JP2019165412A - Imaging apparatus, colorimetry device, and image forming apparatus - Google Patents

Abstract

To enhance colorimetric accuracy.SOLUTION: An imaging apparatus includes a light source which illuminates a subject through an opening, a reference chart which is illuminated by the light source and in a position closer to the light source than the subject, a sensor which images the reference chart with a first exposure time, and a light quantity adjustment part which adjusts the light quantity of the light source according to the result of imaging the reference chart with the first exposure time. The sensor images the subject imaged with the adjusted light quantity with a second exposure time longer than the first exposure time.SELECTED DRAWING: Figure 8

Description

  The present invention relates to an imaging apparatus, a colorimetric apparatus, and an image forming apparatus.

  Conventionally, using a camera unit including an image sensor that captures a reference chart and a subject (colorimetric media) and a light source that illuminates the imaged object, the reference chart and the subject (colorimetric media) are imaged. A technique for correcting the color of a subject (colorimetric media) is disclosed.

  Japanese Patent Application Laid-Open No. 2005-228561 discloses a technique for creating correction values with two types of light amounts and changing the light amounts according to the image density of the subject (colorimetric media) to be colorimetrically measured.

  However, according to the prior art, since the light amount is changed depending on the subject (colorimetric medium) to be colorimetrically measured, there may be a variation in the color of the light source due to the change in the light amount.

  The present invention has been made in view of the above, and an object thereof is to improve colorimetric accuracy.

  In order to solve the above-described problems and achieve the object, the present invention includes a light source that illuminates a subject through an opening, a reference chart that is illuminated by the light source and is closer to the light source than the subject, A sensor that images the reference chart with a first exposure time; and a light amount adjustment unit that adjusts the light amount of the light source according to a result of imaging the reference chart with the first exposure time. The subject imaged with the adjusted light amount is imaged with a second exposure time longer than the first exposure time.

  According to the present invention, there is an effect that the colorimetric accuracy can be increased.

FIG. 1 is a perspective view illustrating the inside of the image forming apparatus according to the first embodiment. 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. 4 is a diagram schematically illustrating a carriage lifting mechanism. FIG. 5A is a longitudinal sectional view of the imaging unit. FIG. 5B is a top view of the inside of the imaging unit seen through. FIG. 5C is a plan view of the bottom surface of the housing as viewed from the X2 direction in FIG. FIG. 6 is a diagram illustrating a configuration example of the illumination light source. FIG. 7 is a diagram illustrating a specific example of the reference chart. FIG. 8 is a block diagram illustrating a schematic configuration of a control mechanism of the image forming apparatus. FIG. 9 is a diagram illustrating an example of image data obtained by simultaneously imaging the reference chart and the imaging target. FIG. 10 is a block diagram illustrating a configuration example of the control mechanism of the color measurement device. FIG. 11 is a diagram for explaining processing for acquiring a reference colorimetric value and a reference RGB value and processing for generating a reference value linear transformation matrix. FIG. 12 is a diagram illustrating an example of the initial reference RGB values. FIG. 13 is a diagram for explaining basic colorimetry processing. FIG. 14 is a diagram for explaining basic colorimetry processing. FIG. 15 is a diagram for explaining RGB output values before balance adjustment. FIG. 16 is a diagram for explaining the ratio and difference from the ideal value. FIG. 17 is a flowchart schematically showing a flow of processing for calculating a colorimetric value. FIG. 18 is a diagram showing the relationship between the interval with the recording medium and the exposure time. FIG. 19 is a longitudinal sectional view of an imaging unit according to the second embodiment.

(First embodiment)
Exemplary embodiments of an imaging apparatus, a colorimetric apparatus, and an image forming apparatus according to the present invention are explained in detail below with reference to the accompanying drawings. In the embodiments described below, an inkjet printer is illustrated as an example of an image forming apparatus to which the present invention is applied. However, the present invention is widely applied to various types of image forming apparatuses that output an image to a recording medium. Applicable.

<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 first embodiment. FIG. 2 is a top view illustrating the internal mechanical configuration of the image forming apparatus 100. FIG. 5 is a diagram for explaining an example of the arrangement of the recording heads 6 mounted on the recording medium.

  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 5 for forming an image on the recording medium 16. 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 mounted on the carriage 5 so that its ejection surface (nozzle surface) faces downward (on the recording medium 16 side). The recording head 6 is a main body of image output means.

  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 by detecting a mark on the encoder sheet 40 by an encoder sensor 41 provided on the carriage 5, for example, as shown in FIG.

  Further, the image forming apparatus 100 according to the present embodiment includes a maintenance mechanism 21 for maintaining the reliability of the recording head 6. The maintenance mechanism 21 performs cleaning and capping of the ejection surface of the recording head 6 and discharging unnecessary ink from the recording head 6.

  A platen plate 22 is provided at a position facing the ejection surface of the recording head 6 as shown in FIG. The platen plate 22 is for supporting the recording medium 16 when ink is ejected from the recording head 6 onto the recording medium 16. 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 plate 22 is constituted by connecting a plurality of plate-like members in the main scanning direction (movement direction of the carriage 5). The recording medium 16 is nipped by a conveyance roller driven by a sub scanning motor (not shown), and is intermittently conveyed on the platen plate 22 in the sub scanning direction.

