JP2017123605A - Image formation device, tone correction method, and tone correction program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To maintain the output characteristics in good state.SOLUTION: An image formation device includes print means for printing a reference screen patch Ps and a correction object screen patch Pc to which a predetermined screen is applied, measurement means for measuring the densities of the reference screen patch Ps and correction object screen patch Pc, prediction means for calculating the prediction density of the correction object screen patch Pc, based on the measurement density of the reference screen patch Ps, evaluation means for determining whether or not the prediction accuracy of the prediction means is sufficient, based on the measurement density of the correction object screen patch Pc, and the prediction accuracy of the correction object screen patch Pc, and correction means for setting a correction value of gamma correction, according to the determination results of the evaluation means.SELECTED DRAWING: Figure 4

Description

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

  In an image forming apparatus such as a copying machine, a facsimile machine, a printer, or a complex machine thereof, it is widely known that image output is performed after screen processing for reproducing halftones of input image data. In such an image forming apparatus, in order to improve the color reproducibility of the output image, the output characteristics are generally corrected by gamma correction processing.

  The gamma correction processing is performed using a gamma correction curve corresponding to the screen applied in the screen processing, and the LUT (Look Up Table) corresponding to each screen is prepared as a gamma correction table. By referring to this gamma correction table, the image forming apparatus can correct to a desired output characteristic according to the applied screen.

  However, the output characteristics of the image forming apparatus fluctuate due to environmental changes such as temperature and humidity at the place where the image forming apparatus is installed, and secular changes of the image forming apparatus itself. In order to suppress this fluctuation in output characteristics, a patch pattern to which a screen is applied is printed, its density is measured, and the measured value is compared with the target gradation value to correct it to the target output characteristic. It is known to generate a gamma correction table.

  In addition, since the variation in output characteristics varies depending on the screen to be applied, in an image forming apparatus having a plurality of screens having different screen shapes and screen line numbers, it is necessary to generate a gamma correction table for each screen. For this reason, in an image forming apparatus having a plurality of screens, it takes time to generate a gamma correction table.

  On the other hand, a fluctuation prediction formula for the output characteristics of each screen is created from the correlation between changes in the output characteristics of the reference screen (reference screen) and other screens (other screens) in advance. It is considered to calibrate multiple screens.

  For example, Patent Document 1 discloses gamma correction for a plurality of types of screens by predicting density fluctuation values of other screens from density fluctuation values of a reference screen using a fluctuation prediction formula constructed based on multiple regression analysis. It is disclosed to shorten the table update time.

  However, in the conventional method of calibrating the other screen by predicting the output characteristics of the other screen from the density of the reference screen, it has not been possible to confirm whether the output characteristics of the other screen can be correctly predicted.

  In other words, when the correlation between the output characteristics of the reference screen and the other screens changes and the density fluctuation value of the other screens cannot be predicted correctly, calibration with poor accuracy is performed.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of maintaining a good output characteristic by calibration even when the correlation between a reference screen and another screen changes.

  In order to achieve this object, an image forming apparatus according to the present invention is an image forming apparatus that corrects output characteristics by gamma correction, and prints a reference screen patch to which a predetermined screen is applied and a correction target screen patch. Measuring means for measuring the density of the reference screen patch and the correction target screen patch; prediction means for calculating a predicted density of the correction target screen patch based on the measured density of the reference screen patch; and the correction target Based on the measured density of the screen patch and the predicted density of the correction target screen patch, an evaluation unit that determines whether or not the prediction accuracy of the prediction unit is sufficient, and according to a determination result of the evaluation unit And a correction means for setting a correction value for gamma correction.

