JP2015176001A - Control device, image forming system, program, and calibration sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform calibration of a white toner to an image forming apparatus that can form images with a white toner so that the stable degree of whiteness can be output from the image forming apparatus.SOLUTION: There is provided a control device that controls an image forming apparatus that can form images with a white toner, and has an output control part that outputs, from the image forming apparatus, a calibration sheet including a first layer formed with a toner other than the white toner, and a second layer formed in an area overlapped with the first layer and including a patch area, which is a density detection area and formed with a white toner.

Description

  The present invention relates to a control device that controls an image forming apparatus, an image forming system, a program, and a calibration sheet.

  2. Description of the Related Art Conventionally, in addition to toners corresponding to CMYK four process colors, there is an image forming apparatus in which a white toner that contains a white pigment and a binder resin component as main components and does not contain a color material component other than a single white color.

  In recent years, white toner has been used as a color material that provides various added values such as printing on transparent recording media, fabrics, and colored paper, in addition to faithful color reproduction by process colors. For example, there is an image forming apparatus that obtains a desired white color by arranging white toner in the lowermost layer of a recording medium and blocking the color development of the recording medium with the white toner. In addition, there is an image forming apparatus that prints white toner from the back surface of a transparent recording medium and provides a high added value image that cannot be expressed only by the transparent recording medium and process color toner.

  In addition, in an image forming apparatus that detects an optical density of a toner image formed on an intermediate transfer member with an optical sensor, a technique using a solid image of white toner instead of a white reference plate for calibration is known. .

  However, the conventional image forming apparatus equipped with the white toner has a problem that the white toner cannot be calibrated and stable whiteness cannot be obtained.

  For example, Patent Document 1 discloses an image forming apparatus that uses an image pattern printed with white toner as a reference pattern for calibration of an optical sensor. However, the image forming apparatus disclosed in Patent Document 1 cannot perform white toner calibration, and thus cannot obtain stable whiteness.

  For example, Patent Document 2 discloses image processing for outputting correction patches to a plurality of types of screens when performing gradation correction for suppressing density fluctuations in CMYK process colors due to changes over time. The program is disclosed. In this image processing program, many correction patches are assigned to a screen used in an area where gradation is important, so that image quality, cost, and speed can be improved in a balanced manner. However, the image processing program disclosed in Patent Document 2 cannot calibrate white toner and cannot obtain stable whiteness.

  Further, for example, Patent Document 3 discloses an image forming apparatus that forms white toner on the entire surface or the lowermost layer of a specific region when the opacity of the transfer paper is a predetermined value or less (that is, when the paper is thin). ing. In this image forming apparatus, it is possible to prevent the show-through that occurs when duplex printing is performed on a thin sheet. However, Patent Document 3 does not mention calibration. For this reason, even the image forming apparatus described in Patent Document 3 cannot obtain stable whiteness.

  The present invention has been made in view of the above, and an object of the present invention is to provide a control device, an image forming system, a program, and a calibration sheet that can calibrate white toner and obtain stable whiteness. And

  In order to solve the above-described problems and achieve the object, a control device according to the present invention is a control device that controls an image forming apparatus capable of forming an image with white toner, and is formed with toner other than white. A calibration sheet having a first layer and a second layer formed in a region overlapping with the first layer and including a patch region formed of white toner that is a density detection region is output from the image forming apparatus. An output control unit is provided.

  According to the present invention, the white toner is calibrated and stable whiteness can be obtained.

FIG. 1 is a diagram illustrating a schematic configuration of an image forming system according to an embodiment. FIG. 2 is a diagram showing the relationship between the area ratio and density of black toner. FIG. 3 is a diagram showing the relationship between the area ratio and density of white toner. FIG. 4 is a diagram illustrating an example of a calibration sheet according to the present embodiment. FIG. 5 is a diagram illustrating a result of reading the density of each patch region by the scanner from the calibration sheet of FIG. FIG. 6 is a diagram illustrating a hardware configuration when the image forming system is implemented as an MFP. FIG. 7 is a diagram illustrating a functional configuration of the control device together with a printer and a scanner. FIG. 8 is a diagram showing a calibration procedure. FIG. 9 is a diagram illustrating an example of the gradation value of the patch area. FIG. 10 is a diagram illustrating the relationship between the density and the scanner reading value when the calibration sheet is read by the scanner. FIG. 11 is a diagram illustrating the relationship between the white toner area ratio and the expected density value, and the relationship between the white toner area ratio and the density (measured value) read by the scanner. FIG. 12 is a diagram illustrating the relationship between the white toner area ratio and the expected density value, and the relationship between the white toner area ratio and the corrected measurement value. FIG. 13 is a diagram showing a table in which the numerical values of the area ratio, expected value, measured value, and corrected measured value of white toner are described. FIG. 14 is a diagram for explaining a method of generating gradation correction parameters. FIG. 15 is a diagram illustrating a configuration of an image forming system according to a first modification. FIG. 16 is a diagram illustrating an example of a calibration sheet according to the first modification. FIG. 17 is a diagram showing a procedure for generating tone correction parameters in the first modification. FIG. 18 is a diagram schematically illustrating a calibration sheet according to the second modification. FIG. 19 is a diagram schematically illustrating a first example of a calibration sheet according to the third modification. FIG. 20 is a diagram schematically illustrating a second example of the calibration sheet according to the third modification.