  The recording head 6 includes a plurality of nozzle arrays, and forms an image on the recording medium 16 by ejecting ink from the nozzle arrays onto the recording medium 16 conveyed on the platen plate 22. In this embodiment, in order to secure a large width of an image that can be formed on the recording medium 16 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 16 in the sub scanning direction, and moves the carriage 5 in the main scanning direction while the conveyance of the recording medium 16 in the sub scanning direction is stopped. Then, ink is ejected from the nozzle array of the recording head 6 mounted on the carriage 5 onto the recording medium 16 on the platen plate 22 to form an image on the recording medium 16.

  In particular, when calibration for adjusting the output characteristics of the image forming apparatus 100 is performed, ink is ejected from the nozzle row of the recording head 6 mounted on the carriage 5 onto the recording medium 16 on the platen plate 22. Thus, the patch image 200 to be colorimetric is formed on the recording medium 16. The patch image 200 is an image obtained when the image forming apparatus 100 outputs a reference color patch, and reflects the output characteristics of the image forming apparatus 100. Therefore, a color conversion parameter is generated based on the difference between the colorimetric value of the patch image 200 and the corresponding color value of the reference color in the standard color space, and color conversion is performed using this color conversion parameter. By outputting an image based on the image data, the image forming apparatus 100 can output an image with high reproducibility.

  The image forming apparatus 100 according to the present embodiment includes a color measurement device for measuring the color of the patch image 200 output to the recording medium 16. The colorimetric device includes an image pickup unit 42 that takes a patch image 200 to be colorimetrically formed on the recording medium 16 by the image forming apparatus 100 as a subject and images the patch image 200 and a reference chart 400 described later. The colorimetric device calculates the colorimetric value of the patch image 200 based on the image data of the reference chart 400 obtained by imaging by the imaging unit 42 and the image data of the patch image 200. Note that this color measurement device uses not only the function of calculating the color measurement value of the patch image 200 but also the amount of positional deviation of the image output by the image forming apparatus 100 using the image data obtained by the imaging unit 42. A function for calculating and a function for calculating a dot diameter of an image output from the image forming apparatus 100 using image data obtained by imaging by the imaging unit 42 are also provided.

  As shown in FIG. 2, the imaging unit 42 is provided fixed to the carriage 5 and reciprocates in the main scanning direction together with the carriage 5. Then, the imaging unit 42 takes the image formed on the recording medium 16 (the patch image 200 to be colorimetric when the patch image 200 is colorimetric) as a subject, and moves to a position facing this subject. And one frame of image data including the reference chart 400 is acquired.

  Here, FIG. 4 is a view schematically showing the lifting mechanism 600 of the carriage 5. When a strong paper, folded paper, or the like is used as the recording medium 16, the recording medium 16 tends to float from the platen plate 22. In such a case, the recording head 6 may be damaged or damaged by the recording medium 16. Therefore, as shown in FIG. 4, the image forming apparatus 100 according to the present embodiment includes an elevating mechanism 600 that elevates the carriage 5. The lift mechanism 600 includes a carriage lift motor 601 and a carriage lift cam 602. In the lifting mechanism 600, the carriage 5 moves up and down as the carriage lifting cam 602 rotates by driving the carriage lifting motor 601. The lifting mechanism 600 of the carriage 5 is not limited to the configuration shown in FIG.

<Specific example of imaging unit>
5A to 5C are diagrams illustrating specific examples of the imaging unit 42. FIG. 5A is a vertical cross-sectional view of the imaging unit 42 (cross-sectional view taken along line X1-X1 in FIG. 5-2). FIG. 5-2 is a top view showing the inside of the imaging unit 42 as seen through, and FIG. 5-3 is a plan view of the bottom surface of the housing as viewed from the X2 direction in FIG. 5-1.

  The imaging unit 42 includes a housing 421 configured by combining a frame body 422 and a substrate 423. The frame 422 is formed in a bottomed cylindrical shape in which one end side which is the upper surface of the housing 421 is opened. The substrate 423 is fastened to the frame body 422 by the fastening member 424 and integrated with the frame body 422 so as to close the open end of the frame body 422 and configure the upper surface of the housing 421.

  The housing 421 is fixed to the carriage 5 so that the bottom surface portion 421a thereof faces the recording medium 16 on the platen plate 22 with a predetermined gap d. An opening for allowing the subject (patch image 200) formed on the recording medium 16 to be photographed from the inside of the casing 421 is provided on the bottom surface (first surface) 421 a of the casing 421 facing the recording medium 16. 425 is provided.

  A sensor unit 430 that captures an image is provided inside the housing 421. The sensor unit 430 includes a two-dimensional image sensor 431 such as a CCD sensor or a CMOS sensor, and an imaging lens 432 that forms an optical image in the imaging range of the sensor unit 430 on the sensor surface of the two-dimensional image sensor 431. The two-dimensional image sensor 431 is mounted on, for example, the inner surface (component mounting surface) of the substrate 423 so that the sensor surface faces the bottom surface portion 421a side of the housing 421. The imaging lens 432 is fixed in a state of being positioned with respect to the two-dimensional image sensor 431 so as to maintain the positional relationship determined according to the optical characteristics.

