KR20160040330A - A method of correcting for distorted image from fish-eye lens by using concentric circles type standard patterns - Google Patents

Abstract

The present invention relates to a method for correcting a distorted image obtained from a fish-eye lens. According to the present invention, the method for correcting a distorted image obtained from a fish-eye lens by using a concentric circular standard pattern comprises the following steps: obtaining a second-dimensional image before correction through an oval fish-eye lens having an angle of view greater than or equal to 180 degrees, and arranging the image on a first plane; generating a three-dimensional oval image corresponding to the oval fish-eye lens; mapping a first coordinate of the image before correction to a second coordinate one to one by vertically reflecting the image before correction on the three-dimensional oval image; and mapping the second coordinate to a third coordinate one to one on a plane identical to the first plane by extending the second coordinate from an optical center point of the three-dimensional oval image, and correcting a distorted image of the image before correction to an image after correction.

Description

[0001] The present invention relates to a method of correcting a distorted image obtained from a fish-eye lens using a concentric circular standard pattern,

The present invention relates to a method of correcting a distorted image obtained from a fish-eye lens, more specifically, focusing on the fact that the structure of a fish-eye lens is close to an ellipsoid, And a method of correcting the distorted image by using a standard pattern and mapping it to radial coordinates.

Image distortion caused by a general lens is largely divided into radial distortion and tangential distortion. Among them, the degree of tangential distortion is very small. However, radial distortion varies from a very small degree of distortion to a severe one, depending on the characteristics of the lens.

These radial distortions are classified into barrel distortion and pincushion distortion depending on the distortion shape.

The barrel distortion is a distortion phenomenon that occurs mainly in a wide-angle lens with short focal length, which means that information of the image is curved outward. The degree of bending outward is characterized by getting worse to the edge than to the center.

The failure type distortion is a distortion phenomenon that occurs mainly in a telephoto lens having a long focal length. In contrast to the barrel type distortion, the image information is warped inward, and distortion occurs at the edge of the image rather than in the center.

The fisheye lens is an ultra-wide-angle lens with the shortest focal length, and the degree of distortion that occurs during image acquisition is very high.

The general method of correcting the distortion caused by the characteristics of the fisheye lens can be roughly divided into two methods.

First, it is a distortion correction method through mathematical modeling considering lens characteristics.

This approach is the most widely used lens correction method, in which the lens is considered as one system and the response function of the lens is estimated.

Modeling the degradation process of the lens through the response function analysis, the degradation process is corrected by inverse filtering the process.

However, since the distortion correction method using the mathematical modeling does not consider all the various environments, various unexpected problems arise when applied to a commercialization process. In addition, distortion correction methods using many mathematical modeling methods have a long time to perform the inverse filtering process.

In order to solve these problems, various technologies that have been studied recently are being developed based on existing mathematical modeling so that various factors that cause deterioration including the external environment can be adaptively applied to real products.

Another method for correcting the distortion of the fisheye lens is to use a correction method based only on the obtained image irrespective of the type of lens. In this method, a parameter for correcting image distortion is set, and the degree of distortion correction is determined according to this value (See Patent Document 1).

The distortion correction method through most images has a limitation that the degree of distortion correction is determined as the degree of distortion of the straight line and the parameter when the result of the distortion correction on the straight line is expressed as an actual straight line is determined as the distortion correction parameter .

1. Patent Application No. 10-2012-0105249, entitled " Image distortion correction apparatus and method

The present invention relates to a method for correcting image distortion of a fisheye lens described in the above-mentioned prior art, wherein a radial distortion parameter of a fisheye lens using a radial concentric circular standard pattern instead of a straight line- And correcting the distorted image.

A method of correcting a distorted image obtained from a fish-eye lens according to the present invention by using a concentric circular standard pattern is a method of acquiring a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an image angle of 180 degrees or more, Placing; Generating a three-dimensional ellipsoid image corresponding to the ellipsoidal fisheye lens; Vertically projecting a first coordinate of the pre-correction image on the three-dimensional ellipsoid and mapping the first coordinate of the pre-correction image one-to-one with a second coordinate, which is an elliptical coordinate system; And the step of correcting the distorted image of the pre-correction image into an after-correction image by mapping the second coordinate from the optical center point of the three-dimensional ellipsoid to one-to-one mapping on the same plane as the first plane with the third coordinate.

