Image forming apparatus, information processing apparatus, and control method for image forming apparatus

Abstract

To provide an image forming apparatus that can check a hue with high accuracy.SOLUTION: An image forming apparatus 100 comprises: a printer 150 that forms an image on recording paper; a reader 160 that reads the image formed on the recording paper; and a controller 110 that forms an image in a specific color on the recording paper with a printer 150, reads the image in the specific color formed on the recording paper by the reader 160, and on the basis of, a result of reading of the image in the specific color performed by the reader 160, checks a hue of the image in the specific color. The controller 110 creates a color calibration chart for performing color calibration of the reader 160 with the printer 150, creates a color calibration matrix for calibrating a measurement result from the reader 160 on the basis of a result of reading of the color calibration chart performed by the reader 160, and checks the hue by comparing a color difference between a color value of the result of reading of the image in the specific color and a color value of the specific color obtained from the color calibration matrix with a hue check threshold value.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an image forming apparatus having a function of inspecting the color tone of an image printed on a printed matter.

Background Art

[0002] Corporate colors used for corporate logos, design marks, etc. are defined as components for identifying a company. Therefore, printed matters containing corporate colors need to have their colors strictly adjusted and managed. In recent years, a color inspection system has been proposed that reads the color of an image on a printed matter during printing and inspects the color tone of the read color. Patent Document 1 discloses an image forming apparatus that performs color management. This image forming apparatus prints a measurement patch for a specific color designated by a user. The image forming apparatus performs color stabilization control based on the result of color measurement of the measurement patch by an image sensor. If the result of color measurement is not within the allowable range, the image forming apparatus notifies the user to that effect and performs color stabilization control again.

[0003] An image sensor used for color measurement of an image printed on a printed matter outputs luminance values (RGB data) of three colors, R (red), G (green), and B (blue), as color measurement results. This RGB data is converted into L, a, and b data in the CIELab color space. A color conversion table, which is a look-up table, is used for the conversion of RGB data into the CIELab color space. Generally, the color conversion table does not register color conversion values for all input values (luminance values of R, G, and B), but only registers color conversion values at a plurality of regularly arranged grid points in the input color space. When performing color conversion using such a color conversion table, color conversion values other than those at the grid points are obtained by interpolation operations based on the color conversion values registered at the grid points (Patent Document 2).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

[0005] Color conversion using a color conversion table is performed by a method of uniformly converting the entire color gamut that can be expressed in three colors of R, G, and B into Lab values. This method performs color conversion at a level without a sense of incongruity for the entire color gamut. However, in a color gamut where Lab easily changes for each color of RGB data, the conversion error becomes large, making it difficult to perform high-precision color inspection.

[0006] The present invention has been made in view of the above problems, and a main object thereof is to provide an image forming apparatus capable of performing high-precision color inspection. [Means for Solving the Problems]

[0007] The image forming apparatus of the present invention includes an image forming unit that forms an image on a recording sheet, a reading unit that reads the image formed on the recording sheet and outputs read data, a specifying unit used to specify a color to be inspected, an inspection unit that inspects whether a color difference between the color of the image read by the reading unit and the color specified by the specifying unit is equal to or less than a threshold value based on a result of converting the read data output by the reading unit based on conversion conditions, and a control unit that causes the image forming unit to form a color calibration chart for color calibration of the reading unit, causes the reading unit and a sensor device to read the color calibration chart, and generates the conversion conditions based on a result of reading the color calibration chart by the reading unit and the sensor device. [Effects of the Invention]

[0008] According to the present invention, high-precision color inspection for a specific color becomes possible. [Brief Description of the Drawings]

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the solution means of the invention.

[0011] (Printing System) FIG. 1 is a configuration explanatory diagram of a printing system including an image forming apparatus according to the present embodiment. The printing system includes an image forming apparatus 100 and a host computer 101. The image forming apparatus 100 and the host computer 101 are communicably connected via a network 105. The network 105 is composed of a communication line such as, for example, a LAN (Local Area Network), a WAN (Wide Area Network), or a public communication line. Note that a plurality of the image forming apparatus 100 and the host computer 101 may be respectively connected to the network 105.

[0012] The host computer 101 is, for example, a server device, and transmits a print job to the image forming apparatus 100 via the network 105. The print job includes various types of information necessary for printing, such as image data, the type of recording paper to be used for printing, the number of printed sheets, and an instruction for double-sided or single-sided printing.

[0013] The image forming apparatus 100 includes a controller 110, an operation panel 120, a paper feeding unit 140, a printer 150, and a reader 160. The controller 110, the operation panel 120, the paper feeding unit 140, the printer 150, and the reader 160 are communicably connected to each other via a system bus 116. The image forming apparatus 100 controls the operation of the printer 150 based on the print job acquired from the host computer 101, and forms an image corresponding to the image data on the recording paper.

