that the position is within the region between the opening 25 and the reference chart 400 and is symmetric with respect to the sensor unit 26. In other words, the housing 23 is located at a position where the line connecting the two LEDs used as the illumination light source 29 passes through the center of the imaging lens 28 of the sensor unit 26 and is symmetrical with respect to the line connecting the two LEDs. The opening 25 provided in the bottom surface 23a and the reference chart 400 are arranged. By arranging the two LEDs used as the illumination light source 29 in this way, the patch 200 and the reference chart 400 can be illuminated under substantially the same conditions.

  By the way, in order to illuminate the patch 200 outside the housing 23 under the same illumination conditions as the reference chart 400 arranged inside the housing 23, the external light does not hit the patch 200 during imaging, and the illumination light source It is necessary to illuminate the patch 200 only with the illumination light from 29. In order to prevent the external light from hitting the patch 200, the gap d between the bottom surface portion 23 a of the housing 23 and the recording medium P is made small so that the external light toward the patch 200 is blocked by the housing 23. It is effective to do. However, if the gap d between the bottom surface portion 23a of the housing 23 and the recording medium P is made too small, the recording medium P will come into contact with the bottom surface portion 23a of the housing 23 and the image cannot be captured properly. There is a fear. Therefore, the gap d between the bottom surface 23a of the housing 23 and the recording medium P is a small value in a range where the recording medium P does not contact the bottom surface 23a of the housing 23 in consideration of the flatness of the recording medium P. It is desirable to set to. For example, when the gap d is set to about 1 mm to 2 mm, the recording medium P is effectively prevented from being exposed to the patch 200 formed on the recording medium P without coming into contact with the bottom surface portion 23a of the casing 23. it can.

  In order to appropriately irradiate the patch 200 with illumination light from the illumination light source 29, the size of the opening 25 provided in the bottom surface portion 23 a of the housing 23 is made larger than that of the patch 200, and the edge of the opening 25 is It is desirable to prevent the shadow caused by the illumination light from being reflected on the patch 200.

  Further, if the gap d between the bottom 23a of the housing 23 and the recording medium P is reduced, the difference between the optical path length from the sensor unit 26 to the patch 200 and the optical path length from the sensor unit 26 to the reference chart 400 is achieved. Can be within the range of the depth of field of the sensor unit 26. The colorimetric camera 20 according to the present embodiment is configured to simultaneously image the patch 200 outside the housing 23 and the reference chart 400 provided inside the housing 23 by the sensor unit 26. Therefore, when the difference between the optical path length from the sensor unit 26 to the patch 200 and the optical path length from the sensor unit 26 to the reference chart 400 exceeds the range of the depth of field of the sensor unit 26, the patch 200 and the reference chart 400 are used. It is not possible to take an image that is focused on both of the two.

  The difference between the optical path length from the sensor unit 26 to the patch 200 and the optical path length from the sensor unit 26 to the reference chart 400 is generally a value obtained by adding the gap d to the thickness of the bottom surface part 23 a of the housing 23. Therefore, if the gap d is set to a sufficiently small value, the difference between the optical path length from the sensor unit 26 to the patch 200 and the optical path length from the sensor unit 26 to the reference chart 400 is determined as the range of the depth of field of the sensor unit 26. As an inside, an image focused on both the patch 200 and the reference chart 400 can be taken. For example, if the gap d is set to about 1 mm to 2 mm, the difference between the optical path length from the sensor unit 26 to the patch 200 and the optical path length from the sensor unit 26 to the reference chart 400 is expressed as the depth of field of the sensor unit 26. Can be within range.

  Note that the depth of field of the sensor unit 26 is determined according to the aperture value of the sensor unit 26, the focal length of the imaging lens 28, the distance between the sensor unit 26 and the subject, and the like. It is. In the colorimetric camera 20 of the present embodiment, when the gap d between the bottom surface portion 23a of the housing 23 and the recording medium P is set to a sufficiently small value of about 1 mm to 2 mm, for example, the patch 200 from the sensor unit 26 is used. The sensor unit 26 is designed so that the difference between the optical path length up to and the optical path length from the sensor unit 26 to the reference chart 400 is within the depth of field.

<Specific examples of reference chart>
Next, the reference chart 400 arranged inside the housing 23 of the colorimetric camera 20 will be described in detail with reference to FIG. FIG. 5 is a diagram illustrating a specific example of the reference chart 400.

  A reference chart 400 shown in FIG. 5 includes a plurality of reference patch rows 401 to 404 in which colorimetric patches are arranged, a dot diameter measurement pattern row 406, a distance measurement line 405, and a chart position specifying marker 407.

  The reference patch rows 401 to 404 are a reference patch row 401 in which YMCK primary color patches are arranged in gradation order, a reference patch row 402 in which RGB secondary color patches are arranged in gradation order, and a grayscale patch. A reference patch array (achromatic color gradation pattern) 403 arranged in the order of gradation and a reference patch array 404 arranged with tertiary color patches. The dot diameter measurement pattern row 406 is a geometric shape measurement pattern row in which circular patterns of different sizes are arranged in order of size, and is used for measuring the dot diameter of an image recorded on the recording medium P. it can.

  The distance measurement line 405 is formed as a rectangular frame surrounding the plurality of reference patch rows 401 to 404 and the dot diameter measurement pattern row 406. The chart position specifying markers 407 are provided at the positions of the four corners of the distance measuring line 405 and function as markers for specifying each patch position. By specifying the distance measurement line 405 and the chart position specifying markers 407 at the four corners thereof from the image data of the reference chart 400 obtained by imaging by the colorimetric camera 20, the position of the reference chart 400 and the position of each pattern are specified. can do.

  Each patch constituting the colorimetric reference patch rows 401 to 404 is used as a color reference reflecting an imaging condition when the colorimetric camera 20 performs imaging. The configuration of the colorimetric reference patch rows 401 to 404 arranged in the reference chart 400 is not limited to the example shown in FIG. 5, and any patch row can be applied. For example, a patch that can specify a color range as wide as possible may be used, and the YMCK primary color reference patch row 401 and the grayscale reference patch row 403 are used in the image forming apparatus 100. It may be composed of patches of ink colorimetric values. The RGB secondary color reference patch row 402 may be configured with patches of colorimetric values that can be developed with ink used in the image forming apparatus 100, and further, colorimetric values such as Japan Color are used. A predetermined reference color chart may be used.

