JP2018081244A - Image forming apparatus, image processing apparatus, and method for measuring patches - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy in measuring the colors of patches.SOLUTION: An image forming apparatus comprises: an image forming part that forms a plurality of patches in different colors on a sheet; an image reading part that reads the surface of the sheet to create image data; and a calibration part that acquires measurements of the colors of the patches from the created image data and executes calibration (S9). The calibration part includes an extraction part that extracts image areas of the patches from the created image data (S3), a profile creation part that averages pixel values of pixels arranged in one of a main scanning direction and a sub scanning direction in the image areas of the patches and creates profile data (S4), a noise removal part that executes noise removal processing on the profile data (S5), and a measuring part that averages the pixel values equal to or less than a threshold, of the pixel values of the profile data after the noise removal processing and outputs the averaged pixel values as the measurements of the colors of the patches (S6 to S8).SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus, an image processing apparatus, and a patch measuring method.

  In an image forming apparatus such as a printer or a copying machine, a plurality of patches having different colors are formed on a sheet, and the measured value of each patch color is obtained from image data generated by reading the sheet surface. Based on the above, calibration is performed to control the color and density of an image to be constant.

  There are image forming devices that place an image reading unit such as a line sensor on the internal conveyance path and read the surface of the paper being conveyed. However, foreign matter such as dust, dirt, and paper dust can enter between the paper and the image reading unit. In some cases, streak-like noise extending in the paper conveyance direction is generated in the image data generated by the image reading unit. When noise is superimposed, an accurate measurement value cannot be obtained, and the accuracy of calibration is reduced.

Conventionally, a foreign matter pattern is searched for in image data obtained by reading a background, and a noise portion where an approximate pattern is detected is replaced with a peripheral pixel to remove or dilute the noise to remove the foreign matter noise ( For example, see Patent Document 1.)
However, it is cumbersome to search for all foreign substances by pattern matching at the time of calibration, resulting in a delay in calibration that requires feedback. Further, the removal or dilution is performed by overwriting the data on the noise part, but if the image area of the calibration patch is overwritten, the purpose of obtaining the original measurement value may not be achieved.

In order to avoid noise superposition, it is also possible to form a patch avoiding a position where unevenness and streaks specified in advance occur (see, for example, Patent Document 2).
According to this method, noise is not superimposed on the measured value of the patch, but unevenness and streaks are avoided when the area where the patch is formed is limited, such as when a patch is formed with a job image. In some cases, there is not enough room to deal with it.

JP 2010-161694 A JP 2007-30340 A

  An object of the present invention is to improve the accuracy of patch color measurement.

According to the invention of claim 1,
An image forming unit that forms a plurality of patches of different colors on paper;
An image reading unit that reads the paper surface on which the plurality of patches are formed and generates image data;
A calibration unit that acquires a measurement value of the color of each patch from the image data generated by the image reading unit, and performs calibration of an image formed by the image forming unit according to the acquired measurement value. ,
The calibration unit
An extraction unit that extracts an image area of each patch from the image data generated by the image reading unit;
In the image area of each patch extracted by the extraction unit, a profile creation unit that averages the pixel values of the pixels arranged in one direction in the main scanning direction or the sub-scanning direction and creates profile data;
A noise removing unit that performs a noise removing process on the profile data;
Among the pixel values of the profile data after the noise removal processing, each pixel value below a threshold is averaged, and a measurement unit that outputs the average value as a measurement value of the color of each patch;
An image forming apparatus is provided.

According to invention of Claim 2,
The extraction unit acquires patch information including information on an arrangement position, size, and color of each patch on a sheet, and extracts an image area of each patch based on the acquired patch information. An image forming apparatus according to claim 1 is provided.

According to invention of Claim 3,
The image forming apparatus according to claim 1, wherein the noise removal process is a median filter process.

According to invention of Claim 4,
The image forming apparatus according to claim 3, wherein the noise removing unit changes a filter size of the median filter processing according to a size of noise to be removed.

