JP7618487B2 - Calibration pattern light projection device - Google Patents

Description

The present invention relates to a device that projects a calibration pattern light for measuring lens distortion aberration.

Conventionally, a method is known in which a calibration pattern with a specific pattern printed on it is used to measure the distortion aberration of a lens.

Figure 14 is a diagram explaining a conventional method for measuring lens distortion using a calibration pattern. In the conventional method, a calibration pattern 101 is used, which is a specific pattern (e.g., a checkerboard pattern) printed on a flat surface, and the user photographs the calibration pattern 101 using a camera 102 attached to a housing 112 of the lens 110 to be measured.

The distortion aberration measuring device 103 inputs the image of the calibration pattern 101 obtained on the focal plane 111 of the camera 102, measures the distortion aberration of the measurement target lens 110 based on the image of the calibration pattern 101, and outputs this as a distortion aberration parameter.

For example, the distortion aberration measuring device 103 determines the center of gravity of each pattern element that constitutes the calibration pattern 101 from the image of the calibration pattern 101, and determines the distortion aberration based on the center of gravity of each pattern element.

A method is also known in which a collimated thin laser beam is incident on the lens being measured from the subject side, and various aberrations, including distortion, are measured based on the imaging state (imaging position and blur condition).

In addition, a weak calibration method is known in which the same subject is photographed multiple times while changing the relative position between the camera and the subject, and camera calibration parameters including distortion aberration are measured based on the multiple images (see, for example, Patent Document 1).

This weak calibration method extracts multiple characteristic image patterns (feature points) from multiple images obtained by shooting, matches the feature points between the multiple images, and measures distortion aberrations and the like from the multiple image coordinate pairs obtained as a result (see paragraphs 56 to 67 of Patent Document 1).

Patent No. 4372328

In the method using the calibration pattern 101 shown in FIG. 14, it is necessary that the calibration pattern 101 be captured so that it fits just within the angle of view α of the camera 102. In addition, it is preferable that the calibration pattern 101 be perpendicular to the optical axis β of the measurement target lens 110.

In a method using such a calibration pattern 101, for example, the wider the angle of the lens 110 to be measured and the longer the distance between the camera 102 and the calibration pattern 101, the larger the area of the calibration pattern 101 needs to be. This can make it difficult to install or handle the calibration pattern 101. Furthermore, when the area of the calibration pattern 101 becomes larger, it becomes more difficult to maintain its planarity, resulting in a problem of deterioration in the measurement accuracy of distortion aberration.

In addition, the aforementioned method using laser light involves attaching a dedicated measuring device to the camera and directing laser light at a precisely calibrated position and angle onto the lens to be measured. With this method, during construction, the camera is brought to a location where the dedicated measuring device is located, and the dedicated measuring device is attached to the camera to measure distortion aberration and the like. Then, during operation, the camera needs to be moved from the location where the dedicated measuring device is located to the operation location, and there is a possibility that distortion aberration and the like may deviate from the state at the time of calibration due to vibrations or temperature changes during transport.

In addition, the weak calibration method described above does not require a specific calibration pattern, but it does require preparing a subject whose feature points can be sufficiently captured, and then capturing multiple images while changing the relative position between the camera and the subject.

The subject must be large enough to fully cover the camera's angle of view; the wider the angle of the lens being measured and the greater the distance between the camera and the subject, the larger the subject must be.

When the camera is moved to change the relative position, the camera parameters may shift due to the effects of vibration, etc. On the other hand, when the subject is moved to change the relative position, the subject may become distorted, especially if the subject is large, which may result in an error in the distortion aberration.

The present invention has been made to solve the above problems, and its purpose is to provide a calibration pattern light projection device that reduces the effort required to measure lens distortion and can measure distortion with high accuracy.

In order to solve the above problem, the calibration pattern light projection device of claim 1 is a calibration pattern light projection device that projects a calibration pattern light for measuring the distortion aberration of a lens attached to a camera onto a predetermined object, and is equipped with a pattern light generation unit that generates the calibration pattern light using a light source, and a half mirror that reflects the calibration pattern light generated by the pattern light generation unit and projects it onto the predetermined object, characterized in that the optical path length from the light source to the predetermined object via the half mirror is equal to the optical path length from the first principal point of the lens to the predetermined object via the half mirror, and when the calibration pattern light is projected onto the predetermined object, the reflected light reflected on the surface of the predetermined object passes through the half mirror and is imaged on the focal plane of the camera via the lens.

The calibration pattern light projection device of claim 2 is the calibration pattern light projection device of claim 1, characterized in that the pattern light generating unit is provided with a movable unit capable of moving the light source in the optical axis direction between the light source and the half mirror.

The calibration pattern light projection device of claim 3 is the calibration pattern light projection device of claim 1 or 2, further comprising a device movable part that moves the calibration pattern light projection device relative to the camera in the optical axis direction between the first principal point of the lens and the half mirror while the position of the light source relative to the half mirror is fixed.

