JP2014137247A - Color detecting device, color measuring device, image forming apparatus, and color measuring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to appropriately acquire color data for measuring colors with high accuracy.SOLUTION: A color measuring camera 42 of an embodiment includes: a white LED light source 426a that has a plurality of peak wavelengths in a wavelength range of 380 nm to 780 nm; a blue-green LED light source 426b; and a two-dimensional image sensor that receives reflection light of light from the white LED light source 426a reflected on a patch of a color measurement target and a reference chart part 400, and reflection light of light from the blue-green LED light source 426b reflected on the patch of a color measurement target and the reference chart part 400, and outputs image data including the patch of a color measurement target and the reference chart part 400. The blue-green LED light source 426b is a light source that has a peak wavelength in at least one wavelength range in which the total spectrum sensitivity becomes equal to or less than a predetermined value, where the total spectrum sensitivity is obtained by multiplying a light emission intensity distribution of the white LED light source 426a by the spectrum sensitivity of the two-dimensional image sensor.

Description

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

  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 correcting a device profile of an image forming apparatus, a test pattern in which color charts (patches) of a large number of reference colors are actually arranged on a recording medium is formed by the image forming apparatus. Then, color measurement is performed on each patch included in the test pattern using a color measurement device.

  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, in Patent Document 1, a two-dimensional image sensor is used to simultaneously capture a color measurement target patch and a reference chart portion including a plurality of patches whose colorimetric values are known in advance, and are obtained by imaging. A technique for calculating a colorimetric value of a color measurement target patch based on the RGB value of the color measurement target patch and the RGB value of the patch included in the reference chart portion is described. Patent Document 1 describes that an LED (Light Emitting Diode), which is advantageous for space saving and power saving, is used as a light source for illuminating a color measurement target patch and a reference chart portion during imaging.

  However, a white LED that has been widely used as an illumination light source is configured to emit pseudo white light by applying a yellow phosphor to a blue LED element (referred to as a pseudo white LED), and has a wavelength of 500 nm. A drop in emission intensity is observed in the vicinity. For this reason, when imaging is performed using such a white LED as a light source, there is a concern that the obtained RGB value may cause a decrease in S / N near a wavelength of 500 nm, which may cause a decrease in colorimetric accuracy.

  The present invention has been made in view of the above, and uses a color detection device capable of appropriately acquiring color data for performing high-precision colorimetry, and the color data acquired by the color detection device. It is an object of the present invention to provide a color measurement device that performs high-precision color measurement, an image forming apparatus including the color measurement device, and a color measurement system.

  In order to solve the above-described problems and achieve the object, a color detection device according to the present invention is reflected by a first light source having a plurality of peak wavelengths in a wavelength range of 380 nm to 780 nm, a second light source, and an object. A sensor that receives the reflected light of the light from the first light source and the reflected light of the light from the second light source reflected by the object, and outputs color data of the object; The second light source has a peak wavelength in at least one of a wavelength range in which the total spectral sensitivity, which is a value obtained by multiplying the emission intensity distribution of the first light source and the spectral sensitivity of the sensor, is a predetermined value or less. It is characterized by that.

  The colorimetric device according to the present invention includes the color detection device according to the present invention, and a calculation unit that calculates a colorimetric value of the object based on color data output from the sensor. To do.

  The image forming apparatus according to the present invention includes the color measurement device according to the present invention and an image output unit that outputs an image to a recording medium, and the object is output from the image output unit to the recording medium. It is characterized by being an image.

  The color measurement system according to the present invention is a color measurement system including the color detection device according to the present invention and an external device, wherein the external device is color data output by the sensor of the color detection device. And a calculation unit for calculating a colorimetric value of the object based on the above.

  According to the present invention, it is possible to appropriately acquire color data of an object and perform highly accurate color measurement.

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. FIGS. 4-4 is a figure explaining the regular reflection area | region which is an irradiation position of the regular reflection light which injects into the two-dimensional image sensor of a sensor part. FIG. 5 is a diagram illustrating a specific example of the reference chart portion. 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 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. 9 is a diagram illustrating an example of the initial reference RGB values. FIG. 10 is a diagram for explaining the outline of the color measurement process. FIG. 11 is a diagram for describing processing for generating a linear conversion matrix between reference RGB. FIG. 12 is a diagram illustrating the relationship between the initial reference RGB value and the colorimetric reference RGB value. FIG. 13 is a diagram for explaining basic colorimetry processing. FIG. 14 is a diagram for explaining basic colorimetry processing. FIG. 15A is a vertical cross-sectional view (cross-sectional view taken along line X10-X10 in FIG. 15B) of the reflective colorimetric device. FIG. 15B is a bottom view of the reflection type colorimetric apparatus. FIG. 16 is a block diagram illustrating a schematic configuration of a control mechanism of the reflection type colorimetry apparatus. FIG. 17 is a cross-sectional view showing an example of a white LED light source. FIG. 18 is a diagram showing the emission intensity distribution of the white LED light source. FIG. 19 is a diagram showing the spectral sensitivity of the two-dimensional image sensor. 20 is a diagram showing total spectral sensitivity that is a value obtained by multiplying the emission intensity distribution of the white LED light source shown in FIG. 18 and the spectral sensitivity of the two-dimensional image sensor shown in FIG. FIG. 21 is a diagram showing a light emission intensity distribution of a blue-green LED light source. 22 is a diagram showing the total spectral sensitivity obtained by multiplying the emission intensity distribution of the blue-green LED light source shown in FIG. 21 and the spectral sensitivity of the two-dimensional image sensor shown in FIG. FIG. 23 is a diagram showing total spectral sensitivity when an illumination unit that combines a white LED light source and a blue-green LED light source is used. FIG. 24 is a diagram illustrating a result of calculating the ν factor in each of the case where only the white LED light source is used for the illumination unit and the case where the combination of the white LED light source and the blue-green LED light source is used. FIG. 25 is a longitudinal sectional view of a colorimetric camera of a first modification. FIG. 26 is a longitudinal sectional view of a colorimetric camera of a second modified example. FIG. 27 is a longitudinal sectional view of a colorimetric camera of a third modified example. FIG. 28A is a longitudinal sectional view of a colorimetric camera of a fourth modified example. FIG. 28-2 is a plan view of the bottom surface of the housing of the colorimetric camera of the fourth modification when viewed from the X3 direction in FIG. 28-1. FIG. 29 is a longitudinal sectional view of a colorimetric camera of a fifth modification. FIG. 30 is a longitudinal sectional view of a colorimetric camera according to a sixth modification. FIG. 31 is a diagram illustrating an example of image data obtained by simultaneously capturing an image of a color measurement target patch and a reference chart portion. FIG. 32 is a diagram for explaining a modification of the patch colorimetry method. FIG. 33 is a diagram showing a conversion formula for converting between Lab values and XYZ values. FIG. 34 is a flowchart showing the procedure of patch colorimetry. FIG. 35 is a flowchart illustrating another example of the patch colorimetry procedure. FIG. 36 is a diagram for explaining a method of specifying RGB values corresponding to Lab standard values of patches. FIG. 37 is a diagram showing a schematic configuration of the color measurement system.

  Exemplary embodiments of a color detection apparatus, a color measurement apparatus, an image forming apparatus, and a color measurement system according to the present invention will be explained below in detail 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 form images on 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 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 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).

  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 22 is provided at a position facing the ejection surface of the recording head 6 as shown in FIG. The platen 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 22 is configured by connecting a plurality of plate-like members in the main scanning direction (movement direction of the carriage 5). The recording medium 16 is sandwiched between transport rollers driven by a sub scanning motor (not shown), and is intermittently transported on the platen 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 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 row of the recording head 6 mounted on the carriage 5 onto the recording medium 16 on the platen 22 to form an image on the recording medium 16.

  In particular, when adjusting the color of the image forming apparatus 100, ink is actually ejected from the nozzle array of the recording head 6 mounted on the carriage 5 onto the recording medium 16 on the platen 22, and a large number of patches are obtained. 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 color measurement camera (color measurement device) 42 for performing color measurement on each patch 200 included in a test pattern formed on the recording medium 16. The colorimetric camera 42 uses the patch 200 formed on the recording medium 16 by the image forming apparatus 100 as a subject, and images the patch 200 and a reference chart unit 400 described later simultaneously. Then, the colorimetric camera 42 calculates the colorimetric value of the patch 200 based on the patch 200 obtained by imaging and the image data of the reference chart unit 400 (the RGB value of the patch 200 and the RGB value of the reference chart unit 400). .

  As shown in FIG. 2, the colorimetric camera 42 is fixed to the carriage 5 and reciprocates in the main scanning direction together with the carriage 5. Then, when the colorimetric camera 42 moves to a position facing the patch 200 included in the test pattern formed on the recording medium 16 on the platen 22, the colorimetric camera 42 images the patch 200 simultaneously with the reference chart unit 400. Here, simultaneous imaging means that one frame of image data including the patch 200 and the reference chart unit 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 unit 400 is acquired in one frame, the patch 200 and the reference chart unit 400 are captured simultaneously. .