  Hereinafter, an image forming system 10 according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

<Schematic Configuration of Image Forming System 10 and Outline of Tone Correction Parameter Generation>
FIG. 1 is a diagram illustrating a schematic configuration of an image forming system 10 according to the embodiment. The image forming system 10 includes a printer 22 (image forming apparatus), a scanner 24, and a control device 30.

  The printer 22 includes a developing unit for W (white) toner in addition to a developing unit for four process color toners of C, M, Y, and K. Therefore, the printer 22 can form an image on a recording medium (paper or the like) with each of C, M, M, and K toners, and can further form an image with a white toner on the recording medium. is there.

  Further, the printer 22 has a circulation conveyance path, and after the first round of fixing, the recording medium can be re-supplied through the circulation conveyance path to transfer and fix the second round toner image on the recording medium. . As a result, the printer 22 can form an image with a toner other than white (for example, black toner (K toner)), and then can form an image with the white toner in the overlapping region. Alternatively, the printer 22 can form an image with white toner, and then form an image with toner other than white in the overlapping area. Such a circulation conveyance path is described in, for example, FIGS. 1 and 2 of JP-A-2002-268318.

  Further, the printer 22 has a reverse conveyance path, and can transfer and fix the toner image to the opposite surface of the recording medium after the toner image is transferred and fixed to one surface of the recording medium. Thus, the printer 22 can form an image with white toner on one side of the recording medium and can form an image with toner other than white on the other side.

  The scanner 24 optically reads the density of the surface of the recording medium in units of pixels. The scanner 24 includes a color line sensor composed of a color CCD or color CMOS photoelectric conversion element, and an A / D converter. The scanner 24 optically scans a recording medium placed on the contact glass, A / D converts the reflected light, and performs image processing such as gamma conversion. Then, the scanner 24 generates RGB image data having a predetermined resolution, for example, each of RGB represented by 8 to 10 bits.

  The control device 30 is a data processing device having a processor such as a CPU (Central Processing Unit) and a memory, and controls the printer 22 and the scanner 24 by executing a program. Moreover, the control apparatus 30 performs various arithmetic processing.

  The image forming system 10 may be a multi function printer (MFP) in which the printer 22, the scanner 24, and the control device 30 are integrated.

  Here, in the printer 22, even when image data having the same pixel value is given due to changes over time in parts, an assembling unit, and the like, the density of pixels actually formed on the recording medium differs. There is a case. For this reason, in the image forming system 10, for example, in accordance with an operation start instruction from the user, calibration is performed so that the density on the recording medium is constant for each pixel value.

  In the present embodiment, the user switches the mode of the image forming system 10 from a print mode for printing data generated by, for example, a word processor program or the like to a calibration mode. When switched to the calibration mode, the control device 30 gives pre-stored patch data and a print command to the printer 22 to output a recording medium on which an image corresponding to the patch data is formed. A recording medium on which an image corresponding to patch data is formed is called a calibration sheet.

  Subsequently, the control device 30 causes the scanner 24 to optically read the calibration sheet and obtains read data (image data). Subsequently, the control device 30 acquires the density of the region where the image corresponding to the patch data is formed from the read data, and the gradation correction data that is correction data for each pixel value of the image data is acquired from the acquired density. Generate. Subsequently, the control device 30 registers the generated gradation correction data in, for example, the printer 22. Thereafter, when image data to be printed is given, the printer 22 performs printing by correcting the pixel value of the image data with the registered gradation correction data. As a result, according to the image forming system 10, it is possible to suppress a change in density due to a change with time of the printer 22 and form an image with a stable density.

  FIG. 2 is a diagram showing the relationship between the area ratio and density of black toner. Here, the patch data is image data for printing a calibration sheet having a plurality of patch areas from the printer 22 to be calibrated. The patch area is an area for density detection.

  When normal process color calibration is performed, each of the plurality of patch areas is formed of a single color of C, M, Y, or K, and has different predetermined toner density instruction values (that is, levels). Key value).

  For example, the calibration sheet includes 0, 16, 32, 48, 64, 80, 96, 112, 128, 143, 159, 175, 191, 207, 223, for each color of C, M, Y, K. A plurality of patch areas 239 and 255 having 17 different gradation values are formed.

  The image forming system 10 can obtain a density graph with respect to the toner area ratio as shown in FIG. 2 by reading the density of each patch area of the calibration sheet. A value obtained by multiplying the gradation value by 100/255 is the toner area ratio. The image forming system 10 can generate gradation correction data for each color based on a density graph with respect to the toner area ratio.

  FIG. 3 is a diagram showing the relationship between the area ratio and density of white toner. On the other hand, when white toner calibration is performed, a calibration sheet is output using a general white paper as a recording medium (transfer paper) with patch data similar to a normal process color. .

