COLOR DETECTION DEVICE, IMAGE FORMING DEVICE, COLOR DETECTION METHOD, AND PROGRAM

Abstract

To accurately correct a periodic fluctuation of colors even though a position in a conveyance direction and a fluctuation amount of the colors of an image are not accurately detected.SOLUTION: A color detection device according to an embodiment of the present invention is the color detection device for detecting colors of an image formed on the basis of image data on a recording medium conveyed in a prescribed conveyance direction and comprises: a reference luminance acquisition unit which refers to prescribed period information on the basis of positions in the conveyance direction of a plurality of partial regions having the same color in the image data and acquires a reference luminance value for each of the plurality of partial regions; a selection unit which selects a set of the partial regions whose sum of the reference luminance values satisfy a prescribed condition among the plurality of partial regions; a reading unit which reads the image; and an output unit which outputs color data of the image acquired on the basis of a read luminance value by the reading unit at a position corresponding to the partial region included in the set.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a color detection device, an image forming device, a color detection method, and a program. [Background technology]

[0002] 2. Description of the Related Art Conventionally, in an image forming apparatus such as a printer, a configuration is known in which the color of an image formed by the image forming apparatus is corrected based on a detection value of the color of the image formed on a recording medium.

[0003] Also, a configuration has been disclosed that corrects periodic color fluctuations in an image formed by an image forming device based on the amount of density fluctuation in an image formed on a recording medium using a photosensitive drum and the amount of rotation of the photosensitive drum (see, for example, Patent Document 1). Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the configuration of Patent Document 1, if the position in the transport direction corresponding to the amount of rotation of the photosensitive drum, etc., and the amount of color fluctuation in the image are not accurately detected, the periodic color fluctuation cannot be accurately corrected, and the color detection accuracy may decrease.

[0005] An object of the present invention is to accurately correct periodic color fluctuations without accurately detecting the position in the transport direction and the amount of color fluctuation in an image. [Means for solving the problem]

[0006] The color detection device according to one aspect of the present invention detects a recording medium conveyed in a predetermined conveyance direction. Contains 1 or more pages A color detection device for detecting the color of an image formed based on image data, The colors of the pixels contained within the area fall within a certain range. A reference luminance acquisition unit that acquires a reference luminance value for each of a plurality of partial regions; Based on the position in the transport direction, by referring to predetermined periodic information, an appropriateThe image processing device includes a selection unit that selects a set of the partial regions, a reading unit that reads the image, and an output unit that outputs color data of the image obtained based on a read luminance value by the reading unit at a position corresponding to the partial region included in the set. The partial regions are distributed over one or more pages, and the colors of the pixels included in the regions fall within a certain range. . Effect of the Invention

[0007] According to the present invention, it is possible to accurately correct periodic color fluctuations without accurately detecting the position in the transport direction and the amount of color fluctuation in the image. [Brief description of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating an example of the configuration of an image forming system according to an embodiment. [Diagram 2] FIG. 2 is a block diagram of an example of a hardware configuration of an information processing device according to an embodiment. [Diagram 3] 1 is a block diagram of an example of a hardware configuration of an image forming apparatus according to an embodiment; [Figure 4] 1 is a diagram illustrating an example of the configuration of an image forming apparatus according to an embodiment. [Diagram 5] 1 is a block diagram illustrating an example of a functional configuration of a color detection device according to a first embodiment. [Figure 6] FIG. 4 is a flowchart of an example of a correction operation performed by the image forming apparatus according to the first embodiment. [Figure 7] FIG. 13 is a diagram showing an example of extraction of a partial region. [Figure 8] 11A and 11B are diagrams showing an example of processing by a selection unit, in which (a) is a diagram showing an example of reference luminance values, (b) is a diagram showing the reference luminance values ​​displayed on a unit circle, and (c) is a diagram showing the sum of the reference luminance values. [Figure 9] 11A and 11B are diagrams showing an example of processing by a color data acquisition unit, in which (a) is a diagram showing an example of vector display of reference luminance values, (b) is a diagram showing an example of vector synthesis, and (c) is a diagram showing the sum of reference luminance values. [Figure 10] FIG. 11 is a diagram illustrating an example of the functional configuration of a color detection device according to a second embodiment. [Figure 11] FIG. 13 is a diagram illustrating an example of a divided region. [Figure 12]FIG. 11 is a flowchart of an example of a correction operation performed by an image forming apparatus according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The color detection device according to the embodiment is a device that detects the color of an image formed on a recording medium transported in a predetermined transport direction based on image data.

[0010] For example, in a device that transfers a toner image carried on a photosensitive drum to form an image on a recording medium, if there is uneven rotation due to eccentricity of the photosensitive drum, the color of the image formed on the recording medium will vary according to the rotation period of the photosensitive drum along the transport direction in which the recording medium is transported during image formation.

[0011] Since such color fluctuations are periodic fluctuations corresponding to the rotation period in the transport direction, by detecting the color of an image formed in a position on the recording medium that cancels out the color fluctuations in the transport direction, it is possible to detect the color of the image while suppressing the effects of the periodic fluctuations.

[0012] In the embodiment, a reference luminance value is obtained for each of a plurality of partial regions having the same color in the image data, based on the positions in the transport direction of the plurality of partial regions having the same color, by referring to predetermined periodic information. Furthermore, a set of partial regions whose sum of the reference luminance values ​​satisfies a predetermined condition is selected from the plurality of partial regions.

