JP7238518B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus for forming an image on a recording medium.

In image forming apparatuses such as copiers and printers that form color images on a recording medium, even when a large number of images are continuously output, the quality of the formed images, for example, the colors that are output, must be kept within a certain range. It is required to reproduce or manage it internally.

In such an image forming apparatus, a configuration is known in which a measurement sensor that measures the color of an output image is used to correct the color gradation so as to reduce the error between the measured value and the reference value (for example, Japanese Unexamined Patent Application Publication No. 2002-200013). 6).
As a configuration for performing such gradation correction, even if the sample data is small or the gradation of the color is biased, it is possible to correct the gradation based on a plurality of change mode data for the gradation characteristics prepared for each basic color. There is a method of correcting a color tone correction curve (TRC) for the entire color reproduction tone range by estimating a change in tone characteristics using the method.

However, by estimating changes in the color gradation characteristics of the entire image by using a minute colorimetric area measured by the measurement sensor as a sample, it is possible to estimate the color composition (mixed color) of the part that is close to the part measured as the colorimetric area. can be corrected with high accuracy, but the accuracy of correction is lowered for portions different from the extracted mixed color.
Therefore, it is possible to simply acquire a large number of samples, but it is desirable to reduce the number of measurement sensors and the number of sample data as much as possible in order to reduce the time required for correction work and reduce costs.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of stably reproducing colors by accurately performing gradation correction, which tends to attract attention in the entire image. .

In order to solve the above-described problems, an image forming apparatus according to the present invention provides image output for outputting an image on a recording medium by mixing a plurality of basic colors based on an image data array formed by combining a plurality of basic colors. means for correcting the image output by the image output means using a tone correction value for correcting the tone characteristics of the basic colors for each of the basic colors; a measurement sensor for measuring the reflection characteristics of all or part of the at least one measurement channel having spectral characteristics ; an area specifying means for specifying an arbitrary range in the image by user selection; and by the area specifying means an area extracting means for extracting a first colorimetric area from within the specified arbitrary range and extracting a plurality of colorimetric areas having gradation characteristics different from the gradation characteristics of the colorimetric area; and the measurement sensor. a plurality of measured values including measured values of the colorimetric regions formed by combinations of the basic colors measured by; the image data array; and gradation correction value generating means for synthesizing the gradation correction values of the respective basic colors based on . A color combination is defined as a color of interest , and the measurement values relating to the color of interest measured by the measurement sensor are included as the plurality of measurement values, and the gradation correction values are synthesized.

According to the image forming apparatus of the present invention, it is possible to stably reproduce colors by accurately performing gradation correction that tends to attract attention in the entire image.

1 is a diagram illustrating an example of a configuration of an image forming apparatus according to an embodiment of the invention; FIG. 2 is a schematic diagram showing an example of a configuration of a control unit of the image forming apparatus shown in FIG. 1; FIG. 2 is a schematic diagram showing an example of the configuration of an image forming system of the image forming apparatus shown in FIG. 1; FIG. 4 is a flow chart showing an example of the operation of the image forming system shown in FIG. 3; FIG. 4A and 4B are diagrams showing an example of the operation of the area designating means and the area extracting means shown in FIG. 3; FIG. 4 is a diagram showing an example of another configuration of the area designating means shown in FIG. 3; FIG. FIG. 10 is a flow diagram showing an example of an operation for calculating a gradation correction value;

FIG. 1 shows an outline of the overall configuration of an image forming apparatus as an example of an image forming system according to this embodiment.
In this embodiment, the image forming apparatus 100 includes a paper feeding unit 2 that conveys paper P as a recording medium, a control unit 3 that forms image information based on input document data, and a transfer belt using image information. 47 has an image forming section 4 as image output means which is an electrophotographic printer engine for forming a toner image.
The image forming apparatus 100 also has a registration roller pair 22 that feeds the paper P supplied from the paper feed section 2 to the transfer section 5 at a predetermined timing.
The image forming apparatus 100 also includes a transfer section 5 as secondary transfer means for transferring the toner image carried on the transfer belt 47 onto the sheet P at a secondary transfer position N which is a nip portion with the transfer belt 47; It has a fixing section 6 that fixes the formed image, and a paper discharge section 7 that discharges the paper P to the outside.
The image forming apparatus 100 has a measurement sensor 45 that measures the reflective properties of the image. For example, the measurement sensor 45 is located downstream of the secondary transfer position N in the direction in which the paper P is conveyed, and measures the reflection characteristics of all or part of the image formed on the paper P. FIG.

The paper feed unit 2 has a paper feed port 20 and a plurality of paper feed rollers 21 for conveying the paper P fed from the paper feed port 20 to the transfer unit 5 .