  According to the present invention, the output characteristics can be maintained in a good state.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus. 2 is a hardware configuration diagram of an image forming apparatus. FIG. It is a functional block diagram of a controller. It is explanatory drawing which shows an example of a density | concentration detection pattern. It is an example of the graph which shows the relationship between an input gradation value and an output gradation value. It is a flowchart which shows an example of a gradation correction process.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

  The image forming apparatus according to the present embodiment is an image forming apparatus (image forming apparatus 100) that corrects output characteristics by gamma correction, and includes a reference screen patch (reference screen patch Ps) to which a predetermined screen is applied and a correction target screen. Printing means for printing patches (correction target screen patch Pc) (density detection pattern creation section 110 and the like), measurement means for measuring the density of the reference screen patch and correction target screen patches (density detection section 112 and the like), and a reference screen Based on the prediction means (density variation prediction unit 113 and the like) for calculating the predicted density of the correction target screen patch based on the measured density of the patch, the measured density of the correction target screen patch, and the predicted density of the correction target screen patch. Evaluation means for judging whether or not the prediction accuracy of the prediction means is sufficient ( And measuring accuracy evaluating unit 117, etc.), depending on the judgment result of the evaluation means, and correcting means for setting a correction value of the gamma correction (such as the correction value determination section 118), but with a. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of a tandem type color copier that is an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG. In this embodiment, an electrophotographic color image forming apparatus will be described as an example. However, even if the image forming apparatus is an image forming apparatus that forms an image by another method such as an ink jet method, a monochrome image forming device is used. It may be.

  The image forming apparatus 100 includes a writing unit 2 that emits laser light based on input image information, a document transport unit 3 that transports a document to a document reading unit 4, a document reading unit 4 that reads image information of a document, and a sheet such as transfer paper , A registration roller 9 for adjusting the sheet conveyance timing, and photosensitive drums 11Y, 11M, 11C, on which toner images of respective colors (yellow Y, magenta M, cyan C, black K) are formed. 11K, a charging unit 12 that charges each of the photosensitive drums 11Y, 11M, 11C, and 11K, a developing unit 13 that develops an electrostatic latent image formed on each of the photosensitive drums 11Y, 11M, 11C, and 11K, and each photosensitive member A transfer bias roller (primary transfer bias roller) 14 for transferring the toner images formed on the body drums 11Y, 11M, 11C, and 11K on the paper, and each photosensitive drum 1; Y, and includes 11M, 11C, a cleaning unit 15 for collecting the untransferred toner on the 11K.

  Further, an intermediate transfer belt cleaning unit 16 for cleaning the intermediate transfer belt 17, an intermediate transfer belt 17 on which a plurality of color toner images are transferred in an overlapping manner, and a color toner image 2 on the intermediate transfer belt 17 are transferred onto a sheet. A next transfer bias roller 18 and a fixing device 10 for fixing the toner image on the paper are provided.

  Hereinafter, an operation at the time of normal color image formation in the image forming apparatus 100 will be described. First, the document is transported from the document table in the direction of the arrow in the drawing by the transport roller of the document transport unit 3 and placed on the contact glass 5 of the document reading unit 4. Then, the document reading unit 4 optically reads the image information of the document placed on the contact glass 5. Specifically, the document reading unit 4 scans an image of a document on the contact glass 5 while irradiating light emitted from an illumination lamp. Then, the light reflected from the original is imaged on the color sensor via the mirror group and the lens. The color image information of the original is read for each color separation light of RGB (red, green, blue) by the color sensor, and then converted into an electrical image signal. Further, color conversion processing, color correction processing, spatial frequency correction processing, and the like are performed by the image processing unit based on the RGB color separation image signals to obtain yellow, magenta, cyan, and black color image information.

  Then, the image information of each color of yellow, magenta, cyan, and black is transmitted to the writing unit 2. The writing unit 2 emits laser light (exposure light) based on the image information of each color toward the corresponding photosensitive drums 11Y, 11M, 11C, and 11K.

  On the other hand, the four photosensitive drums 11Y, 11M, 11C, and 11K rotate in the clockwise direction in FIG. First, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are uniformly charged at a portion facing the charging unit 12 (charging process). Thus, a charging potential is formed on the photoconductive drums 11Y, 11M, 11C, and 11K. Thereafter, the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K reach the irradiation positions of the respective laser beams.

  In the writing unit 2, laser light corresponding to the image signal is emitted from the four light sources corresponding to each color. Each laser beam passes through a different optical path for each color component of yellow, magenta, cyan, and black (exposure process).