[0014] The controller 110 controls the operation of each unit of the image forming apparatus 100. The controller 110 is an information processing apparatus including a ROM (Read Only Memory) 112, a RAM (Random Access Memory) 113, and a CPU (Central Processing Unit) 114. The controller 110 includes a communication control unit 111 and a storage 115. Each module is communicably connected to each other via the system bus 116.

[0015] The communication control unit 111 is a communication interface that communicates with the host computer 101 and other devices via the network 105. The storage 115 is a large-capacity storage device such as an HDD (Hard Disk Drive) or an SSD (Solid State Drive). The storage 115 stores computer programs and various types of data used for image forming processing (printing processing). The CPU 114 executes the computer programs stored in the ROM 112 and the storage 115 to control the operation of the image forming apparatus 100. The RAM 113 provides a work area when the CPU 114 executes the computer program.

[0016] The operation panel 120 is a user interface and includes an input interface and an output interface. The input interface is, for example, operation buttons, a numeric keypad, a touch panel, etc. The output interface is, for example, a display such as an LCD (Liquid Crystal Display), a speaker, etc. The user can input a print job, commands, print settings, etc. into the image forming apparatus 100 via the operation panel 120. The operation panel 120 displays a setting screen and the state of the image forming apparatus 100 on the display.

[0017] The paper feeding unit 140 includes a plurality of paper feeding stages described later for accommodating recording paper. The paper feeding unit 140 feeds paper from a paper feeding stage that accommodates the type of recording paper instructed in the print job. A plurality of sheets of recording paper (a bundle of recording paper) are accommodated in the paper feeding stage, and the paper is fed in order from the topmost recording paper. The paper feeding unit 140 conveys the recording paper fed from the paper feeding stage to the printer 150. The same type of recording paper may be accommodated in each paper feeding stage, or different types of recording paper may be accommodated.

[0018] The printer 150 generates a printed matter by printing an image on the recording paper supplied from the paper feeding unit 140 based on the image data included in the print job. The reader 160 is an image reading device that reads an image from the printed matter generated by the printer 150 and transmits the reading result to the controller 110. The image read by the reader 160 is an image (detection image) for adjusting the image forming conditions when the printer 150 performs image formation. The controller 110 detects the image state such as image quality from the reading result of the detection image by the reader 160, and adjusts the image forming conditions based on the detected image state. In the present embodiment, the image density is detected from the detection image, and the image forming conditions are adjusted based on the detected image density.

[0019] (Image Forming Apparatus) FIG. 2 is a configuration diagram of the image forming apparatus 100. The image forming apparatus 100 includes, in order from the upstream side in the conveyance direction of the recording paper, paper feed stages 140a to 140e, a printer 150, a reader 160, and a finisher 190. The paper feed stages 140a to 140e constitute the paper feeding unit 140. Here, the finisher 190 is a post-processing device that performs post-processing on the printed matter by the printer 150. The finisher 190 performs, for example, staple processing and sorting processing on a plurality of printed matters.

[0020] The printer 150 includes a plurality of image forming units that form images of different colors. The printer 150 of the present embodiment includes four image forming units in order to form images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). Each image forming unit only differs in the color of the image to be formed, and performs the same operations with the same configuration.

[0021] One image forming unit includes a photosensitive drum 153, a charger 220, an exposure device 223, and a developing device 152. The photosensitive drum 153 is a drum-shaped photoreceptor having a photosensitive layer on its surface, and is rotationally driven in the direction of arrow R1 by a motor (not shown). The charger 220 charges the surface (photosensitive layer) of the rotating photosensitive drum 153. The exposure device 223 exposes the charged surface of the photosensitive drum 153 with laser light. The laser light scans the surface of the photosensitive drum 153 in the axial direction of the photosensitive drum 153. The direction in which the laser light scans the surface of the photosensitive drum 153 is the main scanning direction of the printer 150 (the depth direction in FIG. 2). As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 153. The developing device 152 develops the electrostatic latent image using a developer (toner). As a result, an image (toner image) in which the electrostatic latent image is visualized is formed on the surface of the photosensitive drum 153.

[0022] Printer 150 includes an intermediate transfer belt 154 onto which the toner images generated by each image forming unit are transferred. The intermediate transfer belt 154 is rotationally driven in the direction of arrow R2. The toner images of each color are transferred at a timing corresponding to the rotation of the intermediate transfer belt 154. As a result, a full-color toner image in which the toner images of each color are superimposed is formed on the intermediate transfer belt 154. The full-color toner image is conveyed by the rotation of the intermediate transfer belt 154 to a nip portion formed by the intermediate transfer belt 154 and the transfer roller 221. The full-color toner image is transferred to the recording paper by the nip portion.

[0023] The recording paper is stored in the paper feed stages 140a, 140b, 140c, 140d, 140e of the paper feed unit 140 and is fed according to the timing of image formation by each image forming unit. The paper feed stage that is the source of the recording paper is indicated by the print job. The recording paper is conveyed to the nip portion at the timing when the full-color toner image is conveyed to the nip portion formed by the intermediate transfer belt 154 and the transfer roller 221. Thereby, the toner image is transferred to a predetermined position on the recording paper. The conveyance direction of the recording paper is the sub-scanning direction orthogonal to the main scanning direction.