According to the invention of claim 5,
5. The threshold value according to claim 1, wherein the threshold value is a threshold value for detecting a pixel value that causes the measured value of each patch to change to a measured value in which a color difference from the original measured value is a certain value or more. An image forming apparatus according to claim 1 is provided.

According to the invention of claim 6,
The calibration unit sets, as the threshold value, a pixel value when a color difference with a measured value when there is no noise of a patch of the smallest size among all the patches that can be formed is a certain value or more when there is no noise. Two threshold values obtained by adding and subtracting to the measured value of each patch are used, or the pixel value when the color difference from the average value of the profile data of the patch of the minimum size is a certain value or more, 6. The image forming apparatus according to claim 5, wherein two threshold values obtained by adding and subtracting to an average value of the profile data of the patch are used.

According to the invention of claim 7,
The image forming apparatus according to claim 1, wherein the calibration unit performs at least one calibration of an image density characteristic, a color, and a maximum density.

According to the invention described in claim 8,
A measured value of the color of each patch is acquired from image data generated by reading a sheet surface on which a plurality of patches having different colors are formed by the image forming unit by the image reading unit, and according to the acquired measured value, the image A calibration unit for calibrating an image formed by the forming unit;
The calibration unit
An extraction unit that extracts an image area of each patch from the image data generated by the image reading unit;
In the image area of each patch extracted by the extraction unit, a profile creation unit that averages the pixel values of the pixels arranged in one direction in the main scanning direction or the sub-scanning direction and creates profile data;
A noise removing unit that performs a noise removing process on the profile data;
Among the pixel values of the profile data after the noise removal processing, each pixel value below a threshold is averaged, and a measurement unit that outputs the average value as a measurement value of the color of each patch;
An image processing apparatus is provided.

According to the invention of claim 9,
Forming a plurality of patches of different colors on a sheet by an image forming unit;
A step of reading the sheet surface on which the plurality of patches are formed by an image reading unit to generate image data;
In the calibration unit, acquiring a measurement value of the color of each patch from the image data generated by the image reading unit, and performing calibration of an image formed by the image forming unit according to the acquired measurement value; With
The step of performing the calibration includes:
Extracting an image area of each patch from the image data generated by the image reading unit;
Averaging the pixel values of the pixels arranged in one direction of the main scanning direction or the sub-scanning direction in the image area of each extracted patch, and creating profile data;
Applying noise removal processing to the profile data;
Out of the pixel values of the profile data after the noise removal processing, averaging each pixel value below a threshold, and outputting the average value as a measured value of the color of each patch;
The method for measuring a patch is further provided.

  According to the present invention, the accuracy of patch color measurement can be increased.

1 is a block diagram illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention for each function. 6 is a flowchart illustrating a processing procedure when performing calibration in the image forming apparatus. FIG. 10 is a diagram illustrating an example of patches formed on the same page as a job image. FIG. 6 is a diagram illustrating an example of patches formed on a page different from a job image. It is a figure which shows the example of the image data produced | generated by reading. It is a figure which shows the example of the image data obtained by the image reading part with which the foreign material adhered to the reading surface. It is a figure which shows the example of profile data when there is no foreign material. It is a figure which shows the example of profile data when there exists a foreign material.

  Embodiments of an image forming apparatus, an image processing apparatus, and a patch measuring method according to the present invention will be described below with reference to the drawings.

FIG. 1 shows the main configuration of the image forming apparatus G of the present embodiment for each function.
As shown in FIG. 1, the image forming apparatus G includes a control unit 11, a storage unit 12, an operation unit 13, a display unit 14, a communication unit 15, an image generation unit 16, an image reading unit 17, an image memory 18, and an image processing unit. 19, an image forming unit 20, an image reading unit 30, and a calibration unit 40 are provided.

