JP2020077948A - Image forming apparatus, gradation correction method, and program - Google Patents

Abstract

To provide an image forming apparatus, a gradation correction method, and a program with which smooth gradation characteristics can be maintained through gradation correction, and the number of gradations after the correction can be maintained.SOLUTION: An image forming apparatus comprises: an information acquisition unit that acquires a dither matrix and dither information; a patch creation unit that creates a patch for gradation correction obtained by connecting patches of each of gradations in growth steps; a print control unit that prints the patch for gradation correction on a print medium; a patch separation unit that separates an image obtained by reading the patch for gradation correction into patches; a characteristic value acquisition unit that acquires the characteristic values of each patch; a dot characteristic calculation unit that calculates the growth characteristics of one dot based on the difference between the characteristic value of each of the gradations in the growth steps and the characteristic value of the gradation in a growth step immediately therebefore; a gradation characteristic calculation unit that calculates gradations in growth steps approximate to target values of each of the gradations and the number of necessary growth dots; and a correction matrix creation unit that creates a gradation correction dither matrix for performing gradation correction based on a result of the calculation.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus, a gradation correction method and a program.

  In an image forming apparatus such as a laser printer, the output density of the density changes due to the temperature and humidity, the printing environment such as the type and quality of the output paper, the deterioration of consumable parts over time, and the variation of the output characteristics of each device There is. As a countermeasure, automatic gradation that maintains the image quality by scanning the paper on which the patch of each gradation is printed by the image forming device with a scanner and gamma-correcting the output gradation value according to the read value of the patch of each gradation The correction function is known.

  As a technique using such an automatic gradation correction function by gamma correction, there is one that performs gamma correction on a fixed dither pattern, and the color value of a correction pattern composed of gradations whose gradation values change continuously is used. A technique has been disclosed in which the acquired amount is obtained, the conversion amount for the gradation value is obtained, and the exposure amount is corrected so that the change amount becomes uniform (for example, Patent Document 1).

  However, in the technique described in Patent Document 1, the exposure amount of each hierarchical level is changed based on the acquired color value, and the colorimetric values of several parts of all the gradations are used, and the other values are used. Since the gradation is interpolated and the gradation correction value is calculated on the assumption that the characteristics of the dither pattern are not smooth, the gradation correction value is calculated. There is a problem that it will end up. Further, depending on the correction result, the same gradation may be continuous, which causes a problem that the number of effective gradations decreases.

  The present invention has been made in view of the above problems, and an image forming apparatus capable of maintaining smooth gradation by gradation correction and maintaining the number of gradations after correction, It is intended to provide a correction method and a program.

  In order to solve the problems described above and achieve the object, the present invention is based on an information acquisition unit that acquires a dither matrix and dither information, and the dither matrix and the dither information acquired by the information acquisition unit, A patch generation unit that generates a tone correction patch in which patches of each growth step tone are connected, a print control unit that causes the printing unit to print the tone correction patch on a print medium, and a print control unit that prints on the print medium. From the image in which the gradation correction patch is read by the reading unit, a patch separating unit that separates into patches corresponding to the growth step gradations and a characteristic value of each patch separated by the patch separating unit are acquired. Based on a difference between the characteristic value of the patch of the growth step gradation and the characteristic value of the patch of the growth step gradation immediately before the growth step gradation. A dot characteristic calculation unit that calculates a growth characteristic of one dot in each growth step gradation, and the growth step gradation that approximates a target value of each gradation based on the growth characteristic of one dot in each growth step gradation, And a gradation characteristic calculation unit for calculating the number of required growth dots in the growth step gradation, and a gradation correction dither matrix for performing gradation correction based on the calculation result of the gradation characteristic calculation unit. And a correction matrix generation unit for performing the above.

  According to the present invention, smooth gradation can be maintained by gradation correction, and the number of gradations after correction can be maintained.

FIG. 1 is a diagram illustrating an example of the overall configuration of the image forming apparatus according to the embodiment. FIG. 2 is a diagram illustrating an example of the hardware configuration of the image forming apparatus according to the embodiment. FIG. 3 is a diagram illustrating an example of a configuration of functional blocks of the image forming apparatus according to the embodiment. FIG. 4 is a diagram illustrating the base matrix. FIG. 5 is a diagram showing an example of the aggregated dither matrix. FIG. 6 is a diagram showing an example of base matrix rank information indicating the growth order of the pace matrix. FIG. 7 is a diagram illustrating the growth step gradation. FIG. 8 is a diagram showing an example of a dither density characteristic graph. FIG. 9 is a diagram showing an example of a patch at each step for gradation correction. FIG. 10 is a diagram showing an example of the gradation correction patch. FIG. 11 is a diagram showing an example of a tone correction patch separated into two columns. FIG. 12 is a diagram showing an example of regions to be excluded in the patches of the separated growth step gradations. FIG. 13 is an example of a flowchart showing an example of the flow of automatic gradation correction processing of the image forming apparatus according to the embodiment. FIG. 14 is a diagram showing an example of a growth step gradation that exceeds a target value and a required number of dots in the growth step gradation.

  Hereinafter, embodiments of an image forming apparatus, a gradation correction method, and a program according to the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following embodiments, and constituent elements in the following embodiments include those that can be easily conceived by those skilled in the art, those that are substantially the same, and those that are within a so-called equivalent range. Is included. Furthermore, various omissions, replacements, changes and combinations of the constituent elements can be made without departing from the scope of the following embodiments.

(Overall structure of image forming apparatus)
FIG. 1 is a diagram illustrating an example of the overall configuration of the image forming apparatus according to the embodiment. The overall configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  The image forming apparatus 1 according to the present embodiment shown in FIG. 1 uses a multi-value dither method that expresses gradations by using pixels that can be set by switching a plurality of density values based on an input image of multi-gradation. Is an image forming apparatus for forming a. The image forming engine section of the image forming apparatus 1 includes four image forming units for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Further, as shown in FIG. 1, the image forming apparatus 1 includes an intermediate transfer belt 16, a driving roller 17, a belt tension roller 19, a secondary transfer roller 20, a secondary transfer counter roller 21, and a registration roller pair. 22, a fixing device 23, a cleaning backup roller 27, and a belt cleaning device 28.

  The four image forming units use Y, M, C, and K toners of different colors, but otherwise have the same configuration. Note that the four image forming units may be replaced at the same time by being held in a common holding body and integrally attached to and detached from the main body of the image forming apparatus 1.

  Here, the configuration of the image forming unit for C that forms a C toner image will be described as an example. As shown in FIG. 1, the image forming unit for C includes a photosensitive drum 11C, a charging roller 12C, a writing laser beam 13C, a developing device 14C, a primary transfer roller 15C, and a drum cleaning device 18C. Including.

  The photoconductor drum 11C is a drum that functions as a latent image carrier. The photoconductor drum 11C is rotationally driven in the direction of the arrow shown in FIG. 1 by a driving unit (not shown), and while being in contact with or in proximity to the charging roller 12C to which a charging bias is applied, by the discharge generated with the charging roller 12C The surface is uniformly charged. As a method for uniformly charging the photosensitive drum 11C, a method using a charging charger may be adopted instead of a method in which a charging member such as the charging roller 12C is brought into contact with or close to the photosensitive drum 11C. ..