  In the present embodiment, the reference chart 400 having the reference patch rows 401 to 404 having a general patch (color chart) shape is used. However, the reference chart 400 is not necessarily limited to such reference patch rows 401 to 404. It may not be the form which has. The reference chart 400 may be configured so that a plurality of colors that can be used for colorimetry are arranged so that their positions can be specified.

  Since the reference chart 400 is arranged on the bottom surface 23 a of the housing 23 of the colorimetric camera 20 so as to be adjacent to the opening 25, it can be imaged simultaneously with the patch 200 by the sensor unit 26.

  The mechanical configuration of the colorimetric camera 20 described above is merely an example, and is not limited to this configuration. The colorimetric camera 20 of the present embodiment only needs to be configured to capture an image using at least the two-dimensional image sensor 27, and various modifications and changes can be made to the above configuration.

<Schematic configuration of control mechanism of image forming apparatus>
Next, a schematic configuration of the control mechanism of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG. FIG. 6 is a block diagram illustrating a schematic configuration of a control mechanism of the image forming apparatus 100.

  As shown in FIG. 6, the image forming apparatus 100 according to the present embodiment includes a CPU 101, a ROM 102, a RAM 103, a recording head driver 104, a main scanning driver 105, a sub scanning driver 106, and a control FPGA (Field-Programmable Gate Array) 110. A recording head 6, a colorimetric camera 20, an encoder sensor 13, a main scanning motor 8, and a sub-scanning motor 12. The CPU 101, ROM 102, RAM 103, print head driver 104, main scanning driver 105, sub scanning driver 106, and control FPGA 110 are mounted on the main control board 120. The recording head 6, the encoder sensor 13, and the colorimetric camera 20 are mounted on the carriage 5 as described above.

  The CPU 101 governs overall control of the image forming apparatus 100. For example, the CPU 101 uses the RAM 103 as a work area, executes various control programs stored in the ROM 102, and outputs control commands for controlling various operations in the image forming apparatus 100.

  The recording head driver 104, the main scanning driver 105, and the sub scanning driver 106 are drivers for driving the recording head 6, the main scanning motor 8, and the sub scanning motor 12, respectively.

  The control FPGA 110 controls various operations in the image forming apparatus 100 in cooperation with the CPU 101. The control FPGA 110 includes, for example, a CPU control unit 111, a memory control unit 112, an ink ejection control unit 113, a sensor control unit 114, and a motor control unit 115 as functional components.

  The CPU control unit 111 communicates with the CPU 101 to transmit various information acquired by the control FPGA 110 to the CPU 101 and inputs a control command output from the CPU 101.

  The memory control unit 112 performs memory control for the CPU 101 to access the ROM 102 and the RAM 103.

  The ink discharge control unit 113 controls the operation of the print head driver 104 in accordance with a control command from the CPU 101, thereby controlling the discharge timing of ink from the print head 6 driven by the print head driver 104.

  The sensor control unit 114 performs processing on sensor signals such as encoder values output from the encoder sensor 13.

  The motor control unit 115 controls the main scanning motor 105 driven by the main scanning driver 105 by controlling the operation of the main scanning driver 105 in accordance with a control command from the CPU 101, and moves the carriage 5 in the main scanning direction. Control the movement of. In addition, the motor control unit 115 controls the sub-scanning motor 106 driven by the sub-scanning driver 106 by controlling the operation of the sub-scanning driver 106 in accordance with a control command from the CPU 101, and records on the platen 16. Controls the movement of the medium P in the sub-scanning direction.

  Each of the above-described units is an example of a control function realized by the control FPGA 110, and various other control functions may be realized by the control FPGA 110. Moreover, the structure which implement | achieves all or one part of said control function with the program run by CPU101 or another general purpose CPU may be sufficient. Further, a configuration in which a part of the control function is realized by dedicated hardware such as another FPGA different from the control FPGA 110 or an ASIC (Application Specific Integrated Circuit) may be used.

  The recording head 6 is driven by a recording head driver 104 whose operation is controlled by the CPU 101 and the control FPGA 110, and ejects ink onto the recording medium P on the platen 16 to form an image.

As described above, the colorimetric camera 20 captures an image while moving on the recording medium P when performing colorimetry on each patch 200 included in the test pattern formed on the recording medium P. The colorimetric camera 20 selects image data obtained by imaging the patch 200 from a plurality of frames of image data obtained by imaging, and based on the selected image data, the colorimetric value (standard color space) of the patch 200 is selected. a color value in, for example, ^L * ^a * ^{b * L} * ^a * ^{b *} values in a color space ^(hereinafter referred to L ^* a * ^{b *} and Lab.)) is calculated. The colorimetric values of the patch 200 calculated by the colorimetric camera 20 are sent to the CPU 101 via the control FPGA 110.

  The encoder sensor 13 outputs an encoder value obtained by detecting the mark on the encoder sheet 14 to the control FPGA 110. This encoder value is sent from the control FPGA 110 to the CPU 101 and used, for example, to calculate the position and speed of the carriage 5. The CPU 101 generates and outputs a control command for controlling the main scanning motor 8 based on the position and speed of the carriage 5 calculated from the encoder value.

<Configuration of colorimetric camera control mechanism>
Next, the control mechanism of the colorimetric camera 20 will be specifically described with reference to FIG. FIG. 7 is a block diagram illustrating a configuration example of the control mechanism of the colorimetric camera 20.

  As shown in FIG. 7, the colorimetric camera 20 includes a two-dimensional image sensor 27, an interface unit 30, a selection unit 31, a frame memory 32, an averaging processing unit 33, a colorimetric value calculation unit 34, a non-volatile memory 35, and a timing. A signal generation unit 36, a light source drive control unit 37, and an illumination light source 29 are provided. Each of these units is mounted on a substrate 22 that constitutes the upper surface of the housing 23 of the colorimetric camera 20, for example.

  The two-dimensional image sensor 27 converts light from the imaging range incident through the imaging lens 28 into an electrical signal and outputs image data in the imaging range. In particular, in the colorimetric camera 20 of the present embodiment, when performing colorimetry of each patch 200 included in the test pattern formed on the recording medium P, the two-dimensional image sensor 27 moves along with the movement of the carriage 5. Imaging is performed while moving in the main scanning direction on P, and image data of a plurality of frames constituting a moving image is output.