The control unit 11 includes a CPU (Central Processing Unit), a RAM (Random Access Memory), and the like, and controls each unit by reading and executing various programs from the storage unit 12.
For example, the control unit 11 causes the image processing unit 19 to perform image processing on the image data generated by the image generation unit 16 or the image reading unit 17 and held in the image memory 18, and based on the image data after the image processing. Then, the image forming unit 20 forms an image on the sheet.

  The storage unit 12 stores a program that can be read by the control unit 11 and the like, a file that is used when the program is executed, and the like. As the storage unit 12, a large-capacity memory such as a hard disk can be used.

  The operation unit 13 generates an operation signal corresponding to a user operation and outputs the operation signal to the control unit 11. As the operation unit 13, a keypad, a touch panel configured integrally with the display unit 14, or the like can be used.

  The display unit 14 displays an operation screen and the like according to instructions from the control unit 11. As the display unit 14, an LCD (Liquid Crystal Display), an OELD (Organic Electro Luminescence Display), or the like can be used.

The communication unit 15 communicates with external devices on the network, such as a user terminal, a server, and other image forming apparatuses.
The communication unit 15 receives data (hereinafter referred to as PDL data) in which an instruction content for forming an image is described in a page description language (PDL) from a user terminal or the like via a network.

  The image generation unit 16 rasterizes the PDL data received by the communication unit 15 to generate bitmap format image data. The image generation unit 16 can generate image data in which each pixel has pixel values of four colors of C (cyan), M (magenta), Y (yellow), and K (black), and R (red). , G (green), and B (blue) after generating image data having three color pixel values, image data of four colors C, M, Y, and K can be obtained by color conversion processing. The pixel value is a data value representing the density of the image. For example, an 8-bit data value represents the density of 0 to 255 gradations.

  The image reading unit 17 reads the paper surface set manually, and generates bitmap format image data having pixel values of R, G, and B colors. This image data may be converted into C, M, Y, and K color image data by the control unit 11 or a dedicated color conversion unit. As the image reading unit 17, a scanner or the like provided under the platen glass can be used, and an original can be automatically fed to the scanner with an automatic document reader (ADF).

  The image memory 18 is a buffer memory that temporarily holds the image data generated by the image generation unit 16. As the image memory 18, a DRAM (Dynamic RAM) or the like can be used.

The image processing unit 19 reads out image data from the image memory 18 and performs various image processing such as density correction processing, color correction processing, and halftone processing.
The density correction process is a process of converting each pixel value of the image data so that the density characteristic of the image to be formed becomes the target density characteristic. The color correction process is a process for converting the pixel value of each color of the image data so that the color of the image becomes a target color. The halftone process is a process for reproducing a pseudo multi-tone such as a screen process using an dither method and an error diffusion process.

  The image processing unit 19 converts pixel values using a look-up table (LUT) during density correction processing and color correction processing. The LUT is a table in which input values and output values are associated with each other so that a target density characteristic or color can be reproduced.

The image forming unit 20 forms an image of four colors on a sheet according to the four color gradation values of C, M, Y, and K of each pixel of the image data output from the image processing unit 19.
Specifically, the image forming unit 20 includes an exposure unit, a photoconductor, a development unit, and the like for each of C, M, Y, and K colors. The image forming unit 20 irradiates a laser beam modulated according to the gradation value of each pixel of the image data from the exposure unit, scans the charged photoreceptor, supplies toner from the development unit, and performs exposure. The electrostatic latent image formed on the photoreceptor is developed. In this way, the image forming unit 20 sequentially forms C, M, Y, and K color images on the respective photoconductors, and then superimposes them on the transfer body such as an intermediate transfer belt from each photoconductor. Transcript. The obtained color image is secondarily transferred from the transfer body onto the paper, and then a fixing process for heating and pressurizing the paper is performed.

  The image reading unit 30 is arranged on the sheet conveyance path, reads the sheet surface on which the image is formed by the image forming unit 20, and generates bitmap format image data having pixel values of R, G, and B colors. . As the image reading unit 30, a line sensor in which sensors such as a CCD are arranged one-dimensionally, an area sensor arranged in two dimensions, and the like can be used.