  The charging roller 12C is a roller that uniformly charges the surface of the photosensitive drum 11C by applying a charging bias to the rotationally driven photosensitive drum 11C.

  The writing laser beam 13C is a laser beam emitted from an optical writing unit (not shown) to form an electrostatic latent image for C on the surface of the charged photosensitive drum 11C. This optical writing unit has, for example, a laser diode as a light source, and a laser driving unit that drives the laser diode by a pulse width modulation (PWM) method, and uses image information of an input image to be formed. It is controlled based on. The laser drive unit sets, for example, an exposure control PWM value sent from the printer controller 100, which will be described later, and a period in which the writing laser beam 13C can be applied to a region of one pixel on the photosensitive drum 11C in one cycle. The laser diode is driven based on the predetermined pixel clock. The exposure control PWM value is a value that specifies, for each pixel, the time for which the writing laser beam 13C is applied to the area for one pixel in one cycle of the pixel clock, and is set according to the density value in each pixel. It is a value. The exposure control PWM value of each pixel is generated by the multi-value dither method based on image information sent from an external device such as the scanner controller 110 or a PC (Personal Computer). The writing laser light 13C from the optical writing unit is optically scanned in the main scanning direction on the surface of the photoconductor drum 11C by dividing the image portion and the non-image portion based on the image information of the input image.

  The developing device 14C is a device for developing the C electrostatic latent image carried (formed) on the photosensitive drum 11C.

  The primary transfer roller 15C is a roller that primarily transfers the C toner image developed on the photosensitive drum 11C onto the intermediate transfer belt 16. The primary transfer rollers 15C, 15M, 15Y, and 15K sandwich the endlessly moving intermediate transfer belt 16 between the photosensitive drums 11C, 11M, 11Y, and 11K, respectively. As a result, primary transfer nips for C, M, Y, and K where the surface of the intermediate transfer belt 16 and the photoconductor drums 11C, 11M, 11Y, and 11K contact each other are formed. The primary transfer bias is applied to the primary transfer roller 15C by a primary transfer bias power source (not shown). As a result, a primary transfer electric field is formed between the C toner image on the photoconductor drum 11C and the primary transfer roller 15C. The Y toner image formed on the surface of the C photoconductor drum 11C enters the C primary transfer nip as the photoconductor drum 11C rotates. Then, by the action of the primary transfer electric field and the nip pressure, the primary transfer is performed from the photoconductor drum 11C onto the intermediate transfer belt 16. The toner images formed on the primary transfer rollers 15M, 15Y, and 15K are also primarily transferred to the intermediate transfer belt 16 in the same manner.

  The drum cleaning device 18C is a device that removes transfer residual toner adhering to the surface of the photosensitive drum 11C after the primary transfer process.

  The configuration of the M, Y, and K image forming units is similar to that of the C image forming unit as described above.

  The intermediate transfer belt 16 is an endless belt, and is stretched around a drive roller 17, a belt tension roller 19, a secondary transfer counter roller 21, a cleaning backup roller 27, primary transfer rollers 15C, 15M, 15Y, 15K and the like. ing. Then, the intermediate transfer belt 16 is endlessly moved by being rotationally driven by the driving roller 17, and the toner images formed on the photoconductor drums 11C, 11M, 11Y, and 11K are primarily transferred as described above. Specifically, after the toner image for Y is primarily transferred from the photoconductor drum 11Y, the toner image for Y is primarily transferred from the photoconductor drum 11Y by sequentially passing through the primary transfer nips for C, M, and K. The images are sequentially superposed on the image and primarily transferred. By this primary transfer of superposition, superposed toner images of four colors are formed on the intermediate transfer belt 16.

  The secondary transfer roller 20 is a roller that secondarily transfers (prints) the four-color superimposed toner images formed on the intermediate transfer belt 16 onto a print medium (paper or the like). The secondary transfer roller 20 is arranged in a direction outside the loop of the intermediate transfer belt 16 under pressure via the intermediate transfer belt 16, and is disposed between the secondary transfer roller 20 and the secondary transfer counter roller 21 inside the loop. 16 are sandwiched. As a result, the secondary transfer roller 20 rotates while contacting the intermediate transfer belt 16 or the print medium (paper or the like), and the secondary transfer nip where the surface of the primary transfer roller 15 and the secondary transfer counter roller 21 come into contact with each other is formed. It is formed. The secondary transfer roller 20 is grounded, while the secondary transfer opposing roller 21 is applied with a secondary transfer bias by a secondary transfer bias power source (not shown). As a result, a secondary transfer electric field that electrostatically moves negative polarity toner from the secondary transfer counter roller 21 side toward the secondary transfer roller 20 side between the secondary transfer roller 20 and the secondary transfer counter roller 21. Is formed.

  The registration roller pair 22 is a roller that feeds the print medium (paper or the like) conveyed from a paper feed cassette (not shown) to the above-mentioned secondary transfer nip. The paper feed cassette accommodates a plurality of paper sheets in the form of a stack of paper sheets. In this paper feed cassette, a paper feed roller (not shown) is brought into contact with the top paper of the paper bundle. By rotating the paper roller at a predetermined timing, the paper is sent out toward the transport path 25. The registration roller pair 22 is disposed near the end of the transport path 25, and immediately stops the rotation of both rollers when the sheet sent from the paper feed cassette is sandwiched between the rollers. Then, the registration roller pair 22 restarts the rotation drive at the timing of synchronizing the sandwiched paper with the superimposed toner images of four colors formed on the intermediate transfer belt 16 in the secondary transfer nip, and the paper is secondary-printed. Send it toward the transfer nip. The four-color superposed toner images on the intermediate transfer belt 16 that are brought into close contact with the paper at the secondary transfer nip are secondarily transferred onto the paper by the action of the secondary transfer electric field and the nip pressure, and the secondary transfer electric field. Combined with the white color of the paper, it becomes a full-color toner image. The sheet on which the full-color toner image is formed on the surface in this way is separated from the secondary transfer roller 20 and the intermediate transfer belt 16 by the curvature when passing through the secondary transfer nip.

  The fixing device 23 is disposed on the rear side of the secondary transfer nip in the sheet conveyance path, and heats and presses the full-color toner image secondary-transferred onto the sheet to soften the toner and thereby the full-color image. Is a device for fixing the paper on the paper. The fixing device 23 forms a fixing nip by a fixing roller that includes a heat source such as a halogen lamp and a pressure roller that rotates while contacting the fixing roller with a predetermined pressure. On the sheet conveyed into the fixing device 23, the toner in the full-color toner image is softened by the influence of heating and pressurization in the fixing nip, and the full-color image is fixed on the sheet. The sheet discharged from the fixing device 23 is discharged to the outside of the image forming apparatus 1.

  The belt cleaning device 28 is a device that removes and cleans the residual toner adhering to the intermediate transfer belt 16 that has passed through the secondary transfer nip.

(Hardware configuration of image forming apparatus)
FIG. 2 is a diagram illustrating an example of the hardware configuration of the image forming apparatus according to the embodiment. The hardware configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 2, the image forming apparatus 1 includes a printer controller 100, a scanner controller 110, a printer device 120 (printing unit), a scanner device 130 (reading unit), an input / output device 140, and an external I / O device. And F150. The above units are connected to each other via a bus 160 so that they can communicate with each other.

