KR101912758B1 - Method and apparatus for rectifying document image - Google Patents

Abstract

A method and apparatus for smoothing a document image, the method for smoothing a document image comprises: designing a first cost function based on properties of lines contained in a non-text area of the document image; Designing a second cost function based on properties of text lines included in a text area of the text area, generating a third cost function by combining the first cost function and the second cost function, And removing distortion existing in the document image.

Description

METHOD AND APPARATUS FOR RECTIFIING DOCUMENT IMAGE < RTI ID = 0.0 >

The embodiments disclosed herein relate to a method and apparatus for smoothing document images.

In recent years, the performance of cameras provided in personal devices such as smart phones has been improved. Therefore, instead of scanning a document using a scanner, a document is photographed using a camera provided in a smart phone or the like, Is often used instead of a scan image.

However, in the case of a document image photographed with a camera, there is a high possibility that distortion occurs due to the positional relationship between the camera and the document and the geometric shape of the document surface. However, in order to digitally document a document image, it is necessary to increase the accuracy of character recognition, and therefore, a rectification process is required to remove the distortion included in the document image before performing character recognition.

Korean Patent Laid-Open Publication No. 10-2015-0037374, which is related to the prior art, extracts a text line from a single document image taken by a general camera, and optimizes a projection expression for projecting the extracted text line onto a scanned document plane To thereby convert an irregular document image into a scanned document without using a scanner.

On the other hand, the background art described above is technical information acquired by the inventor for the derivation of the present invention or obtained in the derivation process of the present invention, and can not necessarily be a known technology disclosed to the general public before the application of the present invention .

SUMMARY OF THE INVENTION The embodiments disclosed herein are aimed at providing a method and apparatus for smoothing a document image, and effectively eliminating distortion, especially in non-text areas.

According to an embodiment of the present invention, there is provided a document image smoothing method comprising: designing a first cost function based on properties of lines included in a non-text area of a document image; Designing a second cost function based on properties of text lines included in a text area of a document image, combining the first cost function and a second cost function to produce a third cost function, And removing the distortion existing in the document image using the function.

According to another embodiment, there is provided a computer program for performing a document image smoothing method, the method comprising: designing a first cost function based on properties of lines contained in a non-text area of a document image; Designing a second cost function based on properties of text lines included in a text area of a document image, combining the first cost function and a second cost function to produce a third cost function, And removing the distortion existing in the document image using the function.

According to yet another embodiment, there is provided a computer-readable medium having recorded thereon a program for performing a document image smoothing method, the document image smoothing method comprising the steps of: determining, based on properties of lines included in a non- Designing a second cost function based on properties of text lines included in a text area of the document image; combining the first cost function and the second cost function to generate a third cost function; And removing distortion existing in the document image using the third cost function.

According to another embodiment, the document image smoothing apparatus includes an input / output unit for receiving an input related to processing of a document image and displaying a situation and a result of processing of the document image, a program for performing smoothing of document image And a control unit for performing smoothing of the document image by executing the program, wherein the control unit is configured to design a first cost function based on properties of lines included in a non-text area of the document image Designing a second cost function based on properties of text lines included in a text area of the document image, and using the third cost function generated by combining the first cost function and the second cost function, It is possible to eliminate distortion existing in the image.

According to any one of the above-mentioned problems, the cost function reflecting the property of the line segment included in the non-text area of the document image is designed and used in the smoothing process, so that the distortion existing in the non- It is expected that the effect can be removed.

The effects obtained in the disclosed embodiments are not limited to the effects mentioned above, and other effects not mentioned are obvious to those skilled in the art to which the embodiments disclosed from the following description belong It can be understood.

1 is a block diagram illustrating a configuration of a document image smoothing apparatus according to an embodiment.
2 is a diagram showing a relationship between a hard copy document and a document image captured by the camera.
FIGS. 3 and 4 are views showing a document image including a distortion according to an embodiment.
5 is a diagram illustrating a result of grouping line segments included in a document image according to an exemplary embodiment.
6 is a diagram illustrating a document image including a distortion according to an exemplary embodiment.
FIG. 7 is a flowchart for explaining a document image smoothing method according to an embodiment.
FIG. 8 is a view comparing the result of performing the document image smoothing method according to the embodiment with the result of performing the smoothing method.