  FIG. 8 is a timing chart for explaining the operation of the two-dimensional image sensor 27. As shown in FIG. 8, the two-dimensional image sensor 27 starts imaging when the carriage 5 starts to move, performs exposure according to the shutter speed (number of electronic shutters) set by the CPU 101, and outputs image data. . The two-dimensional image sensor 27 repeats the above process while the carriage 5 is moving in the main scanning direction, and outputs a plurality of frames of image data constituting a moving image. Therefore, the image data output from the two-dimensional image sensor 27 includes image data obtained by imaging the gap 200 between the patches 200 arranged in the main scanning direction, in addition to image data obtained by imaging the patch 200 included in the test pattern. .

  The two-dimensional image sensor 27 includes an image processing unit 27a that performs various types of image processing such as AD conversion, shading correction, white balance correction, γ correction, and image data format conversion on image data obtained by exposure. doing. The two-dimensional image sensor 27 outputs image data on which various types of image processing have been performed in the image processing unit 27a. Various image processing on the image data may be performed partly or entirely outside the two-dimensional image sensor 27.

  The interface unit 30 outputs image data from the two-dimensional image sensor 27, and also receives various setting signals sent from the CPU 101 via the control FPGA 110 and timing signals generated by the timing signal generation unit 36. It is an interface for input to. The various setting signals include a signal for setting the operation mode of the two-dimensional image sensor 27 and a signal for setting the imaging conditions such as the shutter speed and the AGC gain described above.

  The selection unit 31 selects image data obtained by capturing the patch 200 from among a plurality of frames of image data output from the two-dimensional image sensor 27.

  As described above, the two-dimensional image sensor 27 captures an image as a moving image while moving in the main scanning direction on the recording medium P on which the test pattern is formed. The image data includes image data obtained by imaging the gap area between the patches 200. Therefore, the selection unit 31 selects image data obtained by capturing the patch 200 from among a plurality of frames of image data output from the two-dimensional image sensor 27 as image data used for color measurement of the patch 200. The image data selected by the selection unit 31 is stored in the frame memory 32, and other image data is discarded.

  FIG. 9 is an explanatory diagram illustrating image data selected by the selection unit 31. In FIG. 9, seven frames of image data i <b> 1 to i <b> 7 output when the two-dimensional image sensor 27 moving in the main scanning direction (the horizontal direction in the figure) passes over the patch 200 are shown. The image data i1 to i7 are image data whose output is started when the center of the sensor surface of the two-dimensional image sensor 27 is located at the positions p1 to p7 in the drawing. Here, the moving speed of the carriage 5 (that is, the speed at which the two-dimensional image sensor 27 moves in the main scanning direction) is 50 mm / sec, the size of the patch 200 is 7 × 7 mm, and the two-dimensional image sensor 27 is 30 f. An image of / sec (30 frames per second) is taken.

  Among the seven frames of image data i1 to i7 output from the two-dimensional image sensor 27, the image data i1 and i7 are image data obtained by imaging a gap area between the patches 200 arranged in the main scanning direction. The image data i2 and i6 are image data obtained by imaging the edge portion of the patch 200. These image data i1, i2, i6, and i7 cannot be used to calculate the colorimetric values of the patch 200. Therefore, the selection unit 31 selects the remaining image data i3 to i5 excluding these image data i1, i2, i6, and i7 as image data used for color measurement of the patch 200, and the image data i3 to i5. Is stored in the frame memory 32. The selection of the image data by the selection unit 31 is performed, for example, by storing the RGB values of the background color of the recording medium P and excluding image data having many pixel values close to the RGB values, This can be realized by performing a known edge detection process on the image and excluding the image data in which the edge is detected.

  In the above description, the selection unit 31 selects a plurality of frames of image data as the image data used for the color measurement of the patch 200. However, the selection unit 31 captures one frame obtained by capturing the patch 200. You may comprise so that image data may be selected as image data used for the colorimetry of the patch 200. When the selection unit 31 selects one frame of image data, the AGC gain is decreased to increase the shutter speed so that one frame of image data obtained by capturing the patch 200 by long exposure can be obtained. Also good.

  Whether the image data of a plurality of frames is used for color measurement of the patch 200 or the image data of one frame obtained by imaging the patch 200 by long exposure is used, the patch 200 is imaged with the two-dimensional image sensor 27 stopped. This means that image data of a wide area in the patch 200 is used for color measurement as compared with the case where the image data is used. This is because in the image data used for color measurement, the number of dots of the patch 200 formed by halftone printing increases, and the number of pixel data averaged by the averaging processing unit 33 in the subsequent stage increases. As a result, there is an effect of improving the accuracy of colorimetry. Further, in the present embodiment, since the two-dimensional image sensor 27 captures an image while moving, each pixel data included in the image data is averaged with the movement, and the accuracy of colorimetry is improved. effective.

  FIG. 10 is an explanatory diagram for explaining that the number of dots of the patch 200 formed by halftone printing increases by using image data of a wide area in the patch 200 for color measurement. FIG. 10A shows an area of the patch 200 used for color measurement when an image is taken with the two-dimensional image sensor 27 stopped, and FIG. 10B shows the movement of the two-dimensional image sensor 27. The area of the patch 200 used for colorimetry when an image is captured is shown. The circles in the figure indicate halftone dots, Y indicates yellow ink dots, M indicates magenta ink dots, and C indicates cyan ink dots.

  The patch 200 formed by halftone dot printing has different dot positions depending on the area. Therefore, if the number of dots reflected in the image data used for colorimetry is small as shown in FIG. There is a concern that the value cannot be calculated. On the other hand, as shown in FIG. 10B, by using the image data of a wide area in the patch 200 for the color measurement, the number of dots reflected in the image data used for the color measurement increases, Accuracy can be increased.

  FIG. 11 is an explanatory diagram for explaining that the influence of an abnormal portion whose color changes locally in the patch 200 is mitigated by using image data of a wide area in the patch 200 for colorimetry. is there. FIG. 10A shows an area of the patch 200 used for color measurement when an image is taken with the two-dimensional image sensor 27 stopped, and FIG. 10B shows the movement of the two-dimensional image sensor 27. The area of the patch 200 used for colorimetry when an image is captured is shown.

  As shown in FIG. 11A, when the area of the patch 200 used for colorimetry is small, when there is an abnormal part in the patch 200, the ratio of the abnormal part in the entire area is relatively large. The impact is great. On the other hand, as shown in FIG. 11B, by using image data of a wide area in the patch 200 for the colorimetry, the ratio of the abnormal part in the whole area is reduced, and the influence of the abnormal part on the colorimetry. Is alleviated.

