JP2023020165A - Image processing apparatus and image forming apparatus and method for controlling these, and program - Google Patents

Abstract

To detect the image quality characteristics of a printed thin line precisely with high accuracy.SOLUTION: An image processing apparatus 102 comprises: an image input unit 201 that acquires image data of a thin line image created by reading, with a scanner 101, a printed material on which a thin line with a known line width is formed; a paper white area extraction unit 202 that extracts a paper white area in the thin line image; a paper noise analysis unit 203 that analyzes image data of the paper white area to detect paper noise of the thin line image; a paper noise reduction unit 204 that reduces the paper noise of the thin line image detected by the paper noise analysis unit 203; and a thin line measuring unit 205 that measures the image quality characteristics of the thin line from the thin line image whose paper noise is reduced by the paper noise reduction unit 204.SELECTED DRAWING: Figure 2

Description

The present invention implements an image processing apparatus for inspecting the image quality characteristics of fine lines printed on a recording material such as paper, a control method thereof, an image forming apparatus including this image processing apparatus, a control method thereof, and each control method. about the program for

One of the performances required of an image forming apparatus using an electrophotographic system (hereinafter referred to as "printer") is the performance of forming fine lines on paper with high reproducibility. However, in a printer using an electrophotographic system, thin lines are often printed thinly and blurred. Therefore, the reproducibility is improved by thickening or darkening the fine lines through correction. In printers using an electrophotographic system, the print reproducibility of fine lines varies from device to device, so the line width of fine lines is accurately measured for each device, and corrections are made based on the measured line width. You need to control the amount.

An example of technology for measuring the width and density of a line image formed on a sheet is described in Japanese Patent Application Laid-Open No. 2002-200012. Specifically, in Patent Document 1, first, a standard line image with clear edges prepared by photoengraving or the like is first read by a CCD camera, and a slice level as a line width is obtained from the profile of the read line image. Then, from the obtained slice level and the profile of the line image obtained by reading the image to be inspected (printed matter), the line width of the thin line in the image to be inspected is obtained. In the line width measurement, first, the maximum reflectance Rmax, the minimum reflectance Rmin, and the reflectance Rn for the line width are obtained within the integrated reflectance profile of the standard line image. Next, a thin line in the image to be inspected is similarly processed, and the distance corresponding to the reflectance Rn is taken as the line width of the thin line.

JP-A-10-283483

The minimum reflectance Rmin has a small value at the portion where the density of the thin line is the highest, that is, the portion where the thin line is printed with the highest density. When the minimum reflectance Rmin increases, that is, when the fine line density decreases (thin lines become thin), the reflectance Rn, which is the reference value for determining the line width, increases, and nothing is printed on the surface of the paper. The reflectance Rn approaches the density of unevenness of the area (hereinafter referred to as "paper noise"). As a result, by measuring the paper noise as the reflectance Rn, the line width is measured as a value larger than the value that should be measured. Thus, when the density of the printed thin line is low, it may not be possible to measure the line width accurately.

To address this problem, there is a method of increasing the accuracy of line width measurement by increasing the resolution when reading (images of) printed matter. However, the higher the resolution at the time of reading, the more clearly the unevenness of the fibers on the surface of the paper can be read. may be read as

Furthermore, from the viewpoint of effective use of resources, the frequency of use of recycled paper is increasing. However, since the unevenness of the fibers on the surface (printing surface) of recycled paper is easy to see, when the image is read with a high-resolution scanner, the above-mentioned False positives are more likely to occur. In this way, there are increasing situations where it is not easy to measure the line width accurately.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing apparatus capable of detecting the image quality characteristics of printed fine lines with high accuracy.

An image processing apparatus according to the present invention includes an acquisition means for acquiring image data of a fine line image generated by reading a printed matter on which fine lines having a known line width are printed with a scanner, and a paper white area in the fine line image. extraction means for extracting, analysis means for detecting paper noise in the fine line image by analyzing image data of the paper white area, reduction means for reducing paper noise in the fine line image detected by the analysis means, measuring means for measuring image quality characteristics of the fine lines from the fine line image in which the paper noise has been reduced by the reducing means.

According to the present invention, it is possible to accurately detect the image quality characteristics of printed thin lines with high accuracy.

1 is a diagram showing a schematic configuration of a fine line measurement system including an image processing device according to a first embodiment; FIG. 1 is a diagram showing a schematic configuration of functional blocks of an image processing apparatus according to a first embodiment; FIG. 5 is a flow chart showing a line width measurement procedure of a fine line in the fine line measurement system; FIG. 2 is a diagram showing an image reading surface of a printed matter whose image is read by a scanner; 4A and 4B are schematic diagrams showing states of paper noise in a paper white area before and after paper noise reduction processing; FIG. FIG. 4 is an enlarged view of a measurement region cut out from a thin line image; 10 is a flowchart showing details of line width measurement processing in S306. FIG. 4 is a diagram representing a reflectance profile on a horizontal line with a measurement area; FIG. 4 is a schematic diagram showing an example of a reflectance profile of a low-density thin line and a method of measuring line width; FIG. 10 is a diagram showing a schematic configuration of a printing system including an image forming apparatus according to a second embodiment; FIG. 2 is a diagram showing a schematic configuration of functional blocks of the image forming apparatus; FIG. 2 is a block diagram showing an example of an image processing section included in the image forming apparatus; FIG. 4 is a flowchart showing an example of automatic fine line correction processing executed by the image forming apparatus; 4 is a diagram showing an example of a UI screen displayed on the UI display unit 4 when automatic fine line correction processing is executed; FIG. It is a figure which shows an example of the relationship between a line width measurement value, a correction amount, and an additional pixel value. It is a schematic diagram explaining a fine line correction method. FIG. 4 is a schematic diagram showing a method of modulating the exposure amount by adjusting the laser power; FIG. 4 is a diagram showing functional blocks and a measurement example for obtaining a line width from the center of a thin line;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a diagram showing a schematic configuration of a fine wire measurement system 100 according to an embodiment of the present invention. A fine line measurement system 100 has a scanner 101 , an image processing device 102 and a monitor 103 . The scanner 101 scans (reads) an image on a sheet, which is an example of a recording material, to generate image data, and supplies the image data to the image processing apparatus 102 . The scanner 101 is connected to the image processing apparatus 102 via a network 104 such as LAN or WAN, or via a USB cable or the like so as to be able to communicate bidirectionally.