<Specific example of mechanical configuration of colorimetric camera>
4A to 4D are diagrams illustrating an example of the mechanical configuration of the colorimetric camera 42. FIG. 4A is a longitudinal sectional view of the colorimetric camera 42 (X1-X in FIG. 4-2). FIG. 4-2 is a top view of the colorimetric camera 42 seen through, and FIG. 4-3 is a plan view of the bottom surface of the housing viewed from the X2 direction in FIG. 4-1. FIGS. 4A and 4B are diagrams for explaining the regular reflection region that is the irradiation position of the regular reflection light incident on the two-dimensional image sensor of the sensor unit.

  The colorimetric camera 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 22 with a predetermined gap d. An opening 425 for allowing the patch 200 formed on the recording medium 16 to be photographed from the inside of the casing 421 is provided on the bottom surface 421 a of the casing 421 facing the recording medium 16.

  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 portion 400 is formed is disposed on the inner surface of the bottom surface portion 421a of the housing 421 facing the sensor portion 430 so as to be adjacent to the opening 425 provided in the bottom surface portion 421a. ing. 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 portion 400 is formed, being attached to the housing 421. Are held in a fixed state. Note that the reference chart portion 400 may be formed directly 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. For example, the reference chart unit 400 is imaged together with the patch 200 by the sensor unit 430 as a comparison target of the patch 200 to be measured. That is, the sensor unit 430 captures an image of the patch 200 outside the housing 421 through the opening 425 provided on the bottom surface 421a of the housing 421, and at the same time, the chart disposed on the inner surface side of the bottom surface 421a of the housing 421. The reference chart 400 on the plate 410 is imaged. The details of the reference chart unit 400 will be described later.

  In addition, an illumination unit 426 that illuminates the patch 200 and the reference chart unit 400 when the sensor unit 430 simultaneously images the patch 200 and the reference chart unit 400 is provided inside the housing 421. In this embodiment, as the illumination unit 426, a white LED light source (first light source) 426a that emits pseudo white light by applying a yellow phosphor to a blue LED element, and blue light having an emission wavelength of about 480 nm to 540 nm. A combination of a green LED light source (second light source) 426b is used. The white LED light source 426a and the blue-green LED light source 426b 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 white LED light source 426a and the blue-green LED light source 426b may be disposed at a position where the patch 200 and the reference chart unit 400 can be illuminated, and may not necessarily be directly mounted on the substrate 423. Details of the illumination unit 426 will be described later.

  In the color measurement camera 42 of the present embodiment, two illumination units 426 are used to illuminate the imaging range of the sensor unit 430 substantially uniformly. These two illumination parts 426 are arrange | positioned in the position used as object centering on the sensor part 430, as shown to FIGS. 4-2. Specifically, the projection position on the bottom surface portion 421a when the two illumination portions 426 are vertically viewed from the substrate 423 side to the bottom surface portion 421a side of the housing 421 is between the opening 425 and the reference chart portion 400. These two illumination units 426 are arranged at positions where the distance from the center of the two-dimensional image sensor 431 of the sensor unit 430 is substantially equal. In other words, the line connecting the two illumination units 426 passes through the central portion of the two-dimensional image sensor 431 of the sensor unit 430 and is in a position symmetrical with respect to the line connecting the two illumination units 426. An opening 425 provided in the bottom surface portion 421a of the 421 and the reference chart portion 400 are disposed. By arranging the two illumination units 426 in this manner, the patch 200 and the reference chart unit 400 can be illuminated under substantially the same conditions.

  Further, the white LED light source 426a and the blue-green LED light source 426b constituting the illumination unit 426 are configured such that the specularly reflected light incident on the two-dimensional image sensor 431 of the sensor unit 430 is a colorimetric target patch 200 and the reference chart unit 400. It is arranged at a position where the region between the two is irradiated. That is, as shown in FIG. 4-4, the positions where the white LED light source 426a and the blue-green LED light source 426b are installed include a regular reflection area SA which is an irradiation position of regular reflection light incident on the two-dimensional image sensor 431. 421 is determined so as to be positioned in an area (hereinafter referred to as a blanking area) between the opening 425 of the bottom surface part 421a (that is, the patch 200 imaged through the opening 425) and the reference chart part 400. ing.

  Among the images captured by the sensor unit 430, the output of the two-dimensional image sensor 431 is saturated in the image region corresponding to the regular reflection region SA, and an appropriate RGB value reflecting the color cannot be obtained. For this reason, when the white LED light source 426a and the blue-green LED light source 426b are arranged so that the regular reflection area SA overlaps the color measurement target patch 200 and the reference chart unit 400, the color measurement of the color measurement target patch 200 is performed. There is a risk that it cannot be performed properly. On the other hand, as described above, by arranging the white LED light source 426a and the blue-green LED light source 426b so that the regular reflection area SA is located in the blanking area of the bottom surface portion 421a of the housing 421, the patch 200 and The RGB values of the reference chart unit 400 can be appropriately acquired, and the color measurement of the patch 200 can be appropriately performed. Note that, in the image captured by the sensor unit 430, the image region corresponding to the blanking region is not used for the colorimetry of the patch 200, so there is no problem even if the output of the two-dimensional image sensor 431 is saturated.

  By the way, in order to illuminate the patch 200 outside the casing 421 under the same illumination conditions as the reference chart unit 400 disposed inside the casing 421, the external light does not hit the patch 200 during imaging, and illumination is performed. It is necessary to illuminate the patch 200 only with the illumination light from the unit 426. In order to prevent the external light from hitting the patch 200, the gap d between the bottom surface portion 421 a of the housing 421 and the recording medium 16 is made small so that the external light toward the patch 200 is blocked by the housing 421. It is effective to do. However, if the gap d between the bottom surface portion 421a of the housing 421 and the recording medium 16 is made too small, the recording medium 16 comes into contact with the bottom surface portion 421a of the housing 421, so that the patch 200 can be appropriately imaged. There is a risk of disappearing. Therefore, the gap d between the bottom surface portion 421a of the housing 421 and the recording medium 16 is a small value in a range where the recording medium 16 does not contact the bottom surface portion 421a of the housing 421 in consideration of the flatness of the recording medium 16. It is desirable to set to. For example, if the gap d between the bottom surface portion 421a of the housing 421 and the recording medium 16 is set to about 1 mm to 2 mm, the recording medium 16 does not contact the bottom surface portion 421a of the housing 421. It is possible to effectively prevent external light from hitting the formed patch 200.

  In order to appropriately irradiate the patch 200 with illumination light from the illumination unit 426, the size of the opening 425 provided in the bottom surface 421a of the housing 421 is made larger than that of the patch 200, and the edge of the opening 425 is formed. 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 surface portion 421a of the housing 421 and the recording medium 16 is reduced, the optical path length from the sensor unit 430 to the patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 are reduced. The difference may be within the range of the depth of field of the sensor unit 430. The colorimetric camera 42 of the present embodiment is configured to simultaneously image the patch 200 outside the housing 421 and the reference chart unit 400 provided inside the housing 421 by the sensor unit 430. Therefore, if the difference between the optical path length from the sensor unit 430 to the patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 exceeds the range of the depth of field of the sensor unit 430, the patch 200 and the reference chart An image focused on both the unit 400 and the unit 400 cannot be captured.

  The difference between the optical path length from the sensor unit 430 to the patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 is generally a value obtained by adding the gap d to the thickness of the bottom surface part 421a of the housing 421. 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 patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 is expressed as the depth of field of the sensor unit 430. Within the range, an image focused on both the patch 200 and the reference chart unit 400 can be captured. 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 patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 is expressed as the depth of field of the sensor unit 430. Can be within the range.

  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 colorimetric camera 42 of the present embodiment, when the gap d between the bottom surface portion 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 patch 200 from the sensor unit 430 is used. The sensor unit 430 is designed so that the difference between the optical path length up to and the optical path length from the sensor unit 430 to the reference chart unit 400 is within the depth of field.

<Specific example of the reference chart section>
Next, the reference chart unit 400 on the chart plate 410 disposed inside the housing 421 of the colorimetric camera 42 will be described in detail with reference to FIG. FIG. 5 is a diagram illustrating a specific example of the reference chart unit 400.

  The reference chart unit 400 illustrated 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 16. 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 from the image data of the reference chart unit 400 obtained by imaging by the colorimetric camera 42, the position of the reference chart unit 400 and the position of each pattern Can be specified.

  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 42 performs imaging. The configuration of the colorimetric reference patch rows 401 to 404 arranged in the reference chart unit 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 unit 400 having the reference patch rows 401 to 404 having a general patch (color chart) shape is used. However, the reference chart unit 400 is not necessarily limited to such a reference patch row 401. It may not be a form which has -404. The reference chart unit 400 may have a configuration in which a plurality of colors that can be used for colorimetry are arranged so that their positions can be specified.