  The calibration unit 40 performs at least one calibration of the density, color, and maximum density of the image formed by the image forming unit 20, and controls the reproducibility of the image to be constant. Specifically, the calibration unit 40 causes the image forming unit 20 to form a calibration patch on a sheet, and causes the image reading unit 30 to read the sheet surface to generate image data. The calibration unit 40 acquires the measurement value of the color of each patch from the image data, and adjusts the image forming condition in the image forming unit 20 or adjusts the image processing condition of the image data according to the acquired measurement value. To do.

The calibration unit 40 includes an extraction unit 41, a profile creation unit 42, a noise removal unit 43, a measurement unit 44, and the like, as shown in FIG. 1, in order to acquire measurement values of the colors of the patches.
The processing content of the extraction unit 41, the profile creation unit 42, the noise removal unit 43, the measurement unit 44, and the like of the calibration unit 40 is an image processing circuit such as an ASIC (Application Specific Integrated Circuit) or FPGA (Field-Programmable Gate Array). It can also be realized by hardware processing, or can be realized by software processing in which a processor such as a CPU or GPU (Graphics Processing Unit) reads and executes a program.

  The extraction unit 41 extracts the image area of each patch from the image data generated by the image reading unit 30.

  The profile creation unit 42 creates profile data by averaging pixel values of pixels arranged in one direction in the main scanning direction or the sub-scanning direction in the image area of each patch extracted by the extraction unit 41.

  The noise removal unit 43 performs noise removal processing on the profile data created by the profile creation unit 42.

  The measurement unit 44 averages pixel values equal to or less than the threshold value among the pixel values of the profile data subjected to noise removal processing by the noise removal unit 43, and outputs the average value as a measurement value of the color of each patch.

FIG. 2 shows a processing procedure when performing calibration in the image forming apparatus G.
As shown in FIG. 2, in the image forming apparatus G, the calibration unit 40 generates image data in which a plurality of patches having different calibration colors are arranged on the image data generated by the image generation unit 16 or the like in the job. Based on the image data, the image forming unit 20 forms each patch on the sheet together with the job image (step S1). Job images and patches can be placed on the same page of paper, or on different pages of paper. The image reading unit 30 reads this sheet surface and generates image data (step S2).

FIG. 3A shows an example of a patch formed with a job image on one page of paper.
As shown in FIG. 3A, a job image 51 is formed in the center of the sheet S, and a plurality of calibration patches 52 are formed in the margin in the sheet S and the empty area Sn to be cut. When all the patches 52 cannot be formed on one page of paper S, each patch 52 can be formed separately on a plurality of pages of paper S.

FIG. 3B shows an example of a patch formed on a sheet of a page different from the job image.
As shown in FIG. 3B, a plurality of calibration patches 52 are formed on the entire surface of the sheet S. The patch 52 can be formed before or after the job image is formed on each sheet.

  In the calibration unit 40, the extraction unit 41 acquires patch information of each patch. The patch information includes information such as the arrangement position, size, and color of each patch on the paper, and can be acquired from image data generated by arranging each patch during patch formation. For example, the patch placement position information includes the patch start point and the coordinate positions of the pixels at the four corners (coordinate positions in the main scanning direction x and the sub-scanning direction y with the paper start point as the origin), and the size information includes The length (number of pixels) in the main scanning direction x and the sub-scanning direction y is mentioned. The patch size may differ depending on the calibration target such as density, color, and maximum density. The patch color information includes C, M, Y, and K pixel values set in the patch. The extraction unit 41 extracts the image area of each patch from the image data generated by the image reading unit 30 based on the acquired patch information (step S3).