  A chart plate 410 on which a reference chart 400 is formed is disposed on the inner surface of the bottom surface 421a of the housing 421 facing the sensor unit 430 so as to be adjacent to the opening 425 provided in the bottom surface 421a. Yes. For example, the chart plate 410 is bonded to the inner surface side of the bottom surface portion 421a of the housing 421 with an adhesive or the like, with the surface opposite to the surface on which the reference chart 400 is formed, being attached to the housing 421. It is held in a fixed state. The reference chart 400 may be directly formed on the inner surface side of the bottom surface portion 421a of the housing 421 instead of on the chart plate 410. In this case, the chart plate 410 is not necessary. The reference chart 400 is taken together with the subject (patch image 200) by the sensor unit 430. Details of the reference chart 400 will be described later.

  In addition, an illumination light source 426 that illuminates the subject (patch image 200) and the reference chart 400 when the sensor unit 430 simultaneously captures the subject (patch image 200) and the reference chart 400 is provided inside the housing 421. Is provided. For example, an LED is used as the illumination light source 426. In the present embodiment, two LEDs are used as the illumination light source 426. These two LEDs used as the illumination light source 426 are mounted on the inner surface of the substrate 423 together with the two-dimensional image sensor 431 of the sensor unit 430, for example. However, the illumination light source 426 only needs to be disposed at a position where the subject (patch image 200) and the reference chart 400 can be illuminated, and is not necessarily mounted directly on the substrate 423. Moreover, in this embodiment, although LED is used as the illumination light source 426, 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 426. When organic EL is used as the illumination light source 426, illumination light close to the spectral distribution of sunlight can be obtained, so that improvement in colorimetric accuracy can be expected.

  FIG. 6 is a diagram illustrating a configuration example of the illumination light source 426. The illumination light source 426 is a white light source. As shown in FIG. 6, the illumination light source 426 has a blue LED element 102 mounted on a printed board 108. The illumination light source 426 is adjusted so that, for example, a yellow phosphor 106 is applied to a GaN-based blue LED element 102 of 500 × 500 μm, and white light is emitted by blue and yellow. The light from the blue LED element 102 is directly or partly reflected by the reflecting plate 104 and extracted outside. Note that the LED element used for the illumination light source 426 is not limited to the blue LED, and it is sufficient that substantially white light can be emitted.

  Further, in the present embodiment, as shown in FIG. 5B, the projection on the bottom surface portion 421a when two LEDs used as the illumination light source 426 are vertically looked down from the substrate 423 side to the bottom surface portion 421a side of the housing 421. These two LEDs are arranged so that the position is within the region between the opening 425 and the reference chart 400 and is symmetric with respect to the sensor unit 430. In other words, the housing 421 is located at a position where the line connecting the two LEDs used as the illumination light source 426 passes through the center of the imaging lens 432 of the sensor unit 430 and is symmetrical with respect to the line connecting the two LEDs. The opening 425 provided in the bottom surface portion 421a and the reference chart 400 are arranged. By arranging the two LEDs used as the illumination light source 426 in this way, the subject (patch image 200) and the reference chart 400 can be illuminated under substantially the same conditions.

  Further, if the gap d between the bottom surface 421a of the housing 421 and the recording medium 16 is reduced, the optical path length from the sensor unit 430 to the subject (patch image 200) and the optical path from the sensor unit 430 to the reference chart 400 The difference from the length may be within the range of the depth of field of the sensor unit 430. The imaging unit 42 of the present embodiment has a configuration in which a sensor unit 430 captures a subject (patch image 200) outside the housing 421 and a reference chart 400 provided inside the housing 421. Therefore, if the difference between the optical path length from the sensor unit 430 to the subject (patch image 200) and the optical path length from the sensor unit 430 to the reference chart 400 exceeds the range of the depth of field of the sensor unit 430, the subject ( An image focused on both the patch image 200) and the reference chart 400 cannot be captured.

  The difference between the optical path length from the sensor unit 430 to the subject (patch image 200) and the optical path length from the sensor unit 430 to the reference chart 400 is approximately a value obtained by adding the gap d to the thickness of the bottom surface part 421a of the housing 421. Become. Therefore, if the gap d is set to a sufficiently small value, the difference between the optical path length from the sensor unit 430 to the subject (patch image 200) and the optical path length from the sensor unit 430 to the reference chart 400 is calculated. An image focused on both the subject (patch image 200) and the reference chart 400 can be captured within the depth of field. 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 430 to the subject (patch image 200) and the optical path length from the sensor unit 430 to the reference chart 400 is determined by the sensor unit 430. It can be within the depth of field.