  Since the reference chart unit 400 is disposed on the bottom surface 421a of the housing 421 of the colorimetric camera 42 so as to be adjacent to the opening 425, it can be imaged simultaneously with the patch 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. 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 42, an encoder sensor 41, 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 41, and the colorimetric camera 42 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 41.

  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. Further, 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 according to the control command from the CPU 101, and records on the platen 22. Controls the movement of the medium 16 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 16 on the platen 22 to form an image.

As described above, when the colorimetric camera 42 performs colorimetry of the patch 200 included in the test pattern formed on the recording medium 16, the colorimetric camera 42 is placed on the chart plate 410 disposed inside the patch 200 and the housing 421. The reference chart unit 400 is simultaneously imaged by the sensor unit 430, and based on the image data including the patch 200 and the reference chart unit 400, the colorimetric values of the patch 200 (color values in the standard color space, such as L ^* a Calculate the L ^* a ^* b ^* value in the ^* b ^* color space (hereinafter, L ^* a ^* b ^* is expressed as Lab). The colorimetric values of the patch 200 calculated by the colorimetric camera 42 are sent to the CPU 101 via the control FPGA 110.

  The encoder sensor 41 outputs an encoder value obtained by detecting the mark on the encoder sheet 40 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 42 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 42.

  As shown in FIG. 7, the colorimetric camera 42 includes a two-dimensional image sensor 431, an interface unit 46, a frame memory 51, a colorimetric value calculation unit 52, a nonvolatile memory 53, a timing signal generation unit 54, and a light source drive control unit 55. , And an illumination unit 426. Each of these units is mounted on a substrate 423 that constitutes the upper surface of the housing 421 of the colorimetric camera 42, for example.

  The two-dimensional image sensor 431 converts light from the imaging range incident through the imaging lens 432 into an electric signal, and outputs image data (color data of the object) in the imaging range. The two-dimensional image sensor 431 has a function of performing various image processing on image data, 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. A portion 455. Various image processing on the image data may be performed outside the two-dimensional image sensor 431.

  The AD conversion unit 451 AD converts an analog signal obtained by photoelectrically converting the optical image of the subject.

  The shading correction unit 452 corrects an error in image data caused by uneven illumination of illumination from the illumination unit 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 two-dimensional image sensor 431.

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

  The interface unit 46 outputs image data from the two-dimensional image sensor 431, and the two-dimensional image sensor 431 receives various setting signals sent from the CPU 101 via the control FPGA 110 and the timing signal generated by the timing signal generation unit 54. It is an interface for input to. The various setting signals include a signal for setting an operation mode of the two-dimensional image sensor 431 and a signal for setting an imaging condition such as a shutter speed and an AGC gain.

  The frame memory 51 is a memory that temporarily stores the image data output from the two-dimensional image sensor 431.

  When the colorimetric camera 42 images the color measurement target patch 200 and the reference chart unit 400 simultaneously, the colorimetric value calculation unit 52 is based on the patch 200 and the image data of the reference chart unit 400 obtained by the imaging. The colorimetric value of the patch 200 is calculated. The colorimetric value of the patch 200 calculated by the colorimetric value calculator 52 is sent to the CPU 101 via the control FPGA 110. A specific example of processing by the colorimetric value calculation unit 52 will be described later in detail.

  The nonvolatile memory 53 stores various data necessary for the colorimetric value calculation unit 52 to calculate the colorimetric values of the patch 200.

  The timing signal generation unit 54 generates a timing signal for controlling the timing of imaging by the colorimetric camera 42 and inputs the timing signal to the two-dimensional image sensor 431 via the interface unit 46.

  The light source drive control unit 55 generates a light source drive signal for lighting the white LED light source 426a and the blue-green LED light source 426b of the illumination unit 426, supplies the light source drive signal to the illumination unit 426, and supplies the white LED light source 426a and The operation of the blue-green LED light source 426b is controlled. The light source drive control unit 55 may control the white LED light source 426a and the blue-green LED light source 426b to turn on alternately, or control the white LED light source 426a and the blue-green LED light source 426b to turn on simultaneously. May be. When the white LED light source 426a and the blue-green LED light source 426b are alternately turned on, the colorimetric value calculation unit 52 outputs image data output from the two-dimensional image sensor 431 when the white LED light source 426a is turned on, The colorimetric value of the patch 200 is calculated based on the image data output from the two-dimensional image sensor 431 when the blue-green LED light source 426b is on. When the white LED light source 426a and the blue-green LED light source 426b are turned on at the same time, the colorimetric value calculation unit 52 is a two-dimensional image sensor when the white LED light source 426a and the blue-green LED light source 426b are turned on simultaneously. Based on the image data output by 431, the colorimetric value of the patch 200 is calculated.

<Specific examples of patch colorimetry>
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. 8 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. 8 are implemented as pre-processing. 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 unit 400 provided in the colorimetric camera 42.

  First, at least one of Lab values and XYZ values (both Lab values and XYZ values in the example of FIG. 8) 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, the nonvolatile memory 53 mounted on the substrate 423 of the colorimetric camera 42. 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 22 and the movement of the carriage 5 is controlled, so that the colorimetric camera 42 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 42 are stored in the memory table Tb1 of the nonvolatile memory 53 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 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 nonvolatile memory 53, 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 to each other is generated and stored in the nonvolatile memory 53. 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 42 images a plurality of reference patches KP on the reference sheet KS, the reference chart unit 400 provided in the colorimetric camera 42 is also imaged simultaneously. The RGB values of each patch of the reference chart unit 400 obtained by this imaging are also stored in the memory table Tb1 of the nonvolatile memory 53 in association with the patch number. The RGB values of the patches of the reference chart unit 400 stored in the memory table Tb1 by this preprocessing are referred to as “initial reference RGB values”. FIG. 9 is a diagram illustrating an example of the initial reference RGB values. FIG. 9A shows a state in which the initial reference RGB value (RdGdBd) is stored in the memory table Tb1, and the initial reference Lab 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. 9B is a scatter diagram in which initial reference RGB values of each patch of the reference chart unit 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, the recording medium 16 is intermittently conveyed in the sub-scanning direction, and the carriage 5 is moved in the main scanning direction, and ink is ejected from the recording head 6 to form an image on the recording medium 16. . 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 16 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. 10 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 16 set on the platen 22 to form a color measurement target patch 200. Hereinafter, the recording medium 16 on which the patch 200 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 the color measurement target patch 200 is stored in advance in the nonvolatile memory 53 or the like.

  Next, as shown in FIG. 10, the image forming apparatus 100 sets the adjustment sheet CS on the platen 22 or holds the adjustment sheet CS on the platen 22 without discharging the sheet when the adjustment sheet CS is created. In the state, the movement of the carriage 5 is controlled to move the colorimetric camera 42 to a position facing the patch 200 formed on the adjustment sheet CS on the platen 22. Then, the colorimetric camera 42 images the patch 200 and the reference chart unit 400 provided in the colorimetric camera 42 at the same time. The patch 200 and the image data of the reference chart unit 400 simultaneously captured by the colorimetric camera 42 are temporarily stored in the frame memory 51 after necessary image processing is performed inside the two-dimensional image sensor 431. Hereinafter, among the image data captured by the colorimetric camera 42 and temporarily stored in the frame memory 51, the image data (RGB value) of the patch 200 is referred to as “colorimetric RGB value”, and the patch image data of the reference chart unit 400. (RGB value) is referred to as “color measurement reference RGB value (RdsGdsBds)”. The “color measurement reference RGB value (RdsGdsBds)” is stored in the nonvolatile memory 53 or the like.

  The colorimetric value calculation unit 52 of the colorimetric camera 42 uses the reference RGB linear conversion matrix, which will be described later, to convert the colorimetric RGB values temporarily stored in the frame memory 51 into initialization colorimetric RGB values (RsGsBs). (Step S10). The initialization colorimetric object RGB values (RsGsBs) are the imaging conditions of the colorimetric camera 42 that are generated from the colorimetric object RGB values from the initial state where preprocessing is performed to the adjustment time when performing colorimetry processing. For example, the influence of a change with time, for example, a change with time of the illumination light source 426 or a change with time of the two-dimensional image sensor 431 is eliminated.

  Thereafter, the colorimetric value calculation unit 52 performs basic colorimetry processing, which will be 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. 11 is a diagram illustrating a process of generating a linear conversion matrix between reference RGB, and FIG. 12 is a diagram illustrating a relationship between an initial reference RGB value and a colorimetric reference RGB value. The colorimetric value calculation unit 52 generates a reference RGB linear conversion matrix to be used for this conversion before performing the process (step S10) of converting the colorimetric target RGB values into the initialization colorimetric target RGB values (RsGsBs). . That is, as shown in FIG. 11, the colorimetric value calculation unit 52 uses 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. A reference RGB value (RdsGdsBds) is read from the nonvolatile memory 53, and a reference RGB inter-RGB linear conversion matrix for converting the colorimetric reference RGB value RdsGdsBds to the initial reference RGB value RdGdBd is generated. Then, the calorimetric value calculation unit 52 stores the generated reference RGB linear conversion matrix in the nonvolatile memory 53.