Various embodiments are described in detail below with reference to the accompanying drawings. The embodiments described below may be modified and implemented in various different forms. In order to more clearly describe the features of the embodiments, detailed descriptions of known matters to those skilled in the art are omitted. In the drawings, parts not relating to the description of the embodiments are omitted, and like parts are denoted by similar reference numerals throughout the specification.

Throughout the specification, when a configuration is referred to as being "connected" to another configuration, it includes not only a case of being directly connected, but also a case of being connected with another configuration in between. In addition, when a configuration is referred to as "including ", it means that other configurations may be included, as well as other configurations, as long as there is no specially contradicted description.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

1 is a block diagram illustrating a configuration of a document image smoothing apparatus according to an embodiment.

The document image smoothing device according to an embodiment may be a device for directly photographing a document and performing smoothing of the photographed document image. For example, the document image smoothing device may be a terminal such as a smart phone or a tablet equipped with an application for performing smoothing of a document image.

Alternatively, the document image smoothing apparatus according to an exemplary embodiment may be a device that receives a document image from another apparatus and smoothes the received document image. For example, the document image smoothing device may be a desktop or a notebook equipped with a program for performing document image smoothing.

Alternatively, the document image smoothing apparatus according to an exemplary embodiment may be a server that receives a document image from a user's terminal through a network, performs smoothing, and transmits the document image to the user's terminal.

1, a document image smoothing apparatus 100 according to an embodiment may include an input / output unit 110, a control unit 120, a storage unit 130, and a communication unit 140. Although not shown in FIG. 1, the document image smoothing apparatus 100 may further include a photographing unit.

The input / output unit 110 receives input related to the processing of the document image from the user, and can display a screen showing the progress of the processing of the document image and the result. For example, the input / output unit 110 may include an operation panel for receiving user input and a display panel for displaying a screen.

In particular, the input unit may include devices capable of receiving various types of user input, such as a keyboard, a physical button, a touch screen, a camera or a microphone. Also, the output unit may include a display panel or a speaker. However, the present invention is not limited to this, and the input / output unit 110 may include various input / output support structures.

The control unit 120 controls the overall operation of the document image smoothing apparatus 100 and may include a process such as a CPU. According to one embodiment, the control unit 120 may include at least one processor. The control unit 120 may perform processes for smoothing the document image by executing a program stored in the storage unit 130. [

Various types of data such as files, applications, programs, and the like may be installed and stored in the storage unit 130. According to an exemplary embodiment, a program for performing a document image smoothing method may be installed in the storage unit 130.

The communication unit 140 can perform wire / wireless communication with another device or a network. To this end, the communication unit 140 may include a communication module supporting at least one of various wired / wireless communication methods. For example, the communication module may be implemented in the form of a chipset. According to one embodiment, the communication unit 140 can receive a document image from another apparatus.

The wireless communication supported by the communication unit 140 may be Wi-Fi (Wireless Fidelity), Wi-Fi Direct, Bluetooth, UWB (Ultra Wide Band), NFC (Near Field Communication), or the like. The wired communication supported by the communication unit 140 may be, for example, USB or High Definition Multimedia Interface (HDMI). Also, the communication unit 140 may transmit data or messages to a destination via the Internet or a mobile communication network.

Hereinafter, a process of smoothing a document image by the document image smoothing apparatus 100 according to an embodiment will be described in detail.

Before describing the specific operation of the document image smoothing apparatus 100 according to an embodiment, a description will be given of a distortion occurring in a document image obtained by photographing a hard copy document with a camera and a smoothing process for eliminating such distortion .

2 is a diagram showing a relationship between a hard copy document and a document image captured by the camera.

Referring to FIG. 2, when the hard copy document 20 is photographed using the camera 10, the document image 21 is obtained. At this time, if the coordinate values on the document image 21 corresponding to the coordinate values (X, Y, Z) on the hard copy document 20 are (?,?), Then between the two coordinate values, The relationship is established.

