JP7070046B2 - Color inspection device, image forming device, color inspection method and program - Google Patents

Description

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

In the field of production printing where high-quality printed images are required, in order to improve the color reproducibility and color stability of the printed images, an image reading means is provided in the image forming apparatus to detect the printed images and the results are obtained. A technique for feeding back to a printing mechanism is known. The image reading means used in this technique generally uses a reading method similar to that of a scanner, exposes the object to be read by an LED (Light Emitting Diode) light source, and reads the reflected light by a line sensor. Then, the read RGB values are converted into a color space such as L * a * b * or CMYK using a color conversion formula generated in advance, and the converted color information is fed back to the subsequent stage.

Further, there is a technique for detecting the presence or absence of an abnormality in a printed image by comparing a scanned image obtained by reading a printed image with an image reading means and a user's print data. In this abnormality detection, since the scanned image and the print data are compared, it is desirable to read with the same resolution in the main scanning direction and the sub-scanning direction. Usually, in an image forming apparatus, there are a plurality of linear speeds in preparation for the case where productivity is prioritized, the image quality in thick paper printing (fixability of color material) is prioritized, and the like. In this case, even in the place where the image reading means is arranged, the linear speed of paper transport often changes in synchronization with the above-mentioned linear speed, and the resolution in the sub-scanning direction changes due to the change of the linear speed. In such a case, a technique is disclosed in which the reading speed is adjusted according to the transport speed (line speed) so that the resolution is constant, and the amount of light that illuminates the paper in synchronization with the reading speed is adjusted (. See Patent Document 1).

However, in the technique of Patent Document 1, since the reading speed (line period) of the image reading means and the light amount (current) of the light source are changed, when an LED or the like is used as the light source, the spectral characteristics change due to the change of the current. There is a problem that the color conversion accuracy deteriorates.

The present invention has been made in view of the above, and provides a color inspection device, an image forming device, a color inspection method, and a program capable of suppressing changes in the spectral characteristics of a light source and suppressing deterioration of color conversion accuracy. The purpose is to provide.

In order to solve the above-mentioned problems and achieve the object, the present invention has a lighting unit that illuminates a subject with light, a reading unit that reads reflected light of the light from the subject to obtain a reading value, and the subject . A lighting control unit that controls the driving conditions of the lighting unit to be constant even if the linear velocity of the lighting unit is changed, and a color conversion unit that converts information based on the reading value into color information in a predetermined color space. A reading control unit that controls the reading speed of the reading unit to be constant even if the linear speed of the subject changes, and the reading unit that reads the subject even if the linear speed of the subject changes. It is characterized by including a resolution conversion unit that performs resolution conversion so that the resolution of the scanned image composed of values is constant.

According to the present invention, it is possible to suppress changes in the spectral characteristics of the light source and suppress deterioration of color conversion accuracy.

FIG. 1 is a diagram showing an example of the overall structure of the image forming apparatus according to the embodiment. FIG. 2 is a diagram illustrating the effect of the prior art. FIG. 3 is a diagram illustrating problems in the prior art. FIG. 4 is a diagram illustrating problems in the prior art. FIG. 5 is a diagram showing an example of the hardware configuration of the image forming apparatus according to the embodiment. FIG. 6 is a diagram showing an example of the configuration of the functional block of the image forming apparatus according to the embodiment. FIG. 7 is a diagram showing an example of the configuration of the functional block of the color inspection device according to the embodiment. FIG. 8 is a diagram illustrating the effect when the current of the light source is fixed. FIG. 9 is a diagram illustrating a change in resolution in the sub-scanning direction. FIG. 10 is a diagram illustrating an operation of converting the resolution in the sub-scanning direction. FIG. 11 is a flowchart showing an example of the flow of the color conversion process of the color inspection apparatus according to the embodiment. FIG. 12 is a diagram illustrating variations in the light emission characteristics of the light source for each device. FIG. 13 is a flowchart showing an example of the flow of the process of generating the color conversion formula in the modification 2.

Hereinafter, embodiments of a color inspection apparatus, an image forming apparatus, a color inspection method, and a program according to the present invention will be described in detail with reference to the drawings. Further, the present invention is not limited to the following embodiments, and the components in the following embodiments include those easily conceived by those skilled in the art, substantially the same, and so-called equivalent ranges. Is included. Further, various omissions, substitutions, changes and combinations of components can be made without departing from the gist of the following embodiments.

(Overall structure of image forming apparatus)
FIG. 1 is a diagram showing an example of the overall structure of the image forming apparatus according to the embodiment. The configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. 1. The image forming apparatus according to the present embodiment will be described as being a multifunction device (MFP: Multifunction Peripheral). Here, the multifunction device is a device having at least two functions of a printing function, a copying function, a scanner function, and a fax function.

As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an image reading apparatus 101, an automatic document feeder (ADF: Auto Document Feeder) 102, a paper feeding unit 103, and a main body 104. ing.

The image reading device 101 is a device that acquires image data by reading an image of a document placed on a contact glass. The automatic document feeder 102 is a device that automatically feeds the placed originals onto the contact glass.

The paper feed unit 103 is a unit that feeds printing paper for image formation to the main body 104. The transport path 107 in the paper feed unit 103 is a transport path for transporting the printing paper fed from the paper feed cassette to the main body 104.