The image forming section 4 has four process units 4Y, 4M, 4C, and 4K corresponding to yellow Y, magenta M, cyan C, and black K, which are a plurality of basic colors.
Since all of the process units 4Y, 4M, 4C, and 4K have the same configuration and the description is redundant, only the process unit 4Y corresponding to yellow Y will be described here.
The process unit 4Y includes a drum-shaped photoreceptor 40Y as an image carrier rotating in the direction A, which is the counterclockwise direction shown in FIG. 1, and a laser unit 53Y as an optical writing device as an optical scanning device. have. A photosensitive layer is formed on the surface of the photoreceptor 40Y, which is a surface to be scanned by the scanning light emitted from the laser unit 53Y.
The process unit 4Y also includes a charging device 42Y provided upstream in the A direction around the photoreceptor 40Y, a developing device 43Y as developing means, and a primary transfer means provided around a transfer belt 47. It has a next transfer roller 475Y.
The process unit 4Y also has a cleaning device 44Y provided downstream in the A direction from the contact position between the primary transfer roller 475Y and the photoreceptor 40Y.
The process unit 4Y also has a potential sensor, which is a surface potential sensor as surface potential detection means for detecting the surface potential of the photoreceptor 40Y.
The process unit 4Y forms a toner image of the basic color of yellow by forming a latent image on the photosensitive member 40Y with the laser unit 53Y.
The image forming section 4 produces images on the paper P by mixing basic colors based on image information, which is an image data array formed by combining a plurality of basic colors using the process units 4Y, 4M, 4C, and 4K. It is image output means for outputting a toner image as an image. That is, the image output means outputs a mixed-color image based on the image data array formed with a plurality of colors.

The transfer unit 5 includes a transfer belt 47, a drive roller 471 driven by a drive source so as to rotate in the B direction in FIG. 1, a driven roller 472 rotating in the B direction like the drive roller 471, and a secondary transfer roller. 473 and a secondary transfer opposing roller 474 provided to face the secondary transfer roller 473 .
In the transfer section 5, the secondary transfer facing roller 474 contacts the transfer belt 47 at the secondary transfer position N to form a nip section. At the secondary transfer position N, the transfer unit 5 sandwiches the transfer belt 47 together with the paper P between the secondary transfer facing roller 474 and the secondary transfer roller 473, and applies a secondary transfer bias to the surface of the transfer belt 47. The toner image is transferred to the paper P.
As the secondary transfer bias of the transfer unit 5 , a charge opposite to the static charge charged on the surface of the transfer belt 47 is applied.
The secondary transfer facing roller 474 conveys the sheet P after the secondary transfer at the secondary transfer position N to the fixing section 6 .

The transfer belt 47 is made of polyimide resin, which has little elongation, in which carbon powder is dispersed to adjust electrical resistance. 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, 475C, 475M, and 475K.

The measurement sensor 45 is an in-line type that combines multiple monochrome line sensors with band-pass filters corresponding to the three target colors of red, green, and blue attached to the front stage so as to have sensitivity to the three target colors of red, green, and blue. is a chromaticity measuring instrument. The measuring sensor 45 thus has measuring channels with three spectral characteristics, here corresponding to the three colors red, green and blue (R, G, B). The number of measurement channels that the measurement sensor 45 has is called the number of measurement channels.
The measurement sensor 45 may be a sensor having at least one measurement channel having spectral characteristics, in other words, a measurement channel sensitive to one or more basic colors, and may be a so-called color scanner. Also, as will be described later, a monochrome line sensor having a single spectral characteristic may be used.

The control unit 3 operates as communication control means for controlling two-way communication with a host device (for example, a personal computer) via a communication network or the like.
The control section 3 also operates as an image data processing means for sending image data created based on document data from a host device to the image forming section 4 .
As shown in FIG. 2, the control unit 3 includes an image processing unit 30 for receiving document data transmitted from a host device such as a personal computer 200 or a server 201 storing document data, and an image developed by the image processing unit 30. and a gradation processing unit 31 that converts information into image data in a format that the image forming unit 4 can receive.
The control unit 3 also includes an image inspection unit 33 that inspects the image output by the image forming unit 4 inline to detect image information, and a gradation processing unit that detects color tone variations of the image from the detected image information. and a color tone control unit 32 that gives a tone correction value to the color tone control unit 31 .
The control section 3 also has an engine control section 39 that controls the image forming section 4 .
Of the control unit 3 , the engine control unit 39 , the color tone control unit 32 , the gradation processing unit 31 and the image inspection unit 33 are provided in the image forming apparatus 100 . The image processing unit 30 is composed of software on a personal computer separate from the image forming apparatus 100 and an expansion board, and is a system that can be replaced independently of the image forming apparatus 100 .
Note that the image processing unit 30 may be provided on a terminal separate from the image forming apparatus 100 as long as it is arranged on the image forming system that performs the image forming, or may be provided on the server 201 or the personal computer 200 via a network. It may be provided above or above the image forming apparatus 100 .