  The transfer paper is white and the density with the white toner is almost the same. Therefore, even if the density is measured, the density with respect to the toner area ratio hardly changes as shown in FIG. Further, when the white toner has a higher whiteness than the transfer paper, the density may slightly decrease as the area ratio increases. Therefore, tone correction data for correcting white toner cannot be generated from such data, as with other colors.

  FIG. 4 is a diagram illustrating an example of a calibration sheet according to the present embodiment. Therefore, in the present embodiment, when calibrating white toner, the control device 30 causes the printer 22 to output a calibration sheet as shown in FIG. 4, which is different from a normal process color calibration sheet.

  In the example of FIG. 4, the calibration sheet includes 17 patch areas W00 to W16 and a peripheral area formed of black toner. This calibration sheet is generated as follows. First, in the first fixing process, a first layer of black toner (K toner) is formed on an area that is slightly larger than the entire 17 patch areas on the recording medium (transfer paper). Subsequently, in the second fixing process, a second layer including 17 patch areas W00 to W16 is printed with white toner in an overlapping area from the top of the first layer. The 17 patch areas are smaller than the area formed by the first layer of black toner. Accordingly, a peripheral region of black toner is formed around the 17 patch regions.

  Here, the data for forming the first layer of black toner is 100% uniform area (solid area) image data (gradation value 255). The data for forming the second layer including 17 patch regions W00 to W16 with white toner is 0, 16, 32, 48, 64, 80, 96, 112, 128 as in the process color data. , 143, 159, 175, 191, 207, 223, 239, and 255, data of 17 different gradation values. However, the data for forming the first layer is not limited to the image data for forming a 100% solid area with black toner, but may be image data having a uniform gradation value other than 100%. The data for forming the first layer may use a toner other than the white toner. Further, the data for forming the second layer using the white toner is not limited to the above-described gradation value.

  Here, the reason why the first layer of black toner is formed in an area that is slightly larger than the 17 patch areas W00 to W16 is as follows. That is, when the calibration sheet is read by the scanner 24, if the reflectance of the peripheral region is high, the scattered light will circulate, and the reflectance will be higher than when the measurement is performed with a true black back.

  For example, it is assumed that 17 patch areas W00 to W16 are arranged in the vertical direction in order from W00. In this case, as an example, the peripheral black toner regions are formed on the right side and the left side of each patch region with a width equal to or greater than the horizontal width of the patch region W00. Further, the peripheral black toner region is formed on the upper side of the patch region W00 with a length equal to or longer than the vertical length of the patch region W00. Further, the peripheral black toner region has a length equal to or longer than the vertical length of the patch region W16 and is formed below the patch region W16.

  Further, the calibration sheet may include a mark indicating the reference position (for example, an arrow in FIG. 4). Thereby, the scanner 24 can set the reading position with reference to the mark when reading the calibration sheet.

  FIG. 5 is a diagram showing the result of reading the density of each patch area from the calibration sheet of FIG. 4 by the scanner 24. Since the patch area of the stepwise gradation value by the white toner is superimposed on the 100% solid area of the black toner, the measurement result of the part with the white toner area ratio of 0% (patch area W00) Represents 100% concentration. In addition, the density decreases as the area ratio of the white toner increases. The image forming system 10 generates gradation correction data for the white toner based on the density graph with respect to the area ratio of the white toner. A method for generating gradation correction data for white toner will be specifically described below.

<Hardware configuration of MFP>
FIG. 6 is a diagram illustrating a hardware configuration when the image forming system 10 is mounted as an MFP. When implemented as an MFP, the image forming system 10 includes a controller 101, an operation panel 102, a FAX control unit 103, a printer 22, and a scanner 24.

  The controller 101 includes a CPU 111, a system memory 112, an NB 113 (north bridge), an SB 114 (south bridge), an ASIC 115 (application specific integrated circuit), a local memory 116, an HDD 117 (hard disk device), and an NIC 118 (network). Interface card) and a USB device 119.

  An external memory device (not shown) can be attached to and removed from the USB device 119 in the controller 101. The program stored in the external memory device is installed in the HDD 117 through the external memory device. Further, the program may be installed in the HDD 117 via a NIC 118 from a server (not shown).

  The CPU 111 controls the entire image forming system 10 that is an MFP. For example, the CPU 111 starts and executes a process on an OS (Operating System).

  The NB 113 is a bridge. The SB 114 is a bridge for connecting the PCI bus, ROM (Read Only Memory), peripheral devices, and the like. The system memory 112 is a memory used as a drawing memory or the like. The local memory 116 is a memory used as a copy image buffer and a code buffer.

  The ASIC 115 is an IC for image processing applications having hardware elements for image processing. The HDD 117 is a storage (auxiliary storage device) that stores image data, document data, programs, font data, and the like. The NIC 118 is an interface device that connects the MFP to a network. The USB device 119 is an interface conforming to each standard.