  The printer controller 100 is a controller that controls the printing operation of the printer device 120. The printer controller 100 includes a CPU (Central Processing Unit) 101, a ROM (Read Only Memory) 102, a RAM (Random Access Memory) 103, an I / F 104, and a storage device 105.

  The CPU 101 is an arithmetic device that controls the overall operation of the printer controller 100. The CPU 101 executes a program stored in the ROM 102, and uses the RAM 103 as a work area to control the overall operation of the printer controller 100.

  The I / F 104 is an interface for performing data communication with the scanner controller 110, the printer device 120, the scanner device 130, the input / output device 140, and the external I / F 150 via the bus 160. The I / F 104 performs, for example, transmission of a command for print control of the printer device 120, transfer of print data, read control of the scanner device 130 via the scanner controller 110, reception of read data, and the like. Used for. The I / F 104 is also used to control the display contents of the input / output device 140, receive input data, and the like.

  The storage device 105 is a device that stores control codes, font data, dither matrix data, which will be described later, and dither pattern information. The storage device 105 is configured by, for example, an HDD (Hard Disk Drive), an SSD (Solid State Drive), a flash memory, or the like.

  The scanner controller 110 is a controller that controls the reading operation by the scanner device 130. The scanner controller 110 includes a read data generation device 111, a color conversion device 112, an I / F 113, and a storage device 114.

  The read data generation device 111 is a digital image (TIFF (Tagged Image File Format), JPEG (Joint Photographic Experts Group), or the like) (read image) based on the colorimetric values of the RGB three primary colors read by the scanner device 130. Is a device for generating. The data of the read image generated by the read data generation device 111 is transmitted to an external device via the external I / F 150 or to the printer controller 100 via the I / F 113.

  The color conversion device 112 is a device that converts the values of the RGB light three primary colors read by the scanner device 130 into CMY color three primary colors, K color data, and the like. This processing is used when a read image is generated by the read data generating device 111, and is used for conversion of a read value of a gradation correction patch which will be described later.

  The I / F 113 is an interface for performing data communication with the printer controller 100, the printer device 120, the scanner device 130, the input / output device 140, and the external I / F 150 via the bus 160. The I / F 113 is used, for example, for transmitting a command for reading control of the scanner device 130, receiving read data, and the like. The I / F 113 is also used for controlling display contents of the input / output device 140, receiving input data, transmitting image data to an external device, transmitting device status, and the like.

  The storage device 114 is a device that stores the read image and the like generated by the read data generation device 111. The storage device 114 is composed of, for example, an HDD, SSD, flash memory, or the like.

  The printer device 120 is a device that performs a printing operation (image forming process) on a printing medium (paper or the like) according to a command from the printer controller 100. The printer device 120 includes a printing device 121 and an I / F 122.

  The printing device 121 is a device that performs print processing on a print medium based on print data transferred from an external device or the printer controller 100.

  The I / F 122 is an interface for performing data communication with the printer controller 100, the scanner controller 110, the scanner device 130, the input / output device 140, and the external I / F 150 via the bus 160. The I / F 122 is used to receive print data from an external device or the printer controller 100, for example.

  The scanner device 130 is a device that reads a print medium on which an image arranged on the scanner tray is printed, according to a command from the scanner controller 110. The scanner device 130 includes a reading device 131 and an I / F 132.

  The reading device 131 is a device that reads a print medium on which an image is printed and acquires the values of RGB three primary colors.

  The I / F 132 is an interface for performing data communication with the printer controller 100, the scanner controller 110, the printer device 120, the input / output device 140, and the external I / F 150 via the bus 160. The I / F 132 transmits read data read by the scanner device 130 to the scanner controller 110, for example.

  The input / output device 140 is a device for inputting / outputting data. The input / output device 140 includes an input device 141, an output device 142, and an I / F 143.

  The input device 141 is, for example, a device such as a numeric keypad or a dedicated key for a user to perform operation input and data input. The output device 142 is, for example, a display device such as an LCD (Liquid Crystal Display) or an organic EL (Electro-Luminescence) display. The input device 141 and the output device 142 may be realized by a touch panel display having both functions.

  The I / F 143 is an interface for performing data communication with the printer controller 100, the scanner controller 110, the printer device 120, the scanner device 130, and the external I / F 150 via the bus 160. The I / F 143 is used, for example, to transmit data input by the input device 141, receive display data to be displayed on the output device 142, and the like.

  The external I / F 150 is an interface for performing data communication with a device external to the image forming apparatus 1. The external I / F 150 receives print data from an external device and transfers the print data to the printer controller 100, for example.

  The hardware configuration of the image forming apparatus 1 shown in FIG. 2 is an example, and may include other components.

(Structure of functional block of image forming apparatus)
FIG. 3 is a diagram illustrating an example of a configuration of functional blocks of the image forming apparatus according to the embodiment. An example of functional blocks of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG.

  As shown in FIG. 3, the image forming apparatus 1 includes a pattern information acquisition unit 201 (information acquisition unit), a gradation number calculation unit 202, a patch size calculation unit 203 (size calculation unit), and a patch generation unit 204. A patch print control unit 205 (print control unit), a read control unit 206, a patch separation unit 207, a characteristic acquisition unit 208, a dot characteristic calculation unit 209, a gradation characteristic calculation unit 210, and a correction matrix generation unit. It has 211, the memory | storage part 212, the input part 213, and the communication part 214.

  The pattern information acquisition unit 201 is a functional unit that acquires dither pattern information (dither information) including the number of growth step gradations, the number of layer levels, the number of base matrices, the aggregate dither matrix (dither matrix), and the dither size, which will be described later. is there. The pattern information acquisition unit 201 acquires, for example, the dither pattern information stored in the storage unit 212, or acquires the dither pattern information from outside via the communication unit 214. Note that the dither pattern information (dither information) does not necessarily include all of the above information, and for example, the aggregated dither matrix (dither matrix) may be acquired as information different from the dither pattern information. .

  Here, the above-mentioned base matrix and the number of hierarchical levels will be described with reference to FIG. FIG. 4 is a diagram illustrating the base matrix.

  The areas indicated by different hatching in FIG. 4 are dots for pseudo-expressing the density of the density when the printer device 120 prints on a print medium (hereinafter, simply described as paper). It is a unit area that constitutes the dither pattern that is the source of generation, and is referred to as a base matrix. The numbers described in the dots forming each base matrix shown in FIG. 4 indicate the growth order indicating the order in which the gradation of dots is changed when the density of the entire base matrix is increased. In the example shown in FIG. 4, since each base matrix is composed of 32 dots, 0 to 31 are assigned as the growth order. Further, as shown in FIG. 4, the growth order of each dot forming each pace matrix is common. That is, the dot number of a specific position in a specific base matrix and the dot number of the same position in a different base matrix are the same. In order to change the gradation of dots, for example, by expressing the exposure amount of 1 dot by 1 bit, 2 bits, or 4 bits, it is possible to express the density of dots by changing the exposure amount stepwise. Becomes Then, each level of this light and shade (exposure amount) is called a hierarchy level, and the number of hierarchy levels that can be represented by each dot is called a hierarchy level number. For example, it is possible to express light and shade with a hierarchy level number of 1 step for 1 bit, 3 steps at maximum for 2 bits, and 15 steps at maximum for 4 bits. Further, for example, when the number of hierarchy levels is 3 (that is, 2 bits), the number of gradations of the density that can be expressed by one base matrix shown in FIG. 4 is (the number of dots in the base matrix) × (the number of hierarchy levels). = 32 × 3 = 96 [gradation].