  Returning to FIG. 7, the frame memory 32 temporarily stores the image data selected by the selection unit 31 from the plurality of frames of image data output from the two-dimensional image sensor 27.

  The averaging processing unit 33 averages the image data selected by the selection unit 31 and stored in the frame memory 32, and obtains the RGB value of the patch 200 used for the calculation of the colorimetric value of the patch 200. Specifically, for example, when a plurality of frames of image data are selected by the selection unit 31, the averaging processing unit 33 first calculates pixel data (RGB values) for each pixel between the image data of the plurality of frames. Averaging is performed to obtain image data for one frame in which pixel data is averaged.

  FIG. 12 is an explanatory diagram for explaining processing by the averaging processing unit 33 when the selection unit 31 selects three frames of image data i3 to i5. In the example of FIG. 12, the averaging processing unit 33 averages pixel data at the same position among the three frames of image data i3 to i5, and image data i_ave for one frame that is a set of averaged pixel data. Get. If only one frame of image data is selected by the selection unit 31, this process is omitted.

  Next, the averaging processing unit 33 compares each pixel data included in the obtained image data i_ave with a predetermined threshold, and excludes pixel data exceeding the threshold. This process is a process for removing noise components and the like from the image data. Then, the averaging processing unit 33 averages the remaining pixel data, thereby finally obtaining RGB values used for calculating the colorimetric values of the patch 200.

  The colorimetric value calculation unit 34 is based on the RGB value of the patch 200 obtained by the processing by the averaging processing unit 33 and the RGB value of the reference chart 400 captured simultaneously with the patch 200 by the colorimetric camera 20. 200 colorimetric values are calculated. The colorimetric values of the patch 200 calculated by the colorimetric value calculation unit 34 are sent to the CPU 101 via the control FPGA 110. A specific example of processing by the colorimetric value calculation unit 34 will be described later in detail.

  The nonvolatile memory 35 stores various data necessary for the colorimetric value calculation unit 34 to calculate the colorimetric values of the patch 200.

  The timing signal generation unit 36 generates a timing signal for controlling the timing of starting imaging by the two-dimensional image sensor 27 and inputs the timing signal to the two-dimensional image sensor 27 via the interface unit 30. In the present embodiment, since the two-dimensional image sensor 27 captures an image as a moving image while the carriage 5 is moving, the timing signal is a signal synchronized with the drive signal for starting the movement of the carriage 5.

  The light source drive control unit 37 generates a light source drive signal for driving the illumination light source 29 and supplies the light source drive signal to the illumination light source 29.

<Overview of operation during color measurement>
Next, an outline of an operation when performing color measurement of the patch 200 by the image forming apparatus 100 of the present embodiment configured as described above will be described.

  First, the image forming apparatus 100 forms a test pattern in which patches 200 for color measurement are arranged. In other words, the image forming apparatus 100 drives the main scanning motor 8, the sub-scanning motor 12, and the recording head 6 under the control of the CPU 101 and the control FPGA 110, and the recording medium P set on the platen 16. A test pattern in which a large number of patches 200 are arranged is formed.

  FIG. 13 is a diagram illustrating an example of a test pattern formed on the recording medium P. As shown in FIG. 13, the test pattern has a configuration in which a plurality of patch rows in which a plurality of patches 200 to be measured are arranged in the main scanning direction are arranged in the sub scanning direction. The size of each patch 200 included in the test pattern may be a size that allows the patch 200 to be imaged while the two-dimensional image sensor 27 moves in the main scanning direction. That is, the minimum size of the patch 200 is determined by the moving speed of the carriage 5 and the frame period of the moving image captured by the two-dimensional image sensor 27. As an example, the size of each patch 200 is, for example, 7 × 7 mm.

  However, if the length of the patch 200 in the main scanning direction is set to a size that includes one period of the periodic fluctuation component accompanying the movement of the carriage 5, the periodic fluctuation component is obtained by the averaging process described above. Can alleviate the effect of colorimetry. That is, the patch 200 is formed by ejecting ink from the recording head 6 while the carriage 5 moves in the main scanning direction. At this time, depending on the characteristics of the moving mechanism that moves the carriage 5, a periodic fluctuation component may occur in the movement of the carriage 5. For example, the carriage 5 is moved by driving the main scanning motor 8, but due to the cogging of the main scanning motor 8, the movement speed of the carriage 5 varies periodically. Due to the periodic fluctuation component accompanying the movement of the carriage 5, there may be a case where the patch 200 has periodic color unevenness along the main scanning direction. Here, if the length of the patch 200 in the main scanning direction is less than the length of one period of the periodic fluctuation component, the influence of the color unevenness of the patch 200 is eliminated even if the above-described averaging process is performed. There is a concern that the colorimetric accuracy may be lowered.

  Therefore, in the image forming apparatus 100 according to the present embodiment, when a periodic variation component accompanying the movement of the carriage 5 appears as color unevenness of the patch 200, the ink ejection control unit 113 of the control FPGA 110 performs the following. In accordance with a command from the CPU 101, the recording head driver 104 is driven so that the patch 200 having a size including one cycle of the periodic fluctuation component accompanying the movement of the carriage 5 is formed, and the ink by the recording head 6 is driven. It is desirable to control the discharge. For example, in order to include one cycle of the cyclic fluctuation component due to cogging of the main scanning motor 8, a patch having a length in the main scanning direction of 20 to 30 mm may be formed.

  When the recording medium P on which the test pattern as shown in FIG. 13 is formed is set on the platen 16, the image forming apparatus 100 performs colorimetry on each patch 200 included in the test pattern. In other words, the image forming apparatus 100 drives the main scanning motor 8 and the sub-scanning motor 12 and controls the colorimetric camera 20 under the control of the CPU 101 and the control FPGA 110, and the carriage 5 moves in the main scanning direction. During this period, the two-dimensional image sensor 27 of the colorimetric camera 20 performs imaging. And the selection part 31 selects the image data which imaged the patch 200 among the image data of several frames output from the two-dimensional image sensor 27. FIG. Then, the RGB value of the patch 200 is obtained from the selected image data by the processing by the averaging processing unit 33, and the colorimetric value calculation unit 34 calculates the colorimetric value of the patch 200 using the RGB value of the patch 200. To do.