  The operation panel 102 is an operation unit that receives an input operation from an operator via a touch panel and performs display for the operator. A physical keyboard is arranged around the operation panel 102.

  The printer 22 has, for example, a one-drum color plotter, and forms an image for each page based on print job data including patch data or image data read by the scanner 24, and transfers the image to a recording medium (such as paper). . For example, the printer 22 uses an electrophotographic process using a laser beam to transfer a toner image formed on the photosensitive drum onto a recording medium (such as paper), and fixes and outputs the toner image with heat and pressure by a fixing device.

  In the present embodiment, the printer 22 corresponds to the printer 22 shown in FIG. In the present embodiment, the printer 22 prints an image corresponding to the patch data on a recording medium (paper or the like) and outputs a calibration sheet.

  For example, the scanner 24 converts a recording medium (such as paper) placed on the contact glass into digital data having a predetermined resolution, and generates image data. In the present embodiment, the scanner 24 corresponds to the scanner 24 shown in FIG. The scanner 24 reads the calibration sheet and generates read data.

  The FAX control unit 103 is connected to a public communication network via an NCU (Network Control Unit), and performs facsimile transmission / reception according to a communication procedure (communication protocol) corresponding to, for example, a G3 or G4 standard facsimile. The FAX control unit 103 has a memory. For example, facsimile data received when the power of the main body is OFF is stored in this memory in order to temporarily store it.

<Functional Configuration of Control Device 30>
FIG. 7 is a diagram illustrating the functional configuration of the control device 30 together with the printer 22 and the scanner 24. The control device 30 includes a patch data storage unit 41, an output control unit 42, an acquisition unit 43, a calculation unit 44, a setting unit 45, and a gradation correction parameter storage unit 46.

  The patch data storage unit 41 is realized by a storage device such as a RAM, a ROM, or an HDD, for example. The patch data storage unit 41 stores patch data that is image data for outputting a calibration sheet.

  The output control unit 42 is realized by a CPU or the like executing a program. The output control unit 42 outputs the calibration sheet from the printer 22 by providing the printer 22 with the patch data stored in the patch data storage unit 41. That is, the output control unit 42 includes a first layer formed of toner other than white and a patch region formed in a region overlapping the first layer and formed of white toner that is a density detection region. A calibration sheet having a layer is output from the printer 22.

  In this case, as an example, the first layer is formed with a black toner at a uniform density. The second layer includes a plurality of patch regions having different white toner densities. More specifically, the first layer is formed directly on the recording medium (paper), and the second layer is smaller than the area of the first layer and formed on the first layer.

  The acquisition unit 43 is realized by a CPU or the like executing a program. The acquisition unit 43 causes the scanner 24 to optically read the calibration sheet and receives the read image data. Then, the acquisition unit 43 acquires the density of each of the plurality of patch areas formed on the calibration sheet.

  The calculation unit 44 is realized by a CPU or the like executing a program. The calculation unit 44 calculates a gradation correction parameter based on the respective densities of the plurality of patch areas acquired by the acquisition unit 43.

  The setting unit 45 is realized by a CPU or the like executing a program. The setting unit 45 registers the gradation correction parameter calculated by the calculation unit 44 in the gradation correction parameter storage unit 46.

  The gradation correction parameter storage unit 46 is realized by a storage device such as a RAM, a ROM, or an HDD, for example. The gradation correction parameter storage unit 46 stores the gradation correction parameters registered by the setting unit 45. The gradation correction parameters stored in the gradation correction parameter storage unit 46 are used to correct the gradation of image data given to the printer 22 when the printer 22 performs printing.

  Note that the gradation correction parameter may be held by the printer 22. In this case, the gradation correction parameter storage unit 46 is realized by the storage device of the printer 22. Further, the gradation correction parameter may be held by the printer driver. In this case, the gradation correction parameter storage unit 46 is included in an information processing apparatus such as a personal computer.

  The output control unit 42, the acquisition unit 43, the calculation unit 44, and the setting unit 45 may be partially or entirely realized by a circuit such as an ASIC.

<Tone correction parameter generation method>
FIG. 8 is a diagram showing a calibration procedure. The image forming system 10 executes processing in the procedure shown in FIG. 8 in calibration.

  First, in step S10, the image forming system 10 performs screen processing. Subsequently, in step S20, the image forming system 10 outputs a calibration sheet. Subsequently, in step S30, the image forming system 10 optically reads the calibration sheet. Subsequently, in step S40, the image forming system 10 generates a gradation correction parameter. Subsequently, in step S50, the image forming system 10 registers gradation correction parameters. Hereinafter, the details of the patch data and the processing of each step will be described.

(Patch data)
The patch data is image data printed on a recording medium of a predetermined size (for example, A4 size paper). As shown in FIG. 4, the patch data is image data for forming a series of patch region rows (also referred to as patch rows) in which gradation values change. The width of the increase in gradation value between patch areas is not necessarily uniform. For example, the increase width may be set so that the brightness difference is equal when printed as a calibration sheet, the density difference may be set equal, or otherwise. May be set so as to increase monotonically. In the example of FIG. 4, only the gradation patch for white toner is drawn on the calibration sheet, but patch regions of other colors may be drawn together on the same sheet.