  Next, the above-mentioned aggregated dither matrix and dither size will be described with reference to FIGS. FIG. 5 is a diagram showing an example of the aggregated dither matrix. FIG. 6 is a diagram showing an example of base matrix rank information indicating the growth order of the pace matrix.

  As shown in FIG. 5, an aggregated dither matrix is one in which the base matrix shown in FIG. 4 is periodically arranged. In the example shown in FIG. 5, an aggregated dither matrix 501 including 32 base matrices is shown. Using this aggregate dither matrix as a unit, gradations of light and shade are switched and expressed step by step. The size of this aggregate dither matrix will be referred to as the dither size.

  Further, the above-mentioned growth order is not only for dots but also for each base matrix as shown in FIG. The information on the growth rank assigned to each base matrix in the aggregate dither matrix is referred to as base matrix rank information. The base matrix rank information 502 shown in FIG. 6 is base matrix rank information corresponding to the aggregate dither matrix 501 shown in FIG. Since the aggregate dither matrix 501 shown in FIG. 5 is composed of 32 base matrices, 0 to 31 are assigned as the growth order of the base matrix as shown in FIG.

  The above-described aggregated dither matrix 501 shown in FIG. 5 includes 32 base matrices capable of 96-density density expression. The number of possible density gradations × (the number of base matrices) = 96 × 32 = 3072 [gradation]. The base matrix rank information described above may be included in the information of the aggregated dither matrix, or may be managed as information different from the aggregated dither matrix.

  Next, the above-mentioned growth step gradation will be described with reference to FIG. FIG. 7 is a diagram illustrating the growth step gradation.

  In FIG. 7, the number of hierarchical levels is set to 3 (that is, 2 bits), and the above-mentioned aggregated dither matrix 501 in which 32 base matrices are periodically arranged is used to uniformly grow all the base matrices. The state of concentration is shown. Actually, the growth order is also assigned to each base matrix as described above, but FIG. 7 shows the gradation when dots at the same position are uniformly grown in all the base matrices. The gradation in this case is referred to as a growth step gradation. That is, the growth of one dot in each growth step gradation is the same. The number of growth step gradations (the number of steps) is the same as the number of gradations of the density that can be expressed by the base matrix, and is 96 steps. That is, FIG. 7 shows the state of each growth step gradation of 1 to 96 steps.

  Here, regarding the density characteristic due to the change of the gradation, when the exposure amount for the same dot is changed like 1 step, 2 steps, 3 steps, the exposure amount varies depending on the hierarchical level, and so on. White) → 1 step, 1 step → 2 steps, 2 steps → 3 steps may have different growth characteristics. Further, as in the case of 2 steps, 5 steps, ..., 89 steps, 92 steps, 95 steps, even in the growth of the same hierarchical level, the influence of the charging of the surrounding dots due to the difference in the way the surrounding dots are filled, and In some cases, the growth characteristics may be different in each growth step gradation due to the influence of toner crushing of adjacent dots.

  Here, the density characteristic of each growth step gradation when the aggregated dither matrix is used will be described. FIG. 8 is a diagram showing an example of a dither density characteristic graph. The dither density characteristic graph is a graph of density when colorimetry is performed at each growth step gradation when the aggregated dither matrix is used. In the graph shown in FIG. 8, the horizontal axis represents each growth step gradation (step) and the vertical axis represents the density. Of these, FIG. 8A shows a graph of the density from 0 step (white paper) to 96 steps, and FIG. 8B is a graph in which the range of 0 step to 12 steps is enlarged. As shown in FIG. 8B, it can be seen that the density characteristics vary among the growth step gradations.

  In the conventional automatic gradation correction, the number of patches that can be printed on one sheet is limited. Therefore, for example, a gradation correction sheet in which gradation correction patches are arranged at intervals of 6 steps is used, and each patch is used. The density characteristics of the gradation between are determined by interpolation as shown by the broken line graph in FIG. However, in reality, as shown in FIG. 8B, since the density characteristics vary among the growth step gradations, the interpolated density characteristics may differ from the actual density characteristics. Therefore, the result of the automatic gradation correction may be affected, and the gradation may deteriorate. The details of the automatic gradation correction of this embodiment for eliminating the adverse effect on the gradation will be described later.

  Returning to FIG. 4, the description of the functional blocks of the image forming apparatus 1 will be continued.

  The gradation number calculation unit 202 is a functional unit that calculates the number of growth step gradations using the dither pattern information acquired by the pattern information acquisition unit 201. For example, when the number of growth step gradations is included in the dither pattern information, the gradation number calculation unit 202 may extract the number of growth step gradations from the dither pattern information. On the other hand, when the number of growth step gradations is not included in the dither pattern information and the number of dots in the pace matrix is included, the gradation number calculation unit 202 multiplies the number of dots in the base matrix by the number of hierarchical levels. Thus, the number of growth step gradations can be calculated. The number of growth step gradations calculated by the gradation number calculation unit 202 is the number of patches included in the gradation correction patch described later.

  The patch size calculation unit 203 determines the size of the patch corresponding to each growth step gradation from the size or printable range of the paper as the print medium and the number of growth step gradations calculated by the gradation number calculation unit 202. Is a functional unit that calculates

  The patch generation unit 204 generates a patch having the density of each growth step gradation by the size of the patch of each growth step gradation calculated by the patch size calculation unit 203, and connects the generated patches for gradation correction. It is a functional unit that generates patch print data.

  The patch print control unit 205 is a functional unit that causes the printer apparatus 120 to print on paper based on the print data of the gradation correction patch generated by the patch generation unit 204.

  Here, the above-mentioned growth step gradation patches and gradation correction patches will be described with reference to FIGS. 9 to 11. FIG. 9 is a diagram showing an example of a patch at each step for gradation correction. FIG. 10 is a diagram showing an example of the gradation correction patch. FIG. 11 is a diagram showing an example of a tone correction patch separated into two columns.

  Each patch 601 shown in FIG. 9 is an image of a patch in which the effective dots of each growth step gradation shown in FIG. 7 are reflected, and has the same size calculated by the patch size calculation unit 203. The patch generation unit 204 connects the patches 601 of the growth step gradations shown in FIG. 9 to generate a gradation correction patch 611 as shown in FIG. The print data of the gradation correction patch 611 is actually printed by the printer device 120. Further, as shown in FIG. 10, the patch generation unit 204 generates a dummy patch 612 adjacent to the dark side of the tone correction patch 611 and includes it in the print data. The dummy patch 612 is a patch of a size calculated by the patch size calculation unit 203, and is a dummy patch that is not a patch for acquiring the density. This dummy patch 612 has a size calculated by the patch size calculation unit 203 from the read image of the gradation correction patch 611 generated by the read control unit 206 described later, and a patch of each growth step gradation by the patch separation unit 207. Is used to detect the lower end of the tone correction patch 611 in order to separate. That is, as described later, the patch separation unit 207 first detects the separation start position of the gradation correction patch 611 by detecting the dummy patch 612 adjacent to the lower end of the gradation correction patch 611. The density of the dummy patch 612 may be 100%, for example.