The main body 104 is a portion for forming an image on the printing paper fed from the paper feeding unit 103. The main body 104 includes a resist roller 108, an image forming unit 105, an optical writing device 109, an intermediate transfer belt 113, a fixing transfer unit 110, a reading device 114, a white reference plate 115, and a double-sided tray 111. I have.

The resist roller 108 is a roller that feeds the printing paper fed from the feeding unit 103 so as to synchronize with the color toner image on the intermediate transfer belt 113.

The image forming unit 105 is a tandem type device that forms (images) images of each color of yellow (Y), cyan (C), magenta (M), and black (K). The image forming unit 105 includes a developer 106 and a photoconductor drum 112 for each color.

The developer 106 is a member that supplies toner of each color to the photoconductor drum 112 on which an electrostatic image is formed to develop an electrostatic latent image and forms a toner image of each color. The surface of the photoconductor drum 112 is charged, and the optical writing device 109 irradiates the charged surface with a laser beam modulated and polarized based on the image data of each color, and an electrostatic latent image of each color is formed on the charged surface. It is a member.

The optical writing device 109 irradiates the surface of the photoconductor drum 112 of each color with a laser beam modulated based on the image data of each color to form an electrostatic latent image of the image of each color on the photoconductor drum 112. It is a device.

The intermediate transfer belt 113 is a belt tension-tensioned by a plurality of tension rollers, and by applying an intermediate transfer bias from a power source (not shown), toner images on each photoconductor drum 112 are sequentially superimposed in multiple layers. It is a belt to which the color toner image is transferred (primary transfer).

The fixing transport unit 110 is a member that fixes the color toner image on the printing paper by heating the printing paper on which the color toner image is secondarily transferred from the intermediate transfer belt 113, and transports the printing paper to the paper ejection unit side. be.

The reading device 114 is a device that performs reading (imaging) in order to perform color conversion processing of a printed image. The white reference plate 115 is arranged at a position facing the reading device 114, and is a white reference plate for performing shading correction of the reading device 114.

The double-sided tray 111 is arranged below the fixing and conveying section 110, and the image-formed printing paper that has passed through the fixing and conveying section 110, which has been sent by switching the conveying path, is turned upside down and again on the resist roller 108. It is a unit to carry.

(Problems of conventional technology)
FIG. 2 is a diagram illustrating the effect of the prior art. 3 and 4 are diagrams illustrating problems of the prior art. The problems of the prior art will be described with reference to FIGS. 2 to 4.

As described above, in the prior art, the resolution in the sub-scanning direction of the scanned image read by the image reading means changes due to the change in the linear velocity, but the transport speed (linear velocity) so that the resolution becomes constant. ), And the amount of light from the light source that illuminates the paper is adjusted in synchronization with the reading speed. For example, as shown in FIG. 2 (b), the linear speed is doubled as compared with the case where the paper transport speed (line speed) as shown in FIG. 2 (a) is A [mm / s]. When a certain 2A [mm / s] is set, the resolution in the sub-scanning direction of the scanned image read by the image reading means (hereinafter, may be referred to as “sub-scanning resolution”) is halved. Therefore, as shown in FIG. 2 (c), the reading speed (line period) is set to B / 2 [μs], which is 1/2 of B [μs], and the amount of light is set to 2C [lx], which is twice. By setting lx], the same reading performance can be obtained before and after the change of the linear velocity. By halving the reading speed (line period), the resolution of the scanned image can be made the same before and after the change of the line speed. Here, when the line speed is doubled, the light storage time of the image reading means (line sensor) is halved, so it is necessary to double the amount of light in order to obtain the same reading performance.

Further, in the image reading means, an LED is often used as a light source, and a method of adjusting the amount of light of the LED by changing the driving current is common. Here, for example, it is assumed that the image forming apparatus has two types of linear speeds of 500 [mm / s] (A) and 1000 [mm / s] (B). When reading is performed by the image reading means at a reading resolution of 300 [dpi], the line periods are A: 169.3 [μm] and B: 84.67 [μm, respectively, as shown in (Table 1) below. ], And when the linear velocity changes from 500 [mm / s] (A) to 1000 [mm / s] (B), the optical storage time of the image reading means (line sensor) is halved, which is equivalent. In order to obtain reading performance, it is necessary to set the LED current from 15 [mA] (A) to 30 [mA].

As described above, when the linear velocity is changed from 500 [mm / s] (A) to 1000 [mm / s] (B), the LED current is changed from 15 [mA] (A) to 30 [mA] (B). ), But in this case, as shown in FIG. 3 (a), the chromaticity changes to the blue side (the direction in which the values of x and y become smaller), and as shown in FIG. 3 (b). In addition, the spectral characteristics of the LED also change. In this case, even if the image reading means reads exactly the same image, the RGB values are different, and the different RGB values are converted into color information such as the L * a * b * value, so that the LED current (light amount) is used. ) Will cause a color difference in the image read by the image reading means.

For example, when the region 601 which is a specific patch region of the color chart shown in FIG. 4 is read with an LED current of 15 [mA], the RGB value is r1 / g1 / b1, and the RGB value is L * a * b. * The value converted into a value is defined as l1 / a1 / b1. Then, the RGB value when the region 601 is read with the LED current 30 [mA] is r2 / g2 / b2, and the color-converted RGB value to the L * a * b * value is l2 / a2 /. Let it be b2. At this time, the color difference ΔE of the region 601 when read with the LED current of 15 [mA] and when read with the LED current of 30 [mA] is represented by the following equation (1).