The image processing device 102 is, for example, a personal computer (PC). Although not shown, the image processing apparatus 102 has a CPU that executes arithmetic processing and a ROM that stores an OS and the like for performing basic operations of the image processing apparatus 102 . The image processing apparatus 102 also includes a RAM for the CPU to expand various programs and temporarily store calculation results, and a storage device such as an SSD for storing various applications (programs). One of the applications stored on the memory device is a program that executes an algorithm for measuring fine line quality characteristics. The CPU of the image processing apparatus 102 measures the image quality characteristics of fine lines by executing this program. The monitor 103 displays an operation screen for executing an algorithm for measuring fine line image quality characteristics, and also displays results of measurement of fine line image quality characteristics by the image processing device 102 .

FIG. 2 is a diagram showing a schematic configuration of functional blocks of the image processing apparatus 102. As shown in FIG. The image processing apparatus 102 includes an image input unit 201 , a paper white area extraction unit 202 , a paper noise analysis unit 203 , a paper noise reduction unit 204 and a fine line measurement unit 205 . The CPU of the image processing apparatus 102 functions as each of these units by executing a predetermined program stored in the storage device.

The image input unit 201 receives image data (hereinafter referred to as "fine line image data") of an image (hereinafter referred to as "fine line image") generated by scanning the image on the printed material with the scanner 101 to measure the line width of the fine line on the printed material. ) is obtained. Note that the fine line image will be described later with reference to FIG. Note that the image input unit 201 may have a function of instructing the scanner 101 to read the image on the printed matter.

A paper white area extraction unit 202 extracts a paper white area from the fine line image. The paper noise analysis unit 203 uses the extracted image data of the paper white area to analyze paper noise such as unevenness of fibers on the printing surface of the printed matter. The paper noise reduction unit 204 performs processing (paper noise reduction processing) for reducing paper noise included in the fine line image on the fine line image data. A fine line measurement unit 205 obtains image quality characteristics of fine lines from fine line image data after paper noise reduction processing.

FIG. 3 is a flow chart showing the procedure for measuring the line width of a fine line by the fine line measuring system 100. As shown in FIG. Each process (step) denoted by S number in the flowchart of FIG. 3 is implemented by the CPU expanding the program stored in the storage device into the RAM and functioning as each unit shown in FIG.

In S301, the CPU executes an algorithm for measuring fine line image quality characteristics. Here, a case of measuring the line width as one of the image quality characteristics of fine lines will be described. However, as the image quality characteristics of fine lines, other than the line width, such as raggedness, blur, and density can be measured in the same manner as the line width measurement.

In S<b>302 , the CPU functions as the image input unit 201 and acquires fine line image data from the scanner 101 . Here, the fine line image data will be described. FIG. 4 is a diagram showing the surface (image reading surface) of a printed matter 400 whose image is read by the scanner 101. As shown in FIG. The thin line image data is obtained by reading the surface of the printed matter 400 on which thin lines 401 having a predetermined line width are printed at predetermined positions with the scanner 101 . The resolution of image reading by the scanner 101 is assumed to be 2400 dpi.

Here, as an example, the scanner 101 reads a printed matter 400 on which a plurality of fine lines 401 having a line width of 0.12 pt (a width of 1 dot at 600 dpi (approximately 42 μm)) is printed, thereby obtaining fine line image data. there is The reason why the printed material 400 printed with the thin line 401 having a known line width is used is to know the printing characteristics of a printing device (not shown) that prints the thin line 401 . Although 0.12 pt is used as the line width of the thin line 401 here, the line width of the thin line 401 is not limited to this as long as it is known. A configuration for feeding back the measured value of the line width of the thin line 401 to the printing apparatus will be described in a second embodiment.

Returning to the description of the flowchart in FIG. In S303, the CPU functions as the paper white area extraction unit 202, and extracts the image data of the area 402 where nothing is printed on the printed material 400 (hereinafter referred to as "paper white area 402") from the thin line image data acquired in S302. do. Extraction of the paper white area 402 is performed, for example, by specifying the coordinates of an area where nothing is printed on the printed material 400 in advance and extracting the image data of the corresponding area from the fine line image data. However, the present invention is not limited to this, and an area where nothing is printed may be extracted from the fine line image data and used as the paper white area 402 .