As shown in FIG. 3, the image processing unit 30 includes an original color Lab converting means 310 for converting the original data Q into the Lab format, a LabCMYK converting means 311 for converting the Lab format into the CMYK format, and a selected color profile. and user gradation conversion means 312 for correcting the gradation based on.
The image processing unit 30 has a storage device 302 as a hard disk drive, which is storage means for temporarily or continuously storing each value of the calculated image data R and the like during image formation.

The gradation processing unit 31 calculates 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. ), a gradation correction unit 316 as gradation correction means for correcting an image to be output by the image forming unit 4, and a gradation conversion unit 317 for converting into a format that can be expressed by the image forming unit 4. ,have. In other words, the gradation correction unit 316 corrects the gradation characteristics of colors based on the gradation correction values.
Here, Δc(c) and the like indicate that the correction amount for the cyan C input tone value c is Δc(c). In the following description, Δc is simply written when the input gradation does not necessarily need to be specified.

The image inspection unit 33 has a scanner color Lab conversion means 318 for converting the image measured by the measurement sensor 45 into a Lab value, that is, obtaining a measured value.

The color tone control unit 32 includes a colorimetric prediction unit 34 that predicts and outputs the gradation of an image to be formed based on the image information input from the image processing unit 30, and a gradation prediction unit that generates a gradation correction value ΔCT. and a color tone correction amount determination unit 319 as tone correction value generation means.
The colorimetry prediction unit 34 includes a CMYKLab conversion unit 313 that converts the CMYK format into the Lab format, a scanner correction unit 325 that corrects the input value based on the reading error of the measurement sensor 45 given in advance, and a scanner color Lab conversion unit. 315. Here, the scanner color Lab conversion unit 315 and the scanner color Lab conversion unit 318 are conversion units having the same functions, and thus description thereof will be omitted.
A color tone correction amount determination unit 319 generates a tone correction value for each color by synthesizing correction arrays based on the reflection characteristics and the image data array.

When forming an image using the image forming apparatus 100 having such a configuration, first, as shown in FIG.
The manuscript data Q has a complicated data format including drawing commands for bitmaps, texts, and graphics whose colors are designated by RGB, CMYK, or the like.
The image processing unit 30 develops the received document data Q, and converts a pixel array composed of the basic colors of cyan C, magenta M, yellow Y, and black K possessed by the image forming unit 4, for example, color information of each pixel. It is transmitted to the gradation processing unit 31 as bitmap data arranged in a lattice.

The gradation processing unit 31 further converts the pixels into the number of gradations that can be expressed by the image forming unit 4, and transmits them to the image forming unit 4 as image data R, which is an image data array.
Based on the image data R received from the gradation processing unit 31, the image forming unit 4 outputs a toner image onto the transfer belt 47 by mixing yellow Y, magenta M, cyan C, and black K. The toner image on the transfer belt 47 is transferred to the paper P at the secondary transfer position N of .
The image inspection unit 33 scans the image on the sheet P using the reflection characteristics of the toner image detected by the measurement sensor 45, as will be described later. The color tone control unit 32 performs a tone correction operation, which will be described later, so as to minimize the deviation between the target reproduced color and the color development of the output image. By correcting the correction amount, the coloring of the image output to the paper P is stabilized.

After the toner images of all colors are transferred to the paper P having the toner image formed on its surface, the paper P enters the fixing section 6 and passes through the fixing nip portion N2 between the heating roller 161 and the fixing roller 162. At this time, the carried toner image is fixed by the action of heat and pressure, and a good color image is formed on the paper P.
The fixed paper P that has passed through the fixing section 6 is discharged from the paper discharging section 7 to the outside of the image forming apparatus 100 .
Alternatively, a switching claw and a double-sided unit may be provided in the paper ejection 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.