FIG. 4 shows an example of image data generated by reading.
Since the reading range of the image reading unit 30 is larger than the size of the paper, the image data includes an image area 61 of the paper and an image area 62 of the background as shown in FIG. The extraction unit 41 detects the outline of the image area 61 of the paper from the difference between the pixel values of the image areas 61 and 62, and based on the positions of the four corners of the outline of the detected image area 61, the four corners of each acquired patch are detected. A rectangular area connecting the four corners of each patch in the image area 61 whose position is specified by projective transformation of the coordinate position can be extracted as the image area 63 of each patch.

Similarly, the position of one of the four corners of the patch in the image area 61 is specified, and the rectangular area having the size in the main scanning direction x and the sub-scanning direction y of the acquired patch is obtained from the specified one point. It can also be extracted as an image area 63.
Further, a window area larger than the patch size is expanded within a certain range from the position coordinates of the four corners of the patch in the image area 61, and a rectangular area having a pixel value matching the patch color information is patched in the window area. The image area 63 can be extracted.

  Alternatively, as shown in FIG. 4, the image forming unit 20 forms reference images 64 for detecting the positions of registration marks and the like together with the patches at the four corners of the sheet, and the extracting unit 41 generates the reference image 64 in the image area 61 of the sheet. The position of each patch may be identified by the above-described projective transformation based on the position of the reference image 64, and the image area 63 may be extracted.

  In order to avoid mixing image areas other than the target patch such as adjacent patches, the extraction unit 41 is further inward from the image area 63 of the extracted patch by a certain distance such as an internal image area, for example, 10 pixels. It is preferable to extract the located image region.

  Next, in the extracted image area of each patch, the profile creation unit 42 averages the pixel values of the pixels arranged in one direction of the main scanning direction x or the sub scanning direction y to create profile data (step S4). . When the number of pixels in the main scanning direction x of the image area of the patch is represented as N and the number of pixels in the sub scanning direction y is represented as M, the profile data obtained by averaging in the sub scanning direction y has a size of N × 1 pixel. The profile data obtained by averaging in the main scanning direction x has a size of M × 1 pixel.

  The calibration unit 40 averages the pixel values of the pixels arranged in the other direction in the generated profile data, and outputs the obtained average value as a measured value of the color of each patch. In the case where a foreign substance has entered, if the pixel value in the image area of the patch varies greatly due to the foreign substance, an accurate measurement value cannot be acquired.

FIG. 5 shows an example of image data obtained by the image reading unit 30 in which foreign matter adheres to the reading surface.
When a foreign object adheres to the reading surface, the image data obtained by the image reading unit 30 continuously reading in the sheet conveyance direction includes a sub image at the position where the foreign object has adhered, as indicated by a black arrow in FIG. Striped noise extending in the scanning direction y is generated.

6A and 6B show examples of G profile data when there is no foreign matter and when there is no foreign matter, respectively.
When an inner patch image region 65 is extracted from the patch image region 63, the pixel values of the pixels arranged in the sub-scanning direction y in the image region 65 are averaged as shown in FIGS. 6A and 6B. In addition, profile data in the main scanning direction x can be created. If the pixel values of the pixels arranged in the main scanning direction x of the profile data are further averaged, a measured value of the color of the patch can be obtained.

  When there is no foreign matter, the pixel value of the profile data is the same value for every pixel in the main scanning direction x as shown in FIG. 6A, but when there is a foreign matter, the image area of the patch is shown in FIG. 6B. A streak-shaped noise is superimposed on 65, and the pixel value greatly fluctuates locally. If the pixel values of the pixels arranged in the main scanning direction x of the profile data are further averaged, the average value when there is a foreign object is shifted from the average value when there is no foreign object due to noise. If this deviation is large, the accuracy of calibration decreases.

  In order to remove such noise due to foreign matter, the noise removal unit 43 performs noise removal processing on the created profile data (step S5).

Examples of the noise removal processing include moving average filter processing, median filter processing, and the like. Among these, median filter processing is preferable because noise can be accurately removed.
The median filter process is a process of replacing the pixel value of the target pixel with the median value when the pixel values of the target pixel and the peripheral pixels of the target pixel are arranged in the order of size. Noise that differs greatly from the original patch pixel value is removed by replacing it with the median value, that is, the patch pixel value.