The calibration pattern light projection device of claim 4 is characterized in that, in the calibration pattern light projection device of any one of claims 1 to 3, the pattern light generation unit includes a mask having a plurality of transmitting parts and a plurality of light-shielding parts for forming the pattern of the calibration pattern light, and the calibration pattern light is generated in a solid angle with the light source as the apex using the mask.

The calibration pattern light projection device of claim 5 is the calibration pattern light projection device of any one of claims 1 to 3, characterized in that the pattern light generation unit includes a scanning mechanism that scans the light beam emitted by the light source, and generates the calibration pattern light in a solid angle with the light source as the apex by using the scanning mechanism.

As described above, the present invention reduces the effort required to measure lens distortion and enables distortion to be measured with high accuracy.

1 is a configuration diagram showing an example of an entire system including a calibration pattern light projection device according to an embodiment of the present invention. FIG. 2 is a configuration diagram showing a first example of a pattern light generating unit. 1A is a diagram illustrating a mask for a sequence of points, and FIG. 1B is a diagram illustrating a mask for a checkerboard pattern. 1A is a diagram illustrating a mask using a lens array, FIG. 1B is a diagram illustrating an example of a mask cross section (A-A' surface), and FIG. 1C is a diagram illustrating another example of a mask cross section (A-A' surface). FIG. 13 is a configuration diagram showing a second example of the pattern light generating unit. FIG. 13 is a configuration diagram showing a third example of the pattern light generating unit. 11A and 11B are diagrams illustrating the optical path length when the calibration pattern light projection device according to the embodiment of the present invention is used. FIG. 1A is a diagram illustrating an example of imaging when an object is close to the camera, and FIG. 1B is a diagram illustrating an example of imaging when the object is far away, when the distance between the light source and the half mirror is appropriate. 1A is a diagram illustrating an example of imaging when an object is close to the camera, and FIG. 1B is a diagram illustrating an example of imaging when the light source is far from the half mirror. 1A is a diagram illustrating an example of imaging when an object is close to a camera in the case where the light source is close to the half mirror, and FIG. 1B is a diagram illustrating an example of imaging when the object is far away. FIG. 13A is a diagram illustrating an example of imaging when there is no distortion when a point sequence mask is used, and FIG. 13B is a diagram illustrating an example of imaging when there is distortion. FIG. 13A is a diagram illustrating an example of imaging when there is no distortion aberration, and FIG. 13B is a diagram illustrating an example of imaging when there is distortion aberration, when a checkerboard pattern mask is used. 1A and 1B are diagrams for explaining blurring of an image caused by unevenness on the surface of an arbitrary object. 1A and 1B are diagrams illustrating a conventional method for measuring lens distortion using a calibration pattern.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
[Overall system]
1 is a configuration diagram showing an example of an overall system including a calibration pattern light projection device according to an embodiment of the present invention. This system is configured with a calibration pattern light projection device 1, a camera 102, a distortion aberration measurement device 103, and an arbitrary object 104, and measures the distortion aberration of a measurement target lens 110 based on an image formed by projecting a calibration pattern light onto the arbitrary object 104.

The calibration pattern light projection device 1 generates a calibration pattern light of a predetermined pattern for measuring the distortion aberration of the measurement target lens 110, and projects the calibration pattern light onto an arbitrary object 104.

A measurement target lens 110 is attached to the camera 102. The camera 102 is configured with the measurement target lens 110 and a housing 112, and the housing 112 supports the measurement target lens 110.

The camera 102 captures an image of the arbitrary object 104 and forms an image of the arbitrary object 104 on the focal plane 111. Specifically, the calibration pattern light projected by the calibration pattern light projection device 1 is irradiated onto the arbitrary object 104, and the reflected light from the arbitrary object 104 is incident on the focal plane 111 via the measurement target lens 110, and an image of the arbitrary object 104 is formed on the focal plane 111.

The distortion aberration measuring device 103 inputs data on the image of an arbitrary object 104 formed on the focal plane 111 of the camera 102 in a state in which a predetermined optical path length has been adjusted by the user in the initial adjustment described below. The distortion aberration measuring device 103 then determines the position of the center of gravity of each pattern element that constitutes the image, and measures the distortion aberration of the measurement target lens 110 based on the position of the center of gravity of each pattern element. The distortion aberration measuring device 103 then outputs this as a distortion aberration parameter.

[Calibration Pattern Light Projection Device 1]
Next, a calibration pattern light projection device 1 according to an embodiment of the present invention will be described. The calibration pattern light projection device 1 is attached to a camera 102 on the side of an arbitrary object 104 with respect to a measurement target lens 110 attached to the camera 102, as shown in FIG.

The calibration pattern light projection device 1 includes a pattern light generating unit 10, a half mirror 11, and a housing 12.

The pattern light generating unit 10 generates a calibration pattern light having a predetermined solid angle (e.g., spreading in a cone shape) with the light source as the apex, and projects the calibration pattern light onto the half mirror 11. The pattern light generating unit 10 in FIG. 1 shows a first example in FIG. 2, which will be described later, that includes a movable unit 21, a light source 22, and a mask 23. The pattern light generating unit 10 will be described in detail later.

