JP4642889B2 - 3D field for calibration, 3D field for calibration - Google Patents

Description

  The present invention provides a three-dimensional calibration for accurately measuring internal parameters {eg, lens principal point position, screen distance (focal length), distortion parameters, etc.) required to correct camera image distortion. Regarding the field. The present invention also relates to a method for photographing a calibration three-dimensional field used for photographing a calibration chart for measuring an internal parameter of a camera.

  Conventionally, in the field of photogrammetry and photo measurement, it is important to obtain an image with less aberration. Therefore, as described in Patent Document 1, in the field of photogrammetry and photo measurement, a high-precision lens with little aberration is used as a lens for a photographing camera. Furthermore, in the photogrammetry field, the internal parameters of the camera (principal point position, screen distance, distortion parameters) can be analyzed analytically by measuring a large number of precisely arranged three-dimensional points from multiple directions. Looking for. In the case of a measurement camera used in the field of photo measurement, the internal parameters of the camera are obtained by precisely measuring the manufactured camera.

Japanese Patent Laid-Open No. 2001-280956 [0014], FIG.

  However, in recent years, digital cameras using a CCD image sensor (charge coupled device image sensor) have become widespread. Many digital cameras are equipped with a zoom lens having a variable focal length. The zoom lens is convenient because the size of the subject image of the measurement object in the image projected on the film can be adjusted without moving the distance between the camera and the measurement object. Therefore, if the zoom lens can be used for photo measurement, three-dimensional image measurement can be easily performed. However, the zoom lens has a problem that the calibration work becomes complicated because the internal parameters of the camera fluctuate according to the focal length.

  That is, when a calibration object that is measured precisely and has a large number of points (targets) arranged in three dimensions is photographed by a camera to be calibrated, the calibration object is projected onto a film or CCD. It is desirable to capture the full image. However, in a zoom lens, the size of a subject that is shot with a projected image varies according to the focal length. Therefore, in order to shoot the calibration body with the full projection image, the distance between the calibration body and the camera is shortened for a wide angle with a short focal length, and the calibration body and camera are used for a telephoto with a long focal length. It is necessary to increase the interval. Then, in the telephoto state, there may be a case where the distance between the calibration body and the camera needs to be separated by, for example, about 10 m to 20 m, and a large space is required as a place for installing the calibration body. There is a problem that the space in which calibration work can be performed is limited.

  In the calibration body photographing operation, it is desirable to photograph with a camera to be calibrated in such a manner that the calibration body target can be clearly recognized. On the other hand, there are many cases where an instrument irrelevant to the calibration is installed in the vicinity of the calibration body, and if a useless object is imprinted in the captured calibration body image, it is performed for each focal length of the zoom lens. There was also a problem that it became noise for the calibration work.

  The present invention solves the above-described problems, and a first object is to perform a photographing operation and calibration of a calibration body using a calibration body in a relatively narrow space even in the case of a zoom lens having a variable focal length. It is to provide a three-dimensional field for calibration that can be worked on. The second object is to provide a method for photographing a three-dimensional field for calibration that can be photographed in such a manner that the target of the calibration body can be clearly recognized.

  As shown in FIGS. 1 and 2, the calibration three-dimensional field of the present invention that achieves the above object includes a wide-angle area 110 and a telephoto area 120 provided in an area overlapping the wide-angle area 110. A telescopic coarse alignment reference mark 122, a telephoto fine alignment reference mark 124, and a wide-angle region 110, which are three-dimensional fields for calibration. In addition, a wide-angle coarse alignment reference mark 112 and a wide-angle fine alignment reference mark 114 are provided.