  Note that the depth of field of the sensor unit 430 is determined according to the aperture value of the sensor unit 430, the focal length of the imaging lens 432, the distance between the sensor unit 430 and the subject, and the like. It is. In the imaging unit 42 of the present embodiment, when the gap d between the bottom surface 421a of the housing 421 and the recording medium 16 is set to a sufficiently small value, for example, about 1 mm to 2 mm, the subject (patch) The sensor unit 430 is designed such that the difference between the optical path length to the image 200) and the optical path length from the sensor unit 430 to the reference chart 400 is within the depth of field.

<Specific examples of reference chart>
Next, the reference chart 400 on the chart plate 410 disposed inside the housing 421 of the imaging unit 42 will be described in detail with reference to FIG. FIG. 7 is a diagram illustrating a specific example of the reference chart 400.

  A reference chart 400 shown in FIG. 7 includes a plurality of reference patch rows 401 to 404 in which colorimetric patches are arranged, a dot 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 YMC 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 gradation pattern) 403 arranged in gradation order and a patch array 404 arranged with tertiary color patches. The dot measurement pattern row 406 is a geometric shape measurement pattern row in which circular patterns having different sizes are arranged in order of size.

  The distance measurement line 405 is formed as a rectangular frame (a combination of a pair of main scanning distance reference lines and a pair of sub-scanning distance reference lines) surrounding the plurality of reference patch arrays 401 to 404 and the dot diameter measuring pattern array 406. Has been. 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. The position of the reference chart 400 and the position of each pattern are specified 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 imaging unit 42. be able to.

  Each patch constituting the colorimetric reference patch rows 401 to 404 is used as a color reference reflecting imaging conditions when the imaging unit 42 performs imaging. The configuration of the colorimetric reference patch arrays 401 to 404 arranged in the reference chart 400 is not limited to the example shown in FIG. 7, and any patch array 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 disposed on the bottom surface 421a of the housing 421 of the imaging unit 42 so as to be adjacent to the opening 425, the reference chart 400 can be imaged simultaneously with the subject such as the patch image 200 by the sensor unit 430.

<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. 8 is a block diagram illustrating a schematic configuration of a control mechanism of the image forming apparatus 100.

  The control mechanism of the image forming apparatus 100 according to the present embodiment includes a host CPU 107, a ROM 118, a RAM 119, a main scanning driver 109, a recording head driver 111, a color measurement control unit 50, a paper conveyance unit 112, a sub scanning driver 113, and a recording head 6. An encoder sensor 41 and an imaging unit 42. The recording head 6, the encoder sensor 41, and the imaging unit 42 are mounted on the carriage 5 as described above.

  The host CPU 107 supplies image data and drive control signals (pulse signals) to be formed on the recording medium 16 to each driver, and controls the entire image forming apparatus 100. Specifically, the upper CPU 107 controls driving of the carriage 5 in the main scanning direction via the main scanning driver 109. The host CPU 107 controls the ink ejection timing by the recording head 6 via the recording head driver 111. Further, the upper CPU 107 controls driving of the paper conveyance unit 112 including a conveyance roller and a sub scanning motor via the sub scanning driver 113.

  The encoder sensor 41 outputs an encoder value obtained by detecting the mark on the encoder sheet 40 to the upper CPU 107. The upper CPU 107 controls driving of the carriage 5 in the main scanning direction via the main scanning driver 109 based on the encoder value from the encoder sensor 41.

  As described above, the imaging unit 42 detects the patch image 200 and the reference chart 400 on the chart plate 410 disposed inside the housing 421 at the time of color measurement of the patch image 200 formed on the recording medium 16. Images are simultaneously captured at 430, and image data including the patch image 200 and the reference chart 400 are output to the colorimetric control unit 50.

  FIG. 9 is a diagram illustrating an example of image data obtained by simultaneously imaging the reference chart and the imaging target. As shown in FIG. 9, the imaging unit 42 images each patch of the reference chart 400 arranged inside the frame body 32. The image data shown in FIG. 9 is an example in which the reference chart 400 is fixed to the left half surface with respect to the two-dimensional image sensor 431 and the color measurement target is imaged on the right half surface. The RGB signal value to be imaged is obtained by averaging a part of the right imaging area. In the example shown in FIG. 12, the RGB signals in the broken line area are obtained by averaging. By averaging a large number of pixels, the influence of noise can be reduced and the bit resolution can be improved.

  The colorimetric control unit 50 calculates the colorimetric value (colorimetric value in the standard color space) of the patch image 200 based on the image data of the patch image 200 acquired from the imaging unit 42. The colorimetric values of the patch image 200 calculated by the colorimetry control unit 50 are sent to the host CPU 107. The color measurement control unit 50 constitutes a color measurement device together with the imaging unit 42. In the present embodiment, the colorimetric control unit 50 is configured separately from the imaging unit 42, but the colorimetric control unit 50 may be integrated with the imaging unit 42. For example, a control circuit that functions as the colorimetric control unit 50 may be mounted on the substrate 423 of the imaging unit 42.