  Laser light corresponding to the yellow component is irradiated on the surface of the first photosensitive drum 11Y from the left side of the drawing. At this time, the yellow component laser light is scanned in the rotation axis direction (main scanning direction) of the photosensitive drum 11Y by a polygon mirror that rotates at high speed. Thus, an electrostatic latent image corresponding to the yellow component is formed on the photosensitive drum 11Y charged by the charging unit 12.

  Similarly, the laser beam corresponding to the magenta component is irradiated onto the surface of the second photosensitive drum 11M from the left side of the paper, and an electrostatic latent image corresponding to the magenta component is formed. The cyan component laser light is applied to the surface of the third photosensitive drum 11C from the left side of the paper, and an electrostatic latent image of the cyan component is formed. The black component laser light is applied to the surface of the fourth photosensitive drum 11K from the left side of the paper, and an electrostatic latent image of the black component is formed.

  Thereafter, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K on which the electrostatic latent images of the respective colors are formed reach positions facing the developing unit 13, respectively. Then, the respective color toners are supplied from the developing units 13 onto the photosensitive drums 11Y, 11M, 11C, and 11K, and the latent images on the photosensitive drums 11Y, 11M, 11C, and 11K are developed (developing step).

  Thereafter, the surfaces of the photoconductive drums 11Y, 11M, 11C, and 11K after the development process reach the portions facing the intermediate transfer belt 17, respectively. Here, a transfer bias roller 14 is installed at each facing portion so as to contact the inner peripheral surface of the intermediate transfer belt 17. Then, the toner images of the respective colors formed on the photosensitive drums 11Y, 11M, 11C, and 11K are sequentially transferred and superimposed on the intermediate transfer belt 17 at the position of the transfer bias roller 14 (primary transfer process). .

  Then, the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K after the transfer process reach positions facing the cleaning unit 15, respectively. The untransferred toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11K is collected by the cleaning unit 15 (cleaning process).

  Thereafter, the surfaces of the photoconductor drums 11Y, 11M, 11C, and 11K pass through a static elimination unit (not shown), and a series of image forming processes on the photoconductor drums 11Y, 11M, 11C, and 11K is completed.

  On the other hand, the intermediate transfer belt 17 on which the toners of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11K are transferred (carrying) are run in the clockwise direction in the drawing and are connected to the secondary transfer bias roller 18. Reach the opposite position. Then, a color toner image carried on the intermediate transfer belt 17 is transferred onto the sheet at a position facing the secondary transfer bias roller 18 (secondary transfer step).

  Thereafter, the surface of the intermediate transfer belt 17 reaches the position of the intermediate transfer belt cleaning unit 16. Then, the untransferred toner adhered on the intermediate transfer belt 17 is collected by the intermediate transfer belt cleaning unit 16, and a series of transfer processes in the intermediate transfer belt 17 is completed.

  Here, the sheet conveyed between the intermediate transfer belt 17 and the secondary transfer bias roller 18 (secondary transfer nip) is conveyed from the sheet feeding unit 7 via the registration roller 9 and the like.

  Specifically, the paper fed by the paper feed roller 8 from the paper feed unit 7 that stores the paper is guided to the registration roller 9 after passing through the conveyance guide. The sheet that has reached the registration roller 9 is conveyed toward the secondary transfer nip in time.

  The sheet on which the full-color image is transferred is guided to the fixing device 10 by the conveyance belt. In the fixing device 10, a color image (toner) is fixed on a sheet at a nip between a fixing roller as a fixing member and a pressure roller as a pressure member.

  The paper after the fixing step is discharged as an output image by the paper discharge roller to the outside of the apparatus main body, and a series of image forming processes is completed.

  Next, the hardware configuration of the image forming apparatus 100 will be described with reference to FIG. As illustrated in FIG. 2, the image forming apparatus 100 includes a controller 20 as a control unit of the image forming apparatus 100, a printer engine 40 that outputs an original image, a scanner engine 50 that reads an original, and an input operation by a user. And an operation panel 60 as selection means for receiving.

  The controller 20 is a control unit that controls the operation of the image forming apparatus 100, and as shown in FIG. 2, a CPU (Central Processing Unit) 21, a ROM (Read Only Memory) 22, a RAM (Random Access Memory) 23, and an NVRAM (Non Volatile RAM) 24 and the like.