[0024] Printer 150 includes a first fuser 155 and a second fuser 156 that fix the toner image to the recording paper by heating and pressurizing. The first fuser 155 includes a fixing roller having a built-in heater and a pressure belt for pressing the recording paper against the fixing roller. The fixing roller and the pressure belt are driven by a motor (not shown) to sandwich and convey the recording paper. The second fuser 156 is disposed downstream of the first fuser in the conveyance direction of the recording paper. The second fuser 156 is used to increase the gloss and ensure the fixability of the image on the recording paper that has passed through the first fuser 155. The second fuser 156 includes a fixing roller having a built-in heater and a pressure roller having a built-in heater. Depending on the type of recording paper, the second fuser 156 is not used. In this case, the recording paper is not conveyed to the second fuser 156 but is conveyed to the conveyance path 130. For this purpose, a flapper 131 for guiding the recording paper to either the conveyance path 130 or the second fuser 156 is provided on the downstream side of the first fuser 155.

[0025] Downstream of the position where the conveyance path 130 merges downstream of the second fixing device 156, a conveyance path 135 and a discharge path 139 are provided. For this purpose, at the position where the conveyance path 130 merges downstream of the second fixing device 156, a flapper 132 for guiding the recording paper to either the conveyance path 135 or the discharge path 139 is provided. The flapper 132 guides, for example, the recording paper with an image formed on the first side to the conveyance path 135 in the double-sided printing mode. The flapper 132 guides, for example, the recording paper with an image formed on the first side to the discharge path 139 in the face-up paper discharge mode. The flapper 132 guides, for example, the recording paper with an image formed on the first side to the conveyance path 135 in the face-down paper discharge mode.

[0026] The recording paper conveyed to the conveyance path 135 is conveyed to the inversion unit 136. The recording paper conveyed to the inversion unit 136 switches back in order to reverse the conveyance direction after the conveyance operation is once stopped. The recording paper is guided from the inversion unit 136 to either the conveyance path 135 or the conveyance path 138 by the flapper 133. The flapper 133 guides, for example, the switched-back recording paper to the conveyance path 138 for printing an image on the second side in the double-sided printing mode. The recording paper conveyed to the conveyance path 138 is conveyed toward the nip portion between the intermediate transfer belt 154 and the transfer roller 221. Thereby, the front and back of the recording paper are reversed when passing through the nip portion, and image formation on the second side is performed. The flapper 133 guides, for example, the switched-back recording paper to the conveyance path 135 in the face-down paper discharge mode. The recording paper conveyed to the conveyance path 135 by the flapper 133 is guided to the discharge path 139 by the flapper 134.

[0027] The recording paper on which an image is formed by the printer 150 is conveyed from the discharge path 139 to the reader 160. The reader 160 is an image reading device that reads a detection image of the image density printed on the recording paper together with the user image printed on the recording paper according to the print job. The recording paper conveyed from the printer 150 to the reader 160 is conveyed to the conveyance path 313 in the reader 160. The reader 160 includes an original detection sensor 311, a line sensor unit 312, and a spectral sensor unit 315 in the conveyance path 313. A flow-through glass 314 is disposed between the line sensor unit 312 and the conveyance path 313. A white plate 316 is disposed at a position facing the spectral sensor unit 315 with the conveyance path 313 interposed therebetween. The reader 160 measures color by the line sensor unit 312 and the spectral sensor unit 315 while conveying the recording paper on which the detection image is printed by the printer 150 to the conveyance path 313.

[0028] The original detection sensor 311 is, for example, an optical sensor having a light emitting element and a light receiving element. The original detection sensor 311 detects the leading end in the conveyance direction of the recording paper conveyed through the conveyance path 313. The detection result of the leading end of the recording paper by the original detection sensor 311 is transmitted to the controller 110. The controller 110 starts the reading operation by the reader 160 (the line sensor unit 312 and the spectral sensor unit 315) based on the detection timing of the leading end of the recording paper by the original detection sensor 311. The line sensor unit 312 is provided on the image forming surface side of the recording paper in the conveyance path 313 in order to read the detection image of the recording paper during conveyance. The spectral sensor unit 315 is provided on the image forming surface side of the recording paper in the conveyance path 313 in order to be driven in the main scanning direction and measure the color of the image on the recording paper.

[0029] (Reader) FIG. 3 is a configuration explanatory diagram of the reader 160. The reader 160 includes an image memory 303 and a color detection processing unit 305 in addition to a line sensor unit 312, a spectroscopic sensor unit 315, and an original detection sensor 311. The line sensor unit 312, the spectroscopic sensor unit 315, the image memory 303, the color detection processing unit 305, and the original detection sensor 311 are controlled in operation by the CPU 114 of the controller 110.