  FIG. 9 is a diagram illustrating an example of the gradation value of the patch area. As described above, the gradation values of W00 to W16 that are regions constituting a series of patch rows do not need to increase evenly. It should be noted that the peripheral portions of W00 to W16 have gradation values with the value of the W plate (gradation value by white toner) being zero.

  The gradation value (that is, the pixel value of the image data) is expressed by an integer value of 0 or more and 255 or less, and the larger the value, the higher the density. However, the read data read by the scanner 24 has a lower density as the reflectance is higher, so that the smaller the value is, the higher the density is.

  Further, the calibration sheet is not a print of the gradation value specified by the patch data as it is, but the patch data is subjected to gradation correction processing using the gradation correction parameter generated last time by the image forming system 10. It may be output. That is, if the gradation value used for printing the calibration sheet is known, it may be output with or without being corrected.

(Step S10 Screen processing)
In the screen processing in step S10, the following processing is performed. For example, when the user operates the operation panel to switch the mode to the gradation correction mode, the output control unit 42 reads the patch data from the patch data storage unit 41. Subsequently, the output control unit 42 decomposes the read patch data into C, M, Y, K, and W color components. Subsequently, the output control unit 42 performs halftone processing (screen processing) for determining the output gradation value from the relationship between the gradation value and the threshold value sequentially for each pixel of color.

  Halftone processing (screen processing) refers to processing for converting multi-value image data into low-value image data using a predetermined screen shape such as a halftone dot while maintaining a global density. As halftone processing, for example, processing by a dither method or processing by an error diffusion method is known. In the present embodiment, the output control unit 42 performs a halftone process on the patch data by the dither method and outputs the patch data. In this example, the output gradation values of the image data after halftone processing are four values “0, 85, 170, 255”.

(Step S20 Calibration sheet output)
In the calibration sheet output process in step S20, the following process is performed. The output control unit 42 requests the printer 22 to print patch data that has been subjected to halftone processing. In S10, the printer 22 determines which of “0, 85, 170, and 255” a value corresponding to each pixel is to be output, and outputs a calibration sheet on which an image is drawn with the determined value. .

(Step S30 Optical reading of calibration sheet)
In the optical reading process of the calibration sheet in step S30, the following process is performed. When the user places a calibration sheet on the contact glass of the scanner 24 and performs a predetermined operation, the scanner 24 optically scans the calibration sheet. In the calibration mode, it is assumed that the read original is a calibration sheet, and the orientation of the calibration sheet on the contact glass is correctly placed with respect to the reference position.

  The scanner 24 scans the calibration sheet as described above, and acquires the density information of the calibration sheet. The density information is represented by, for example, 600 dpi 8-bit RGB data. The acquisition unit 43 acquires shading information from the scanner 24 and performs shading correction and the like. The acquisition unit 43 extracts, from the shade information acquired from the scanner 24, the shade information of a plurality of pixels (for example, 128 × 128 pixels at 600 dpi) in a predetermined region near the center for each of the series of patch regions W00 to W16. To do. Here, the reason why the density information of the pixels near the center of the patch area is extracted is to prevent the influence of other adjacent patch areas. Another reason is to suppress a decrease in reading accuracy when the calibration sheet is placed with a deviation from the contact glass.

  The acquisition unit 43 calculates an average value of a plurality of shade information in a predetermined area for one patch area, and uses the calculated average value as a measurement value of the shade information of the patch area. Note that the calibration sheet for white toner is composed of an achromatic color. Therefore, in the present embodiment, the acquisition unit 43 acquires an average value of 128 × 128 pixels located near the center of the patch area of the green channel G data of the scanner 24 as a measurement value of the shade information of the patch area. .

(Step S40: Generation of gradation correction parameters)
In the gradation correction parameter generation processing in step S40, the following processing is performed.

  FIG. 10 is a diagram illustrating the relationship between the density and the scanner read value when the scanner 24 reads the calibration sheet. First, the calculation unit 44 stores a table or the like indicating the correspondence between the density and the scanner reading value (light / dark information). This table is calculated by a prior experiment or the like. The calculation unit 44 refers to the table representing the correspondence between the density and the scanner read value (darkness information) for each of the patch areas W00 to W16, and calculates the scanner read value (lightness information) acquired by the acquisition unit 43. Convert to concentration. Hereinafter, the density measured value read by the scanner 24 represents the density converted from the relationship of FIG.

  FIG. 11 is a diagram showing the relationship between the white toner area ratio and the expected density value, and the relationship between the white toner area ratio and the density (measured value) read by the scanner 24. More specifically, the white circles in FIG. 11 indicate the measured values of the density read by the scanner 24 in the respective patch areas W00 to W16. The black circles in FIG. 12 indicate the expected density values in the respective patch areas W00 to W16.