If the streak is thick and the range in which noise occurs is larger than ½ of the size of the filter, noise may remain even after median filtering.
In order to remove noise as much as possible, the noise removal unit 43 preferably changes the filter size of the median filter according to the size of noise to be removed. For example, if noise remains even after median filter processing with a filter size of 5x5 pixels, increase the filter size stepwise, such as switching to a larger size of 7x7 pixels, and then repeat median filter processing. Just give it. The size of the filter after switching may be the size specified by the user.

Next, the measurement unit 44 compares each pixel value of the profile data after the noise removal processing with the threshold value Th, and determines whether all the pixel values are equal to or less than the threshold value Th (step S6).
The threshold value Th is a threshold value for detecting a pixel value that changes the measured value of each patch to a measured value in which the color difference from the original measured value is a constant value, for example, 1 or more. The constant value can be set according to the accuracy of the target calibration. However, when the constant value is 1, the color difference caused by noise can be made less than 1, and sufficient calibration accuracy can be obtained. it can.

  The threshold value Th has a constant color difference from the measured value when there is no noise of the smallest patch among all patches that can be formed for various calibrations such as density correction, color correction, and maximum density correction. The pixel values as described above can be obtained by adding or subtracting to the measured value of each patch when there is no noise. The measurement value when there is no noise is, for example, the original measurement value (pixel value of each patch in the image data) or the measurement value obtained by the measurement unit 44 from the image area of each patch that is confirmed to be free of noise. It is.

  Specifically, assuming that noise having a pixel width that cannot be removed by the median filter, for example, 14 pixels or more, is generated, the minimum size patch is 66 pixels wide. When the average value of the entire image area of the patch changes by one, the threshold value Th can be obtained by adding or subtracting the pixel value C to the measurement value when there is no noise.

  Alternatively, the threshold value Th is obtained by adding or subtracting a pixel value C having a color difference equal to or greater than a certain value from the average value of the profile data of the smallest size patch among all the patches that can be formed. Also good. In this case, the threshold value Th can be determined every time the color of the patch is measured, and it is possible to cope with a difference in the model of the image forming apparatus G.

  Since there is a noise of not only the maximum peak as shown in FIG. 6B but also a minimum peak depending on the foreign matter, the threshold value Th is a pixel value C at which the color difference is equal to or greater than a certain value in the measured value of each patch when there is no noise. It is preferable to use two threshold values obtained by addition and subtraction. As a result, not only the black streak noise component but also the white streak noise component can be removed.

The color difference is the R, G, and B of the measured value of each patch and the original measured value (the R, G, and B pixel values converted from the C, M, Y, and K pixel values of each patch in the image data). The respective color differences ΔR, ΔG, and ΔB may be used, or ΔEab may be used. ΔEab can be obtained by converting each pixel value of R, G, and B to be compared to a pixel value of L ^* a ^* b ^* and calculating the difference from each difference ΔL ^* , Δa ^*, and Δb ^* by the following equation.
ΔEab = {(ΔL ^* ) ² + (Δa ^* ) ² + (Δb ^* ) ² } ^1/2

  When all the pixel values of the profile data are within the threshold value Th (step S6: Y), the measurement unit 44 averages the pixel values of the profile data and outputs the obtained average value as a measured value of the color of the patch. (Step S8). When the profile data is created by averaging in the sub-scanning direction y, the measurement unit 44 averages the pixel values of the pixels arranged in the main scanning direction x of the profile data, and creates the profile data by averaging in the sub-scanning direction y. In this case, the pixel values of the pixels arranged in the sub-scanning direction y of the profile data are averaged.