Here, f is the focal length of the camera 10, c _x and c _y are the x-axis coordinate value and the y-axis coordinate value of the principal point corresponding to the center of the document image 21, respectively , R is the pose of the camera 10 and T is the position difference vector between the camera 10 and the hardcopy document 20.

On the other hand, in the case of a booklet, which is a representative form of the hard copy document 20, the geometric shape of its surface is generally curved. In order to mathematically model the warpage of the surface of the hard copy document 20, it is assumed that the curled document surface of the hard copy document 20 is in the form of a generalized cylindrical surface. Then, the coordinate values (X, Y, Z) of the specific point on the hard copy document 20 in FIG. 2 satisfy the following equation (2).

In the case of the document image 21 obtained by photographing the hard copy document 20 with the camera 10, distortion occurs due to the geometric shape such as the position of the camera 10 and the curvature of the surface of the hard copy document 20 at the time of photographing . The process of removing the distortion of the document image 21 and correcting it as if a flat document is photographed from the front is referred to as smoothing.

The smoothing of the document image 21 is performed by estimating the parameter values related to the pose of the camera and the warping form of the document surface so as to eliminate the distortion existing in the document image 21 using the above Equations 1 and 2 . In this case, in order to estimate the variable values to remove the distortion, a cost function that reduces the result as the distortion is removed can be designed and variable values that minimize the cost function can be estimated. The embodiments described below relate to a method for designing a cost function used to remove distortion of a document image 21. [

The document image smoothing apparatus 100 according to an embodiment combines a cost function reflecting the property of a text line existing in a text area and a cost function reflecting a property of a line segment existing in a non-text area, By using the generated cost function, not only the text region but also the distortion existing in the non-text region can be effectively removed.

First, the process of designing the cost function reflecting the property of the text line will be described.

As the distortion is removed from the document image, the text lines included in the document image are more likely to satisfy the following properties. First, the text line is a straight line in the horizontal direction. Second, the spacing between the lines of text in the same paragraph is constant. Third, the text lines contained in the same paragraph are arranged on the left or right side.

Therefore, the controller 120 may design the cost functions of the following equations (3) to (5) to reflect the respective properties.

는 k번째 텍스트 라인에 있는 i번째 문자의 y축 좌표 값이고,

는 k번째 텍스트 라인의 y축 좌표 값이다. 또한,

는 k번째 텍스트 라인의 가장 좌측에 있는 x축 좌표 값(좌정렬 기준)이며,

은 문단 정렬 선의 x축 좌표 값이다.At this time,

Is the y-axis coordinate value of the i-th character in the k-th text line,

Is the y-axis coordinate value of the kth text line. Also,

Is the leftmost x-axis coordinate value (left-aligned reference) of the k-th text line,

Is the x-axis coordinate value of the paragraph alignment line.

The cost functions of Equations (3) to (5) have smaller values as the line of the text line is in the horizontal direction, the interval between the text lines is constant, and the text line is arranged in the left side. The control unit 120 can design a cost function for document smoothing by combining these cost functions with appropriate coefficients. For example, the controller 120 may design a cost function as shown in Equations (6) and (7) below.

및

는 텍스트 라인의 각 성질을 반영한 비용 함수간의 가중치를 나타내는 계수로서, 설계 환경에 따라서 적절한 값으로 설정될 수 있다.At this time,

And

Is a coefficient indicating a weight between the cost functions reflecting each property of the text line, and can be set to an appropriate value according to the design environment.

For example, smoothing may be performed using Equation (6) for a document image that substantially satisfies the left alignment (or linearity), or smoothing may be performed for a document image whose interval between text lines is substantially constant using Equation (7) May be effective.

In addition, the control unit 120 may design the cost function by combining the equations (4) and (5) as necessary, or may combine all the equations (3) to (5) to design the cost function.

Hereinafter, the process of designing the cost function reflecting the property of the line segment included in the non-text area will be described in detail.

