JP2022088207A - Image processing system, image processing method and program - Google Patents

Abstract

To provide processing for correcting image inclination, which is suitable for highly accurate noise evaluation.SOLUTION: An image processing system includes: calculation means that calculates an inclination angle of an input image with a certain direction as a reference; specification means that specifies a direction of noise components contained in the input image; and correction means that corrects the input image on the basis of the inclination angle and the direction of noise components.SELECTED DRAWING: Figure 4

Description

The present invention relates to a technique for evaluating image noise.

Conventionally, as a method of evaluating the quality of an image printed on a recording medium by a printer, a subjective evaluation in which an evaluator subjectively evaluates and an objective evaluation in which an objective evaluation is performed by measuring an image are known. There is. As an element in evaluating the quality of a printed image, there is banding or streak-like density unevenness called banding. When measuring an image and objectively evaluating noise having directionality such as banding, if the image is tilted, accurate evaluation cannot be performed, so tilt correction is performed. Patent Document 1 discloses a technique in which the edge of a scanned image is determined by scanning pixels from a margin of paper, and the average value of the tilt in the main scanning direction and the tilt in the sub-scanning direction is used as the tilt of the scanned image. ing.

Japanese Unexamined Patent Publication No. 2007-280273

Patent Document 1 performs tilt correction and noise evaluation using the average value of the tilt in the main scanning direction and the tilt in the sub-scan direction as the tilt of the scanned image, but is suitable for highly accurate noise evaluation depending on the direction of noise in the image. There is a problem that the tilt correction cannot be performed.

Therefore, an object of the present invention is to provide a process for correcting the inclination of an image, which is suitable for highly accurate noise evaluation.

In order to solve the above problems, the image processing apparatus according to the present invention has a calculation means for calculating the tilt angle of the input image with respect to a certain direction and a specific means for specifying the direction of the noise component included in the input image. It is characterized by having a correction means for correcting the input image based on the tilt angle and the direction of the noise component.

According to the present invention, it is possible to correct the inclination of an image, which is suitable for highly accurate noise evaluation.

Block diagram showing the configuration of the image processing device Diagram showing an example of a tilted image Diagram to explain the effect of image tilt on noise evaluation A flowchart showing the processing executed by the image processing device. Diagram for explaining the process of specifying the direction of the banding component A flowchart showing the processing executed by the image processing device. Diagram to explain the target area Diagram to explain the printing direction

Hereinafter, each embodiment will be described with reference to the drawings. The following embodiments do not necessarily limit the present invention. Moreover, not all combinations of features described in each embodiment are essential for the means of solving the present invention.

[First Embodiment]
First, the influence of the tilt of the image on the noise evaluation will be described with reference to FIG. In banding evaluation and character / line drawing evaluation, the analysis result of the image changes due to the inclination of the streaks and lines to be evaluated. FIG. 3A shows an example of an image in which the vertical streak component is not tilted. FIG. 3B shows an example of an image in which the vertical streak component is tilted. For example, in order to analyze the streak component in the vertical direction, consider calculating the average value of the pixel values in the vertical direction. In this case, the calculation result of the average value in the image shown in FIG. 3A is as shown in FIG. 3C. Further, the calculation result of the average value in the image shown in FIG. 3 (b) is as shown in FIG. 3 (d). In FIG. 3C, the difference between the maximum luminance value and the minimum luminance value is large, and the edge is clear. On the other hand, in FIG. 3D, the difference between the maximum luminance value and the minimum luminance value is small, the luminance value corresponding to the halftone is also generated, and the edge is not clear. As described above, the image shown in FIG. 3B is evaluated as an image containing less noise than the noise actually contained due to the inclination of the image with respect to the image shown in FIG. 3A. Therefore, in the present embodiment, the angle to be corrected with respect to the tilt of the image is determined according to the printing conditions, and the noise (banding) having directionality in the image is evaluated.