  In addition, the colorimetric control unit 50 supplies various setting signals, timing signals, light source driving signals, and the like to the image pickup unit 42 and controls image pickup by the image pickup unit 42. The various setting signals include a signal for setting an operation mode of the sensor unit 430 and a signal for setting an imaging condition such as a shutter speed and an AGC gain. These setting signals are acquired by the colorimetric control unit 50 from the host CPU 107 and supplied to the imaging unit 42. The timing signal is a signal that controls the timing of imaging by the sensor unit 430, and the light source driving signal is a signal that controls the driving of the illumination light source 426 that illuminates the imaging range of the sensor unit 430. These timing signals and light source drive signals are generated by the colorimetric control unit 50 and supplied to the imaging unit 42.

  The ROM 118 stores, for example, programs such as processing procedures executed by the host CPU 107, various control data, and the like. The RAM 119 is used as a working memory for the upper CPU 107.

<Configuration of control mechanism of color measuring device>
Next, the control mechanism of the color measuring device will be described in detail with reference to FIG. FIG. 1010 is a block diagram illustrating a configuration example of the control mechanism of the color measurement device.

  The color measurement device includes an imaging unit 42 and a color measurement control unit 50. The imaging unit 42 further includes an image processing unit 45 and an interface unit 46 in addition to the sensor unit 430 and the illumination light source 426 described above. In the present embodiment, the image processing unit 45 is configured separately from the sensor unit 430. However, the two-dimensional image sensor 431 of the sensor unit 430 may have the function of the image processing unit 45.

  The image processing unit 45 processes image data captured by the sensor unit 430, and includes an AD conversion unit 451, a shading correction unit 452, a white balance correction unit 453, a γ correction unit 454, and an image format conversion unit 455. .

  The AD conversion unit 451 converts the analog signal output from the sensor unit 430 from analog to digital.

  The shading correction unit 452 corrects an error in image data caused by uneven illumination of illumination from the illumination light source 426 with respect to the imaging range of the sensor unit 430.

  The white balance correction unit 453 corrects the white balance of the image data.

  The γ correction unit 454 corrects the image data so as to compensate for the sensitivity linearity of the sensor unit 430.

  The image format conversion unit 455 converts the image data into an arbitrary format.

  The interface unit 46 is used for the imaging unit 42 to acquire various setting signals, timing signals, and light source driving signals sent from the colorimetry control unit 50, and to send image data from the imaging unit 42 to the colorimetry control unit 50. Interface.

  The color measurement control unit 50 includes a frame memory 51, a calculation unit 53, a timing signal generation unit 54, a light source drive control unit 55, a nonvolatile memory 60, and a gap adjustment unit 56.

  The frame memory 51 is a memory that temporarily stores the image data sent from the imaging unit 42.

  As shown in FIG. 11, the non-volatile memory 60 is a colorimetric value L * that is a colorimetric value of a plurality of reference color patches KP arrayed on the reference sheet KS by a spectroscope (colorimetry device) BS. At least one of the a * b * value and the XYZ value (both L * a * b * value and XYZ value in FIG. 11) is patched to the memory table Tb1 of the nonvolatile memory 125 as a reference colorimetric value. Stored in correspondence with the number.

  The calculation unit 53 includes a colorimetric value calculation unit (calculation unit) 531 that is a light amount adjustment unit, and a distance calculation unit 532. The computing unit 53 includes a processor such as a CPU, for example, and implements the functions of the colorimetric value calculating unit 531 and the distance calculating unit 532 by executing a predetermined program by the processor. In this embodiment, the colorimetric value calculation unit 531 and the distance calculation unit 532 of the calculation unit 53 are realized by software. However, some or all of these are implemented by ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable). It can also be realized using dedicated hardware such as (Gate Array).

  When the sensor unit 430 of the imaging unit 42 simultaneously captures the color measurement target patch image 200 and the reference chart 400, the colorimetric value calculation unit 531 captures the patch image 200 and the reference chart 400 image obtained by the imaging. Based on the data, colorimetric values of the patch image 200 are calculated. The colorimetric values of the patch image 200 calculated by the colorimetric value calculation unit 531 are sent to the upper CPU 107. Details of a specific example of processing by the colorimetric value calculation unit 531 will be described later.

  The distance calculation unit 532 analyzes the image captured by the sensor unit 430 of the imaging unit 42 and temporarily stored in the frame memory 51, thereby forming a subject (formed on the recording medium 16) outside the housing 421 and the housing 421. The distance to the measured colorimetric patch image 200) is calculated. The distance may be calculated using the method disclosed in Japanese Patent Application Laid-Open No. 2017-003570.

  The timing signal generation unit 54 generates a timing signal for controlling the timing of imaging by the sensor unit 430 of the imaging unit 42 and supplies the timing signal to the imaging unit 42.

  The light source drive control unit 55 generates a light source drive signal for driving the illumination light source 426 of the imaging unit 42 and supplies the light source drive signal to the imaging unit 42.

  The gap adjusting unit 56 controls the driving of the carriage lifting / lowering motor 601 to change the interval between the sensor unit 430 and the recording medium 16.

<Color measurement method for patch images>
Next, a color measurement method of the patch image 200 by the image forming apparatus 100 according to the present embodiment will be described in detail. This color measurement method is performed during 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 during adjustment that performs color adjustment of the image forming apparatus 100. Color measurement processing to be performed.