  The CPU 21 is a calculation means and controls the operation of each part of the controller 20. The ROM 22 is a read-only nonvolatile storage medium, and stores programs such as firmware. A plurality of ROMs 22 may be provided.

  The RAM 23 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 21 processes information. The NVRAM 24 is a non-volatile storage medium that can read and write information, and stores device-specific information such as a counter value of the number of copies, control parameters, and the like.

  The controller 20 also has a printer engine I / F 25 that is an interface with the printer engine 40, a scanner engine I / F 26 that is an interface with the scanner engine 50, and a panel I that is an interface with the operation panel 60. / F27 and a host I / F 28 for connecting the host PC 70 in a serial, parallel or network connection. Examples of the type of host I / F 28 include local connections such as IEEE1284 and USB, and network connections such as wired and wireless Ethernet (registered trademark). Note that the above-described units of the controller 20 are connected via an internal bus 30.

  FIG. 3 is a functional block diagram of the controller 20. The controller 20 includes a system control unit 101 that controls the entire image forming apparatus 100, a printer control unit 102 that controls the printer engine 40, a scanner control unit 103 that controls the scanner engine 50, and image processing that executes various types of image processing. A control unit 104 is provided.

  The image processing control unit 104 rasterizes the drawing data according to print control data such as PDL (Page Description Language) received from the host PC 70 and causes the printer engine 40 to output an image. Further, the controller 20 reads a program and setting information stored in a storage device such as the ROM 22 or the NVRAM 24 and expands it in a memory area of the RAM 23 that provides a work memory area of the CPU 21. Each process is realized by using as. In addition, the controller 20 performs predetermined image processing on the data captured by the scanner engine 50.

  The image processing control unit 104 also creates and updates the tone correction process and the gamma correction table necessary for the tone correction process. Further, it controls the calculation and storage of correction values based on the output, reading, and reading results of calibration density detection pattern images (hereinafter referred to as density detection patterns P) used in the creation and update of the gamma correction table.

  The output of the density detection pattern P is executed by the printer engine 40 under the control of the image processing control unit 104 and the printer control unit 102, and the reading of the density detection pattern P is performed under the control of the image processing control unit 104 and the scanner control unit 103. It is executed by the scanner engine 50.

(Tone correction processing)
Hereinafter, gradation correction processing (gamma correction processing) by the image forming apparatus 100 according to the present embodiment will be described. As shown in FIG. 3, the image processing control unit 104 includes a density detection pattern creation unit 110, an image storage unit 111, a density detection unit 112, a density variation prediction unit 113, a density difference calculation unit 114, a reference density holding unit 115, a density. A difference holding unit 116, a prediction accuracy evaluating unit 117, a correction value determining unit 118, a correction value holding unit 119, a previous correction value holding unit 120, and a correction value restoring unit 121 are provided.

  The density detection pattern creating unit 110 creates a density detection pattern P using a correction value stored as a result of the previous gradation correction process, and outputs the density detection pattern P from the printer engine 40. Control.

  FIG. 4 is an explanatory diagram illustrating an example of the density detection pattern P output from the image forming apparatus 100. The density detection pattern P shown in FIG. 4 includes at least a reference screen patch Ps for predicting the density of the other screen (correction target screen) and another screen patch for checking whether the density of the other screen can be predicted ( Correction target screen patch Pc).

  The reference screen patch Ps is a quantized image in which the density of each color of cyan C, magenta M, yellow Y, and black K is changed stepwise according to the number of gradations of the reference screen.

  The correction target screen patch Pc may be a patch having an arbitrary density for each color. For example, the correction target screen patch Pc has a density that greatly increases the difference in screen shape from the reference screen patch Ps, or the previous gradation correction process. It is preferable to use a density that sometimes has a large correction value (such as a density having a large difference between a target density (target density) described later and a predicted density).

  As an example of the reference screen patch Ps and the correction target screen patch Pc, for example, when the reference screen patch Ps is a halftone screen, and the density of a screen that changes from a halftone dot type to a parallel line type is predicted, the shape is Since the different line portions are more difficult to predict the density, it is possible to use the line portions as the correction target screen patch Pc.