According to another aspect of the present invention, there is provided a method of correcting a distorted image obtained from a fish-eye lens using a concentric circular standard pattern, comprising: obtaining a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an image angle of 180 degrees or more; Acquiring a structural parameter of the ellipsoidal fisheye lens from the pre-correction image to generate a three-dimensional ellipsoid; Disposing the pre-correction image on a first plane having a first horizontal coordinate system; Vertically projecting all the first coordinates displayed in the first horizontal coordinate system of the pre-correction image on the three-dimensional ellipsoid and mapping them one-to-one with a second coordinate system that is an elliptical coordinate system; Correcting the distorted image of the pre-correction image into an after-correction image by mapping the second coordinate system one-to-one with a third horizontal coordinate system disposed on the same plane as the first plane, extending from an optical center point on the three- .

The method of correcting a distorted image obtained from a fish-eye lens proposed in the present invention by using a concentric circular standard pattern has the following advantages.

In general, various distortion compensation algorithms have been proposed based on the assumption that the shape of the fisheye lens is spherical. In the present invention, however, it is assumed that the fisheye lens has an ellipsoid shape having a difference in radial radius, And then performing a mapping process to a radial coordinate system, there is an advantage that distortion image compensation according to actual situations can be performed.

1 and 2 are views showing a state in which a pre-correction image obtained through a fish-eye lens according to the present invention is arranged on a first plane.
3 is a diagram illustrating a process in which the pre-correction image is vertically mapped to an ellipsoid coordinate system.
4 is a view for explaining a process in which a coordinate vertically mapped to an ellipsoidal phase coordinate system is radially extended and compensated by a plane left coordinate system.
5 is a reference diagram for explaining the plane coordinate system of FIG.
FIG. 6 is a chessboard-like standard pattern used in the image-only correction method.
Fig. 7 is a diagram showing a standard pattern of concentric circles proposed by the present invention.
8 is a pre-correction image of Fig. 6
9 is a pre-correction image of Fig.
Fig. 10 is a post-correction image when the method according to the present invention is used with respect to Fig.
Fig. 11 is a corrected image when the method according to the present invention is used for Fig. 9; Fig.
FIG. 12 is a view for explaining a phenomenon in which distortion due to a degree of image distortion caused by a fish-eye lens is radially separated from an optical center point, and curvature is closer to an ellipse than a circle.

Hereinafter, a method of correcting a distorted image obtained from a fish-eye lens proposed in the present invention using a concentric standard pattern will be described with reference to the drawings.

1 and 2 are views showing a state in which a pre-correction image obtained through a fisheye lens according to the present invention is arranged on a first plane, FIG. 3 is a view showing a state in which a pre- 4 is a view for explaining a process in which coordinates vertically mapped to the ellipsoid phase coordinate system are radially extended and compensated by the plane left coordinate system, 6 is a chessboard-type standard pattern used in a correction method using only an image, FIG. 7 is a diagram of a concentric circle standard pattern proposed in the present invention, and FIG. 9 is a pre-correction image of Fig. 7, Fig. 10 is a post-correction image when the method according to the present invention is applied to Fig. 8, and Fig. In the case of using the method according to the present invention.

The present invention proposes a new image distortion correction method suitable for the ellipsoid structure of a real fish-eye lens in consideration of the fact that a normal fisheye lens is not a spherical shape having a radial radius equal to the optical center point but smaller than an ellipsoidal image structure.

The method of correcting a distorted image of a new fish-eye lens proposed in the present invention is a method of correcting a distorted image by mapping an acquired image to an ellipsoidal image coordinate of a fish-eye lens and re- I suggest.

1 is a view showing a state in which a pre-correction image obtained through a fish-eye lens according to the present invention is arranged on a first plane. For reference, the ellipsoid shown in Fig. 1 is an ellipsoid programmed to have the same structure as a fish-eye lens of an ellipsoid, but will be hereinafter referred to as a fish-eye lens for convenience of explanation.