  In the apparatus configured as described above, the wide-angle region 110 is used for capturing a calibration image on the wide-angle side of the zoom lens, and is used for general alignment in the captured calibration image. A wide-angle coarse alignment reference mark 112 and a wide-angle fine alignment reference mark 114 used for detailed alignment in the captured calibration image are provided. The telephoto area 120 is used for capturing a calibration image on the telephoto side of the zoom lens, and a telephoto coarse alignment reference mark 122 used for general alignment in the captured calibration image. A telephoto precision alignment reference mark 124 used for detailed alignment in the captured calibration image is provided. Since the telephoto area 120 is provided in a narrow area on the inner side of the area overlapping the wide-angle area 110, the calibration image can be obtained even when a sufficient interval between the camera for photographing and the three-dimensional field for calibration cannot be secured. Can shoot.

  In the three-dimensional field for calibration according to the present invention, preferably, when the reference mark (112, 114, 122, 124) is formed of a reflective target, the reference mark is high in the calibration image photographed by the camera. The brightness is reflected and the contrast between the background surface of the calibration three-dimensional field and the reference mark can be easily secured.

  In the three-dimensional field for calibration according to the present invention, preferably, at least one of the wide-angle rough alignment reference marks 112 is located at the approximate center position of the wide-angle area 110 and in the telephoto area 120. The telephoto precision alignment reference mark 124 is disposed inside the telephoto area 120, and at least one of the wide-angle precision alignment reference marks 114 is a wide-angle area positioned on the outer edge of the telephoto area 120. 110, the alignment of the wide-angle area 110 and the telephoto area 120 is enhanced, and the wide-angle area is at an intermediate focal length corresponding to the boundary between the wide-angle side and the telephoto side of the zoom lens. Both 110 and the telephoto area 120 can be used for calibration.

  In the calibration three-dimensional field of the present invention, preferably, the telephoto or wide-angle coarse alignment reference mark (112, 122) is distinguished from the telephoto or wide-angle fine alignment reference mark (114, 124). When formed in a possible manner, it is possible to easily distinguish between a general alignment and a reference mark used for precise alignment in a calibration image taken by a camera. Here, the identifiable aspect refers to an aspect in which identification is possible using at least one type of form, color, and pattern, for example.

  In the three-dimensional field for calibration according to the present invention, preferably, the telephoto or wide-angle coarse alignment reference mark (112, 122) and the telephoto or wide-angle fine alignment reference mark (114, 124). If at least one has a height different from that of the other reference marks, three-dimensional calibration can be performed on the calibration image taken by the camera.

  In the three-dimensional field for calibration of the present invention, preferably, the wide-angle coarse alignment reference mark 112 has a larger outer shape than the telephoto coarse alignment reference mark 122, and the wide-angle fine alignment reference mark. If the lens 114 has a larger outer shape than the telephoto precision alignment reference mark 124, the calibration reference image captured by the camera captures a smaller reference mark for telephoto when captured at the wide angle side. This makes it easy to identify the reference mark. In addition, when taking a picture on the telephoto side, the reference mark for telephoto is shown in an appropriate size, and identification becomes easy.

  In the three-dimensional field for calibration according to the present invention, preferably, at least one of the telephoto coarse alignment reference mark 122 and the wide-angle coarse alignment reference mark 112 is used as the same reference mark. If this is done, the consistency between the wide-angle area 110 and the telephoto area 120 is enhanced, and at an intermediate focal length corresponding to the boundary between the wide-angle side and the telephoto side of the zoom lens, the wide-angle area 110 and the telephoto area Any of 120 can be used for calibration.

  The calibration three-dimensional field imaging method of the present invention that achieves the above object is characterized in that the calibration three-dimensional field 100 according to any one of claims 1 to 7 is calibrated as shown in FIG. In the method for photographing a three-dimensional field for calibration in which a calibration chart image is obtained by photographing with a photographing camera, the exposure setting of the calibration chart photographing camera is set in the background area excluding the reference mark of the three-dimensional field for calibration 100. On the other hand, the exposure is underexposed and overexposure is set with respect to the reference mark of the calibration three-dimensional field 100 (S100), and the calibration three-dimensional field 100 is photographed by strobe photographing of the calibration chart photographing camera ( S102), so that the contrast of the calibration chart image is enhanced And it has a development to (S104) process.