More detailed processing of tone correction will be described. In the following description, the format handled by the color tone control unit 32 is the Lab (CIELab) format, and the CMYK format color data of the document data Q is converted to the Lab format. A color expression format such as

Also, the original color Lab conversion means 310, LabCMYK conversion means 311, CMYKLab conversion means 313, scanner color Lab conversion means 315, 318, and Lab scanner color conversion 314 use basic data called a color profile for each color space conversion. need. Of these color profiles, those attached to the document data Q or prepared in advance are used as the color profiles required for conversion from document colors to Lab values. Color profiles necessary for the scanner color Lab conversion units 315 and 318 and the Lab scanner color conversion 314 are preset in the color tone control unit 32 and the image inspection unit 33, respectively.
Color profiles necessary for the LabCMYK conversion means 311 and CMYKLab conversion means 313 are selected from a plurality of color profiles stored in advance in the server 201 to match the type of paper P, because the color reproduction characteristics are affected by the type of paper P. It is desirable to select and set an appropriate color profile.
Such change of the color profile according to the type of paper P may be performed arbitrarily by the user, or may be performed automatically by the image processing unit 30 in accordance with the selection of the paper P that matches the input document data Q. .
As such a color profile, for example, an ICC profile defined by the ICC (International Color Consortium) may be used.

As shown in FIG. 4, the document data Q transmitted to the image processing unit 30 is converted by the document color Lab conversion means 310 from the color data expressed in the RGB format or the CMYK format to the device-independent Lab format table. The color values are converted into docLab values (step S100).
The LabCMYK conversion means 311 converts the docLab values of the basic colors cyan C, magenta M, yellow Y, and black K of the image forming unit 4 into gradation values prnCMYK, which are pairs of 8-bit integer gradation values (step S101).
In the initial state, the user gradation conversion means 312 outputs the gradation value prnCMYK as it is as the image data R without changing it (step S102).
These processes are performed simultaneously with vector data and font development. The image data R obtained as a result is output as bitmap data for four basic colors C, M, Y, and K obtained by quantizing the color information of the document data Q. FIG.
The output image data R is held in the storage device 302 of the image processing unit 30 for each document used for printing.

The gradation correction unit 316 corrects the gradation characteristics of colors based on the gradation correction values. For example, a gradation correction table (TRC: Tone Response Correction) is provided for each of the basic colors C, M, Y, and K, and the gradation of each basic color is corrected using a gradation correction value and a gradation correction table, which will be described later. The key is corrected (step S103).
The gradation conversion unit 317 converts the color value sent in 8 bits for each basic color so as to match the number of gradations expressible by the image forming unit 4, using the area gradation method or the error diffusion method. (Step S104).
The image forming section 4 thus receives the image data R that has been adjusted by the gradation processing section 31 into a format expressible by the image forming section 4, and forms a toner image (step S105).

The toner image formed by the image forming section 4 is transferred onto the sheet P by the transfer section 5 and then scanned using the reflection characteristics of the toner image measured by the measurement sensor 45 .
The image inspection unit 33 inputs the scanned image information to the scanner color Lab conversion unit 318 as the output measurement value mesCol.
The scanner color Lab conversion unit 318 converts the input output measurement value mesCol into a Lab value, thereby obtaining a Lab colorimetric value mesLab (step S106).

From the bitmap data accumulated in the storage device 302, the color tone correction amount determination unit 319 reads the required part of the gradation values prnCMYK in advance into the page buffer (step S107).
On the other hand, the color tone control unit 32 converts the CMYK format into the Lab format by the CMYKLab conversion means 313, and saves it as an output prediction value prnLab (step S108).
The output prediction value prnLab obtained by the color tone control unit 32 at this time is a value obtained by simulating the reproduction color of the image data R to be output as a Lab value.

Since the predicted output value prnLab does not include the reading error specific to the measurement sensor 45, if the predicted output value prnLab 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 predicted output value prnLab is There is a possibility that the output measurement value mesCol scanned by the measurement sensor 45 may be significantly different.
The scanner correction unit 325 calculates the scanner reading prediction value scnCol by correcting the output prediction value prnLab based on the reading error of the measurement sensor 45 given in advance (step S109).
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

When the scanner color Lab conversion unit 315 receives the scanner read prediction value scnCol from the scanner correction unit 325, it converts it into a Lab value and calculates a target value targetLab (step S110).
The colorimetry prediction unit 34 stores in the storage device 302 the result of calculating the target value targetLab for the entire print area to be printed in advance.

Based on the target value targetLab, the colorimetric value mesLab, and the tone value prnCMYK for the print area, the tone correction amount determination unit 319 determines the tone correction value ΔCT=( Δc, Δm, Δy, Δk).

Next, a method for determining the tone correction value ΔCT by the color tone correction amount determination unit 319 will be described.
First, prior to processing, a plurality of minute colorimetric areas {(xi, yi)}i=1, . . . , N are extracted. Here, the colorimetry area is represented by its center coordinates (x, y). 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.
It should be noted that x and y of the coordinate symbols described here assume the paper feeding direction in which the paper P is conveyed in the image forming apparatus, that is, the so-called sub-scanning direction, to be the coordinate y, and the main scanning direction orthogonal to the sub-scanning direction to be the coordinate. described as x.

