TWI576652B - Conical calibration target used for calibrating image acquisition device - Google Patents

Description

Correcting a cone correction piece used by an image capture device

The present invention relates to a calibrator for use in calibrating an image capture device; more particularly, the invention relates to a conical surface correction member for use in calibrating an image capture device that provides a plurality of projection distance information simultaneously.

When shooting a global space scene, multiple image capturing devices are simultaneously photographed to obtain image information of any position in the space. At this time, correction of the image capturing devices needs to be established to determine the image capturing. The devices can cooperate with each other to obtain applicable information, wherein the correction refers to the process of obtaining internal and external parameters of the image capture device. For calibration, a correction member is generally provided outside the image capturing device for obtaining internal and external parameters of the image capturing device, and the position and orientation of the image capturing device are defined by a right angle coordinate system (card type) Coordinate system) because it provides system directivity of the azimuthal position of the image capture device relative to the correction member.

The internal parameters of the image capturing device reflect the mapping relationship between the three-dimensional target point and the two-dimensional image point in the coordinate system of the image capturing device, and the external parameters of the image capturing device refer to the world coordinate system and image of the target point at the target point. The relationship between rotation and translation between the coordinate system of the device is captured. Commonly used image capture device internal parameters include focal length, the position of the lens projection center image on the image, the aspect ratio of the pixel, and the distortion of the lens. Generally, if the internal mechanism and the lens of the image capturing device do not change, the internal parameters of the image capturing device are fixed regardless of the position of the image capturing device; however, the image capturing device with the zoom lens is provided. In terms, its intrinsic parameters (such as focal length, etc.) will change with the focus. The external parameters of the commonly used image capturing device include the position and shooting direction of the image capturing device in the three-dimensional coordinate, including the rotation matrix and the displacement matrix, and the difference between the internal parameters of the image capturing device is: the external parameters of the image capturing device and The position of the image capturing device is related to the shooting direction. Therefore, each time the image capturing device is moved once, the external parameters need to be recalibrated again.

The conventional correction member includes a three-dimensional correction member, a two-dimensional correction member, and a one-dimensional correction member, as shown in "1A", "1B", and "1C", respectively.

The three-dimensional correcting member is calibrated by two or three mutually perpendicular planes or a plane through a simple and known translation, which can obtain precise correction results, but requires a precise mechanical moving platform and is difficult to use in a wide range. Correction of the image capture device for monitoring.

A two-dimensional correction piece has a known distance pattern, and the plane correction piece performs rotation and displacement in different directions to achieve the purpose of correction, and only needs to print the image as a correction point and attach it to a surface that is not arbitrarily twisted. Just go up. Then, by taking an image generated by the rotation or displacement of the plane at different angles, the parameters of the image capturing device can be obtained. The main disadvantage is that the two-dimensional plane correction member can not observe the correction point information when it is rotated to a certain angle.

If the one-dimensional correcting member is of known length, the parameters of the image capturing device can be estimated by fixing one end and moving the other end. When it is necessary to correct the external parameters of multiple interactive overlapping image capturing devices, the calibration points need to be seen by multiple image capturing devices at the same time. The main disadvantage is that it requires a fixed end and moves the other end to produce multiple sets of corrected images.

It is known from the correction parts of various dimensions that three-dimensional has difficulty in practical application, and one-dimensional and two-dimensional ones have shielding effects on the correction target point caused by the flat surface, and two different points may be different when the flat correction member is rotated. One or two points will be blocked and the correction will be lost.

In view of the shadowing effect of the correction target point existing in the above-mentioned prior art, there is indeed a need to propose a more desirable correction mode.

In view of the improvement of the prior art, the present invention proposes a conical surface correcting member which can effectively avoid the shadowing effect of the correction point on the correcting member, and includes a conical object and a plurality of correction points, the conical object having a pole/ The coordinate described by the ball coordinate system, the coordinates are represented by a radius and an angle; the plurality of correction points are set on the surface of the conical object, selected from the coordinate system, each for indicating a pair of image captures A mapping relationship between a three-dimensional target point and a two-dimensional target image point in the image capturing device coordinate system of the device.

In an embodiment, the conic correction member comprises a conical correction member, a half circle correction member, and a cylinder correction member.

In an embodiment, the conical surface correcting member has a structure having a plurality of target points on the surface.