In S304, the CPU functions as the paper noise analysis unit 203, analyzes the paper noise characteristics of the paper white area 402 extracted in S303, and determines paper noise reduction settings to be used in the next paper noise reduction process in S305. Specifically, first, the paper white area 402 is transformed into the frequency space by FFT (Fast Fourier Transform) processing, frequency analysis is performed, and the power (frequency intensity) Ps of the main frequency (peak in the frequency space) of paper noise Ask for Then, a paper noise reduction setting S (Pt/Ps) is determined to set the obtained power Ps to a power Pt at which the unevenness of the fibers of the paper of the printed matter 400 becomes inconspicuous.

Note that, in this embodiment, general smoothing processing such as moving average is not used for paper noise reduction processing, and the reason for this will be described later. In addition, the unevenness of the fibers in the paper white area 402 of the printed matter 400 is large when recycled paper is used for the printed matter 400, and is very small when coated paper is used. Therefore, the value of the paper noise reduction setting S is small for recycled paper and close to 1 for coated paper. In this embodiment, paper noise varies depending on the type of paper and may also vary depending on the manufacturer of the paper.

In S305, the CPU functions as the paper noise reduction unit 204, and executes noise reduction processing on the entire thin line image with the paper noise reduction setting S determined in S304. That is, FFT processing is used to transform the frequency space, the power of the main frequency of paper noise is reduced to Pt in the frequency space, and inverse FFT processing is performed to restore the real space. Note that the noise reduction process may be performed by narrowing down to the area 404 including the fine line 401, for example, thereby shortening the processing time and reducing the processing load of the CPU. Also, although FFT and inverse FFT have been described as noise reduction processing, the present invention is not limited to this as long as paper noise reduction processing can be executed.

FIG. 5A is a diagram schematically showing the state of paper noise in the paper white area 402 before executing paper noise reduction processing. In FIG. 5(a), the paper noise is represented by increasing the contrast and binarizing for convenience in order to clarify the magnitude of the paper noise. For example, if general recycled paper is used for the printed material 400, unevenness of fibers on the surface of the paper appears as paper noise. As a result, paper noise appears as a pattern in which dark colors and light colors are finely mixed as shown in FIG. 5(a).

FIG. 5B is a diagram showing the state after the paper noise reduction processing is executed on the paper white area 402 of FIG. Comparing FIGS. 5A and 5B, it can be seen that the effect of the noise reduction processing has appeared since the dark color portion is reduced by the paper noise reduction processing.

In S306, the CPU functions as the fine line measurement unit 205, executes line width measurement processing of the fine line 401 on the fine line image data after the paper noise reduction processing has been executed in S305, and terminates this processing after the execution. Next, details of the line width measurement process will be described.

The line width measurement process is a process of measuring the line widths of all the fine lines 401 one by one. First, the image data of the measurement area 403 (see FIG. 4) including one fine line 401 is cut out from the fine line image data after the paper noise reduction processing has been executed in S305. In FIG. 4 , a region including a portion of one fine wire 401 in the length direction is cut out, but the measurement region 403 may be the entire length direction without being limited to this.

FIG. 6 is an enlarged view of the measurement area 403 cut out from the thin line image. FIG. 7 is a flow chart showing details of the line width measurement process in S305 for measuring the line width of one thin line 401 from the measurement area 403 cut out from the thin line image. The processing shown in the flowchart of FIG. 7 is for one thin line 401 included in the thin line image area 404 in FIG. 4, and is similarly executed for other thin lines in the thin line image. 7 is realized by the CPU of the image processing apparatus 102 functioning as the fine line measuring unit 205. In FIG. FIG. 6 will be described in conjunction with the description of the flowchart of FIG.

In S701, when the color space of the image (FIG. 6) of the measurement area 403, which is the input image, is sRGB, the fine line measurement unit 205 converts each pixel (x, y) of the image into CIEY color using Equation 1 below. Perform spatial transformation processing. Note that the color space conversion method is not limited to this as long as it converts to brightness according to the RGB color space.

In S<b>702 , the fine line measurement unit 205 obtains the maximum reflectance Rmax in the measurement area 403 . In S703, the thin line measurement unit 205 obtains the minimum reflectance Rmin at 403 in the measurement area. In S704, the thin line measurement unit 205 obtains the reflectance Rn, which is the reference value when measuring the line width, from the maximum reflectance Rmax and the minimum reflectance Rmin, using the following equation 2. In addition, in the following formula 2, n=0.4, for example.

In S705, the fine line measuring unit 205 initializes the internal counter K to K=1. In S<b>706 , the thin line measurement unit 205 obtains the line width of the thin line 401 as the range in which the reflectance is equal to or less than the reflectance Rn on the K-th horizontal line of the measurement area 403 . Details of how to obtain the line width of the thin line 401 will be described later with reference to FIG. When performing the process of S706 for the first time, since K=1, the line width of the fine line 401 for the first horizontal line 601 is obtained.

The thin line measuring unit 205 sequentially performs the process of S706 from the first horizontal line 601 to the last horizontal line 602 . Therefore, in S707, the thin line measuring unit 205 determines whether or not the line width of the thin line 401 for the last horizontal line 603 has been obtained. For example, if the total number of horizontal lines is N (>K), then it is determined whether the value of K has reached N.

If the thin line measuring unit 205 determines in S707 that the line width of the thin line 401 in the last horizontal line 602 has not been obtained (No in S707), the process proceeds to S708. In S708, the fine line measuring unit 205 increments the value of the internal counter K, and then returns the process to S706. Then, when the thin line measuring unit 205 determines in S707 that the line width of the thin line 401 in the last horizontal line 603 has been obtained (Yes in S707), the process proceeds to S709.

In step S709, the thin line measurement unit 205 has obtained the line widths of all horizontal lines. is the line width measurement value, and then the process is terminated.