<Hardware configuration of image processing device>
FIG. 1A is a block diagram showing a hardware configuration of the image processing device 1. The image processing device 1 includes a CPU 1001, a ROM 1002, and a RAM 1003. Further, the image processing device 1 includes a VC (video card) 1004, a general-purpose I / F (interface) 1005, a SATA (serial ATA) I / F 1006, and a NIC (network interface card) 1007. The CPU 101 uses the RAM 1003 as a work memory to execute an OS (operating system) and various programs stored in the ROM 1002, the HDD (hard disk drive) 1013, and the like. Further, the CPU 1001 controls each configuration via the system bus 1008. The process according to the flowchart described later is executed by the CPU 1001 after the program code stored in the ROM 1002, the HDD 1013, or the like is expanded into the RAM 1003. A display device 1015 is connected to the VC1004. An input device 1010 such as a mouse or a keyboard and an image forming device 1011 are connected to the general-purpose I / F 1005 via the serial bus 1009. A general-purpose drive 1014 for reading and writing the HDD 1013 and various recording media is connected to the SATAI / F1006 via the serial bus 1012. NIC1007 inputs and outputs information to and from an external device. The CPU 1001 uses various recording media mounted on the HDD 1013 or the general-purpose drive 1014 as a storage location for various data. The CPU 1001 displays a UI (user interface) provided by the program on the display device 1015, and receives an input such as a user instruction received via the input device 1010. The display device 1015 may be a touch panel display having a touch panel function of detecting the position of touch by an indicator such as a finger.

<Functional configuration of image processing device>
FIG. 1B is a block diagram showing a functional configuration of the image processing apparatus 1. The CPU 1001 functions as the functional configuration shown in FIG. 1 (b) by reading and executing a program stored in the ROM 1002 or the HDD 1013 using the RAM 1003 as a work memory. It should be noted that it is not necessary that all of the processes shown below are executed by the CPU 1001, and even if the image processing device 1 is configured so that a part or all of the processes are performed by one or a plurality of processing circuits other than the CPU 1001. good.

The image processing device 1 has an input unit 101, a calculation unit 102, a specific unit 103, a correction unit 104, and an evaluation unit 105. The input unit 101 inputs image data representing the image to be evaluated. The input image data may be image data obtained by reading a printed matter using a scanner or a digital camera, or may be image data created by simulation. The image represented by the input image data is a grayscale image, and each pixel has a pixel value (brightness value) represented by 8 bits.

The calculation unit 102 calculates the tilt angle of the image with respect to the horizontal direction and the tilt angle of the image with reference to the vertical direction by detecting the markers and borders arranged in the image to be evaluated. do. FIG. 2 shows an example of an image tilted. The shaded area in the image shown in FIG. 2 indicates an evaluation area that is the target of banding evaluation. In the image shown in FIG. 2, the evaluation area is surrounded by a black frame line, and the inclination angle can be calculated by detecting the apex of this frame line. The calculation unit 102 detects the upper left vertex 201, the upper right vertex 202, and the lower left vertex 203 of the evaluation area based on the input image data. Further, the calculation unit 102 has an angle 204 between the upper side of the evaluation area connecting the apex 201 and the apex 202 and the horizontal direction, and a side perpendicular to the left side of the evaluation area connecting the apex 201 and the apex 203. Calculate the angle 205.

The specifying unit 103 specifies the direction of the banding component included in the image based on the printing conditions of the image forming apparatus 1011. The printing conditions in this embodiment are a printing method and a printing direction when printing an image. First, the printing direction will be described. The printing direction includes a main scanning direction and a sub-scanning direction. The main scanning direction is the line direction when the image is divided into a plurality of lines and formed, and the sub-scanning direction is the transport direction of the recording medium (paper). For example, when A4 size paper is conveyed in the vertical direction of the paper, as shown in FIG. 8A, the horizontal direction of the paper is the main scanning direction and the vertical direction of the paper is the sub-scanning direction. As shown in FIG. 8B, when two A4 size images are arranged on A3 size paper and the paper is conveyed in the vertical direction of the paper, the horizontal direction of the paper is irrespective of the direction of the A4 size image. Is the main scanning direction, and the vertical direction of the paper is the sub-scanning direction.

Next, the printing method will be described. The printing method includes an electrophotographic method and an inkjet method. In printing by the electrophotographic method, density unevenness tends to occur perpendicular to the rotation direction of the drum (paper transport direction). Therefore, the direction of the banding component included in the printed image is a direction parallel to the main scanning direction at the time of printing. Further, the inkjet method includes a multi-pass method and a single-pass method. In printing by the multi-pass method, the printed image contains a banding component in a direction parallel to the main scanning direction at the time of printing due to the influence of paper transport, ink beading, and the like. In printing by the single-pass method, the printed image contains a banding component in a direction parallel to the sub-scanning direction at the time of printing due to the influence of nozzle variation and non-ejection of ink.