  In FIG. 12, the thinly drawn points in FIG. 12A 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. 12A, the value of the colorimetric reference RGB value RdsGdsBds varies from the value of the initial reference RGB value RdGdBd, and the variation direction in the rgb space is shown in FIG. 12B. 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 when the patches of the same reference chart unit 400 are imaged include the temporal change of the illumination unit 426 and the temporal change of the two-dimensional image sensor 431.

  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 42 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 RGB values obtained by imaging the patch 200 with the colorimetric camera 42 are converted into initialization colorimetric 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 52 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).

  13 and 14 are diagrams for explaining basic colorimetric processing. The colorimetric value calculation unit 52 first reads the reference value linear conversion matrix generated in the preprocessing and stored in the nonvolatile memory 53, 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 53 (step S21). FIG. 13 shows an example in which the initialization colorimetric object 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 52 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. 53 (step S22). FIG. 13 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 52 searches a plurality of reference colorimetric values (Lab values) stored in the memory table Tb1 of the non-volatile memory 53 in the preprocessing, and calculates 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 to each other (in FIG. 13, Lab values that are hatched) can be used.

  Next, as shown in FIG. 14, the colorimetric value calculation unit 52 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 52 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 selected RGB value. The linear transformation matrix is stored in the nonvolatile memory 53 (step S25).

  Next, the colorimetric value calculation unit 52 converts the initialization 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 52 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 42 described above has a configuration in which the reference chart unit 400 is provided in the housing 421 and the patch 200 to be measured and the reference chart unit 400 are simultaneously imaged by the sensor unit 430. However, as described above, the initial reference RGB value and the colorimetric reference RGB value obtained by imaging the reference chart unit 400 are the colorimetric object RGB values obtained by imaging the colorimetric object patch 200. On the other hand, it is used to eliminate the influence of the temporal change of the imaging condition of the colorimetric camera 42, for example, the temporal change of the illumination light source 426 and the temporal change of the two-dimensional image sensor 431. That is, for the initial reference RGB value and the colorimetric reference RGB value obtained by imaging of the reference chart unit 400, the above-described reference RGB linear conversion matrix is calculated, and the color measurement target is calculated using the reference RGB linear conversion matrix. Used to convert RGB values into initialization colorimetric object RGB values (RsGsBs).

  Therefore, if the change over time of the imaging condition of the colorimetric camera 42 is negligible with respect to the required colorimetric accuracy, the patch 200 is configured using the colorimetric camera 42 having a configuration in which the reference chart unit 400 is omitted. Colorimetric values may be calculated. Further, instead of the colorimetric camera 42, the colorimetric value of the patch 200 can be calculated by a reflection type colorimetric device having a simple configuration including a light source and a plurality of light receiving elements having sensitivity for each color. In these cases, the process (step S10 in FIG. 10) for converting the colorimetry target RGB values into the initialization colorimetry target RGB values is omitted, and the basic colorimetry process (steps in FIG. 10) is performed on the colorimetry target RGB values. S20, FIG. 12 and FIG. 13) are performed.

<Specific example of a reflection type colorimetry device>
15-1 and 15-2 are diagrams illustrating an example of the mechanical configuration of the reflective colorimetric device 30, and FIG. 15-1 is a longitudinal sectional view of the reflective colorimetric device 30, FIG. 15-2. These are bottom views of the reflective colorimetric device 30.

  As shown in FIG. 15A, the reflective colorimetric device 30 has a configuration in which an illumination unit 32, a light receiving unit 33, and a light shielding wall 34 are mounted on a substrate 31 fixed to the carriage 5. As illustrated in FIG. 15B, the illumination unit 32 is configured by combining a white LED light source 32a and a blue-green LED light source 32b. The light receiving unit 33 is configured by combining a plurality of light receiving elements 33a, 33b, and 33c having different spectral sensitivities (RGB sensitivities). In the example of FIG. 15B, the light receiving unit 33 is configured by a combination of a light receiving element 33a having high R sensitivity, a light receiving element 33b having high G sensitivity, and a light receiving element 33c having high B sensitivity. In addition to the light receiving elements 33a, 33b, and 33c, the light receiving unit 33 may be configured by further combining light receiving elements having spectral sensitivities of other colors such as gray, cyan, and orange.

  As shown by the arrow in FIG. 15A, the reflective colorimetric device 30 irradiates the patch 200 formed on the recording medium 16 with illumination light from the illumination unit 32 and is reflected by the patch 200. By making the reflected light enter the light receiving unit 33, the color data of the patch 200 is acquired. The light shielding wall 34 is disposed on the substrate 31 so as to surround each of the illumination unit 32 and the light receiving unit 33, blocks the influence of external light, and the illumination light from the illumination unit 32 directly enters the light receiving unit 33. It has a function to prevent (block stray light).

  FIG. 16 is a block diagram showing a schematic configuration of a control mechanism of the reflection type colorimetric device 30. In addition to the illumination unit 32 and the light receiving unit 33, the reflection type colorimetric device 30 includes an amplifier 35, an AD conversion unit 36, a colorimetric value calculation unit 37, a nonvolatile memory 38, and a light source drive control unit 39.

  Each light receiving element 33a, 33b, 33c of the light receiving unit 33 outputs an RGB signal corresponding to the amount of received light. The RGB signals recorded from the light receiving elements 33 a, 33 b, and 33 c are amplified by the amplifier 35, converted into a digital value by the AD converter 36, and input to the colorimetric value calculator 37. The colorimetric value calculator 37 calculates the colorimetric value of the patch 200 using the nonvolatile memory 38, similarly to the colorimetric value calculator 52 of the colorimetric camera 42. However, the process (step S10 in FIG. 10) of converting the colorimetric object RGB values into the initialization colorimetric object RGB values in the colorimetry method described above is omitted, and the basic colorimetric process (step S10 in FIG. 10) is performed. Step S20 of FIG. 10, FIG. 12, and FIG. 13) are performed. The light source drive control unit 39 controls the operations of the white LED light source 32a and the blue-green LED light source 32b of the illumination unit 32, similarly to the light source drive control unit 55 of the colorimetric camera 42.

<Details of lighting unit>
Next, details of the illumination unit 426 of the colorimetric camera 42 will be described. In the following description, the illumination unit 426 of the colorimetric camera 42 is described. However, the following description also applies to the illumination unit 32 of the reflective colorimetric device 30 described above.

  As described above, the illumination unit 426 is configured by combining the white LED light source 426a and the blue-green LED light source 426b. The reason why the white LED light source 426a and the blue-green LED light source 426b are combined is that the output of the wavelength range in which the output of the two-dimensional image sensor 431 cannot be appropriately obtained only by the illumination by the white LED light source 426a is obtained by the illumination by the blue-green LED light source 426b. This is to compensate.

  FIG. 17 is a cross-sectional view showing an example of the white LED light source 426a. The white LED light source 426a has, for example, a 500 × 500 μm GaN-based blue LED element 501 (emission wavelength: around 450 nm) mounted on a printed circuit board 502, and a yellow phosphor 503 is applied around the GaN-based blue LED element 501. The configuration is adjusted so that pseudo white light is emitted by blue and yellow (also referred to as pseudo white LED). A part of the light from the GaN blue LED element 501 is reflected by the reflecting plate 504, and is extracted to the outside as pseudo white light. The white LED light source 426a only needs to emit substantially white light and does not necessarily have a configuration using the GaN-based blue LED element 501.

  FIG. 18 is a diagram showing the light emission intensity distribution of the white LED light source 426a. The horizontal axis indicates the relative light emission intensity when the wavelength is on the horizontal axis and the highest light emission intensity is 1 on the vertical axis. As shown in FIG. 18, the emission intensity distribution of the white LED light source 426a has a peak with a large emission intensity around 450 nm, which is the emission wavelength of the blue LED element 501 as a base, and a yellow phosphor 503 is applied. Therefore, it has a peak of emission intensity even at a wavelength near 550 nm. Thus, the white LED element 426a emits pseudo white light having a plurality of peak wavelengths in a wavelength range of 380 nm to 780 nm, which is known as a human visible light range. However, since the pseudo white light has a wavelength range in which the relative light emission intensity is low (in the example of FIG. 18, the wavelength is around 500 nm), the illumination using only the white LED light source 426a reproducibility of the illuminated object. Insufficient color rendering properties.

  FIG. 19 is a diagram showing the spectral sensitivity of the two-dimensional image sensor 431 (in this case, a CMOS sensor). The horizontal axis indicates the relative sensitivity when the wavelength is on the horizontal axis and the highest sensitivity is 1 on the vertical axis. 20 is a diagram showing the total spectral sensitivity obtained by multiplying the emission intensity distribution of the white LED light source 426a shown in FIG. 18 and the spectral sensitivity of the two-dimensional image sensor 431 shown in FIG. The wavelength and the vertical axis indicate the total spectral sensitivity. The total spectral sensitivity reflects the characteristics of both the light source and the sensor, and is correlated with the S / N of the output of the two-dimensional image sensor 431. That is, the output of the two-dimensional image sensor 431 has a relatively high S / N in the wavelength range where the total spectral sensitivity is high and a relatively low S / N in the wavelength range where the total spectral sensitivity is low.