[0030] The line sensor unit 312 includes a line sensor 301, a memory 300, and an AD converter 302. The line sensor 301 is, for example, a CIS (Contact Image Sensor). The memory 300 stores correction information such as variations in light amount between pixels, steps between pixels, and distances between pixels of the corresponding line sensor 301. The AD converter 302 acquires an analog signal that is a reading result by the line sensor 301. The AD converter 302 converts the acquired analog signal into a digital signal and transmits it to the color detection processing unit 305. The digital signal is RGB (Red, Green, Blue) image data.

[0031] The spectroscopic sensor unit 315 includes a spectroscopic sensor 306, a memory 304, an AD converter 307, and a spectroscopic sensor drive unit 308. The spectroscopic sensor 306 is composed of, for example, a light source, a lens, a diffraction grating surface, and a light receiving unit. The spectroscopic sensor 306 irradiates light from the light source onto the measurement target and disperses the reflected light by wavelength using the diffraction grating. The spectroscopic sensor 306 receives the light dispersed by wavelength with pixels provided separately for each wavelength in the light receiving unit and photoelectrically converts it into a voltage value for each wavelength. The output value of the light for each wavelength converted into a voltage value is an analog signal. The AD converter 307 converts this analog signal into a digital signal and transmits it to the color detection processing unit 305 as spectroscopic reflectance data. The memory 304 stores various correction information such as stray light data and dark current data of the spectroscopic sensor 306. The spectroscopic sensor drive unit 308 is a drive source that drives the spectroscopic sensor unit 315 in the main scanning direction.

[0032] The color detection processing unit 305 calculates the average value (average luminance value) of the RGB luminance values of the detection image portion from the RGB image data acquired from the line sensor unit 312, and transmits the calculation result to the CPU 114. The color detection processing unit 305 is composed of semiconductor devices such as an FPGA (Field-Programmable Gate Array) and an ASIC (Application Specific Integrated Circuit). The image memory 303 stores the image data necessary for image processing in the CPU 114.

[0033] (Line sensor) FIG. 4 is a configuration explanatory diagram of the line sensor 301. The line sensor 301 includes a light emitting unit 400a, 400b, a light guide 402a, 402b, a lens array 403, and a sensor chip group 401. The line sensor 301a is substantially a rectangular parallelepiped and reads an image with the longitudinal direction as the main scanning direction.

[0034] The light emitting units 400a, 400b are light sources composed of, for example, LEDs (Light Emitting Diodes) that emit white light. The light guide 402a has the light emitting unit 400a disposed at an end, and irradiates the light emitted from the light emitting unit 400a toward the recording paper. The light guide 402b has the light emitting unit 400b disposed at an end, and irradiates the light emitted from the light emitting unit 400b toward the recording paper. The light guides 402a, 402b are formed linearly in the main scanning direction. Therefore, the line sensor 301 irradiates light linearly in the main scanning direction. The main scanning direction of the line sensor unit 312 and the main scanning direction of the printer 150 are the same direction.

[0035] The lens array 403a is an optical system that guides the reflected light of the light irradiated from the light emitting units 400a and 400b by the recording paper to the sensor chip group 401a. The sensor chip group 401a is configured by arranging a plurality of photoelectric conversion elements (sensor chips) linearly in the main scanning direction. One sensor chip reads an image of one pixel. The plurality of sensor chips in the present embodiment has a three-line configuration. An R (red) color filter is applied to one line, a G (green) color filter is applied to another line, and a B (blue) color filter is applied to another line. The light guided by the lens array 403a is imaged on the light receiving surface of each sensor chip of the sensor chip group 401a.

[0036] The light emitted from the light emitting units 400a and 400b diffuses inside the light guides 402a and 402b, and is emitted from the curved portions, illuminating the entire area in the main scanning direction of the recording paper. The light guide 402a and the light guide 402b are arranged with the lens array 403a interposed therebetween in the sub-scanning direction orthogonal to the main scanning direction. Therefore, the line sensor 301a has a two-side illumination configuration that irradiates light from two directions in the sub-scanning direction with respect to the lens array 403a (image reading line). The sub-scanning direction of the line sensor unit 312a is the same as the sub-scanning direction of the printer 150.

[0037] (Spectral sensor unit) FIG. 5 is a configuration explanatory diagram of the spectral sensor unit 315. The spectral sensor unit 315 is a substantially rectangular parallelepiped with the main scanning direction as the longitudinal direction. The recording paper is conveyed in the sub-scanning direction on the back side of the spectral sensor unit 315 in FIG. 5. The spectral sensor 306, the memory 304, and the AD converter 307 are integrally configured. The AD converter 307 is connected to the color detection processing unit 305 by wiring such as a flexible flat cable (not shown).

[0038] The spectral sensor 306 is provided on a rail 309 extending in the main scanning direction from the spectral sensor drive unit 308. The spectral sensor 306 moves on the rail 309 by the spectral sensor drive unit 308. The spectral sensor drive unit 308 incorporates a stepping motor and is controlled according to an instruction from the CPU 114. The spectral sensor drive unit 308 can move the spectral sensor 306 to a predetermined position in the main scanning direction with high precision.