The half mirror 11 reflects the calibration pattern light generated by the pattern light generating unit 10, and projects the reflected calibration pattern light onto an arbitrary object 104. The half mirror 11 is positioned obliquely relative to the measurement target lens 110.

Preferably, the half mirror 11 is positioned so that when an axis J passing through the center of the mask 23 from the light source 22 provided in the pattern light generating unit 10 is moved symmetrically with respect to the surface normal n of the half mirror 11, the axis coincides with the optical axis β1 of the lens 110 to be measured.

The reflectance and transmittance of the half mirror 11 are arbitrary. For example, if the calibration pattern light projection device 1 is attached to the camera 102 only when measuring distortion aberration, the reflectance may be set to approximately 0.5. If the calibration pattern light projection device 1 is attached not only when measuring distortion aberration but also during normal operation of the camera 102, the reflectance may be set to a smaller value (for example, reflectance = 0.1, transmittance = approximately 0.9, etc.). Figure 1 shows an example of an arrangement where the angle between the half mirror 11 and the optical axis β1 from the half mirror 11 to the measurement target lens 110 is 45 degrees.

The housing 12 supports the pattern light generating unit 10 so that the pattern light generating unit 10 (movable unit 21) moves in the moving direction D during the initial adjustment described below, and has openings on both the camera 102 side and the arbitrary object 104 side. The calibration pattern light projection device 1 is attached to the camera 102 by inserting the opening of the housing 112 provided on the camera 102 into the opening on the camera 102 side of the housing 12.

(First Example of Pattern Light Generator 10)
Next, a detailed description will be given of an example of the configuration of the pattern light generating unit 10 shown in Fig. 1. Fig. 2 is a configuration diagram showing a first example of the pattern light generating unit 10. This pattern light generating unit 10-1 is configured to include a movable unit 21, a light source 22, and a mask 23, and is supported so as to move in a moving direction D relative to the housing 12.

A recess 40 is formed in the movable part 21, the light source 22 is fixed to the bottom surface of the recess 40, and the mask 23 is fixed to the opening of the recess 40. The movable part 21 is movable in a movement direction D relative to the housing 12. Therefore, the light source 22 and the mask 23 are also movable in the movement direction D relative to the housing 12. The movement direction D is the direction of the optical axis (axis J shown in FIG. 1) between the light source 22 and the half mirror 11 (point B shown in FIG. 7 described later).

The movable part 21 may be structured to simply slide in the moving direction D, or may be structured to convert rotational motion into linear motion in the moving direction D, for example, using a helicoid. The movable part 21 is operated by the user during the initial adjustment described below, and its position is adjusted.

When the movable part 21 moves in the moving direction D, the light source 22 fixed to the movable part 21 also moves in the moving direction D, and the distance from the light source 22 to the arbitrary object 104 via the half mirror 11 can be changed (see FIG. 1). In other words, the optical path length L2 of the optical axis β2 (see FIG. 7 described later) from the light source 22 to the arbitrary object 104 via the half mirror 11 can be changed.

The light source 22 is fixed to the bottom surface of the recess 40 of the movable part 21. The light source 22 is preferably a point light source, but the area of the light source 22 may be narrowed down sufficiently (for example, a diameter of 2 mm or less) by using an aperture plate, a diffusion plate, a lens, a reflector, etc. In addition, the directionality of the light emitted by the light source 22 is set to optically cover the opening in the recess 40 of the movable part 21 where the mask 23 described later is fixed.

The mask 23 has a plurality of transmitting portions and a plurality of light-shielding portions for generating a predetermined calibration pattern light from the light emitted by the light source 22. The plurality of transmitting portions of the mask 23 transmit the light from the light source 22, and the plurality of light-shielding portions block the light.

As a result, the light from the light source 22 that is transmitted through multiple transmission sections provided on the mask 23 of the pattern light generating unit 10-1 is generated as a calibration pattern light of a certain pattern, and is projected onto the arbitrary object 104 via the half mirror 11.

Figure 3 (a) is a diagram illustrating an example of a dot array mask 23. This mask 23-1 has a pinhole array with transmissive and light-shielding parts arranged in a two-dimensional lattice pattern. The white areas are transmissive parts, and the black areas are light-shielding parts. The light emitted by the light source 22 passes through the transmissive parts of the pinhole array to generate a calibration pattern light.

Figure 3(b) is a diagram illustrating an example of a checkerboard pattern mask 23. This mask 23-2 has a checkerboard pattern of transmissive and light-shielding parts. As in Figure 3(a), the white areas are transmissive parts and the black areas are light-shielding parts. The light emitted by the light source 22 passes through the transmissive parts of the checkerboard pattern to generate a calibration pattern light.

Figure 4 (a) is a diagram illustrating an example of a mask 23 using a lens array. This mask 23-3 has a lens array consisting of multiple microlenses 30 with transmissive portions and light-shielding portions. As with Figures 3 (a) and (b), the multiple microlenses 30 in the white areas are the transmissive portions, and the black areas are the light-shielding portions. The light emitted by the light source 22 passes through the transmissive portions of the lens array to generate a calibration pattern light.