Generally, as the distortion in the document image is removed, the line segments included in the non-text area of the document image are more likely to satisfy the following properties. First, line segments are straight lines. Second, line segments corresponding to the borders of the table or figure are arranged in the horizontal or vertical direction.

First, a method of designing a cost function reflecting the first property (line segment) is described as follows.

FIGS. 3 and 4 are views showing a document image including a distortion according to an embodiment. Referring to FIG. 3, line segments included in the 31 and 32 regions of the document image 30 are curved. Referring to FIG. 4, it can be seen that a line segment corresponding to the border of the document in the document image 40, that is, a line segment included in the area 41 is a curved line. These are all distortions caused by the warping of the document surface.

In order to remove such distortion, a preprocessing process for grouping small lines constituting one long line segment is required. Accordingly, when the distance between the line segments is equal to or more than a certain standard and the direction of the lines is similar, the control unit 120 groups the lines into one group. The process of removing distortion from the line segments for which the grouping is completed will be described below with reference to FIG.

5 is a diagram illustrating a result of grouping line segments included in a document image according to an exemplary embodiment. Referring to FIG. 5, N line segments 51, 52, 53, ..., 5N are grouped into one group.

,

)이라고 하고, 마지막 선분(5N)의 끝점(P2)의 좌표를 (

,

)이라고 하면, 두 점들(P1, P2)을 잇는 직선은 아래의 수학식 8 및 9와 같이 나타낼 수 있다.In FIG. 5, the coordinates of the starting point P1 of the first line segment 51 are denoted by (

,

), And the coordinates of the end point P2 of the last line segment 5N are denoted by (

,

), A straight line connecting the two points P1 and P2 can be expressed by the following equations (8) and (9).

As the starting points of the N line segments 51, 52, 53, ..., 5N approach the straight line connecting P1 and P2, the long line segment 50 has a straight line shape, The cost function can be designed as shown in Equation (10) below.

According to the expression (10), as the starting points of each of the N line segments 51, 52, 53, ..., 5N approach the straight line connecting P1 and P2, the value of the cost function becomes smaller.

This time, we will explain how to design a cost function that reflects the second property (the line segment of the table or figure is arranged horizontally or vertically).

6 is a diagram illustrating a document image including a distortion according to an exemplary embodiment. Referring to FIG. 6, it can be confirmed that the line segments corresponding to the border of the table included in the document image 60 are deviated from the horizontal direction or the vertical direction. The control unit 120 can correct the distortion by designing a cost function such that the value becomes smaller as the line segments approach the horizontal direction or the vertical direction.

In general, the line segment corresponding to the border of the table or picture has a length longer than the average length of the text line, so that the control unit 120 can extract the line segment corresponding to the border of the table or picture in the document image have.

,

)이고, 끝점의 좌표가 (

,

)라면, 아래의 수학식 11의 비용 함수는 추출된 선분들이 가로 방향 또는 세로 방향에 가까워질수록 값이 작아진다.The coordinates of the starting point of the i-th line segment among the extracted line segments are (

,

), And the coordinates of the end point are (

,

), The cost function of the following Equation (11) becomes smaller as the extracted line segments approach the horizontal direction or the vertical direction.

Accordingly, the controller 120 may combine the cost functions of Equations (6), (7), (10) and (11) as described above to design the cost function of Equation (12).

는 수학식 6 또는 7 중에서 어느 하나이거나, 또는 수학식 3 내지 5의 비용 함수들을 다른 형태로 적절히 결합하여 생성된 비용 함수일 수도 있다.At this time,

May be any of the expressions (6) and (7), or may be a cost function generated by appropriately combining the cost functions of the expressions (3) to (5) in other forms.

In Equation (12), coefficients are not included in each term of the right side, but a coefficient having an arbitrary value may be included in order to give a weight to the cost function of each term of the right side as necessary.

On the other hand, although the cost functions of Equations (10) and (11) are all included in the right side of Equation (12), a cost function may be designed to include only one of them.

The controller 120 estimates the variable values minimizing the cost function of Equation (12), and performs smoothing of the document image using the estimated variable values.