  Further, when there are many growth step gradations and the size of each patch included in the gradation correction patch is smaller than the specified size, that is, the patch corresponding to each growth step gradation calculated by the patch size calculation unit 203. If the size is smaller than the specified size, the patch generation unit 204 separates the connected tone correction patches into two rows to generate tone correction patches 621a and 621b, as shown in FIG. You can In this case, the dummy patch 622a is generated adjacent to the dark side (lower end) of the tone correction patch 621a, and the dummy patch 622b is adjacent to the dark side (lower end) of the tone correction patch 621b. Just generate it.

  Returning to FIG. 4, the description of the functional blocks of the image forming apparatus 1 will be continued.

  The reading control unit 206 is a functional unit that causes the scanner device 130 to read the sheet of the gradation correction patch printed by the printer device 120 under the control of the patch printing control unit 205. The read control unit 206 is implemented by the scanner controller 110 shown in FIG. 2 (implemented by a program executed by the scanner controller 110).

  The patch separation unit 207 determines a dummy patch (for example, the dummy patch shown in FIG. 10) adjacent to the tone correction patch for the read image of the tone correction patch read by the scanner device 130 under the control of the reading control unit 206. 612), the separation start position is detected, and the patch is separated into each patch for each size calculated by the patch size calculation unit 203 from the position.

  Here, the patch separated by the patch separation unit 207 is ideally a patch corresponding to each growth step gradation, but it may not be accurately separated at the boundary of the patch of each growth step gradation. In consideration of the above, the operation of removing several pixels at both vertical and horizontal ends of each separated patch will be described with reference to FIG. FIG. 12 is a diagram showing an example of regions to be excluded in the patches of the separated growth step gradations.

  For example, assuming that the separation patch 631 shown in FIG. 12 is a patch separated by the patch separation unit 207, the patch separation unit 207 removes a region 631a of several pixels at both vertical and horizontal end portions of the separation patch 631. , And a new patch after separation. This makes it possible to acquire highly accurate characteristic values as a patch corresponding to each growth step gradation. Note that, as shown in FIG. 12, it is not limited to removing both vertical and horizontal end portions of the separation patch 631, and there is a possibility that the separation cannot be accurately separated at the boundary of the patch. Since is a boundary in the vertical direction, only some pixels at both ends in the vertical direction may be removed.

  The characteristic acquisition unit 208 is a functional unit that acquires the density as the characteristic value from the image of the patch corresponding to each growth step gradation separated by the patch separation unit 207. It should be noted that the characteristic value is not limited to the density, and may be, for example, the lightness or a unique digital value. Alternatively, when the value of the patch having the highest density is 100 and the value of the paper white patch is 0, the density or the ratio of lightness may be acquired as the characteristic value.

  The dot characteristic calculation unit 209 calculates a difference between the characteristic value of the patch of each growth step gradation and the characteristic value of the patch of the immediately preceding growth step gradation, and the difference is calculated as a base included in the aggregated dither matrix. It is a functional unit that calculates the growth characteristics of one dot at each growth step gradation by dividing by the number of matrices. Here, an example of the above-mentioned difference and the growth characteristics of one dot at each growth step gradation is shown in (Table 1) below.

  The characteristic value of the patch corresponding to each growth step gradation acquired by the characteristic acquisition unit 208 corresponds to the “growth step gradation characteristic value” in (Table 1). The difference between the characteristic value of the patch of each growth step gradation calculated by the dot characteristic calculation unit 209 and the characteristic value of the patch of the previous growth step gradation is “Growth step gradation growth” in (Table 1). Value. Then, the dot characteristic calculation unit 209 divides the difference by the number of base matrices included in the aggregated dither matrix (32 in the example of (Table 1)) to calculate the growth characteristic of one dot at each growth step gradation. Corresponds to the “growth step 1 dot characteristic value” in (Table 1).

  The gradation characteristic calculation unit 210 is a growth step gradation that satisfies a target value of a characteristic value (density, etc.) of each gradation to be corrected by the automatic gradation correction processing according to the present embodiment, and necessary for the growth step gradation. It is a functional unit that calculates the number of different dots. The target value of each gradation may be set in advance by the manufacturer of the image forming apparatus 1, for example. Hereinafter, the growth step gradation that satisfies the target value (exceeds the target value) and the required number of dots in the growth step gradation may be referred to as “gradation characteristics”. Here, the target values for the characteristic values (density, etc.) of each gradation to be corrected by the automatic gradation correction process, the above-mentioned gradation characteristics, and the values necessary for obtaining the gradation characteristics are summarized. , As shown in (Table 2) below.

  The “target value” in (Table 2) is a target value for the characteristic value (density etc.) of each gradation corrected by the automatic gradation correction processing according to the present embodiment. It is assumed that the number of gradations corrected by the automatic gradation correction processing according to the present embodiment is 256 (0 gradation to 255 gradations). Note that the number of gradations is not limited to 256 and may be other gradations.

  The “target value excess growth step gradation” in (Table 2) indicates a growth step gradation that satisfies the target value (exceeds the target value) in the gradation characteristics. In addition, the "growth step gradation characteristic value before target value excess" in (Table 2) indicates the characteristic value of the growth step gradation one before the "target value excess growth step gradation". For example, when the “target value excess growth step gradation” is 3 steps, the “growth step gradation characteristic value before target value excess” is a characteristic value in 2 steps which is the growth step gradation one before. It becomes "0.910".

  The “target value excess growth step 1 dot characteristic value” in (Table 2) indicates the “growth step 1 dot characteristic value” corresponding to the “target value excess growth step gradation”. For example, when the "target value excess growth step gradation" is 4 steps, the corresponding "growth step 1 dot characteristic value" is "0.000625" from (Table 1). 1 dot characteristic value ”.

  The "required number of dots in excess of target value overgrowth step" in (Table 2) means that the characteristic value of the corresponding gradation is "target" from the state of the growth step gradation immediately before the "over target value growth step gradation". The number of grown dots required to exceed the “value” is indicated, which corresponds to the required number of dots in the growth step gradation that satisfies the target value (exceeds the target value) among the gradation characteristics. The method of calculating the "target value excess growth step required dot number" will be described in detail later with reference to FIGS. 13 and 14.

  The “predicted characteristic value” in (Table 2) indicates the characteristic value of the target gradation predicted from the gradation characteristic calculated by the gradation characteristic calculation unit 210. The “difference between the expected characteristic value and the target value” in (Table 2) is the difference between the “estimated characteristic value” and the “target value”.

  The correction matrix generation unit 211 is a functional unit that generates a gradation correction dither matrix based on the gradation characteristics calculated by the gradation characteristic calculation unit 210 and the dither pattern information acquired by the pattern information acquisition unit 201. is there. The gradation correction dither matrix will be described in detail later with reference to FIG.