  FIG. 11 is a diagram for explaining processing for acquiring a reference colorimetric value and a reference RGB value and processing for generating a reference value linear transformation matrix. These processes shown in FIG. 11 are implemented as a pre-process. In the preprocessing, a reference sheet KS on which a plurality of reference patches KP are formed is used. The reference patches KP of the reference sheet KS may be the same as the patches of the reference chart 400 included in the imaging unit 42, but it is preferable that the number is larger than the patches included in the reference chart 400.

  First, at least one of L * a * b * values and XYZ values that are colorimetric values of a plurality of reference patches KP of the reference sheet KS (in the example of FIG. 11, L * a * b * values and XYZ values). Are stored in a memory table Tb1 provided in, for example, the non-volatile memory 60 in the colorimetric control unit 50, corresponding to each patch number. 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 plate 22, and the movement of the carriage 5 is controlled, so that the imaging unit 42 performs imaging using the plurality of reference patches KC of the reference sheet KS as subjects.

  Then, the RGB value of each patch of the reference sheet KS obtained by imaging by the imaging unit 42 is stored in the memory table Tb1 of the nonvolatile memory 60 in correspondence with the patch number. 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 imaging unit 42.

  When the reference colorimetric value and the reference RGB value of the reference patch KP are stored in the memory table Tb1 of the non-volatile memory 60, the host CPU 107 of the image forming apparatus 100 uses the XYZ value that is the reference colorimetric value of the same patch number and the reference A reference value linear transformation matrix for mutually converting the RGB value pair is generated and stored in the nonvolatile memory 60. When only the L * a * b * value is stored as the reference colorimetric value in the memory table Tb1, L * a * b is converted using a known conversion formula for converting the L * a * b * value into an XYZ value. * After converting values to XYZ values, a reference value linear conversion matrix may be generated.

  Further, when the imaging unit 42 images the plurality of reference patches KP of the reference sheet KS, the reference chart 400 provided in the imaging unit 42 is also imaged 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 60 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. 12 is a diagram illustrating an example of the initial reference RGB values. FIG. 12A shows a state in which the initial reference RGB value (RdGdBd) is stored in the memory table Tb1, and the initial reference RGB value (RdGdBd) is set to the L * a * b * value together with the initial reference RGB value and (RdGdBd). This shows that the converted initial reference L * a * b * value (Ldadbd) and the initial reference XYZ value (XdYdZd) converted to the XYZ value are also stored in association with each other. FIG. 12B 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 allows the upper CPU 107 to control the main scanning movement of the carriage 5 and the recording medium P by the paper conveyance unit 112 based on image data input from the outside, print settings, and the like. The control of the recording head 6 and the drive control of the recording head 6 are performed to control the ink ejection from the recording head 6 while the recording medium P is intermittently conveyed, and an image is output to the recording medium P. 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 image 200 at a predetermined timing for color adjustment. And color reproducibility is improved by performing color adjustment based on the colorimetric value obtained by the colorimetric processing.

  13 and 14 are diagrams for explaining basic colorimetric processing. The colorimetric value calculation unit 531 first reads the reference value linear conversion matrix generated in the preprocessing and stored in the nonvolatile memory 60, and uses the reference value linear conversion matrix to calculate the colorimetric target RGB values (RsGsBs) in the first XYZ. It converts into a value and stores it in the non-volatile memory 60 (step S21). FIG. 13 shows an example in which the 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 531 converts the first XYZ value converted from the colorimetric target RGB value (RsGsBs) in step S21 into a first L * a * b * value using a known conversion formula. It stores in the non-volatile memory 60 (step S22). FIG. 13 shows an example in which the first XYZ values (20, 80, 10) are converted to the first L * a * b * values (75, −60, 8) by a known conversion formula.

  Next, the colorimetric value calculation unit 531 searches a plurality of reference colorimetric values (L * a * b * values) stored in the memory table Tb1 of the nonvolatile memory 60 in the preprocessing, and the reference colorimetric values. Among (L * a * b * values), it has a reference colorimetric value (L * a * b * value) that is close to the first L * a * b * value in the L * a * b * space. A set of a plurality of patches (neighboring color patches) is selected (step S23). As a method for selecting a patch having a short distance, for example, the distance from the first L * a * b * value to all the reference colorimetric values (L * a * b * values) stored in the memory table Tb1. A plurality of patches having L * a * b * values (L * a * b * values that are hatched in FIG. 13) that are close to the first L * a * b * values are calculated. A method of selecting can be used.

  Next, as shown in FIG. 14, the colorimetric value calculation unit 531 refers to the memory table Tb1 and makes a pair with the L * a * b * value for each of the neighboring color patches selected in step S23. RGB values (reference 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 531 obtains a selected RGB value linear conversion matrix for converting the RGB value of the selected combination (selected set) into an XYZ value using a least square method or the like, and obtains the selected RGB value obtained. The linear transformation matrix is stored in the nonvolatile memory 60 (step S25).

  Next, the colorimetric value calculation unit 531 converts the colorimetric target 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 531 converts the second XYZ value obtained in step S26 into a second L * a * b * value using a known conversion formula (step S27), and obtains the obtained second L * a. The * b * value is the final colorimetric value of the patch image 200 to be measured. The image forming apparatus 100 improves color reproducibility by performing color adjustment based on the colorimetric values obtained by the above colorimetric processing.