[0013] For example, the periodic information is sine wave information corresponding to the rotation period of a photosensitive drum that conveys a recording medium when an image is formed on the recording medium, etc. The predetermined condition is a condition as to whether or not the sum of the reference luminance values ​​of the plurality of partial regions is equal to or less than a predetermined luminance threshold value, etc.

[0014] For example, by satisfying the condition that the sum of the reference luminance values ​​is less than or equal to a predetermined luminance threshold value, it is possible to select a set of partial areas corresponding to positions on the recording medium that cancel out color variations in the transport direction.

[0015] In an embodiment, an image formed on a recording medium is read by a reading unit, color data of the image is obtained based on the brightness value read by the reading unit at a position corresponding to a partial region included in a selected set, and the obtained color data is output as a color detection value. By referring to periodic information such as the rotation period of the photosensitive drum, accurate information on the position in the transport direction and the amount of color fluctuation of the image is not required, and periodic color fluctuation can be accurately corrected without accurately detecting the position in the transport direction and the amount of color fluctuation of the image.

[0016] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicated explanations will be omitted as appropriate.

[0017] In the following, an embodiment will be described using an image forming system equipped with an image forming apparatus including a color detection device as an example. This image forming system is, for example, an image forming system for commercial printing (production printing) that prints a desired image on a large number of sheets of paper. Paper is an example of a recording medium. Note that the terms printing, image formation, and printing in the embodiments are all synonymous.

[0018] Furthermore, the embodiments shown below are examples of a color detection device and an image forming device for embodying the technical concept of the present invention, and the present invention is not limited to the embodiments shown below. Unless otherwise specified, the shapes of the components described below, their relative positions, parameter values, etc. are intended to be illustrative and not to limit the scope of the present invention. Furthermore, the sizes and positional relationships of the components shown in the drawings may be exaggerated to clarify the explanation.

[0019] <Example of Overall Configuration of Image Forming System 100> First, referring to FIG. 1, an example of the configuration of the image forming system 100 will be described. FIG. 1 is a diagram for explaining an example of the configuration of the image forming system 100. As shown in FIG. 1, the image forming system 100 includes a client PC (Personal Computer) 101, a DFE (Digital Front End) 102, an image forming apparatus 103, and a management server 104. These are connected to be communicable with each other via the Internet or the like.

[0020] The client PC 101 creates a print job that the user wants to print and transmits the print job to the DFE 102 or the management server 104. It is equipped with a display unit that is a liquid crystal display and input devices such as a mouse and a keyboard.

[0021] The DFE 102 receives a print job from the client PC 101 or the management server 104, creates drawing data by a RIP (Raster Image Processor) engine based on the received print job, and transmits the drawing data to the image forming apparatus 103. Here, the DFE 102 is an example of an information processing device.

[0022] The image forming apparatus 103 forms an image on a recording medium based on the drawing data received from the DFE 102.

[0023] The management server 104 manages the print job received from the client PC 101. Also, in response to a request from the DFE 102, it transmits the print job to the DFE 102.

[0024] Note that a plurality of image forming apparatuses and a plurality of client PCs may be communicably connected to the image forming system 100.

[0025] <Example of the hardware configuration of the DFE 102> Next, referring to FIG. 2, the hardware configuration of the DFE 102 will be described. FIG. 2 is a block diagram for explaining an example of the hardware configuration of the DFE 102.

[0026] As shown in FIG. 2, the DFE 102 includes a central processing unit (CPU) 201, a read only memory (ROM) 202, a random access memory (RAM) 203, a hard disk (HDD) / solid state drive (SSD) 204, and an interface (I / F) 205.

[0027] Of these, the CPU 201 uses the RAM 203 as a working area and executes programs stored in the ROM 202 to control the overall operation of the DFE 102 .

[0028] The HDD / SSD 204 is used as a storage unit and stores preset setting values. The information stored in the HDD / SSD 204 may be read by the CPU 201 and used when executing a program.

[0029] The I / F 205 is an interface that enables communication between the DFE 102 and the client PC 101, the image forming apparatus 103, and the management server 104.

[0030] <Example of Hardware Configuration of Image Forming Apparatus 103> Next, the hardware configuration of the image forming apparatus 103 will be described with reference to Fig. 3. Fig. 3 is a block diagram illustrating an example of the hardware configuration of the image forming apparatus 103.

[0031] As shown in FIG. 3, the image forming apparatus 103 includes a CPU 301, a ROM 302, a RAM 303, an HDD / SSD 304, an I / F 305, an image forming unit 306, and a reading unit 307.

[0032] Of these, the CPU 301 uses a RAM 303 as a working area and executes a program stored in a ROM 302 to control the overall operation of the image forming apparatus 103 .

[0033] The HDD / SSD 304 is used as a storage unit and stores preset setting values. The information stored in the HDD / SSD 304 may be read by the CPU 301 and used when executing a program.

[0034] The I / F 305 is an interface that enables communication between the image forming apparatus 103, the DEF 102, the client PC 101, and the management server 104.

[0035] The image forming unit 306 is a print engine that forms an image on paper. The reading unit 307 is a reading device that reads the image formed on the paper.