  When only the white LED light source 426a is used as the illumination unit 426, the white LED light source 426a has a characteristic that the relative light emission intensity decreases in the vicinity of the wavelength of 500 nm (see FIG. 18). Therefore, as shown in FIG. The overall spectral sensitivity decreases in the wavelength range. That is, in the vicinity of the wavelength of 500 nm, the total spectral sensitivity is 0.1 or less (predetermined value or less). Therefore, when only the white LED light source 426a is used as the illumination unit 426, the S / N of the output of the two-dimensional image sensor 431 decreases in the wavelength range near the wavelength of 500 nm, and the patch 200 having a color in this wavelength range. There is a possibility that the colorimetric accuracy of the image quality is lowered. Therefore, in the present embodiment, the illumination unit 426 is configured by combining the blue-green LED light source 426b having a peak wavelength in the wavelength range near the wavelength of 500 nm with the white LED light source 426a. The total spectral sensitivity is 0.1 or less (predetermined value or less) even in the wavelength range of 440 nm or less and the wavelength range of 640 or more, but these ranges hardly affect the colorimetry of the patch 200. You can ignore it.

  FIG. 21 is a diagram showing the light emission intensity distribution of the blue-green LED light source 426b. The horizontal axis shows the relative light emission intensity when the wavelength is on the horizontal axis and the highest light emission intensity is 1 on the vertical axis. As shown in FIG. 21, the blue-green LED light source 426b is a light source having an emission intensity peak in the vicinity of 500 nm. That is, the blue LED light source 426b is a light source having a peak wavelength in a wavelength range in which the total spectral sensitivity shown in FIG. 20 is 0.1 (predetermined value) or less. Therefore, by combining the blue-green LED light source 426b with the white LED light source 426a to form the illumination unit 426, the S / N of the output of the two-dimensional image sensor 431 can be improved and the colorimetric accuracy of the patch 200 can be improved. it can.

  FIG. 22 is a diagram showing the total spectral sensitivity obtained by multiplying the emission intensity distribution of the blue-green LED light source 426b shown in FIG. 21 and the spectral sensitivity of the two-dimensional image sensor 431 shown in FIG. The vertical axis indicates the total spectral sensitivity. FIG. 23 is a diagram showing the overall spectral sensitivity when using the illumination unit 426 in which the white LED light source 426a and the blue-green LED light source 426b are combined. The overall spectral sensitivity shown in FIG. 20 and the overall spectral sensitivity shown in FIG. This is the total spectral sensitivity.

  As shown in FIG. 23, by using an illuminating unit 426 that combines a white LED light source 426a and a blue-green LED light source 426b, particularly in the vicinity of 500 nm as compared with the case of using only the white LED light source 426a (see FIG. 20) It can be seen that the total spectral sensitivity of the patch 200 is improved and the colorimetric accuracy of the patch 200 can be improved.

  In the present embodiment, the blue-green LED light source 426b having the emission intensity distribution shown in FIG. 21 is used in combination with the white LED light source 426a capable of obtaining the total spectral sensitivity shown in FIG. However, if the light emission intensity distribution of the white LED light source 426a and the spectral sensitivity of the two-dimensional image sensor 431 are different, the above-described total spectral sensitivity value is also different. For this reason, what is necessary is just to determine the light source combined with the white LED light source 426a according to the total spectral sensitivity obtained by a combination. That is, a light source having a peak wavelength in a wavelength region where the total spectral sensitivity obtained by multiplying the emission intensity distribution of the white LED light source 426a and the spectral sensitivity of the two-dimensional image sensor 431 is equal to or less than a predetermined value is combined with the white LED light source 426a. The lighting unit 426 may be configured.

  When the illumination unit 426 is configured by combining the white LED light source 426a and the blue-green LED light source 426b, the following two methods can be considered as illumination methods by the illumination unit 426. One is a method of turning on the white LED light source 426a and the blue-green LED light source 426b alternately (hereinafter referred to as individual lighting). The other is a method of lighting the white LED light source 426a and the blue-green LED light source 426b at the same time (hereinafter referred to as simultaneous lighting).

  In the case of individual lighting, for example, first, the white LED light source 426a is turned on, and R, G, B three-band data is acquired from the two-dimensional image sensor 431. Next, the blue-green LED light source 426b is turned on to acquire one-band data of B (hereinafter, referred to as B 'in distinction from B when the white LED light source 426a is turned on) from the two-dimensional image sensor 431. Then, the colorimetric values of the patch 200 are calculated using the four band data of R, G, B, and B ′. In this case, in the specific example of the color measurement method described above, RGB values are handled as 4-band data of R, G, B, and B ′. That is, the above-described reference RGB value, initial reference RGB value, colorimetric object RGB value, colorimetric time reference RGB value, and initialization colorimetric object RGB value are respectively four-band data of R, G, B, and B ′. Become.

  In the case of individual lighting, since it is necessary to illuminate twice in order to calculate the colorimetric value of one patch 200, the processing time becomes long. Further, by handling the RGB values as 4-band data, the calculation amount of the colorimetric value calculation unit 52 for calculating the colorimetric values of the patch 200 increases. However, since the amount of information for calculating the colorimetric value increases, it can be expected to improve the colorimetric accuracy. In this example, the B data B ′ of the output of the two-dimensional image sensor 431 when the blue-green LED light source 426b is turned on is used as 4-band data, but the blue-green LED light source 426b is turned on. Of the outputs of the two-dimensional image sensor 431, G data G ′ may be used to obtain 4-band data.

  In the case of simultaneous lighting, the white LED light source 426a and the blue-green LED light source 426b are turned on simultaneously, and R, G, B three-band data is acquired from the two-dimensional image sensor 431. Then, the colorimetric values of the patch 200 are calculated using the three band data of R, G, and B. In the case of simultaneous lighting, it is possible to expect a reduction in processing time and a load reduction in the colorimetric calculation unit 52 than in the case of individual lighting.

  As described above, in the colorimetric camera 42 of the present embodiment, the white LED light source 426a is used as the illumination unit 426 that illuminates the patch 200 and the reference chart unit 400 when imaging the patch 200 and the reference chart unit 400 to be measured. And a combination of blue and green LED light sources 426b are used. The blue-green LED light source 426b is a light source having a peak wavelength in a wavelength range in which the total spectral sensitivity obtained by multiplying the emission intensity distribution of the white LED light source 426a and the spectral sensitivity of the two-dimensional image sensor 431 is a predetermined value or less. Accordingly, when only the white LED light source 426a is used, in the wavelength range where the S / N of the output of the two-dimensional image sensor 431 is not sufficient, the blue / green LED light source 426b can supplement the output to improve the S / N. The colorimetric accuracy of the patch 200 can be increased.

The ν factor is known as one of spectral characteristic evaluation methods for color input systems (see the following reference). The ν factor takes a value between 0 and 1, and the closer to 1, the better the spectral characteristics of the color input system (the colorimetric camera 42 in this embodiment).
Reference: edited by the Institute of Image Electronics Engineers, supervised by Naoto Kawamura + Fumitaka Ono, “Color Management Technology Extended Color Space and Color Appearance”, Tokyo Denki University Press, p. 50-52, “3.3.2 Quality evaluation index of color input system”

  FIG. 24 is a diagram illustrating a result of calculating the ν factor in each of the case where only the white LED light source 426a is used for the illumination unit 426 and the case where the combination of the white LED light source 426a and the blue-green LED light source 426b is used. The white bar graph in the figure indicates the ν factor when only the white LED light source 426a is used, and the hatched bar graph indicates the ν factor when the combination of the white LED light source 426a and the blue-green LED light source 426b is used. Is shown. For the calculation of the ν factor, p. The formula (3.25) described in 52 was used. Here, two white LEDs from different manufacturers are assumed as the white LED light source 426a, and for each white LED, the ν factor when only the white LED is used, and the blue-green LED light source 426b are combined. The calculation results of the ν factor are shown separately on the left and right in the figure.

  As shown in FIG. 24, both of two white LEDs from different manufacturers have a higher ν factor when used in combination with blue-green LEDs than when only white LEDs are used. From this result, the spectral of the colorimetric camera 42 is better when the combination of the white LED light source 426a and the blue-green LED light source 426b is used as the illumination unit 426 of the colorimetric camera 42 than when only the white LED light source 426a is used. It was confirmed that the characteristics were improved and the colorimetric accuracy of the patch 200 could be improved.