Therefore, the specifying unit 103 acquires information indicating the printing method and the printing direction as printing conditions, and specifies the direction of the banding component to be evaluated based on the acquired information. FIG. 5 shows the correspondence between the printing conditions and the direction of the banding component to be evaluated. For example, when the printing method is an electrophotographic method and the main scanning direction is the horizontal direction, the specific unit 103 uses the horizontal banding component in the image as the banding component to be evaluated. Further, when the printing method is an inkjet single-pass method and the main scanning direction is the horizontal direction, the specific unit 103 uses the banding component in the vertical direction in the image as the banding component to be evaluated.

The correction unit 104 corrects the image based on the tilt angle calculated by the calculation unit 102 and the direction of the banding component specified by the specific unit 103. Specifically, the correction unit 104 rotates the image around the vertex 201 in FIG. 2 by the correction angle. The evaluation unit 105 evaluates the banding in the image corrected by the correction unit 104. As the banding evaluation method, a known ISO / IEC24790 method is used, but other evaluation methods may be used. The evaluation unit 105 also functions as a display control unit that displays the evaluation value obtained as the banding evaluation result on the display device 1015. The evaluation unit 105 may output the banding evaluation value to a storage device such as the HDD 1013.

<Processes executed by the image processing device>
FIG. 4 is a flowchart showing a process executed by the image processing device 1. The process shown in the flowchart of FIG. 4 starts when an instruction is input by the user via the input device 1010 and the CPU 1001 receives the input instruction. Hereinafter, each step (process) is represented by adding S in front of the reference numeral.

In S401, the input unit 101 inputs image data from the HDD 1013, a scanner, or the like. In S402, the calculation unit 102 calculates the tilt angle Ah of the image with respect to the horizontal direction and the tilt angle Av of the image with respect to the vertical direction based on the input image data. In S403, the specific unit 103 determines whether or not the tilt angle Ah and the tilt angle Av are different. If the tilt angle Ah and the tilt angle Av are different, the process proceeds to S404, and if the tilt angle Ah and the tilt angle Av are the same, the process proceeds to S406.

In S404, the specific unit 103 acquires condition information representing printing conditions. The condition information is information indicating the printing method and whether the main scanning direction at the time of printing is the horizontal direction or the vertical direction of the image. In S405, the specifying unit 103 specifies the direction of the banding component to be evaluated based on the condition information.

In S406, the correction unit 104 determines the correction angle. When it is determined in S403 that the tilt angle Ah and the tilt angle Av are the same, the angle −A for correcting the tilt angle A (= Ah = Av) is set as the correction angle. When it is determined in S403 that the tilt angle Ah and the tilt angle Av are different, the angle for correcting the tilt angle with respect to the direction parallel to the direction of the banding component specified in S405 is used as the correction angle. .. Specifically, when it is specified in the horizontal direction in S405, the correction unit 104 sets the angle −Ah for correcting the tilt angle Ah as the correction angle. When the direction is specified as the vertical direction in S405, the correction unit 104 sets the correction angle −Av for correcting the tilt angle Av as the correction angle.

In S407, the correction unit 104 corrects the image based on the correction angle determined in S406. As described above, the correction unit 104 rotates the image around the apex 201 of FIG. 2 by the correction angle. In S408, the evaluation unit 105 derives the banding evaluation value based on the image data representing the corrected image. Further, the evaluation unit 105 displays the derived evaluation value of the banding on the display device 1015.

<Effect of the first embodiment>
As described above, the image processing apparatus in the present embodiment calculates the tilt angle of the input image with respect to a certain direction. In addition, the direction of the noise component included in the input image is specified. Then, the input image is corrected based on the calculated tilt angle and the direction of the specified noise component. This makes it possible to correct the tilt of the image, which is suitable for highly accurate noise evaluation.