Furthermore, the extracted minute colorimetric regions (hereinafter referred to as colorimetric regions) are sorted according to the following conditions.
First, the area designating means 320 sets the area in which the image of the paper P is formed, that is, the area having the largest area in the printing area, with respect to the area suitable for colorimetry on a single page or a plurality of pages.
As for the size of the occupied area at this time, the area occupied within the print area may be obtained, but obtaining the area of the irregularly shaped image area results in an enormous processing time.

Therefore, in this embodiment, the image forming apparatus 100 has an area designating means 320 and an area extracting means 321 as shown in FIG.
The area designating means 320 determines the degree of color mixture, which is the image data array configured for each colorimetric area described above, that is, the color configuration of the basic colors, and determines the degree of color mixture that is similar (or identical) in the color configuration. count areas. At this time, the region with the largest number of N colorimetric regions extracted with the same color configuration is the “colorimetric region of interest 322”.
In addition to the colorimetric region of interest 322, the region extracting means 321, when the color configuration of the selected colorimetric region of interest 322 is the color configuration colA, the color gradation of each basic color that composes the color configuration colA is , colorimetric regions 323 and 324 each having a color gradation corresponding to each range other than the range included when the color gradation range is divided into a plurality of areas are additionally selected.

Specifically, when printing the image data as shown in FIG. 5, the area designating means 320 designates the hatched area F among the areas filled with the same color (same color configuration) as the "designated arbitrary area". "the range of
Further, the region extracting means 321 extracts a colorimetry region within such an arbitrary range as a first colorimetry region, ie, a "target colorimetry region 322". In this embodiment, as already described, the area F is "the area having the largest area among the areas having the same or similar image data arrangement".
Since the plurality of colorimetric regions (x, y) included in the region F all have the same or similar color configuration, regardless of the position extracted from the region F, the "colorimetric region of interest 322" is Since they have the same color configuration, they do not depend on the positions shown in FIG.
Also, the color configuration of the colorimetry area of interest 322 is referred to as "color configuration colA".

Now, when the color configuration colA of the colorimetry area of interest 322 is represented by a mixture of the four basic colors of CMYK, it is assumed that colA = (C: 40%, M: 75%, Y: 45%, K: 10%). Suppose it is.
Thus, the color configuration colA is a numerical representation of the "combination of basic colors".
Furthermore, the color gradation range (gradation halftone dot rate 0 to 100%) of each basic color of the color configuration colA is changed to range 1 (0% to 39%), range 2 (40% to 69%), range 3 ( 70% to 100%). can be represented.

The region extracting means 321 extracts a second colorimetric region "colorimetric region 323" and a third colorimetric region "colorimetric region 324" having gradation characteristics of a color configuration different from the color configuration colA. and extract .
The colorimetry area 323 is, for example, a colorimetry area of color configuration colB=(C: 25%, M: 30%, Y: 75%, K: 50%). can be expressed as (C: Range 1, M: Range 1, Y: Range 3, K: Range 2).
In the present embodiment, the gradation characteristic of the color configuration colB is merely selected to be different from that of the color configuration colA, but the colorimetry area 323 is used as the second colorimetry area, and the first colorimetry area The gradation characteristic may be selected so as to have a gradation characteristic brighter than the gradation characteristic of the area.
The colorimetry area 324 is, for example, a colorimetry area of color configuration colC=(C: 72%, M: 10%, Y: 35%, K: 70%), and the gradation characteristics of the color configuration colC are can be expressed as (C: Range 3, M: Range 1, Y: Range 1, K: Range 3).
In this embodiment, the gradation characteristics of the color configuration colC are merely selected to be different from those of the color configuration colA. The gradation characteristics may be selected to have gradation characteristics that are darker than the gradation characteristics of the region.
Also, the colorimetric regions 323 and 324 may be colorimetric regions having gradation characteristics different from the color configuration colA, but all four basic colors have different gradation characteristics (that is, range 1 for C). , 3, one of ranges 1 and 2 for M, one of ranges 1 and 3 for Y, and one of ranges 2 and 3 for K).
However, if such a characteristic colorimetric area does not fall within the print area, the area extracting means 321 refers to the image data array of the document data Q across a plurality of pages, and extracts the colorimetric areas 323, 324 may be selected to extract the color configuration.

Alternatively, for each of C, M, Y, and K, for example, when looking at the basic color C, the color configuration colC-a (C: 20%, M: 40%, Y: 60% , K: 40%) and the color configuration colC-b (C: 70%, M: 0%, Y: 0%, K: 0%). A third colorimetric region may be selected to extract the color configuration.