  The present invention will be described below with reference to the drawings. FIG. 1 is an overall view for explaining a first embodiment of the present invention and is shown as a light and dark binary image. FIG. 2 is an explanatory view of a main part in which the telephoto area is enlarged in the overall view of FIG. In the figure, the calibration three-dimensional field 100 has a wide-angle area 110 and a telephoto area 120 provided in an area overlapping the wide-angle area 110.

  The wide-angle area 110 is used for capturing a calibration image on the wide-angle side of the zoom lens, and a wide-angle rough alignment reference mark 112 used for general alignment in the captured calibration image. A wide-angle precision alignment reference mark 114 used for detailed alignment in the captured calibration image is provided. Seven wide-angle rough alignment reference marks 112 are provided in the vicinity of the telephoto area 120 so that even when the angle of view of the zoom lens to be photographed is small, the image is taken reliably. The wide-angle precision alignment reference marks 114 are provided, for example, 100 to 200, and are arranged at an equal density so that they can be captured uniformly in the captured calibration image. The wide-angle coarse alignment reference mark 112 has the same shape as that of the wide-angle fine alignment reference mark 114 (for example, a circle “◯” may be a star “★” or a triangle mark “△”). And a rectangular frame surrounding the center point. The frame line may be a round shape or a polygon having a triangle shape or more instead of a rectangle, and may be any shape that can be identified as the coarse alignment reference mark 112 for wide angle.

  The telephoto area 120 is used for capturing a calibration image on the telephoto side of the zoom lens, and a telephoto coarse alignment reference mark 122 used for general alignment in the captured calibration image. A telephoto precision alignment reference mark 124 used for detailed alignment in the captured calibration image is provided. Since the telephoto area 120 is provided in a narrow area on the inner side of the area overlapping the wide-angle area 110, even when the distance between the camera for photographing and the three-dimensional field for calibration cannot be sufficiently secured, Calibration images can be taken with a lens that is set to a small focal length.

  Seven telephoto coarse alignment reference marks 122 are provided near the center of the telephoto area 120 so that even when the angle of view of the zoom lens to be photographed is small, the image is taken with certainty. For example, 100 to 200 precision alignment reference marks 124 for telephoto are provided, and are arranged at an equal density so that they can be captured uniformly in the captured calibration image. The telephoto coarse alignment reference mark 122 includes a center point having the same shape as the telephoto fine alignment reference mark 124 and a rectangular frame surrounding the center point. The frame line may be a round shape or a polygon having a triangle shape or more instead of a rectangle, and may be any shape that can be identified as the telephoto coarse alignment reference mark 122.

  The wide-angle coarse alignment reference mark 112 has a larger outer shape than the telephoto coarse alignment reference mark 122, and the wide-angle fine alignment reference mark 114 is larger than the telescopic fine alignment reference mark 124. Has a large outer shape. In the calibration image taken by the camera, if the wide-angle side of the zoom lens is photographed, the telephoto reference marks 122 and 124 are photographed small, so that the wide-angle reference marks 112 and 114 can be easily identified. In addition, when photographing on the telephoto side of the zoom lens, the telephoto reference marks 122 and 124 are captured in an appropriate size, and the telephoto reference marks 122 and 124 in the calibration image photographed by the camera can be easily identified.

  Next, the site where the calibration three-dimensional field 100 is installed will be described with reference to the drawings. FIG. 3 is an overall view for explaining the site where the calibration three-dimensional field 100 is installed, and FIG. 4 is an explanatory view of a main part of the overall view of FIG. The calibration three-dimensional field 100 is installed in an environment with little temperature change, such as a basement, so that the relative positional relationship between the wide-angle reference marks 112 and 114 and the telescopic reference marks 122 and 124 does not change. Is considered. For the wide-angle reference marks 112 and 114 and the telescopic reference marks 122 and 124, a target plate indicating the reference mark is fixed to a wall surface such as a concrete wall, for example.