에는 문서 영상에서 추출된 텍스트 라인이 대입되어야 하는데, 오검출된 텍스트 라인이 있을 경우, 즉 실제로는 텍스트 라인이 아닌데 텍스트 라인으로 검출된 성분이 있을 경우에는 평활화 성능이 낮아지는 문제가 있다. 또한, 수학식 12의

및

의 비용 함수들은 문서 영상에 포함된 선분들이 직선이거나, 가로 방향 또는 세로 방향으로 배치된다는 전제 하에 설계된 것이므로, 문서 영상에 곡선이 포함되어 있거나, 또는 문서 영상에 포함된 선분들이 가로 방향 또는 세로 방향의 배치가 아닌 경우라면 역시 평활화 성능이 낮아지게 되는 문제가 있다.On the other hand,

There is a problem that smoothing performance is lowered when there is a component that is detected as a text line when there is an erroneously detected text line, that is, when the text line is not actually a text line. Further, in Equation 12,

And

The cost functions of the document image are designed on the assumption that the line segments included in the document image are straight lines or are arranged in the horizontal direction or the vertical direction. Therefore, if the document image includes a curve or the line segments included in the document image are horizontal There is a problem that the smoothing performance is also lowered if it is not arranged.

Accordingly, in order to solve such a problem, the controller 120 repeatedly performs the process of performing the smoothing by applying the cost function, and removes the components that increase the value of the cost function each time the process is performed, .

For example, the controller 120 performs the primary smoothing of the document image using the cost function of Equation (12), and in the process of performing the primary smoothing, the components that make the values of the rightmost terms of Equation (12) Remove. Then, the controller 120 performs second-order smoothing again using the cost function of Equation (12) for the result image subjected to the first-order smoothing. When the secondary smoothing is performed, the controller 120 performs smoothing by excluding the components removed in the primary smoothing process. In addition, the controller 120 also removes components that maximize the value of the right-hand side of Equation (12) in the process of performing the second-order smoothing. The control unit 120 can increase the smoothing performance by repeatedly performing this process.

By using the document image smoothing apparatus 100 according to an embodiment, the cost function is designed by reflecting the property of the segment included in the non-text area of the document image, and by using the cost function for the smoothing process, It is possible to effectively remove the distortion occurring in the non-text area.

FIG. 7 is a flowchart for explaining a document image smoothing method according to an embodiment.

The document image smoothing method according to the embodiment shown in FIG. 7 includes steps that are processed in a time-series manner in the service apparatus 100 shown in FIG. Therefore, even though omitted from the following description, the above description of the document image smoothing apparatus 100 shown in FIG. 1 can be applied to the document image smoothing method according to the embodiment shown in FIG.

Referring to FIG. 7, in step 701, a first cost function is designed based on the property of lines included in a non-text area of a document image so that the value decreases as distortion existing in the document image is removed. In detail, the fourth cost function is designed so that the value decreases as the line segment included in the non-text area becomes closer to the straight line, and when the line segment included in the non-text area approaches the horizontal direction or the vertical direction, Function, and combining the fourth cost function and the fifth cost function to generate a first cost function.

The process of designing the fourth cost function will be described in more detail. Some of the line segments included in the non-text area are grouped according to a preset reference, so that the value becomes smaller the closer the starting point of each grouped line segment is to a straight line A fourth cost function can be designed. The details are described with reference to Figs. 3 to 5, and the fourth cost function can be designed as shown in Equation (10).

The fifth cost function designing process will be described in more detail. The line segments longer than the average length of the text lines included in the document image are extracted from the line segments included in the non-text area. The fifth cost function can be designed so that the value becomes smaller as the direction becomes closer to the direction. The details are described with reference to FIG. 6, and the fifth cost function can be designed as shown in Equation (11).

On the other hand, the first cost function may be designed to include only one of the fourth cost function or the fifth cost function. Alternatively, the first cost function may be designed to include a coefficient that weights at least one of the fourth cost function or the fifth cost function.

In step 702, a second cost function is designed based on the property of the text lines included in the text area of the document image so that the value decreases as the distortion existing in the document image is removed. In step 703, a third cost function is designed by combining the first cost function and the second cost function. In step 704, the distortion existing in the document image is removed using the third cost function.

