Information processing equipment and method for controlling image forming apparatus

Abstract

An information processing apparatus and a method for controlling an image forming apparatus are disclosed. The information processing apparatus includes: an acquisition unit configured to acquire color information about a specific color included in an inspection image and determination conditions for determining a color offset relative to the specific color; and a controller configured to: determine test image data representing a plurality of test images to be formed by the image forming apparatus based on the color information acquired by the acquisition unit and the determination conditions; output the determined test image data to the image forming apparatus to form the plurality of test images; acquire brightness data about the plurality of test images, the brightness data being output from a color sensor; and acquire spectral data about the plurality of test images, the spectral data being output from a spectral sensor.

Description

Technical Field

[0001] This disclosure relates to techniques for examining the color of an image printed on printed material. Background Technology

[0002] In an image forming apparatus that forms an image using electrophotographic processing, the characteristics of each process—charging, developing, transferring, and fixing—change depending on time and environmental conditions. Consequently, the image density or color of the printed material may change. Therefore, image stabilization control is performed in the image forming apparatus. Image stabilization control involves detecting a detection image (used to detect the density of the image formed on an image carrier member) via an optical sensor, and adjusting the image forming conditions based on the detection results to ensure that the image on the image carrier member has an appropriate image density. Image forming conditions refer to various settings used during image forming, such as the charge on the image carrier member and the amount of energy emitted by the laser used to scan the image carrier member.

[0003] Image stabilization control is a control applied to processes performed before an image is transferred onto a recording sheet. Therefore, image stabilization control cannot control the effects on image density caused by processes occurring from the transfer stage onwards. For example, when a toner image is transferred from an image carrier to the recording sheet, image stabilization control cannot handle changes in transfer efficiency caused by environmental variations. Consequently, the image density of the final image formed on the recording sheet may vary. In contrast, the image forming apparatus in Japanese Patent Application Publication No. 2012-53089 detects the image after it has been fixed onto the recording sheet using an optical sensor, and adjusts the image forming conditions based on the detection result, thereby suppressing the effects on image density caused by processes occurring from the transfer stage onwards.

[0004] Company colors, used for purposes such as company logos or design markings, are identified as an important component for company identification. Therefore, there is a need to output printed materials that include the company colors, ensuring that even when colors are unique, they are strictly defined. However, in related technologies, color reproduction calibration is performed by referencing colors with high usage frequency in the image to be printed, making it difficult to strictly reproduce the specific color specified by the user.

[0005] In recent years, color inspection systems have been proposed that read the color of an image of printed material during printing and check the color of the read color. U.S. Patent Application Publication No. 2012 / 0327435 A1 discloses an image forming apparatus for performing color inspection. This image forming apparatus prints a measurement patch on a recording sheet for measuring a specific color specified by a user. The image forming apparatus performs color stabilization control based on the results of color measurements of the measurement patch by an image sensor. If the measured color result is outside the allowable range, the image forming apparatus informs the user of this fact and performs color stabilization control again.

[0006] Image sensors used to measure the color of images printed on printing materials output luminance values ​​(RGB data) of three colors: red (R), green (G), and blue (B) as color measurement results. This RGB data is converted into spectral data formed by L*, a*, and b* of the CIELab color space. To convert the RGB data to the CIELab color space, a color conversion table is used as a lookup table. In the color conversion table, typically not all color conversion values ​​(Lab values) for all input values ​​(luminance values ​​of R, G, and B) are registered; instead, only the color conversion values ​​at a number of regularly arranged grid points in the input color space are registered. When performing color conversion using this color conversion table, the color conversion values ​​outside the grid points are obtained through interpolation operations performed based on the color conversion values ​​registered at the grid points (Japanese Patent Application Publication No. 2002-64719).

[0007] Optical sensors are frequently used as image sensors. Optical sensors produce output values ​​from light received through red (R), green (G), and blue (B) color filters, whose sensitivity differs from that of human vision. Therefore, when performing color measurements using optical sensors, the accuracy is difficult to achieve depending on the color. This also affects the results of color inspection. Therefore, there is a need for image forming apparatuses capable of performing color measurements on images intended for color inspection with high accuracy.

[0008] Furthermore, color conversion using a color conversion table is performed by converting the entire color gamut, which can be represented by R, G, and B colors, to Lab values. Using this method, the entire color gamut undergoes color conversion at a seamless level. However, in a color gamut where Lab values ​​easily change relative to each color in the RGB data, conversion errors increase, and highly accurate color checking becomes difficult. Therefore, an image forming apparatus capable of checking colors with high precision is needed. Summary of the Invention

[0009] An information processing apparatus according to this disclosure includes: an acquisition unit configured to acquire color information about a specific color included in an inspection image and determination conditions for determining a color offset relative to the specific color; and a control unit configured to: determine test image data indicating a plurality of test images to be formed by an image forming apparatus based on the color information acquired by the acquisition unit and the determination conditions; output the determined test image data to the image forming apparatus to form the plurality of test images; acquire brightness data about the plurality of test images, the brightness data being output from a color sensor; acquire spectral data about the plurality of test images, the spectral data being output from a spectral sensor; and generate a conversion function based on the spectral data and the brightness data. The process involves: converting the reading results obtained by the color sensor into conversion conditions; acquiring luminance data about the image to be formed by the image forming apparatus, the luminance data being output from the color sensor; converting the luminance data about the image to be formed by the image forming apparatus based on the conversion conditions; and determining a color shift relative to a specific color in the test image based on the converted luminance data and the determination conditions, wherein the plurality of test images includes a first test image of a first color having a first value of color difference with the specific color and a second test image of a second color having a second value of color difference with the specific color, wherein the first value is less than the value of the color difference corresponding to the determination conditions, and wherein the second value is greater than the value of the color difference corresponding to the determination conditions.

[0010] A method for controlling an image forming apparatus according to the present disclosure, the image forming apparatus being used to form an image onto a sheet, the method comprising: a first acquisition step of acquiring color information regarding a specific color included in an inspection image; a second acquisition step of acquiring determination conditions for determining a color offset relative to the specific color; a determination step of determining test image data representing a plurality of test images based on the color information and the determination conditions; a test printing step of printing the plurality of test images based on the test image data; a first reading step of reading the plurality of test images via a color sensor configured to receive reflected light from a measurement target and output red brightness data, green brightness data, and blue brightness data regarding the measurement target; and a second reading step of reading the plurality of test images via a spectral sensor configured to receive reflected light from the measurement target and detect light reflected from the measurement target. The test images consist of: a light intensity of more than three wavelengths, and outputting spectral data based on the light intensity of each of the multiple wavelengths; a generation step, generating conversion conditions for converting the reading results obtained by the color sensor based on the spectral data and brightness data; a printing step, printing an inspection image; a third reading step, reading the inspection image through the color sensor; a conversion step, converting the brightness data of the inspection image based on the conversion conditions; and a determination step, determining the color shift in the inspection image relative to a specific color based on the converted brightness data and the determination conditions, wherein the multiple test images include a first test image of a first color having a first value of color difference with the specific color and a second test image of a second color having a second value of color difference with the specific color, wherein the first value is less than the value of the color difference corresponding to the determination conditions, and wherein the second value is greater than the value of the color difference corresponding to the determination conditions.

[0011] Other features of the invention will become clear from the following description of exemplary embodiments (with reference to the accompanying drawings). Attached Figure Description

[0012] Figure 1 It is an illustrative diagram showing the configuration of the printing system.

[0013] Figure 2 This is a view of the configuration of the image forming apparatus.

[0014] Figure 3 This is an illustrative diagram showing the configuration of the reader.

[0015] Figure 4 This is an illustrative diagram showing the configuration of a line sensor.

[0016] Figure 5 This is an illustrative diagram showing the configuration of the spectral sensor unit.

[0017] Figure 6 This is a flowchart illustrating a printing process that includes color checking.

[0018] Figure 7 This is an example diagram of a color calibration chart.

[0019] Figure 8 This is a flowchart used to illustrate the color calibration process.

[0020] Figure 9 It is an illustrative diagram illustrating the method for calculating the L*, a*, and b* of the surrounding colors of a specific color.