  When a reflective target having a high reflectance is used for the reference marks 112, 114, 122, and 124, a calibration image can be easily captured with a light and dark binary image. For example, if a high-reflectance reference mark such as an aluminum-deposited glass plate is used as the reflection target, the reference mark appears in the calibration image captured by the camera with high brightness, and the background surface of the calibration three-dimensional field Contrast with the reference mark can be easily secured. The height of the reference mark is adjusted, for example, by changing the height of the target plate from the concrete wall surface. By arranging reference marks of various heights uniformly in the calibration image, the internal parameters of the zoom lens to be calibrated can be accurately calculated.

  FIG. 5 is a flowchart for explaining a procedure for photographing a three-dimensional field for calibration with a zoom lens to be calibrated. First, the exposure setting of the calibration chart photographing camera is underexposed with respect to the background area excluding the reference mark of the calibration three-dimensional field 100 and overexposed with respect to the reference mark of the calibration three-dimensional field 100. Set (S100). Next, the calibration three-dimensional field 100 is photographed by stroboscopic photographing of the calibration chart photographing camera (S102). Since the zoom lens can shoot with the aperture set to the maximum, the depth of field becomes deep, and a clear analysis image can be easily obtained even if focus is not achieved.

  Subsequently, the photographed calibration chart image is developed so as to enhance the contrast (S104). In the calibration chart image photographed in this way, the background image of the calibration three-dimensional field such as a concrete wall is darkened, and the wide-angle reference marks 112 and 114 and the telephoto reference marks 122 and 124 are brightened. A binary image is obtained (S106).

  The calibration chart image photographed in this way includes the three-dimensional measurement position of the developed binary image and the three-dimensional coordinates of the reference marks 112 and 114 for wide angle and the reference marks 122 and 124 for telephoto that have been measured in advance. Are used for analytically determining camera internal parameters (main point position, screen distance, distortion parameter) for each focal length of the zoom lens. Since the background area excluding the reference mark of the calibration three-dimensional field 100 is a uniform dark area image, in the calibration work using the calibration chart image performed in a later process, the wide-angle reference marks 112 and 114 and The reference marks 122 and 124 for telephoto can be detected accurately. For example, according to the experiment by the present inventor, the accuracy of detecting the center of gravity of the reference mark (target) is about 1/10 pixel in the binary image, but 1 when the background wall surface is imprinted. / 4 pixels and roughly 2 to 3 times rougher.

  In the above embodiment, the case where the reference mark for wide angle and the reference mark for telephoto are fixedly installed on a common wall surface is shown, but the present invention is not limited to this. . For example, a wide-angle reference mark is fixedly installed on a wall surface, while a telephoto reference mark is fixed to a movable panel and the movable panel is appropriately positioned with respect to the wall surface. The reference mark for telescope and the reference mark for telephoto may be positioned.

  As described above, the calibration three-dimensional field of the present invention captures a wide-angle region as long as the focal length is on the wide-angle side, even when a sufficient distance between the camera for photographing and the calibration three-dimensional field cannot be secured. On the telephoto side, a calibration image can be captured by adjusting the focal length without adjusting the distance between the camera that performs imaging and the three-dimensional field for calibration by imaging the telephoto area.

  Further, according to the method for photographing a three-dimensional field for calibration according to the present invention, the calibration chart photographing camera can shoot with a maximum aperture, so that the depth of field becomes deep and the focus is not focused. It is easy to obtain a clear calibration image. Further, when the calibration image is photographed so as to be a binary image as in the embodiment, the accuracy of detecting the center of gravity position of the reference mark (target) in the calibration operation is increased.

BRIEF DESCRIPTION OF THE DRAWINGS It is the whole figure explaining the 1st Embodiment of this invention, and has shown with the light and dark binary image. In the overall view of FIG. 1, it is an explanatory view of a main part in which the telephoto area is enlarged, and is shown as a light and dark binary image. It is a general view explaining the field where the three-dimensional field for calibration 100 is installed. It is principal part explanatory drawing which expanded the telephoto area | region among the whole drawings of FIG. It is a flowchart explaining the procedure which image | photographs the three-dimensional field for calibration with the zoom lens used as calibration object.