FIG. 8 is a diagram showing a reflectance profile 801 on a horizontal line with measurement area 403 . The reflectance Rn, which is the line width of the fine line 401, is obtained by the above equation 2 with n=0.4. Point 805 on the line of reflectance Rn is the point where reflectance profile 801 first intersects the line of reflectance Rn from the left edge of measurement area 403 to the right. A point 806 on the line of reflectance Rn is the point where the reflectance profile 801 first intersects the line of reflectance Rn from the right end of the measurement area 403 toward the left. A distance 807 between points 805 and 806 is obtained as the thin line 401 and line width.

As shown in FIG. 8, when the difference between the maximum reflectance Rmax and the minimum reflectance Rmin is large, the line width of the thin line can be determined relatively easily and accurately. However, when the density of the fine line 401 is low (the fine line 401 is thin and faint), the difference between the maximum reflectance Rmax and the minimum reflectance Rmin becomes small. Moreover, the reflectance profile of the horizontal line may change in a complicated manner between the maximum reflectance Rmax and the minimum reflectance Rmin, which have a small difference. In such a case, the accuracy of measurement of the line width of the fine line 401 is lowered.

In order to solve this problem, a method of measuring the line width of the thin line 401 when the difference between the maximum reflectance Rmax and the minimum reflectance Rmin is small will now be described. FIG. 9A is a diagram showing an example of a reflectance profile 901 of a horizontal line with a measurement area 403 obtained from fine line image data before executing paper noise reduction processing in S305.

The reflectance profile 801 in FIG. 8 has a large difference between the maximum reflectance Rmax and the minimum reflectance Rmin, so it can be determined that the thin line 401 is printed darkly (at high density). On the other hand, in the reflectance profile 901 of FIG. 9A, the difference between the maximum reflectance Rmax and the minimum reflectance Rmin is small, so it can be determined that the thin line 401 is printed thin (low density).

Since the maximum reflectance Rmax is obtained in the area where nothing is printed, it is usually the color of the paper (generally white). Therefore, the maximum reflectance Rmax in FIG. 9A is substantially the same as the maximum reflectance Rmax in FIG. On the other hand, when the density of the fine lines is low, the minimum reflectance Rmin increases, so the reflectance Rn also increases, and the reflectance Rn approaches the maximum reflectance Rmax.

Point 905 is the point where reflectance profile 901 first intersects the line of reflectance Rn from the left edge of measurement area 403 to the right. A point 906 is a point where the reflectance profile 901 first intersects the line of reflectance Rn from the right end of the measurement area 403 toward the left. In this case, the distance 909 between points 905 and 906 is the line width of the thin line, but the actual line width of the thin line in reflectance profile 901 is the distance between points 907 and 908 . Therefore, paper noise reduction processing is required to reduce such erroneous measurements.

FIG. 9B is a diagram showing an example of a reflectance profile 911 on the same horizontal line as the horizontal line representing the reflectance profile 901, which is obtained from the thin line image data after the paper noise reduction processing has been performed in S305. .

In the reflectance profile 911, since the influence of unevenness caused by the fibers of the paper is reduced, the points 905 and 906 detected in the case of the reflectance profile 901 are no longer detected. The distance 917 between 916 is measured as the line width. Thus, by using the paper noise reduction process described in S305, the line width of the fine line can be accurately measured even if the density of the fine line is low.

By the way, as described above, in S305, paper noise reduction processing based on general smoothing processing using a simple blurring filter is not adopted, and the reason for this will be described here. FIG. 9C is a diagram showing an example of a reflectance profile 921 on the same horizontal line as the horizontal line indicating the reflectance profile 901, which is obtained from thin line image data after paper noise reduction processing by smoothing processing has been performed. be.

Compared to the reflectance profile 911, the reflectance profile 921 reduces paper noise and blurs even fine lines, resulting in a line width 927 that is wider than the original line width. put away. As described above, when a general smoothing process is performed, the line width of a fine line tends to be measured with a larger value than the original line width, resulting in a decrease in measurement accuracy. Therefore, in this embodiment, as described in S304, the paper noise reduction setting optimized for the unevenness of the fibers of the paper is used.

In this embodiment, when determining the line width of the thin line, as described above, the reflectance profile and the reflectance Rn first intersect. By using such a line width method, the line width of the thin line can be measured with high accuracy even when the thin line is not in the center of the measurement area 403 . On the other hand, in this method, if the difference between the maximum reflectance Rmax and the minimum reflectance Rmin is small as in the reflectance profile 901 and the density of the thin line is small, the line width becomes a value larger than the original value if it is applied as it is. may be measured. However, in this embodiment, this problem is avoided by using the reflectance profile 911 after paper noise reduction processing.

As described above, according to the first embodiment of the present invention, it is possible to accurately measure the image quality characteristics of fine lines printed on paper even if the paper has conspicuous unevenness of fibers.

<Second embodiment>
In the second embodiment, an image forming apparatus having the functions of the image processing apparatus 102 described in the first embodiment will be described. In general, the image forming apparatus according to the second embodiment prints fine lines on paper in the image forming section, measures the image quality characteristics of the printed fine lines, and feeds back the measurement results to the image forming section. It enables maintenance and improvement of print quality.