In one embodiment, the cone correcting member includes a round correcting member, an elliptical correcting member, a parabolic correcting member, and a hyperbolic cross-section correcting member.

Through the above technical means, the present invention can achieve the technical effect that all the images of possible correction points on the correcting member can be smoothly obtained.

The features and embodiments of the present invention will be described in detail below with reference to the drawings and embodiments, which are sufficient to enable those skilled in the art to fully understand the technical means to which the present invention solves the technical problems, and The achievable effects of the present invention.

Hereinafter, the conical surface correcting tool disclosed in the present invention will be described first. Please refer to "2A" to "2C". "2A", "2B" and "2C" are respectively three embodiments of the conical surface correction member of the present invention, which are a conical correction member 10, a half circle correction member 20, and a cylindrical correction member. 30, all of which belong to various deformation derivatives of the conic correction member.

A conic curve or a quadratic curve is a delivery curve obtained by a plane crossing a cone in mathematical geometry, including a circle, an ellipse, a parabola, a hyperbola, and some types of degradation, such as "3A" to "3D". As shown, "3A", "3B", "3C" and "3D" are the shape equations, morphological appearances, individual appearances, and shapes of various cones. Schematic diagram of the standard equation.

The coordinates of the conical correcting member 10 and the semicircular correcting member 20, and the cylindrical correcting member 30 are respectively described by the following formulas (1) and (2) and (1) and (3): , , (1) , , and (2) . (3)

Equation (1) represents the representation of the polar coordinate system. If an angle θ is given, the only ray passing through the angle between the pole and the pole axis is θ (the angle is rotated from the polar axis to the ray in the counterclockwise direction). If a real number r is given, it can be found. On the above ray, the distance from the pole is a point of the integer r. In a polar coordinate system, a target (r, θ) will only correspond to a unique point, but each point can correspond to many coordinates. For example, the coordinates (r, θ), (r, θ+2π), and (−r, θ+π) are all different coordinates corresponding to the same point. The coordinates of the pole are (0, θ), and θ can be any value. Polar coordinates with Can be converted to a right angle coordinate using the formula (1), from a right angle coordinate with It can also be converted to a polar coordinate system using equation (1).

Formula (2) represents the cylindrical coordinate representation, cylindrical coordinate system Right angle coordinate system Converted. Where r is the radius length coordinate value ( r ≧0), which is the distance from point P to the central axis. φ is the angular coordinate value (0 ≤ φ ≤ 2π), which is the counterclockwise rotation angle from the polar axis (X axis). z is the height coordinate value, that is, the distance from the P point to the bottom surface, which is equivalent to the Z coordinate value of the Cartesian coordinate system (-∞<z<∞). The side view and top view of the coordinate system corresponding to the cylinder are shown in Figure 4A and Figure 4B, respectively.

As is generally known, a cone can be considered as a part of the degradation of the ball, so it is generally modeled with the spherical coordinates. A point in the ball coordinate system is defined by two angles φ, θ and a radius length r. Ball coordinates And right angle coordinates Correspondence relationship is shown in formula (3), where For the origin, the coordinate r is the coordinate value of the radius length, that is, the distance from the P point to the center of the coordinate. φ is the azimuth angle coordinate value (0 ≤ φ ≤ 2π), that is, the counterclockwise rotation angle from the X axis. θ is an Elevation angle coordinate value (0 ≤ θ ≤ π), that is, an upward rotation angle from XY. The side view and top view of the coordinate system corresponding to the cone are shown in Figure 5A and Figure 5B, respectively.

Hereinafter, how the conic curve correcting member of the present invention obtains the internal and external parameters of the camera can be corrected. Here, only the conical correction member will be described. Please refer to "2A".

The conical correction piece is exemplified by the following parameters: the size is 150×150 mm, the radius r is 75 mm, and the φ angle is 1 correction point every 10 ⁰ (0 ⁰ , 10 ⁰ , ..., 360 ⁰ A total of 36 lines), a correction point of 8 mm in diameter, and 9 arrays of correction point arrays arranged along the z-axis direction. 3D world coordinate value of the correction point on the cone correction member According to the above formula (3) and the 2D image coordinate value Relationship:

(4) where, versus They are the proportional constants in the u and v axis directions, respectively, in units of pixels/length (Pixels/Unit Length); versus The focal length in the u and v axis directions, respectively, in units of pixels; Is the angle between the u and the v axis The coordinates of the Skew Factor. Ideally simplified to ,then , and . when ,then , , , , . For 9 camera internal parameters (Intrinsic Parameters), including , , , , And lens distortion parameter d ( , , , )Wait. Consider the lens distortion parameter as a 5×1 matrix It refers to Radar Distortion and Tangential Distortion, which are used to describe the degree of deformation of the image after lens imaging. The positive and negative values represent Pincushion Distortion or Barrel Deformation respectively. Distortion). , with Indicates the radial distortion factor of the lens. A tangential distortion diagram that describes whether the process of assembling the lens and camera sensor is parallel to each other. with Representing the tangential distortion coefficient, the matrix is solved by equations (5) and (6), and the distortion coefficient solution is accompanied by the camera correction process. (5) Among them, Is the coordinate value of any point on the undeformed image plane, Is the coordinate value after radial distortion; ; , with Yes It is obtained after the Taylor series expansion as a point at which the optical center is distorted to zero. (6) Among them, Is the coordinate value of any point on the undeformed image plane, It is the coordinate value after tangential distortion. with Indicates the tangential distortion factor. Finishing (5) radial distortion and equation (6) tangential distortion become the equation (7) distortion image equation is: (7) Among them, Is the coordinate value of any point on the undeformed image plane, It is the coordinate value after radial and tangential distortion. 6 versus For camera external parameters, including 3 rotation matrices With 3 translation matrices . and The rotation matrix represents the rotation relationship of the two coordinate systems and the translation relationship of the two coordinate systems of the translation matrix table. R = ( φ , θ , φ ) is a 3 × 3 rotation matrix, φ , θ and φ represent the tilt (Tilt), translation (Pan) and swing (Swing) angles around the x-axis, y-axis and z-axis, respectively. ; Then it is a 3×1 translation matrix. and Expressed as: , (8) defined by equation (4) Projection transformation matrix , , rewritten as: = (9) =H = (10) Solution of H H = (11) (12) (13) Order The matrix can be expressed in the following form: (14) 3D world coordinate value of the correction point on the cone correction member And 2D image coordinates Relationship, by taking n sets of calibration point measurements into the above equation, you can find : (15) Let the above formula be , can be obtained (16) where = The combination of row vectors can be expressed as And It can be obtained by the formulas (11)-(16). By equation (11), = , Is a proportional constant. due to , , Is an orthogonal matrix, resulting in 9 internal parameter matrices Restrictions: , , , , , , , , . , solve camera parameters: (17) Finally, the internal and external parameters of the camera can be obtained from the obtained H and B. (1) Internal parameters: , , , , , (18) (2) External parameters: , , , (19) As long as the correction point of the image of the local area of the cone correction piece is taken, the internal parameters and external parameters of the camera can be obtained. Can be used for single/multi-camera to collect omnidirectional image information, which can avoid the influence of correction point shadowing effect compared to the conventional planar calibration plate. It is also possible to simultaneously correct multiple cameras that are interlaced and interlaced to define the optimal measurement range for a total circle center. Viewed from "Fig. 6A" and "Fig. 6B", it is a schematic diagram of two different focal planes of the cone correction member. The camera directivity of the camera relative to the azimuth position of the plane correction member is corrected between the confocal circular surface 1 and the confocal circular surface 2 range. With the optical center of focal plane 1 and focal plane 2, the three points intersect at the origin of the z-axis, which defines the camera's visible range. The descriptions of the other semi-circular correcting members 20 and the cylindrical correcting members are similar to those of the present conical correcting member 10, which are respectively displayed in "No. 7A" and "No. 7B", and "No. 8A" and "No. 8B". in.

According to the technical means of the present invention, the present invention can achieve the technical effect of smoothly obtaining the internal and external parameters of the image capturing device by smoothly obtaining images of all possible correction points on the correction member used in the image capturing device, thereby solving the prior art. The problem in the middle.

While the embodiments of the present invention have been described above, the above description is not intended to limit the scope of the invention. Any modification of the form and details of the practice of the present invention, which is a matter of ordinary skill in the art to which the present invention pertains, is a patent protection of the present invention. range. The scope of the invention is to be determined by the scope of the appended claims.