[0021] Figure 10A and Figure 10B This is an illustrative diagram of a color conversion lookup table.

[0022] Figure 11 This is an example diagram of a color calibration chart.

[0023] Figure 12 This is a flowchart used to illustrate the color calibration process.

[0024] Figure 13 It is an illustrative diagram illustrating the method for calculating the L*, a*, and b* of the surrounding colors of a specific color. Detailed Implementation

[0025] Embodiments of the present disclosure will now be described in detail with reference to the accompanying drawings. However, the following embodiments do not limit the scope of the disclosure as defined in the claims, and not all combinations of features described in the embodiments are essential to the solutions provided by the present disclosure.

[0026] <First Embodiment>

[0027] <Printing System>

[0028] Figure 1 This is an illustrative diagram illustrating the configuration of a printing system. 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 communicatively connected via a network 105. The network 105 is formed by communication lines such as a local area network (LAN), a wide area network (WAN), or a public communication line. Multiple image forming apparatuses 100 and multiple host computers 101 can be connected to the network 105.

[0029] The host computer 101 is, for example, a server device, and transmits printing jobs to the image forming apparatus 100 via a network 105. A printing job includes various printing information required for printing, such as image data, the type of recording sheet to be used in printing, the quantity of sheet to be printed, and instructions for performing double-sided or single-sided printing.

[0030] The image forming apparatus 100 includes a controller 110, an operation panel 120, a sheet feed unit 140, a printer 150, and a reader 160. The controller 110, operation panel 120, sheet feed unit 140, printer 150, and reader 160 are communicatively connected to each other via a system bus 116. The image forming apparatus 100 controls the operation of the printer 150 based on printing jobs acquired from a host computer 101 to form an image based on image data on a recording sheet.

[0031] The controller 110 controls the operation of each unit of the image forming apparatus 100. The controller 110 is an information processing device including a read-only memory (ROM) 112, a random access memory (RAM) 113, and a central processing unit (CPU) 114. The controller 110 includes a communication control unit 111 and a storage device 115. Modules are communicatively connected to each other via a system bus 116.

[0032] The communication control unit 111 is a communication interface for communicating with the host computer 101 and other devices via the network 105. The storage device 115 is a large-capacity storage device, such as a hard disk drive (HDD) or a solid-state drive (SSD). The storage device 115 stores various data and computer programs used in the image forming process (printing process). The CPU 114 executes the computer program stored in the ROM 112 or the storage device 115 to control the operation of the image forming apparatus 100. The RAM 113 provides the working area used by the CPU 114 when executing the computer program.

[0033] The operation panel 120 is a user interface and includes input and output interfaces. Input interfaces include, for example, operation buttons, numeric keys, or a touch panel. Output interfaces include, for example, a liquid crystal display (LCD) or other display, or a speaker. Users can input printing jobs, commands, and printing settings to the image forming apparatus 100 via the operation panel 120. The operation panel 120 displays settings and the status of the image forming apparatus 100 on the display.

[0034] The sheet feed unit 140 includes multiple sheet feed tables, which will be described later, for accommodating recording sheets. The sheet feed unit 140 feeds recording sheets of a specified type for the printing job from the sheet feed tables containing the recording sheets. Each sheet feed table accommodates multiple recording sheets (bundles of recording sheets), and the sheet feed unit 140 feeds the recording sheets sequentially from the top. The sheet feed unit 140 conveys the recording sheets fed from the sheet feed tables to the printer 150. Each sheet feed table can accommodate the same type of recording sheet, or it can accommodate different types of recording sheets.

[0035] Printer 150 prints an image onto a recording sheet fed from sheet feed unit 140 based on image data included in the printing job, thereby generating printed material. Reader 160 is an image reading device for reading images from the printed material generated by printer 150 and transmitting the reading results to controller 110. The image read by reader 160 is an image (detection image) used to adjust the image forming conditions to be used when printer 150 forms an image. Controller 110 detects the state of the image, such as image quality, from the result of reading the detection image by reader 160, and adjusts the image forming conditions based on the detected image state. In a first embodiment, controller 110 detects image density from the detection image and adjusts the image forming conditions based on the detected image density.

[0036] Image forming apparatus

[0037] Figure 2 This is a view of the configuration of the image forming apparatus 100. The image forming apparatus 100 includes, from upstream of the recording sheet transport direction, sheet feed tables 140a to 140e, a printer 150, a reader 160, and a finisher 190. The sheet feed tables 140a to 140e form the sheet feed section 140. The finisher 190 is a post-processing device for performing post-processing on the printed material produced by the printer 150. The finisher 190, for example, performs binding and sorting on multiple printed materials.

[0038] Printer 150 includes a plurality of image forming units 222 for forming images of different colors respectively. In a first embodiment, printer 150 includes four image forming units 222 for forming images of four colors: yellow (Y), magenta (M), cyan (C), and black (K). The image forming units 222 differ only in the color of the image to be formed and perform similar operations in a similar configuration.

[0039] An image forming unit 222 includes a photosensitive drum 153, a charging device 220, an exposure device 223, and a developing device 152. The photosensitive drum 153 is a drum-shaped photosensitive member with a photosensitive layer on its surface and is driven by a motor (not shown) to rotate in the direction of arrow R1. The charging device 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 using a laser. The laser scans the surface of the photosensitive drum 153 in the axial direction. The direction in which the laser scans the surface of the photosensitive drum 153 is the main scanning direction of the printer 150. Figure 2(in the depth direction). As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 153. The developing apparatus 152 develops the electrostatic latent image using a developer (toner). As a result, an image (toner image) obtained by visualizing the electrostatic latent image is formed on the surface of the photosensitive drum 153.

[0040] Printer 150 includes an intermediate transfer belt 154 onto which toner images generated by each image forming unit 222 are transferred. The intermediate transfer belt 154 is driven to rotate in the direction of arrow R2. Toner images of each color are transferred at timings corresponding to the rotation of the intermediate transfer belt 154. As a result, a full-color toner image, obtained by superimposing the toner images of each color, is formed on the intermediate transfer belt 154. As the intermediate transfer belt 154 rotates, the full-color toner image is conveyed to a clamping section formed by the intermediate transfer belt 154 and the transfer roller 221. The full-color toner image is transferred onto the recording sheet through the clamping section.

[0041] The recording sheet is housed in the sheet feeding stages 140a, 140b, 140c, 140d, and 140e of the sheet feeding unit 140 and fed according to the timing of image formation by the image forming unit 222. The sheet feeding stages for feeding the recording sheet are indicated by the printing operation. At the timing of the toner image being transferred to the clamping section, the recording sheet is transferred to the clamping section formed by the intermediate transfer belt 154 and the transfer roller 221. As a result, the toner image is transferred to a predetermined position on the recording sheet. The transport direction of the recording sheet is a sub-scanning direction orthogonal to the main scanning direction.

[0042] Printer 150 includes a first fixing device 155 and a second fixing device 156, each of which fixes a toner image onto a recording sheet by heating and pressurizing. The first fixing device 155 includes a fixing roller with a heater and a pressure belt for pressurizing the recording sheet against the fixing roller. The fixing roller and pressure belt are driven by a motor (not shown) to clamp and convey the recording sheet. The second fixing device 156 is arranged downstream of the first fixing device in the conveying direction of the recording sheet. The second fixing device 156 is used to increase gloss and ensure fixing for the image on the recording sheet after passing through the first fixing device 155. The second fixing device 156 includes a fixing roller with a heater and a pressure roller with a heater. Depending on the type of recording sheet, the second fixing device 156 is not used. In this case, the recording sheet is not conveyed to the second fixing device 156, but is conveyed to the transport path 130. For this purpose, a baffle 131 is provided on the downstream side of the first fixing device 155 to guide the recording sheet to either the transport path 130 or the second fixing device 156.

[0043] Downstream of the junction of the transport paths 130 on the downstream side of the second fixing device 156, a transport path 135 and an ejection path 139 are provided. Therefore, at the junction of the transport paths 130 on the downstream side of the second fixing device 156, a baffle 132 is provided to guide the recording sheet to either the transport path 135 or the ejection path 139. For example, in double-sided printing mode, the baffle 132 guides the recording sheet with an image formed on its first surface to the transport path 135. For example, in face-up ejection mode, the baffle 132 guides the recording sheet with an image formed on its first surface to the ejection path 139. For example, in face-down ejection mode, the baffle 132 guides the recording sheet with an image formed on its first surface to the transport path 135.