FIG. 10 is a diagram showing a schematic configuration of a printing system including an image forming apparatus 1000 according to the second embodiment. The printing system includes an image forming apparatus 1000 , a personal computer 1020 and a monitor 1030 . The personal computer 1020 creates PDL data using a printer driver from digital data created by an application, and transmits the created PDL data to the image forming apparatus 1000 via the network 1040 . A monitor 1030 displays various images created by the personal computer 1020 so that the user can check the colors and shapes of the created images. The personal computer 1020 and the image forming apparatus 1000 are connected, for example, via a network 1040 such as LAN or WAN, or via a USB cable or the like so as to be able to communicate bidirectionally.

The image forming apparatus 1000 includes a CPU 1001, a memory 1002, an HDD section 1003, a UI display section 1004, an image processing section 1005, a printing section 1006, a scanner section 1007, and a network I/F 1008, which are communicably connected via a bus 1009. .

The CPU 1001 controls the entire image forming apparatus 1000, interprets PDL data received from the personal computer 1020 with a PDL interpreter, and converts the data into bitmap data for printing by rendering. Although rendering is performed by software using the CPU 1001 here, it may be configured to be performed by hardware. A memory 1002 includes a RAM that is used as a work area for the CPU 1001 and a ROM that stores various programs such as an OS.

The HDD unit 1003 is a hard disk drive that is an example of a storage device that stores software for realizing various operations and processes of the image forming apparatus 1000, PDL data received from the personal computer 1020, and the like. The CPU 1001 expands predetermined software (program) from the HDD section 1003 into the RAM of the memory 1002 and controls the operation of each section of the image forming apparatus 1000 . Note that the HDD unit 1003 is not limited to the HDD, and may be configured by a flash memory or the like.

The UI display unit 1004 has a display for performing various displays, and displays and provides various types of information to the user. Also, the UI display unit 1004 has a touch panel superimposed on the display, and functions as an operation means for receiving operations from the user. An image processing unit 1005 performs image processing for converting bitmap data into print data, and has various functions that will be described later with reference to FIG. A printing unit 1006 performs printing processing (image forming processing) on a recording material such as paper based on the print data processed by the image processing unit 1005 . A network I/F 1008 is an interface for communicably connecting the image forming apparatus 1000 to a personal computer 1020 or an external device (not shown) via a network 1040 .

FIG. 11 is a diagram showing a schematic configuration of functional blocks of the image forming apparatus 1000. As shown in FIG. The image forming apparatus 1000 includes an image input unit 1111 , a paper white area extraction unit 1112 , a paper noise analysis unit 1113 , a paper noise reduction unit 1114 and a fine line measurement unit 1115 that constitute a fine line measurement device 1110 . The CPU 1001 of the image forming apparatus 1000 operates as each functional block constituting the fine line measuring apparatus 1110 by executing a predetermined program stored in the HDD section 1003 storage device. Each functional block of the fine line measuring device 1110 is the same as the functional block of the image processing device 102 (see FIG. 2) in the first embodiment, so description thereof will be omitted here.

The image forming apparatus 1000 also has a chart image generation unit 1101 , a fine line image generation unit 1102 and a fine line correction amount determination unit 1103 . The CPU 1001 of the image forming apparatus 1000 operates as these functional blocks by executing a predetermined program stored in the HDD unit 1003 storage device.

A chart image generation unit 1101 generates image data of a fine line correction chart for printing a plurality of fine lines with known line widths. The image data of the fine line correction chart is sent from the chart image generation unit 1101 to the printing unit 1006, and the printing unit 1006 prints the fine line correction chart on a predetermined sheet of paper, thereby producing a printed material used for measuring the line width of the fine line. can get. The fine line image generating unit 1102 scans (reads) a printed matter on which the fine line correction chart is printed by the scanner unit 1007 at a predetermined resolution, thereby generating image data of an image (fine line image) for measuring the line width of the fine line. (thin line image data) is generated.

A fine line measuring device 1110 measures the line width of a fine line from fine line image data in the same manner as the image processing device 102 in the first embodiment. A fine line correction amount determination unit 1103 determines a correction amount for correcting a fine line printed by the printing unit 1006 to a target line width based on the line width measurement value of the fine line obtained by the fine line measuring device 1110 . Specifically, the fine line correction amount determination unit 1103 holds a lookup table that defines the correction amount for the line width measurement value of the thin line, and determines the correction amount from the lookup table. In addition to the lookup table, a graph representing the correlation between the line width measurement value and the correction amount or a relational expression (computational expression) for calculating the correction amount from the line width measurement value is stored, and from the graph or the relational expression The configuration may be such that the correction amount is determined.

The image forming apparatus 1000 includes a fine line correction amount setting unit 1104 and a fine line correction unit 1105 . In this embodiment, the fine line correction amount setting unit 1104 and the fine line correction unit 1105 are functional blocks provided in the image processing unit 1005, as will be described later with reference to FIG. However, the configuration is not limited to such a configuration, and the fine line correction amount setting unit 1104 and the fine line correction unit 1105 may also be implemented by the CPU 1001 executing a predetermined program.

FIG. 12 is a block diagram showing an example of the image processing unit 1005 included in the image forming apparatus 1000. As shown in FIG. The image processing unit 1005 has a luminance density conversion unit 1202 , a fine line thickness determination unit 1203 , a fine line correction amount setting unit 1104 , a fine line correction unit 1105 and a halftone processing unit 1206 .

A luminance/density conversion unit 1202 converts the bitmap data 1201 into density data for printing when the bitmap data 1201 is luminance data for display. A thin line thickness determination unit 1203 determines whether or not the correction condition is met. A specific example of the correction condition will be described later.