[0036] <Example of configuration of image forming apparatus 103> Next, the configuration of the image forming apparatus 103 will be described with reference to Fig. 4. Fig. 4 is a diagram for explaining an example of the configuration of the image forming apparatus 103. As shown in Fig. 4, the image forming apparatus 103 has tandem electrophotographic photoconductor drums 403K, 403C, 403M, and 403Y, an intermediate transfer belt 402, a secondary transfer roller 404, a paper feed section 500, a pair of conveying rollers 401, a fixing roller 405, in-line sensors 406a and 406b, a reversing path 407, and a conveying path 408.

[0037] 3 includes photoconductor drums 403K, 403C, 403M, and 403Y, an intermediate transfer belt 402, a secondary transfer roller 404, and a fixing roller 405. Moreover, the reading unit 307 in FIG. 3 includes in-line sensors 406a and 406b.

[0038] Image forming apparatus 103 is a so-called tandem type image forming apparatus having a configuration in which photoconductor drums 403Y, 403M, 403C, and 403K of each color (hereinafter collectively referred to as photoconductor drums 403) are arranged along intermediate transfer belt 402, which is an endless moving means. Photoconductor drums 403Y, 403M, 403C, and 403K are arranged in order from the upstream side in the transport direction of intermediate transfer belt 402 along intermediate transfer belt 402, on which an intermediate transfer image to be transferred to paper fed from paper feeder 500 and transported by transport roller pair 401 is formed.

[0039] The image forming device 103 carries a toner image of each color developed with toner on the surface of the photosensitive drum 403 of each color, and transfers the carried toner images in a superimposed manner onto the intermediate transfer belt 402, thereby forming a full-color image on the intermediate transfer belt 402.

[0040] The image forming device 103 transfers the full-color image formed on the intermediate transfer belt 402 onto the surface of the paper transported on the transport path 408 at a position closest to the paper transport path 408, indicated by the dashed line in the figure, by using the function of the secondary transfer roller 404.

[0041] The paper with the image formed on its surface is further transported, and the image is fixed (image formed) by fixing rollers 405. Fixing rollers 405 are an example of a fixing section that thermally fixes an image onto paper. Fixing rollers 405 fix the full-color toner image onto the paper by applying heat and pressure to the paper onto which the full-color toner image has been transferred. Fixing rollers 405 can generate heat using a built-in heater such as a halogen heater to heat the paper.

[0042] When double-sided printing is performed, the image forming device 103 forms an image on the front side, then transports the paper to a reversing path 407 in a transport path 408, where the paper is inverted and then transported again to the position of the secondary transfer roller 404.

[0043] The paper feed section 500 includes a paper feed tray 501 , a pickup roller 502 , and a paper feed roller 503 .

[0044] A plurality of sheets of paper are stacked and stored in the paper feed tray 501. The recording medium may be paper such as recording paper (transfer paper), but is not limited to this, and may be coated paper, cardboard, an overhead projector (OHP) sheet, a plastic film, a prepreg, copper foil, or the like, as long as it is a medium on which an image can be formed (recorded).

[0045] The paper feed unit 500 picks up the papers stacked and stored in the paper feed tray 501 in order from the top by a pickup roller 502, and supplies the picked up papers to the conveying roller pair 401 by using a pair of rollers, paper feed rollers 503. The paper feed unit 500 may be configured to have other rollers for conveying the papers.

[0046] In-line sensors 406a and 406b (hereinafter collectively referred to as in-line sensor 406) are provided downstream of fixing roller 405 in the paper transport direction.

[0047] In-line sensor 406 reads both sides of the paper by fixing roller 405, and obtains a read image of the image fixed on the paper. Note that two in-line sensors 406 (406a, 406b) are not necessarily required, and only in-line sensor 406a may be used. When only sensor 406a is used, reading is performed by in-line sensor 406a when an image is formed on the front side, and then image formation on the back side is performed.

[0048] Here, the in-line sensor 406 is a CCD (Charge Coupled Device) line sensor in which pixels that output electric signals according to the intensity of received light are arranged in a one-dimensional array. The direction in which the pixels are arranged intersects with the paper transport direction. The in-line sensor 406 also includes a pixel array that receives red light (R), a pixel array that receives green light (G), and a pixel array that receives blue light (B). In the following, red may be represented as R, green as G, and blue as B, respectively.

[0049] The in-line sensor 406 outputs an electrical signal according to the light intensity of the reflected light from the image formed on the paper by the pixel array of each color. The image forming apparatus 103 uses the light intensity (density) of each color of the image read by the in-line sensor 406 as color information for correcting the color of the image.

[0050] In-line sensor 406 may include a light source that irradiates light onto the paper. Irradiating light from the light source onto the paper ensures sufficient brightness for reading by in-line sensor 406. In-line sensor 406 may be configured with a complementary metal-oxide-semiconductor (CMOS) or a photodiode (PD) array instead of a CCD.

[0051] <Example of functional configuration of color detection device 1> Next, the functional configuration of the color detection device 1 included in the image forming apparatus 103 will be described with reference to Fig. 5. Fig. 5 is a block diagram illustrating an example of the functional configuration of the color detection device 1.

[0052] 5, the image forming apparatus 103 includes a color detection device 1. The image forming apparatus 103 also includes a communication unit 308, an image forming unit 306, and a correction unit 309. The image forming apparatus 103 forms an image on a sheet of paper transported in a predetermined transport direction, based on image data received from the client PC 101 via the communication unit 308.