ΔE = ((l1-l2) ^ 2 + (a1-a2) ^ 2 + (b1-b2) ^ 2) ^ (1/2) ... (1)

In this case, although it depends on the color conversion formula used, when the LED current changes from 15 [mA] to 30 [mA], a color difference of about ΔE = 0.5 may occur. ΔE = 0.5 is an acceptable difference in a normal scanner, but it is an unacceptable characteristic difference in the field of production printing where high color reproducibility is required.

(Hardware configuration of image forming device)
FIG. 5 is a diagram showing an example of the hardware configuration of the image forming apparatus according to the embodiment. The hardware configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

As shown in FIG. 5, the image forming apparatus 1 according to the present embodiment includes a controller 200, an operation display unit 210, an FCU (Facsimile Control Unit) 220, a plotter 231 (forming unit), a scanner 232, and an illumination. The control circuit 241 and the read control circuit 251 are connected by a PCI (Peripheral Component Interface) bus. Further, the lighting control circuit 241 is connected to the LED lighting 242 in order to control the lighting operation of the LED lighting 242. The reading control circuit 251 is connected to the reading sensor 252 in order to control the reading operation of the reading sensor 252. The lighting control circuit 241, the LED lighting 242, the reading control circuit 251 and the reading sensor 252 described above are components included in the reading device 114 shown in FIG. 1 described above.

The controller 200 is a device that controls control of the entire image forming apparatus 1, drawing, communication, control of various engines, and input from the operation display unit 210.

The operation display unit 210 is, for example, a touch panel or the like, and is a device that receives input to the controller 200 (input function) and displays the state of the image forming apparatus 1 (display function), and is an ASIC (Application Specific Integrated Circuit) described later. It is directly connected to the Circuit) 206.

The FCU 220 is a device that realizes a fax function, and is connected to the ASIC 206 by, for example, a PCI bus.

The plotter 231 is a device that realizes a printing function, and is connected to the ASIC 206 by, for example, a PCI bus. The scanner 232 is a function that realizes a scanner function, and is connected to the ASIC 206 by, for example, a PCI bus.

The lighting control circuit 241 is a drive circuit that controls the lighting operation of the LED lighting 242. The lighting control circuit 241 is connected to the ASIC 206 by, for example, a PCI bus. The LED lighting 242 is an LED light source whose lighting operation is controlled by the lighting control circuit 241.

The reading control circuit 251 is a drive circuit that controls the reading (imaging) operation of the reading sensor 252. The read control circuit 251 is connected to the ASIC 206 by, for example, a PCI bus. The reading sensor 252 is a line sensor or the like whose reading operation is controlled by the reading control circuit 251.

The controller 200 includes a CPU 201, a system memory (MEM-P) 202, a north bridge (NB) 203, a south bridge (SB) 204a, a network I / F204b, a USB (Universal Serial Bus) I / F204c, and the like. It has a centronics I / F 204d, an ASIC 206, a local memory (MEM-C) 207, and an auxiliary storage device 208.

The CPU 201 controls the entire image forming apparatus 1, is connected to a chipset including a system memory 202, a north bridge 203, and a south bridge 204a, and is connected to other devices via this chipset.

The system memory 202 is a memory used as a memory for storing programs and data, a memory for expanding programs and data, a memory for drawing a printer, and the like, and has a ROM (Read Only Memory) and a RAM (Random Access Memory). are doing. Of these, the ROM is a read-only memory used as a memory for storing programs and data, and the RAM is a writeable and readable memory used as a memory for expanding programs and data, a memory for drawing a printer, and the like. ..

The north bridge 203 is a bridge for connecting the CPU 201 to the system memory 202, the south bridge 204a, and the AGP (Accelerated Graphics Port) bus 205, and is a memory controller that controls reading and writing to the system memory 202, a PCI master, and a PCI master. It has an AGP target.

The south bridge 204a is a bridge for connecting the north bridge 203 to a PCI device and peripheral devices. The south bridge 204a is connected to the north bridge 203 via a PCI bus, and networks I / F204b, USB I / F204c, Centronics I / F204d, and the like are connected to the PCI bus.

The AGP bus 205 is a bus interface for a graphics accelerator card proposed for speeding up graphic processing. The AGP bus 205 is a bus that speeds up the graphics accelerator card by directly accessing the system memory 202 with a high throughput.

The ASIC 206 is an IC (Integrated Circuit) for image processing applications having hardware elements for image processing, and has a role of a bridge connecting the AGP bus 205, the PCI bus, the auxiliary storage device 208, and the local memory 207, respectively. The ASIC 206 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 206, a memory controller that controls the local memory 207, and a plurality of DMACs (Direct Memory Access) that rotate image data by hardware logic or the like. It is composed of a controller) and a PCI unit that transfers data between a plotter 231, a scanner 232, a lighting control circuit 241 and a read control circuit 251 via a PCI bus. For example, the FCU 220, the plotter 231 and the scanner 232, the illumination control circuit 241 and the read control circuit 251 are connected to the ASIC 206 via the PCI bus. Further, the ASIC 206 is also connected to a host PC (Personal Computer), a network, and the like (not shown).