Figure 4(b) is a diagram illustrating an example of a mask cross section (A-A' plane) of mask 23-3 in Figure 4(a). In the cross section of mask 23-3 shown in Figure 4(b), the lens array is arranged in a straight line. This mask 23-3 is formed in a planar shape overall, and multiple microlenses 30 are arranged on the plane.

Figure 4(c) is a diagram illustrating another example of the mask cross section (A-A' surface) of mask 23-3 in Figure 4(a). In the cross section of mask 23-3 shown in Figure 4(c), the lens array is arranged in a curved shape. This mask 23-3 is formed in a curved shape overall, and has a structure in which a square portion is cut out from a spherical surface centered on light source 22. Note that mask 23-3 may also have a structure in which a square portion is cut out from a surface of any curved shape, such as a cylindrical shape.

In both masks 23-3 shown in Figures 4(b) and (c), the optical axis of the multiple microlenses 30 that make up the lens array passes through the center of the light emission of the light source 22. In addition, the focal length of each microlens 30 is the same as the distance from the principal point of the microlens 30 on the light source 22 side to the center of the light emission of the light source 22.

When multiple microlenses 30 are arranged on a plane, as in the mask 23-3 shown in Figure 4(b), the focal length of the microlenses 30 near the center of the mask 23-3 is shorter than the focal length of the surrounding microlenses 30.

In addition, when multiple microlenses 30 are arranged on a sphere centered on the center of the light emission of the light source 22, as in the mask 23-3 shown in Figure 4 (c), the focal length of the microlenses 30 will match the radius of the sphere.

The three-dimensional arrangement of each microlens 30 is arbitrary, as long as the optical axis of each microlens 30 passes through the center of the light emission of the light source 22 and the focal length is the distance from the principal point of the microlens 30 on the light source 22 side to the center of the light emission of the light source 22.

In this way, by using the mask 23-1 shown in FIG. 3(a), the mask 23-2 shown in FIG. 3(b), and the mask 23-3 shown in FIG. 4(a), a certain pattern of calibration pattern light is generated from the light emitted by the light source 22. Then, the calibration pattern light generated by the pattern light generating unit 10-1 is reflected by the half mirror 11 and projected onto the arbitrary object 104.

In the pattern light generating unit 10-1 shown in FIG. 2, the light source 22 and mask 23 move together with the movable unit 21, but the mask 23 may be fixed to the half mirror 11. For example, the mask 23 is fixed to a predetermined location on the housing 12 that does not interfere with the movement of the movable unit 21. In this case, the pattern light generating unit 10-1 is configured with the pattern light generating unit 10, which includes the movable unit 21 and light source 22, the mask 23, the half mirror 11, and the housing 12, and only the light source 22 moves together with the movement of the movable unit 21.

(Second Example of Pattern Light Generator 10)
Next, a second example of the pattern light generating unit 10 shown in Fig. 1 will be described. Fig. 5 is a configuration diagram showing the second example of the pattern light generating unit 10. This pattern light generating unit 10-2 is configured to include a movable unit 21, a scanning mechanism 24, and a light source 25, and is supported so as to move in a moving direction D relative to the housing 12.

The movable part 21 has a recess 40 formed therein, similar to the pattern light generating part 10-1 shown in FIG. 2. A scanning mechanism 24 is provided on the bottom surface of the recess 40. The movable part 21 can move in a moving direction D relative to the housing 12. As described below, a light source 25 is provided in the scanning mechanism 24, and therefore the scanning mechanism 24 and the light source 25 can also move in the moving direction D relative to the housing 12.

When the movable part 21 moves in the movement direction D, the light source 25 also moves in the movement direction D, and the distance (optical path length) from the light source 25 to the arbitrary object 104 via the half mirror 11 can be changed.

The scanning mechanism 24 is a swivel mechanism installed on the bottom surface of the recess 40 of the movable part 21. A light source 25 is disposed in the scanning mechanism 24. The scanning mechanism 24 scans the light beam emitted by the light source 25 using the swivel mechanism. The scanning mechanism 24 may be capable of scanning in multiple axes (e.g., by changing the elevation angle and azimuth angle) to achieve planar scanning.

The light source 25 generates a light beam (narrowed collimated light γ1) that is sufficiently narrowed (e.g., the diameter of the light-emitting part is 2 mm or less) and sufficiently parallelized (e.g., the spread of the light beam is 5 arc minutes or less). For example, a combination of a laser and a collimating lens can be used as the light source 25.

The pattern light generating unit 10-2 also includes a control unit (not shown), which controls the scanning of the scanning mechanism 24 and the blinking (whether or not light is emitted) or the amount of light emitted of the light source 25 according to a predetermined control pattern. For example, the control unit scans the scanning mechanism 24 and blinks the light source 25 so that a calibration pattern light corresponding to the dot sequence mask 23-1 in FIG. 3(a) is generated. For example, the control unit also scans the scanning mechanism 24 with the light source 25 turned on so that a calibration pattern light of grid-like lines is generated. For example, the control unit also scans the scanning mechanism 24 with the light source 25 turned on so that one or more circular calibration pattern lights are generated.