<Modification of colorimetric camera>
Next, a modified example of the colorimetric camera 42 will be described. In the following description, the color measurement camera 42 of the first modification is represented as a color measurement camera 42A, the color measurement camera 42 of the second modification is represented as a color measurement camera 42B, and the color measurement camera 42 of the third modification is measured. The color measurement camera 42C is described, the color measurement camera 42 of the fourth modification example is expressed as a color measurement camera 42D, the color measurement camera 42 of the fifth modification example is expressed as a color measurement camera 42E, and the color measurement camera of the sixth modification example. The camera 42 is referred to as a colorimetric camera 42F. In each modified example, the same reference numerals are given to the same components as those of the colorimetric camera 42 described above, and a duplicate description is omitted.

<First Modification>
FIG. 25 is a longitudinal sectional view of the colorimetric camera 42A of the first modified example, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG.

  In the color measurement camera 42 </ b> A of the first modified example, an opening 427 different from the opening 425 for imaging the color measurement target patch 200 is provided on the bottom surface 421 a of the housing 421. And the chart board 410 is arrange | positioned so that this opening part 427 may be obstruct | occluded from the outer side of the housing | casing 421. FIG. That is, in the colorimetric camera 42 described above, the chart plate 410 is disposed on the inner surface side facing the sensor unit 430 of the bottom surface part 421a of the housing 421, whereas in the colorimetric camera 42A of the first modification example. The chart plate 410 is disposed on the outer surface of the bottom surface 421a of the housing 421 facing the recording medium 16.

  Specifically, for example, a recess having a depth corresponding to the thickness of the chart plate 410 is formed on the outer surface side of the bottom surface portion 421 a of the housing 421 so as to communicate with the opening 427. And in this recessed part, the chart board 410 is arrange | positioned with the surface in which the reference | standard chart part 400 was formed facing the sensor part 430 side. For example, the chart plate 410 is joined to the bottom surface portion 421a of the housing 421 by an adhesive or the like near the edge of the opening 427 and integrated with the housing 421.

  In the color measurement camera 42A of the first modified example configured as described above, the color measurement described above is performed by arranging the chart plate 410 on which the reference chart portion 400 is formed on the outer surface side of the bottom surface portion 421a of the housing 421. Compared with the camera 42, the difference between the optical path length from the sensor unit 430 to the patch 200 and the optical path length from the sensor unit 430 to the reference chart unit 400 is small. Therefore, even when the depth of field of the sensor unit 430 is relatively shallow, it is possible to capture an image focused on both the patch 200 and the reference chart unit 400.

<Second Modification>
FIG. 26 is a longitudinal sectional view of the colorimetric camera 42B of the second modification, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG.

  In the colorimetric camera 42B of the second modified example, the chart plate 410 is disposed on the outer surface side of the bottom surface portion 421a of the housing 421, similarly to the colorimetric camera 42A of the first modified example. However, in the colorimetric camera 42A of the first modified example, the chart plate 410 is joined to the bottom surface portion 421a of the housing 421 by an adhesive or the like and integrated with the housing 421, whereas the second modified example. In the colorimetric camera 42B, the chart plate 410 is detachably held with respect to the housing 421.

  Specifically, for example, similarly to the color measurement camera 42A of the first modified example, a recess communicating with the opening 427 is formed on the outer surface side of the bottom surface portion 421a of the housing 421, and the chart plate 410 is disposed in the recess. Has been placed. Further, the color measurement camera 42B of the second modification includes a holding member 428 that holds the chart plate 410 disposed in the recess from the outer surface side of the bottom surface portion 421a of the housing 421. The holding member 428 is detachably attached to the bottom surface portion 421a of the housing 421. Therefore, in the colorimetric camera 42B of the second modified example, the chart plate 410 can be taken out by removing the holding member 428 from the bottom surface portion 421a of the housing 421.

  As described above, in the colorimetric camera 42B of the second modified example, the chart plate 410 is detachably held from the housing 421, and the chart plate 410 can be taken out. When the chart plate 410 is deteriorated, an operation of replacing the chart plate 410 can be easily performed. Further, when the above-described shading correction unit 452 obtains shading data for correcting illuminance unevenness by the illumination light source 426, the chart plate 410 is taken out and a white reference plate is placed instead, and the white reference plate is used as the sensor unit 430. If the image is picked up, shading data can be easily acquired.

<Third Modification>
FIG. 27 is a longitudinal sectional view of a colorimetric camera 42C of the third modification, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG. 4-1.

  In the color measurement camera 42C of the third modified example, the housing 421 is provided with an opening 425C that opens widely from the bottom surface 421a to the side wall, and the patch 200 is imaged through the opening 425C. That is, in the colorimetric camera 42 described above, the external light traveling toward the colorimetric target patch 200 is blocked by the housing 421 so that the patch 200 is illuminated only by the illumination light from the illumination light source 426. The opening 425 for imaging the patch 200 is provided so as to open only at the bottom surface 421 a of the housing 421. On the other hand, the color measurement camera 42C of the third modified example has an opening 425C that opens widely from the bottom surface 421a of the housing 421 to the side wall on the premise that the color measurement camera 42C is disposed in an environment where external light does not enter. Is provided.

  For example, as shown in FIG. 1, the exterior body 1 in a state where the cover member 2 is closed can be set in an environment where outside light does not enter. Since the colorimetric camera 42C is mounted on the carriage 5 disposed inside the exterior body 1, it can be disposed in an environment where external light does not enter. Therefore, the patch 200 can be illuminated only by the illumination light from the illumination light source 426 even when the opening 425C that opens greatly from the bottom surface 421a of the housing 421 to the side wall is provided.

  As described above, the color measurement camera 42C according to the third modified example is provided with the opening 425C that greatly opens from the bottom surface 421a to the side wall, so that the housing 421 can be reduced in weight and power consumption can be reduced. Can be reduced.

<Fourth Modification>
FIG. 28A is a longitudinal sectional view of a colorimetric camera 42D of the fourth modified example, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG. FIG. 28-2 is a plan view of the bottom surface portion 421a of the housing 421 when viewed from the X3 direction in FIG. 28-1. In FIG. 28-2, the vertical projection position of the illumination light source 426 on the bottom surface portion 421a of the housing 421 (the position projected when looking down perpendicular to the bottom surface portion 421a) is indicated by a broken line.

  In the color measurement camera 42D of the fourth modified example, the bottom surface portion 421a of the housing 421 is positioned on a vertical line that is perpendicular to the bottom surface portion 421a from the sensor portion 430 (that is, the optical axis center of the sensor portion 430). Thus, an opening 425D is provided, and the colorimetric target patch 200 is imaged through the opening 425D. That is, in the colorimetric camera 42D of the fourth modified example, the opening 425D for imaging the patch 200 outside the housing 421 is provided so as to be positioned substantially at the center in the imaging range of the sensor unit 430.

  In the colorimetric camera 42D of the fourth modified example, the chart plate 410D on which the reference chart portion 400 is formed is disposed on the bottom surface portion 421a of the housing 421 so as to surround the opening 425D. For example, the chart plate 410D is formed in an annular shape centering on the opening 425D, and the inner surface side of the bottom surface portion 421a of the housing 421 with the surface opposite to the surface on which the reference chart portion 400 is formed as an adhesive surface It is adhered to the housing 421 and held in a fixed state with respect to the housing 421.

  Further, in the colorimetric camera 42D of the fourth modified example, four LEDs arranged at the four corners on the inner peripheral side of the frame body 422 constituting the side wall of the housing 421 are used as the illumination light source 426. These four 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. By arranging the four LEDs used as the illumination light source 426 in this manner, the patch 200 to be measured and the reference chart unit 400 can be illuminated under substantially the same conditions.

  In the color measurement camera 42D of the fourth modified example configured as described above, an opening 425D for imaging a subject (patch 200) outside the housing 421 is provided, and a sensor unit 430 in the bottom surface 421a of the housing 421. Since the chart plate 410D on which the reference chart portion 400 is formed is disposed so as to be provided on the vertical line from the base plate and further surround the opening 425D, the imaging of the patch 200 to be measured and the reference chart portion 400 is performed. Can be performed appropriately.

<Fifth Modification>
FIG. 29 is a longitudinal sectional view of a colorimetric camera 42E of a fifth modification, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG. 4-1.

  In the color measurement camera 42E of the fifth modification example, four LEDs arranged at the four corners on the inner peripheral side of the frame 422 are used as the illumination light source 426, as in the color measurement camera 42D of the fourth modification example. However, in the colorimetric camera 42E of the fifth modified example, the illumination light source is set so that the specularly reflected light that is regularly reflected by the colorimetric target patch 200 and the reference chart unit 400 does not enter the two-dimensional image sensor 431 of the sensor unit 430. These four LEDs used as 426 are arranged closer to the bottom surface portion 421a of the housing 421 than the colorimetric camera 42D of the fourth modified example.