Furthermore, if the colorimetry areas that meet the conditions are not available within a certain number of pages or within a certain processing time, the colorimetry area of interest 322 may be selected again under different conditions.

In the present embodiment, the colorimetry area of interest 322 is selected from the area F, that is, the area set by the area designating means 320 as the "specified arbitrary range".
However, the configuration is not limited to such a configuration, and the colorimetry area 322 may be extracted from an area G set as "an arbitrary range specified by the user" within the print area.
In this case, for example, as shown in FIG. may be specified in
The area specifying means 320 selects an arbitrary range specified by the user as an area G, and the area extracting means 321 extracts a colorimetry area of interest 322 from the area G. FIG.
Assuming that an arbitrary range designated by the user is selected as the region G in this way, the user designates a region of interest (in FIG. By doing so, the colorimetric area of interest 322 of the color configuration colA is determined.
With this configuration, the sample contains the "most noticeable" color configuration in the image as the color of interest. Colors can be reproduced stably.

Also in such a case, the region extracting means 321 extracts colorimetric regions 323 and 324 having color configurations colB and colC different from the color configuration colA, respectively.
In this way, by using at least three colorimetric regions to be extracted, and by using as samples the color configuration composed of the image data arrays different from each other, duplication of samples can be prevented and the number of samples can be minimized. While suppressing, it is possible to reproduce colors stably.

For the minute colorimetry area (xi, yi), N colorimetry areas are extracted from a single page or several consecutive pages, and the target value targetLab, the colorimetry value mesLab, and the gradation corresponding to the colorimetry area are extracted. A value prnCMYK is obtained for each tone area range (r). The gradation area range (r) is divided into gradation area ranges corresponding to a plurality of change mode numbers d. For example, in this embodiment, the change mode number d=3, and the gradation area range is divided into three areas.
Based on the target value targetLab corresponding to the colorimetric area acquired for each tone area range (r), the colorimetric value mesLab, and the tone value prnCMYK, the color tone correction amount determination unit 319 determines the change mode number d Each mode parameter θ(rd) corresponding to is calculated.
As a method of calculating the gradation correction value ΔCT based on each mode parameter θ(rd) thus calculated, there are calculation methods such as those described in paragraphs “0059” to “0074” of Patent Document 2, for example. The configuration is not limited, and a method of calculating the gradation correction value ΔCT using another feedback method may be used. Such a mode parameter θ(rd) functions as “change mode data that serves as a basis for approximating changes in gradation characteristics” in this embodiment.

FIG. 7 extracts a colorimetry area of interest 322 from within an area F that occupies the largest area in the print area, with respect to the area suitable for colorimetry, assuming that it is "within an arbitrary specified range". FIG. 10 is a flow chart for determining a mode parameter θ(rd) when colorimetry regions 323 and 324 having color configurations different from color configuration colA are extracted by region extracting means 321, with color configuration colA forming region F;

First, the area designating means 320 selects the area F, which is the area occupying the largest area within the printing area, from the image data Q of a single page or a plurality of pages to be printed as "within any specified range". (Step S300).
Selection of the area F may be performed by the user arbitrarily designating an area in the image in which the user particularly wants to stabilize the coloring.

Next, the area extracting means 321 extracts the colorimetric area 322 of the color configuration colA of the area F (step S301).
The region extracting means 321 extracts a colorimetric region 323 having a color configuration different from the color configuration colA, or having a gradation characteristic different from the gradation characteristics obtained when the color gradation range of the color configuration colA is divided into a plurality of areas. , 324 are extracted (step S302).

In step S302, the color configurations colB and colC of the extracted colorimetric regions 323 and 324 are determined to be "composed of color gradations corresponding to a color gradation range other than the color gradation range included in the color configuration colA. , in other words, a second colorimetric area "colorimetric area 323" and a third colorimetric area "colorimetric area 324" having gradation characteristics of a color configuration different from color configuration colA. and are extracted (step S303).

In step S303, if the extracted colorimetric regions 323 and 324 have different color configurations from the color configuration colA, the extraction process ends and the process proceeds to step S304. If the gradations of the color configurations colB and colC of the colorimetric regions 323 and 324 are in the same color gradation range as the color configuration colA, the process returns to step S302 to change the conditions of the colorimetric regions 323 and 324. to re-extract.

If the colorimetry areas 322, 323, and 324 having three mutually different color configurations colA, colB, and colC are not found even after repeating step S303 for a predetermined number of pages or for a predetermined time or more, the process returns to step S300. The color configuration colA may be reselected by reselecting the area F under different conditions.