The fine line correction amount setting unit 1104 sets the correction amount determined by the fine line correction amount determination unit 1103 to the fine line correction unit 1105 . The fine line correction unit 1105 performs the fine line printing with the correction amount set by the fine line correction amount setting unit 1104 only when the fine line thickness determination unit 1203 determines that the correction condition is satisfied. settings. The printing unit 1006 executes printing on paper with the density corrected by the fine line correction unit 1105 . The details of the printing process with the corrected density will be described later. Since the density data is 8 bits, the halftone processing unit 1206 converts it into print data 1207 with the number of gradations supported by the printing unit 1006 .

FIG. 13 is a flow chart showing an example of automatic fine line correction processing executed by the image forming apparatus 1000 . Predetermined processing (steps) indicated by S number in the flowchart of FIG. 13 is realized by the CPU 1001 expanding the program stored in the storage device into the RAM and functioning as each unit shown in FIG. 13 is realized by the image processing unit 1005 executing predetermined processing in accordance with instructions from the CPU 1001. A part of the processing (step) indicated by S number in the flowchart of FIG. Here, as in the first embodiment, line width is taken up as an image quality characteristic of fine lines, but other than line width, such as raggedness, blur, and density can also be measured in the same manner as the line width measurement. .

FIG. 14 is a diagram showing an example of a UI screen displayed on the UI display unit 1004 when automatic fine line correction processing is executed. FIG. 14A is a diagram showing an example of an adjustment/maintenance screen for starting automatic fine line correction processing. The adjustment/maintenance screen is displayed on the UI display unit 1004 by pressing an “adjustment/maintenance” icon displayed on the home screen (not shown) of the UI display unit 1004, for example. When the CPU 1001 detects that "automatic fine line correction" has been selected on the adjustment/maintenance screen, it starts automatic fine line correction processing. Accordingly, the adjustment/maintenance screen transitions to the UI screen shown in FIG. 14(b).

In step S1301, the CPU 1001 functions as the chart image generation unit 1101, and upon detecting that "print chart" has been selected on the UI screen of FIG. 14B, generates image data of a fine line correction chart. Then, the chart image generation unit 1101 sends the generated image data of the fine line correction chart to the printing unit 1006 to print the fine line correction chart on a predetermined sheet.

When the printed material for line width measurement is created in S1301, the UI screen in FIG. 14(b) transitions to the UI screen in FIG. 14(c). A plurality of 1-dot fine lines are printed on the fine-line correction chart at 600 dpi in the same manner as the printed matter 400 shown in FIG. The reason for printing a 1-dot thin line at 600 dpi is as described in the first embodiment.

In S1302, the CPU 1001 functions as the fine line image generation unit 1102, and the scanner unit 1007 scans the printed matter on which the fine line correction chart is printed at a predetermined resolution, thereby generating fine line image data. In S1303, the CPU 1001 functions as the fine line measuring device 1110 and measures the line width of the fine line. Note that the method for measuring the line width of the fine line is the same as the method for measuring the line width of the fine line in the first embodiment, so detailed description thereof will be omitted here. In addition, eight fine lines are printed on the fine line correction chart created in S1301. Width measurement value.

In S1304, the CPU 1001 functions as the fine line correction amount determination unit 1103 and obtains the correction amount from the line width measurement value. FIG. 15 is a diagram showing an example of a lookup table that defines the relationship between line width measurement values, correction amounts, and additional pixel values held by the fine line correction amount determination unit 1103 . From the lookup table, for example, when the measured line width is 40 μm, the correction amount is determined to be 1.4 times.

In the lookup table of FIG. 15, the amount of correction for achieving the target line width of 70 μm, which is not blurred with respect to the line width measurement value of a fine line of 1 dot at 600 dpi, is obtained in advance. Note that the target line width is not limited to 70 μm, and can be set in accordance with the performance of the printing unit 1006 to improve correction accuracy.

In S1305, the CPU 1001 functions as the fine line correction amount determination unit 1103, and based on the lookup table in FIG. Processing ends.

Next, the setting of the additional pixel value in S1305 and the accompanying actual line width correction method for the fine line will be described. FIG. 16 is a schematic diagram for explaining the thin line correction method. One square in each of FIGS. 16(a) to (d) represents one pixel of 600 dpi, and one pixel is specified by multi-valued 8-bit data, with a maximum of 255 (black) and a minimum of 0 ( white).

FIG. 16A shows the output of the luminance density conversion unit 1202 and shows a line with a thickness of 1 dot at 600 dpi. The pixel value of the pixel 1601 is 0, the pixel value of the pixel 1602 is 255, the pixel value of the pixel 1603 is 0, and an example of a black line (vertical line) with a width of 1 pixel is shown. In FIG. 16A, only the vertical line for one pixel (1 dot at 600 dpi) is black. Determine that there is. In this case, as shown in FIG. 16B, the fine line correction unit 1105 thickens the line width by darkening the white pixels 1601 and 1603 adjacent to the black pixel 1602 in column units. That is, FIG. 16(b) is a diagram showing an example in which the line width of the vertical line in FIG. 16(a) is corrected. The pixel values of pixels 1604 and 1605 in FIG. 16B are corrected to 51 with 8-bit data based on the lookup table in FIG. 15 for each column. By performing automatic fine line correction in this manner, a correction amount is set to 1.4 times the line width of one pixel with a line width measurement value of 40 μm, and the line width is corrected to the target value of 70 μm. This makes it possible to reduce the occurrence of fading.