The local memory 207 is a memory used as a copy image buffer and a code buffer.

The auxiliary storage device 208 is a storage device such as an HDD (Hard Disk Drive), SSD (Solid State Drive), SD (Secure Digital) card, or flash memory, and stores image data, programs, font data, and the like. And storage for accumulating forms.

The above-mentioned program of the image forming apparatus 1 may be recorded and distributed on a computer-readable recording medium (auxiliary storage device 208 or the like) by a file in an installable format or an executable format. good.

Further, the hardware configuration of the image forming apparatus 1 shown in FIG. 5 is an example, and it is not necessary to include all the constituent devices, or it may be provided with other constituent devices.

(Configuration and operation of functional blocks of image forming apparatus)
FIG. 6 is a diagram showing an example of the configuration of the functional block of the image forming apparatus according to the embodiment. FIG. 7 is a diagram showing an example of the configuration of the functional block of the color inspection device according to the embodiment. FIG. 8 is a diagram illustrating the effect when the current of the light source is fixed. FIG. 9 is a diagram illustrating a change in resolution in the sub-scanning direction. FIG. 10 is a diagram illustrating an operation of converting the resolution in the sub-scanning direction. The configuration and operation of the functional block of the image forming apparatus 1 according to the present embodiment will be described with reference to FIGS. 6 to 10.

As shown in FIG. 6, the image forming apparatus 1 according to the present embodiment includes a color inspection apparatus 300, a density conversion unit 320, a storage unit 321, an input unit 322, a communication unit 323, and a display control unit 324. , A display unit 325 and an image forming unit 326 (forming unit).

The color inspection device 300 is a device that performs various signal processing on the image data obtained by reading a printed image (subject), performs color conversion to a predetermined color space, and outputs the data. The specific configuration of the color inspection device 300 will be described later with reference to FIG.

The density conversion unit 320 is a functional unit that converts color information (for example, L * a * b * value) that has been color-converted into a predetermined color space output from the color inspection device 300 into CMYK density information. The density conversion unit 320 is realized by, for example, a program executed by the CPU 201 shown in FIG. 5 or an ASIC 206.

The storage unit 321 is a functional unit that stores image data storage, programs, font data, color conversion formula information for color conversion processing, and the like. The storage unit 321 is realized by the auxiliary storage device 208 or the system memory 202 shown in FIG.

The input unit 322 is a functional unit that accepts user's operation input. The input unit 322 is realized by the input function of the operation display unit 210 shown in FIG.

The communication unit 323 is a functional unit that communicates with an external device via a network. The communication unit 323 receives, for example, image data or the like for printing from an external device. The communication unit 323 is realized by, for example, a network I / F 204b shown in FIG. 5, a program running on the CPU 201 shown in FIG. 5, and the like.

The display control unit 324 is a functional unit that controls the display operation of the screen of the display unit 325. The display control unit 324 is realized by, for example, a program executed by the CPU 201 shown in FIG. 5 or an ASIC 206.

The display unit 325 is a functional unit that displays various data on the screen according to the control by the display control unit 324. The display unit 325 is realized by the display function (liquid crystal display device or the like) of the operation display unit 210 shown in FIG.

The image forming unit 326 is a functional unit that performs image forming (printing) based on the print data received by the communication unit 323, the print data stored in the storage unit 321 and the like.

As shown in FIG. 7, the color inspection device 300 includes a lighting unit 301, a lighting control unit 302, a reading unit 303, a reading control unit 304, a signal processing unit 305, a resolution conversion unit 306, and a color conversion unit. 307 and.

The illumination unit 301 is a functional unit that illuminates (exposes) light on a printed image (subject) printed on paper, a white reference plate (white reference plate 115 shown in FIG. 1), and the like under the control of the illumination control unit 302. Is. The lighting unit 301 is realized by the LED lighting 242 shown in FIG.

The lighting control unit 302 is a functional unit that controls the lighting (exposure) operation of the lighting unit 301. Specifically, when the lighting control unit 302 controls the lighting operation of the LED lighting 242 whose light source is an LED, the lighting control unit 302 adjusts the amount of light of the LED by controlling the magnitude of the current flowing through the LED. The adjustment of the light amount of the light source by the illumination control unit 302 is not limited to controlling the current flowing through the light source (LED current in the above description). For example, the amount of light may be adjusted by driving PWM (Pulse Width Modulation), or the amount of light may be adjusted by controlling the voltage applied to the light source.

For example, as shown in (Table 2) below, the linear speed of the image forming apparatus 1 has three types of patterns a to c (500 [mm / s], 750 [mm / s], 1000 [mm / s]). In some cases, in the prior art described above, the LED currents are changed according to these linear speeds (eg, 15 [mA], 22.5 [mA], 30 [mA]] in order to keep the reading resolution constant. )Was.

On the other hand, in the image forming apparatus 1 according to the present embodiment, as shown in the following (Table 3), in the lighting control unit 302, the LED current of the lighting unit 301 is a specific current (for example, even if the linear velocity is changed). , 30 [mA]) and control so that the amount of light is constant. That is, the lighting control unit 302 controls so that the driving conditions of the lighting unit 301 are constant.