FIG. 8 is a view comparing the result of performing the document image smoothing method according to the embodiment with the result of performing the smoothing method.

Here, the existing smoothing method refers to a method of smoothing a document image using only a cost function that reflects properties of text lines included in a text area. In this case, since the elements included in the non-text area are not reflected in the smoothing process, the distortion existing in the non-text area is not removed.

8, the first image 81 is a document image taken by a camera, the second image 82 is a result of smoothing using a conventional smoothing method, and the third image 83 is a document image Which is a result of performing smoothing using the smoothing method according to the embodiment. Referring to FIG. 8, it can be seen that the distortion is more effectively removed from the third image 83 than the second image 82.

The term " part " used in the above embodiments means a hardware component such as a software or a field programmable gate array (FPGA) or an ASIC, and the 'part' performs certain roles. However, 'part' is not meant to be limited to software or hardware. &Quot; to " may be configured to reside on an addressable storage medium and may be configured to play one or more processors. Thus, by way of example, 'parts' may refer to components such as software components, object-oriented software components, class components and task components, and processes, functions, , Subroutines, segments of program patent code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables.

The functions provided within the components and components may be combined with a smaller number of components and components or separated from additional components and components.

In addition, the components and components may be implemented to play back one or more CPUs in a device or a secure multimedia card.

The document image smoothing method according to the embodiment described with reference to FIG. 7 may also be implemented in the form of a computer-readable medium for storing instructions and data executable by a computer. At this time, the command and data may be stored in the form of program code, and when executed by the processor, a predetermined program module may be generated to perform a predetermined operation. In addition, the computer-readable medium can be any available media that can be accessed by a computer and includes both volatile and nonvolatile media, removable and non-removable media. The computer-readable medium can also be a computer storage medium, which can be volatile and non-volatile, implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data, Volatile, removable and non-removable media. For example, the computer recording medium may be a magnetic storage medium such as an HDD and an SSD, an optical recording medium such as a CD, a DVD and a Blu-ray Disc, or a memory included in a server accessible via a network.

The document image smoothing method according to the embodiment described with reference to FIG. 7 may also be implemented as a computer program (or a computer program product) including instructions executable by a computer. A computer program includes programmable machine instructions that are processed by a processor and can be implemented in a high-level programming language, an object-oriented programming language, an assembly language, or a machine language . The computer program may also be recorded on a computer readable recording medium of a type (e.g., memory, hard disk, magnetic / optical medium or solid-state drive).

Therefore, the document image smoothing method according to the embodiment described with reference to FIG. 7 can be implemented by a computer program as described above being executed by the computing device. The computing device may include a processor, a memory, a storage device, a high-speed interface connected to the memory and a high-speed expansion port, and a low-speed interface connected to the low-speed bus and the storage device. Each of these components is connected to each other using a variety of buses and can be mounted on a common motherboard or mounted in any other suitable manner.

Where the processor may process instructions within the computing device, such as to display graphical information to provide a graphical user interface (GUI) on an external input, output device, such as a display connected to a high speed interface And commands stored in memory or storage devices. As another example, multiple processors and / or multiple busses may be used with multiple memory and memory types as appropriate. The processor may also be implemented as a chipset comprised of chips comprising multiple independent analog and / or digital processors.

The memory also stores information within the computing device. In one example, the memory may comprise volatile memory units or a collection thereof. In another example, the memory may be comprised of non-volatile memory units or a collection thereof. The memory may also be another type of computer readable medium such as, for example, a magnetic or optical disk.

And the storage device can provide a large amount of storage space to the computing device. The storage device may be a computer readable medium or a configuration including such a medium and may include, for example, devices in a SAN (Storage Area Network) or other configurations, and may be a floppy disk device, a hard disk device, Or a tape device, flash memory, or other similar semiconductor memory device or device array.

