JP7151222B2 - Image forming apparatus, image forming unit and program - Google Patents

Description

The present invention relates to an image forming apparatus, an image forming unit and a program.

2. Description of the Related Art Digital printing apparatuses such as electrophotographic and inkjet systems for mass printing are required to have stable output colors in continuous output of hundreds or thousands of sheets. Especially in use cases where the same type of manuscript is repeated with some content replaced every few pages, such as flyers and catalogs, and in use cases where distributed printing is done at multiple locations. Stable management of reproduced colors is important. However, unlike full-scale commercial printing, the operating environment in which these digital printers are used is often not strictly controlled. And there are many unavoidable instability factors such as ever-changing machine conditions. Therefore, when stable control of the output color is required to some extent, it is necessary to frequently stop the machine and perform calibration. However, if such a calibration operation is performed frequently, problems such as the occurrence of wasted paper, the stoppage of jobs, and an increase in work man-hours occur.

In order to solve this problem, the gradation characteristic change estimated based on a plurality of change mode data for the gradation characteristic prepared in advance for each basic color is used. Even with data, a technology is disclosed that enables stable estimation of changes in gradation characteristics by suppressing noise that is superimposed when measuring color changes and overfitting due to the influence of density variations within a page. (For example, Patent Document 1).

In addition, by accurately approximating typical gradation characteristic changes based on multiple change mode data prepared in advance for each basic color and matched to the change characteristics of each gradation area, even a small number of samples is necessary for color reproduction. A technique for obtaining gradation parameters that cover the entire gradation range is disclosed (for example, Japanese Patent Application Laid-Open No. 2002-200013). In addition, in this technology, when the manuscript data lacks colorimetric data, the gradation correction amount associated with the reflection characteristics of the colorimetric patches formed on the intermediate transfer belt can also be used. To accurately correct gradation characteristic variation.

However, with the technique disclosed in Japanese Patent Laid-Open No. 2002-200012, when measuring the colors in the print area, if the minute colorimetry areas suitable for measurement are biased toward the area in the sub-scanning direction, the colors cannot be measured evenly over the entire print area. In such a case, if there is interference between the periodic variation having a period close to the page interval and the period of the colorimetric points, the effect of the variation may be superimposed as noise on the colorimetric results. There is a problem that the accuracy of estimating changes in tonal characteristics is lowered.

In addition, in the technique of Patent Document 2, the original data is on paper, and in many cases, the color change against the white background is measured. Therefore, the amount of color change may appear different between the original data and the primary color patch due to the optical characteristics of the reading device. There is a problem that the influence cannot be suppressed, and the estimation accuracy of the gradation characteristic change is lowered.

The present invention has been devised in view of the above problems, and suppresses the influence of noise due to periodic fluctuations even when the area of the original data image suitable for colorimetry is biased in the sub-scanning direction. An object of the present invention is to provide an image forming apparatus, an image forming unit, and a program capable of suppressing deterioration in estimation accuracy of gradation characteristic changes and stabilizing reproduced colors.

In order to solve the above-described problems and achieve the object, the present invention provides an image forming apparatus for forming a color image on a print medium by mixing basic colors from an input image composed of a plurality of basic colors. a colorimetric unit that measures colors from at least a partial image area of the color image formed on the print medium to obtain a colorimetric value; and a plurality of divided areas that divide the image area. and based on colorimetric values for each gradation region range divided into a plurality of gradation types, pixel values of the input image, and target values for colorimetry of the colorimetry unit. A first mode parameter is calculated for each region and for each gradation region range, and among the first mode parameters, a distance at which the cycle of the density variation in the image region is in opposite phase, and the cycle of the density variation. The first mode parameters of the divided areas corresponding to the distances for canceling the components are averaged for each of the gradation types to calculate a second mode parameter corresponding to each gradation type, and the second mode parameter is set as the second mode parameter. and a correction unit for correcting the gradation characteristic of each basic color based on the gradation correction value, the generating unit comprising , if the colorimetric unit cannot acquire the colorimetric values in any of the tone area ranges, the colorimetric values of the tone area range in which the colorimetric unit could acquire the colorimetric values and using the first mode parameter of the current gradation area range estimated from the relationship with the colorimetric values of the unacquired gradation area range acquired by the colorimetry unit most recently in the past , wherein the second mode parameter is obtained.

According to the present invention, even if the area of the document data image suitable for colorimetry is biased in the sub-scanning direction, the influence of noise due to periodic fluctuations can be suppressed, and the accuracy of gradation characteristic change estimation can be improved. A decrease can be suppressed, and the reproduced color can be stabilized.

FIG. 1 is a diagram showing an example of a schematic structure of an image forming apparatus according to an 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 showing an example of a schematic configuration of functional blocks of the image forming apparatus according to the embodiment. FIG. 4 is a diagram illustrating an example of a detailed configuration of functional blocks of the image forming apparatus according to the embodiment; FIG. 5 is a flowchart illustrating an example of the image processing flow of the image forming apparatus according to the embodiment. FIG. 6 is a graph showing characteristic trends of the density distribution in the sub-scanning direction. FIG. 7 is a diagram for explaining the operation of obtaining the mode parameters of each change mode from the mode parameters calculated for each sub-scanning pixel area and for each gradation area range. FIG. 8 is a flowchart showing an example of the flow of derivation processing of mode parameters for each change mode of the image forming apparatus according to the embodiment.

Embodiments of an image forming apparatus, an image forming unit, and a program according to the present invention will be described in detail below with reference to the drawings. In addition, the present invention is not limited by the following embodiments, and the constituent elements in the following embodiments can be easily conceived by those skilled in the art, substantially the same, and so-called equivalent ranges. is included. Furthermore, various omissions, replacements, changes and combinations of components can be made without departing from the gist of the following embodiments.

(Schematic structure of image forming apparatus)
FIG. 1 is a diagram showing an example of a schematic structure of an image forming apparatus according to an embodiment. A schematic structure of an image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

As shown in FIG. 1, the image forming apparatus 100 has an image forming unit 4 that forms an image on a sheet P (an example of a print medium) that is a recording medium, and a sheet feeding unit 2 that conveys the sheet P. A transfer unit 5 that transfers a toner image formed on a transfer belt 47 onto a sheet of paper P based on document data (input image) that has been transferred; A fixing unit 6 that fixes the image of the paper P transferred by the unit 5 and a paper discharge unit 7 that discharges the paper P to the outside are provided.

The paper feed unit 2 has a paper feed port 20 , a paper feed roller 21 , and a registration roller pair 22 .

The paper feed port 20 is an opening for feeding the paper P into the image forming section 4 . The paper feed roller 21 is a roller that conveys the paper P fed from the paper feed port 20 to the transfer section 5 . The registration roller pair 22 is a roller pair that feeds the paper P conveyed from the paper feed roller 21 to the transfer section 5 at a predetermined timing.