  Here, FIG. 15 is a diagram for explaining the RGB output values before balance adjustment, and FIG. 16 is a diagram for explaining the ratio and difference from the ideal values. If the grayscale RGB values of the reference chart 400 are output as they are, the output is not balanced as shown in FIG. 15, and is output as a color having saturation. This is because there is an error due to the sensitivity variation of each sensor of the two-dimensional image sensor 431.

  Essentially, all RGB outputs are ideally output as outputs having linearity on the ideal values shown in FIG. For this reason, a difference or ratio with the ideal value as shown in FIG. 16 is taken, temporarily stored in the non-volatile memory 60, and corrected to perform output with linearity.

  As described above, the colorimetric value calculation unit 531 can obtain an RGB output close to the ideal value by correcting the grayscale RGB output value of the reference chart 400 using the ratio or difference from the ideal value. it can.

  Here, FIG. 17 is a flowchart schematically showing a flow of processing for calculating a colorimetric value. As shown in FIG. 17, the colorimetric value calculation unit 531 sets the light amount L = a and the exposure time T = t1 (step S1). a is a predetermined reference value. t <b> 1 is a reference value determined by the light amount a, the distance d <b> 1 between the two-dimensional image sensor 431 and the reference chart 400.

  Here, FIG. 18 is a diagram showing the relationship between the interval with the recording medium 16 and the exposure time. FIG. 18 shows the relationship between the exposure time and the interval at the time of imaging the reference chart 400 and the subject (the color measurement target patch image 200 formed on the recording medium 16). The reference chart 400 for obtaining the target value a of the signal level is d1 (= 0 mm) at the time of imaging, the exposure time is t1, and the subject (the color measurement target patch image 200 formed on the recording medium 16) of the subject. When the imaging interval is d2 and the exposure time is t2, there is a relationship of d1 <d2 and t1 <t2.

  Next, the colorimetric value calculation unit 531 captures an image with the imaging unit 42 and acquires the RGB value of the reference chart 400 from within the imaging region (step S2).

  Next, the colorimetric value calculation unit 531 determines whether or not the RGB value of the patch with the lowest gray scale density (referred to as patch No. 12) in the reference chart 400 is overexposed (step S3). The over condition is equal to or more than a preset first threshold value, and the patch No. 12 and patch no. It is assumed that the difference from the 11 RGB values is equal to or less than a predetermined second threshold value.

  When it is determined that the RGB value is overexposed (Yes in step S3), the colorimetric value calculation unit 531 darkens the light amount by one step from the light amount L at the previous imaging (step S4), and returns to step S2.

  On the other hand, if the RGB value is not determined to be overexposed (No in step S3), the colorimetric value calculation unit 531 proceeds to step S5, and the patch having the highest gray scale density in the reference chart 400 (patch No. 1). ) Determines whether the RGB value is underexposed. The under condition is equal to or more than a preset third threshold value, and the patch No. 1 and patch no. It is assumed that the difference between 2 and the RGB value is equal to or less than a predetermined fourth threshold value.

  If it is determined that the RGB value is underexposed (Yes in step S5), the colorimetric value calculation unit 531 makes the light amount one step brighter than the light amount L at the previous imaging (step S6), and returns to step S2.

  On the other hand, if the RGB value is not determined to be underexposed (No in step S5), the colorimetric value calculation unit 531 proceeds to step S7, and calculates white balance (WB) and parameters for gamma correction. This parameter is data for canceling the difference between the RGB value acquired by imaging the reference chart 400 and the actual color of the reference chart 400. Factors causing this difference are caused by sensitivity variations of the two-dimensional image sensor 431, illumination unevenness, and light amount fluctuation.

  Subsequently, the colorimetric value calculation unit 531 sets the exposure time T = t2 (step S8). t2 is a reference value determined by the light amount L (after imaging of the reference chart 400), the distance d2 between the two-dimensional image sensor 431 and the colorimetric patch (the colorimetric patch image 200 formed on the recording medium 16). It is.

  Next, the colorimetric value calculation unit 531 captures an image with the imaging unit 42, and acquires the RGB value of the colorimetric patch (the colorimetric target patch image 200 formed on the recording medium 16) from within the imaging region (step S9). .

  Then, the colorimetric value calculation unit 531 corrects the RGB values acquired in step S9 using the white balance (WB) and gamma correction parameters calculated in step S7 (step S10).

  Finally, the colorimetric value calculation unit 531 converts the RGB values into the L * a * b * color space and calculates the colorimetric values (step S11).

  Thus, according to the present embodiment, the reference chart and the subject (measurement) are configured by the configuration of the imaging unit including the image sensor that captures the reference chart and the subject (colorimetric media) and the light source that illuminates the imaging target. The color measurement accuracy can be improved by correcting the brightness by changing the exposure time at the time of imaging of the subject (colorimetric media) so that the exposure amount at the time of imaging with the color media) is equal.

  Note that the second exposure time may be changed according to the distance calculated by the distance calculation unit 532.

