JP2001082941A - Three-dimensional pattern for calibration - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an accurate calibration even with zooming with one pattern, by creating a calibration pattern by changing a photographing magnification by zooming so that average grain size of a photographed image of the photographed pattern is uniformed. SOLUTION: A calibration pattern 10 is cubic, a front surface 11, an upper surface 12, and a left surface 13 are provided with a pattern of the same size, a part at an origin O in three-dimensional coordinates is small in size, and the size increases outward. Respective surfaces of the pattern need not same, but coordinates of a marked point, for example a corner point of a black portion having oblique lines are made clear. Therefore, a size with a large number of digits and a size with a irrational number are avoided, and each pattern for forming the pattern is a pattern easy to provide a corresponding point and is not limited to square and rectangle. For example, when a checkered pattern in which the size is changed in geometrical series is applied a substantially same pattern goes into a photographing screen regardless of zooming, reference point coordinates are easily determined, and calibration is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to a technical field for recognizing a shape and the like of a three-dimensional object from a photographed image using a zoom camera. More specifically, it belongs to the technical field of three-dimensional patterns for calibration when using a zoom camera.

[0002]

2. Description of the Related Art In three-dimensional image measurement for recognizing the shape of a target object in a three-dimensional space, it is necessary to know camera parameters (or system parameters). The camera parameters can be obtained by actually measuring the focal length of the lens or by measuring the position and orientation of the camera. However, such a method is difficult and time-consuming to measure accurately. Therefore, a reference object having a point whose three-dimensional coordinates are known is photographed,
2. Description of the Related Art A method of obtaining camera parameters or a method of calibrating (calibrating) based on the correspondence between the dimensional coordinates and the coordinates of points on an image obtained by capturing the dimensional coordinates has conventionally been adopted.

In order to measure the shape of a target object 51 in a three-dimensional space, as shown in FIG. 3, images 1 and 2 taken by cameras 52 and 53 having known camera parameters are required. In order to obtain the camera parameters of the camera 52 (or the camera 53), a calibration pattern provided with a reference point (X, Y, Z) in a three-dimensional space coordinate system is arranged in place of the target object 51, and the camera 52
If one set of coordinates (Xc, Yc) (not shown) of the image of the reference point of the captured image 1 (or the captured image 2) by the (or the camera 53) is known, two equations are obtained. Therefore, the camera parameters including the twelve unknowns can be obtained by knowing the coordinates of the captured images of at least six reference points that are not on the same plane.

FIGS. 4 and 5 show examples of conventionally used calibration patterns. The calibration pattern 55 shown in FIG. 4 includes an xy plane 55a, a yz plane 55b, and a zx plane 55c.
Marks 56 whose coordinate positions are known are drawn on 5a to 55c. Note that the marks 56 need not be the same. The calibration pattern 58 shown in FIG. 5 is a cube in which grids 59 with reference intervals are drawn.

When the size of a target object in a three-dimensional space varies in size, photographing is performed by a camera having a zoom lens instead of a fixed focus camera. Zooming changes the focal length and the shooting magnification. The longer (shorter) focal length, the larger (smaller) the shooting magnification. At this time, since the system parameter also takes a different value, it is necessary to obtain the parameter again. In the conventional calibration pattern, since the size and interval of the marks and the like are substantially the same, if the zooming is performed and the photographing magnification is changed, the number of the marks or the like photographed in the photographed image is too small or too large. It was inconvenient. Also, using a different calibration pattern every time zooming is performed is inconvenient in terms of manufacturing and handling operations.

[0006]

SUMMARY OF THE INVENTION The present invention provides a method for measuring a three-dimensional object using a camera having a zoom lens.
Changing the calibration pattern for each zooming, or using one calibration pattern, to prevent the calibration from being inaccurate or difficult due to too few or too many landmarks, etc. The purpose is. The present invention has been made under the above-described background, and has as its object to provide a calibration pattern that can be accurately calibrated even when zooming with one pattern.