The image forming apparatus 100 performs four processes corresponding to yellow (Y), magenta (M), cyan (C), and black (K), which are basic colors for transferring toner images onto the transfer belt 47 . It has units 4Y, 4M, 4C and 4K. The process units 4Y, 4M, 4C, and 4K have drum-shaped photosensitive members 40Y, 40M, 40C, and 40K, respectively, which are image carriers. Since the process units 4Y, 4M, 4C, and 4K all have the same configuration and the description is redundant, only the configuration of the process unit 4Y corresponding to yellow (Y) will be described here.

The process unit 4Y has a photoconductor 40Y, a charging device 42Y, a laser unit 53Y, a developing device 43Y, a primary transfer roller 475Y, and a cleaning device 44Y.

The photoreceptor 40Y is a drum-shaped member that is an image carrier as a rotating body that rotates in a direction A, which is the counterclockwise direction shown in FIG. layers are formed. The charging device 42Y is a device that charges the photoreceptor 40Y. The laser unit 53Y is a unit that forms a latent image on the photoreceptor 40Y by scanning with scanning light. The developing device 43Y is a device that develops the latent image formed on the photosensitive member 40Y by the laser unit 53Y with yellow (Y) toner to form a toner image. The primary transfer roller 475Y is a roller that transfers the toner image formed on the photoreceptor 40Y to the transfer belt 47 around which it is wound. The cleaning device 44Y is a device that removes excess toner remaining on the photoreceptor 40Y after the toner image is transferred onto the transfer belt 47. FIG.

These process units 4Y, 4M, 4C, and 4K form a toner image, which is a mixed color image, on the transfer belt 47 by mixing basic colors.

The transfer unit 5 includes a transfer belt 47, a drive roller 471 driven by a drive source so as to rotate in direction B in FIG. and a roller 473 .

The transfer belt 47 is a belt in which carbon powder for adjusting electric resistance is dispersed in a polyimide resin having little elongation. The transfer belt 47 is wound around a drive roller 471, a driven roller 472, a secondary transfer roller 473, and primary transfer rollers 475Y, 475M, 475C, and 475K.

The secondary transfer roller 473 is a roller that contacts the transfer belt 47 together with the opposing roller at the secondary transfer position N to form a nip portion. At the secondary transfer position N, the secondary transfer roller 473 sandwiches the transfer belt 47 together with the sheet P, and applies a secondary transfer bias to transfer the toner image on the surface of the transfer belt 47 onto the sheet P. . As the secondary transfer bias, a charge having a polarity opposite to that of the static charge charged on the surface of the transfer belt 47 is applied. The paper P onto which the toner image has been transferred at the secondary transfer position N is conveyed to the fixing section 6 .

The measurement sensor 45 is provided with a band-pass filter corresponding to each color to be measured so as to have sensitivity to three colors to be measured, R (red), G (green), and B (blue). This is an in-line chromaticity measuring instrument combined with a monochrome line sensor. The measurement sensor 45 has measurement channels with three spectral characteristics corresponding to the three colors R (red), G (green), and B (blue). The number of measurement channels that the measurement sensor 45 has is called the number of measurement channels. The measurement sensor 45 is installed downstream of the secondary transfer position N in the transport direction of the paper P, and measures the reflection characteristics of all or part of the image (color image) formed on the paper P. FIG.

Note that the measurement sensor 45 may be a sensor having at least one measurement channel having spectral characteristics, that is, a measurement channel sensitive to one or more basic colors, and may be a so-called color scanner. . Alternatively, the measurement sensor 45 may be a monochrome line sensor having a single spectral characteristic.

The fixing section 6 fixes the toner image carried on the paper P by the action of heat and pressure when the paper P passes through the fixing nip portion N2 formed between the heating roller 61 and the fixing roller 62. , to form a good color image on the paper P. After passing through the fixing section 6 , the sheet P on which the image has been fixed is discharged from the discharge section 7 to the outside of the image forming section 4 . Note that a switching claw and a double-sided unit may be provided in the paper discharge section 7, and the paper P may enter the double-sided unit according to the mode of the switching claw to prepare for double-sided image formation.

(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; A hardware configuration of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

As shown in FIG. 2, the image forming apparatus 100 includes a CPU (Central Processing Unit) 101, a memory 102, an auxiliary storage device 103, a network I/F 104, a printer engine I/F 106, and an image forming section 4. , a scanner 27 . Among them, the CPU 101, memory 102, auxiliary storage device 103, network I/F 104, printer engine I/F 106, and scanner I/F 108 are connected by a bus 109 so as to be able to communicate with each other.

A CPU 101 is an arithmetic unit that controls the operation of the image forming apparatus 100 in a comprehensive manner.

The memory 102 is composed of a ROM (Read Only Memory) that stores programs such as firmware, and a RAM (Random Access Memory) that is used as a work area during arithmetic processing of the CPU 101 .

The auxiliary storage device 103 is a storage device such as a HDD (Hard Disk Drive), SSD (Solid State Drive), or flash memory, and stores an OS (Operating System), various programs, document data, color profiles, and the like.

The network I/F 104 is an interface for connecting with an external network (LAN (Local Area Network), Internet, etc.). The network I/F 104 is, for example, compatible with Ethernet (registered trademark) and compatible with TCP (Transmission Control Protocol)/IP (Internet Protocol) communication standards. Image forming apparatus 100 can perform data communication with external devices (PC 200, server 201, etc.) via network I/F 104 .

The printer engine I/F 106 is an interface for communicably connecting with the image forming unit 4 that forms an image by an electrophotographic method and executes printing of document data. The image forming section 4 is as described above with reference to FIG.

A scanner I/F 108 is an interface for communicably connecting with the scanner 27 having the measurement sensor 45 . The scanner 27 is a device that reads the image of the paper P using the function of the measurement sensor 45 . The measurement sensor 45 is as described above with reference to FIG. The “image reading unit” in the present invention can be considered to correspond to the measurement sensor 45 or the scanner 27 having the measurement sensor 45 .

Note that the hardware configuration of the image forming apparatus 100 shown in FIG. 2 is an example, and may include other components.

(Functional block configuration of image forming apparatus)
FIG. 3 is a diagram showing an example of a schematic configuration of functional blocks of the image forming apparatus according to the embodiment. A schematic configuration of functional blocks of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

As shown in FIG. 3, image forming apparatus 100 can communicate with PC (Personal Computer) 200 and server 201 via network 500 . As shown in FIG. 3 , the image forming apparatus 100 includes an image processing section 30 and an image forming unit 35 .