10‧‧‧Cone Correction
20‧‧‧ Semicircular Correction
30‧‧‧Cylinder correction parts
1‧‧‧ focal plane
1 2‧‧‧ focal plane 2

1A, 1B, and 1C are schematic diagrams of a three-dimensional correction member, a two-dimensional correction member, and a one-dimensional correction member for a conventional image capturing device;

2A, 2B, and 2C are respectively a third embodiment of a conical correction member, a half circle correction member, and a cylinder correction member of the conical surface correction member of the present invention;

3A, 3B, 3C, and 3D are schematic diagrams of the morphological, morphological, and morphological and morphological equations of various types of cones;

4A and 4B are side and top views of a cylindrical coordinate coordinate system;

5A and 5B are side and top views of the ball coordinate coordinate system;

6A and 6B are side and top views of two different focal planes of the cone correction member;

7A and 7B are side and top views of two different focal planes of the semicircular correcting member; and

8A and 8B are side and top views of two different focal planes of the cylindrical correcting member.

10‧‧‧Cone Correction

Claims (12)

A conical surface correcting member for correcting an image capturing device, comprising: a conical object having a coordinate described by a polar coordinate system; and a plurality of calibration points disposed on the conical object according to the image capturing device In the obtained image, all possible correction points on the calibration component are selected from the polar coordinate system, each of which is used to represent a three-dimensional target point and a two-dimensional target image in the image capturing device coordinate system of the image capturing device. The mapping relationship between points. The conical surface correcting member used in the calibration image capturing device of claim 1 is characterized in that the conic correction member comprises a conical correction member, a half circle correction member and a cylinder correction member. The conical surface correction member used in the calibration image capturing device of the first application of the patent scope is made of a hollow metal material. The conical surface correcting member used in the corrected image capturing device of claim 2, wherein the conical correcting member comprises a round correcting member, an elliptical correcting member, a parabolic correcting member and a hyperbolic cross-section correcting member. The conical surface correcting member used in the corrected image capturing device of claim 2, wherein the conical correcting member and the semicircular correcting member describe the correction point on the correcting member in the following coordinate element relationship: x=rcosθ, y=rsinθ, (2) Where x, y, and z are the coordinate values in the four-corner coordinate system, r and θ are the coordinate values in the one-pole coordinate system, and φ is the one-azimuth angle. The conical surface correcting member used in the corrected image capturing device of claim 2, wherein the cylindrical correcting member describes the correction point on the correcting member in the following coordinate element relationship: x=rcosθ, y=rsinθ, (2) Where x, y, and z are the coordinate values in the four-corner coordinate system, r and θ are the coordinate values in the one-pole coordinate system, φ is the angle of one point, and z is also a height. A conical surface correcting member for correcting an image capturing device, comprising: a conical object having a coordinate described by a polar coordinate system, and one of the following groups: a conical correction member and a half circle correction member And a cylindrical correction member; and a plurality of calibration points are disposed on the conical object, and all possible correction points on the calibration component are selected from the polar coordinate system according to the image obtained by the image capturing device, A mapping relationship between a three-dimensional target point and a two-dimensional target image point in the image capturing device coordinate system of the image capturing device. The conical surface correcting member used in the corrected image capturing device of claim 7 is made of a hollow metal material. The conical surface correcting member used in the corrected image capturing device of claim 7 , wherein the conical correcting member comprises a round correcting member, an elliptical correcting member, a parabolic correcting member and a Hyperbolic section correction. The conical surface correcting member used in the corrected image capturing device of claim 7 is characterized in that the conical correction member and the semicircular correcting member describe the correction points on the correcting member in the following coordinate element relationship: x=rcosθ, y=rsinθ, (2) Where x, y, and z are the coordinate values in the four-corner coordinate system, r and θ are the coordinate values in the one-pole coordinate system, and φ is the one-azimuth angle. The conical surface correcting member used in the corrected image capturing device of claim 7 is wherein the cylindrical correcting member describes the correction point on the correcting member in the following coordinate element relationship: x=rcosθ, y=rsinθ, (2) Where x, y, and z are the coordinate values in the four-corner coordinate system, r and θ are the coordinate values in the one-pole coordinate system, φ is the angle of one point, and z is also a height. For example, the corrected image capturing device of claim 7 uses the correction point of the conical surface correcting member, and the optical center of the focal plane 1 and the focal plane 2, and the three points intersect at the origin of the z-axis. The camera's viewable range.