In this way, the scanning mechanism 24 operates according to a control pattern by a control unit (not shown), which controls the direction of the collimated light γ1 from the light source 25 and the lighting or blinking of the light source 25, thereby generating a certain pattern of calibration pattern light. The calibration pattern light generated by the pattern light generating unit 10-2 is then projected onto the arbitrary object 104 via the half mirror 11.

(Third Example of Pattern Light Generator 10)
Next, a third example of the pattern light generating unit 10 shown in Fig. 1 will be described. Fig. 6 is a configuration diagram showing the third example of the pattern light generating unit 10. This pattern light generating unit 10-3 is configured to include a movable unit 21, a galvanometer mirror 26, and a light source 27, and is supported so as to move in a moving direction D relative to the housing 12.

The movable part 21 has a recess 40 formed therein, similar to the pattern light generating parts 10-1 and 10-2 shown in Figures 2 and 5. A galvanometer mirror 26 is installed on the bottom surface of the recess 40. The movable part 21 is movable in the movement direction D relative to the housing 12.

When the movable part 21 moves in the moving direction D, the galvanometer mirror 26 fixed to the movable part 21 also moves in the moving direction D, and the distance (optical path length) from the light source 27 to the arbitrary object 104 via the galvanometer mirror 26 and the half mirror 11 can be changed.

The galvanometer mirror 26 is a movable reflector installed on the bottom surface of the recess 40 of the movable part 21, and reflects the light beam from the light source 27 and projects the reflected light γ2 toward the half mirror 11 (downward in FIG. 6). In other words, the galvanometer mirror 26 scans the reflected light γ2 of the light beam emitted by the light source 27.

The light source 27 is fixedly installed at a predetermined location in the recess 40 of the movable part 21, and generates a light beam that is sufficiently narrowed and sufficiently parallelized (narrowed collimated light γ1) similar to the light source 25 shown in FIG. 5.

The pattern light generating unit 10-3 also includes a control unit (not shown), which controls the scanning of the galvanometer mirror 26 and the degree of blinking or light emission of the light source 27 according to a predetermined control pattern.

In this way, the galvanometer mirror 26 operates according to the control pattern by the control unit, so that the direction of the reflected light γ2 of the collimated light γ1 emitted by the light source 27 and the lighting or blinking of the light source 27 can be controlled, and a certain pattern of calibration pattern light is generated. The calibration pattern light generated by the pattern light generating unit 10-3 is then projected onto the arbitrary object 104 via the half mirror 11.

The pattern light generating unit 10-3 may be provided with a polygon mirror attached to an actuator instead of the galvanometer mirror 26. The galvanometer mirror 26 may also be configured to perform planar scanning by combining two or more movable reflecting mirrors.

The pattern light generating unit 10-3 may further include a scanning mechanism (equivalent to the scanning mechanism 24 shown in FIG. 5) that scans the collimated light γ1 emitted by the light source 27. In this case, the light source 27 is not installed at a predetermined location in the recess 40 of the movable part 21, but is installed in the scanning mechanism, which is installed at a predetermined location in the recess 40 of the movable part 21. In this way, by combining the scanning mechanism with a scanning mechanism using the movable reflecting mirror of the galvanometer mirror 26, planar scanning can be achieved.

[Distance between the light source 22 and the half mirror 11 and image size when the pattern light generating unit 10-1 is used]
8 to 10, the distance between the light source 22 and the half mirror 11 when the pattern light generating unit 10-1 is used and the size of the image pattern formed on the focal plane 111 will be described. The same applies to the cases when the pattern light generating units 10-2 and 10-3 are used.

Referring to FIG. 1, the calibration pattern light generated by the calibration pattern light projection device 1 is partially reflected by the half mirror 11 and projected onto an arbitrary object 104. The calibration pattern light projected onto the arbitrary object 104 is then reflected by the surface of the arbitrary object 104 (only the diffuse reflection component is considered below).

The light reflected by the pattern portion of the calibration pattern light projected onto the surface of the arbitrary object 104 (for example, when the mask 23-1 of the point sequence shown in FIG. 3(a) is used, the point projected onto the arbitrary object 104 by any bright point of the point sequence) is diffused and passes through the half mirror 11. Then, the reflected light from the arbitrary object 104 that passes through the half mirror 11 is imaged (possibly with defocus) on the focal plane 111 via the measurement target lens 110.

Figure 7 is a diagram explaining the optical path length when the calibration pattern light projector 1 shown in Figure 1 is used. As shown in Figure 7, the distance (optical path length) of the optical axis β1 from the first principal point M of the measurement target lens 110 to the arbitrary object 104 is L1, and the distance (optical path length) of the optical axis β2 from the light source 22 to the arbitrary object 104 via the half mirror 11 is L2. Also, point B is the position (transmission point) of the optical axis β1 on the half mirror 11 through which the reflected light from the arbitrary object 104 transmits, and the position (reflection point) of the optical axis β2 on the half mirror 11 through which the light emitted by the light source 22 reflects.