The image processing unit 30 is a functional unit that performs image processing on document data received from the PC 200 via the network 500 so that the image forming unit 4 can print the data. Then, the image processing unit 30 converts the image-processed document data into a pixel array (bitmap data or an equivalent compression format) composed of the basic colors of the image forming unit 4, and performs gradation processing. Send to department 31. Note that the document data is expressed in a data format including bitmap data with RGB or CMYK color designation, text data, graphics drawing commands, and the like.

The image processing section 30 is separate from the image forming unit 35, and is composed of, for example, software on a PC and an expansion board, and is replaceable with respect to the image forming unit 35. FIG. Note that the image processing unit 30 may be provided on a terminal separate from the image forming apparatus 100 as long as it can communicate with the image forming unit 35, or may be provided on the PC 200 or the server 201 via the network 500. Alternatively, it may be integrated with the image forming unit 35 .

The image forming unit 35 includes a gradation processing section 31 , a color tone control section 32 , an image inspection section 33 (colorimetry section), an engine control section 39 and an image forming section 4 . The functions of the image forming section 4 are as described above.

The gradation processing unit 31 is a functional unit that converts image information processed by the image processing unit 30 into image data in a format that the image forming unit 4 can receive. Details of the operation of the gradation processing unit 31 will be described later.

The color tone control unit 32 is a functional unit that detects color tone fluctuations (density fluctuations, etc.) of an image from the image information detected by the image inspection unit 33 and provides a gradation correction value to the gradation processing unit 31 . Details of the operation of the color tone control unit 32 will be described later.

The image inspection section 33 is a functional section that detects (reads) an image from the sheet P printed out by the image forming section 4 by means of the scanner 27 in an in-line format. Specifically, the measurement sensor 45 of the scanner 27 included in the image inspection section 33 irradiates the image formed by the image forming section 4 with light and receives the reflected light, thereby measuring the reflectance of the image. It is measured two-dimensionally on a plane and detected as an image. That is, detecting an image means measuring the colors that make up the image. Then, the image inspection unit 33 detects color tone variations (density variations, etc.) of the detected image. The details of the operation of the image inspection unit 33 will be described later.

The engine control section 39 is a functional section that controls the image forming operation of the image forming section 4 .

Gradation processing unit 31 , color tone control unit 32 , image inspection unit 33 (excluding scanner 27 ), and image forming unit 4 are implemented by CPU 101 executing programs developed in memory 102 . Some or all of the gradation processing unit 31, the color tone control unit 32, the image inspection unit 33 (excluding the scanner 27), and the image forming unit 4 are not software programs but FPGAs (Field-Programmable Gate Arrays). Alternatively, it may be implemented by a hardware circuit such as an ASIC (Application Specific Integrated Circuit).

FIG. 4 is a diagram illustrating an example of a detailed configuration of functional blocks of the image forming apparatus according to the embodiment; Next, a detailed configuration of functional blocks of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG. Note that the data format handled by the color tone control unit 32 is CIELab (hereinafter simply referred to as Lab), and the CMYK format data of the document data is converted into Lab format data, but is not limited to the Lab format. Although any color expression format may be used as long as the amount of color change can be clearly defined, the following explanation will be given assuming that the Lab format is used.

As shown in FIG. 4, the image processing unit 30 of the image forming apparatus 100 includes an original color-Lab conversion unit 310, a Lab-CMYK conversion unit 311, a user tone conversion unit 312, and a storage unit 302. .

The document color-Lab conversion unit 310 is a functional unit that converts document data Q (input image) described in CMYK format or the like received from the PC 200 or the like into device-independent Lab format color values docLab. The Lab-CMYK conversion unit 311 is a functional unit that converts the colorimetric values docLab into 8-bit integer gradation values prnCMYK for each of the basic colors CMYK of the image forming unit 4 . The user gradation conversion unit 312 is a functional unit that corrects the gradation values prnCMYK based on the corresponding color profile. In the initial state, the user tone conversion unit 312 outputs the tone values prnCMYK as they are without changing them. The processing by the Lab-CMYK conversion unit 311, the user tone conversion unit 312, and the CMYK-Lab conversion unit 313 are processed at the same time as the vector data and font development, and the tone values prnCMYK output as a result are CMYK colors that are basic colors. is output as bitmap data. The output bitmap data (tone values prnCMYK) are stored in the storage unit 302 for each print document.

As shown in FIG. 4 , the gradation processing section 31 of the image forming apparatus 100 has a gradation correction section 316 (correction section) and a gradation conversion section 317 .

The gradation correction unit 316 sets gradation correction values ΔCT (=(ΔC(c), ΔM(m), ΔY(y), ΔK(k)) for correcting the gradation characteristics of each basic color for each basic color. )) to correct the image to be output by the image forming unit 4. FIG. Here, c, m, y, and k are gradation values before correction, and for example, ΔC(c) indicates the correction amount for cyan (C) gradation value c before correction. Specifically, the gradation correction unit 316 includes a gradation correction table (hereinafter sometimes referred to as TRC (Tone Response Correction)) for each of the basic colors C, M, Y, and K, and sets a gradation correction value Using ΔCT and TRC, the gradation characteristics of each basic color indicated by the gradation value prnCMYK read from the storage unit 302 are corrected.

The gradation conversion unit 317 converts the 8-bit color value for each basic color corrected by the gradation correction unit 316 into an area gradation method or an error diffusion method so as to match the number of gradations expressible by the image forming unit 4 . It is a functional unit that converts using a modulus or the like. The image forming section 4 forms an image on the paper P based on the CMYK data converted by the gradation converting section 317 .

As shown in FIG. 4, the image inspection unit 33 of the image forming apparatus 100 has the scanner 27 as described above and also has the scanner color-Lab conversion unit 318 .

The scanner color-Lab conversion unit 318 is a functional unit that converts the measured value mesCol of the image on the paper P measured by the scanner 27 into a colorimetric value mesLab in Lab format.

As shown in FIG. 4 , the color tone control unit 32 of the image forming apparatus 100 has a colorimetry prediction unit 34 , a color tone correction amount determination unit 319 (generation unit), and a storage unit 320 .

The colorimetry prediction unit 34 is a functional unit that predicts the gradation of the image formed by the image forming unit 4 based on the gradation values prnCMYK output from the image processing unit 30 . The colorimetry prediction unit 34 has a CMYK-Lab conversion unit 313 , a Lab-scanner color conversion unit 314 , a scanner correction unit 325 , and a scanner color-Lab conversion unit 315 .

The CMYK-Lab conversion unit 313 is a functional unit that converts the gradation values prnCMYK output from the image processing unit 30 into Lab values prnLab again.