  On the sensor surface of the two-dimensional image sensor 431 of the sensor unit 430, accurate information may not be obtained at the position where the specularly reflected light of the illumination light source 426 enters because the pixel value is saturated. For this reason, if the illumination light source 426 is disposed at a position where the specularly reflected light that is specularly reflected by the color measurement target patch 200 or the reference chart unit 400 enters the two-dimensional image sensor 431 of the sensor unit 430, There is a concern that information necessary for colorimetry may not be obtained. Therefore, in the color measurement camera 42E of the fifth modified example, as shown in FIG. 29, these four LEDs used as the illumination light source 426 are arranged at positions close to the bottom surface portion 421a of the housing 421, so The regular reflection light regularly reflected by the patch 200 or the reference chart unit 400 is prevented from entering the two-dimensional image sensor 431 of the sensor unit 430. Note that the one-dot chain line arrow in FIG. 29 is an image of the optical path of specularly reflected light.

  As described above, in the colorimetric camera 42E of the fifth modified example, the specularly reflected light that is specularly reflected by the colorimetric target patch 200 and the reference chart unit 400 does not enter the two-dimensional image sensor 431 of the sensor unit 430. Since the illumination light source 426 is disposed, saturation of pixel values at positions where the optical image of the patch 200 and the reference chart unit 400 is formed on the sensor surface of the two-dimensional image sensor 431 is effectively suppressed, and the patch 200 and The reference chart unit 400 can be appropriately imaged.

  It should be noted that the color measurement camera 42E of the fifth modification example has the same opening 425D and chart plate 410D as those of the color measurement camera 42D of the fourth modification example. The example in which the illumination light source 426 is arranged at a position where the reflected regular reflected light does not enter the two-dimensional image sensor 431 of the sensor unit 430 has been described. However, in the configuration of the colorimetric camera 42, the colorimetric camera 42A of the first modified example, the colorimetric camera 42B of the second modified example, and the colorimetric camera 42C of the third modified example described above, the patch 200 and the reference to be measured. The illumination light source 426 may be arranged at a position where the regular reflection light regularly reflected by the chart unit 400 does not enter the two-dimensional image sensor 431 of the sensor unit 430. In this case, the same effect as that of the colorimetric camera 42E of the fifth modification can be obtained.

<Sixth Modification>
FIG. 30 is a longitudinal sectional view of a colorimetric camera 42F of a sixth modification, and is a sectional view at the same position as the longitudinal sectional view of the colorimetric camera 42 shown in FIG. 4-1.

  In the colorimetric camera 42F of the sixth modified example, 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 (color measurement target patch 200) outside the housing 421 and the sensor unit 430, and the imaging surface of the optical image of the patch 200 is used as the reference chart unit 400. It has a function to bring the optical image closer to the image plane. That is, in the color measurement camera 42F of the sixth modification, the optical path length changing member 440 is arranged in the optical path between the patch 200 to be measured and the sensor unit 430, so that the patch 200 outside the housing 421 Both the image formation surface of the optical image and the image formation surface of the reference chart unit 400 inside the housing 421 are matched with the sensor surface of the two-dimensional image sensor 431 of the sensor unit 430. FIG. 30 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 does not necessarily have to be placed on the bottom surface portion 421a. As long as it is disposed in the optical path between the patch 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)

Further, assuming that the distance between the principal point of the imaging lens 432 of the sensor unit 430 and the reference chart unit 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 (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 that the difference between the distance from the sensor unit 430 to the reference chart unit 400 and the distance to the patch 200 is 3 mm. If the image is taken, the rear focal plane (imaging plane) of the optical image of the reference chart unit 400 and the rear focal plane (imaging plane) of the optical image of the patch 200 are both two-dimensional image sensors of the sensor unit 430. 431 can be matched to the sensor surface.

  In the color measurement camera 42F of the sixth modified example configured as described above, the optical path length changing member 440 is disposed in the optical path between the color measurement target patch 200 and the sensor unit 430, so that the optical of the patch 200 is obtained. Since the imaging plane of the image is brought close to the imaging plane of the optical image of the reference chart unit 400, an appropriate image focused on both the patch 200 and the reference chart unit 400 can be captured.

<Modification of patch colorimetry method>
Next, a modification of the color measurement method of the patch 200 will be described with reference to FIGS. FIG. 31 is a diagram illustrating an example of image data obtained by simultaneously imaging the color measurement target patch 200 and the reference chart unit 400. FIG. 32 is a diagram for explaining a modification of the color measurement method of the patch 200. FIG. 33 is a diagram showing a conversion formula for converting between Lab values and XYZ values. FIG. 34 is a flowchart showing the color measurement procedure of the patch 200. FIG. 35 is a flowchart illustrating another example of the colorimetric procedure for the patch 200. FIG. 36 is a diagram for explaining a method of specifying RGB values corresponding to Lab standard values of patches.

  When performing color measurement of the patch 200, first, the recording medium 16 on which a test pattern including a plurality of patches 200 is formed is set on the platen 22. Then, the colorimetric camera 42 is sequentially moved to a position facing each patch 200 to be measured by intermittent conveyance of the recording medium 16 in the sub-scanning direction and movement of the carriage 5 in the main scanning direction. The sensor unit 430 of the colorimetric camera 42 picks up the patch 200 together with the reference chart unit 400 on the chart plate 410 disposed in the housing 421 when the colorimetric camera 42 is at a position facing the patch 200. To do. As a result, for example, image data including the patch 200 and the reference chart unit 400 as illustrated in FIG. 31 is acquired. The imaging range of the sensor unit 430 includes a reference chart imaging region for imaging the reference chart unit 400 and a subject imaging region for imaging the patch 200 that is a subject to be colorimetric. The image data output from the pixels corresponding to the reference chart imaging area is the image data of the reference chart unit 400, and the image data output from the pixels corresponding to the subject imaging area is the image data of the patch 200.

  Image data of the patch 200 and the reference chart unit 400 captured by the sensor unit 430 is stored in the frame memory 51 after necessary image processing is performed inside the two-dimensional image sensor 431. Then, the colorimetric value calculation unit 52 reads the image data stored in the frame memory 51 and calculates the colorimetric value of the patch 200.

  First, the colorimetric value calculation unit 52 uses the chart position specifying markers 407 at the four corners of the distance measurement lines (main scanning / sub-scanning distance reference lines) 405 of the reference chart unit 400 from the image data read from the frame memory 51. Is specified by pattern matching or the like. Thereby, the position of the reference chart portion 400 in the image data can be specified. After specifying the position of the reference chart unit 400, the position of each patch of the reference chart unit 400 is specified.

  Next, the colorimetric value calculation unit 52 uses the image data (RGB value) of each patch of the reference chart unit 400 to display the image data (RGB value) of the patch 200 to be colorimetrically displayed in the Lab color space. It is converted into a Lab value that is a color value. Hereinafter, a specific method of this conversion will be described in detail.

  FIG. 32C shows the Lab values of the patches in the primary color (YMC) reference patch row 401 and the secondary color (RGB) reference patch row 402 of the reference chart unit 400 shown in FIG. It is plotted in space. Note that the Lab value of each patch is measured in advance and stored in, for example, the nonvolatile memory 53 mounted on the substrate 423 of the colorimetric camera 42.

  FIG. 32A shows the RGB values (obtained by imaging) of the patches of the primary color (YMC) reference patch row 401 and the secondary color (RGB) reference patch row 402 of the reference chart section 400 shown in FIG. Image data) is plotted on the RGB color space.

  FIG. 32B is a graph in which the Lab value shown in FIG. 32C is converted into an XYZ value using a predetermined conversion formula, and the converted XYZ value is plotted on the XYZ color space. When converting a Lab value to an XYZ value, it can be converted by a conversion formula (Lab → XYZ) shown in FIG. Further, when converting an XYZ value into a Lab value, it can be converted by a conversion formula (XYZ⇒Lab) shown in FIG. That is, the Lab value shown in FIG. 32C and the XYZ value shown in FIG. 32B can be converted into each other using the conversion formulas shown in FIGS.

  A procedure for converting the RGB values of the colorimetric target patch 200 obtained from the subject imaging region shown in FIG. 31 into Lab values will be described with reference to the flowchart of FIG. It is assumed that the RGB value of the patch 200 to be measured is at the Prgb point in the RGB color space shown in FIG. In this case, first, the nearest four points that can form a tetrahedron including the Prgb point are searched from among the RGB values of each patch of the reference chart unit 400 shown in FIG. 31 (step S1). In the example of FIG. 32A, four points p0, p1, p2, and p3 are selected. Here, the coordinate values of the four points p0, p1, p2, and p3 in the RGB color space shown in FIG. 32A are represented by p0 (x01, x02, x03), p1 (x1, x2, x3), and p2 ( x4, x5, x6) and p3 (x7, x8, x9).

  Next, the four points q0, q1, q2, and q3 on the XYZ color space shown in FIG. 32 (b) corresponding to the four points p0, p1, p2, and p3 on the RGB color space shown in FIG. 32 (a) are searched. (Step S2). The coordinate values of the four points q0, q1, q2, and q3 on the XYZ color space are expressed as q0 (y01, y02, y03), q1 (y1, y2, y3), q2 (y4, y5, y6), and q3 (y7). , Y8, y9).