Furthermore, the optical axial distance (optical path length) from the first principal point M of the measurement target lens 110 to point B of the half mirror 11 is defined as L11, and the optical axial distance (optical path length) from the light source 22 to point B of the half mirror 11 is defined as L22.

The size of the image pattern formed on the focal plane 111 changes depending on the relationship between the optical path lengths L1 and L2 (optical path lengths L11 and L22). For example, assume that the optical path lengths L1 and L2 match due to an initial adjustment described below (optical path lengths L11 and L22 match), i.e., the distance between the light source 22 and the half mirror 11 is appropriate. In this case, as shown in FIG. 8 described below, the size of the image pattern remains unchanged regardless of the distance between the camera 102 and the arbitrary object 104. A detailed explanation will be given below using FIG. 8 to FIG. 10.

Figure 8 shows an example of imaging when the distance between the light source 22 and the half mirror 11 is appropriate, with (a) being a diagram explaining an example of imaging when the object 104 is close to the camera 102, and (b) being a diagram explaining an example of imaging when it is far away. Note that Figure 8 and Figures 9 and 10 described below show examples of imaging when the point sequence mask 23-1 shown in Figure 3(a) is used.

Figures 8(a) and (b) show the case where the distance between the light source 22 and the half mirror 11 is properly adjusted by the initial adjustment described below, i.e., the case where the movable part 21 of the pattern light generating unit 10 is properly adjusted.

As mentioned above, when properly adjusted, this refers to the case in FIG. 7 where the optical path length L1 and the optical path length L2 are the same (where the virtual image of the first principal point M of the measurement target lens 110 coincides with the position of the light source 22, with the half mirror 11 as the reference). In other words, this is the case where L1 = L2 (L11 = L22).

In this case, the size and distortion of the imaging pattern on the focal plane 111 are constant regardless of the distance between the camera 102 and the arbitrary object 104, as shown in Figures 8(a) and (b). Note that the degree of blurring of the imaging pattern may change. Also, although the arrangement of the imaging pattern may be geometrically distorted, the degree of distortion is constant regardless of the distance.

Figure 9 shows an example of image formation when the light source 22 is far from the half mirror 11, with (a) being a diagram explaining an example of image formation when the object 104 is close to the camera 102, and (b) being a diagram explaining an example of image formation when the object is far away.

Figures 9(a) and (b) show the case where the light source 22 is farther from the half mirror 11 than the appropriate position, i.e., the case where L1<L2 (L11<L22) in Figure 7.

The size of the image pattern on the focal plane 111 becomes smaller as the object 104 is farther away from the camera 102, as shown in Figures 9(a) and (b).

Figure 10 shows an example of imaging when the light source 22 is close to the half mirror 11, with (a) being a diagram explaining an example of imaging when the object 104 is close to the camera 102, and (b) being a diagram explaining an example of imaging when it is far away.

Figures 10 (a) and (b) show the case where the light source 22 is closer to the half mirror 11 than the appropriate position, i.e., the case where L1>L2 (L11>L22) in Figure 7.

The size of the image pattern on the focal plane 111 becomes larger as the object 104 becomes farther away from the camera 102, as shown in Figures 10(a) and (b).

[Procedure for measuring distortion aberration of the measurement target lens 110/initial adjustment]
Next, a procedure for measuring the distortion aberration of the measurement target lens 110 using the calibration pattern light projector 1 will be described.

Initial adjustments are performed before actual measurements so that the properties shown in FIG. 8 when the distance between the light source 22 and the half mirror 11 is appropriate can be obtained based on the properties shown in FIG. 8 from FIG. 10. As an initial adjustment, the user first photographs the arbitrary object 104 while changing the optical path length L1 from the camera 102 to the arbitrary object 104. Then, the user adjusts the position of the movable part 21 by moving the movable part 21 in the moving direction D so that the size of the image pattern does not change depending on the shooting distance.

As a result, the optical path length L1 from the first principal point M of the measurement target lens 110 to the arbitrary object 104 via the half mirror 11 is equal to the optical path length L2 from the light source 22 to the arbitrary object 104 via the half mirror 11 (L1 = L2 (L11 = L22)). In other words, as shown in Figures 8 (a) and (b), the size and distortion of the imaging pattern are invariant regardless of the optical path length L1 between the camera 102 and the arbitrary object 104, and it is possible to establish the projection of the calibration pattern light that is not dependent on the shooting distance to the arbitrary object 104.

After such initial adjustment, the calibration pattern light is projected from the calibration pattern light projection device 1 onto some arbitrary object 104, and the data of the image formed on the focal plane 111 is input to the distortion aberration measurement device 103. Then, the distortion aberration measurement device 103 measures the distortion aberration of the measurement target lens 110 based on the image formation data.

[Image formed on focal plane 111]
Next, the image formed on the focal plane 111 will be described. The image formed on the focal plane 111 is an image that directly reflects the distortion aberration of the measurement target lens 110. In addition, the image may be blurred due to defocus, but this does not affect the degree of distortion and the size of the image pattern. Since the size and shape of this image pattern do not depend on the shooting distance between the camera 102 and the arbitrary object 104, the arbitrary object 104 may have any shape and may be at any shooting distance. In addition, the arbitrary object 104 does not need to be a rigid body.