16A and 16B schematically show vertical lines before and after line width correction, while FIGS. 16C and 16D schematically show horizontal lines before and after line width correction. 16(c) shows the horizontal line before correction, and FIG. 16(d) shows the horizontal line after correction. Similar to the line width correction of the vertical line, the line width is thickened by darkening the white pixels 1606 and 1608 next to the black pixel 1607, and the pixels 1609 and 1610 are corrected based on the lookup table in FIG. is corrected to 51 with 8-bit data.

As described above, according to the second embodiment of the present invention, as in the first embodiment, the image quality characteristics of fine lines printed on paper can be accurately measured even if the paper has conspicuous unevenness of fibers. be able to. Further, in the second embodiment, printing is performed with the target image quality characteristics by automatically performing correction based on the measurement result of the fine line image quality characteristics.

<Third Embodiment>
In the second embodiment, fine lines are corrected by controlling the density of pixels adjacent to the fine line pixels. On the other hand, in the third embodiment, a method of correcting fine line pixels themselves by modulating the amount of exposure in an image forming apparatus that performs electrophotographic printing will be described. Since the schematic configuration of the image forming apparatus conforms to that of the image forming apparatus 1000 described in the second embodiment, description of the overall configuration will be omitted. Also, the printing unit 1006 of the image forming apparatus 1000 forms (prints) an image on paper using an electrophotographic method.

FIG. 17A is a schematic diagram showing a method of modulating the exposure amount by adjusting the laser power when forming a latent image. FIG. 17B is a lookup table showing the relationship between the amount of correction for the line width measurement value of a fine line and the laser power. The lookup table of FIG. 17B defines the laser power for setting the line width of 1 dot at 600 dpi to the target line width of 70 μm, which is less likely to cause blurring. However, the target line width is not limited to 70 μm, and each value of the correction amount and the laser power changes according to the target line width.

If a thin line of black (density 255/255) is expressed with a laser power 1702 that is 100% at maximum, the laser power (output) cannot be increased any more. Therefore, by expressing black (density 255/255) with 70% laser power 170) and optimizing settings other than the laser power in the printing unit 1006, gradation characteristics and density reproducibility are adjusted. .

The one-pixel line determined by the thin line thickness determination unit 1203 is corrected with the laser power in the lookup table of FIG. 17(b). In other words, taking FIG. 16A as an example, the laser power is corrected when printing a black pixel portion. For example, the line width is widened to 70 μm by correcting the laser power to 100% for a line of one pixel with a line width measurement value of 40 μm. Further, no correction is performed for a line for one pixel with a line width measurement value of 70 μm. In this manner, the same effects as those of the second embodiment can be obtained in the third embodiment as well.

<Fourth Embodiment>
In the first embodiment, the line width of the thin line was measured by finding two points where the reflectance Rn and the reflectance profile first intersect from both ends (left end, right end) of the measurement area toward the inside. On the other hand, in the fourth embodiment, the center of the thin line is obtained, and two points at which the reflectance Rn and the reflectance profile first intersect are obtained from the obtained center of the thin line toward the left end and right end of the measurement area, respectively. to measure the line width of a fine line.

FIG. 18(a) is a diagram showing functional blocks for obtaining the center of a thin line and its line width. Here, an example in which the CPU of the image processing apparatus 102 operates as each functional block shown in FIG. 18A will be described. Of course, it is also possible to operate as a block. The CPU of the image processing apparatus 102 functions as an image input unit 1801, a fine line center detection unit 1802, and a fine line measurement unit 1803 by executing predetermined programs.

FIG. 18(b) is a diagram schematically showing a method of obtaining the line width based on the center of the line width for the reflectance profile 901 of the lightly blurred fine line shown in FIG. 9(a). Points 905, 906, 907 and 908 in FIG. 18(b) are the same as points 905, 906, 907 and 908 in FIG. 9(a).

An image input unit 1801 is the same as the image input unit 201 in the first embodiment, and description thereof is omitted here. The fine line center detection unit 1802 obtains the approximate center position of the line width of the fine line (hereinafter referred to as "fine line center") from the reflectance profile. Here, the center of the fine line is often the minimum reflectance Rmin. Therefore, the thin line center detection unit 1802 detects the position of the point 1810 indicating the minimum reflectance Rmin in the reflectance profile 901 as the thin line center.

The thin line measuring unit 1803 detects the first intersection point between the reflectance Rn and the reflectance profile from the thin line center detected by the thin line center detecting unit 1802 toward the end of the thin line in the width direction, and calculates the distance between the detected two points. is the line width of the thin line. In the case of the reflectance profile 901, the thin line measuring unit 1803 detects a point 907 where the reflectance profile 901 and the reflectance Rn first intersect from the center of the thin line to the left. Further, the thin line measuring unit 1803 detects a point 908 where the reflectance profile 901 and the reflectance Rn first intersect from the center of the thin line to the right. A distance 1811 between the points 907 and 908 is used as the line width measurement value of the thin line. Since the line width of the fine line can be obtained accurately from the center position of the fine line in this way, the fourth embodiment can obtain the same effect as the first embodiment.

Although the present invention has been described in detail based on its preferred embodiments, the present invention is not limited to these specific embodiments, and various forms without departing from the gist of the present invention can be applied to the present invention. included. Furthermore, each embodiment described above merely shows one embodiment of the present invention, and it is also possible to combine each embodiment as appropriate.

The present invention supplies a program that implements one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in the computer of the system or apparatus reads and executes the program. It can also be realized by processing to It can also be implemented by a circuit (for example, ASIC) that implements one or more functions.