  Next, a linear transformation matrix for linearly transforming the local space in the tetrahedron is obtained (step S3). Specifically, among the four points p0, p1, p2, and p3 in the RGB color space, an arbitrary pair of corresponding points is determined (in this embodiment, p0 and q0 closest to the achromatic color). The corresponding point (p0, q0) is the origin (the coordinate values of p1 to p3 and q1 to q3 are relative values from p0 and q0).

Assuming that the conversion equation between the RGB color space shown in FIG. 32A and the XYZ color space shown in FIG. 32B can be linearly converted to Y = AX, the following equation (1) is obtained. The

Here, assuming that p1 → q1, p2 → q2, and p3 → q3, each coefficient a can be obtained as in the following formulas (2) to (10).

Next, using this linear transformation matrix (Y = AX), Prgb points (coordinate values of (Pr, Pg,...)) Are RGB values of the patch 200 to be measured in the RGB color space shown in FIG. Pb)) is mapped onto the XYZ color space shown in FIG. 32B (step S4). Since the XYZ value obtained here is a relative value from the origin q0, an actual XYZ value Pxyz (coordinate values are (Px, Py, Pz)) corresponding to the RGB value Prgb of the patch 200 to be measured. As an offset value from the origin q0 (y01, y02, y03), the following equations (11) to (13) are obtained.

  Next, the XYZ value Pxyz of the patch 200 obtained as described above is converted into a Lab value by the conversion formula shown in FIG. 33A, and the Lab value corresponding to the RGB value Prgb of the patch 200 to be measured is obtained. Obtained (step S5). As a result, even when the sensitivity of the sensor unit 430 changes or the wavelength or intensity of the illumination light source 426 changes, the colorimetric value of the patch 200 to be colorimetric can be obtained accurately, and high-precision colorimetry is achieved. It can be performed.

  Note that FIG. 32C used in the processing operation described above shows the reference patch row 401 for the primary color (YMC) and the reference patch row 402 for the secondary color (RGB) in the reference chart section 400 shown in FIG. The Lab value of each patch is plotted on the Lab color space. Since the reference chart unit 400 shown in FIG. 5 is formed on the chart plate 410 arranged inside the housing 421 of the colorimetric camera 42, the number of patches constituting the reference chart unit 400 is limited. become. Therefore, the reference chart unit 400 shown in FIG. 5 is configured by using some patches selected from the standard patches. For example, Japan Color has 928 colors, and the reference chart unit 400 shown in FIG. 5 is configured using a part (for example, 72 colors) selected from the 928 colors. However, when color measurement is performed using only a part of patches selected from the standard patches, there is a concern that the accuracy of color measurement may be reduced. Therefore, it is desirable to infer the RGB value of the standard patch from the RGB values of the patches constituting the reference chart unit 400 and perform the colorimetry of the patch 200 to be measured using the RGB values of the standard patch.

  Specifically, the Lab value of the standard patch is stored, and as shown in FIG. 35, the standard patch patch 400 corresponds to each standard patch based on the RGB value of each patch of the reference chart unit 400 obtained by imaging. The RGB values are specified (step S0), and four points including the RGB values of the colorimetric target patch 200 are searched based on the RGB values of the specified standard patches (step S1 ′).

  As shown in FIG. 36, the RGB value (a) of each patch of the reference chart unit 400 and the Lab value (b) of each patch of the reference chart unit 400 correspond to each other by a conversion formula α (b = A × α), the conversion formula α is calculated based on the RGB values of the patches constituting the reference chart unit 400. In addition, since the Lab value of each patch in the reference chart unit 400 is a part of the Lab value of each standard patch, the RGB value (A) of each standard patch and the Lab value (B) of each standard patch. Corresponds to the conversion equation α (B = A × α). For this reason, the RGB value corresponding to the Lab value of each standard patch can be specified based on the calculated conversion formula α. Thereby, based on the RGB value of each patch of the reference chart unit 400, the RGB value corresponding to the standard Lab value of each patch can be specified.

  Next, based on the XYZ values corresponding to the Lab values of each standard patch, the XYZ values corresponding to the four patches that include the RGB values of the colorimetric target patch 200 are searched (step S2 ').

  Next, a linear transformation matrix is calculated based on the XYZ values corresponding to the four patches searched in step S2 ′ (step S3 ′), and the colorimetric target patch 200 is calculated based on the calculated linear transformation matrix. Are converted into XYZ values (step S4 ′). Next, the XYZ value converted in step S4 'is converted into a Lab value using the conversion formula described above (step S5'). Thereby, the Lab value of the patch 200 to be measured can be obtained based on the RGB value and XYZ value of each standard patch, and the color measurement of the patch 200 can be performed with high accuracy. Note that the standard patch is not limited to Japan Color, and it is also possible to use standard colors such as SWOP used in the US and Euro Press used in Europe.

<Other variations>
In the above-described embodiment, the colorimetric camera 42 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 42. 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 42 is configured to send image data obtained by simultaneously capturing the patch 200 and the reference chart unit 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 42 is moved to a position facing each patch 200 included in the test pattern using the mechanism of the image forming apparatus 100. It may be configured to be separated from the forming apparatus 100 and moved to a position facing each patch 200 included in the test pattern 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 42. 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. 37, 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 52 may be provided in the external device 500 so that the colorimetric values are calculated in the external device 500. That is, the color measurement system includes a color measurement camera 42 provided in the image forming apparatus 100, a color measurement value calculation unit 52 provided in the external device 500, and the color measurement camera 42 and the color measurement value calculation unit 52 (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 image data including a subject such as the patch 200 captured by the colorimetric camera 42 and the reference chart unit 400 to the external apparatus 500 using the communication unit 600. To do. The external apparatus 500 calculates the colorimetric value of the patch 200 using the image data received from the image forming apparatus 100, and the device profile describing the characteristics of the image forming apparatus 100 based on the calculated colorimetric value of the patch 200. Generate or modify 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.

  It should be noted that the control functions of the respective parts constituting the image forming apparatus 100 and the colorimetric apparatus according to the present embodiment described above can be realized using hardware, software, or a combined configuration of both. When the control functions of the respective units constituting the image forming apparatus 100 and the color measurement device according to the present embodiment are realized by software, the processor included in the image formation device 100 or the color measurement device executes a program describing a processing sequence. 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 30 Reflective color measuring device 32 Illumination part 32a White LED light source 32b Blue-green LED light source 33 Light-receiving part 37 Colorimetric value calculating part 42, 42A, 42B, 42C, 42D, 42E, 42F Colorimetric camera 52 Colorimetric value calculating part 100 Image forming apparatus 200 Patch 400 Reference chart unit 426 Illumination unit 426a White LED light source 426b Blue-green LED light source 430 Sensor unit 431 Two-dimensional image sensor

JP 2012-63270 A

Claims (9)

A first light source having a plurality of peak wavelengths in a wavelength range of 380 nm to 780 nm;
A second light source;
The reflected light of the light from the first light source reflected by the object and the reflected light of the light from the second light source reflected by the object are received, and the color data of the object is output. A sensor,
The second light source has a peak wavelength in at least one of a wavelength range in which the total spectral sensitivity, which is a value obtained by multiplying the emission intensity distribution of the first light source and the spectral sensitivity of the sensor, is a predetermined value or less. Characteristic color detection device. It further comprises a reference chart portion having a plurality of patches,
The color detection apparatus according to claim 1, wherein the sensor is a two-dimensional image sensor that outputs image data of an area including the object and the reference chart as the color data. A plurality of illumination units including the first light source and the second light source;
The color detection apparatus according to claim 2, wherein the plurality of illumination units are arranged at positions symmetrical with respect to the two-dimensional image sensor.   The first light source and the second light source are respectively disposed at positions where specularly reflected light incident on the two-dimensional image sensor is irradiated to a region between the object and the reference chart unit. The color detection apparatus according to claim 2. A color detection device according to any one of claims 1 to 4,
A colorimetric apparatus comprising: a calculation unit that calculates a colorimetric value of the object based on color data output from the sensor. The first light source and the second light source are alternately turned on,
The calculation unit is configured to calculate the target based on color data output from the sensor when the first light source is turned on and color data output from the sensor when the second light source is turned on. The colorimetric apparatus according to claim 5, wherein the colorimetric value of an object is calculated. The first light source and the second light source are turned on simultaneously;
The said calculation part calculates the colorimetric value of the said object based on the color data which the said sensor outputs when the said 1st light source and the said 2nd light source are lighted simultaneously. 5. A colorimetric apparatus according to 5. A colorimetric device according to any one of claims 5 to 7,
An image output unit for outputting an image to a recording medium,
The image forming apparatus, wherein the object is an image output by the image output unit to the recording medium. A color measurement system comprising the color detection device according to any one of claims 1 to 4 and an external device,
The external device includes a calculation unit that calculates a colorimetric value of the object based on color data output from the sensor of the color detection device.