  In the example of FIG. 4, a plurality of correction target screen patches Pc are illustrated for each color. However, any correction target screen patch Pc having at least one gradation for each color may be used. By evaluating the prediction accuracy for each of the plurality of correction target screen patches Pc, it is possible to realize an accurate gradation correction process. In addition, for a plurality of types of screens for each color, a representative correction target screen patch Pc having one or more gradations may be included.

  Returning to the description of FIG. The image storage unit 111 reads the density detection pattern P by the scanner engine 50 and stores it in the RAM 23.

  Based on the density detection pattern P read by the scanner engine 50, the density detection unit 112 acquires the density of the reference screen patch Ps and the correction target screen patch Pc of the density detection pattern P. The density acquired by the density detector 112 is referred to as measured density.

  The density fluctuation prediction unit 113 predicts the density of the other screen by a prediction formula for calculating the density of the other screen (correction target screen patch Pc) from the measured density of the reference screen patch Ps. The density of the correction target screen patch Pc predicted by the density fluctuation prediction unit 113 is referred to as a predicted density.

  As a method of constructing a prediction formula, the output characteristics of the reference screen and other screens are acquired in advance multiple times in advance, and the density of the other screens is predicted from the density of the reference screen using a technique such as multiple regression analysis or neural network. Any method for calculating an expression may be used. In addition, the construction method of a prediction formula is not restricted to this, You may construct | assemble a prediction formula based on the other well-known or new method.

  FIG. 5 is an example of a graph showing the relationship (output characteristics) between the input gradation value and the output gradation value. In FIG. 5, a represents an ideal relationship (a: target density) of the image forming apparatus 100. It is desirable that the input gradation value and the output gradation value have an ideal linear relationship as indicated by a, and a is an output characteristic that is an output target of the image forming apparatus 100.

  However, actually, the relationship is not ideal, and for example, output characteristics (b: detected density value) as shown in b are shown. The detected density value b is acquired by a method of predicting output characteristics by the above-described density fluctuation prediction unit 113, a method of acquiring density from the density detection pattern P, or the like.

  c and d are gamma correction tables for bringing the detected density value b closer to the target density a, and are shown as correction curves for canceling the distortion of the detected density value b. The gamma correction table c is an example of a feedback rate (also referred to as a correction rate) of 100%, and the gamma correction table d is an example of a feedback rate of 50%.

  When the image forming apparatus 100 is printed, by applying the gamma correction table, it is possible to print with a constant density value without depending on the output characteristics of the image forming apparatus 100.

  Here, when the detected density value b is the predicted density predicted by the density fluctuation prediction unit 113, a difference may occur between the actual output characteristics of the image forming apparatus 100 and the predicted density. For this reason, for example, by reducing the feedback rate of the detected density value b according to the predicted density (for example, from the gamma correction table c to the gamma correction table d), it is possible to avoid deterioration of output characteristics due to overcorrection. Details will be described later.

  Returning to the description of FIG. The reference density holding unit 115 is a storage unit that holds the target density a of the image forming apparatus 100. Then, the density difference calculation unit 114 calculates the difference between the measured density of the reference screen patch Ps and the target density a held in the reference density holding unit 115 and the correction target screen patch Pc predicted by the density fluctuation prediction unit 113. The difference between the predicted density and the target density a is calculated.

  The density difference holding unit 116 causes the NVRAM 24 to hold the value calculated by the density difference calculating unit 114. Further, the prediction accuracy evaluation unit 117 determines whether the prediction accuracy in the density fluctuation prediction unit 113 is sufficient based on the value held in the density difference holding unit 116 or the like. Further, the correction value determination unit 118 determines the correction value according to the determination result in the prediction accuracy evaluation unit 117.

  The correction value holding unit 119 stores and acquires correction values in the NVRAM 24. The previous correction value holding unit 120 stores and acquires a correction value (previous correction value) before execution of the gradation correction processing in the NVRAM 24.