[0053] The color detection device 1 detects the color of the paper formed by the image forming device 103, and provides color data indicating the detected color to the image forming device 103. The correction unit 309 of the image forming device 103 is capable of correcting the image formation conditions by the image forming unit 306 based on the color data received from the color detection device 1, and correcting the color of the image formed on the paper. Note that the information processing device 102 may be provided with the function of the correction unit 309.

[0054] As shown in Figure 5, the color detection device 1 has a partial area extraction unit 11, a reference brightness acquisition unit 12, a periodic information storage unit 13, a selection unit 14, a color data acquisition unit 15, a conversion table storage unit 16, an output unit 17, and a reading unit 307.

[0055] Each of these units is a function or a means for performing a function that is realized when any of the components shown in Fig. 3 operates in response to an instruction from CPU 301 in accordance with a program loaded from ROM 302 onto RAM 303. Note that, although Fig. 5 shows only the main components, image forming apparatus 103 may also include components other than those described above.

[0056] The partial region extraction unit 11 extracts a plurality of partial regions having the same color within the image data input via the communication unit 308. The partial region extraction unit 11 predetermines the number of partial regions to be extracted, the shape of each partial region, the area of ​​each partial region, and the position of each partial region within the image data. For example, the partial regions can be formed as squares, and the area of ​​each partial region can be determined in units of the number of pixels, such as 20×20 pixels. It is preferable to determine a plurality of positions within the image data that are as random as possible.

[0057] Image data is data in which the color of each pixel is expressed by the brightness values ​​of R, G, and B. A partial region is a region in which the pixels contained within the partial region have the same color. However, colors may differ between multiple partial regions.

[0058] After extracting a plurality of partial regions, the partial region extraction unit 11 provides the reference luminance acquisition unit 12 with position information indicating the position of each of the extracted partial regions.

[0059] The reference luminance acquisition unit 12 acquires a reference luminance value for each of the partial regions by referring to predetermined periodic information stored in the periodic information storage unit 13 based on the position of each of the partial regions in the transport direction.

[0060] The period information is sine wave information corresponding to the rotation period of the photoconductor drum 403 that conveys a sheet when the image forming apparatus 103 forms an image on the sheet. The photoconductor drum 403 is an example of a rotating body. The period information is determined for each of the photoconductor drums 403K, 403C, 403M, and 403Y.

[0061] Here, if the rotation axis of the photoconductor drum 403, which is a rotating body, is eccentric, uneven rotation occurs, and the distance between the surface of the photoconductor drum 403 and an image forming unit such as a developing roller varies with rotation. This may cause fluctuations in the density of the toner image formed on the surface of the photoconductor drum 403. When the density of the toner image fluctuates, the color of the color image formed by superimposing the toner images of each color varies according to the density of the toner image.

[0062] Such color fluctuations follow a reference luminance value A(y)=A·sin(2·π·y / T+φ), where T is the rotation period of the photoconductor drum 403 and Y is the position of the paper in the transport direction. The period T corresponds to the outer periphery of the photoconductor drum 403. The amplitude A and the initial phase φ are arbitrary values.

[0063] The periodic information storage unit 13 stores a reference luminance value A(y)=A·sin(2·π·y / T+φ). This reference luminance value A(y) is an example of sine wave information. The reference luminance acquisition unit 12 acquires a reference luminance value A(y) for each of a plurality of partial regions based on the position y of the plurality of partial regions in the transport direction. The periodic information storage unit 13 may store the sine wave as a mathematical formula, or may store a table in which the position y corresponds to the reference luminance value A(y).

[0064] The reference luminance acquisition unit 12 provides information on the acquired reference luminance value A(y) for each of the multiple partial regions to the selection unit 14. Since the amount of eccentricity differs between the photoconductor drums 403K, 403C, 403M, and 403Y, it is preferable to acquire the reference luminance value A(y) for each of the photoconductor drums 403K, 403C, 403M, and 403Y.

[0065] The selection unit 14 selects, from among the plurality of partial regions, a set of partial regions whose sum of reference luminance values ​​satisfies a predetermined condition, for example, that the sum of the reference luminance values ​​is equal to or less than a predetermined luminance threshold value.

[0066] However, the predetermined condition is not limited to this, and may be a condition that minimizes the sum of the reference luminance values. In addition, the following conditions may be used as the predetermined condition. Each of the conditions may be combined to set the predetermined condition. There are no edges within the subregion. The difference between the maximum and minimum color values ​​of pixels in a partial region is within a threshold. The partial area must be at least a specified distance away from the edge of the paper. The average color value in the subarea must be within a predefined range, e.g. away from white and solid colors. The average color value within the partial area does not exceed the specified total toner amount. The number of partial regions is equal to or greater than a predetermined number threshold.

[0067] The color under the specified conditions may be either a color expressed by R, G, and B, or a color expressed by cyan (C), magenta (M), yellow (Y), and black (K). In the following, cyan may be represented as C, magenta as M, yellow as Y, and black as K.

[0068] The selection unit 14 provides information on the set of selected partial regions to the color data acquisition unit 15 .

[0069] The color data acquisition unit 15 inputs data of a read image obtained by reading an image formed on a sheet of paper by the reading unit 307. The read image has colors expressed using R, G, and B.

[0070] Color data acquisition unit 15 acquires, as read-out luminance values, luminance values ​​of pixels of the read image at positions corresponding to each of the partial areas included in the set selected by selection unit 14. Then, by adding up the read-out luminance values ​​for each of the partial areas included in the set, R, G, and B color data of the image formed on the paper is acquired.