The Lab-scanner color conversion unit 314 is a functional unit that converts the Lab values prnLab converted by the CMYK-Lab conversion unit 313 into colorimetric values scnCol in the scanner color space. The scanner correction unit 325 corrects the colorimetric value scnCol (an example of information based on the pixel value of the input image) converted by the Lab-scanner color conversion unit 314 based on the reading error of the measurement sensor 45 given in advance. is a functional unit that obtains the read predicted value scnCol'. The correction by the scanner correction unit 325 improves the prediction accuracy of colors read by the scanner 27 .

The scanner color-Lab conversion unit 315 is a functional unit that converts the predicted reading value scnCol′ corrected by the scanner correction unit 325 into the predicted colorimetric value targetLab, which is a device-independent Lab value.

Through the series of processes of the Lab-scanner color conversion unit 314, the scanner correction unit 325, and the scanner color-Lab conversion unit 315 as described above, the color gamut that can be read by the scanner 27 is changed to the color gamut that the image forming unit 4 can output. It also has the effect of simulating the saturation of readout colors (gamut compression) that occurs when the value is less than .

As described above, the colorimetric prediction unit 34 including the CMYK-Lab conversion unit 313, the Lab-scanner color conversion unit 314, the scanner correction unit 325, and the scanner color-Lab conversion unit 315 generates the colorimetric prediction value targetLab, It requires a large computational load (amount of memory used and processing time). For this reason, the colorimetric prediction unit 34 generates in advance the colorimetric prediction value tagtLab from data for the required number of pages and stores it in the storage unit 320. The colorimetric predicted value targetLab stored in the storage unit 320 is used. In this way, by pre-storing the colorimetric prediction targetLab as the result of scanner reading, including the error characteristics on the scanner 27 side, the tone correction value ΔCT can be calculated in the subsequent color tone correction amount determination unit 319 . It can be done efficiently in time. As a result, the gradation values prnCMYK obtained by the Lab-CMYK conversion unit 311 and the user gradation conversion unit 312 are converted into colorimetric prediction values targetLab to be measured by the image inspection unit 33 .

The color tone correction amount determination unit 319 determines the colorimetric predicted value targetLab which is the target color, the colorimetric value mesLab actually obtained from the image inspection unit 33, and the gradation value prnCMYK which is the input value to the gradation correction unit 316. , and engine information from the engine control unit 39, to generate a gradation correction value ΔCT for each basic color for correcting the TRC. The gradation correction value ΔCT generated by the color tone correction amount determination unit 319 minimizes the deviation between the target reproduced color and the output color development, thereby stabilizing the color development of the image output to the paper P. can be made

Note that each functional unit of the image forming apparatus 100 shown in FIG. 4 conceptually shows the function, and the configuration is not limited to this. For example, a plurality of functional units illustrated as independent functional units in the image forming apparatus 100 shown in FIG. 4 may be configured as one functional unit. On the other hand, in the image forming apparatus 100 shown in FIG. 4, the functions of one functional section may be divided into a plurality of functional sections.

Further, the document color-Lab conversion unit 310, the Lab-CMYK conversion unit 311, the CMYK-Lab conversion unit 313, the Lab-scanner color conversion unit 314, the scanner color-Lab conversion unit 315, and the scanner color-Lab conversion unit 318 are Each color space conversion requires basic data called a color profile. As such a color profile, for example, an ICC profile defined by the ICC (International Color Consortium) may be used.

Among these color profiles, the color profiles necessary for the document color-Lab conversion unit 310 are attached to the document data Q or prepared in advance. Color profiles required for the Lab-scanner color conversion unit 314, the scanner color-Lab conversion unit 315, and the scanner color-Lab conversion unit 318 are fixedly preset in the color tone control unit 32 and the image inspection unit 33, respectively. there is Color profiles required for the Lab-CMYK conversion unit 311 and the CMYK-Lab conversion unit 313 have different color reproduction characteristics depending on the type of paper P. It is desirable to select and set an appropriate color profile that matches the type. Such change of the color profile according to the type of paper P may be arbitrarily performed by the user, or may be automatically performed in accordance with the selection of the paper P that matches the document data Q input by the image processing unit 30. good.

(Flow of Image Processing of Image Forming Apparatus)
FIG. 5 is a flowchart illustrating an example of the image processing flow of the image forming apparatus according to the embodiment. A flow of image processing of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG.

<Step S100>
The document color-Lab conversion unit 310 of the image processing unit 30 converts the input document data Q described in the CMYK format or the like into device-independent Lab format color values docLab. Then, the process proceeds to step S101.

<Step S101>
The Lab-CMYK conversion unit 311 of the image processing unit 30 converts the colorimetric values docLab into 8-bit integer gradation values prnCMYK for each of the basic colors CMYK of the image forming unit 4 . Then, the process proceeds to steps S102 and S107.

<Step S102>
The user gradation conversion unit 312 of the image processing unit 30 corrects the gradation values prnCMYK based on the corresponding color profile, and outputs them as image data. In the initial state, the user gradation conversion unit 312 outputs the gradation value prnCMYK as it is as image data without changing it. The processing by the Lab-CMYK conversion unit 311, the user tone conversion unit 312, and the CMYK-Lab conversion unit 313 are processed at the same time as the vector data and font development, and the tone values prnCMYK output as a result are CMYK colors that are basic colors. is output as bitmap data. The output bitmap data (tone values prnCMYK) are stored in the storage unit 302 for each print document. Then, the process proceeds to step S103.

<Step S103>
The gradation correction unit 316 of the gradation processing unit 31 uses the gradation correction value ΔCT and the TRC for each of the basic colors C, M, Y, and K to obtain the gradation value prnCMYK read from the storage unit 302. Correct the gradation characteristics of each basic color (gradation correction). Then, the process proceeds to step S104.

<Step S104>
The gradation conversion unit 317 of the gradation processing unit 31 converts the 8-bit color value for each basic color corrected by the gradation correction unit 316 into a format that matches the number of gradations that the image forming unit 4 can represent. , using the area coverage gradation method, the error diffusion method, or the like. Then, the process proceeds to step S105.

<Step S105>
The image forming section 4 forms an image (toner image) on the paper P based on the CMYK data converted by the gradation converting section 317 . Then, the process proceeds to step S106.

<Step S106>
The scanner 27 (measurement sensor 45) of the image inspection section 33 measures the image formed on the paper P to obtain the measurement value mesCol. A scanner color-Lab conversion unit 318 of the image inspection unit 33 converts the measured value mesCol of the image on the paper P measured by the scanner 27 into a colorimetric value mesLab in Lab format. The scanner color-Lab conversion unit 318 sends the converted colorimetric value mesLab to the color tone correction amount determination unit 319 .

<Step S107>
The color tone correction amount determination unit 319 of the color tone control unit 32 reads the necessary part of the tone values prnCMYK in advance from the bitmap data accumulated in the storage unit 302 into the page buffer. Then, the process proceeds to step S108.