[0039] Outside the conveyance area where the spectral sensor unit 315 can read the recording paper, a home position HP is provided. The white plate 316 is arranged at the home position HP. The recording paper is conveyed one line at a time in the sub-scanning direction and stops at the timing of color measurement. An opening 310 is provided at a position corresponding to the original conveyance area of the spectral sensor unit 315, and the spectral sensor 306 reads the recording paper through the opening 310.

[0040] The spectral sensor 306 is located at the home position HP before the start of color measurement. When an instruction to start color measurement is given from the CPU 114, the spectral sensor 306 reads the white plate 316 and performs calibrations such as light source light quantity adjustment and white reference alignment. After calibration, the spectral sensor 306 starts moving in the main scanning direction at a constant speed from the home position HP, and starts color measurement for one line using the detection of the trigger patch as a trigger. When the color measurement for one line is completed, the spectral sensor 306 returns to the home position HP. Then, when the recording paper moves one line in the sub-scanning direction, the spectral sensor 306 starts moving in the main scanning direction again and performs color measurement for one line. By repeating such movement of the recording paper for one line and color measurement of the spectral sensor 306 for one line, color measurement of one sheet of recording paper is performed.

[0041] (Color and taste inspection) FIG. 6 is a flowchart showing a printing process including a color and taste inspection process. This process is started when the user inputs an instruction for color and taste inspection and an instruction to start copying through the operation panel 120. The instruction for color and taste inspection includes the recording paper size, printing mode, number of printed sheets P MAX , color values to be inspected for color and taste (specific color: L 00*, a 00 *, b 00 *) Color and flavor inspection specified area (area X = X on the paper S ~X E , Y = Y S ~Y E ) includes color and flavor inspection threshold Cth, etc.

[0042] The CPU 114 acquires an instruction for color and flavor inspection from the operation panel 120, and performs mode setting (S600) by setting information necessary for the print job to each device based on the instruction and storing various parameters included in the instruction in the RAM 113. The CPU 114 waits for a copy start instruction from the operation panel 120 after mode setting (S601: N).

[0043] When the CPU 114 acquires a copy start instruction (S601: Y), it performs color calibration of the line sensor 301 according to the instruction content of the color and flavor inspection, and creates a color calibration matrix M of the line sensor 301 (S602). The color calibration matrix M is a conversion condition for converting L*, a*, b* converted from the reading result of the line sensor unit 312 into color values for color calibration. Details of the process of S602 will be described later. The CPU 114 initializes the print count value P to "0" after color calibration (S603). The print count value P represents the number of sheets of recording paper on which an image is formed by the printer 150.

[0044] The CPU 114 performs print processing of an image of a specific color under conditions according to the instruction of the color and flavor inspection by the printer 150 to generate a printed matter (S604). The CPU 114 measures the color of the printed matter by the line sensor unit 312 (S605). The color measurement is performed on the color and flavor inspection specified area of the printed matter (area X = X on the paper S ~X E , Y = Y S ~Y E ). As a result of the color measurement of the printed matter, RGB image data is transmitted from the line sensor unit 312 to the color detection processing unit 305. The color detection processing unit 305 calculates the average luminance value (R A , R G , RB ) is derived and sent to the CPU 114.

[0045] The CPU 114 has a color conversion look-up table LUT that converts the luminance values (RGB data) of each RGB color to L*, a*, b*. IN The CPU 114 has a color conversion look-up table LUT IN Using this, the average luminance value (R A , R G , R B ) of each color is converted to L a* , a a* , b a* values. The CPU 114 uses the color calibration matrix M created in the process of S602 to derive the color values (L A , R G , R B ) from the conversion result of the average luminance value (R a* , a a* , b a* values to L Pa* , a Pa* , b Pa* ).

[0046] The CPU 114 derives the color difference ΔE00 between the color values (L Pa* , a Pa* , b Pa* ) obtained as a result of colorimetry and the color values of a specific color (L 00 *, a 00 *, b 00 *) (S606). The CPU 114 compares the derived color difference ΔE00 with the color tone inspection threshold Cth (S607). Based on the comparison result between the color difference ΔE00 and the color tone inspection threshold Cth, the result of the color tone inspection is determined.