[0071] In other words, the selection unit 14 selects a set of multiple partial regions such that the sum of the reference luminance values ​​A(y) for each of the multiple partial regions is cancelled out and becomes equal to or less than a predetermined luminance threshold. The color data acquisition unit 15 adds up the colors of the multiple partial regions in the set. Since color fluctuations caused by eccentricity of the photoconductor drum 403, etc., are periodic fluctuations, the periodic color fluctuation components are cancelled out by the processing of the selection unit 14 and the color data acquisition unit 15. As a result, it is possible to detect colors in which the effects of periodic color fluctuations are suppressed.

[0072] Color data acquisition unit 15 then converts the R, G, and B color data into C, M, Y, and K color data by referring to a correspondence table between R, G, and B color data and C, M, Y, and K color data stored in conversion table storage unit 16. Color data acquisition unit 15 outputs the converted C, M, Y, and K color data to correction unit 309 via output unit 17.

[0073] <Example of operation of color detection device 1> Next, the operation of the color detection device 1 will be described with reference to Fig. 6. Fig. 6 is a flowchart showing an example of the operation of the color detection device 1. Fig. 6 shows the operation triggered by the time point when the color detection device 1 starts detecting a color.

[0074] First, in step S61, the reading unit 307 acquires the read image by reading the color of the image formed on the paper by the image forming apparatus 103. The acquired read image data is temporarily stored in the RAM 303 in FIG.

[0075] Next, in step S62, the partial area extraction unit 11 extracts multiple partial areas having the same color within the image data input via the communication unit 308, and provides positional information indicating the positions of each of the extracted multiple partial areas to the reference brightness acquisition unit 12.

[0076] Next, in step S63, the reference luminance acquisition unit 12 acquires a reference luminance value for each of the partial regions based on the positions of the partial regions in the transport direction, with reference to the predetermined periodic information stored in the periodic information storage unit 13. Then, the acquired reference luminance value for each of the partial regions is provided to the selection unit 14.

[0077] Next, in step S64, the selection unit 14 selects, from the multiple partial regions, a set of partial regions whose sum of reference luminance values ​​satisfies a predetermined condition, and provides the color data acquisition unit 15 with information indicating the selected set of partial regions.

[0078] Next, in step S65, color data acquisition unit 15 inputs data of the read image obtained by reading an image formed on paper by reading unit 307 from RAM 303, etc. Furthermore, color data acquisition unit 15 acquires, as read luminance values, luminance values ​​of pixels of the read image located at positions corresponding to partial areas included in the set selected by selection unit 14. Then, color data acquisition unit 15 acquires R, G, and B color data of the image formed on paper by adding up the read luminance values ​​for each of the partial areas included in the set.

[0079] Next, in step S66, the color data acquisition unit 15 refers to the correspondence table stored in the conversion table storage unit 16 and converts the R, G, and B color data into C, M, Y, and K color data.

[0080] Next, in step S 67 , the color data acquisition unit 15 outputs the color data of C, M, Y, and K to the correction unit 309 of the image forming apparatus 103 via the output unit 17 .

[0081] In this manner, the color detection device 1 can detect the color of the image formed on the paper by the image forming device 103.

[0082] <Data example> Next, an example of data handled by the color detection device 1 will be described with reference to Figures 7 to 9. First, Figure 7 is a diagram showing an example of a partial region.

[0083] Fig. 7 shows a plurality of partial regions 71 in image data D extracted by partial region extraction unit 11. Note that partial region 71 is a collective term for a plurality of partial regions. Each of the small circles displayed in image data D in Fig. 7 corresponds to a partial region 71.

[0084] The shading shown in image data D in Fig. 7 represents periodic fluctuations in color. The y-axis indicated by an arrow in Fig. 7 represents the transport direction, and the reference luminance value A(y) represents a sine wave in accordance with the reference luminance value A(y)=A·sin(2·π·y / T+φ) stored in the periodic information storage unit 13.

[0085] It is preferable that the image data D includes a chart pattern such as a color patch used for color detection by the color detection device 1. However, the image data is not limited to this, and may include any pattern selected by the user of the image forming device 103. In either case of image data, it is preferable that the partial region extraction unit 11 extracts partial regions 71 in as random a position as possible within the image data D without bias.

[0086] The reference luminance acquisition section 12 can refer to the period information storage section 13 based on the positions y of the partial regions 71 to acquire the reference luminance value A(y) corresponding to the positions y.

[0087] Next, Fig. 8 is a diagram illustrating an example of processing by the selection unit 14. Fig. 8(a) is a diagram showing an example of reference luminance values, Fig. 8(b) is a diagram showing a unit circle representation of the reference luminance values, and Fig. 8(c) is a diagram showing the sum of the reference luminance values.

[0088] 8(a), the horizontal axis indicates the position y on the paper P in the transport direction, and the vertical axis indicates the reference luminance value A(y). For example, a reference luminance value A(y1) is obtained for a partial area at position y1, and a reference luminance value A(y2) is obtained for a partial area at position y2.

[0089] As shown in Fig. 8(b), the reference luminance values ​​A(y1) and A(y2) can be expressed as vectors using a unit circle 81, and the sum of the reference luminance values ​​A(y1) and A(y2) can be obtained by combining the vectors of the reference luminance values ​​A(y1) and A(y2). Note that to convert the vector back to a scalar, the unit circle can be mapped to a sine wave as shown in Fig. 8(c).