[0044] The recording sheet conveyed to transport path 135 is conveyed to reversing section 136. The recording sheet conveyed to reversing section 136 has a reversed transport direction after the transport operation stops once. The recording sheet is guided from reversing section 136 to either transport path 135 or transport path 138 by baffle 133. For example, in double-sided printing mode, baffle 133 guides the recording sheet with its transport direction reversed to transport path 138 so that an image can be printed on the second surface. The recording sheet conveyed to transport path 138 is conveyed toward the clamping section between intermediate transfer belt 154 and transfer roller 221. As a result, the front and back sides of the recording sheet are reversed when passing through the clamping section, and an image is formed on the second surface. For example, in face-down discharge mode, baffle 133 guides the recording sheet with its transport direction reversed to transport path 135. The recording sheet conveyed by baffle 133 to transport path 135 is guided to discharge path 139 by baffle 134.

[0045] A recording sheet with an image formed on it by printer 150 is conveyed from ejection path 139 to reader 160. Reader 160 is an image reading device for performing color measurement of a user image printed on the recording sheet according to a printing job and reading the image density of the detected image printed on the recording sheet. The recording sheet conveyed from printer 150 to reader 160 is conveyed along conveying path 313 included in reader 160. Reader 160 includes an original document detection sensor 311, a line sensor unit 312, and a spectral sensor unit 315 on conveying path 313. A flow reading glass 314 is arranged between line sensor unit 312 and conveying path 313. A white plate 316 is arranged at a position opposite to spectral sensor unit 315 across conveying path 313. Reader 160 performs color measurement via line sensor unit 312 and spectral sensor unit 315 while conveying the recording sheet with the image printed on it by printer 150 along conveying path 313.

[0046] The document inspection sensor 311 is, for example, an optical sensor including a light-emitting element and a light-receiving element. The document inspection sensor 311 detects the leading edge of the recording sheet being transported along the transport path 313 in the transport direction. The result of the document inspection sensor 311 detecting the leading edge of the recording sheet is transmitted to the controller 110. Based on the timing of the document inspection sensor 311 detecting the leading edge of the recording sheet, the controller 110 initiates the reading operation of the reader 160 (line sensor unit 312 and spectral sensor unit 315). The line sensor unit 312 is an optical sensor disposed on one side of the surface of the recording sheet on which the image is formed, so as to read the detection image printed on the transported recording sheet. The spectral sensor unit 315 is disposed on one side of the surface of the recording sheet on which the image is formed, so as to be driven in the main scanning direction to measure the color of the image formed on the recording sheet.

[0047] <Reader>

[0048] Figure 3 This is an illustrative diagram showing the configuration of the reader 160. In addition to the line sensor unit 312, the spectral sensor unit 315, and the original document detection sensor 311, the reader 160 also includes an image memory 303 and a color detection processing unit 305. The operation of the line sensor unit 312, the spectral sensor unit 315, the image memory 303, the color detection processing unit 305, and the original document detection sensor 311 is controlled by the CPU 114 of the controller 110.

[0049] The line sensor unit 312 includes a line sensor 301, a memory 300, and an A / D converter 302. The line sensor 301 is, for example, a contact image sensor (CIS). The line sensor 301 is a color sensor formed by light-receiving elements comprising individual red, green, and blue color filters. The light-receiving element including the red color filter primarily receives 630nm light from reflected light from the target being measured and outputs a signal based on the brightness value of the 630nm light. The light-receiving element including the green color filter primarily receives 530nm light from reflected light from the target being measured and outputs a signal based on the brightness value of the 530nm light. The light-receiving element including the blue color filter primarily receives 440nm light from reflected light from the target being measured and outputs a signal based on the brightness value of the 440nm light. The memory 300 stores correction information such as light intensity variations between pixels of the line sensor 301, level differences between pixels, and distances between pixels. The A / D converter 302 acquires an analog signal as a readout result obtained by the line sensor 301. The A / D converter 302 converts the acquired analog signal into a digital signal and transmits the digital signal to the color detection and processing unit 305. The digital signal is the read data (brightness data) of red (R), green (G), and blue (B).

[0050] The spectral sensor unit 315 includes a spectral sensor 306, a memory 304, an A / D converter 307, and a spectral sensor driving unit 308. The spectral sensor 306 is formed from, for example, a light source, a lens, a diffraction grating surface, and a light receiver. The light receiver is, for example, a CMOS sensor. The spectral sensor 306 illuminates the measurement target with light from the light source and disperses the reflected light for each wavelength through a diffraction grating. The spectral sensor 306 receives the light dispersed for each wavelength at pixels individually set in the light receiver for each wavelength and performs photoelectric conversion to a voltage value for each wavelength. For example, the light receiver of the spectral sensor 306 receives light divided into wavelengths of 10 nm, from 380 nm to 780 nm. The light receiver outputs a voltage based on the light intensity of each wavelength as an analog signal. The output value of light for each wavelength, which has been converted into a voltage value, is an analog signal. The A / D converter 307 converts the analog signal into a digital signal and sends the digital signal as spectral data to the color detection processing unit 305. The memory 304 stores various correction information, such as stray light data and dark current data of the spectral sensor 306. The spectral sensor drive unit 308 is a drive source for driving the spectral sensor unit 315 in the main scanning direction.

[0051] The color detection processing unit 305 is formed of a semiconductor device such as a field-programmable gate array (FPGA) or an application-specific integrated circuit (ASIC). The color detection processing unit 305 derives the average brightness value (average brightness value (R²)) of each color (each of the RGB values) in the color measurement area (detection image portion) based on the RGB brightness data acquired from the line sensor unit 312. A G A B A The average value is then transferred to CPU 114. CPU 114 includes a Color Transformation Lookup Table (LUT) for converting the luminance values ​​(RGB data) of each color in the RGB array into L*, a*, b* values. IN CPU 114 uses a color conversion lookup table (LUT). IN The average brightness value (R) of each color A G A B A ) converted to L a* ,a a* ,b a* The color detection processing unit 305 calculates the L*, a*, and b* values ​​based on the spectral data acquired from the spectral sensor unit 315. The color detection processing unit 305 outputs the calculated L*, a*, and b* values ​​to the CPU 114.

[0052] The operation of the line sensor unit 312, the spectral sensor unit 315, the image memory 303, the color detection and processing unit 305, and the original document detection sensor 311 is controlled by the CPU 114 of the controller 110. The image memory 303 stores the image data required for image processing performed by the CPU 114.

[0053] <Line Sensor>

[0054] Figure 4 This is an illustrative diagram showing the configuration of the line sensor 301. The line sensor 301 includes light-emitting units 400a and 400b, light guide members 402a and 402b, a lens array 403, and a sensor chipset 401. The line sensor 301 has a generally cuboid shape and reads images with its longitudinal direction as the main scanning direction.

[0055] Each of the light-emitting portions 400a and 400b is, for example, a light source formed by a light-emitting diode (LED) that emits white light. The light guide member 402a has a light-emitting portion 400a disposed at its end, and illuminates the recording sheet using light emitted from the light-emitting portion 400a. The light guide member 402b has a light-emitting portion 400b disposed at its end, and illuminates the recording sheet using light emitted from the light-emitting portion 400b. Each of the light guide members 402a and 402b is formed as a straight line in the main scanning direction. Therefore, the line sensor 301 illuminates the recording sheet using light that is linear in the main scanning direction. The main scanning direction of the line sensor unit 312 is the same as the main scanning direction of the printer 150.

[0056] Lens array 403 is an optical system for guiding reflected light from the recording sheet illuminated by light-emitting parts 400a and 400b to sensor chip group 401. Sensor chip group 401 is formed by a plurality of photoelectric conversion elements (sensor chips) arranged in rows in the main scanning direction. One sensor chip reads an image of one pixel. In a first embodiment, the plurality of sensor chips are arranged in three rows. One row is covered with a red (R) filter, another row with a green (G) filter, and yet another row with a blue (B) filter. Light guided by lens array 403 forms an image on the light-receiving surface of each sensor chip in sensor chip group 401.