  On the other hand, when all the pixel values are not equal to or less than the threshold value Th and there are pixel values exceeding the threshold value Th in the profile data (step S6: N), the measurement unit 44 does not exceed the threshold value Th among the pixel values of the profile data. Are extracted (step S7). For example, the measurement unit 44 discards the pixel value portion (hatched portion) exceeding the threshold value Th in FIG. 6B and extracts the remaining pixel values below the threshold value Th. The measuring unit 44 averages the extracted pixel values, and outputs the obtained average value as a measured value of the patch (step S8). As a result, a noise component that reduces the accuracy of calibration can be removed, and a measured value of the color of the patch can be obtained using pixel values that do not affect the calibration. As shown in FIG. 6B, the average value of the pixel values equal to or less than the threshold value Th after the noise removal processing is the same as that when there is no foreign object shown in FIG. 6A.

  When the measurement value of the color of each patch is obtained, the calibration unit 40 performs calibration using the measurement value of the color of each patch (step S9). Specifically, the calibration unit 40 is used for the density correction process and the color correction process so that the density characteristic or color of the image becomes the target density characteristic or color according to the acquired measurement value of each patch. Image processing conditions are adjusted by updating the LUT. In addition, the calibration unit 40 sets image forming conditions such as a developing bias potential and a laser power of a laser beam at the time of exposure so that the maximum density of the image becomes a target density according to the acquired measurement value of each patch. It can also be adjusted.

  In the above-described processing procedure, the calibration unit 40 can acquire measurement values for all the colors R, G, and B as the measurement values for the color of the patch. It is also possible to select a color complementary to the color and obtain only the measured value of the selected color. For example, in the case of a C color patch, an R measurement value, in the case of an M color patch, a G measurement value, in a Y color patch, a B measurement value, and in a K color patch, a G measurement value. Get it. Since the color having the complementary color relationship has high sensitivity to the color of the patch, the accuracy of the calibration is improved by using the measurement value of the color having the complementary color relationship for the calibration. If the patch is a mixed color, for example, if it is a mixed color of C and M, the measured values of R and G can be acquired and calibration can be performed according to the ratio of the mixed color.

  As described above, the image forming apparatus G according to the present embodiment includes the image forming unit 20 that forms a plurality of patches having different colors on a sheet, and the image reading unit 30 that reads the sheet surface and generates image data. A calibration unit 40 that acquires a measurement value of the color of each patch from the image data generated by the image reading unit 30 and performs calibration of an image formed by the image forming unit 20 according to the acquired measurement value; The calibration unit 40 extracts an image area of each patch from the image data generated by the image reading unit 30, and the main scanning direction in the image area of each patch extracted by the extraction unit 41. a profile creating unit 42 that averages pixel values of pixels arranged in one direction of x or the sub-scanning direction y and creates profile data; The noise removal unit 43 that performs noise removal processing on the image data, averages each pixel value that is equal to or lower than the threshold Th among the pixel values of the profile data after the noise removal processing, and outputs the average value as a measurement value of the color of each patch And a measurement unit 44 that performs the measurement.

  Even when noise is superimposed, noise removal processing is performed on the profile data, and noise that cannot be removed is excluded by removing large noise components that exceed the threshold, and the average value of the pixel values in the image area of the patch is obtained. Thus, an accurate measurement value close to the original patch measurement value without noise can be obtained, and the patch color measurement accuracy can be improved. By using accurate measurements, calibration accuracy is also improved. Since noise removal is performed on the average value in the image area of the patch, it is simple and efficient.

The above embodiment is a preferred example of the present invention, and the present invention is not limited to this. Modifications can be made as appropriate without departing from the spirit of the present invention.
For example, calibration can be performed by reading the sheet surface on which each patch is formed by the image reading unit 17, and in this case, the measurement accuracy of the color of the patch can be improved by the above processing procedure.
In addition to the image forming apparatus G, an image processing apparatus such as a general-purpose PC can include the calibration unit 40 and execute the above-described processing procedure.

  As a computer-readable medium for the program, a non-volatile memory such as a ROM and a flash memory, and a portable recording medium such as a CD-ROM can be applied. A carrier wave is also used as a medium for providing program data via a communication line.