The image correction method proposed by the present invention comprises the following steps.

First, a method for correcting a distorted image according to the present invention comprises the steps of acquiring a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an angle of view of 180 degrees or more and arranging the two-dimensional image on a first plane (see FIG. 1) The first plane means a plane in which a quadrangular plane is in contact with the ellipsoid horizontally.

In the present invention, a three-dimensional ellipsoid image is generated in which the focal length f of the fish-eye lens and the radius r of the lens are respectively long and short.

The coordinates (x, y, z (= f)) of the coordinate system (u _x , u _y , u _z ) in Fig. 2 represent a coordinate system according to the display time.

Axis unit vector u _z of the initial coordinate system is defined from the vector passing through the optical center point (0,0, f) of the lens in the pre-correction image and the center point (0,0,0) on the ellipsoid, and Z Define the initial coordinate system by defining the remaining Y-axis unit vector (u _y ) and X-axis unit vector (u _x ) based on the axis unit vector (u _z ).

Coordinates in Fig. 3 (x ', y', z ') is orthogonal projection in which points on the ellipsoid, in accordance with the point (x, y, z) to the coordinate system _{(u x, u y, u} z) which is located in the uncorrected image .

When the coordinate system (u _x , u _y , u _z ) is defined as shown in Fig. 3, the coordinates in the pre-correction image are orthogonally projected on the three-dimensional ellipsoid in order to correct the distorted image of the pre-correction image.

That is, the coordinates in the pre-correction image are transformed into the coordinates on the surface on the ellipsoid.

As a result, the subject of the pre-correction image projected onto the surface of the ellipsoid is again converted into a three-dimensional object, and has no distortion as in the actual three-dimensional scene.

At this time, the specific coordinates (x ', y', z ') on the ellipsoid have a relationship as shown in Equation (1) with respect to the coordinates (x, y, z (= f)) of the image before correction.

Equation (1)

(x ', y', z ') = (x, y, f')

Next, in order to obtain the corrected image at the display time, as shown in Fig. 4, the coordinates on the surface on the ellipsoid are projected in a perspective manner with respect to the center point on the ellipsoid, and are converted into the coordinates in the corrected image.

As a result, the subject on the surface of the ellipsoid is projected as the subject of the corrected image.

This is illustrated in more detail by a two-dimensional drawing, as shown in FIG.

The coordinates (X, Y, Z) represent the points of the corrected image obtained by projecting a point on the surface of the ellipsoid with respect to the center point on the ellipsoid in accordance with the coordinate system (u _x , u _y , u _z ).

Referring to FIG. 5, the relationship between the coordinates of (X, Y, Z) in the corrected image at the display time and the coordinates of (x ', y', z ') in the surface of the ellipsoid is as follows.

The distance between the coordinates of (x ', y', z ') and the center point on the ellipsoid is equal to the focal length (f) on the ellipsoid, and the distance between the center point of the corrected image and the center point on the ellipsoid is the focal length (f).

이 된다. And the z 'value (f') of the coordinates of (x ', y', z ') in the surface on the ellipsoid is determined by the Pythagorean definition

.

Therefore, the X value of the corrected image at the display time is

라는 공식에 의해

By the formula

의 값을 가지게 되고,

Lt; / RTI >

라는 공식에 의해The Y value is

By the formula

의 값을 가지게 된다.

. ≪ / RTI >

And the Z value is the focal length (f) on the ellipsoid.

That is, the relationship (2) is established between the coordinates (X, Y, Z) of the corrected image at the initial display time and the coordinates (x ', y', z ') on the surface of the ellipsoid.

Equation (2)

(3) between the coordinate value (X, Y, Z) of the image after correction at the display time and the coordinate value (x, y, z) of the pre-correction image because x '= x, y = Respectively.

Equation (3)

에 따라 변환하고, The x value in the pre-correction image is

Respectively,

에 따라 변환하면, 디스플레이 시점에서의 보정 후 이미지는 왜곡 영상 보정된 피사체를 획득할 수 있게 된다.y value

The post-correction image at the display time can acquire the distorted image-corrected subject.