[0057] Light emitted from light-emitting units 400a and 400b diffuses within light guide members 402a and 402b and exits from the curved portion to illuminate the entire area of ​​the recording sheet in the main scanning direction. Light guide members 402a and 402b are arranged across lens array 403 in a sub-scanning direction orthogonal to the main scanning direction. Therefore, the line sensor 301 has a side-illumination configuration where the lens array 403 (image readout line) is illuminated by light from both directions of the sub-scanning direction. The sub-scanning direction of the line sensor unit 312 is the same as the sub-scanning direction of the printer 150.

[0058] <Spectral Sensor Unit>

[0059] Figure 5 This is an illustrative diagram showing the configuration of the spectral sensor unit 315. The spectral sensor unit 315 has a generally cuboid shape, with its longitudinal direction being the main scanning direction. The recording sheet is in... Figure 5 The depth side of the spectral sensor unit 315 is transmitted in the sub-scanning direction. The spectral sensor 306, memory 304, and A / D converter 307 are integrally formed. The A / D converter 307 is connected to the color detection processing unit 305 via wiring such as a flexible flat cable (not shown).

[0060] A spectral sensor 306 is mounted on a track 309 extending from the spectral sensor drive unit 308 in the main scanning direction. The spectral sensor 306 moves on the track 309 via the spectral sensor drive unit 308. The spectral sensor drive unit 308 incorporates a stepper motor and is controlled based on instructions 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.

[0061] A home position HP is set outside the area (transfer area) where the spectral sensor unit 315 can read the recording sheet. A white plate 316 is arranged at the home position HP. The recording sheet is transferred line by line in the sub-scanning direction and enters a stop state at the timing of color measurement. The spectral sensor unit 315 has an opening 310 at a position corresponding to the transfer area. The spectral sensor 306 reads the recording sheet through the opening 310.

[0062] Before initiating color measurement, the spectral sensor 306 is positioned at its home position HP. Upon receiving a command from the CPU 114 to begin color measurement, the spectral sensor 306 reads the white plate 316 to perform calibrations such as light source intensity adjustment or white reference matching. After calibration, the spectral sensor 306 moves at a constant speed in the main scan direction from its home position HP and begins color measurement for one line in response to the detection of a trigger block. Upon completion of color measurement for one line, the spectral sensor 306 returns to its home position HP. Subsequently, after the recording sheet has moved one line in the sub-scan direction, the spectral sensor 306 again begins moving in the main scan direction to perform color measurement for one line. This process of moving one line of recording sheet and performing one line of color measurement by the spectral sensor 306 is repeated to perform color measurement for one recording sheet.

[0063] <Color Check>

[0064] Figure 6 This is a flowchart illustrating a printing process that includes color checking. The process begins when the user inputs a color check command via the operation panel 120 to initiate copying. For example, the color check command might include recording the sheet size, printing mode, and the quantity P of sheets to be printed. MAX The color value to be checked (specific color: L) 00 *、a 00 *、b 00 *), Color inspection of designated areas (areas X=X on the sheet) S to X E Y = Y S To Y E ) and the color inspection threshold Cth.

[0065] The CPU 114 obtains a color check instruction from the operation panel 120, sets the information required for each device to perform a printing job based on the instruction, and stores the various parameters included in the instruction into the RAM 113, thereby performing mode setting (step S600). After performing mode setting, the CPU 114 waits for a copy start instruction from the operation panel 120 (step S601: No).

[0066] After the CPU 114 receives the copy start instruction (step S601: Yes), the CPU 114 performs color calibration of the line sensor 301 according to the content of the color check instruction and creates a color calibration matrix M for the line sensor 301 (step S602). The color calibration matrix M is a conversion condition used to convert L*, a*, b*, which are converted from the reading results obtained from the line sensor 312, into color values ​​for color calibration. Details of the processing steps in step S602 are then described. After performing color calibration, the CPU 114 initializes the print count value P to "0" (step S603). The print count value P represents the number of recording sheets with an image formed thereon by the printer 150.

[0067] CPU 114 instructs printer 150 to perform printing processing, including printing an inspection image of a specific color, under conditions corresponding to a color inspection instruction, and generates printing material (step S604). CPU 114 instructs line sensor unit 312 to perform color measurement of the printing material (step S605). The color measurement is relative to a designated area for color inspection of the printing material (area X = X). S To X E Y = Y S To Y E The process is performed as follows: As a result of color measurement of the printing material, RGB brightness data is transmitted from the line sensor unit 312 to the color detection processing unit 305. The color detection processing unit 305 derives the average brightness value (R²) of each RGB color in the color measurement area based on the RGB brightness data acquired from the line sensor unit 312. A G A B A The average brightness value is then transmitted to CPU 114.

[0068] CPU 114 includes a color transformation lookup table (LUT) for converting the luminance values ​​(RGB data) of each color in the RGB spectrum into L*, a*, and b* values. IN CPU 114 uses a color conversion lookup table (LUT). IN The average brightness value (R) of each color A G A B A ) converted to L a* a a* b a* The CPU 114 uses the color calibration matrix M created in the processing step S602 to obtain the average luminance value (R). A G A B A ) to L a* a a* b a*The color value (L) is derived from the result of the value conversion. Pa* a Pa* b Pa* ).

[0069] CPU 114 derives the color value (L) obtained as a result of color measurement. Pa* a Pa* b Pa* ) and color values ​​(L) used as color information about a specific color 00 *、a 00 *、b 00 The CPU 114 compares the derived color difference ΔE00 with the color inspection threshold Cth used as a determination criterion (step S607). The color inspection result is determined based on the comparison result between the color difference ΔE00 and the color inspection threshold Cth.

[0070] If the color difference ΔE00 is equal to or less than the color inspection threshold Cth (step S607: Yes), the CPU 114 determines that the difference between the specific color of the image printed on the recording sheet and the specified specific color for which color inspection is expected is small. In this case, because printing is performed normally with the specific color, the CPU 114 increments the print count value P by 1 (step S608). The CPU 114 determines whether the print count value P has reached the number of sheets P to be printed. MAX (Step S610). Before the printing count value P reaches the number of sheets P to be printed. MAX In the case of (step S610: No), CPU 114 repeats step S604 and subsequent processing steps until the print count value P reaches the number of sheets to be printed. MAX The printing count P has reached the number of sheets P to be printed. MAX In the case of (step S610: Yes), CPU 114 ends the printing process including color checking.

[0071] If the color difference ΔE00 is greater than the color inspection threshold Cth (step S607: No), the CPU 114 determines that the difference between a specific color of the image printed on the recording sheet and the specified specific color for which color inspection is expected is large. In this case, because printing was not performed normally with the specified color, the CPU 114 causes the operation panel 120 to display a warning (step S609). The warning indicates that the specified area for color inspection has a large difference with the specified color L. 00 *、a 00 *、b 00* Separate colors with a large permissible color difference (color inspection threshold Cth) and an unsuitable color inspection result. In addition to an indication on the display, a warning can also be issued by generating an audio signal from a speaker. After the CPU 114 displays the warning, the CPU 114 terminates the printing process, including the color inspection process.

[0072] <Color Calibration Processing>

[0073] The color calibration process in step S602 is described. Figure 7 This is an illustration of an example color calibration chart used in the color calibration process of the online sensor unit 312. The color calibration chart 501 is created by printing 98 block images 504 as detection images on a recording sheet long in the sub-scanning direction. The block images 504 are arranged in 7 rows and 14 columns in the main scan direction and the sub-scanning direction, respectively. A margin 502 is set at the left end of the color calibration chart 501 in the main scan direction. A black trigger block 503 is provided to the right of the margin 502. To the right of the trigger block 503, 98 block images 504 are provided. The 98 block images 504 used for color calibration include 49 block images written as "Axx" and 49 block images written as "Pxx".