<Patch color measurement method>
Next, a specific example of the color measurement method of the patch 200 by the image forming apparatus 100 according to the present embodiment will be described in detail with reference to FIGS. The color measurement method described below performs pre-processing that is performed when the image forming apparatus 100 is in an initial state (when the image forming apparatus 100 is in an initial state due to manufacturing, overfall, or the like) and color adjustment of the image forming apparatus 100. Colorimetric processing performed at the time of adjustment.

  FIG. 14 is a diagram for explaining processing for obtaining a reference colorimetric value and a reference RGB value and processing for generating a reference value linear transformation matrix. These processes shown in FIG. 14 are implemented as a preprocess. In the preprocessing, a reference sheet KS on which a plurality of reference patches KP are formed is used. The reference patch KP of the reference sheet KS is equivalent to the patch of the reference chart 400 provided in the colorimetric camera 20.

  First, at least one of Lab values and XYZ values (both Lab values and XYZ values in the example of FIG. 14) that are colorimetric values of a plurality of reference patches KP of the reference sheet KS is assigned to each patch number. Correspondingly, it is stored in a memory table Tb1 provided in, for example, a non-volatile memory 35 mounted on the substrate 22 of the colorimetric camera 20. The colorimetric value of the reference patch KP is a value obtained in advance by colorimetry using the spectroscope BS or the like. If the colorimetric value of the reference patch KP is known, that value may be used. Hereinafter, the colorimetric values of the reference patch KP stored in the memory table Tb1 are referred to as “reference colorimetric values”.

  Next, the reference sheet KS is set on the platen 16 and the movement of the carriage 5 is controlled, so that the colorimetric camera 20 takes an image using a plurality of reference patches KP of the reference sheet KS as subjects. Then, the RGB values of the reference patch KP obtained by imaging with the colorimetric camera 20 are stored in the memory table Tb1 of the nonvolatile memory 35 in correspondence with the patch numbers. That is, in the memory table Tb1, the colorimetric values and RGB values of the plurality of reference patches KP arranged on the reference sheet KS are stored in correspondence with the patch numbers of the respective reference patches KP. Hereinafter, the RGB values of the reference patch KP stored in the memory table Tb1 are referred to as “reference RGB values”. The reference RGB value is a value reflecting the characteristics of the colorimetric camera 20.

  When the reference colorimetric value and the reference RGB value of the reference patch KP are stored in the memory table Tb1 of the nonvolatile memory 35, the CPU 101 of the image forming apparatus 100 stores the XYZ value and the reference RGB that are the reference colorimetric values of the same patch number. A reference value linear conversion matrix for converting these values into each other is generated and stored in the nonvolatile memory 35. When only Lab values are stored as reference colorimetric values in the memory table Tb1, after converting Lab values to XYZ values using a known conversion formula for converting Lab values to XYZ values, a reference value linear conversion matrix Should be generated.

  Further, when the colorimetric camera 20 captures a plurality of reference patches KP on the reference sheet KS, the reference chart 400 provided in the colorimetric camera 20 is also captured at the same time. The RGB values of each patch of the reference chart 400 obtained by this imaging are also stored in the memory table Tb1 of the nonvolatile memory 35 in association with the patch number. The RGB values of the patches of the reference chart 400 stored in the memory table Tb1 by this preprocessing are referred to as “initial reference RGB values”. FIG. 15 is a diagram illustrating an example of the initial reference RGB values. FIG. 15A shows a state in which the initial reference RGB value (RdGdBd) is stored in the memory table Tb1, and the initial reference Lab value obtained by converting the initial reference RGB value (RdGdBd) into the Lab value together with the initial reference RGB value and (RdGdBd). It shows that the initial reference XYZ value (XdYdZd) converted into the value (Ldadbd) and the XYZ value is also stored in association with each other. FIG. 15B is a scatter diagram in which initial reference RGB values of each patch of the reference chart 400 are plotted.

  After the above preprocessing is completed, the image forming apparatus 100 controls the main scanning motor 8, the sub-scanning motor 12, and the recording head under the control of the CPU 101 based on image data input from the outside, print settings, and the like. 6 is driven to form an image on the recording medium P by ejecting ink from the recording head 6 while intermittently transporting the recording medium P in the sub-scanning direction and moving the carriage 5 in the main scanning direction. . At this time, the amount of ink ejected from the recording head 6 may change depending on the characteristics inherent to the device or changes over time. When this ink ejection amount changes, the color differs from the color of the image intended by the user. As a result, the color reproducibility deteriorates. Therefore, the image forming apparatus 100 performs a color measurement process for obtaining a color measurement value of the patch 200 formed on the recording medium P at a predetermined timing for color adjustment. A device profile is generated or corrected based on the colorimetric value of the patch 200 obtained by the colorimetric processing, and color adjustment is performed based on the device profile, thereby improving the color reproducibility of the output image.

  FIG. 16 is a diagram for explaining the outline of the color measurement process. When performing color adjustment, the image forming apparatus 100 first ejects ink from the recording head 6 onto the recording medium P set on the platen 16 to form a test pattern in which a large number of patches 200 are arranged. Hereinafter, the recording medium P on which the test pattern is formed is referred to as an “adjustment sheet CS”. The adjustment sheet CS is formed with a patch 200 that reflects output characteristics during adjustment of the image forming apparatus 100, in particular, output characteristics of the recording head 6. Note that image data for forming a test pattern is stored in advance in the nonvolatile memory 35 or the like.

  Next, as shown in FIG. 16, the image forming apparatus 100 sets the adjustment sheet CS on the platen 16 or holds the adjustment sheet CS on the platen 16 without discharging the sheet when the adjustment sheet CS is created. In the state, the two-dimensional image sensor 27 of the colorimetric camera 20 captures an image while moving the carriage 5 on the adjustment sheet CS in the main scanning direction. And the selection part 31 selects the image data which imaged the patch 200 among the image data of several frames output from the two-dimensional image sensor 27. FIG. Then, the RGB value of the patch 200 is obtained from the selected image data by the processing by the averaging processing unit 33. Further, since the two-dimensional image sensor 27 images the reference chart 400 at the same time as the color measurement target patch 200, the RGB value of each patch included in the reference chart 400 is also obtained. Hereinafter, the RGB value of the color measurement target patch 200 is referred to as “color measurement target RGB value”, and the RGB value of the patch of the reference chart 400 is referred to as “color measurement time reference RGB value (RdsGdsBds)”. The “color measurement reference RGB value (RdsGdsBds)” is stored in the nonvolatile memory 35 or the like.