<Step S108>
On the other hand, the CMYK-Lab conversion unit 313 of the colorimetry prediction unit 34 converts the gradation values prnCMYK output from the image processing unit 30 again into Lab values prnLab (output prediction values). Then, the process proceeds to step S109.

<Step S109>
The Lab-scanner color conversion unit 314 of the colorimetry prediction unit 34 converts the Lab values prnLab converted by the CMYK-Lab conversion unit 313 into colorimetric values scnCol in the scanner color space. Here, since the colorimetric value scnCol does not include the reading error specific to the measurement sensor 45 , if the colorimetric value scnCol is used for correction as it is, the reading error of the measurement sensor 45 is included in the correction. For example, when the color gamut that can be read by the measurement sensor 45 is smaller than the color gamut that can be output by the image forming unit 4, the color gamut is compressed by the measurement sensor 45, so the Lab value prnLab (output predicted value) may be significantly different from the measured value mesCol obtained by the measurement sensor 45 . Therefore, the scanner correction unit 325 of the colorimetry prediction unit 34 corrects the colorimetric value scnCol converted by the Lab-scanner color conversion unit 314 based on the reading error of the measurement sensor 45 given in advance, and predicts reading. A value scnCol' (predicted scanner reading value) is obtained. By having such a scanner correction unit 325, even when the color gamut that can be read by the measurement sensor 45 is smaller than the color gamut that can be output by the image forming unit 4, the color reading value can be predicted with high accuracy. will be Then, the process proceeds to step S110.

<Step S110>
The scanner color-Lab conversion unit 315 of the colorimetry prediction unit 34 converts the read prediction value scnCol′ corrected by the scanner correction unit 325 into the colorimetry prediction value targetLab (target value), which is a device-independent Lab value. Convert. The colorimetry prediction unit 34 causes the storage unit 302 to store the calculated colorimetry prediction value targetLab (target value) for the entire print area to be printed in advance. Then, the process proceeds to step S111.

<Step S111>
If extraction of colorimetric values mesLab and colorimetric predicted values targetLab (target values) has not been completed in all colorimetric regions (small colorimetric regions to be described later) (step S111: No), return to step S107 and end. If so (step S111: Yes), the image processing ends.

(Method of Generating Gradation Correction Value ΔCT)
Next, a method of generating the gradation correction value Δ by the color tone correction amount determination unit 319 in this embodiment will be described.

First, prior to the process of generating the gradation correction value ΔCT, the color tone correction amount determination unit 319 selects a plurality of numbers suitable for color measurement (colorimetry) from the print area of each page and with little change in color. A minute colorimetric area (xi, yi) (i=1, . Here, the minute colorimetry area is represented by its center coordinates (xi, yi). Regarding the coordinates (x, y) here, the paper feed direction (conveyance direction) in which the paper P is conveyed in the image forming apparatus 100 (that is, the sub-scanning direction) is defined as the coordinate y, and the direction perpendicular to the sub-scanning direction. (main scanning direction) is described as the coordinate x. As a method for extracting the minute colorimetry area (xi, yi), for example, a method of selecting and extracting an area of 41×41 pixels at 400 [dpi] from an arbitrary area of about 5 [mm] square can be used.

The color tone correction amount determination unit 319 extracts N minute colorimetric areas (xi, yi) from a single page or several consecutive pages, and extracts a plurality of small colorimetric areas (xi, yi) in the sub-scanning direction. For each sub-scanning pixel region (y) (divided region) divided into , and for each gradation region range (rd), the average value of the colorimetric values of the minute colorimetric regions (xi, yi) (colorimetric average value ) is calculated. Here, the gradation area range (rd) indicates an area of drawing elements (graphics, etc.) included in the gradation range of one of a plurality of change modes defined in the print area. Further, the change mode indicates each gradation range when the gradation of the drawing element in the print area is divided into a predetermined number of stages (gradation types). Therefore, the gradation area range (rd) is divided into area ranges corresponding to each of a plurality of change modes. For example, if the change mode number d is 3, the gradation area range (rd) is divided into three types of gradation range areas.

Then, the color tone correction amount determination unit 319 calculates for each sub-scanning pixel region (y) based on the colorimetric average value calculated for each sub-scanning pixel region (y) and for each gradation region range (rd). Each mode parameter θ(rd)(y) (first mode parameter) is calculated according to the change mode number d. Here, in calculating each mode parameter θ(rd)(y) by the color tone correction amount determination unit 319, the above-described colorimetric prediction value targetLab, which is the target color, and the gradation, which is the input value to the tone correction unit 316, are used. Tone values prnCMYK and are used. Note that, as a method of calculating the mode parameter θ(rd)(y) for each change mode based on the colorimetric average value, for example, the calculation method disclosed in Japanese Unexamined Patent Application Publication No. 2017-204786 can be applied. Further, among the mode parameters θ(rd)(y) for each sub-scanning pixel region (y) obtained by the color tone correction amount determination unit 319 and for each gradation region range (rd), a predetermined change mode The mode parameters corresponding to are collectively represented as mode parameter θ(rd).

In addition, the color tone correction amount determination unit 319 determines the density variation described later among the mode parameters θ(rd)(y) calculated for each sub-scanning pixel region (y) and for each gradation region range (rd). The mode parameters .theta.(rd)(y) that coincide with the predetermined distance about the period are obtained as the mode parameters .theta.(rd) for each change mode. Further, the color tone correction amount determination unit 319 averages the obtained set data of the mode parameter θ(rd) for each change mode, and the mode parameter θRd (second mode parameter). That is, the mode parameters .theta.R1, .theta.R2, .theta.R3, .

FIG. 6 is a graph showing characteristic trends of the density distribution in the sub-scanning direction. Next, referring to FIG. 6, periodic variations in density (density variations) that occur in the sub-scanning direction will be described.

The horizontal axis of the graph shown in FIG. 6 represents the sub-scanning position of the print area for five pages, with the start of the first page as the reference, including the paper interval that is not actually printed, and the vertical axis represents the density. represents. The characteristic of the density fluctuation in the sub-scanning direction is that the periodic fluctuation shown by the solid line and other random fluctuations are superimposed on the gentle drift of density over several pages shown by the broken line. ing. Such periodic fluctuations of several [cm] to several tens [cm] are often caused by the photoreceptors 40Y, 40M, 40C, and 40K for forming latent images in the image forming section 4, and the developing device 43Y for developing. (In addition, M, C, and K developing devices are included). Estimated from the colorimetric values measured in the area indicated by the " " mark because the period of density fluctuation indicated by the "▽" mark in FIG. 6 and the sampling period indicated by the upward arrow are slightly different The amount of drift indicated by the one-dot chain line is evaluated with a deviation from the actual amount of drift indicated by the dashed line. The effects of these moderate periodic fluctuations of several [cm] to several tens [cm] are avoided for each gradation area range (rd), and the effects of drift over several pages are suppressed. The operation of obtaining the mode parameter θRd for each gradation area range (rd) that suppresses the influence of fluctuation will be described below.