As a result, as shown in FIG. 8A, the chromaticity does not change due to the change in the LED current, and as shown in FIG. 8B, the spectral characteristics of the LED do not change. It is possible to suppress the occurrence of color difference in the scanned image read by 303.

The lighting control unit 302 is realized by the lighting control circuit 241 shown in FIG.

The reading unit 303 reads the light reflected by the lighting unit 301 from the printed image (subject) printed on the paper, the white reference plate (white reference plate 115 shown in FIG. 1), etc., according to the control of the reading control unit 304 (the reading unit 303). It is a functional unit that obtains an RGB value (reading value) by taking an image. The reading unit 303 is realized by the reading sensor 252 shown in FIG.

The reading control unit 304 is a functional unit that controls the reading (imaging) operation of the reading unit 303. Specifically, the reading control unit 304 controls the reading speed (line period) by the reading unit 303.

In the present embodiment, as described above, since the LED current of the lighting unit 301 is fixed to a specific current (for example, 30 [mA]), the reading control unit 304 reads the same even if the linear velocity changes. As shown in (Table 4) below, the reading speed (line cycle) of the reading unit 303 is fixed to a specific speed (cycle) (for example, 84.67 [μm]) so as to have performance. Control.

However, as described above, since the reading speed (line period) of the reading unit 303 is fixed regardless of the change in the linear speed, the image read by the reading unit 303 is as shown in FIG. 9 and (Table 4). , The sub-scanning resolution changes depending on the linear velocity. Specifically, in the case of the line speed of pattern a in (Table 4) of 500 [mm / s], as shown in FIG. 9 (a), the sub-scanning resolution is 600 [dpi], and the line speed of pattern b is 750. In the case of [mm / s], as shown in FIG. 9 (b), the sub-scanning resolution is 450 [dpi], and in the case of the linear speed of pattern c of 1000 [mm / s], as shown in FIG. 9 (c). In addition, the sub-scanning resolution is 300 [dpi], and in the case of low linear velocity, the scanned image is extended from the same magnification. Therefore, as will be described later, the resolution conversion unit 306 performs resolution conversion on the scanned image.

The read control unit 304 is realized by the read control circuit 251 shown in FIG.

The signal processing unit 305 is a functional unit that performs signal processing such as shading correction on the scanned image (RGB value) read by the reading unit 303. The signal processing unit 305 is realized by, for example, a program executed by the CPU 201 shown in FIG. 5 or an ASIC 206.

The resolution conversion unit 306 is a functional unit that performs resolution conversion for the resolution in the sub-scanning direction by performing scaling processing on the scanned image (RGB value) that has been signal-processed by the signal processing unit 305. Specifically, the resolution conversion unit 306 performs resolution conversion in the sub-scanning direction of the scanned image according to the linear velocity of the image forming apparatus 1 so that the sub-scanning resolution becomes constant. For example, when the linear speed is 500 [mm / s], the resolution conversion unit 306 performs resolution conversion so that the sub-scanning resolution changes from 600 [dpi] to 300 [dpi] as shown in FIG. 10 (a). In the case of a linear speed of 750 [mm / s], as shown in FIG. 10B, resolution conversion is performed so that the sub-scanning resolution is from 450 [dpi] to 300 [dpi]. As described above, the resolution conversion unit 306 has a constant sub-scanning resolution (sub-scanning resolution when the linear speed is 1000 [mm / s]) shown in FIG. 10 (c) regardless of the change in the linear velocity. Resolution is converted so that it becomes (resolution). As a result, even if the linear velocity changes, the sub-scanning resolution (constant resolution) can always be set to the same magnification.

By keeping the scanned image constant in this way, for example, the color inspection device 300 is particularly effective when using an application for detecting an abnormality in a printed image. In an application that performs abnormality detection to detect whether an abnormality (streak, stain, etc.) has occurred in a printed image, the print data when the user prints is compared with the scanned image, but the color inspection device 300 If the resolution of the scanned image is always constant, it can be compared with the print data.

The resolution conversion unit 306 is realized by, for example, a program executed by the CPU 201 shown in FIG. 5 or an ASIC 206.

The color conversion unit 307 uses color information (L * a *) in an arbitrary color space (L * a * b * color space in this embodiment) for the scanned image (RGB value) whose resolution has been converted by the resolution conversion unit 306. It is a functional part that converts color to b * value). The color conversion unit 307 outputs the color-converted color information as an output value of the color inspection device 300, and outputs the color information to the density conversion unit 320. The color conversion unit 307 is realized by, for example, a program executed by the CPU 201 shown in FIG. 5 or an ASIC 206.

As shown in FIG. 7, the density conversion unit 320 is described as a functional unit outside the color inspection device 300, but may be included in the color inspection device 300.

Further, each functional unit of the image forming apparatus 1 shown in FIGS. 6 and 7 conceptually shows a function, and is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in the image forming apparatus 1 shown in FIGS. 6 and 7 may be configured as one functional unit. On the other hand, in the image forming apparatus 1 shown in FIGS. 6 and 7, the functions of one functional unit may be divided into a plurality of parts and configured as a plurality of functional units.