  The pattern information acquisition unit 201, the gradation number calculation unit 202, the patch size calculation unit 203, the patch generation unit 204, the patch print control unit 205, the patch separation unit 207, the characteristic acquisition unit 208, the dot characteristic calculation unit 209, and the gradation described above. The characteristic calculation unit 210 and the correction matrix generation unit 211 are realized, for example, by a program executed by the CPU 101 of the printer controller 100 shown in FIG. The pattern information acquisition unit 201, the gradation number calculation unit 202, the patch size calculation unit 203, the patch generation unit 204, the patch print control unit 205, the patch separation unit 207, the characteristic acquisition unit 208, the dot characteristic calculation unit 209, and the gradation. Part or all of the characteristic calculation unit 210 and the correction matrix generation unit 211 may be realized by a hardware circuit such as an FPGA (Field-Programmable Gate Array) or an ASIC (Application Specific Integrated Circuit) instead of a program that is software. Good.

  The storage unit 212 stores the dither pattern information, the read image obtained by the read control unit 206, the calculation results of the dot characteristic calculation unit 209 and the gradation characteristic calculation unit 210 (growth characteristic of one dot, gradation characteristic, etc.), and It is a functional unit that stores print data and the like of the gradation correction patch generated by the patch generation unit 204. The storage unit 212 is realized by the storage device 105 of the printer controller 100 shown in FIG.

  The input unit 213 is, for example, a functional unit such as a numeric keypad or a dedicated key that receives a user's operation input and data input. The input unit 213 is realized by the input device 141 of the input / output device 140 shown in FIG.

  The communication unit 214 is a functional unit that performs data communication with an external device. The communication unit 214 may receive the above-mentioned dither pattern information from an external device and send it to the pattern information acquisition unit 201, for example. The communication unit 214 is realized by the external I / F 150 shown in FIG.

  It should be noted that each functional unit shown in FIG. 3 conceptually shows a function and is not limited to such a configuration. For example, a plurality of functional units illustrated as independent functional units in FIG. 3 may be configured as one functional unit. On the other hand, the function of one functional unit in FIG. 3 may be divided into a plurality of functions and configured as a plurality of functional units.

(Flow of automatic gradation correction processing of the image forming apparatus)
FIG. 13 is an example of a flowchart showing an example of the flow of automatic gradation correction processing of the image forming apparatus according to the embodiment. FIG. 14 is a diagram showing an example of a growth step gradation that exceeds a target value and a required number of dots in the growth step gradation. The flow of automatic gradation correction processing of the image forming apparatus 1 according to this embodiment will be described with reference to FIGS. 13 and 14.

<Step S11>
The pattern information acquisition unit 201 acquires dither pattern information including the number of growth step gradations, the number of hierarchical levels, the number of base matrices, the aggregate dither matrix, the dither size, and the like. Then, the process proceeds to step S12.

<Step S12>
The gradation number calculation unit 202 calculates the number of growth step gradations using the dither pattern information acquired by the pattern information acquisition unit 201. The number of growth step gradations calculated by the gradation number calculation unit 202 is the number of patches included in the gradation correction patch. Then, the process proceeds to step S13.

<Step S13>
The patch size calculation unit 203 determines the size of the patch corresponding to each growth step gradation from the size or printable range of the paper as the print medium and the number of growth step gradations calculated by the gradation number calculation unit 202. To calculate. Then, the process proceeds to step S14.

<Step S14>
The patch generation unit 204 generates a patch having a density of each growth step gradation by the size of the patch of each growth step gradation calculated by the patch size calculation unit 203, and connects the generated patches for gradation correction. Generate print data for the patch. In addition, the patch generation unit 204 generates a dummy patch used to separate the patch of each growth step gradation from the gradation correction patch, and includes it in the print data. Then, the process proceeds to step S15.

<Step S15>
The patch print control unit 205 causes the printer device 120 to print on a sheet based on the print data of the gradation correction patch generated by the patch generation unit 204. Then, the process proceeds to step S16.

<Step S16>
The reading control unit 206 reads the sheet of the gradation correction patch printed by the printer device 120 by the scanner device 130 under the control of the patch printing control unit 205, and obtains the read image of the gradation correction patch. Then, the process proceeds to step S17.

<Step S17>
The patch separation unit 207 detects the dummy patch adjacent to the gradation correction patch in the read image of the gradation correction patch read by the scanner device 130 based on the control of the reading control unit 206, thereby detecting the separation start position. Is detected, and each patch is separated from the position by the size calculated by the patch size calculation unit 203. The patches separated by the patch separation unit 207 are patches corresponding to each growth step gradation. Further, the patch separation unit 207 removes the regions of several pixels at both vertical and horizontal end portions of each separated patch to obtain a new separated patch. Then, the process proceeds to step S18.

<Step S18>
The characteristic acquiring unit 208 acquires the density as the characteristic value from the image of the patch corresponding to each growth step gradation separated by the patch separating unit 207. The characteristic value is not limited to the density. For example, it may be brightness or a unique digital value or the like. Alternatively, the ratio of the density or the brightness when the value of the patch with the highest density is 100 and the value of the patch of paper white is 0 may be acquired as the characteristic value. Then, the process proceeds to step S19.

<Step S19>
The dot characteristic calculation unit 209 calculates a difference between the characteristic value of the patch of each growth step gradation and the characteristic value of the patch of the immediately preceding growth step gradation, and the difference is calculated as a base included in the aggregated dither matrix. By dividing by the number of matrices, the growth characteristic of one dot at each growth step gradation is calculated. Then, the process proceeds to step S20.

<Step S20>
The gradation characteristic calculation unit 210 satisfies a target value (exceeds the target value) as a gradation characteristic for a characteristic value (density or the like) of each gradation to be corrected by the automatic gradation correction processing according to the present embodiment. The gradation and the required number of dots in the growth step gradation are calculated. This calculation operation will be specifically described with reference to FIG.

  For example, of the 0 to 255 gradations shown in (Table 2) above, 10 gradations will be described as an example. Since the target value of 10 gradations is “0.108000”, the gradation characteristic calculation unit 210 has four growth step gradations that exceed the target value, as shown in (Table 1), and its characteristics. It specifies that the value is "0.1200". Then, the gradation characteristic calculation unit 210 pays attention to 3 steps which is one step before 4 steps, and the characteristic value of the step is “0.1000” as shown in (Table 1). Specify. Further, the growth characteristic of 1 dot in the growth step gradation of 4 steps is calculated as “0.000625” by the dot characteristic calculation unit 209. Here, FIG. 14A shows an image (an image corresponding to the size of the aggregated dither matrix) showing a grayscale expression when the growth step gradation is 3 steps.

  Next, the gradation characteristic calculation unit 210 uses the characteristic value of “0.1000” in three steps (indicated as “0.100000” in (Table 2)) and “0. "000625" is added. Here, FIG. 14B shows an image showing a grayscale expression in a state where the growth characteristic of 1 dot for 12 dots in 4 steps is added to the characteristic value “0.1000” in 3 steps. In this state, the predicted characteristic value (indicated as “predicted value” in FIG. 14B) is 0.1000 + 0000625 × 12 = 0.107500, so that the target value “0.108000” for 10 gradations is obtained. Not achieved.