<Modification example>
In the present embodiment, when the tilt angle Ah and the tilt angle Av are different, the correction angle is determined so as to correct the tilt angle based on either the horizontal direction or the vertical direction. If the difference from the tilt angle Av is less than the threshold value, other processing may be performed. For example, when the difference between the tilt angle Ah and the tilt angle Av is less than the threshold value, the average value of the tilt angle Ah and the tilt angle Av may be used for the tilt correction without performing the processes of S404 and S405.

Further, in the present embodiment, when the tilt angle Ah and the tilt angle Av are different, the correction angle is determined so as to correct the tilt angle based on either the horizontal direction or the vertical direction, but the weighted average. The correction angle may be determined by. For example, the weight with respect to the direction of the banding component to be evaluated may be increased, and the average value with the other direction may be used as the correction angle.

Further, in the present embodiment, a marker or a border for calculating the tilt angle is arranged in the image, but when there is no marker or the border, the tilt angle is calculated by edge detection processing for the image and function approximation. You may.

Further, although the input image data in the present embodiment is image data representing a grayscale image, it may be image data representing a color image having a color signal value such as (R, G, B) in each pixel. ..

Further, in the present embodiment, two tilt angles are calculated based on an image including one evaluation region, but the number of evaluation regions and the calculated tilt angles is not limited to this. For example, the tilt angles of the four sides of the image may be calculated for one evaluation area. Further, when a plurality of evaluation areas are set in the image, a plurality of tilt angles may be calculated for each evaluation area.

Further, when determining the correction angle, if the correction angle is small, the correction angle may be set to 0 degrees, that is, tilt correction may not be performed. Whether or not the correction angle is small can be determined based on an angle that does not affect the banding evaluation value, an angle that the rotation processing affects the banding evaluation value more than the image tilt, and the like.

[Second Embodiment]
In the first embodiment, the direction of the banding component to be evaluated is specified based on the printing conditions. In the present embodiment, the direction of the banding component to be evaluated is specified for an image whose printing conditions such as a printing method and a printing direction are unknown. Since the hardware configuration and the functional configuration of the image processing apparatus in this embodiment are the same as those in the first embodiment, the description thereof will be omitted. Hereinafter, the differences between the present embodiment and the first embodiment will be mainly described. The same configuration as that of the first embodiment will be described with the same reference numerals.

<Processes executed by the image processing device>
FIG. 6A is a flowchart showing the processing executed by the image processing apparatus 1. The process shown in the flowchart of FIG. 6A starts when an instruction is input by the user via the input device 1010 and the CPU 1001 receives the input instruction. Since the processes of S401 to S403 and S406 to S408 are the same as those of the first embodiment, the description thereof will be omitted.

In S601, the specific unit 103 specifies the direction of the banding component to be evaluated. FIG. 6B is a flowchart showing a process of specifying the direction of the banding component to be evaluated. In S611, the specific unit 103 cuts out a target area for specifying the direction of the banding component to be evaluated from the image. The target area in the present embodiment is an area designated by the user inside the evaluation area, but may be a predetermined area. FIG. 7 shows an example of the relationship between the evaluation area and the target area. The target area 702 is set inside the evaluation area 701.

In S612, the specific unit 103 generates one-dimensional data based on the pixel value of the cut out target area. Specifically, the specific unit 103 generates one-dimensional data in the horizontal direction and one-dimensional data in the vertical direction by averaging the pixel values of the target region in the horizontal direction and the vertical direction, respectively. In S613, the specific unit 103 determines in which direction the banding occurs in the horizontal direction or the vertical direction of the image, based on the one-dimensional data in the horizontal direction and the one-dimensional data in the vertical direction. Specifically, the specific unit 103 determines whether or not there is a variation in the average value of the pixel values represented by the one-dimensional data, determines that banding occurs in the direction in which the average value varies, and averages. It is determined that no banding has occurred in the direction in which the value is substantially constant. FIG. 7 shows the horizontal one-dimensional data 703 and the vertical one-dimensional data 704 of the target area 702. In this case, since the average value of the pixel values is substantially constant in the one-dimensional data 704 in the vertical direction and the average value of the pixel values varies in the one-dimensional data 703 in the horizontal direction, the specific unit 103 is the horizontal direction. It is determined that banding has occurred in.