(About the color conversion formula)
In the above-mentioned prior art, the operation of changing the light amount (LED current) of the LED as a light source according to the linear velocity has been described, and the color difference is generated in the read image due to the change of the light amount of the LED. In order to suppress such a color difference, it is possible to generate an optimum color conversion formula for each LED current and use a color conversion formula for color conversion according to the LED current to be used. In such a color conversion formula, for example, a color chart including a plurality of colors and a plurality of gradations such as CMYK as shown in FIG. 4 is printed and printed by an image forming apparatus equipped with an image reading means. The obtained color chart is generated using the RGB value read by the image reading means and the L * a * b * value (an example of the color measurement value) obtained by measuring the same color chart with a colorimeter. be able to. The color information measured by the colorimeter is not limited to the L * a * b * value, and may be, for example, the color information (an example of the color measurement value) in the XYZ color space. good.

When there are multiple line speeds in the same image forming device, a color conversion formula is generated in advance for each LED current (light amount of the light source). For example, when the image forming device has three types of line speeds, one image is formed. Each device requires three types of color conversion formula generation steps. In this case, as shown in (Table 5) below, if the time required to generate one type of color conversion formula is, for example, about 13 minutes, there are three types of linear speeds, and the color conversion to be generated. If there are three types of formulas, the required time will be tripled to 39 minutes, which requires an increase in the size of the generation process and increases the cost. In addition, one image forming apparatus must hold (store) only three types of color conversion formulas, and a storage area for storage means for that purpose is also required, resulting in high cost.

On the other hand, in the image forming apparatus 1 according to the present embodiment, the illumination control unit 302 is such that the LED current of the illumination unit 301 is fixed to a specific current even if the linear velocity is changed (driving conditions are constant). In order to control the lighting unit 301, the LED current of the lighting unit 301 may be one type, and the color conversion formula may be generated by one type. As shown in (Table 6) below, the color conversion formula is generated by the prior art. It takes only 1/3 of the time required for the process. As a result, it is possible to suppress the increase in size of the generation process, and since there is only one type of color conversion formula that must be held (stored) in one image forming apparatus 1, the storage means (for example, FIG. 5) shows. The storage area stored (stored) in the auxiliary storage device 208) shown can also be reduced, which is cost advantageous.

(Flow of color conversion process)
FIG. 11 is a flowchart showing an example of the flow of the color conversion process of the color inspection apparatus according to the embodiment. The flow of the color conversion process of the color inspection apparatus 300 according to the present embodiment will be described with reference to FIG. 11.

<Step S11>
The image forming unit 326 of the image forming apparatus 1 prints a color chart (for example, the color chart shown in FIG. 4) (color inspection chart) on paper in order to perform color conversion processing. Then, the process proceeds to step S12.

<Step S12>
The reading unit 303 of the color inspection device 300 reads the color chart printed by the image forming unit 326 to obtain an RGB value read image. Then, the process proceeds to step S13.

<Step S13>
The signal processing unit 305 of the color inspection device 300 performs signal processing such as shading correction on the read image (RGB value) read by the reading unit 303. Then, the process proceeds to step S14.

<Step S14>
The resolution conversion unit 306 of the color inspection device 300 performs resolution conversion on the resolution in the sub-scanning direction by performing scaling processing on the read image (RGB value) signal-processed by the signal processing unit 305. In this case, the resolution conversion unit 306 performs resolution conversion so that the sub-scanning resolution becomes constant according to the linear velocity of the image forming apparatus 1. Then, the process proceeds to step S15.

<Step S15>
The color conversion unit 307 of the color inspection device 300 color-converts the read image (RGB value) whose resolution has been converted by the resolution conversion unit 306 into an L * a * b * value. The color conversion unit 307 outputs the color-converted color information as an output value of the color inspection device 300, and outputs the color information to the density conversion unit 320. Then, the color conversion process is terminated.

According to the flow shown in steps S11 to S15 above, the color inspection device 300 performs the color conversion process.

As described above, in the color inspection device 300 according to the present embodiment, the light amount (LED current) by the illumination unit 301 is controlled to be fixed even if the line speed changes, and the reading speed (line) by the reading unit 303 is controlled. The cycle) is controlled to be fixed at a specific speed. As a result, the chromaticity does not change due to the change in the amount of light of the illumination unit 301, which is the light source, and the spectral characteristics do not change. Deterioration of conversion accuracy can be suppressed. Further, by equipping the image forming apparatus 1 with such a color inspection apparatus 300, it is possible to provide an image forming apparatus 1 having high color reproducibility.

Further, in the image forming apparatus 1 according to the present embodiment, the illumination control unit 302 is set so that the LED current of the illumination unit 301 is fixed to a specific current even if the linear velocity is changed (driving conditions are constant). In order to control the lighting unit 301, the LED current of the lighting unit 301 may be one type, and the color conversion formula used by the color conversion unit 307 may be one type, so that the time required in the process of generating the color conversion formula can be shortened. Can be done. As a result, it is possible to suppress the increase in size of the generation process, and since there is only one type of color conversion formula that must be held (stored) in one image forming apparatus 1, it is held (stored) in the storage means. The storage area can also be reduced, which is a cost advantage.