[0074] 49 block images written as "Axx" 504 are obtained by matching a specific color L 00 *、a 00 *、b 00 *and is calculated as being related to a specific color L 00 *、a 00 *、b 00 An image is obtained by selecting, in a single step, the L*, a*, and b* values ​​corresponding to the surrounding colors that have reached a predetermined color difference. In this case, the image density value is referred to as the "YMCK value". Figure 7 In the image, the middle block is a color L 00 *、a 00 *、b 00 *Image of YMCK values. YMCK values ​​are set for each of the following colors: Yellow (Y), Magenta (M), Cyan (C), and Black (K).

[0075] 49 block images written as "Pxx" 504 are obtained by matching a specific color L 00 *、a 00 *、b 00 *and is calculated as being related to a specific color L 00 *、a 00 *、b 00* An image obtained by secondary selection of the YMCK values ​​corresponding to the L*, a*, and b* values ​​of surrounding colors that have reached a predetermined color difference value. The primary and secondary selections have different selection criteria.

[0076] The method for selecting YMCK values ​​for the L*, a*, and b* values ​​of the 98 block images 504 is then described. The location of the block images 504 that form the color calibration chart 501 is not limited to... Figure 7 The location.

[0077] Figure 8 This is a flowchart used to illustrate the color calibration process. Figure 9 It is an illustrative diagram illustrating the method for calculating the L*, a*, and b* of the surrounding colors of a specific color. Figure 10A and Figure 10B It is a color conversion lookup table (LUT) used to perform color conversion from L*, a*, b* values ​​to YMCK values. OUT An illustrative diagram.

[0078] CPU 114 from a specific color L 00 *、a 00 *、b 00 *Calculate the L*, a*, and b* values ​​of the surrounding colors (step S800). To perform the calculation, the CPU 114 first retrieves the specific color L from the RAM 113. 00 *、a 00 *、b 00 *. CPU 114 calculates the specific color L 00 *、a 00 *、b 00 *The surrounding colors are separated by a predetermined color difference. For example, such as... Figure 9 As shown in the diagram, 48 surrounding colors are selected. The CPU 114 calculates L*, a*, and b* as predetermined color differences for the following 48 surrounding colors corresponding to ΔE00 = 2, 4, 6, 8, 10, and 12.

[0079] - Colors are separated by a color difference ΔE00 = 2, from surrounding color 01 to surrounding color 08.

[0080] →L*, a*, b* = L 01 *、a 01 *、b 01 *To L 08 *、a 08 *、b 08 *

[0081] - Colors are separated by a color difference ΔE00 = 4, with surrounding colors ranging from 09 to 16.

[0082] →L*, a*, b* = L 09 *、a09 *、b 09 *To L 16 *、a 16 *、b 16 *

[0083] - Colors are separated by a color difference ΔE00 = 6, with surrounding colors 17 to 24.

[0084] →L*, a*, b* = L 17 *、a 17 *、b 17 *To L 24 *、a 24 *、b 24 *

[0085] - Colors are separated by a color difference ΔE00 = 8, with surrounding colors ranging from 25 to 32.

[0086] →L*, a*, b* = L 25 *、a 25 *、b 25 *To L 32 *、a 32 *、b 32 *

[0087] - Colors are separated by a color difference ΔE00 = 10, with surrounding colors ranging from 33 to 40.

[0088] →L*, a*, b* = L 33 *、a 33 *、b 33 *To L 40 *、a 40 *、b 40 *

[0089] - Colors are separated by a color difference ΔE00 = 12, with surrounding colors 41 to 48.

[0090] →L*, a*, b* = L 41 *、a 41 *、b 41 *To L 48 *、a 48 *、b 48 *

[0091] CPU 114 calculates the block color as the color of the block image to be used in color calibration chart 501 (performs a selection once) (step S801). The block color is an image density value (YMCK value). CPU 114 bases its calculations on a color transformation lookup table (LUT) stored in ROM 112. OUT To convert L calculated in step S800 00 *、a00 *、b 00 *To L 48 *、a 48 *、b 48 * The result is the calculation of the YMCK value corresponding to each L*, a*, b* value (a single calculation of the block color (L*, a*, b*)). Reference Figure 10A and Figure 10B This describes a color conversion lookup table (LUT) used to convert L*, a*, and b* values ​​into YMCK values, which are used as printing parameters. OUT .

[0092] Figure 10A and Figure 10B The color conversion lookup table (LUT) is shown. OUT The concept. Figure 10A It is a three-dimensional color transformation lookup table (LUT) for the input color space (Lab color space). OUT In the color conversion lookup table (LUT) OUT In this example, cubes are arranged at equal intervals in the Lab color space. In this case, the Lab color space is the CIE 1976 (L*, a*, b*) color space, but it could also be the Hunter 1948 L, a, b color space. Each vertex (grid point) of the cube represents a position (L*, a*, b* value) in the Lab color space. In this case, L* represents lightness, and a* and b* represent chroma. At each grid point, a block color (YMCK value) corresponding to the L*, a*, b* value at that position is assigned.

[0093] For example, L at the grid point β *、a β *、b β *When the L*, a*, b* values ​​are specified as the values ​​to be converted, the output is a color conversion lookup table (LUT). OUT The corresponding block color (YMCK value) of Y β M β C β and K β .

[0094] exist Figure 10B The table interpolation method is described below. The L*, a*, and b* values ​​for which color conversion is expected are located in the region surrounded by grid points 1 to 8. Given that the distances from the L*, a*, and b* values ​​to grid points 1 to 8 are d1 to d8 respectively, the block color (YMCK value) is calculated based on the distance to each grid point as follows.

[0095] Y=(Y1 / d1+Y2 / d2+…+Y8 / d8) / (1 / d1+1 / d2+…+1 / d8)

[0096] M=(M1 / d1+M2 / d2+…+M8 / d8) / (1 / d1+1 / d2+…+1 / d8)

[0097] C=(C1 / d1+C2 / d2+…+C8 / d8) / (1 / d1+1 / d2+…+1 / d8)

[0098] K=(K1 / d1+K2 / d2+…+K8 / d8) / (1 / d1+1 / d2+…+1 / d8)

[0099] Color Conversion Lookup Table (LUT) OUT It is stored in ROM 112 and the CPU 114 performs the conversion operation from L*, a*, b* values ​​to block color (YMCK value).

[0100] CPU 114 performs the calculation of the block color (YMCK value) (performs secondary selection) (step S802). CPU 114 specifies the L value of the specific color and the surrounding colors. 00 *、a 00 *、b 00 *To L 48 *、a 48 *、b 48 *The color conversion lookup table (LUT) stored in ROM 112 OUT ( Figure 10A Which position on )? The color conversion lookup table (LUT) was confirmed on CPU 114. OUT After determining the position, CPU 114 selects the grid point with the smallest distance among the surrounding grid points. CPU 114 sets the YMCK value associated with the selected grid point as the calculation result (a secondary calculation of the block color (L*, a*, b*)).

[0101] For example, in Figure 10B In the diagram, the values ​​of L*, a*, and b* for which color conversion is desired lie within the region surrounded by grid points 1 to 8. The distances from the values ​​of L*, a*, and b* to grid points 1 to 8 are d1 to d8, respectively, with d1 having the minimum value. In this case, the YMCK value is calculated as follows.

[0102] Y = Y1

[0103] M = M1

[0104] C = C1

[0105] K = K1

[0106] CPU 114 causes printer 150 to create based on the block color (YMCK value) calculated in steps S801 and S802. Figure 7 Color calibration chart 501 (step S803). CPU 114 performs color measurement of the created color calibration chart via line sensor 301 and spectral sensor unit 315 (step S804).

[0107] The line sensor 301 outputs the brightness values ​​(RGB data) of each color as a color measurement result to the color detection processing unit 305. The color detection processing unit 305 calculates the average brightness value (R²) of each RGB color in the measurement area based on the RGB data acquired from the line sensor unit 312. A G A B A CPU 114 uses a color transformation lookup table (LUT) to convert the luminance values ​​of R, G, and B into L*, a*, and b* values. IN Average brightness value (R) A G A B A The values ​​are converted into L*, a*, and b* values. The CPU 114 acquires 98 Lab values ​​as the color measurement results obtained by the line sensor unit 312. These 98 Lab values ​​are L*, a*, and b* values. L_A00 *、a L_A00 *、b L_A00 *To L L_A48 *、a L_A48 *、b L_A48 *and L L_P00 *、a L_P00 *、b L_P00 *To L L_P48 *、a L_P48 *、b L_P48 The value of *.