It will be apparent to those skilled in the art that the above-described embodiments are for illustrative purposes only and that those skilled in the art will readily understand that various changes and modifications can be made without departing from the spirit or scope of the present invention. You will understand. It is therefore to be understood that the above-described embodiments are to be considered in all respects only as illustrative and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

It is to be understood that the scope of the present invention is defined by the appended claims rather than the foregoing description and should be construed as including all changes and modifications that come within the meaning and range of equivalency of the claims, .

100: document image smoothing device 110: input /
120: control unit 130:
140:

Claims (16)

A method for smoothing a document image,
Designing a first cost function based on properties of lines contained in a non-text area of a document image;
Designing a second cost function based on properties of text lines included in a text area of the document image;
Combining the first cost function and the second cost function to generate a third cost function; And
And removing distortion existing in the document image using the third cost function,
Wherein designing the first cost function comprises:
Designing a fourth cost function in which a value of a line segment included in the non-text area becomes smaller as the line segment is closer to a straight line;
Designing a fifth cost function in which a value of a line segment included in the non-text area decreases as the line segment approaches the horizontal direction or the vertical direction; And
Combining the fourth cost function and the fifth cost function to generate the first cost function,
Wherein designing the fourth cost function comprises:
Grouping a part of the line segments included in the non-text area according to a preset reference; And
And designing the fourth cost function so that the starting point of each of the grouped line segments becomes smaller as the line segment connecting the starting point and the ending point of two line segments located at both ends of the grouped line segments becomes closer . ≪ / RTI > delete delete The method according to claim 1,
Wherein the grouping comprises:
Extracting line segments satisfying a condition that a distance between line segments is equal to or less than a preset predetermined value and a difference in direction between line segments is equal to or less than a preset constant value is extracted and grouped Way. The method according to claim 1,
Wherein designing the fifth cost function comprises:
Extracting line segments longer than an average length of text lines included in the document image, among line segments included in the non-text area; And
And designing the fifth cost function such that the value of the extracted line segments decreases as the line segments approach the horizontal or vertical direction. The method according to claim 1,
Wherein the first cost function comprises only one of the fourth cost function or the fifth cost function. The method according to claim 1,
Wherein the first cost function comprises a coefficient giving a weight to at least one of the fourth cost function or the fifth cost function. A computer-readable recording medium on which a program for carrying out the method according to claim 1 is recorded. A computer program stored in a medium for performing the method of claim 1, which is performed by a document image smoothing device. A document area dividing device comprising:
An input / output unit for receiving an input related to processing of a document image and for displaying a status and a result of processing of the document image;
A storage unit for storing a program for performing smoothing of a document image; And
And a control unit for performing smoothing of the document image by executing the program,
The control unit may design a first cost function based on properties of lines included in the non-text area of the document image, and calculate a second cost function based on properties of the text lines included in the text area of the document image And removing a distortion existing in the document image using a third cost function generated by combining the first cost function and the second cost function,
Wherein the control unit designates a fourth cost function in which a value of the line segment included in the non-text area becomes smaller as the line segment is closer to a straight line and designates a fourth cost function in which the value decreases as the line segment included in the non- 5 cost function, combining the fourth cost function and the fifth cost function to generate the first cost function,
Wherein the control unit groups a part of the line segments included in the non-text area according to a preset reference, and the start point of each of the grouped line segments is divided into two line segments positioned at both ends of the grouped line segments And designing the fourth cost function so that the value becomes smaller as it is located closer to the straight line connecting the start point and the end point. delete delete 11. The method of claim 10,
Wherein,
Extracting line segments satisfying a condition that a distance between line segments is equal to or less than a preset predetermined value and a difference in direction between line segments is equal to or less than a preset constant value is extracted and grouped Device. 11. The method of claim 10,
Wherein,
Extracting line segments that are longer than an average length of the text lines included in the document image from the line segments included in the non-text area, and reducing the value of the extracted line segments as the line segments are closer to the horizontal direction or the vertical direction, And designing a cost function. 11. The method of claim 10,
Wherein,
And designing the first cost function to include only the fourth cost function or the fifth cost function. 11. The method of claim 10,
Wherein,
And to design the first cost function to include a coefficient that weights at least one of the fourth cost function or the fifth cost function.

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