(Second Embodiment)
Next, a second embodiment will be described.

  In the image forming apparatus 100 of the second embodiment, the imaging unit is different from that of the first embodiment. Hereinafter, in the description of the second embodiment, the description of the same parts as those of the first embodiment will be omitted, and different parts from the first embodiment will be described.

  Here, FIG. 19 is a longitudinal sectional view of the imaging unit 42F according to the second embodiment, and is a sectional view at the same position as the longitudinal sectional view of the imaging unit 42 shown in FIG.

  In the imaging unit 42F according to the second embodiment, an optical path length changing member 440 is disposed inside the housing 421. The optical path length changing member 440 is an optical element having a refractive index n (n is an arbitrary number) that transmits light. The optical path length changing member 440 is disposed in the optical path between the subject (patch image 200) outside the housing 421 and the sensor unit 430, and the imaging surface of the optical image of the subject (patch image 200) is the reference chart 400. It has a function to bring the optical image closer to the image plane. In other words, in the imaging unit 42F according to the second embodiment, the optical path length changing member 440 is arranged in the optical path between the subject (patch image 200) and the sensor unit 430, so that the subject outside the casing 421 is located. The imaging surface of the optical image of (patch image 200) and the imaging surface of the reference chart 400 inside the housing 421 are both matched with the sensor surface of the two-dimensional image sensor 431 of the sensor unit 430. FIG. 19 illustrates an example in which the optical path length changing member 440 is placed on the bottom surface portion 421a of the housing 421. However, the optical path length changing member 440 is not necessarily placed on the bottom surface portion 421a. It is only necessary to be disposed in the optical path between the subject (patch image 200) outside the housing 421 and the sensor unit 430.

When light passes through the optical path length changing member 440, the optical path length is extended according to the refractive index n of the optical path length changing member 440, and the image appears to float. The image floating amount C can be obtained by the following equation, where Lp is the length of the optical path length changing member 440 in the optical axis direction.
C = Lp (1-1 / n)

When the distance between the principal point of the imaging lens 432 of the sensor unit 430 and the reference chart 400 is Lc, the front focal plane of the optical image transmitted through the principal point of the imaging lens 432 and the optical path length changing member 440 ( The distance L to the imaging surface can be obtained by the following equation.
L = Lc + Lp (1-1 / n)

  Here, when the refractive index n of the optical path length changing member 440 is 1.5, L = Lc + Lp (1/3), and the optical path length of the optical image transmitted through the optical path length changing member 440 is set to the optical path length changing member 440. The length can be increased by about 1/3 of the length Lp in the optical axis direction. In this case, for example, if Lp = 9 [mm], L = Lc + 3 [mm], so the difference between the distance from the sensor unit 430 to the reference chart 400 and the distance to the subject (patch image 200) is 3 mm. In this state, the sensor unit includes both the rear focal plane (imaging plane) of the optical image of the reference chart 400 and the rear focal plane (imaging plane) of the optical image of the subject (patch image 200). It can be matched with the sensor surface of the two-dimensional image sensor 431 of 430.

  In the imaging unit 42F according to the second embodiment configured as described above, the optical path length changing member 440 is disposed in the optical path between the subject (patch image 200) and the sensor unit 430, so that the subject ( Since the image plane of the optical image of the patch image 200) is brought close to the image plane of the optical image of the reference chart 400, an appropriate image focused on both the subject (patch image 200) and the reference chart 400. Can be imaged.

6 Image output means 42 Imaging device,
42, 50 Color measuring device 45 Correction unit 50 Calculation unit 100 Image forming device 400 Reference chart 426 Light source 431 Sensor 531 Light amount adjustment unit

JP 2013-51672 A

Claims (5)

A light source that illuminates the subject through the opening;
A reference chart illuminated by the light source and closer to the light source than the subject;
A sensor for imaging the reference chart with a first exposure time;
A light amount adjustment unit that adjusts the light amount of the light source according to a result of imaging the reference chart with the first exposure time;
With
The sensor images a subject imaged with the adjusted light amount with a second exposure time longer than the first exposure time;
An imaging apparatus characterized by that. The light amount adjustment unit determines a correction value of data captured by the sensor according to a result of imaging the reference chart with the first exposure time,
A correction unit that corrects data obtained by imaging the subject in the second exposure time with the determined correction value;
The imaging apparatus according to claim 1. A distance calculation unit that calculates a distance between the sensor and the subject based on an image captured by the sensor;
Changing the second exposure time according to the distance calculated by the distance calculation unit;
The imaging apparatus according to claim 1 or 2, wherein The imaging apparatus according to any one of claims 1 to 3,
A calculation unit that calculates a colorimetric value of the subject based on the subject imaged by the imaging device and imaging data of a reference chart;
A colorimetric device comprising: Image output means for outputting an image to a recording medium;
A colorimetric device according to claim 4;
With
The colorimetric device calculates a colorimetric value of the image output from the image output unit as the subject,
The image output means outputs an image based on image data color-adjusted using the colorimetric value after the colorimetric device calculates the colorimetric value.
An image forming apparatus.