[0007]

The present invention employs the following means to solve the above-mentioned problems. That is, claim 1
According to the invention described above, in a calibration three-dimensional pattern for recognizing the shape of a three-dimensional object from a captured image of a zoom camera, the average granularity of a captured image of a calibration pattern captured by changing a capturing magnification by zooming is reduced. It is characterized in that the pattern is configured to be uniform. The particle size means the density of the pattern or the density. That is, a large grain size means that the pattern pattern is coarse, and a small grain size means that the pattern pattern is dense. The zoom camera is not limited to a camera using a mechanical zoom mechanism, but may be a camera using an electronic zoom.

According to a second aspect of the present invention, there is provided a three-dimensional calibration pattern for recognizing the shape and the like of a three-dimensional object from an image captured by a zoom camera. It is characterized in that the grain size of the three-dimensional pattern is made finer and the grain size of the three-dimensional pattern in the outer peripheral portion photographed when the photographing magnification is reduced is made coarse.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the three-dimensional pattern is formed by changing the size of the grain size substantially in a geometric progression.

According to a fourth aspect of the present invention, in the first to third aspects of the present invention, the three-dimensional pattern includes a straight line portion for facilitating obtaining a distortion parameter of the lens.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the three-dimensional pattern is obtained by attaching a pattern to three surfaces of a cube or a rectangular parallelepiped, and Is configured to be a photographing surface.

[0012]

FIG. 1 is an overall view of a calibration pattern according to an embodiment of the present invention, and FIG. 2 is a view for explaining the size of each pattern. Hereinafter, embodiments of the present invention will be described with reference to the drawings.

In FIG. 1, a calibration pattern 10 is a cube, and has a front surface 11, an upper surface 12, and a left side surface 13.
Is provided with a calibration pattern. This pattern has the same size on each of the surfaces 11 to 13. The size of the portion of the origin O (front side) of the three-dimensional coordinates (X, Y, Z) is small, and the size increases toward the outside. . The pattern on each surface does not need to be the same, and may be different, but the coordinates of the mark points, for example, the corners of the black portions with diagonal lines, must be clear. Therefore, dimensions having a large number of digits and dimensions such as irrational numbers must be avoided. Further, it is desirable that each pattern forming the pattern is a pattern in which a corresponding point can be easily obtained, and is not limited to a square or a rectangle.

FIG. 2 shows a case where a checkerboard pattern whose dimensions are changed geometrically is attached. In FIG. 2, the length L of one side of the square 11 is 1200 mm, and the zooming range is a photographing magnification (1 to 3 times). As shown in FIG. 2, the X direction and the Y direction are divided in order to form a square or rectangular pattern, and the length of each side is a1, a2. . . and an. If the ratio an of the maximum side an to L (an / L) is R, and the ratio of the geometric series is r, then an +. . . + A2 + a1 = an (1 + r + r2
+. . . . + Rn) = L. By ignoring values after r to the (n + 1) th power, L =
an {1 / (1-r)}, and R = 1-r.

If R = 1/4, r = 3/4.
When n = 18 and the length of each side is appropriately rounded so that L = 1200 mm, {a18,. . . a3, a2, a
1｝ is {300, 225, 165, 120, 100, 75, 55, 40, 30, 2}
0, 20, 10, 10, 10, 5, 5, 5, 5}. However, the unit of the above numerical value is mm. By setting the length of each side as the above numerical value and forming a square and a rectangle in a cube and appropriately attaching a pattern, a calibration pattern can be obtained. In this pattern, when the photographing magnification is 1 (minimum), that is, when the focal length of the zoom lens is the shortest, the photographing screen is widest, and 18 patterns from the smallest element to the largest element, that is, from the origin O, The entire 1200 mm pattern enters the shooting screen.
When the photographing magnification is set to 3 times (maximum), the photographing screen becomes the narrowest, and 14 patterns from the origin O to 390 mm enter the photographing screen. Although the above numerical example has been described for the case where n = 18, the present invention is not limited to this, and n may be smaller or larger than 18.