[0090] The selection unit 14 selects a set of partial regions such that the composite value of the vectors of the reference luminance values ​​A(y) for each of the partial regions is equal to or smaller than a predetermined luminance threshold. When the reference luminance value A(y) is normalized, the luminance threshold becomes a value equal to or smaller than 1, such as 0.1.

[0091] Next, Fig. 9 is a diagram for explaining an example of processing by the color data acquisition unit 15. Fig. 9(a) is a diagram showing an example of vector display of reference luminance values, Fig. 9(b) is a diagram showing an example of vector synthesis, and Fig. 9(c) is a diagram showing the sum of reference luminance values.

[0092] Here, if the amount of influence of the reference luminance value per partial region is called a deviation evaluation value, the deviation evaluation value can be calculated as follows.

[0093] 9(a), the vector direction of the reference luminance value A(y1) of partial region a is α, and the vector direction of the reference luminance value A(y2) of partial region b is β. The combination of these two vectors can be calculated using the following formula, where π is the circular constant. [Direction of composite vector] = ([Sub-scanning coordinate] / [Outer circumference of rotating body]) × 2 × π

[0094] The reference luminance value vector of partial area a is (cosα, sinα), and the reference luminance value vector of partial area b is (cosβ, sinβ), so the resultant vector can be expressed as (cosα+cosβ, sinα+sinβ). Therefore, the magnitude of this resultant vector can be calculated as follows:

number

[0095] The deviation evaluation value is obtained by dividing this by the number of partial regions.

number

[0096] If the direction of the reference luminance value vector of each partial region is x and the number of partial regions is N, then the following can be expressed as a generalization.

number

[0097] When selecting a partial region, the effect of color variation can be suppressed by making the deviation evaluation value as small as possible. When the deviation evaluation value is 0≦[deviation evaluation value]≦1, the effect of color variation is completely canceled out when the deviation evaluation value is 0, and when the deviation evaluation value is 1, the color variation is greatest.

[0098] One example of an algorithm for minimizing the deviation evaluation value is a method in which the deviation evaluation value is used as an objective function, and those subregions that have the smallest deviation evaluation value are removed from the possible subregions, and the subregion that remains when the deviation evaluation value can no longer be reduced is adopted.

[0099] The color data obtained by minimizing the deviation evaluation value can be used for color correction in subsequent image formation, or can be recorded as information for later reference. Also, the color data can be displayed on a display unit or the like to inform the user.

[0100] <Functions and Effects of Color Detection Device 1> As described above, in this embodiment, based on the positions in the transport direction of multiple partial areas that have the same color within the image data, reference luminance values ​​are obtained for each of the multiple partial areas by referring to sine wave information corresponding to the rotation period of the photosensitive drum 403.

[0101] Furthermore, from among the plurality of partial regions, a set of partial regions whose sum of the reference luminance values ​​is equal to or less than a predetermined luminance threshold value is selected, thereby making it possible to select a set of partial regions corresponding to a position on the recording medium that cancels out color variation in the transport direction.

[0102] Then, the image formed on the paper is read by the reading unit 307, and color data of the image is obtained based on the brightness value read by the reading unit at the position corresponding to the partial area included in the selected set, and the obtained color data is output as a color detection value.

[0103] By referring to the rotation period information of the photoconductor drum 403, accurate information on the position in the transport direction and the amount of color variation in the image is not required, so the periodic color variation can be accurately corrected without accurately detecting the position in the transport direction and the amount of color variation in the image. Also, by accurately correcting the periodic color variation, high color detection accuracy can be ensured. Also, image processing such as density correction processing is not required, and processing can be simplified.

[0104] [Second embodiment] Next, a color detection device 1a according to a second embodiment will be described. Note that the same components as those described in the first embodiment are given the same part numbers, and duplicated descriptions will be omitted as appropriate.

[0105] In the present embodiment, the partial region is included in any of a plurality of divided regions obtained by dividing the image data along the transport direction. The selection unit selects a set of divided regions whose sum of the reference luminance values ​​satisfies a predetermined condition. This makes the processing by the selection unit more efficient.

[0106] The color detection device 1a according to this embodiment is included in an image forming device 103 provided in an image forming system 100a. Fig. 10 is a block diagram illustrating an example of the functional configuration of the color detection device 1a.

[0107] As shown in Fig. 10, the color detection device 1a has a division unit 18 and a selection unit 14a. Each of these units is a function or a means for performing a function that is realized when any of the components shown in Fig. 3 operates in response to an instruction from the CPU 301 in accordance with a program loaded from the ROM 302 onto the RAM 303.

[0108] The dividing unit 18 divides the image data into a plurality of equally spaced divided regions along the transport direction. The image data is divided into a plurality of rectangular divided regions extending in a direction perpendicular to the transport direction.

[0109] The selection unit 14a selects a set of divided regions such that the sum of the reference luminance values ​​of the partial regions included in each divided region satisfies a predetermined condition, for example, that the sum of the reference luminance values ​​of the partial regions included in each divided region is equal to or smaller than a predetermined luminance threshold value.

[0110] Here, Fig. 11 is a diagram for explaining an example of divided regions. In Fig. 11, image data D is divided into eight divided regions 72. Note that divided region 72 is a general term for the eight divided regions. Also, eight is just an example, and there is no particular limit to the number of divided regions 72. Each of the eight divided regions 72 includes multiple partial regions.