  Then, the growth characteristic of 1 dot is added to the state of FIG. 14 (b) to FIG. 14 (c), that is, the characteristic value “0.1000” of 3 steps corresponds to 1 dot of 13 dots in 4 steps. The image which showed the gradation expression of the state which added the growth characteristic is shown. In this state, the gradation characteristic calculation unit 210 calculates the expected characteristic value as 0.1000 + 0000625 × 13 = 0.108125, and detects that the target value “0.108000” for 10 gradations is exceeded. Then, the gradation characteristic calculation unit 210 sets the four gradations, which are the growth step gradations that exceed the target value in the ten gradations, and the 13 dots as the required number of dots in the four steps, to the gradations in the ten gradations. Calculate as a characteristic.

  The gradation characteristic calculation unit 210 stores the gradation characteristic calculated for each gradation in the storage unit 212. It should be noted that the growth step gradation that exceeds the target value is defined as the growth step gradation that satisfies the target value of the characteristic value of each gradation to be corrected included in the gradation characteristics, but the invention is not limited to this. The growth step gradation immediately before the target value is exceeded may be used. Then, the process proceeds to step S21.

  Note that, as shown in FIG. 14C, the number of dots when the predicted characteristic value exceeds the target value is set as the required number of dots in the growth step gradation that exceeds the target value, but is not limited to this. However, the number of dots immediately before the expected characteristic value exceeds the target value may be used, or the difference between the expected characteristic value and the target value when the expected characteristic value is exceeded, and the expected characteristic value and the target value immediately before they are exceeded. The number of dots corresponding to the smaller one of the differences may be set.

<Step S21>
The correction matrix generation unit 211, based on the gradation characteristic calculated by the gradation characteristic calculation unit 210, the aggregate dither matrix and the base matrix rank information included in the dither pattern information acquired by the pattern information acquisition unit 201, the gradation Generate a corrected dither matrix.

  As a specific configuration of the gradation correction dither matrix, for example, a configuration similar to that of the aggregated dither matrix 501 shown in FIG. 5 is used. Have vector values. For example, when the number of hierarchical levels is 3, each dot of the matrix includes a vector value having three components of a first component, a second component and a third component. The first component corresponds to the first hierarchical level, the second component corresponds to the second hierarchical level, and the third component corresponds to the third hierarchical level. Then, in accordance with the growth order of the dots indicated by the aggregated dither matrix 501 and the growth order of the base matrix indicated by the base matrix order information 502, the gradation is increased by one for each correction gradation shown in (Table 2) above. In this case, in order to indicate which dot grows to which stage, the increased gradation number is stored in the corresponding component of the vector value of the corresponding dot. For example, in the example of (Table 2), in the case of one gradation, the “target value excess growth step gradation” is 1 and the “target value excess growth step required dot number” is 27, so the base matrix rank information The gradation number "1" is stored in the first component of the vector value corresponding to the dot growth order 0 in each base matrix corresponding to the base matrix growth order 0 to 26 in 502.

  Next, when there are two gradations, which is one gradation higher than one gradation, the “target value excess growth step gradation” is 2 and the “target value excess growth step required dot number” is 13. Therefore, in each base matrix corresponding to the growth order of the base matrix in the base matrix order information 502 of 27 to 31, the first component of the vector value corresponding to the dot growth order of 0 is the gradation number "2". Is stored. Further, the second component of the vector value corresponding to the dot growth order 0 in each of the base matrices corresponding to the base matrix growth order 0 to 13 in the base matrix order information 502 is also the gradation number. 2 ”is stored.

  Further, for example, when the gradation increases from 20 gradations by 1 to 21 gradations, the "target value excess growth step gradation" at 20 gradations is 5, and "target value excess growth step required dots" Since the "number" is 27, the "target value excess growth step gradation" at 21 gradations is 6, and the "target value excess growth step required dot number" is 5, the gradation number is as follows. To store. The fact that the “target value excess growth step gradation” is 5 means that the dot having the dot growth rank of 1 is in the growth stage from the second stage to the third stage. Therefore, the gradation number is “21” in the second component of the vector value corresponding to the dot growth rank of 1 in each base matrix corresponding to the base matrix growth rank of 27 to 31 in the base matrix rank information 502. Is stored. Furthermore, in each base matrix corresponding to the base matrix growth ranks 0 to 4 in the base matrix rank information 502, the third component of the vector value corresponding to the dot growth rank 1 is the gradation number “21”. Is stored. As described above, by storing any one of the gradation numbers (0 to 255) in each component of the vector value corresponding to each dot of the gradation correction dither matrix, the gradation correction dither matrix becomes Is generated.

  When performing gradation correction using the gradation correction dither matrix, when performing density expression at a specific gradation, among the components of the vector value that each dot has, the components that are below the gradation of the characteristic It may be expressed by the density of the hierarchical level indicated by the maximum component of. For example, when the vector value of a specific dot is (1, 3, 5), when expressing the density of 4 gradations, the maximum component of 3 which is the component of 4 or less is 3 It is sufficient to express the density of the specific dot with the density of the second stage which is the hierarchical level corresponding to. Further, when expressing the density of 210 gradations, the specific dot is represented by the density of the third stage which is the hierarchical level corresponding to the maximum component 5 of the components 1, 3 and 5 of 210 or less. The density expression may be expressed.

  Note that the configuration of the tone correction dither matrix as described above is an example, and any configuration may be used as long as the density can be expressed with the same purpose.

  After that, the printer controller 100 performs gradation correction on the print data using the gradation correction dither matrix, and then causes the printer device 120 to perform the printing process. By the gradation correction using this gradation correction dither matrix, the gradation expression of printing is normalized by a predetermined gradation number (256 gradation numbers in the above example) and corrected. For example, when normalizing the number of gradations to 256, it is desirable that the number of gradations of the density that can be expressed as the entire aggregated dither matrix is 512 or more.

  The automatic gradation correction processing of the image forming apparatus 1 is performed through the flow of steps S11 to S21 described above.

  As described above, the image forming apparatus 1 according to the present embodiment generates and prints the tone correction patch in which the patches of the density of each growth step tone are connected, and prints the tone correction patch. The image of the gradation correction patch is read and separated into patches corresponding to each growth step gradation. Then, the image forming apparatus 1 obtains the characteristic value of the separated patch of each growth step gradation and divides it by the number of pace matrices to calculate the growth characteristic of one dot at each growth step gradation. Then, the image forming apparatus 1 calculates the growth step gradation that approximates the target value of each gradation to be corrected, and the required number of dots in the growth step gradation, and based on these, creates the gradation correction dither matrix. It is supposed to be generated. Thereby, when expressing with a specific density, gradation correction can be performed by adjusting the number of dots to be grown from the corresponding growth step gradation within a limited exposure amount (hierarchical level) range. .. By this gradation correction, smooth gradation can be maintained, and since each gradation is distinguished by gradation characteristics, the number of gradations after correction can be maintained. In addition, it is possible to reduce the cost in terms of hardware, as compared with the case where the gradation is changed only by adjusting the exposure amount.