REFERENCE SIGNS LIST 100 fine line measurement system 102 image processing device 201 image input unit 202 paper white area extraction unit 203 paper noise analysis unit 204 paper noise reduction unit 205 fine line measurement unit 1000 image forming apparatus 1001 CPU
1007 scanner section 1101 chart image generation section 1102 fine line image generation section 1103 fine line correction amount determination section 1104 fine line correction amount setting section 1105 fine line correction section 1110 fine line measuring device 1802 fine line center detection section

Claims (16)

Acquisition means for acquiring image data of a fine line image generated by reading a printed matter on which fine lines having a known line width are printed with a scanner;
an extracting means for extracting a paper white area in the fine line image;
analysis means for detecting paper noise in the fine line image by analyzing image data of the paper white area;
reduction means for reducing paper noise of the fine line image detected by the analysis means;
and measuring means for measuring an image quality characteristic of the thin line from the thin line image in which the paper noise is reduced by the reducing means. The analysis means transforms into a frequency space by FFT processing, obtains the peak of the main frequency of the paper noise of the fine line image,
2. The image processing apparatus according to claim 1, wherein said reducing means reduces said peak in the frequency space of said fine line image so that paper noise is not conspicuous. The measurement means cuts out a region including at least part of one of the thin lines from the thin line image, and measures the reflectance profile of the horizontal line of the cut out region from both ends toward the center of the cut out region and a predetermined 3. The image processing apparatus according to claim 1, wherein the line width of the thin line is defined as a distance between two points at which the reflectance of and first intersects. The measurement means cuts out a region including at least a part of one fine line from the fine line image, and measures the cutout region from a point exhibiting a minimum reflectance in the cutout region toward both ends of the region. 3. The image processing apparatus according to claim 1, wherein a distance between two points where a reflectance profile of a horizontal line and a predetermined reflectance first intersect is defined as a line width of the thin line. a printing unit that forms an image on paper;
a reading unit that scans the printed material output from the printing unit and generates image data;
a measuring means for measuring the characteristics of the thin line from the image data of the thin line image obtained by scanning the printed matter in which the thin line having a known line width is printed by the printing unit by the reading unit;
an image forming apparatus comprising: a correcting unit for correcting settings in the printing unit for printing on paper based on the measured value by the measuring unit,
The measuring means are
an extracting means for extracting a paper white area in the fine line image;
analysis means for detecting paper noise in the fine line image by analyzing image data of the paper white area;
reduction means for reducing paper noise of the fine line image detected by the analysis means;
and fine line measuring means for measuring image quality characteristics of the fine line from the fine line image in which the paper noise is reduced by the reducing means. The correcting means is
determining means for determining a correction amount for correcting the thin line formed on the paper by the printing unit to a target thin line from the measurement value by the thin line measuring means;
setting means for setting the correction amount determined by the determination means to the printing unit;
6. The image forming apparatus according to claim 5, wherein said printing unit forms an image on a sheet using the correction amount set by said setting unit. 7. The image forming apparatus according to claim 5, further comprising instruction means for instructing the printing unit to print the thin line of the known line width on the paper. 8. The image forming apparatus according to claim 5, wherein said correction means corrects pixel values of pixels adjacent to pixels of said thin line. The printing unit forms an image on paper by an electrophotographic method,
8. The image forming apparatus according to claim 5, wherein said correcting means corrects laser power when forming a latent image on said fine line pixels by said electrophotographic method. . The analysis means transforms into a frequency space by FFT processing, obtains the peak of the main frequency of the paper noise of the fine line image,
10. The image forming apparatus according to any one of claims 5 to 9, wherein the reducing unit reduces the peak in the frequency space of the fine line image so that paper noise is not conspicuous. The thin line measuring means cuts out a region including at least a part of one fine line from the thin line image, and measures the reflectance profile of the horizontal line of the cut out region from both ends toward the center of the cut out region. 11. The image forming apparatus according to any one of claims 5 to 10, wherein a distance between two points where a predetermined reflectance first intersects is defined as a line width of the thin line. The fine line measuring means cuts out a region including at least part of one fine line from the fine line image, and measures the cutout region from a point exhibiting a minimum reflectance in the cutout region toward both ends of the region. 11. The image according to any one of claims 5 to 10, wherein the line width of the thin line is defined as the distance between two points where the reflectance profile of the horizontal line and the predetermined reflectance first intersect. forming device. A control method for an image processing device,
Acquiring image data of a thin line image including the thin line generated by reading a printed matter on which a thin line having a known line width is printed with a scanner;
extracting a paper white area in the fine line image;
detecting paper noise in the fine line image by analyzing image data of the paper white area;
reducing paper noise in the detected fine line image;
and measuring an image quality characteristic of the thin line from the thin line image in which the paper noise has been reduced. A control method for an image forming apparatus,
a step of outputting a printed matter in which thin lines of a known line width are printed on paper from a printing unit that forms an image on paper;
a step of scanning the printed matter to generate image data of a fine line image including the fine lines;
extracting a paper white area in the fine line image;
detecting paper noise in the fine line image by analyzing image data of the paper white area;
reducing paper noise in the detected fine line image;
measuring image quality characteristics of the thin line from the paper noise-reduced thin line image;
and a step of correcting settings of the printing unit for printing on paper based on the measured image quality characteristics of the fine lines. A program that causes a computer to function as each means of the image processing apparatus according to any one of claims 1 to 4. A program that causes a computer to function as each means of the image forming apparatus according to any one of claims 5 to 12.

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