[0108] The spectral sensor 306 outputs spectral data from the measurement area of ​​the color calibration chart 501, which serves as the color measurement result, to the color detection and processing unit 305. The spectral data consists of 98 L*, a*, and b* values. Specifically, the spectral data is L... S_A00 *、a S_A00 *、b S_A00 *To L S_A48 *、a S_A48 *、b S_A48 *and L S_P00 *、a S_P00 *、b S_P00 *To L S_P48 *、a S_P48 *、b S_P48 * The color detection processing unit 305 calculates the L*, a*, and b* values ​​based on the spectral data acquired from the spectral sensor unit 315. The color detection processing unit 305 outputs the calculated L*, a*, and b* values ​​to the CPU 114.

[0109] CPU 114 selects from 98 L*, a*, b* values ​​measured by spectral sensor 306 that have an L* value calculated in step S800. 00 *、a 00 *、b 00 *To L 48 *、a 48 *、b 48 The 49 data points whose values ​​are closest to the * value (step S805). The 49 selected L*, a*, b* values ​​are determined by Z. A00 Z B00 Z C00 To Z A48 Z B48 Z C48 This indicates that the CPU 114 selects the color measurement data from the line sensor 301, based on the measurement data obtained by the line sensor 301 and the Z-axis. A00 Z B00 Z C00 To Z A48 Z B48 Z C48 Forty-nine L*, a*, b* values ​​were obtained when the colors of the same block image were being analyzed. The selected 49 L*, a*, b* values ​​were determined by X. A00 X B00 X C00 To X A48 X B48 X C48 express.

[0110] CPU 114 generates the color calibration matrix M of line sensor 301 (step S806). CPU 114 uses Z... A00 Z B00 Z C00 To Z A48 Z B48 Z C48 and X A00 X B00 X C00 To X A48 X B48 X C48 The color calibration matrix M, used as training data, is calculated from the measurement results of the calibration line sensor 301 using the following expression. The color calibration matrix M is a 3×10 matrix. The CPU 114 stores the calculated color calibration matrix M in RAM 113. As described above, the color calibration matrix M is obtained through color calibration processing.

[0111]

[0112]

[0113] Where: X T It is the transpose of matrix X, and (X) T *X) -1 Yes (X) T The inverse matrix of *X).

[0114] As described above, in the first embodiment, a color calibration chart, on which a block image to be used for color calibration of the line sensor 301 is printed, can be created in a single printing process. As a result, color calibration of the line sensor 301 can be performed with high precision, and highly accurate color measurement of the image is allowed. Therefore, a highly accurate color inspection system can be realized.

[0115] <Second Embodiment>

[0116] The image forming apparatus 100 in the second embodiment of this disclosure is configured similarly to the configuration in the first embodiment. The second embodiment differs from the first embodiment in the content of the color calibration process, but other parts of the second embodiment are the same as some parts of the first embodiment. The different parts are described below.

[0117] <Color Calibration Processing>

[0118] describe Figure 6 The color calibration process in step S602. Figure 11 This is an illustration of an example of a color calibration chart used in the color calibration process of the online sensor unit 312. A color calibration chart 501 is created by printing 49 block images 504 as detection images on a recording sheet that is long in the sub-scanning direction. The block images 504 are arranged in 7 rows and 7 columns in the main scan direction and the sub-scanning direction, respectively. A margin 502 is set at the left end of the color calibration chart 501 in the main scan direction. A black trigger block 503 is set to the right of the margin 502. The 49 block images 504 are set to the right of the trigger block 503.

[0119] The 49 block images 504 used for color calibration are those with a specific color L 00 *、a 00 *、b 00 *and is calculated as being related to a specific color L 00 *、a 00 *、b 00 * An image of the image density values ​​corresponding to the L*, a*, and b* values ​​of the surrounding colors that have reached a predetermined color difference value. Figure 11 In the image, the middle block is a color L 00 *、a 00 *、b 00*Image of image density values. Image density values ​​are set for each of the colors yellow (Y), magenta (M), cyan (C), and black (K). In this case, the image density values ​​are referred to as "YMCK values". The location of the block image 504 forming the color calibration chart 501 is not limited to... Figure 11 The location.

[0120] Figure 12 This is a flowchart used to illustrate the color calibration process. Figure 13 It is an illustrative diagram illustrating the method for calculating the L*, a*, and b* of the surrounding colors of a specific color.

[0121] CPU 114 from a specific color L 00 *、a 00 *、b 00 *Calculate the L*, a*, and b* values ​​of the surrounding colors (step S900). To perform the calculation, the CPU 114 first retrieves the specific color L from the RAM 113. 00 *、a 00 *、b 00 *And the color check threshold Cth. CPU114 calculates the value relative to a specific color L. 00 *、a 00 *、b 00 * Separate surrounding colors to achieve a predetermined color difference. Select surrounding colors such that the range of the predetermined color difference spans the color inspection threshold Cth(ΔEmin). <Cth<ΔEmax)。

[0122] For example, such as Figure 13 As shown in the diagram, select one of 48 surrounding colors. Figure 13 An example is shown where the color inspection threshold Cth is "5". CPU 114 selects ΔE00 = 2 and 4 (less than ΔE00 = 5) and ΔE00 = 6, 8, 10, and 12 (greater than ΔE00 = 5) as predetermined color differences, such that the range of ΔE00 spans ΔE00 = 5. CPU 114 calculates L*, a*, and b* for the following 48 surrounding colors corresponding to the selected ΔE00.

[0123] - Colors are separated by a color difference ΔE00 = 2, from surrounding color 01 to surrounding color 08.

[0124] →L*, a*, b* = L 01 *、a 01 *、b 01 *To L 08 *、a 08 *、b 08 *

[0125] - Colors are separated by a color difference ΔE00 = 4, with surrounding colors ranging from 09 to 16.

[0126] →L*, a*, b* = L 09 *、a 09 *、b 09 *To L 16 *、a 16 *、b 16 *

[0127] - Colors are separated by a color difference ΔE00 = 6, with surrounding colors 17 to 24.

[0128] →L*, a*, b* = L 17 *、a 17 *、b 17 *To L 24 *、a 24 *、b 24 *

[0129] - Colors are separated by a color difference ΔE00 = 8, with surrounding colors ranging from 25 to 32.

[0130] →L*, a*, b* = L 25 *、a 25 *、b 25 *To L 32 *、a 32 *、b 32 *

[0131] - Colors are separated by a color difference ΔE00 = 10, with surrounding colors ranging from 33 to 40.

[0132] →L*, a*, b* = L 33 *、a 33 *、b 33 *To L 40 *、a 40 *、b 40 *

[0133] - Colors are separated by a color difference ΔE00 = 12, with surrounding colors 41 to 48.

[0134] →L*, a*, b* = L 41 *、a 41 *、b 41 *To L 48 *、a 48 *、b 48 *

[0135] CPU 114 calculates the block colors (Y, M, C, K) of the block image to be used in color calibration chart 501 (step S901). CPU 114 uses the color transformation lookup table (LUT) stored in ROM 112 as a reference. OUT To convert L 00 *、a00 *、b 00 *To L 48 *、a 48 *、b 48 * The result is the calculation of the YMCK value corresponding to each L*, a*, b* value (the calculation of the block color (L*, a*, b*)). A color conversion lookup table (LUT) is used to convert the L*, a*, b* values ​​into YMCK values ​​as printing parameters. OUT It refers to the first embodiment. Figure 10A and Figure 10B Described.

[0136] CPU 114 causes printer 150 to create based on the block color (YMCK value) calculated in the processing step S901. Figure 11 The color calibration chart 501 is generated (step S902). The CPU 114 performs color measurements on the created color calibration chart via the line sensor 301 and the spectral sensor unit 315 (step S903).