  In the above-described embodiment, when at least one of the functional units of the image forming apparatus 1 (printer controller 100) is realized by executing a program, the program is provided in advance in a ROM or the like. Further, the program executed by the image forming apparatus 1 (printer controller 100) according to the above-described embodiment is a file in an installable format or an executable format, which is a CD-ROM (Compact Disc Read Only Memory) or a flexible disk ( It may be configured to be recorded and provided on a computer-readable recording medium such as an FD), a CD-R (Compact Disk-Recordable), or a DVD (Digital Versatile Disc). Further, the program executed by the image forming apparatus 1 (printer controller 100) according to the above-described embodiment is stored in a computer connected to a network such as the Internet and is provided by being downloaded via the network. You may. The program executed by the image forming apparatus 1 (printer controller 100) according to the above-described embodiment may be provided or distributed via a network such as the Internet. Further, the program executed by the image forming apparatus 1 (printer controller 100) of the above-described embodiment has a module configuration including at least one of the above-described functional units, and the actual hardware is a CPU ( The CPU 101) reads the program from the above-mentioned storage device (ROM 102 or the like) and executes the program, so that the above-mentioned functional units are loaded onto the main storage device (RAM 103 or the like) and generated.

1 image forming apparatus 11C, 11M, 11Y, 11K photoconductor drum 12C charging roller 13C writing laser light 14C developing device 15C, 15M, 15Y, 15K primary transfer roller 16 intermediate transfer belt 17 drive roller 18C drum cleaning device 19 belt tension roller 20 Secondary transfer roller 21 Secondary transfer counter roller 22 Registration roller pair 23 Fixing device 25 Conveying path 27 Cleaning backup roller 28 Belt cleaning device 100 Printer controller 101 CPU
102 ROM
103 RAM
104 I / F
105 Storage Device 110 Scanner Controller 111 Read Data Generation Device 112 Color Conversion Device 113 I / F
114 storage device 120 printer device 121 printing device 122 I / F
130 Scanner Device 131 Reading Device 132 I / F
140 input / output device 141 input device 142 output device 143 I / F
150 External I / F
160 bus 201 pattern information acquisition unit 202 gradation number calculation unit 203 patch size calculation unit 204 patch generation unit 205 patch print control unit 206 read control unit 207 patch separation unit 208 characteristic acquisition unit 209 dot characteristic calculation unit 210 gradation characteristic calculation unit 210 211 correction matrix generation unit 212 storage unit 213 input unit 214 communication unit 501 aggregated dither matrix 502 base matrix rank information 601 patch 611 gradation correction patch 612 dummy patches 621a, 621b gradation correction patch 622a, 622b dummy patch 631 separation patch 631a area

JP, 2013-240952, A

Claims (10)

An information acquisition unit that acquires a dither matrix and dither information,
A patch generation unit that generates a tone correction patch in which patches of each growth step tone are connected based on the dither matrix and the dither information acquired by the information acquisition unit;
A print control unit that causes the print unit to print the gradation correction patch on a print medium;
A patch separation unit that separates the gradation correction patch printed on the print medium from the image read by the reading unit into patches corresponding to the growth step gradations,
A characteristic value acquisition unit that acquires the characteristic value of each patch separated by the patch separation unit,
Based on the difference between the characteristic value of the patch at each growth step gradation and the characteristic value of the patch at the growth step gradation immediately before the respective growth step gradation, 1 A dot characteristic calculation unit that calculates dot growth characteristics,
Based on the growth characteristics of one dot in each growth step gradation, the growth step gradation that approximates the target value of each gradation and the gradation characteristic calculation that calculates the number of necessary growth dots in the growth step gradation Department,
A correction matrix generation unit that generates a gradation correction dither matrix for performing gradation correction based on the calculation result of the gradation characteristic calculation unit;
An image forming apparatus equipped with. The information acquisition unit acquires the dither matrix indicating the growth order of dots for each base matrix, and the dither information including at least information indicating the number of hierarchical levels in dots,
The patch generation unit generates, based on the dither matrix and the dither information, the patch for each of the growth step gradations, which is the gradation in which dots at the same position in each of the base matrices uniformly grow, The image forming apparatus according to claim 1, wherein the gradation correction patch is generated by connecting patches. A gradation number calculation unit that calculates the number of the growth step gradations based on the dither information;
A printable range of the print medium, and a size calculation unit that calculates the size of the patch from the number of the growth step gradations calculated by the gradation number calculation unit;
Further equipped with,
The image forming apparatus according to claim 1, wherein the patch generation unit generates the patches for each of the growth step gradations so as to have a size calculated by the size calculation unit. The patch generation unit generates, together with the gradation correction patch, a dummy patch having the same size as the patch and adjacent to the gradation correction patch,
The print control unit causes the print unit to print the gradation correction patch and the dummy patch on a print medium,
The patch separation unit detects a separation start position by detecting the dummy patch in the image in which the gradation correction patch printed on the print medium is read by the reading unit, and from the separation start position, The image forming apparatus according to claim 1, wherein the image is separated into the patches corresponding to the growth step gradations.   The image forming apparatus according to claim 1, wherein the patch separating unit removes at least a portion near a boundary of another patch from the separated patch.   The print control unit performs gradation correction on print data using the gradation correction dither matrix generated by the correction matrix generation unit, and causes the print unit to print the print data. The image forming apparatus according to item 1.   The image forming apparatus according to claim 1, wherein the characteristic value is a density or a lightness of the patch corresponding to each of the growth step gradations.   The image forming apparatus according to claim 1, wherein the characteristic value is a density ratio or a lightness ratio of the patch corresponding to each of the growth step gradations. An information acquisition step of acquiring a dither matrix and dither information,
A patch generation step for generating a tone correction patch in which patches of each growth step tone are connected based on the obtained dither matrix and the dither information;
A print control step of causing the print section to print the gradation correction patch on a print medium;
A patch separation step of separating the gradation correction patch printed on the print medium from the image read by the reading unit into patches corresponding to the growth step gradations;
A characteristic value acquisition step of acquiring the characteristic value of each of the separated patches,
Based on the difference between the characteristic value of the patch at each growth step gradation and the characteristic value of the patch at the growth step gradation immediately before the respective growth step gradation, 1 A dot characteristic calculation step for calculating dot growth characteristics,
Based on the growth characteristics of one dot in each growth step gradation, the growth step gradation that approximates the target value of each gradation and the gradation characteristic calculation that calculates the number of necessary growth dots in the growth step gradation Steps,
A correction matrix generating step of generating a gradation correction dither matrix for performing gradation correction based on the calculation result of the gradation characteristic calculating step;
A gradation correction method having. An information acquisition step of acquiring a dither matrix and dither information,
A patch generation step for generating a tone correction patch in which patches of each growth step tone are connected based on the obtained dither matrix and the dither information;
A print control step of causing the print section to print the gradation correction patch on a print medium;
A patch separation step of separating the gradation correction patch printed on the print medium from the image read by the reading unit into patches corresponding to the growth step gradations;
A characteristic value acquisition step of acquiring the characteristic value of each of the separated patches,
Based on the difference between the characteristic value of the patch at each growth step gradation and the characteristic value of the patch at the growth step gradation immediately before the respective growth step gradation, 1 A dot characteristic calculation step for calculating dot growth characteristics,
Based on the growth characteristics of one dot in each growth step gradation, the growth step gradation that approximates the target value of each gradation and the gradation characteristic calculation that calculates the number of necessary growth dots in the growth step gradation Steps,
A correction matrix generation step of generating a gradation correction dither matrix for performing gradation correction based on the calculation result of the gradation characteristic calculation step;
A program that causes a computer to execute.