  First, attention is focused on the patch region W00 having a white toner area ratio of 0%. The patch region W00 having a white toner area ratio of 0% has a density of black toner of 100% regardless of the characteristics of the white toner. That is, the difference between the measured value read by the scanner 24 and the expected value in the patch area W00 with the white toner area ratio of 0% is the density fluctuation amount of the black toner. Therefore, the calculation unit 44 uniformly corrects the measured values of the patch areas W01 to W16 of other white toner area ratios based on the density fluctuation amount.

That is, first, the calculation unit 44 uses the difference between the measured value read by the scanner 24 and the expected value in the patch region W00 with the white toner area ratio of 0% as the correction amount, as shown in the following equation (1). calculate.
(Correction amount) = (measured value of W00) − (expected value of W00) (1)

Subsequently, the arithmetic unit 44 calculates a corrected measurement value by subtracting the correction amount from the measurement value read by the scanner 24 for each of the other patch regions W01 to W16 as in the following equation (2). To do.
(Correction measurement value) = (measurement value of Wi) − (correction amount) (2)

  FIG. 12 is a diagram illustrating the relationship between the white toner area ratio and the expected density value, and the relationship between the white toner area ratio and the corrected density (corrected measurement value). FIG. 13 is a diagram showing a table in which the numerical values of the area ratio, expected value, measured value, and corrected measured value of white toner are described.

  The results of the calculations of equations (1) and (2) are as shown in FIG. The relationship between the area ratio of the white toner, the expected value, the measured value, and the corrected measured value is as shown in the table of FIG.

  FIG. 14 is a diagram for explaining a method of generating gradation correction parameters. The dotted line connecting the white circles in FIG. 14 is a graph showing the relationship of the corrected measurement value to the area ratio of the white toner. Further, the solid line connecting the black circles in FIG. 14 is a graph showing the relationship of the expected density value to the area ratio of the white toner.

  Here, when the corrected measurement value matches the expected value, this is an ideal state that does not need to be corrected by the tone correction parameter. However, in the example of FIG. 14, at the position where the white toner area ratio is 94%, the expected value of density is 0.31, but the corrected measurement value is 0.181, and the corrected measurement value is the expected value. Does not match. This is an influence due to the density fluctuation due to the change over time of the parts and the assembly part of the printer 22 and indicates that the amount of white toner necessary for realizing the expected density is low.

  The calculation unit 44 calculates the area ratio of the white toner necessary for realizing each density by linear interpolation, and calculates the tone correction parameter for each density. That is, the calculation unit 44 detects a value that is higher than the expected density value and one lower than the expected density value among the adjacent corrected measurement values. In this example, two points of the white toner area ratio of 87% and 94% are applicable. The white toner area ratio corresponding to the expected density value is calculated by linear interpolation between the two points. When actually calculated, a solution of 89.1% is obtained. In other words, 89.1% of white toner is assigned to an image that requires 94% area ratio data as white toner, thereby correcting the density fluctuation due to the change over time and obtaining the expected gradation characteristics. Can do. The area ratio can be converted to 8-bit gradation value data by multiplying by 255/100. The gradation values corresponding to 89.1% and 94% are “227” and “240”.

  The calculation unit 44 performs the above calculation to generate a conversion table corresponding to discrete 16-point gradation values corresponding to the density of the expected value. Then, the calculation unit 44 gently interpolates between the 16 points of the conversion table using a spline interpolation process or the like, and sets the gradation correction parameter in increments of one gradation from the gradation value “0” to “255”. Generate.

(Step S50: Registration of gradation correction parameters)
In the gradation correction parameter registration process in step S50, the following process is performed.

  When the gradation correction parameter is generated by the calculation unit 44, the setting unit 45 causes the gradation correction parameter storage unit 46 to store the generated gradation correction parameter. When the gradation correction process is performed by the printer 22, the gradation correction parameter storage unit 46 is provided in the printer 22. When the driver program executes the gradation correction process, the gradation correction parameter storage unit 46 is provided in a storage area of a computer where the driver program is installed.

  When printing, the printer 22 or the computer on which the driver program is installed converts the pixel value of each pixel included in the image data using the gradation correction parameter, and performs halftone adjustment on the converted image data. Process and print. For example, when the printer 22 or the computer in which the driver program is installed is given the pixel of the gradation value “240” of the white toner plate, the corresponding gradation correction parameter is subtracted from the gradation value “240”. The gradation correction processing is performed on the gradation value “227”.

<Print processing using tone correction parameters>
In the image forming system 10, when the gradation correction parameter is stored in the gradation correction parameter storage unit 46 by calibration, the gradation correction is performed on the image data in the following procedure when normal image data is printed. A gradation correction process using parameters is performed.

  When the image forming system 10 is implemented as the MFP of FIG. 6, for example, the scanner 24 or the FAX control unit 103 functions as an image input unit for inputting image data. Also, the CPU 111 functions as a gradation correction unit that performs gradation correction processing by executing a program. For example, an interface or printer 22 connected to the ASIC 115 having an engine unit functions as an image output unit that outputs image data subjected to gradation correction.