Explanation of symbols

100 Three-dimensional field for calibration 110 Wide angle area 112 Coarse alignment reference mark 114 Fine alignment reference mark 120 Telephoto area 122 Coarse alignment reference mark 124 Precision alignment reference mark

Claims (6)

In the method for photographing a calibration three-dimensional field for photographing a calibration three-dimensional field with a camera, obtaining a calibration chart image, and measuring an internal parameter of the camera;
The three-dimensional field for calibration includes a wide-angle area used for photographing a wide-angle calibration image of the zoom lens and an area overlapping with the wide-angle area by the camera to be calibrated equipped with a zoom lens. provided, and the telephoto area to be used for shooting the telephoto side calibration images of the zoom lens;
Than the telephoto coarse alignment reference mark and the telephoto coarse alignment reference mark, which are arranged in the telephoto area and used for general alignment in the photographed telephoto side calibration image A telephoto precision alignment reference mark used for detailed alignment;
Wherein arranged in the wide angle region, detailed rough alignment reference marks for wide-angle utilized in general alignment in the photographed the wide-angle side calibration image, and than the wide angle rough alignment reference marks With a wide-angle precision alignment reference mark used for alignment ;
The telephoto coarse alignment reference mark, the telephoto fine alignment reference mark, the wide-angle coarse alignment reference mark, and the wide-angle fine alignment reference mark are composed of a reflective target, and each includes a plurality of Each of which has at least one height different from other fiducial marks;
When taking a three-dimensional field for the calibration,
The exposure setting of the camera is set to be underexposed with respect to a background area excluding the reference mark of the calibration three-dimensional field and overexposed with respect to the reference mark of the calibration three-dimensional field;
Photographing the three-dimensional field for calibration by the flash photography of the camera;
How to shoot 3D field for calibration . The three-dimensional field for calibration has a glass plate on which the reference mark is vapor-deposited aluminum;
Imaging so that the calibration chart image is a light and dark binary image;
The method for photographing a three-dimensional field for calibration according to claim 1 . The three-dimensional field for calibration, at least one of the rough alignment reference marks for the wide angle, a substantially central position of the wide-angle region, have been and are disposed in the telephoto region;
At least one fine alignment reference marks for the wide angle, and is disposed in the wide angle region located on the outer edge of the telephoto region;
Photographing the three-dimensional field for calibration at an intermediate focal length corresponding to the boundary between the wide-angle side and the telephoto side of the zoom lens;
The method for photographing a three-dimensional field for calibration according to claim 1 or 2. The calibration three-dimensional field includes a telephoto or wide-angle coarse alignment reference mark having a center mark having the same shape as the corresponding telephoto or wide-angle fine alignment reference mark, and a frame surrounding the center mark. by being composed of a line, it is formed by the fine alignment reference marks and identifiable manner of telephoto or wide-angle;
Photographing a wide-angle region or a telephoto region of the three-dimensional field for calibration;
The method for photographing a three-dimensional field for calibration according to any one of claims 1 to 3. The three-dimensional field for calibration, rough alignment reference marks for the wide-angle has a larger outer shape than the rough alignment reference marks for the telephoto;
Fine alignment reference marks for the wide angle, and have a larger outer shape than the fine alignment reference marks for the telephoto;
Photographing a wide-angle region or a telephoto region of the three-dimensional field for calibration;
The method for photographing a three-dimensional field for calibration according to any one of claims 1 to 4 . A rough alignment reference marks for the telephoto, at least one of the wide-angle rough alignment reference mark is configured to be shared by the same reference marks;
Photographing the three-dimensional field for calibration at an intermediate focal length corresponding to the boundary between the wide-angle side and the telephoto side of the zoom lens;
The method for photographing a three-dimensional field for calibration according to any one of claims 1 to 4 .

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