In the present invention, in order to obtain the parameters in the derived formula, a concentric circular standard pattern is used instead of the chess plate type standard pattern mainly used in the correction method using only the obtained image.

This is because most of the radial distortion occurs when using a fisheye lens, and the present invention uses a concentric circle standard pattern which is easy to overcome this disadvantage.

The result after the distortion image correction according to the present invention was as shown in Fig. 10 and Fig.

The above-described present invention uses a method of generating and processing a 3-dimensional ellipsoid image corresponding to a ellipsoidal fisheye lens in a programmatic manner.

However, if desired, a predetermined parameter for the ellipsoidal image of the fisheye lens may be programmed using a standard concentric circle pattern, the method of which is shown in Fig.

As shown in FIG. 12, the image distortion due to the fisheye lens appears due to the degree of distortion depending on the degree of radial deviation from the optical center point, and the curvature is closer to the ellipse than to the circle

Accordingly, the present invention proposes a method of obtaining a curvature of a distortion function from a distorted image by a fisheye lens using a concentric circle standard image and using the same.

In FIG. 12, when a standard image having the same concentric width before distortion is photographed through a fish-eye lens, a phenomenon that the width of the concentric circle is radially symmetrically distorted can be seen. The distortion has an elliptical structure, not a spherical shape.

Accordingly, in the present invention, the long and short axes of the ellipse are obtained by obtaining the distorted curvature, and then the coordinates after the distortion correction can be obtained from the previously derived expression.

The embodiment of the present invention can be realized by the following steps.

That is, another embodiment of a method of correcting a distorted image obtained from a fisheye lens of the present invention using a concentric circular standard pattern is to obtain a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an image angle of 180 degrees or more step; Acquiring a structural parameter of the ellipsoidal fisheye lens from the pre-correction image to generate a three-dimensional ellipsoid; Disposing the pre-correction image on a first plane having a first horizontal coordinate system; Vertically projecting all the first coordinates displayed in the first horizontal coordinate system of the pre-correction image on the three-dimensional ellipsoid, and mapping the one-to-one mapping to a second coordinate system that is an elliptical coordinate system; Correcting the distorted image of the pre-correction image into an after-correction image by mapping the second coordinate system one-to-one with a third horizontal coordinate system disposed on the same plane as the first plane, extending from an optical center point on the three- ≪ / RTI >

For reference, this distortion correction process according to the present invention corresponds to the distortion correction direction in the direction of the blue arrow in FIG. 12, and acquiring the color correction after distortion correction has the same effect as that of obtaining the distortion correction function shown in FIG. 12 .

Claims (2)

Acquiring a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an angle of view of 180 degrees or more and placing it on a first plane having a first horizontal coordinate system;
Generating a three-dimensional ellipsoid image corresponding to the ellipsoidal fisheye lens;
Vertically projecting all the first coordinates displayed in the first horizontal coordinate system of the pre-correction image on the three-dimensional ellipsoid, and mapping the one-to-one mapping to a second coordinate system that is an elliptical coordinate system;
Correcting the distorted image of the pre-correction image into an after-correction image by mapping the second coordinate system one-to-one with a third horizontal coordinate system disposed on the same plane as the first plane, extending from an optical center point on the three- And correcting the distorted image obtained from the fish-eye lens by using a concentric circle-shaped standard pattern. Acquiring a two-dimensional pre-correction image through an ellipsoidal fisheye lens having an angle of view of 180 degrees or more;
Acquiring a structural parameter of the ellipsoidal fisheye lens from the pre-correction image to generate a three-dimensional ellipsoid;
Disposing the pre-correction image on a first plane having a first horizontal coordinate system;
Vertically projecting all the first coordinates displayed in the first horizontal coordinate system of the pre-correction image on the three-dimensional ellipsoid, and mapping the one-to-one mapping to a second coordinate system that is an elliptical coordinate system;
Correcting the distorted image of the pre-correction image into an after-correction image by mapping the second coordinate system one-to-one with a third horizontal coordinate system disposed on the same plane as the first plane, extending from an optical center point on the three- And correcting the distorted image obtained from the fish-eye lens by using a concentric circle-shaped standard pattern.

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