[0111] When minimizing the deviation evaluation value described above, it is not realistic to calculate and compare all possible partial regions one by one in terms of the processing load. Therefore, by utilizing the fact that the color in the transport direction is the same if the rotation angle of the photoconductor drum is the same, partial regions that are close in position in the transport direction are processed together to make the processing more efficient. The processing procedure is shown below.

[0112] (procedure) (1) The outer periphery of the photoconductor drum 403 is divided into equal intervals, and all possible partial regions are included in one of the divided regions. Even if there is a distance in the transport direction in the image data, if the position y is the same, they are included in the same divided region. If it spans multiple pages, they are included in the divided region in the same way, taking into account the gaps between pages. (2) The number of all partial areas contained in each divided area is tallied, and this number is stored as the number of partial areas in the divided area. (3) Calculate a deviation evaluation value based on the number of partial regions in the divided region, and set this as the initial deviation evaluation value. The deviation evaluation value can be expressed as follows, where y is the position of each divided region, and Ny is the number of partial regions in each divided region.

number

[0113] In the above process (4), the number of partial regions may be reduced too much. To avoid this, the following measures can be taken.

[0114] When the deviation evaluation value becomes small enough that the influence of color fluctuations can be tolerated, the process of (4) above is terminated, and the number of partial regions at that point in time is set as the final value. If the total number of partial regions falls below a predetermined value, the process of (4) above is terminated, and the number of partial regions at that point in time is set as the final value.

[0115] In this way, it is possible to avoid reducing the number of partial regions more than necessary, and to make the processing time more efficient by skipping processing.

[0116] <Operation Example of Color Detection Device 1a> Next, the operation of the color detection device 1a will be described. Fig. 12 is a flow chart showing an example of the operation of the color detection device 1a. Fig. 12 shows the operation triggered by the start of detection by the color detection device 1a.

[0117] Note that steps S111 and S112 in Fig. 12 are the same as steps S61 and S62 in Fig. 6. Also, steps S120 to S122 in Fig. 12 are the same as steps S65 to S67 in Fig. 6. Therefore, overlapping descriptions thereof will be omitted here.

[0118] In step S113, the dividing unit 18 divides the image data into a plurality of equally spaced divided regions along the transport direction.

[0119] Next, in step S114, the reference luminance acquisition unit 12 acquires a reference luminance value for each of the partial regions based on the positions of the partial regions in the transport direction, with reference to the predetermined periodic information stored in the periodic information storage unit 13. Then, the acquired reference luminance value for each of the partial regions is provided to the selection unit 14a.

[0120] Next, in step S115, the selection unit 14a reduces the number of partial regions in each divided region.

[0121] Next, in step S116, the selection unit 14a compares the sum of the reference luminance values ​​before and after the reduction in the number of partial regions.

[0122] Next, in step S117, the selection unit 14a determines whether or not the sum of the reference luminance values ​​before the decrease is greater than the sum of the reference luminance values ​​after the decrease.

[0123] In step S117, if it is determined that the sum is larger (step S117, Yes), the operation proceeds to step S119. On the other hand, if it is determined that the sum is not larger (step S117, No), in step S118, the selection unit 14a determines whether the sum of the reference luminance values ​​after the reduction is smaller than the luminance threshold value.

[0124] If it is determined in step S118 that the partial regions are not small (step S118, No), the operation returns to step S115, and the operations from step S115 onwards are performed again. On the other hand, if it is determined that the partial regions are small (step S118, Yes), the selection unit 14a selects a set of partial regions in step S119.

[0125] In this manner, the color detection device 1 can detect the color of the image formed on the paper by the image forming device 103.

[0126] <Functions and Effects of Color Detection Device 1a> As described above, in this embodiment, the partial region is included in any of a plurality of divided regions obtained by dividing the image data along the transport direction, and the selection unit 14a selects a set of divided regions whose sum of the reference luminance values ​​satisfies a predetermined condition, thereby making it possible to improve the efficiency of the processing by the selection unit 14a.

[0127] Although the embodiments have been described above, the present invention is not limited to the above specifically disclosed embodiments, and various modifications and changes are possible without departing from the scope of the claims.

[0128] Note that the image forming system 100 may be configured by providing some of the functions of the image forming apparatus 103, or some or all of the functions of the DFE 102 in an external device. An example of the external device is a cloud server. Alternatively, the DFE 102 may include some of the functions of the image forming apparatus 103.

[0129] Further, in the above-described embodiment, an image forming system including an electrophotographic image forming apparatus has been described, but the present invention is also applicable to an image forming system including an image forming apparatus of another type, such as an inkjet type.

[0130] In addition, all numbers such as ordinal numbers and quantities used in the description of the embodiments are merely examples for specifically explaining the technology of the present invention, and the present invention is not limited to the exemplified numbers. Furthermore, the connection relationships between the components are merely examples for specifically explaining the technology of the present invention, and the connection relationships for realizing the functions of the present invention are not limited to these.

[0131] In addition, the division of blocks in the functional block diagram is an example, and multiple blocks may be realized as one block, one block may be divided into multiple blocks, and / or some functions may be transferred to another block. Furthermore, the functions of multiple blocks having similar functions may be processed in parallel or in a time-division manner by a single piece of hardware or software.