A target value targetLab, a colorimetric value mesLab, and a gradation value prnCMYK are obtained for all the colorimetric regions 322, 323, and 324 extracted by the region extracting means 321 (step S304).

The color tone correction amount determination unit 319 calculates the tone correction value ΔCT for each tone area range (r) based on the acquired target value targetLab, colorimetric value mesLab, and tone value prnCMYK (step S305). .

By correcting the color gradation applied to the engine control unit 39 and the gradation processing unit 31 based on the calculated gradation correction value ΔCT, the coloring of the image output to the paper P can be stabilized.

Thus, the present invention provides a plurality of colorimetric values mesLab including measurements of colorimetric regions formed by combinations of basic colors measured by the measurement sensor 45, target values targetLab, tone values prnCMYK, a tone correction value generation step for deriving a tone correction value ΔCT for each of the basic colors based on the colorimetry composed of at least three mutually different image data arrays from within an arbitrary range specified in the image; and a region extracting step of extracting a region.
In such a configuration, the gradation correction value generating step sets one of the at least three colorimetric regions extracted by the region extracting step as a combination of basic colors as a target color, and the target color is measured by the measurement sensor 45. Using the measured value as the colorimetric value mesLab, the gradation correction value ΔCT is synthesized.

This embodiment has an area extraction means 321 for extracting a colorimetric area composed of at least three different image data arrays. Further, the color tone correction amount determination unit 319 serving as a tone correction value generation unit generates color tone correction values based on the colorimetric value mesLab obtained from the colorimetric areas 322, 323, and 324 by the measurement sensor 45, the target value targetLab, and the tone value prnCMYK. to synthesize the gradation correction value ΔCT.
With such a configuration, tone correction can be performed with high accuracy by using colorimetric values obtained from a plurality of colorimetric regions having different color configurations, so that colors can be reproduced stably.

Further, in this embodiment, there is an area specifying means 320 for specifying the arbitrary range in the manuscript data Q by user's selection, and the area extracting means 321 extracts at least one colorimetric area specified by the area specifying means 320. Obtained from within the above arbitrary range.
With such a configuration, the color structure of the most noticeable part specified by the user is included as the color of interest. Colors can be reproduced stably.

Further, in the present embodiment, there is an area specifying means 320 for specifying an area having the largest area among areas having the same or similar image data arrangement in the manuscript data Q as "within an arbitrary range", and the area extracting means 321 , at least one colorimetric area 322 is obtained from within an arbitrary range specified by the area specifying means 320 .
Here, the area with the largest area is defined as "within an arbitrary range", but it is not limited to such a configuration, and a portion with a relatively large area may be selected. Any area may be used as long as it allows selective designation of a portion to be emphasized in the image.
With such a configuration, the color structure of the portion that occupies a large area that is most likely to attract attention is included as the color of interest. can stabilize the reproduction of

In this embodiment, the area extracting means 321 extracts the first colorimetric area 322 from within the area F specified by the area specifying means 320, and has gradation characteristics different from the gradation characteristics of the colorimetric area 322. A plurality of colorimetric regions 323 and 324 are extracted.
With such a configuration, it is possible to stabilize the color reproduction of an image even in an image with color bias.
Furthermore, a second colorimetric region 323 having a gradation characteristic brighter than the gradation characteristics of the first colorimetric region 322 and a gradation characteristic darker than the gradation characteristics of the first colorimetric region 322 If the third colorimetry area 324 is extracted, gradation correction can be performed with high accuracy in all the divided gradation ranges when divided into three, so that stable color reproduction can be achieved.

Further, in this embodiment, if a colorimetric region having gradation characteristics different from the gradation characteristics of the colorimetric region 322 is not found, the region extracting means 321 extracts colorimetric data from another image output by the image output means. Regions 323 and 324 are extracted.
In this way, by selecting the colorimetry area over a plurality of pages of the document data Q, tone correction can be performed with high accuracy, so color reproduction can be stably performed.

In this embodiment, if colorimetric regions 323 and 324 having gradation characteristics different from the gradation characteristics of the colorimetric region 322 within the arbitrary range are not found within a predetermined time, the region specifying means 320 , to reset any range.
With such a configuration, if a colorimetry area that meets the conditions cannot be found, the colorimetry area of interest 322 can be reset, which contributes to shortening the time required for the calibration work.

Although preferred embodiments of the present invention have been described above, the present invention is not limited to such specific embodiments, and unless otherwise limited in the foregoing description, the present invention is set forth in the appended claims. Various modifications and changes are possible within the scope of the spirit.

For example, the color tone correction amount determination unit 319 uses the colorimetric value mesLab measured by the image inspection unit 33, the output prediction value prnLab, and the tone value prnCMYK to correct the tone correction table. A gradation correction value may be determined.