  The colorimetric value calculation unit 34 of the colorimetric camera 20 performs a process of converting the colorimetric target RGB values into the initialization colorimetric target RGB values (RsGsBs) using a reference RGB linear conversion matrix described later (step S10). ). The initialization colorimetric object RGB values (RsGsBs) are the imaging conditions of the colorimetric camera 20 that are generated from the colorimetry object RGB values from the initial state where preprocessing is performed to the adjustment time when performing colorimetry processing. This eliminates the influence of changes over time, for example, changes over time of the illumination light source 29 and changes over time of the two-dimensional image sensor 27.

  Thereafter, the colorimetric value calculator 34 performs basic colorimetry processing described later on the initialization colorimetry target RGB values (RsGsBs) converted from the colorimetry target RGB values (step S20), thereby measuring the colorimetry value. The Lab value, which is the colorimetric value of the color-target patch 200, is acquired.

  FIG. 17 is a diagram illustrating processing for generating a linear conversion matrix between reference RGB. FIG. 18 is a diagram illustrating a relationship between an initial reference RGB value and a colorimetric reference RGB value. The colorimetric value calculation unit 34 generates a reference RGB linear conversion matrix to be used for this conversion before performing the process (step S10) of converting the colorimetric object RGB values into the initialization colorimetric object RGB values (RsGsBs). . That is, as shown in FIG. 17, the colorimetric value calculation unit 34 determines the initial reference RGB value (RdGdBd) obtained as preprocessing when the image forming apparatus 100 is in the initial state and the colorimetric time obtained at the time of adjustment. The reference RGB values (RdsGdsBds) are read from the nonvolatile memory 35, and a reference RGB inter-RGB conversion matrix for converting the colorimetric reference RGB values RdsGdsBds into the initial reference RGB values RdGdBd is generated. Then, the colorimetric value calculation unit 34 stores the generated reference RGB linear conversion matrix in the nonvolatile memory 35.

  In FIG. 18, the thinly drawn points in FIG. 18A are points where the initial reference RGB values RdGdBd are plotted in the rgb space, and the filled points are points where the colorimetric reference RGB values RdsGdsBds are plotted in the rgb space. It is. As can be seen from FIG. 18A, the value of the colorimetric reference RGB value RdsGdsBds varies from the value of the initial reference RGB value RdGdBd, and the direction of variation in the rgb space is shown in FIG. 18B. As shown, the directions are generally the same, but the direction of deviation differs depending on the hue. As described above, the factors that cause the RGB values to change even if the patches of the same reference chart 400 are imaged include the temporal change of the illumination light source 29 and the temporal change of the two-dimensional image sensor 27.

  As described above, when the colorimetric values are obtained using the colorimetric target RGB values obtained by imaging the patch 200 in a state where the RGB values obtained by the imaging by the colorimetric camera 20 are fluctuating, only the fluctuations are obtained. An error may occur in the colorimetric value. Therefore, between the initial reference RGB value RdGdBd and the colorimetric reference RGB value RdsGdsBds, an estimation method such as a least square method is used to convert the colorimetric reference RGB value RdsGdsBds to the initial reference RGB value RdGdBd. A linear conversion matrix is obtained, and using this reference RGB linear conversion matrix, the colorimetric object RGB values obtained by imaging the patch 200 with the colorimetric camera 20 are converted into initialization colorimetric object RGB values RsGsBs, By executing the basic colorimetry process described later on the converted initialization colorimetry target RGB value RsGsBs, the colorimetric values of the colorimetric target patch 200 can be obtained with high accuracy.

  This linear conversion matrix between RGB may be not only a first-order but also a higher-order nonlinear matrix. If the nonlinearity is high between the rgb space and the XYZ space, a higher-order matrix can be obtained. , Conversion accuracy can be improved.

  As described above, the colorimetric value calculation unit 34 converts the colorimetric target RGB values obtained by imaging the patch 200 into initialization colorimetric target RGB values (RsGsBs) using the reference RGB linear conversion matrix. (Step S10), the basic colorimetric processing in step S20 is performed on the initialization colorimetric target RGB values (RsGsBs).

  19 and 20 are diagrams for explaining basic colorimetric processing. First, the colorimetric value calculation unit 34 reads the reference value linear conversion matrix generated in the preprocessing and stored in the nonvolatile memory 35, and initializes the colorimetric RGB values (RsGsBs) to be initialized using the reference value linear conversion matrix. The first XYZ value is converted and stored in the nonvolatile memory 35 (step S21). FIG. 19 shows an example in which the initialization colorimetric target RGB values (3, 200, 5) are converted to the first XYZ values (20, 80, 10) by the reference value linear conversion matrix.

  Next, the colorimetric value calculation unit 34 converts the first XYZ value converted from the initialization colorimetric target RGB value (RsGsBs) in step S21 into a first Lab value using a known conversion formula, and stores the non-volatile memory. 35 (step S22). FIG. 19 shows an example in which the first XYZ values (20, 80, 10) are converted into the first Lab values (75, −60, 8) by a known conversion formula.

  Next, the colorimetric value calculation unit 34 searches for a plurality of reference colorimetric values (Lab values) stored in the memory table Tb1 of the non-volatile memory 35 in the preprocessing, and determines the reference colorimetric values (Lab values). Among them, a set of a plurality of patches (neighboring color patches) having a reference colorimetric value (Lab value) close to the first Lab value in the Lab space is selected (step S23). As a method for selecting a patch having a short distance, for example, the distance from the first Lab value is calculated for all reference colorimetric values (Lab values) stored in the memory table Tb1, and the patch is calculated for the first Lab value. A method of selecting a plurality of patches having Lab values that are close in distance (in FIG. 19, Lab values that are hatched) can be used.

  Next, as shown in FIG. 20, the colorimetric value calculation unit 34 refers to the memory table Tb1, and for each of the neighboring color patches selected in step S23, the RGB value (reference value) paired with the Lab value. RGB values) and XYZ values are extracted, and a combination of RGB values and XYZ values is selected from the plurality of RGB values and XYZ values (step S24). Then, the colorimetric value calculation unit 34 obtains a selected RGB value linear conversion matrix for converting the RGB values of the selected combination (selected set) into XYZ values using the least square method or the like, and obtains the selected RGB values obtained. The linear transformation matrix is stored in the nonvolatile memory 35 (step S25).