  The correction value restoration unit 121 performs processing for restoring the current correction value stored in the NVRAM 24 to the previous correction value. As a result of executing the gradation correction process by updating the correction value, the previous correction value can be restored when a desired result cannot be obtained.

  FIG. 6 is a flowchart showing an example of gradation correction processing. With reference to FIG. 6, the tone correction processing executed by the image forming apparatus 100 will be described.

  First, a screen to be calibrated is selected (S101). The selection of the screen in S101 may be performed as long as it is made by a selection operation from the user operation panel 60, for example. In the selection of the screen to be calibrated (S101), when there are a plurality of correction target screens in addition to the reference screen, for example, when three or more types of screens are selected, the respective correction target screens are applied. A patch is printed, and a plurality of correction target screen patches Pc are printed as in the example of FIG. Then, the density detection pattern creation unit 110 generates a density detection pattern P as shown in FIG. 4, and the printer engine 40 prints this (S102).

  Next, the density detector 112 measures the densities of the reference screen patch Ps and the correction target screen patch Pc of the density detection pattern P read by the scanner engine 50 (S103). Further, the density fluctuation prediction unit 113 predicts the density of the correction target screen patch Pc based on the measured density of the reference screen patch Ps (S104).

  Next, the measured density of the correction target screen patch Pc measured by the density detection unit 112, the predicted density of the correction target screen patch Pc predicted by the density variation prediction unit 113, and the target held in the reference density holding unit 115 Based on the density, it is determined whether the prediction accuracy in the density fluctuation prediction unit 113 is sufficient and the prediction result is used for calibration (S105).

  The determination criterion in S105 is, for example, a determination criterion whether or not the difference between the target concentration and the measured concentration is larger than the difference between the predicted concentration and the measured concentration. Further, the target density may not be used, and the difference between the predicted density and the measured density, and whether or not the target density is smaller than a predetermined value set in advance may be used as a determination criterion.

  In S105, when the prediction accuracy is sufficient and the calibration is performed using the predicted density (S105: YES), the prediction is performed based on the measured density, the predicted density, and the target density of the correction target screen patch Pc. The density feedback rate is determined (S106).

The feedback rate of the predicted concentration can be calculated using, for example, the following equation (1).
(Target density-Measured density of correction target screen patch Pc) / (Target density-Predicted density) (1)

  Alternatively, the target density may not be used, and a feedback rate may be set as a table in advance according to the difference between the predicted density and the measured density of the correction target screen patch Pc, and the feedback rate may be switched based on the table.

  Next, the correction value determination unit 118 determines a correction value based on the predicted density calculated in S104 and the feedback rate calculated in S106 (S109).

  On the other hand, when the prediction accuracy is insufficient due to some factor such as an environmental change or a secular change (S105: NO), the density detection pattern creating unit 110 displays the density detection pattern P of the target screen. Is output (S107). The density detection pattern P at this time is a pattern of a portion corresponding to the reference screen patch Ps portion of the density detection pattern P shown in FIG.

  Next, the density detection unit 112 measures the density of the density detection pattern P created in S107 (S108).

  Next, the correction value determination unit 118 determines a correction value based on the measured density and feedback rate in S108 (S109). In this case, since it is the measured concentration, the feedback rate is 100%.

  The above processes are executed for the selected screen (S110: NO), and when the processes for all screens are completed (S110: YES), the process ends. Thereafter, gradation correction processing is executed using the determined correction value.

  According to the image forming apparatus according to the present embodiment described above, when generating or updating the gamma correction table in the gradation correction process, one or more gradations of patches to which the screen to be calibrated is applied are printed, and the reference screen Evaluate whether the density fluctuation value of the screen to be calibrated can be predicted from the density fluctuation value, and execute the process according to the evaluation result. Can be maintained.