[0047] When the color difference ΔE00 is less than or equal to the color tone inspection threshold Cth (S607: Y), the CPU 114 determines that the difference between the specific color of the image printed on the recording paper and the specified specific color for which the color tone is to be inspected is small. In this case, since printing is being performed normally in the specific color, the CPU 114 increments the print count value P by 1 (S608). The CPU 114 determines whether the print count value P has reached the number of printed sheets P MAX (S610). Whether the print count value P has reached the number of printed sheets PMAX If it has not reached (S610: N), the CPU 114 repeats the processes after S604 until the print count value P reaches the number of printed sheets P. MAX When the print count value P reaches the number of printed sheets P (S610: Y), the CPU 114 ends the printing process including the color inspection process. MAX When the color difference ΔE00 is greater than the color inspection threshold Cth (S607: N), the CPU 114 determines that the difference between the specific color of the image printed on the recording paper and the specified specific color to be color-inspected is large. In this case, since the printing is not normally performed in the specific color, the CPU 114 performs a warning display on the operation panel 120 (S609). In the warning display, the color inspection specified area is the specific color L

[0048] *,a 00 *,a 00 *,b 00 *,b is away from the allowable color difference (color inspection threshold Cth) from *, and it is indicated that the result of the color inspection is inappropriate. In addition to the display on the display, the warning may be issued by the sound from the speaker. After performing the warning display, the CPU 114 ends the printing process including the color inspection process.

[0049] (Color correction process) The color correction process of S602 will be described. FIG. 7 is an exemplary diagram of a color correction chart used for the color correction process of the line sensor unit 312. The color correction chart 501 is created by printing 49 patch images 504 as detection images on a recording paper that is long in the sub-scanning direction. The patch images 504 are arranged in 7 rows and 7 columns in the main scanning direction and the sub-scanning direction. A margin 502 is provided at the left end of the color correction chart 501 in the main scanning direction, a black trigger patch 503 is provided on the right side of the margin 502, and 49 patch images 504 are provided on the right side of the trigger patch 503.

[0050] The 49 patch images 504 for color correction are the specific color L 00 *,a 00 *,b 00 * and the specific color L 00 *,a 00 *,b 00An image of the image density value corresponding to each of the L*, a*, and b* values of the peripheral color calculated as a value separated by a predetermined color difference from 00 *, a 00 *, b 00 * of the central patch image. The image density value is set for each color of yellow (Y), magenta (M), cyan (C), and black (K). Here, this image density value is referred to as the "YMCK value". The method of selecting the YMCK value for the L*, a*, and b* values of the 49 patch images 504 for color calibration will be described later. Note that the formation position of the patch image 504 of the color calibration chart 501 is not limited to FIG. 7.

[0051] FIG. 8 is a flowchart showing the color calibration process. FIG. 9 is an explanatory diagram of a method for calculating L*, a*, and b* of the peripheral color of a specific color. FIG. 10 is an explanatory diagram of a color conversion look-up table LUT OUT for converting colors from L*, a*, and b* values to YMCK values.

[0052] The CPU 114 calculates L*, a*, and b* of the peripheral color from the specific color L 00 *, a 00 *, b 00 *(S800). For this purpose, the CPU 114 first obtains the specific color L 00 *, a 00 *, b 00 * and the color taste inspection threshold Cth from the RAM 113. The CPU 114 calculates the peripheral color separated by a predetermined color difference from the specific color L 00 *, a 00 *, b 00 *. The peripheral color is selected such that the range of the predetermined color difference straddles the color taste inspection threshold Cth (ΔEmin < Cth < ΔEmax).

[0053] For example, as shown in FIG. 9, 48 peripheral colors are selected. FIG. 9 illustrates the case where the color taste inspection threshold Cth is "5". The CPU 114 selects ΔE00 = 2, 4 smaller than ΔE00 = 5 and ΔE00 = 6, 8, 10, 12 larger than ΔE00 = 5 so as to straddle a predetermined color difference of ΔE00 = 5. The CPU 114 calculates the L*, a*, b* of the following 48 peripheral colors corresponding to the selected ΔE00.

[0054] · Peripheral colors 01 to 08 with a color separation of color difference ΔE00 = 2 → L*, a*, b* = L 01 *, a 01 *, b 01 * ~ L 08 *, a 08 *, b 08 * · Peripheral colors 09 to 16 with a color separation of color difference ΔE00 = 4 → L*, a*, b* = L 09 *, a 09 *, b 09 * ~ L 16 *, a 16 *, b 16 * · Peripheral colors 17 to 24 with a color separation of color difference ΔE00 = 6 → L*, a*, b* = L 17 *, a 17 *, b 17 * ~ L 24 *, a 24 *, b 24 * · Peripheral colors 25 to 32 with a color separation of color difference ΔE00 = 8 → L*, a*, b* = L 25 *, a 25 *, b 25 * ~ L 32 *, a 32 *, b 32 * · Peripheral colors 33 to 40 with a color separation of color difference ΔE00 = 10 → L*, a*, b* = L 33 *, a 33 *, b 33 * ~ L 40 *, a 40 *, b 40 * ·Peripheral colors 41 to 48 with a color difference of ΔE00 = 12 →L*, a*, b* = L 41 *, a 41 *, b 41 * ~ L 48 *, a 48 *, b 48 *

[0055] The CPU 114 calculates the patch color (Y, M, C, K), which is the color of the patch image used for the color calibration chart 501 (S801). The CPU 114 uses L 00 *, a 00 *, b 00 * ~ L 48 *, a 48 *, b 48 * to convert based on the color conversion look-up table LUT stored in the ROM 112 OUT . As a result, the YMCK values corresponding to each L*, a*, b* value are calculated (calculation of the patch color (L*, a*, b*)). According to FIG. 10, a color conversion look-up table LUT OUT for converting the L*, a*, b* values into the YMCK values, which are the printing parameters, will be described.