  Next, the colorimetric value calculator 34 converts the initialization colorimetric object RGB values (RsGsBs) into the second XYZ values using the selected RGB value linear conversion matrix generated in step S25 (step S26). Further, the colorimetric value calculation unit 34 converts the second XYZ value obtained in step S26 into a second Lab value using a known conversion formula (step S27), and converts the obtained second Lab value into the colorimetric object. The final colorimetric value of the patch 200 is used. The image forming apparatus 100 generates or corrects a device profile based on the colorimetric values obtained by the above colorimetric processing, and performs color adjustment based on the device profile, thereby improving the color reproducibility of the output image. be able to.

  The colorimetric camera 20 described above has a configuration in which the reference chart 400 is provided in the housing 23 and the patch 200 to be measured and the reference chart 400 are simultaneously imaged by the two-dimensional image sensor 27 of the sensor unit 26. Yes. However, as described above, the initial reference RGB value and the colorimetric reference RGB value obtained by imaging the reference chart 400 are colorimetric with respect to the colorimetric target RGB value obtained by imaging the colorimetric target patch 200. This is used to eliminate the influence of the change in the imaging conditions of the camera 20 over time, for example, the change over time of the illumination light source 29 and the change over time of the two-dimensional image sensor 27. That is, for the initial reference RGB value and the colorimetric reference RGB value obtained by imaging the reference chart 400, the above-described reference RGB linear conversion matrix is calculated, and the colorimetric target RGB is calculated using the reference RGB linear conversion matrix. This value is used to convert the value to an initialization colorimetric object RGB value (RsGsBs).

  Therefore, if the change over time of the imaging condition of the colorimetric camera 20 is negligible for the required colorimetric accuracy, the measurement of the patch 200 is performed using the colorimetric camera 20 having a configuration in which the reference chart 400 is omitted. The color value may be calculated. In this case, the process of converting the colorimetric object RGB values into the initialization colorimetric object RGB values (step S10 in FIG. 16) is omitted, and the basic colorimetry process (step S20 in FIG. 16) is performed on the colorimetric object RGB values. 19 and 20) are performed.

  As described above in detail with specific examples, in the image forming apparatus 100 according to the present embodiment, the two-dimensional image sensor 27 of the colorimetric camera 20 attached to the carriage 5 is used to move the carriage 5. Along with this, imaging is performed while moving in the main scanning direction on the recording medium P on which the test pattern is formed. Then, the selection unit 31 selects image data obtained by capturing the patch 200 from a plurality of frames of image data output from the two-dimensional image sensor 27. Then, the colorimetric value calculation unit 34 calculates the colorimetric value of the patch 200 based on the image data selected by the selection unit 31. Therefore, according to the image forming apparatus 100 according to the present embodiment, the color measurement of the patch 200 included in the test pattern can be performed in a short time.

  That is, according to the conventional method, when the image of each patch 200 included in the test pattern is captured and the colorimetric value of the patch 200 is calculated, the movement of the carriage 5 is stopped for each patch 200 and the two-dimensional image sensor 27. The image of the patch 200 was taken in a state where the camera was stationary. For this reason, the carriage 5 is decelerated or accelerated for each patch 200, and particularly when the number of patches 200 included in the test pattern is large, it takes a long time to complete the color measurement of all the patches 200. there were. On the other hand, in the image forming apparatus 100 according to the present embodiment, the two-dimensional image sensor 27 of the colorimetric camera 20 captures an image as a moving image, and the patch 200 is obtained from the obtained image data of a plurality of frames. Is selected and used for colorimetry of the patch 200. Therefore, while the carriage 5 is moving at a constant speed in the main scanning direction, the imaging of all the patches 200 arranged in the main scanning direction is completed, and the time required for the color measurement of the patches 200 can be greatly shortened. .

  For example, it is assumed that a test pattern in which 50 patches 200 are arranged in the main scanning direction is formed on the recording medium P having a length of 500 mm in the main scanning direction. In addition, when the moving speed of the carriage 5 is 50 mm / sec and the carriage 5 is stopped for each patch 200, the time required for deceleration and acceleration to move the carriage 5 between the patches 200 is approximately 0. Suppose it takes 8 seconds. In this case, in the conventional method, it takes 0.8 sec × 50 = 40 sec to capture all the images of the 50 patches 200 arranged in the main scanning direction even if the exposure time of the two-dimensional image sensor 27 is ignored. It was. On the other hand, in the present embodiment, all the images of the 50 patches 200 can be taken in 10 seconds required for the carriage 5 to move 500 mm at a speed of 50 mm / sec. That is, in this embodiment, 30 seconds can be shortened for each movement of the carriage 5 in the main scanning direction as compared with the conventional method.

<Modification>
In the embodiment described above, the colorimetric camera 20 has a function of calculating the colorimetric value of the patch 200. However, the colorimetric value of the patch 200 may be calculated outside the colorimetric camera 20. Good. For example, the CPU 101 and the control FPGA 110 mounted on the main control board 120 of the image forming apparatus 100 can be configured to calculate the colorimetric values of the patch 200 to be colorimetric. In this case, the colorimetric camera 20 is configured to send the RGB values of the patch 200 and the reference chart 400 to the CPU 101 and the control FPGA 110 instead of the colorimetric values of the patch 200.

  In the above-described embodiment, the colorimetric camera 20 is moved on the recording medium P on which the test pattern is formed using the mechanism of the image forming apparatus 100. However, the colorimetric camera 20 is connected to the image forming apparatus. A configuration may be adopted in which the recording medium P is separated from the recording medium P and moved on the recording medium P on which the test pattern is formed by a unique moving mechanism. In other words, the embodiment described above is an example in which the image forming apparatus 100 is provided with a function as a color measuring device. However, the color measuring device is configured as an independent device different from the image forming device 100, and this color measuring device. Thus, the colorimetric value of the patch 200 included in the test pattern formed by the image forming apparatus 100 may be calculated.

  In the above-described embodiment, the function of calculating the colorimetric value of the patch 200 is provided to the image forming apparatus 100 including the colorimetric camera 20. However, the calculation of the colorimetric value of the patch 200 is not necessarily performed. There is no need to execute it inside the image forming apparatus 100. For example, as shown in FIG. 21, an image forming system (colorimetric system) in which the image forming apparatus 100 and the external apparatus 500 are communicably connected is constructed, and the colorimetric value calculation for calculating the colorimetric value of the patch 200 is performed. The function of the unit 34 may be provided to the external device 500 so that the external device 500 may calculate the colorimetric value. That is, the color measurement system includes a color measurement camera 20 provided in the image forming apparatus 100, a color measurement value calculation unit 34 provided in the external device 500, and the color measurement camera 20 and the color measurement value calculation unit 34 (images). The communication apparatus 600 which connects the forming apparatus 100 and the external apparatus 500) is provided. As the external device 500, for example, a computer called DFE (Digital Front End) can be used. The communication unit 600 can use communication using a network such as a LAN or the Internet, in addition to wired or wireless P2P communication.