[0137] The line sensor 301 outputs the brightness values ​​(RGB data) of each color as a color measurement result to the color detection processing unit 305. The color detection processing unit 305 calculates the average brightness value (R²) of each RGB color in the measurement area based on the RGB data acquired from the line sensor unit 312. A G A B A CPU 11 uses a color transformation lookup table (LUT) to convert the luminance values ​​of R, G, and B into L*, a*, and b* values. IN Average brightness value (R) A G A B A Convert L*, a*, and b* values. CPU 114 retrieves L... L_A00 *、a L_A00 *、b L_A00 *To L L_A48 *、a L_A48 *、b L_A48 The 49 L*, a*, b* values ​​are used as color measurement values ​​obtained by the line sensor unit 312.

[0138] The spectral sensor 306 outputs the spectral data from the color calibration chart 501, which serves as the color measurement result, to the color detection and processing unit 305. The color detection and processing unit 305 acquires L... S_A00 *、a S_A00 *、b S_A00 *To L S_A48 *、a S_A48 *、b S_A48The 49 L*, a*, and b* values ​​are used as spectral data. The color detection processing unit 305 calculates the L*, a*, and b* values ​​based on the spectral data acquired from the spectral sensor unit 315. The color detection processing unit 305 outputs the calculated L*, a*, and b* values ​​to the CPU 114.

[0139] The 49 L*, a*, b* values ​​of the spectral data acquired by the color detection and processing unit 305 are derived from Z. A00 Z B00 Z C00 To Z A48 Z B48 Z C48 Indicated. The measurement by line sensor 301 and Z... A00 Z B00 Z C00 To Z A48 Z B48 Z C48 The L*, a*, b* values ​​obtained under the same block image color are determined by X. A00 X B00 X C00 To X A48 X B48 X C48 express.

[0140] CPU 114 generates the color calibration matrix M of line sensor 301 (step S904). CPU 114 uses Z... A00 Z B00 Z C00 To Z A48 Z B48 Z C48 and X A00 X B00 X C00 To X A48 X B48 X C48 The color calibration matrix M is used as training data to calculate the measurement results for calibrating the line sensor 301. The color calibration matrix M is a 3×10 matrix. The CPU 114 stores the calculated color calibration matrix M in RAM 113. The calculation of the color calibration matrix M is as described in the first embodiment.

[0141] As described above, in the second embodiment, printer 150 prints a specific color and surrounding colors with a predetermined color difference from the specific color on a recording sheet as a detection image, thereby creating a color calibration chart. The color calibration chart is read by reader 160. Based on the result of reader 160 reading the color calibration chart, an RGB→Lab color conversion table for the specific color is created. As a result, the conversion accuracy from RGB to Lab for colors near the specific color is improved, and a highly accurate color inspection system can be realized.

[0142] While the invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the appended claims should be given the broadest interpretation to include all such modifications and equivalent structures and functions.

[0143] This application claims the benefit of Japanese Patent Application No. 2021-038570 and Japanese Patent Application No. 2021-038564, filed on March 10, 2021, the entire contents of which are incorporated herein by reference.

Claims

1. An information processing device, comprising: The acquisition component is configured to acquire color information about specific colors included in the inspected image and determination conditions related to the permissible color difference relative to the specific color; as well as The control unit is configured as follows: Test image data representing multiple test images to be formed by the image forming apparatus is determined based on color information acquired by the acquisition component and determination conditions. The determined test image data is output to the image forming apparatus to form the plurality of test images; Brightness data for the plurality of test images is acquired, the brightness data for the plurality of test images being output from a color sensor; Acquire spectral data for the plurality of test images, the spectral data for the plurality of test images being output from a spectral sensor; A conversion condition for converting the readings obtained by the color sensor is generated based on the spectral data and brightness data of the plurality of test images. The brightness data of the image to be formed by the image forming apparatus is acquired from the color sensor. The brightness data of the image to be formed by the image forming apparatus is transformed based on the transformation conditions. as well as The color shift relative to a specific color in the inspected image is determined based on the converted luminance data and specific criteria. The plurality of test images includes a first test image of a first color having a first value of color difference from a specific color, and a second test image of a second color having a second value of color difference from a specific color. Wherein, the first value is less than the allowable color difference, and The second value is greater than the allowable color difference.

2. The information processing device according to claim 1, wherein If the lightness of the first color is greater than the lightness of the specific color, then the lightness of the second color is greater than the lightness of the specific color. Specifically, if the lightness of the first color is less than the lightness of the specific color, then the lightness of the second color is also less than the lightness of the specific color. Specifically, if the value of the "a" component of the first color in the Lab color space is greater than the value of the "a" component of a specific color in the Lab color space, then the value of the "a" component of the second color in the Lab color space is also greater than the value of the "a" component of the specific color in the Lab color space. Specifically, if the value of the "a" component of the first color in the Lab color space is less than the value of the "a" component of a specific color in the Lab color space, then the value of the "a" component of the second color in the Lab color space is also less than the value of the "a" component of the specific color in the Lab color space. Where the value of the "b" component of the first color in the Lab color space is greater than the value of the "b" component of a specific color in the Lab color space, the value of the "b" component of the second color in the Lab color space is also greater than the value of the "b" component of the specific color in the Lab color space. Specifically, if the value of the "b" component of the first color in the Lab color space is less than the value of the "b" component of a specific color in the Lab color space, then the value of the "b" component of the second color in the Lab color space is also less than the value of the "b" component of the specific color in the Lab color space.

3. The information processing device according to claim 1, in, The plurality of test images also includes a third test image of a third color having a third value of color difference from the specific color, a fourth test image of a fourth color having a fourth value of color difference from the specific color, a fifth test image of a fifth color having a fifth value of color difference from the specific color, and a sixth test image of a sixth color having a sixth value of color difference from the specific color. Among them, the third value is less than the allowable color difference. Among them, the fourth value is greater than the allowable color difference. Among them, the fifth value is less than the allowable color difference. Among them, the sixth value is greater than the allowable color difference. The brightness of the third color is different from that of the first color. The chromaticity of the third color differs from that of the first color. The brightness of the fourth color is different from that of the second color. The chromaticity of the fourth color is different from that of the second color. The brightness of the fifth color is different from that of the first color. The chromaticity of the fifth color differs from that of the first color. The brightness of the sixth color is different from that of the second color, and The chromaticity of the sixth color is different from that of the second color.

4. The information processing device according to claim 3, in, The lightness of the first color in the Lab color space is greater than the lightness of a specific color in the Lab color space, but less than the lightness of the second color in the Lab color space. In the Lab color space, the value of the "a" component of the first color is greater than the value of the "a" component of a specific color in the Lab color space, but less than the value of the "a" component of the second color in the Lab color space. In the Lab color space, the value of the "b" component of the first color is greater than the value of the "b" component of a specific color in the Lab color space, but less than the value of the "b" component of the second color in the Lab color space. In the Lab color space, the lightness of the third color is less than the lightness of a specific color in the Lab color space, but greater than the lightness of the fourth color in the Lab color space. In the Lab color space, the value of the "a" component of the third color is greater than the value of the "a" component of a specific color in the Lab color space, but less than the value of the "a" component of the fourth color in the Lab color space. In the Lab color space, the value of the "b" component of the third color is less than the value of the "b" component of a specific color in the Lab color space, but greater than the value of the "b" component of the fourth color in the Lab color space. In the Lab color space, the lightness of the fifth color is less than the lightness of a specific color in the Lab color space, but greater than the lightness of the sixth color in the Lab color space. In the Lab color space, the value of the "a" component of the fifth color is less than the value of the "a" component of a specific color in the Lab color space, but greater than the value of the "a" component of the sixth color in the Lab color space. In the Lab color space, the value of the "b" component of the fifth color is greater than the value of the "b" component of a specific color in the Lab color space, and less than the value of the "b" component of the sixth color in the Lab color space.

5. The information processing device according to claim 3, wherein, The shape formed by connecting the positions of the first, third, and fifth colors in the Lab color space is similar to the shape formed by connecting the positions of the second, fourth, and sixth colors in the Lab color space.

6. The information processing device according to claim 3, in, The plurality of test images also includes a seventh test image of a seventh color having a seventh value of color difference from a specific color, and an eighth test image of an eighth color having an eighth value of color difference from a specific color. The seventh value is less than the allowable color difference. Among them, the eighth value is greater than the allowable color difference. In this case, the brightness of the seventh color is equal to the brightness of the first color. The chromaticity of the seventh color differs from that of the first color. In this case, the brightness of the eighth color is equal to the brightness of the second color, and The chromaticity of the eighth color is different from that of the second color.