[0056] FIG. 10 shows the concept of the color conversion look-up table LUT OUT . FIG. 10(a) shows a three-dimensional color conversion look-up table LUT OUT in the input color space (Lab space). The color conversion look-up table LUT OUT has cubes arranged at equal intervals on the Lab space. Each vertex (lattice point) of the cube represents a position (L*, a*, b* value) in the Lab space. A patch color (YMCK value) corresponding to the L*, a*, b* value of that position is assigned to the lattice point.

[0057] For example, when the L*, a*, b* values to be converted are the L β *, a β *, b β * specified on the lattice point, the color conversion look-up table LUT OUT corresponds to the patch color (YMCK value), which is Y β , Mβ , C β , K β is output.

[0058] Figure 10(b) illustrates the table interpolation method. The L*, a*, b* values to be color-converted are in the area surrounded by lattice points 1 to 8. When the distances from lattice point 1 to lattice point 8 are d1 to d8 respectively, the patch color (YMCK values) is calculated as follows according to the distances to the respective lattice points.

[0059] Y = (Y1 / d1 + Y2 / d2 + … + Y8 / d8) / (1 / d1 + 1 / d2 + … + 1 / d8) M = (M1 / d1 + M2 / d2 + … + M8 / d8) / (1 / d1 + 1 / d2 + … + 1 / d8) C = (C1 / d1 + C2 / d2 + … + C8 / d8) / (1 / d1 + 1 / d2 + … + 1 / d8) K = (K1 / d1 + K2 / d2 + … + K8 / d8) / (1 / d1 + 1 / d2 + … + 1 / d8)

[0060] Note that the color conversion look-up table LUT OUT is stored in the ROM 112, and the conversion operation process from L*, a*, b* values to patch color (YMCK values) is performed by the CPU 114.

[0061] Based on the patch color (YMCK values) calculated in the process of S801, the CPU 114 creates the color calibration chart 501 in Fig. 7 by the printer 150 (S802). The CPU 114 measures the color of the created color calibration chart 501 by the line sensor 301 and the spectroscopic sensor unit 315 (S803).

[0062] The line sensor 301 outputs the luminance value (RGB data) of each color, which is the color measurement result, to the color detection processing unit 305. The color detection processing unit 305 calculates the average luminance value (R A , G A , B ACalculate it. The CPU 114 uses a color conversion look-up table LUT that converts the luminance values of R, G, and B into L*, a*, and b* values. IN to convert the average luminance value (R A , G A , B A ) into L*, a*, and b* values. The CPU 114 obtains 49 L*, a*, and b* values, L L_A00 *, a L_A00 *, b L_A00 * to L L_A48 *, a L_A48 *, b L_A48 * as the color measurement result by the line sensor unit 312.

[0063] The spectral sensor 306 outputs the spectral reflectance data of the color calibration chart 501, which is the color measurement result, to the color detection processing unit 305. The color detection processing unit 305 obtains 49 L*, a*, and b* values, L S_A00 *, a S_A00 *, b S_A00 * to L S_A48 *, a S_A48 *, b S_A48 * from the spectral reflectance data obtained from the spectral sensor unit 315. The color detection processing unit 305 calculates the L*, a*, and b* values from the obtained spectral reflectance data and outputs the calculated L*, a*, and b* values to the CPU 114.

[0064] Let the 49 L*, a*, and b* values of the spectral reflectance data obtained by the color detection processing unit 305 be ZA 00 , Z B00 , Z C00 ~Z A48 , Z B48 , Z C48 . Let Z A00 , Z B00 *, Z C00 ~Z A48 , Z B48 *, Z C48 be the L*, a*, and b* values when the same patch image as Z A00 , X B00 , X C00 ~X A48 , X B48 , X C48 is measured by the line sensor 301.

[0065] The CPU 114 generates the color correction matrix M of the line sensor 301 (S804). The CPU 114 is Z A00 ,Z B00 ,Z C00 ~Z A48 ,Z B48 ,Z C48 and X A00 ,X B00 ,X C00 ~X A48 ,X B48 ,X C48 Using Z to X as the training data, the color correction matrix M for calibrating the measurement results of the line sensor 301 is calculated by the following formula. The color correction matrix M is 3x10. The CPU 114 stores the calculated color correction matrix M in the RAM 113. In this way, the color correction matrix M is obtained by the color correction process.

[0066]

Equation

[0067] As described above, in this embodiment, the printer 150 prints on the recording paper a detection image including a peripheral color located at a predetermined color difference from a specific color and the specific color, thereby creating a color correction chart. The color correction chart is read by the reader 160. From the reading result of the color correction chart by the reader 160, a color conversion table for the specific color from RGB to Lab is created. As a result, the conversion accuracy from RGB to Lab for colors near the specific color is improved, and a high-precision color inspection system can be realized.