  The image input unit inputs image data by data corresponding to one pixel. Here, data corresponding to one pixel of the image data is represented by an integer value of 0 or more and 255 or less, for example.

  The gradation correction unit refers to the gradation correction parameter and γ-converts the gradation value of the image data input from the image input unit pixel by pixel. The image output unit outputs the gradation value converted by the gradation correction unit pixel by pixel. As a result, the laser light is modulated by the converted image data, and a color image can be printed while correcting the density variation with time.

  As described above, the image forming system 10 according to the present exemplary embodiment can generate a gradation correction parameter that corrects a density variation due to a change with time. As a result, according to the image forming system 10, it is possible to correct the density fluctuation of the white toner over time, and it is possible to form an image with stable whiteness.

<First Modification>
FIG. 15 is a diagram illustrating a configuration of the image forming system 10 according to the first modification. FIG. 16 is a diagram illustrating an example of a calibration sheet according to the first modification. In describing the first modification, description of functions and configurations substantially the same as those of the image forming system 10 described with reference to FIGS. 1 to 14 will be omitted. The same applies to other modified examples.

  The image forming system 10 according to the first modification further includes a densitometer 50 together with the scanner 24. Note that the image forming system 10 may include only the densitometer 50 without including the scanner 24.

  The densitometer 50 is a measuring device that reads the density, and reads the density through a small aperture. For this reason, the densitometer 50 can accurately measure the density at a specific position without being affected by the confusion light from the surroundings.

  In the first modification, the control device 30 further includes a designation unit 51. The designation unit 51 designates which of the scanner 24 and the densitometer 50 is to detect the density of the patch area.

  The output control unit 42 causes the printer 22 to output the calibration sheet shown in FIG. 4 when the scanner 24 is used for density detection in the calibration (when the designation unit 51 designates the scanner 24). On the other hand, the output control unit 42 causes the printer 22 to output the calibration sheet shown in FIG. 16 when the densitometer 50 is used for density detection (when the designation unit 51 designates the densitometer 50).

  In the calibration sheet shown in FIG. 16, there is no area formed of black toner (K toner) around the series of patch areas W00 to W16. However, this is the same in that a solid area of black toner is formed below the series of patch areas W00 to W16.

  That is, in the first modification, when the densitometer 50 is used, the output control unit 42 is formed in a first layer formed of toner other than white (for example, black toner) and an area overlapping the first layer. The printer 22 outputs a calibration sheet having a second layer including a patch area formed of white toner having substantially the same size as the first layer.

  FIG. 17 is a diagram showing a procedure for generating tone correction parameters in the first modification. The procedure for generating the tone correction parameter in the first modified example is different from the procedure shown in FIG. 8 in that the process of step S60 is executed instead of the process of step S30.

  In step S60, the densitometer 50 directly measures the density of the patch area of the calibration sheet. Then, the acquisition unit 43 acquires the concentration measurement value acquired by the densitometer 50. In this case, the acquisition unit 43 does not have to perform an operation such as an average value. In step S40, the calculation unit 44 does not have to execute conversion using a conversion table between the measurement value and the density by the scanner 24.

  In the image forming system 10 according to the first modification as described above, since the densitometer 50 measures the density, it is not affected by the confusion light from the surrounding white region. Accordingly, the black toner area around the patch area in the calibration sheet can be eliminated. Thereby, according to the image forming system 10 which concerns on a 1st modification, the usage-amount of the black toner at the time of printing a calibration sheet can be decreased.

<Second Modification>
FIG. 18 is a diagram schematically illustrating a calibration sheet according to the second modification. The image forming system 10 according to the second modified example generates a calibration sheet using an OHP (Overhead Projector) sheet or a transparent recording medium such as a clear file.

  In some cases, after a desired pattern is drawn on a transparent recording medium with process color toner, a solid image of white toner is drawn from the back side. Thus, when the transparent recording medium is viewed from the surface, there is an effect that a white background is drawn on the transparent portion and the contrast is increased. Also, as a design that cannot be simply made with office paper, white characters and patterns are drawn with white toner. In this case, the white toner is observed from the front side across the transparent recording medium.

  Therefore, when the transparent recording medium is used in this way, it is desirable to measure the density from the side sandwiching the transparent recording medium even in calibration. The output control unit 42 according to the second modified example outputs a calibration sheet in which a second layer formed of white toner is formed on a transparent recording medium and a first layer of black toner is formed on the second layer. .

  The densitometer 50 detects the density of the transparent recording medium from the surface on which the first layer and the second layer are not formed. The density may be read by the scanner 24. In this case, as shown in FIG. 4, the output control unit 42 may output a calibration sheet having a layout in which the area of the first layer made of black toner is larger than the patch area made of white toner.

  According to the image forming system 10 according to the second modified example, since the density of the patch area is measured via the transparent recording medium, calibration can be performed in the same state as in actual use.