Further, although the image forming unit of the image forming apparatus uses an electrophotographic method using CMYK as basic colors, it may be an inkjet method, and the types of basic colors may be increased.

In this embodiment, the measurement sensor is installed downstream from the secondary transfer position and measures the reflection characteristics of the entire or part of the toner image formed on the paper. Reflective properties of all or part of the image may be measured.

The effects described in the embodiments of the present invention are merely enumerations of the most suitable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. isn't it.

100 Image forming apparatus 2 Paper feeding unit 3 Control unit 4 Gradation correction means (image forming unit) (Image output means)
5 transfer unit 22 registration roller pair 6 fixing unit 7 paper discharge unit 20 paper feed port 21 paper feed roller 30 image processing unit 31 gradation processing unit 33 image inspection unit 32 color tone control unit 39 engine control unit 45 measurement sensor 47 transfer belt 200 Personal computer 201 Server 302 Storage device 316 Gradation correction means (gradation correction unit)
325 scanner correction unit 34 colorimetric prediction unit 319 gradation correction value generation means (color tone correction amount determination unit)
320 area specifying means 321 area extracting means 322 colorimetric area of interest (first colorimetric area)
323 colorimetric area (second colorimetric area)
324 colorimetric area (third colorimetric area)
C, M, Y, K basic color mesLab measured value (colorimetric value)
F Arbitrary range (region)
f Color difference evaluation function G Arbitrary range (region)
ΔCT Gradation correction value R Image data

JP 2016-092653 A JP 2017-204786 A

Claims (5)

image output means for outputting an image on a recording medium by mixing basic colors based on an image data array formed by combining a plurality of basic colors;
gradation correction means for correcting the image output by the image output means using a gradation correction value for correcting the gradation characteristics of the basic colors for each of the basic colors;
a measurement sensor for measuring the reflective properties of all or part of said image with a measurement channel having at least one spectral property;
an area designating means for designating an arbitrary range in the image by user's selection;
Area extracting means for extracting a first colorimetric area from within the arbitrary range specified by the area specifying means, and extracting a plurality of colorimetric areas having tone characteristics different from tone characteristics of the colorimetric area. and,
a plurality of measured values including measured values of the colorimetric region formed by the combination of the basic colors measured by the measurement sensor; the image data array; gradation correction value generating means for synthesizing the gradation correction values for each of the basic colors based on mode data ;
has
The gradation correction value generating means sets the combination of the basic colors in the first colorimetric area as a color of interest , and includes the measurement values of the color of interest measured by the measurement sensor as the plurality of measurement values. An image forming apparatus, wherein the gradation correction values are synthesized. image output means for outputting an image on a recording medium by mixing basic colors based on an image data array formed by combining a plurality of basic colors;
gradation correction means for correcting the image output by the image output means using a gradation correction value for correcting the gradation characteristics of the basic colors for each of the basic colors;
a measurement sensor for measuring the reflective properties of all or part of said image with a measurement channel having at least one spectral property;
area designating means for designating the area having a large area among the areas having the same or similar image data arrangement in the image as being within an arbitrary range;
Area extracting means for extracting a first colorimetric area from within the arbitrary range specified by the area specifying means, and extracting a plurality of colorimetric areas having tone characteristics different from tone characteristics of the colorimetric area. and,
a plurality of measured values including measured values of the colorimetric region formed by the combination of the basic colors measured by the measurement sensor; the image data array; gradation correction value generating means for synthesizing the gradation correction values for each of the basic colors based on mode data;
has
The gradation correction value generating means sets the combination of the basic colors in the first colorimetric area as a color of interest, and includes the measurement values of the color of interest measured by the measurement sensor as the plurality of measurement values. An image forming apparatus that synthesizes tone correction values . 3. The image forming apparatus according to claim 1 , wherein
The area extracting means includes a second colorimetric area having a gradation characteristic brighter than the gradation characteristic of the first colorimetric area and a gradation characteristic darker than the gradation characteristic of the first colorimetric area. and a third colorimetric region having The image forming apparatus according to any one of claims 1 to 3 ,
If no colorimetric area having gradation characteristics different from the gradation characteristics of the colorimetric area within the arbitrary range specified by the area specifying means is found, the area extracting means causes the image output means to An image forming apparatus , wherein the colorimetric region is extracted from another image to be output . The image forming apparatus according to any one of claims 1 to 4 ,
If no colorimetric area having gradation characteristics different from the gradation characteristics of the colorimetric area within the arbitrary range specified by the area specifying means is found within a predetermined time, the area specifying means An image forming apparatus, wherein the arbitrary range is reset .

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