Since this embodiment is configured as described above,
When the magnification is 1, the length of the largest square is 300.
A square up to a mm square enters the shooting screen. When the shooting magnification is three times, a square having a maximum square length of up to 100 mm enters the shooting screen. Therefore, since substantially the same pattern enters the shooting screen irrespective of zooming, the coordinates of the reference point can be easily obtained, and the effect that calibration can be easily performed can be obtained. In addition, since the straight line portion is included in the pattern, even if there is distortion of the lens, the distortion can be easily detected, and there is an effect that the distortion can be easily checked. In the present embodiment, the calibration pattern is attached to three faces of the cube, and the reference coordinates can be selected from each face, so that the rank of the coefficient matrix does not drop when calculating the projective transformation matrix. Therefore, there is also an effect that calculation becomes easy.

The embodiments and examples of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to the examples, and changes in design and the like may be made without departing from the gist of the present invention. Even if there is, it is included in the present invention. For example, the shape with the calibration pattern is not limited to a cube or a rectangular parallelepiped. In addition, the calibration pattern has a fine-grained part in the center,
It is not limited to the case where there is a coarse-grained part in the surroundings, but when the photographing magnification is increased (focal length is increased), the coarse-grained pattern is cut and the photographing magnification is reduced (focal length is shortened) Any pattern may be used as long as the average grain size is uniformed so that a coarse grain pattern is included in the pattern.

The zoom camera may be a camera using an electronic zoom. That is, even when using a zoom-type camera with an electronic zoom or a video camera or the like that is configured to interpolate an image signal output from the imaging element to obtain an image with a magnification higher than the actual lens focus. The present invention applies.

[0019]

As described above, according to the structure of the present invention, the average grain size is made uniform regardless of the magnitude of the photographing magnification by zooming, and substantially the same pattern can be put on the photographing screen. An effect is obtained that parameter calibration is easy. According to the fourth aspect of the present invention, since the pattern includes a straight line portion, the effect that the degree of lens distortion can be recognized can be obtained.
According to the fifth aspect of the present invention, since a cube or the like is used, when calculating the projective transformation matrix, the rank of the coefficient matrix is not dropped and the calculation is facilitated, and the production is facilitated. can get.

[Brief description of the drawings]

FIG. 1 shows an overall view of a calibration pattern according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating the size of each pattern when the pattern is changed in geometric progression.

FIG. 3 shows an arrangement relationship between a target object and a camera in three-dimensional image measurement.

FIG. 4 shows a conventional calibration pattern.

FIG. 5 shows another conventional calibration pattern.

[Explanation of symbols]

 10 Calibration pattern

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Claims (5)

[Claims] In a three-dimensional calibration pattern for recognizing a shape or the like of a three-dimensional object from an image captured by a zoom camera, the average granularity of a captured image of a calibration pattern captured by changing a capturing magnification by zooming is determined. A three-dimensional pattern for calibration, wherein the pattern is configured to be uniform. 2. In a calibration three-dimensional pattern for recognizing a shape of a three-dimensional object from an image captured by a zoom camera, the granularity of the central three-dimensional pattern captured when the imaging magnification is increased is determined. A three-dimensional pattern for calibration, characterized in that the fineness is reduced and the granularity of the three-dimensional pattern of the outer peripheral portion photographed when the photographing magnification is reduced is coarsened. 3. The three-dimensional pattern for calibration according to claim 1, wherein the three-dimensional pattern is obtained by changing the size of a particle in a substantially geometric series.
Dimensional pattern. 4. The three-dimensional pattern for calibration according to claim 1, wherein the three-dimensional pattern includes a straight line portion for facilitating obtaining a distortion parameter of the lens. . 5. The three-dimensional pattern according to claim 1, wherein a pattern is attached to three surfaces of a cube or a rectangular parallelepiped so that the three surfaces become a photographing surface. Item 3. The three-dimensional pattern for calibration according to any one of Items 4.