7. The information processing device according to claim 1, in, The plurality of test images further includes a third test image of a third color having a third value of color difference with the specific color, a fourth test image of a fourth color having a fourth value of color difference with the specific color, a fifth test image of a fifth color having a fifth value of color difference with the specific color, a sixth test image of a sixth color having a sixth value of color difference with the specific color, a seventh test image of a seventh color having a seventh value of color difference with the specific color, an eighth test image of an eighth color having an eighth value of color difference with the specific color, a ninth test image of a ninth color having a ninth value of color difference with the specific color, a tenth test image of a tenth color having a tenth value of color difference with the specific color, an eleventh test image of an eleventh color having an eleventh value of color difference with the specific color, a twelfth test image of a twelfth color having a twelfth value of color difference with the specific color, a thirteenth test image of a thirteenth color having a thirteenth value of color difference with the specific color, a fourteenth test image of a fourteenth color having a fourteenth value of color difference with the specific color, a fifteenth test image of a fifteenth color having a fifteenth value of color difference with the specific color, and a sixteenth test image of a sixteenth color having a sixteenth value of color difference with the specific color. Among them, the third value is less than the allowable color difference. Among them, the fourth value is greater than the allowable color difference. Among them, the fifth value is less than the allowable color difference. Among them, the sixth value is greater than the allowable color difference. The seventh value is less than the allowable color difference. Among them, the eighth value is greater than the allowable color difference. Among them, the ninth value is less than the allowable color difference. Among them, the tenth value is greater than the allowable color difference. Among them, the eleventh value is less than the allowable color difference. Among them, the twelfth value is greater than the allowable color difference. Among them, the thirteenth value is less than the allowable color difference. Among them, the fourteenth value is greater than the allowable color difference. Wherein, the fifteenth value is less than the allowable color difference, and The sixteenth value is greater than the allowable color difference.

8. The information processing device according to claim 1, wherein, The control unit is configured to determine the color difference based on color information and converted luminance data, and compare the determined color difference with the allowable color difference, thereby determining the color shift in the inspected image relative to a specific color.

9. The information processing device according to claim 8, wherein, The control unit is configured to output an error notification if the determined color difference is greater than the allowable color difference.

10. The information processing device according to claim 1, in, The color sensor is configured to output brightness data based on 630 nm light, brightness data based on 530 nm light, and brightness data based on 440 nm light. The spectral sensor is configured to output spectral data based on light with a wavelength range greater than 3.

11. A method for controlling an image forming apparatus for forming an image onto a sheet, the method comprising: The first acquisition step is to acquire color information about specific colors included in the inspected image; The second acquisition step is to acquire the determining conditions related to the permissible color difference relative to a specific color; The steps involve determining test image data representing multiple test images based on color information and defined conditions. The printing process involves printing the multiple test images based on the test image data. The first reading step involves reading the multiple test images using a color sensor configured to receive reflected light from the target being measured and output red brightness data, green brightness data, and blue brightness data about the target being measured. The second reading step involves reading the plurality of test images using a spectral sensor configured to receive reflected light from the target being measured, detect the light intensity of each of more than three wavelengths for the target being measured, and output spectral data based on the light intensity of each of the plurality of wavelengths. The generation step generates conversion conditions based on spectral and luminance data to convert the readings obtained from the color sensor. Printing steps, printing inspection images; The third reading step involves reading the inspection image using a color sensor. The conversion step involves converting the brightness data of the inspected image based on conversion conditions. as well as The determination process involves identifying the color shift relative to a specific color in the inspected image based on the converted luminance data and defined conditions. The plurality of test images includes a first test image of a first color having a first value of color difference from a specific color, and a second test image of a second color having a second value of color difference from a specific color. Wherein, the first value is less than the allowable color difference, and The second value is greater than the allowable color difference.

12. The method for controlling an image forming apparatus according to claim 11, in, If the lightness of the first color is greater than the lightness of the specific color, then the lightness of the second color is greater than the lightness of the specific color. Specifically, if the lightness of the first color is less than the lightness of the specific color, then the lightness of the second color is also less than the lightness of the specific color. Specifically, if the value of the "a" component of the first color in the Lab color space is greater than the value of the "a" component of a specific color in the Lab color space, then the value of the "a" component of the second color in the Lab color space is also greater than the value of the "a" component of the specific color in the Lab color space. Specifically, if the value of the "a" component of the first color in the Lab color space is less than the value of the "a" component of a specific color in the Lab color space, then the value of the "a" component of the second color in the Lab color space is also less than the value of the "a" component of the specific color in the Lab color space. Where the value of the "b" component of the first color in the Lab color space is greater than the value of the "b" component of a specific color in the Lab color space, the value of the "b" component of the second color in the Lab color space is also greater than the value of the "b" component of the specific color in the Lab color space. Specifically, if the value of the "b" component of the first color in the Lab color space is less than the value of the "b" component of a specific color in the Lab color space, then the value of the "b" component of the second color in the Lab color space is also less than the value of the "b" component of the specific color in the Lab color space.

13. The method for controlling an image forming apparatus according to claim 11, in, The plurality of test images also includes a third test image of a third color having a third value of color difference from the specific color, a fourth test image of a fourth color having a fourth value of color difference from the specific color, a fifth test image of a fifth color having a fifth value of color difference from the specific color, and a sixth test image of a sixth color having a sixth value of color difference from the specific color. Among them, the third value is less than the allowable color difference. Among them, the fourth value is greater than the allowable color difference. Among them, the fifth value is less than the allowable color difference. Among them, the sixth value is greater than the allowable color difference. The brightness of the third color is different from that of the first color. The chromaticity of the third color differs from that of the first color. The brightness of the fourth color is different from that of the second color. The chromaticity of the fourth color is different from that of the second color. The brightness of the fifth color is different from that of the first color. The chromaticity of the fifth color differs from that of the first color. The brightness of the sixth color is different from that of the second color, and The chromaticity of the sixth color is different from that of the second color.

14. The method for controlling an image forming apparatus according to claim 11, in, The plurality of test images further includes a third test image of a third color having a third value of color difference with the specific color, a fourth test image of a fourth color having a fourth value of color difference with the specific color, a fifth test image of a fifth color having a fifth value of color difference with the specific color, a sixth test image of a sixth color having a sixth value of color difference with the specific color, a seventh test image of a seventh color having a seventh value of color difference with the specific color, an eighth test image of an eighth color having an eighth value of color difference with the specific color, a ninth test image of a ninth color having a ninth value of color difference with the specific color, a tenth test image of a tenth color having a tenth value of color difference with the specific color, an eleventh test image of an eleventh color having an eleventh value of color difference with the specific color, a twelfth test image of a twelfth color having a twelfth value of color difference with the specific color, a thirteenth test image of a thirteenth color having a thirteenth value of color difference with the specific color, a fourteenth test image of a fourteenth color having a fourteenth value of color difference with the specific color, a fifteenth test image of a fifteenth color having a fifteenth value of color difference with the specific color, and a sixteenth test image of a sixteenth color having a sixteenth value of color difference with the specific color. Among them, the third value is less than the allowable color difference. Among them, the fourth value is greater than the allowable color difference. Among them, the fifth value is less than the allowable color difference. Among them, the sixth value is greater than the allowable color difference. The seventh value is less than the allowable color difference. Among them, the eighth value is greater than the allowable color difference. Among them, the ninth value is less than the allowable color difference. Among them, the tenth value is greater than the allowable color difference. Among them, the eleventh value is less than the allowable color difference. Among them, the twelfth value is greater than the allowable color difference. Among them, the thirteenth value is less than the allowable color difference. Among them, the fourteenth value is greater than the allowable color difference. Wherein, the fifteenth value is less than the allowable color difference, and The sixteenth value is greater than the allowable color difference.

15. The method for controlling an image forming apparatus according to claim 11, further comprising a notification step of outputting an error notification when the color offset is greater than the allowable color difference.

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