FIG. 7 is a diagram for explaining the operation of obtaining the mode parameters of each change mode from the mode parameters calculated for each sub-scanning pixel area and for each gradation area range. A method for obtaining the mode parameter θRd for each gradation area range (rd) will be described with reference to FIG.

Specifically, in FIG. 7, the mode parameter θ(rd)(y ), the periodic component of the density variation occurring in the sub-scanning direction is calculated based on the combination of the mode parameters θ(rd)(y) corresponding to the distance of N cycles+0.5 cycles (N=integer value). 3 shows an example of a method of obtaining the mode parameter θRd for generating the tone correction value ΔCT. FIG. 7 shows two pages of different images (image areas) that are continuously printed based on the document data. 4 shows a plurality of micro colorimetric regions arranged within. Also, the dashed lines in the page represent sub-scanning pixel regions (y) divided into a plurality of sub-scanning pixel regions (y), and the numbers at the top of the page represent region numbers y for distinguishing the sub-scanning pixel regions (y). there is A mode parameter θ(rd) is calculated by the color tone correction amount determination unit 319 for each gradation region range (rd), which is a region of a predetermined section in the sub-scanning direction, and the calculated mode parameter θ(rd) is added with the region number y as a subscript to obtain the mode parameter θ(rd)(y). Note that the area for specifying the sub-scanning pixel area (y) and the gradation area range (rd) is not limited to the entire image area for one page as shown in FIG. It can be a region.

In FIG. 7, the case where the tone area range (rd) is divided into three types, that is, the case where the number of change modes is d=3 is taken as an example. Separately, they are expressed as a low-density gradation area r1, a medium-density gradation area r2, and a high-density gradation area r3. For convenience of explanation, the minute colorimetry area and the sub-scanning pixel area (y) are expressed on a larger scale. is 41 x 41 pixels, and if the paper used for printing is A4 size, and the lateral direction is the sub-scanning direction, the length of the paper in the sub-scanning direction is about 210 [mm], so the number of pixels is Approximately 3307 pixels at 400 [dpi]. If it is divided by 41 pixels, it goes without saying that the number of sub-scanning pixel regions (y) in the sub-scanning direction per page is about 80.

The two periodic component graphs (density fluctuations A and B) in FIG. 7 are graphs simulating two types of density fluctuations occurring in the sub-scanning direction when an image is printed. For the sake of convenience, they are shown separately, but in reality, these density fluctuations are superimposed on the printed image in a combined state. Of the mode parameters θ(rd)(y) calculated for each sub-scanning pixel area (y) and for each gradation area range (rd), the color tone correction amount determination unit 319 calculates the distance for the period including the inter-paper distance. However, if there is a mode parameter θ(rd)(y) that matches the distance of N cycles+0.5 cycles of each of the density variation A and the density variation B, the average value based on these mode parameters θ(rd)(y) is is obtained as a mode parameter θRd for each change mode (each gradation area range (rd)). That is, the distance of N cycles+0.5 cycles is the distance at which the cycles of the density fluctuations have opposite phases, and is the distance that cancels out the periodic components of the density fluctuations.

First, in the low-density gradation region r1, the color tone correction amount determination unit 319 determines each sub-scanning pixel region (y) of y=1, 2, 3, 4, 5, 6, 15, 16, 17, 18, and 19. , the mode parameter θ(r1)(y) is calculated. Of these, y=1, 3, 5, 15, 17, and 19 (“Δ” and “☆” marks in FIG. 7) coincide with N cycles+0.5 cycles, so the amount of color tone correction is determined. Unit 319 extracts mode parameters θ(r1) corresponding to those region numbers.

Similarly, in the middle-density gradation region r2, the color tone correction amount determination unit 319 performs sub-scanning of y=1, 2, 3, 4, 5, 6, 15, 16, 17, 18, 19, 20, and 21. A mode parameter θ(r2)(y) is calculated in the pixel region (y). Of these, y=2, 4, 6, 16, 18, and 20 (“Δ (filled in black)” and “★” marks in FIG. 7) correspond to N cycles+0.5 cycles. The color tone correction amount determination unit 319 extracts mode parameters (r2) respectively corresponding to those area numbers.

Similarly, in the high-density gradation region r3, the color tone correction amount determination unit 319 determines the mode parameter θ(r3) ( y) is calculated. Of these, y=8, 9, 22, and 23 (“○” and “◇” marks in FIG. 7) match N cycles+0.5 cycles. A mode parameter (r3) corresponding to each of these region numbers is extracted.

Then, the color tone correction amount determination unit 319 averages the set data of the mode parameters θ(r1), θ(r2), and θ(r3) for each of the extracted change modes (each gradation region range (rd)). Based on the mode parameters .theta.R1, .theta.R2, and .theta.R3, the tone correction value .DELTA.CT for each basic color is generated. By generating such a tone correction value ΔCT, it is possible to stably estimate a tone characteristic change with high estimation accuracy in which the influence of noise due to periodic variations in density is suppressed.

Note that when continuous printing is performed, the paper-to-paper distance between adjacent pages is not always the same. Since the paper-to-paper distance at that time can be easily estimated from the timing signal or the like, the color tone correction amount determining unit 319 may obtain the paper-to-paper distance by using the above-described timing signal or the like.

In addition, sub-scanning pixels having a distance corresponding to the distance of N cycles + 0.5 cycles of each density variation, which are suitable for colorimetry and have little change in color, are evenly present in the area within one page. If regions (y) exist for each gradation region range (rd), mode parameters θR1, θR2, and θR3 may be calculated based on the sub-scanning pixel regions (y). Also, if there is no sub-scanning pixel region (y) having a distance that matches the distance of N cycles + 0.5 cycles between two pages, then the distance from the sub-scanning pixel region (y) between three pages matches the above distance. The mode parameter θRd can also be calculated by extracting a sub-scanning pixel region (y) having a distance of . However, if the number of pages to be searched increases, as in the case shown in FIG. 6, there is a risk that the evaluation may deviate from the actual amount of drift. is desirable. Also, if it is not found on the first and second pages, the mode parameter θ(rd)(y) calculated on the first page may be discarded and calculated on the second and third pages. In this case, the number of pages is not limited to two, and may be three or more pages. For example, if it is not found in the 1st to 3rd pages, the mode parameter θ(rd)(y) calculated for the 1st page may be discarded and the 2nd to 4th pages may be found.