Further, in the image forming apparatus 1 according to the present embodiment, the resolution conversion unit 306 performs resolution conversion in the sub-scanning direction of the scanned image according to the linear velocity of the image forming apparatus 1, so that the sub-scanning resolution becomes constant. To. That is, the resolution conversion unit 306 performs resolution conversion so that the sub-scanning resolution becomes a constant resolution regardless of the change in the linear velocity. As a result, even if the linear velocity changes, the sub-scanning resolution (constant resolution) can always be set to the same magnification. In particular, in an application that performs abnormality detection to detect whether an abnormality (streak, stain, etc.) has occurred in a printed image, the print data when the user prints is compared with the scanned image, but a color inspection device is used. If the resolution of the scanned image of 300 is always constant, it can be compared with the print data.

(Modification 1)
The image forming apparatus 1 according to the first modification will be described focusing on the differences from the image forming apparatus 1 according to the above-described embodiment. The hardware configuration of the image forming apparatus 1 and the configuration of the functional block according to this modification are the same as those of the image forming apparatus 1 according to the above-described embodiment.

In the image forming apparatus 1 according to the above-described embodiment, resolution conversion is performed so that the sub-scanning resolution is constant even if the linear velocity changes. In the image forming apparatus 1 according to this modification, the reading control unit 304 changes the reading speed (line period) of the reading unit 303 according to the linear speed while keeping the light amount (LED current) of the lighting unit 301 constant. By doing so, the sub-scanning resolution is made constant. For example, as shown in (Table 7) below, the reading control unit 304 controls so that the line period of the reading unit 303 is 169.34 [μs] when the linear velocity is 500 [mm / s]. When the line speed is 750 [mm / s], the line period is controlled to be 112.89 [μs], and when the line speed is 1000 [mm / s], the line period is set to 84.67 [μs]. To control. As a result, the sub-scanning resolution can always be constant (300 [dpi] in the example of (Table 7)). However, when the line period of the reading unit 303 is lengthened, the light storage time of the reading unit 303 becomes long, and when the LED current of the lighting unit 301 is large, the scanned image may be saturated. Therefore, the line period and the LED current It is necessary to balance with.

Since the sub-scanning resolution of the scanned image can be made constant by making the line period of the reading unit 303 variable as described above, the color inspection apparatus 300 according to this modification has the resolution shown in FIG. 7. The conversion unit 306 may not be provided.

(Modification 2)
The image forming apparatus 1 according to the second modification will be described focusing on the differences from the image forming apparatus 1 according to the above-described embodiment. The hardware configuration of the image forming apparatus 1 and the configuration of the functional block according to this modification are the same as those of the image forming apparatus 1 according to the above-described embodiment.

FIG. 12 is a diagram illustrating variations in the light emission characteristics of the light source for each device. In the configuration of the reading device 114 shown in FIG. 5 above, the spectral characteristics of the color filter of the reading sensor 252 and the spectral characteristics of the LED illumination 242 are strictly different for each device (image forming device 1). For example, as shown in FIG. 12, the spectral characteristics of the LED lighting 242 (illumination unit 301) differ from device to device due to manufacturing variations and the like.

Therefore, in order to suppress individual differences in each image forming apparatus 1 due to manufacturing variations as described above, it is desirable that the color conversion formula used in the color converting unit 307 is generated for each apparatus (image forming apparatus 1). ..

FIG. 13 is a flowchart showing an example of the flow of the process of generating the color conversion formula in the modification 2. With reference to FIG. 13, the flow of the process of generating the color conversion formula for each device (image forming device 1) will be described.

<Step S21>
The image forming unit 326 of the image forming apparatus 1 prints a color chart (for example, the color chart shown in FIG. 4) (reference chart) on paper in order to generate a color conversion formula. Then, the process proceeds to step S22.

<Step S22>
The reading unit 303 of the color inspection device 300 reads the color chart printed by the image forming unit 326 to obtain an RGB value read image. Then, the signal processing unit 305 of the color inspection device 300 performs shading correction on the scanned image (RGB value) read by the reading unit 303, and outputs the scanned image (RGB value) after the shading correction. Then, the process proceeds to step S23.

<Step S23>
Color measurement is performed on the reference chart printed out by the image forming apparatus 1 with a colorimeter or the like, and color information (color measurement value) (for example, L * a * b * value) is acquired. Then, the process proceeds to step S24.

<Step S24>
From the RGB values output from the signal processing unit 305 and the color measured color information (L * a * b * values), the optimum color conversion formula for the device (image forming device 1) is generated. The color conversion formula may be a high-order conversion formula composed of an arbitrary parameter group, or may be a conversion formula using linear approximation or the like depending on the application. Then, the process proceeds to step S25.

<Step S25>
The generated color conversion formula is retained so that it can be used for the color conversion process of the color conversion unit 307. For example, the color conversion formula is stored in the storage unit 321. Then, the process of generating the color conversion formula is completed.

The color conversion formula generation step is performed by the flow shown in the above steps S21 to S25.

As described above, by generating the color conversion formula used in the color conversion unit 307 for each device (image forming device 1), it is possible to absorb the manufacturing variation of the spectral characteristics of the light source and the color filter, and the color conversion can be performed. The accuracy can be improved. Further, by using the reference chart used for generating the color conversion formula printed with the color material of the image forming apparatus 1 itself, it is possible to generate the color conversion formula optimized for the printing characteristics of the image forming apparatus 1. Therefore, it is possible to further improve the color conversion accuracy.