[0132] The embodiment also includes a color detection method. For example, the color detection method is a color detection method by a color detection device that detects the color of an image formed based on image data on a recording medium transported in a predetermined transport direction, and includes the steps of: acquiring a reference luminance value for each of a plurality of partial regions having the same color in the image data by referring to predetermined periodic information based on the positions in the transport direction of the plurality of partial regions; selecting a set of the partial regions from the plurality of partial regions whose sum of the reference luminance values ​​satisfies a predetermined condition; reading the image with a reading unit; and outputting color data of the image acquired based on the read luminance value by the reading unit at a position corresponding to the partial region included in the set. Such a color detection method can provide the same effect as the above-mentioned color detection device.

[0133] The embodiment also includes a program. For example, the program is a program that operates in a color detection device that detects the color of an image formed based on image data on a recording medium transported in a predetermined transport direction, and causes a computer to execute a process of acquiring a reference luminance value for each of a plurality of partial regions having the same color in the image data based on positions in the transport direction of the partial regions with reference to predetermined periodic information, selecting a set of the partial regions among the plurality of partial regions whose sum of the reference luminance values ​​satisfies a predetermined condition, reading the image with a reading unit, and outputting color data of the image acquired based on the read luminance value by the reading unit at a position corresponding to the partial region included in the set. Such a program can provide an effect similar to that of the above-mentioned color detection device.

[0134] Furthermore, each function of the above-described embodiments can be realized by one or more processing circuits. Here, the term "processing circuit" in this specification includes a processor programmed to execute each function by software, such as a processor implemented by an electronic circuit, and a device such as an ASIC (Application Specific Integrated Circuit), a DSP (digital signal processor), an FPGA (field programmable gate array), or a conventional circuit module designed to execute each function described above. [Explanation of symbols]

[0135] 1. Color detection device 11 Partial region extraction part 12 Reference luminance acquisition unit 13 Period information storage section 14 Selection section 15 Color data acquisition section 16 Conversion table storage section 17 Output section 18 Division 71 Partial area 100 Image forming system 103 Image forming device 306 Image forming section 307 Reading Unit 308 Communications Department 309 Correction Section D. Image data y position A(y) Reference luminance value (an example of sine wave information) [Prior art documents] [Patent documents]

[0136] [Patent Document 1] JP 2011-28226 A

Claims

1. A color detection device that detects the color of an image formed on a recording medium transported in a predetermined transport direction based on image data including one or more pages, a reference luminance acquisition unit that acquires a reference luminance value for each of a plurality of partial regions in which the colors of pixels included in the regions fall within a certain range within the image data; a selection unit that selects an appropriate set of the partial regions from among the plurality of partial regions based on positions in the transport direction and with reference to predetermined periodic information; A reading unit that reads the image; an output unit that outputs color data of the image acquired based on a read luminance value read by the reading unit at a position corresponding to the partial region included in the set, A color detection device in which the partial regions are distributed across one entire page or across multiple pages, and the colors of the pixels contained in the regions fall within a certain range.

2. The color detection device according to claim 1 , wherein the selection section selects, from among the plurality of partial regions, a set of partial regions in which the sum of the reference luminance values ​​is equal to or less than a predetermined luminance threshold value.

3. The color detection device according to claim 1 , wherein the selection unit selects the sets of partial regions from the plurality of partial regions such that the number of the partial regions is equal to or greater than a predetermined number threshold.

4. 4. The color detection device according to claim 1, wherein the periodic information is sine wave information corresponding to a rotation period of a rotating body that conveys the recording medium when the image is formed on the recording medium.

5. 5. The color detection device according to claim 4, wherein the rotating body is a photosensitive drum capable of carrying toner.

6. the partial area is included in any one of a plurality of divided areas obtained by dividing the image data along the transport direction, The color detection device according to claim 1 , wherein the selection section selects the set of divided regions in which the sum of the reference luminance values ​​satisfies a predetermined condition.

7. A color detection device according to any one of claims 1 to 6, a correction unit that corrects a color of the image based on the color detected by the color detection device.

8. A color detection method using a color detection device for detecting the color of an image formed on a recording medium transported in a predetermined transport direction based on image data including one or more pages, comprising: acquiring a reference luminance value for each of a plurality of partial regions, each of which has a pixel color falling within a certain range within the image data, by referring to predetermined periodic information based on the positions in the transport direction of the plurality of partial regions; selecting an appropriate set of the partial regions from among the partial regions based on positions in the transport direction and with reference to predetermined periodic information; A step of reading the image by a reading unit; outputting color data of the image acquired based on a luminance value read by the reading unit at a position corresponding to the partial region included in the set; The partial regions are distributed across one or more pages, and the colors of the pixels contained within the regions fall within a certain range.

9. A program that operates on a color detection device that detects the color of an image formed on a recording medium transported in a predetermined transport direction based on image data including one or more pages, acquiring a reference luminance value for each of a plurality of partial regions, the plurality of partial regions being within a certain range of color of pixels included in the image data, by referring to predetermined periodic information based on positions in the transport direction of the plurality of partial regions; selecting an appropriate set of the partial regions from among the partial regions based on positions in the transport direction and with reference to predetermined periodic information; A reading unit reads the image, outputting color data of the image acquired based on the luminance value read by the reading unit at a position corresponding to the partial region included in the set; The process is executed by a computer, A program in which the multiple partial regions are distributed across an entire page or across multiple pages, and the colors of the pixels contained within the regions fall within a certain range.

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