Further, when the colorimetric values in the minute colorimetric area of one of the three tone area ranges (rd) cannot be obtained from the three tone area ranges (rd) as described above, the color tone correction amount determination unit Reference numeral 319 denotes the relationship between the colorimetric values of the tone area range (rd) for which colorimetric values have been acquired and the colorimetric values of the unacquired tone area range (rd) acquired at the most recent control timing in the past. Each mode parameter .theta.Rd may be obtained using the mode parameter .theta.(rd) of each change mode of the current gradation area range (rd) estimated from the characteristics. As a result, stable gradation correction can always be performed without lowering the estimation accuracy.

Also, FIG. 7 illustrates the density fluctuations A and B having two periodic components. is also conceivable. Gradation correction based on mode parameters θR1, θR2, and θR3 obtained from mode parameters θ(rd)(y) that match the distance of N cycles+0.5 cycles for all periodic components that affect density variation. A value ΔCT may be generated. However, when calculating each of the mode parameters θR1, θR2, and θR3 that match the above-described distances for all of the multiple periodic components from the printed image, any one of the multiple periodic components may This will increase the number of cases where the matching mode parameter θ(rd)(y) does not exist. Therefore, while continuous printing is performed, the gradation correction value ΔCT cannot be generated, and there is a risk that the accuracy of estimating changes in gradation characteristics will decrease. It is desirable to extract the periodic component of the type) in advance and obtain the periodic component.

(Flow of processing for generating tone correction value ΔCT)
FIG. 8 is a flowchart showing an example of the flow of derivation processing of mode parameters for each change mode of the image forming apparatus according to the embodiment. A flow of processing for generating the tone correction value ΔCT of the image forming apparatus 100 according to the present embodiment will be described with reference to FIG. 8 .

<Step S300>
The color tone correction amount determination unit 319 acquires samples (colorimetric values) of minute colorimetric regions for each of sub-scanning pixel regions (y) obtained by dividing the print region into a plurality of sub-scanning pixel regions in the sub-scanning direction. Then, the process moves to step S301.

<Step S301>
The color tone correction amount determination unit 319 determines each mode parameter θ ( rd)(y) is calculated. Then, the process proceeds to step S302.

<Step S302>
If calculation of mode parameters (rd)(y) for all sub-scanning pixel regions (y) has been completed (step S302: Yes), the process proceeds to step S303. If not, the process returns to step S300.

<Step S303>
Of the mode parameters θ(rd)(y) calculated for each sub-scanning pixel region (y) and for each gradation region range (rd), the color tone correction amount determination unit 319 determines the sub-scanning value for region number y=0. Sub-scanning pixels in which there is a minute colorimetry area with the same gradation area range (rd) at a distance that matches the distance (specified period distance) of N cycles + 0.5 cycles when the scanned image area (y) is used as a reference Search region (y). Then, the color tone correction amount determining unit 319 obtains the mode parameters (rd) and (y) that match the distance of N cycles+0.5 cycles (designated cycle distance) as the mode parameter θ(rd) for each change mode.

However, when processing is performed on only one page, the search is performed up to an area overlapping the distance of the remaining 0.5 period for the largest period component among the period components to be searched, and N periods + 0.5 between two pages. When searching for a distance that matches the period distance, the search is performed up to the last sub-scanning pixel area (y) of the first page. Then, the process proceeds to step S304.

<Step S304>
For all sub-scanning pixel regions (y), searching for mode parameters (rd) (y) that match the distance of N cycles + 0.5 cycles (designated cycle distance), and deriving (calculating) the mode parameter θ (rd) is completed (step S304: Yes), the process proceeds to step S305, and if not completed (step S304: No), the process returns to step S303.

<Step S305>
The color tone correction amount determination unit 319 averages the set data of the obtained mode parameter θ(rd) for each change mode, and calculates the mode parameter θRd for each change mode for generating the gradation correction value ΔCT. Then, the color tone correction amount determination unit 319 generates the gradation correction value ΔCT for each basic color using the approximation line obtained based on the calculated mode parameter θRd. As for the method of generating (calculating) the gradation correction value ΔCT based on the mode parameter θRd, for example, the method disclosed in Japanese Patent Application Laid-Open No. 2017-204786 can be applied.

Then, based on the generated gradation correction value ΔCT, the amount of color tone correction given to the engine control section 39 and the gradation correction section 316 is corrected. Specifically, for example, the tone correction unit 316 uses the tone correction value ΔCT received from the color tone correction amount determination unit 319 to correct the TRC. As a result, the color development of the image printed out on the paper P is stabilized.

As described above, in the image forming apparatus 100 according to the present embodiment, measurement is performed for each sub-scanning pixel area (y) divided into a plurality of sub-scanning pixel areas in the print area in the sub-scanning direction, and for each gradation area range (rd). Based on the color average value, each mode parameter θ(rd)(y) corresponding to the change mode number d is calculated for each sub-scanning pixel region (y). Then, among the mode parameters θ(rd)(y), the mode parameters θ(rd)(y) that match the distance (designated cycle distance) of N cycles+0.5 cycles of the density variation are selected according to the change mode. A mode parameter .theta.(rd) is determined, average processing is performed on set data of the mode parameter .theta.(rd) for each change mode, and a mode parameter .theta.Rd for each change mode for generating a gradation correction value .DELTA.CT is calculated. Then, a gradation correction value ΔCT for each basic color is generated based on the calculated mode parameter θRd. This makes it possible to estimate changes in gradation characteristics while suppressing the effects of noise due to density fluctuations even when the area suitable for colorimetry of the image of the document data to be continuously printed is biased in the sub-scanning direction. It is possible to suppress deterioration in accuracy and stabilize reproduced colors.

In the above-described embodiment, when at least one of the functional units of the image forming apparatus 100 is realized by executing a program, the program is preinstalled in a ROM or the like and provided. Further, in the above-described embodiment, the program executed by the image forming apparatus 100 is stored as a file in an installable or executable format on a CD-ROM (Compact Disc Read Only Memory), a flexible disk (FD), or a CD-ROM. It may be configured to be provided by being recorded on a computer-readable recording medium such as R (Compact Disk-Recordable) or DVD (Digital Versatile Disc). Further, in the above-described embodiment, the program executed by the image forming apparatus 100 may be stored in a computer connected to a network such as the Internet, and provided by being downloaded via the network. Further, in the above-described embodiment, the program executed by the image forming apparatus 100 may be provided or distributed via a network such as the Internet. In the above-described embodiment, the program executed by the image forming apparatus 100 has a module configuration including at least one of the above-described functional units. By reading and executing the program from (for example, the auxiliary storage device 103, etc.), each of the above functional units is loaded and generated on the main storage device (for example, the memory 102).