When at least one of the functional units of the image forming apparatus 1 and the color inspection apparatus 300 is realized by executing a program in the above-described embodiment and each modification, the program is preliminarily incorporated in a ROM or the like. Provided. Further, in the above-described embodiment and each modification, the program executed by the image forming apparatus 1 and the color inspection apparatus 300 is a CD-ROM (Compact Disk Read Only Memory) in an installable format or an executable format file. , Flexible disc (FD), CD-R (Compact Disk-Recordable), or DVD (Digital Versaille Disc) may be configured to be recorded and provided on a computer-readable recording medium. Further, in the above-described embodiment and each modification, the program executed by the image forming apparatus 1 and the color inspection apparatus 300 is stored on a computer connected to a network such as the Internet and provided by downloading via the network. It may be configured to do so. Further, in the above-described embodiment and each modification, the program executed by the image forming apparatus 1 and the color inspection apparatus 300 may be configured to be provided or distributed via a network such as the Internet. Further, in the above-described embodiment and each modification, the program executed by the image forming apparatus 1 and the color inspection apparatus 300 has a modular configuration including at least one of the above-mentioned functional units, and is an actual hardware. As the hardware, the CPU 201 reads a program from the above-mentioned storage device (for example, system memory 202 or auxiliary storage device 208, etc.) and executes the program so that each of the above-mentioned functional units is loaded and generated on the main storage device. It has become.

1 Image forming device 101 Image reading device 102 Automatic document feeder 103 Feeding section 104 Main body 105 Image drawing section 106 Developer 107 Transport path 108 Resist roller 109 Optical writing device 110 Fixing carrier 111 Double-sided tray 112 Photoreceptor drum 113 Intermediate transfer Belt 114 Reader 115 White reference plate 200 Controller 201 CPU
202 System memory (MEM-P)
203 Northbridge (NB)
204a Southbridge (SB)
204b Network I / F
204c USB I / F
204d Centronics I / F
205 AGP
206 ASIC
207 Local memory (MEM-C)
208 Auxiliary storage 210 Operation display 220 FCU
231 Plotter 232 Scanner 241 Lighting control circuit 242 LED lighting 251 Reading control circuit 252 Reading sensor 300 Color inspection device 301 Lighting unit 302 Lighting control unit 303 Reading unit 304 Reading control unit 305 Signal processing unit 306 Resolution conversion unit 307 Color conversion unit 320 Concentration Conversion unit 321 Storage unit 322 Input unit 323 Communication unit 324 Display control unit 325 Display unit 326 Image forming unit 601 area

Japanese Unexamined Patent Publication No. 2013-179532

Claims (7)

A lighting unit that illuminates the subject with light,
A reading unit that reads the reflected light of the light from the subject to obtain a reading value,
A lighting control unit that controls the driving conditions of the lighting unit to be constant even if the linear velocity of the subject changes .
A color conversion unit that performs color conversion of information based on the reading value into color information in a predetermined color space,
A reading control unit that controls the reading speed of the reading unit to be constant even if the linear speed of the subject changes .
A resolution conversion unit that performs resolution conversion so that the resolution of the scanned image composed of the readings read by the reading unit is constant even if the linear velocity of the subject is changed .
Color inspection device equipped with. The lighting unit is an LED (Light Emitting Diode).
The color inspection device according to claim 1, wherein the lighting control unit controls the current flowing through the LED to be constant. The color conversion unit is a color conversion formula generated from the reading value of the reference subject read by the reading unit and the color measurement value measured for the reference subject for each image forming apparatus provided with the color inspection device. The color inspection apparatus according to claim 1 or 2, wherein the color conversion is performed based on the above. The color inspection device according to claim 1 or 2,
A forming unit that forms an image of a subject to be read by the reading unit, and a forming unit.
An image forming apparatus equipped with. The color inspection device according to claim 3 and
A forming unit that forms an image of a subject to be read by the reading unit, and a forming unit.
Equipped with
The reference subject is an image forming apparatus that is a printed image formed by the forming portion. A lighting step that illuminates the subject with light from the lighting unit,
A reading step in which the reading unit reads the reflected light of the light from the subject to obtain a reading value.
A lighting control step that controls the driving conditions of the lighting unit to be constant even if the linear speed of the subject is changed .
A color conversion step of performing color conversion of information based on the reading value into color information in a predetermined color space, and
A reading control step that controls the reading speed of the reading unit to be constant even if the linear speed of the subject is changed .
A resolution conversion step of performing resolution conversion so that the resolution of the scanned image composed of the readings read by the reading unit is constant even if the linear velocity of the subject is changed .
Color inspection method with. On the computer
A reading step of obtaining a reading value by causing the reading unit to read the reflected light of the light from the subject when the subject is illuminated with light from the illumination unit.
A lighting control step that controls the driving conditions of the lighting unit to be constant even if the linear speed of the subject is changed .
A color conversion step of performing color conversion of information based on the reading value into color information in a predetermined color space, and
A reading control step that controls the reading speed of the reading unit to be constant even if the linear speed of the subject is changed .
A resolution conversion step of performing resolution conversion so that the resolution of the scanned image composed of the readings read by the reading unit is constant even if the linear velocity of the subject is changed .
A program to execute.

Images