Figure 11 shows an example of imaging when there is no distortion aberration, and Figure 11 shows an example of imaging when there is distortion aberration, when the mask 23-1 with the sequence of points shown in Figure 3(a) is used.

When there is no distortion as shown in FIG. 11(a), the arrangement of the centers of gravity of the points that make up the point array is similar to the arrangement of the pinhole array of mask 23-1 at a certain ratio. When there is distortion as shown in FIG. 11(b), the distortion is barrel distortion.

The degree of blur in the image varies depending on the location of the image. In Figures 11(a) and (b) and Figures 12(a) and (b) described below, the degree of blur is greater at the top of the image.

Figure 13 is a diagram explaining the blurring of an image caused by unevenness on the surface of the arbitrary object 104. In Figure 13, the reflected light m1, m2, etc. from a location C1 on the surface of the arbitrary object 104 is imaged at a location R2 on the focal plane 111, and the reflected light n1, n2, etc. from the location C2 is imaged at a location R1 on the focal plane 111. Also, the distance from the camera 102 to the location C1 of the arbitrary object 104 is shorter than the distance from the camera 102 to the location C2 of the arbitrary object 104.

In this case, an image without blur is formed at location R2 on the focal plane 111, but an image with blur is formed at location R1 on the focal plane 111.

In this way, if the reflective surface of the arbitrary object 104 is uneven and the distance from the camera 102 varies depending on the location on the reflective surface, the degree of blur in the image will differ from location to location, as shown in Figures 11(a) and (b). However, even if the distance from the camera 102 varies depending on the location on the reflective surface due to the unevenness of the reflective surface of the arbitrary object 104, the arrangement of the centers of gravity in the sequence of points of the image formed on the focal plane 111 will not change regardless of the presence or absence of distortion aberration.

The calibration pattern light projection device 1 inputs imaging data such as that shown in FIG. 11(a) or (b), determines the center of gravity of each point that constitutes the point sequence based on the imaging data, and measures the distortion aberration of the measurement target lens 110 based on each center of gravity position.

Figure 12 shows an example of an imaging pattern when there is no distortion aberration, and Figure 12 shows an example of an imaging pattern when there is distortion aberration, when the checkerboard pattern mask 23-2 shown in Figure 3(b) is used.

When there is no distortion as shown in FIG. 12(a), the degree of blurring differs from place to place, but the arrangement of the centers of gravity of the elements that make up the checkerboard pattern is similar to the checkerboard pattern arrangement of mask 23-2 at a certain ratio. When there is distortion as shown in FIG. 12(b), the distortion is barrel distortion.

The calibration pattern light projection device 1 inputs imaging data such as that shown in FIG. 12(a) or (b). Then, based on the imaging data, the calibration pattern light projection device 1 determines the center of gravity of each element that constitutes the checkerboard pattern, and measures the distortion aberration of the measurement target lens 110 based on each center of gravity position.

As described above, according to the calibration pattern light projection device 1 of the embodiment of the present invention, the pattern light generation unit 10 has a movable unit 21 for adjusting the distance between itself and the half mirror 11, generates the calibration pattern light, and projects the calibration pattern light onto the half mirror 11. The half mirror 11 is disposed obliquely with respect to the measurement target lens 110, and reflects the calibration pattern light projected from the pattern light generation unit 10 and projects it onto the arbitrary object 104.

Before the distortion error of the measurement target lens 110 is measured by the distortion aberration measuring device 103, the user performs an initial adjustment to move the movable part 21 of the pattern light generating unit 10 to an appropriate position.

In the initial adjustment, the user photographs the arbitrary object 104 while changing the distance from the camera 102 to the arbitrary object 104. Then, the user adjusts the position of the movable part 21 by moving the movable part 21 in the movement direction D so that the size of the image pattern does not change depending on the shooting distance.

7, the optical path length L1 from the first principal point M of the measurement target lens 110 to the arbitrary object 104 can be made to coincide with the optical path length L2 from the light source 22 to the arbitrary object 104 via the half mirror 11. In this case, the optical path length L11 from the first principal point M of the measurement target lens 110 to point B of the half mirror 11 coincides with the optical path length L22 from the light source 22 to point B of the half mirror 11.

When the calibration pattern light is projected onto the arbitrary object 104 with these distances being consistent, the light reflected from the surface of the arbitrary object 104 passes through the half mirror 11 and is imaged on the focal plane 111 via the measurement target lens 110. The size and distortion of this image pattern remain constant regardless of the distance from the camera 102 to the arbitrary object 104, the degree of unevenness on the surface of the arbitrary object 104, and the angle of view of the measurement target lens 110.

As a result, the distortion aberration specific to the measurement target lens 110 can be measured by using an arbitrary object 104 of any shape as a projection target for the calibration pattern light. In other words, the arbitrary object 104 can be a projection target regardless of whether the surface of the arbitrary object 104 has irregularities or not, and regardless of whether the arbitrary object 104 is a rigid body or not. For example, the arbitrary object 104 can be any object that can diffusely reflect light, such as a studio wall, a curtain, an animal, a living thing, etc.