Claims

1. an image forming means for forming an image on a recording sheet; an acquisition means for acquiring color information of a color to be inspected and tolerance information regarding an allowable color difference of the color to be inspected; and a control means for causing the image forming means to form a test chart to be used for the inspection based on the color information and the tolerance information. Image forming device.

2. A reading means for reading an image formed on the recording paper by the image forming means; and a generating unit configured to generate a conversion condition to be used for converting the reading result of the reading unit based on a first reading result of the test chart by the reading unit and a second reading result of the test chart read by a reading device different from the reading unit.

2. The image forming apparatus according to claim 1.

3. the control means causes the reading means to read the image formed by the image forming means, and inspects the color of the image based on a result of converting the read result of the image using the conversion conditions and the tolerance information.

3. The image forming apparatus according to claim 2.

4. The control means determines the color difference between the color to be inspected and the color of the portion of the converted reading result that corresponds to the color to be inspected, and inspects the color by comparing the color difference with the allowable color difference.

4. The image forming apparatus according to claim 3.

5. The method according to claim 1, further comprising: a notification means for notifying the test result of the color to be tested.

2. The image forming apparatus according to claim 1.

6. The test chart is characterized in that it includes a first test image having a color difference smaller than the allowable color difference for the color to be inspected, and a second test image having a color difference larger than the allowable color difference for the color to be inspected.

2. The image forming apparatus according to claim 1.

7. The reading means is a sensor that outputs luminance data of the test chart, The reading device is a sensor that outputs spectral data of the test chart.

3. The image forming apparatus according to claim 2.

8. An acquisition means for acquiring color information of a color to be inspected and tolerance information regarding an allowable color difference of the color to be inspected; and a control unit that causes an image forming apparatus to form a test chart to be used for the inspection based on the color information and the tolerance information. Information processing device.

9. The image forming apparatus further comprises a reading means for reading an image formed on a recording paper, and a generating unit configured to generate a conversion condition used to convert the reading result of the color to be inspected by the reading unit based on a first reading result of the test chart by the reading unit and a second reading result of the test chart read by a reading device different from the reading unit.

9. The information processing device according to claim 8.

10. The control means is characterized in that it acquires the reading result of the image formed by the image forming device read by the reading means, converts the reading result using the conversion conditions, and inspects the color of the image based on the result and the tolerance information.

10. The information processing device according to claim 9.

11. The control means determines a color difference between the color to be inspected and the color of the portion of the converted reading result that corresponds to the color to be inspected, and inspects the color by comparing the color difference with the allowable color difference. The information processing device according to claim 10.

12. The method according to claim 1, further comprising: a notification means for notifying the test result of the color to be tested.

9. The information processing device according to claim 8.

13. The test chart is characterized in that it includes a first test image having a color difference smaller than the allowable color difference for the color to be inspected, and a second test image having a color difference larger than the allowable color difference for the color to be inspected.

9. The information processing device according to claim 8.

14. The reading means is a sensor that outputs luminance data of the test chart, The reading device is a sensor that outputs spectral data of the test chart.

10. The information processing device according to claim 9.

15. An acquisition step of acquiring color information of a color to be inspected and tolerance information regarding an allowable color difference of the color to be inspected; and a test chart forming step of forming a test chart to be used for the inspection based on the color information and the tolerance information. A control method for an image forming apparatus.

16. A first reading step of reading the test chart by a reading means possessed by the image forming apparatus; a second reading step of reading the test chart by a reading device different from the reading means; a generating step of generating a conversion condition used to convert the reading result of the color to be inspected by the reading means based on the reading result of the first reading step and the reading result of the second reading step, 16. The method for controlling the image forming apparatus according to claim 15.

17. An image forming step of forming an image on a recording paper; a third reading step of reading the image formed on the recording paper by the reading means; a conversion step of converting the read result of the third reading step using the conversion conditions; and an inspection step of inspecting the color of the image formed in the image forming step based on the result of the conversion in the conversion step and the tolerance information.

17. The method for controlling the image forming apparatus according to claim 16.

18. The inspection step is characterized in that the color is inspected by determining the color difference between the color to be inspected and the color of the part of the result converted in the conversion step that corresponds to the color to be inspected, and comparing the color difference with the allowable color difference.

18. The method for controlling the image forming apparatus according to claim 17.

19. The method according to claim 1, further comprising a notification step of notifying the inspection result of the color to be inspected.

16. The method for controlling the image forming apparatus according to claim 15.

20. The test chart is characterized in that it includes a first test image having a color difference smaller than the allowable color difference for the color to be inspected, and a second test image having a color difference larger than the allowable color difference for the color to be inspected.

16. The method for controlling the image forming apparatus according to claim 15.

21. The reading means is a sensor that outputs luminance data of the test chart, The reading device is a sensor that outputs spectral data of the test chart.

17. The method for controlling the image forming apparatus according to claim 16.

Images