  In the case of the above configuration, for example, the image forming apparatus 100 transmits the RGB values of the patch 200 and the reference chart 400 obtained by imaging with the colorimetric camera 20 to the external apparatus 500 using the communication unit 600. The external apparatus 500 calculates the colorimetric value of the patch 200 using the RGB values of the patch 200 and the reference chart 400 received from the image forming apparatus 100, and based on the calculated colorimetric value of the patch 200, the image forming apparatus 100. Create or modify a device profile that describes the characteristics of Then, the external apparatus 500 transmits this device profile to the image forming apparatus 100 using the communication unit 600. The image forming apparatus 100 holds the device profile received from the external apparatus 500, and when performing image formation, the image forming apparatus 100 corrects the image data based on the device profile and performs image formation based on the corrected image data. . Thereby, the image forming apparatus 100 can perform image formation with high color reproducibility.

  Further, the external apparatus 500 may hold the device profile of the image forming apparatus 100 generated based on the colorimetric values of the patch 200, and the external apparatus 500 may correct the image data. That is, the image forming apparatus 100 transmits image data to the external apparatus 500 when performing image formation. The external apparatus 500 corrects the image data received from the image forming apparatus 100 based on the device profile of the image forming apparatus 100 held by itself, and transmits the corrected image data to the image forming apparatus 100. The image forming apparatus 100 forms an image based on the corrected image data received from the external apparatus 500. Thereby, the image forming apparatus 100 can perform image formation with high color reproducibility.

  Note that the control functions of the respective parts constituting the image forming apparatus 100 and the colorimetric camera 20 according to the present embodiment described above can be realized using hardware, software, or a combined configuration of both. When the control function of each unit constituting the image forming apparatus 100 and the colorimetric camera 20 according to the present embodiment is realized by software, the processor included in the image forming apparatus 100 or the colorimetric camera 20 executes a program describing a processing sequence. To do. The program executed by the processor is provided by being incorporated in advance in, for example, the image forming apparatus 100 or a ROM in the color measurement apparatus. In addition, a computer-readable recording medium such as a CD-ROM, a flexible disk (FD), a CD-R, a DVD (Digital Versatile Disc), etc., in which the program executed by the processor is an installable or executable file. It may be recorded and provided.

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

DESCRIPTION OF SYMBOLS 5 Carriage 6 Recording head 8 Main scanning motor 20 Colorimetric camera 27 Two-dimensional image sensor 31 Selection part 33 Averaging process part 34 Colorimetric value calculation part 100 Image forming apparatus 101 CPU
113 Ink Ejection Control Unit 200 Patch P Recording Medium

JP 2012-63270 A

Claims (9)

A two-dimensional image sensor that captures images while moving on a recording medium on which patches are formed, and outputs image data of a plurality of frames;
Of the plurality of frames of image data output from the two-dimensional image sensor, image data having a predetermined number or more of pixel values close to the stored RGB values of the recording medium is excluded, and image data obtained by capturing the patch is selected. A selection section;
A colorimetric apparatus comprising: an arithmetic unit that calculates a colorimetric value of the patch based on the image data selected by the selection unit. A two-dimensional image sensor that captures images while moving on a recording medium on which patches are formed, and outputs image data of a plurality of frames;
A selection unit that excludes image data in which an edge is detected from a plurality of frames of image data output from the two-dimensional image sensor, and selects image data obtained by imaging the patch ;
A colorimetric apparatus comprising: an arithmetic unit that calculates a colorimetric value of the patch based on the image data selected by the selection unit. The selection unit selects a plurality of image data obtained by capturing the patch,
An averaging unit that averages the image data selected by the selection unit;
The arithmetic unit, based on said averaged image data by the averaging unit, colorimetry apparatus according to claim 1 or 2, characterized in that to calculate the colorimetric value of the patch. A colorimetric device according to any one of claims 1 to 3 ,
A recording head for discharging the recording material onto the recording medium to form the patch;
A support for supporting the two-dimensional image sensor and the recording head;
An image forming apparatus comprising: a moving mechanism that moves the support on the recording medium. Ejection for controlling ejection of the recording material by the recording head so that the patch having a size including one period of a periodic variation component generated when the moving mechanism moves the support is formed. The image forming apparatus according to claim 4 , further comprising a control unit. A color measurement method executed in a color measurement device including a two-dimensional image sensor,
The two-dimensional image sensor performing imaging while moving on a recording medium on which a patch is formed, and outputting a plurality of frames of image data;
Of the plurality of frames of image data output from the two-dimensional image sensor, image data having a predetermined number or more of pixel values close to the stored RGB values of the recording medium is excluded, and image data obtained by capturing the patch is selected. Process,
Calculating a colorimetric value of the patch based on the selected image data.   A color measurement method executed in a color measurement device including a two-dimensional image sensor,
  The two-dimensional image sensor performing imaging while moving on a recording medium on which a patch is formed, and outputting a plurality of frames of image data;
  A step of excluding image data in which an edge is detected from among a plurality of frames of image data output from the two-dimensional image sensor, and selecting image data obtained by imaging the patch;
  Calculating a colorimetric value of the patch based on the selected image data. To a colorimetric device equipped with a two-dimensional image sensor,
A function in which the two-dimensional image sensor performs imaging while moving on a recording medium on which patches are formed, and outputs image data of a plurality of frames;
Of the plurality of frames of image data output from the two-dimensional image sensor, image data having a predetermined number or more of pixel values close to the stored RGB values of the recording medium is excluded, and image data obtained by capturing the patch is selected. The function to select,
A program for realizing a function of calculating a colorimetric value of the patch based on selected image data.   To a colorimetric device equipped with a two-dimensional image sensor,
  A function in which the two-dimensional image sensor performs imaging while moving on a recording medium on which patches are formed, and outputs image data of a plurality of frames;
  A function of selecting image data obtained by capturing the patch by excluding image data in which an edge is detected from image data of a plurality of frames output from the two-dimensional image sensor;
  A program for realizing a function of calculating a colorimetric value of the patch based on selected image data.