<Third Modification>
FIG. 19 is a diagram schematically illustrating a first example of a calibration sheet according to the third modification. FIG. 20 is a diagram schematically illustrating a second example of the calibration sheet according to the third modification. The image forming system 10 according to the third modified example generates a calibration sheet using a transparent recording medium such as an OHP sheet or a clear file.

  In some cases, a watermark or the like is printed with white toner on the surface side of the transparent recording medium. In this case, the watermark is observed without passing through the transparent recording medium. Therefore, in calibration, it is better to measure the density of the patch area formed with the white toner without using a transparent recording medium.

  Accordingly, as shown in FIG. 19, the output control unit 42 according to the third modification forms a first layer of black toner on the transparent recording medium, and a second layer of white toner on the first layer. The formed calibration sheet is output. The densitometer 50 directly measures the density of the second layer with the white toner.

  Instead, as shown in FIG. 20, the output control unit 42 according to the third modification forms a second layer of white toner on one surface of the transparent recording medium, and the other side of the transparent recording medium. A calibration sheet in which a first layer of black toner is formed on the surface may be output. In this case, the densitometer 50 directly measures the density of the second layer with the white toner. In the example of FIG. 20, since the black toner and the white toner are completely separated from each other, the color toner is not mixed and the characteristics of the white toner can be obtained more purely.

  When the scanner 24 reads the density, as shown in FIG. 4, the output control unit 42 calibrates the layout in which the area of the first layer made of black toner is larger than the patch area made of white toner. Can be output.

  According to the image forming system 10 according to the third modified example, when a watermark or the like is printed on the transparent recording medium, the density of the patch area is measured without using the transparent recording medium. It is possible to perform calibration in the same state as.

  Note that whether to output the calibration sheet of the second modified example or the calibration sheet of the third modified example differs depending on the usage. Accordingly, the image forming system 10 may determine which calibration sheet is to be output in accordance with the user's setting operation, and output the determined type of calibration sheet.

DESCRIPTION OF SYMBOLS 10 Image forming system 22 Printer 24 Scanner 30 Control apparatus 41 Patch data storage part 42 Output control part 43 Acquisition part 44 Calculation part 45 Setting part 46 Gradation correction data storage part 50 Densitometer 51 Specification part 101 Controller 102 Operation panel 103 FAX control Unit 111 CPU
112 System memory 113 NB
114 SB
115 ASIC
116 Local memory 117 HDD
118 NIC
119 USB device

JP 2008-298854 A JP 2010-118927 A JP 2002-268318 A

Claims (11)

A control device for controlling an image forming apparatus capable of forming an image with white toner,
A calibration sheet having a first layer formed of toner other than white and a second layer including a patch region formed in a region overlapping with the first layer and formed of white toner as a density detection region A control device comprising: an output control unit that outputs the image data from the image forming apparatus. The control device according to claim 1, wherein the first layer is formed of black toner. The first layer is formed with a uniform area ratio;
The control device according to claim 1, wherein the second layer includes a plurality of patch regions in which the area ratio of each white toner is different. The control device according to claim 3, wherein the first layer is formed on a recording medium and is larger than a region of the second layer. The second layer is formed on the first layer. The second layer is formed on a transparent recording medium,
The control device according to claim 3, wherein the first layer is formed on the second layer. The first layer is formed on one surface of a transparent recording medium,
The control device according to claim 3, wherein the second layer is formed on the other surface of the recording medium. An image forming apparatus capable of forming an image with white toner;
A calibration sheet having a first layer formed of toner other than white and a second layer including a patch region formed in a region overlapping with the first layer and formed of white toner as a density detection region Output from the image forming apparatus,
An acquisition unit for acquiring the density of each of the plurality of patch regions;
A calculation unit for calculating a gradation correction parameter for correcting a gradation value of image data given to the image forming apparatus based on the density of each of the plurality of patch regions;
An image forming system comprising: The second layer includes a patch area where no white toner is present,
The image forming system according to claim 7, wherein the acquisition unit corrects the density of another patch area formed of white toner based on the density of a patch area where no white toner exists. A scanner that optically reads the calibration sheet;
A densitometer for detecting the density of the patch area of the calibration sheet;
A designation unit that designates whether the density of the patch region is detected by the scanner or the densitometer;
The output control unit
When using the scanner, the first layer is formed on a recording medium, the second layer is smaller than the first layer, and the calibration sheet formed on the first layer is output.
When the densitometer is used, the first layer is formed on a recording medium, the second layer is approximately the same size as the first layer, and the calibration is formed on the first layer. The image forming system according to claim 7 or 8, wherein a sheet is output. A program for causing a computer to function as a control device that controls an image forming apparatus capable of forming an image with white toner,
A calibration sheet having a first layer formed of toner other than white and a second layer including a patch region formed in a region overlapping with the first layer and formed of white toner as a density detection region For causing the computer to execute an output control step of outputting the image from the image forming apparatus. A calibration sheet output from an image forming apparatus capable of forming an image with white toner,
A first layer formed of toner other than white;
A second layer including a patch region formed of white toner that is a density detection region,
The calibration sheet is formed in a region where the second layer overlaps the first layer in the recording medium.

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