2 Paper Feed Section 4 Image Formation Section 4C, 4M, 4Y, 4K Process Unit 5 Transfer Section 6 Fixing Section 7 Paper Discharge Section 20 Paper Feed Port 21 Paper Feed Roller 22 Registration Roller Pair 27 Scanner 30 Image Processing Section 31 Gradation Processing Section 32 Color tone control section 33 Image inspection section 34 Colorimetric prediction section 35 Image forming unit 39 Engine control section 40C, 40M, 40Y, 40K Photoreceptor 42Y Charging device 43Y Developing device 44Y Cleaning device 45 Measurement sensor 47 Transfer belt 53Y Laser unit 61 Heating Roller 62 Fixing roller 100 Image forming apparatus 101 CPU
102 memory 103 auxiliary storage device 104 network I/F
106 printer engine I/F
108 Scanner I/F
109 Bus 200 PC
201 Server 302 Storage Unit 310 Original Color-Lab Conversion Unit 311 Lab-CMYK Conversion Unit 312 User Gradation Conversion Unit 313 CMYK-Lab Conversion Unit 314 Lab-Scanner Color Conversion Unit 315 Scanner Color-Lab Conversion Unit 316 Gradation Correction Unit 317 Tone conversion unit 318 Scanner color-Lab conversion unit 319 Color tone correction amount determination unit 320 Storage unit 325 Scanner correction unit 471 Drive roller 472 Driven roller 473 Secondary transfer roller 475C, 475M, 475Y, 475K Primary transfer roller 500 Network P Paper Q manuscript data

JP 2016-092653 A JP 2017-204786 A

Claims (9)

An image forming apparatus for forming a color image on a print medium by mixing basic colors from an input image composed of a plurality of basic colors,
a colorimetry unit that measures colors from at least a partial image area of the color image formed on the print medium to obtain a colorimetric value;
a colorimetric value for each divided area obtained by dividing the image area into a plurality of areas and for each tone area range divided into a plurality of tone types, a pixel value of the input image, and a colorimetry of the colorimetry unit A first mode parameter is calculated for each divided area and for each gradation area range based on the target value of and the first mode parameters of the divided areas corresponding to the distance that cancels out the periodic component of the density variation are averaged for each gradation type to obtain a second mode corresponding to each gradation type a generator that calculates a parameter and generates a gradation correction value for each basic color based on the second mode parameter;
a correction unit that corrects the gradation characteristics of each of the basic colors based on the gradation correction value;
with
If the colorimetry unit cannot acquire the colorimetric values in any of the tone area ranges, the generation unit generates the first mode of the current gradation area range estimated from the relationship between the colorimetric values and the colorimetric values of the unacquired gradation area range acquired by the colorimetry unit most recently in the past An image forming apparatus that uses parameters to determine the second mode parameters . 2. The image forming apparatus according to claim 1, wherein the divided areas are areas obtained by dividing the image area into a plurality of areas in the sub-scanning direction. The generation unit averages the first mode parameters of the divided regions corresponding to distances at which the cycle of the density fluctuation of the image region is in opposite phase among the first mode parameters for each of the gradation types. 3. The image forming apparatus according to claim 1, wherein the second mode parameter corresponding to each gradation type is calculated. The generation unit generates the colorimetric values for each of the plurality of divided regions in each of the image regions on the two or more print media and for each of the gradation region ranges divided into a plurality of gradation types. and calculating the first mode parameter for each divided area and for each gradation area range based on the pixel value of the input image and the target value for colorimetry of the colorimetric unit. The image forming apparatus according to any one of claims 1 to 3 . The generating unit
Periodic components of density fluctuations of the image regions from the first mode parameters calculated for each of the plurality of divided regions divided in each of the image regions on the two or more print media and for each gradation region range. when the first mode parameters of the divided regions corresponding to the distance to offset are not obtained, the first mode parameter for the first print medium among the print media is discarded, and the two or more print calculating the first mode parameter for the print medium next to the medium;
5. An image according to claim 4 , wherein said second mode parameter is calculated from said first mode parameter calculated for said two or more print media excluding said first print medium and said next print medium. forming device. The generation unit converts the first mode parameters of the divided regions corresponding to distances that cancel each other in two or more periodic components of the density variation of the image region among the first mode parameters to the gradation. The image forming apparatus according to any one of claims 1 to 5 , wherein a second mode parameter corresponding to each tone type is calculated by averaging for each type. The colorimetric unit acquires the colorimetric value obtained from an image reading unit that reads colors from the image area,
7. The method according to any one of claims 1 to 6 , further comprising a colorimetric prediction unit that obtains the target value by correcting information based on pixel values of the input image using reading errors of the image reading unit. image forming device. An image forming unit for forming a color image on a print medium by mixing the basic colors from an input image composed of a plurality of basic colors,
a colorimetry unit that measures colors from at least a partial image area of the color image formed on the print medium to obtain a colorimetric value;
a colorimetric value for each divided area obtained by dividing the image area into a plurality of areas and for each tone area range divided into a plurality of tone types, a pixel value of the input image, and a colorimetry of the colorimetry unit A first mode parameter is calculated for each divided area and for each gradation area range based on the target value of and the first mode parameters of the divided areas corresponding to the distance that cancels out the periodic component of the density variation are averaged for each gradation type to obtain a second mode corresponding to each gradation type a generator that calculates a parameter and generates a gradation correction value for each basic color based on the second mode parameter;
a correction unit that corrects the gradation characteristics of each of the basic colors based on the gradation correction value;
with
If the colorimetry unit cannot acquire the colorimetric values in any of the tone area ranges, the generation unit generates the first mode of the current gradation area range estimated from the relationship between the colorimetric values and the colorimetric values of the unacquired gradation area range acquired by the colorimetry unit most recently in the past An image forming unit that uses the parameters to determine the second mode parameters . to the computer,
Colorimetry for obtaining colorimetric values by measuring colors from at least a partial image area of a color image formed on a print medium by mixing the basic colors from an input image composed of a plurality of basic colors. a step;
a colorimetric value for each divided area obtained by dividing the image area into a plurality of areas and for each tone area range divided into a plurality of tone types; a pixel value of the input image; A first mode parameter is calculated for each divided area and for each gradation area range based on a target value for color, and among the first mode parameters, a cycle of density fluctuation in the image area is reversed. By averaging the first mode parameters of the divided areas corresponding to the phase distance and the distance that cancels out the periodic component of the density variation for each gradation type, the second mode parameters corresponding to each gradation type are obtained. a generation step of calculating a mode parameter and generating a gradation correction value for each of the basic colors based on the second mode parameter;
a correction step of correcting the gradation characteristics of each of the basic colors based on the gradation correction value;
and
In the generating step, if the colorimetric values could not be obtained in any of the tone area ranges in the colorimetry step, the corresponding tone area range for which the colorimetric values could be obtained in the colorimetry step. the first mode parameter of the current gradation area range estimated from the relationship between the colorimetric values and the colorimetric values of the unacquired gradation area range acquired in the most recent past colorimetry step; A program for determining the second mode parameter using

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