Therefore, by using the calibration pattern light projection device 1, the effort required to measure the distortion aberration of the measurement target lens 110 can be reduced, and the distortion aberration can be measured with high accuracy.

Also, as a conventional technique, there is a technique in which the measurement target lens 110 is removed from the camera 102 and the distortion aberration is measured for the measurement target lens 110 alone using laser light or the like. In an embodiment of the present invention, the distortion aberration can be measured with the measurement target lens 110 attached to the camera 102, so that, compared to the conventional technique described above, the distortion aberration caused by play or bending when the measurement target lens 110 is attached can also be measured.

The present invention has been described above using embodiments, but the present invention is not limited to the above embodiments and can be modified in various ways without departing from the technical concept thereof.

For example, in the above embodiment, the pattern light generating unit 10 of the calibration pattern light projector 1 is provided with a movable unit 21 that can move in the movement direction D, but instead of the movable unit 21, it may be provided with a fixed unit that does not move (that is fixed to the housing 12).

This fixing portion is fixed to the housing 12 so that the optical path length L1 and the optical path length L2 shown in FIG. 7 match (so that the optical path length L11 and the optical path length L22 match). In this case, initial adjustment by the user is not required.

In addition, in the above embodiment, the movable part 21 of the pattern light generating unit 10 of the calibration pattern light projector 1 is structured to move in a moving direction D, which is the direction of the optical axis of the light source 22, and moves the light source 22 toward and away from the half mirror 11.

This allows the optical path length L22 from the light source 22 to point B of the half mirror 11 to be changed while keeping the optical path length L11 from the first principal point M of the measurement target lens 110 to point B of the half mirror 11 fixed, thereby making the two distances equal.

In contrast to this, the calibration pattern light projection device 1 may be provided with a device movable part that moves the entire calibration pattern light projection device 1 relative to the camera 102 while the positions of the light source 22 and the mask 23 relative to the half mirror 11 are fixed. The direction of movement of the entire calibration pattern light projection device 1 is the direction of the optical axis β1 shown in FIG. 7. In this case, the pattern light generation unit 10 of the calibration pattern light projection device 1 has the aforementioned fixed part instead of the movable part 21.

This allows the optical path length L11 from the first principal point M of the measurement target lens 110 to point B of the half mirror 11 to be changed, and the two distances can be made to match while keeping the optical path length L22 from the light source 22 to point B of the half mirror 11 fixed.

The calibration pattern light projection device 1 may also include a movable part 21 that moves the light source 22, and may also include the aforementioned device movable part that moves the entire calibration pattern light projection device 1.

1 Calibration pattern light projection device 10, 10-1, 10-2, 10-3 Pattern light generation unit 11 Half mirror 12, 112 Housing 21 Movable unit 22, 25, 27 Light source 23, 23-1, 23-2, 23-3 Mask 24 Scanning mechanism 26 Galvanometer mirror 30 Microlens 40 Concave 101 Calibration pattern 102 Camera 103 Distortion aberration measurement device 104 Arbitrary object 110 Measurement target lens 111 Focal plane α Angle of view β, β1, β2 Optical axis γ1 Collimated light γ2, m1, m2, n1, n2 Reflected light J Axis M First principal point B Point D Moving direction L1, L2, L11, L22 Optical path length C1, C2, R1, R2 Location

Claims (5)

A calibration pattern light projection device that projects a calibration pattern light for measuring distortion aberration of a lens attached to a camera onto a predetermined object, comprising:
a pattern light generating unit that generates the calibration pattern light using a light source;
a half mirror that reflects the calibration pattern light generated by the pattern light generating unit and projects the reflected light onto the predetermined object,
an optical path length from the light source to the predetermined object via the half mirror is equal to an optical path length from a first principal point of the lens to the predetermined object via the half mirror;
a calibration pattern light projection device characterized in that, when the calibration pattern light is projected onto the specified object, the reflected light reflected from the surface of the specified object passes through the half mirror and is imaged on the focal plane of the camera via the lens. 2. The calibration pattern light projection device according to claim 1,
The pattern light generating unit includes:
a movable portion for moving the light source in an optical axis direction between the light source and the half mirror; 3. The calibration pattern light projection device according to claim 1,
The calibration pattern light projection device further comprises a device movable part that moves the calibration pattern light projection device relative to the camera in the optical axis direction between a first principal point of the lens and the half mirror while keeping the position of the light source relative to the half mirror fixed. 4. The calibration pattern light projection device according to claim 1,
The pattern light generating unit includes:
a calibration pattern light projection device comprising: a mask having a plurality of transmitting portions and a plurality of light-shielding portions for forming a pattern of the calibration pattern light, and using the mask, generating the calibration pattern light in a solid angle with the light source as a vertex. 4. The calibration pattern light projection device according to claim 1,
The pattern light generating unit includes:
a scanning mechanism for scanning a light beam emitted by the light source, and using the scanning mechanism, generating the calibration pattern light in a solid angle with the light source as a vertex.

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