  The control program including the gradation correction program executed by the image forming apparatus is provided by being recorded on a computer-readable recording medium as a file in an installable format or an executable format. . Further, the control program executed in the image processing apparatus may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

2 Writing section 3 Document transport section 4 Document reading section 5 Contact glass 7 Paper feed section 8 Paper feed roller 9 Registration roller 10 Fixing device 11Y, 11M, 11C, 11K Photosensitive drum 12 Charging section 13 Development section 14 Transfer bias roller (1 (Next transfer bias roller)
15 Cleaning unit 16 Intermediate transfer belt cleaning unit 17 Intermediate transfer belt 18 Secondary transfer bias roller 20 Controller 21 CPU
22 ROM
23 RAM
24 NVRAM
25 Printer Engine I / F
26 Scanner Engine I / F
27 Panel I / F
28 Host I / F
30 Internal bus 40 Printer engine 50 Scanner engine 60 Operation panel 70 Host PC
DESCRIPTION OF SYMBOLS 100 Image forming apparatus 101 System control part 102 Printer control part 103 Scanner control part 104 Image processing control part 110 Density detection pattern creation part 111 Image storage part 112 Density detection part 113 Density fluctuation prediction part 114 Density difference calculation part 115 Reference density holding part 116 Density difference holding unit 117 Prediction accuracy evaluating unit 118 Correction value determining unit 119 Correction value holding unit 120 Previous correction value holding unit 121 Correction value restoring unit

Japanese Patent No. 5746623

Claims (10)

An image forming apparatus that corrects output characteristics by gamma correction,
Printing means for printing a reference screen patch to which a predetermined screen is applied and a correction target screen patch;
Measuring means for measuring the density of the reference screen patch and the correction target screen patch;
Prediction means for calculating a predicted density of the correction target screen patch based on the measured density of the reference screen patch;
Evaluation means for determining whether or not the prediction accuracy of the prediction means is sufficient based on the measured density of the correction target screen patch and the predicted density of the correction target screen patch;
Correction means for setting a correction value of the gamma correction according to the determination result of the evaluation means;
An image forming apparatus comprising: If the evaluation means determines that the prediction accuracy is not sufficient,
The printing unit prints a patch to which the screen of the correction target screen patch is applied, and the measurement unit measures the density of the patch,
The image forming apparatus according to claim 1, wherein the correction unit sets the correction value based on the measurement result. When the evaluation means determines that the prediction accuracy is sufficient,
3. The correction unit according to claim 1, wherein the correction unit sets the correction value based on the measured density, the predicted density, and a preset target density of the correction target screen patch. The image forming apparatus described. When the evaluation means determines that the prediction accuracy is sufficient,
The correction means sets the correction value based on the measured density of the correction target screen patch, the predicted density, and a table that defines correction contents according to the relationship between the measured density and the predicted density. The image forming apparatus according to claim 1, wherein:   5. The image formation according to claim 1, wherein the printing unit prints the correction target screen patch on a screen having a large correction value in the previous correction by the correction unit. apparatus.   6. The image forming apparatus according to claim 1, wherein the correction unit can apply different correction values for each correction target screen.   The image forming apparatus according to claim 1, wherein the printing unit outputs the reference screen patch and the correction target screen patch as one detection pattern.   The image forming apparatus according to claim 1, further comprising a selection unit that selects a screen on which the correction target screen patch is printed. A gradation correction method for correcting output characteristics by gamma correction,
A printing step for printing a reference screen patch to which a predetermined screen is applied and a correction target screen patch;
A measuring step of measuring the density of the reference screen patch and the correction target screen patch;
A prediction step of calculating a predicted density of the correction target screen patch based on the measured density of the reference screen patch;
An evaluation step for determining whether or not the prediction accuracy in the prediction step is sufficient based on the measured density of the correction target screen patch and the predicted density of the correction target screen patch;
A correction step for setting a correction value for the gamma correction according to the determination result in the evaluation step;
A gradation correction method comprising: A tone correction program for correcting output characteristics by gamma correction,
On the computer,
A printing step for printing a reference screen patch to which a predetermined screen is applied and a correction target screen patch;
A measurement step of measuring the density of the reference screen patch and the correction target screen patch;
A prediction step of calculating a predicted density of the correction target screen patch based on the measured density of the reference screen patch;
An evaluation step for determining whether or not the prediction accuracy in the prediction step is sufficient based on the measured density of the correction target screen patch and the predicted density of the correction target screen patch;
A correction step for setting a correction value for the gamma correction according to the determination result in the evaluation step;
A gradation correction program for executing