G Image forming apparatus 11 Control unit 12 Storage unit 20 Image forming unit 30 Image reading unit 40 Calibration unit 41 Extraction unit 42 Profile creation unit 43 Noise removal unit 44 Measurement unit

Claims (9)

An image forming unit that forms a plurality of patches of different colors on paper;
An image reading unit that reads the paper surface on which the plurality of patches are formed and generates image data;
A calibration unit that acquires a measurement value of the color of each patch from the image data generated by the image reading unit, and performs calibration of an image formed by the image forming unit according to the acquired measurement value. ,
The calibration unit
An extraction unit that extracts an image area of each patch from the image data generated by the image reading unit;
In the image area of each patch extracted by the extraction unit, a profile creation unit that averages the pixel values of the pixels arranged in one direction in the main scanning direction or the sub-scanning direction and creates profile data;
A noise removing unit that performs a noise removing process on the profile data;
Among the pixel values of the profile data after the noise removal processing, each pixel value below a threshold is averaged, and a measurement unit that outputs the average value as a measurement value of the color of each patch;
An image forming apparatus comprising:   The extraction unit acquires patch information including information on an arrangement position, size, and color of each patch on a sheet, and extracts an image area of each patch based on the acquired patch information. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, wherein the noise removal process is a median filter process.   The image forming apparatus according to claim 3, wherein the noise removing unit changes a filter size of the median filter processing according to a size of noise to be removed.   5. The threshold value according to claim 1, wherein the threshold value is a threshold value for detecting a pixel value that causes the measured value of each patch to change to a measured value in which a color difference from the original measured value is a certain value or more. The image forming apparatus according to claim 1.   The calibration unit sets, as the threshold value, a pixel value when a color difference with a measured value when there is no noise of a patch of the smallest size among all the patches that can be formed is a certain value or more when there is no noise. Two threshold values obtained by adding and subtracting to the measured value of each patch are used, or the pixel value when the color difference from the average value of the profile data of the patch of the minimum size is a certain value or more, 6. The image forming apparatus according to claim 5, wherein two threshold values obtained by adding and subtracting to an average value of the profile data of the patch are used.   The image forming apparatus according to claim 1, wherein the calibration unit performs at least one calibration of an image density characteristic, a color, and a maximum density. A measured value of the color of each patch is acquired from image data generated by reading a sheet surface on which a plurality of patches having different colors are formed by the image forming unit by the image reading unit, and according to the acquired measured value, the image A calibration unit for calibrating an image formed by the forming unit;
The calibration unit
An extraction unit that extracts an image area of each patch from the image data generated by the image reading unit;
In the image area of each patch extracted by the extraction unit, a profile creation unit that averages the pixel values of the pixels arranged in one direction in the main scanning direction or the sub-scanning direction and creates profile data;
A noise removing unit that performs a noise removing process on the profile data;
Among the pixel values of the profile data after the noise removal processing, each pixel value below a threshold is averaged, and a measurement unit that outputs the average value as a measurement value of the color of each patch;
An image processing apparatus comprising: Forming a plurality of patches of different colors on a sheet by an image forming unit;
A step of reading the sheet surface on which the plurality of patches are formed by an image reading unit to generate image data;
In the calibration unit, acquiring a measurement value of the color of each patch from the image data generated by the image reading unit, and performing calibration of an image formed by the image forming unit according to the acquired measurement value; With
The step of performing the calibration includes:
Extracting an image area of each patch from the image data generated by the image reading unit;
Averaging the pixel values of the pixels arranged in one direction of the main scanning direction or the sub-scanning direction in the image area of each extracted patch, and creating profile data;
Applying noise removal processing to the profile data;
Out of the pixel values of the profile data after the noise removal processing, averaging each pixel value below a threshold, and outputting the average value as a measured value of the color of each patch;
A method for measuring a patch, further comprising:

Images