<Effect of the second embodiment>
As described above, the image processing apparatus in the present embodiment has specified the direction of the noise component to be evaluated based on the pixel value of the image. As a result, it is possible to correct the tilt of the image, which is suitable for highly accurate noise evaluation, even for the scanned image or the simulated image whose printing conditions are unknown.

<Modification example>
In the present embodiment, the two-dimensional data having the pixel values of the pixels in the target region is converted into the one-dimensional data, but the direction of the banding component may be specified by another method. For example, the direction of the banding component may be specified by performing frequency analysis on the evaluation region. Further, the horizontal banding and the vertical banding in the image may be evaluated without tilt correction, and the direction of the banding component may be specified based on the magnitude of the evaluation value.

[Other embodiments]
In the above-described embodiment, the direction of the banding component to be evaluated is specified based on the printing conditions and the image, but the direction specified by the user may be the direction of the banding component to be evaluated. For example, when the user specifies the horizontal direction of the image, the specific unit 103 selects the inclination angle Ah from the plurality of inclination angles calculated by the calculation unit 102 to determine the correction angle. When the user specifies the vertical direction of the image, the specific unit 103 selects the inclination angle Av from the plurality of inclination angles calculated by the calculation unit 102 to determine the correction angle. Further, the calculation unit 102 may calculate only the tilt angle with respect to the direction specified by the user.

Further, in the above-described embodiment, banding is evaluated as an example of noise generated in an image, but the above-mentioned processing can be applied to noise having directionality such as linear noise.

Further, in the above-described embodiment, some examples of the process for specifying the direction of the noise component have been described, but the content of the process may be switched according to a predetermined condition. For example, the processing of the first embodiment and the processing of the second embodiment may be switched between the case where the information regarding the printing condition of the image can be acquired and the case where the information cannot be acquired. Further, the processing may be switched according to the type of image such as a scanned image or a simulation image, or the processing may be switched according to the noise to be evaluated and the type of evaluation method.

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

1 Image processing device 102 Calculation unit 103 Specific unit 104 Correction unit

Claims (13)

A calculation method for calculating the tilt angle of an input image with respect to a certain direction,
Specific means for specifying the direction of the noise component contained in the input image, and
A correction means for correcting the input image based on the tilt angle and the direction of the noise component,
An image processing device characterized by having. The input image is an image obtained by reading a printed matter, and is an image obtained.
The image processing apparatus according to claim 1, wherein the specifying means specifies the direction of the noise component based on the printing conditions when printing the printed matter. The image processing apparatus according to claim 2, wherein the printing conditions are a printing method and a scanning direction with respect to the input image. In the input image, the specifying means calculates an average value of pixel values in the horizontal direction and the vertical direction of the input image, and specifies the direction of the noise component based on the calculated average value of the pixel values. The image processing apparatus according to claim 1. The image processing apparatus according to claim 1, wherein the specifying means specifies the direction of the noise component based on a user's instruction. The certain direction is the horizontal direction and the vertical direction of the input image.
The calculation means according to any one of claims 1 to 5, wherein the calculation means calculates a tilt angle with respect to the horizontal direction and a tilt angle with reference to the vertical direction. Image processing device. The correction means selects either a tilt angle with respect to the horizontal direction or a tilt angle with reference to the vertical direction based on the direction of the noise component, and is based on the selected tilt angle. The image processing apparatus according to claim 6, wherein the input image is corrected. The correction means calculates a weighted average of a tilt angle with respect to the horizontal direction and a tilt angle with reference to the vertical direction based on the direction of the noise component, and is based on the calculated weighted average. The image processing apparatus according to claim 6, wherein the input image is corrected. The image processing apparatus according to any one of claims 1 to 8, wherein the correction means corrects the input image by rotating the input image. The image processing apparatus according to any one of claims 1 to 9, wherein the calculation means calculates the tilt angle based on a marker or a frame line included in the input image. The image processing apparatus according to any one of claims 1 to 10, further comprising an evaluation means for evaluating the noise component based on the corrected input image. A program for making a computer function as each means of the image processing apparatus according to any one of claims 1 to 11. A calculation step to calculate the tilt angle of the input image with respect to a certain direction,
A specific step for specifying the direction of the noise component contained in the input image, and
A correction step for correcting the input image based on the tilt angle and the direction of the noise component,
An image processing method characterized by having.

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