CN105403173B - A kind of light field deviation art measuring system calibration mirror and its application process - Google Patents

Abstract

The invention belongs to the field of optical measurement, and relates to a calibration mirror of an optical field deflection measurement system and an application method thereof. This calibration mirror is used to calibrate the pose relationship of the light field deflectometry system, and is used to calibrate the relationship between the camera 5 and the double-layer optical plane modulator 3 and 4 and the relationship between the double-layer optical plane modulator 3 and 4, including The mirror surface of a calibration mirror is composed of a standard checkerboard mirror and a reflection mirror in parallel; the checkerboard is described on a part of a plane mirror, so that it has the calibration checkerboard and reflection functions; the calibration method is divided into ordinary camera calibration and optical Field camera calibration method. The calibration method can complete the calibration of all pose relationships with only one shot, and has the advantages of simple and easy operation, high precision, and the like. The light field camera calibration method fills in the domestic and foreign gaps in the calibration of the light field camera mode of the light field deflection measurement system, and provides a basis for the light field deflection measurement system to measure highly reflective objects.

Description

Calibration mirror for light field deflection measurement system and application method thereof

technical field

The invention relates to the field of optical measurement, and relates to a calibration mirror of an optical field deflection measurement system and an application method thereof.

Background technique

Optical three-dimensional shape measurement technology has been widely used in aerospace, automobile manufacturing, reverse engineering, computer-aided design, computer-aided manufacturing and other fields due to its advantages of non-contact, high precision and fast speed. The three-dimensional surface shape obtained by structured light projection has the advantages of fast full-field measurement and high measurement accuracy, and has been widely used in the three-dimensional measurement of diffuse reflective surfaces. Now in the field of manufacturing, there are many measurement requirements for highly reflective surfaces such as mirrors and near mirrors, such as the surface of optical components, mirrors, and polishing abrasives in the field of optical manufacturing. For these highly reflective surfaces, phase deflection is often used for measurement. .

The phase deflection measurement system composed of a single projection device and a CCD camera has the characteristic that the normal line is not unique, and the measurement system has a large error. At present, various solutions based on phase deflection technique have been proposed to realize the topography measurement of the surface of highly reflective objects, but there are certain deficiencies in all of them. In the proposed light field deflectometry measurement system, the 'non-unique problem' of solving the normal is solved, and the system has a higher sensitivity to the change of the surface height of the object and the change of the reflected light caused by it in the light field camera mode. Response characteristics, so higher measurement accuracy can be obtained with respect to the surface of the object to be measured. In the deflectometry measurement system, it is necessary to calibrate the pose relationship between the double-layer planar modulator and the camera, and the pose relationship between the double-layer planar modulators. Since the double-layer planar modulator is not within the field of view of the camera, It brings difficulties to the calibration. At present, there are obvious deficiencies in the calibration methods at home and abroad. For example, Petz uses the method of sticking control points on the calibration mirror. These control points need to be measured by photogrammetry. Obviously, using photogrammetry to measure the coordinates of the control points will increase the measurement time and cost. And at present, the calibration of the light field camera mode for the light field deflectometry measurement system at home and abroad has not yet appeared.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a calibration mirror of light field deflection measurement system and its application method, provide the shape structure of the calibration mirror, and the calibration method using the calibration mirror, so that the light field deflection The pose relationship between the sensing system and the projection system of the technique can be realized by one shot, which provides a basis for the high-precision measurement of highly reflective objects by the deflectometry system.

In order to achieve the above object, the present invention adopts the following technical solutions:

A deflectometry measurement system calibration mirror, used to calibrate the pose relationship of the deflectometry system, suitable for the relationship between cameras and double-layer optical plane modulators and the relationship between double-layer optical plane modulators, It includes a reflective group consisting of a checkerboard mirror and a plane reflector in parallel; the standard checkerboard is carved on a part of the plane reflector, so that it has the functions of calibrating the checkerboard and reflection.

The pose relationship between the calibration camera and the double-layer light plane modulator, the present invention has two situations for the pose relationship between the camera and the double-layer plane modulator, the normal camera mode and the light field camera mode, and the corresponding calibration algorithm is divided into common camera Calibration algorithm and light field camera calibration algorithm.

The common camera calibration algorithm displays a standard checkerboard of the same size as the checkerboard drawn by the calibration mirror on the double-layer planar modulator in time-sharing, and is captured by the camera to obtain a double-layer planar modulator with both the checkerboard grid of the calibration mirror and the reflection of the calibration mirror. The displayed checkerboard pattern is then calibrated by a two-dimensional planar checkerboard calibration method. After calibration, after parameter conversion, the position and attitude relationship of the checkerboard in the calibration mirror and the checkerboard in the calibration mirror under the camera coordinate system can be obtained. According to the theory of mirror mirroring, the actual double-layer planar modulator checkerboard and the internal reflection checkerboard of the calibration mirror are mirror-symmetrical with respect to the calibration mirror, so the camera and the double-layer planar modulator can be obtained by performing mirror calculation on the checkerboard in the calibration mirror with respect to the calibration mirror After the calculation of the pose relationship between the two-layer modulators relative to the camera is completed, the pose relationship between the two-layer planar modulators can be obtained through parameter transformation. From the above, it can be known that the pose relationship between the camera and the double-layer planar modulator and the pose relationship between the two-layer planar modulators can be obtained in one shot.

The light field camera calibration algorithm first needs to calibrate the parameters of the light field camera. The light field camera parameter calibration here mainly refers to the center position of the microlens. In the subsequent calibration experiments, it is mainly used to extract the sub-aperture image composed of the central pixels of the light field microlens. According to the light field imaging model, when a three-dimensional object is clearly imaged on the surface of the microlens array through the main lens of the light field camera, that is, each position on the microlens array only comes from the same point of light on the object surface. Through the spatial multiplexing of the microlens, the pixels on the CCD or CMOS sensor are light information from different directions at this point. Determining the corresponding relationship between pixels and microlenses is transformed into determining the corresponding relationship between pixels and spatial object plane points. The method of multi-frequency phase shift is used to determine the relationship between the object surface point and the pixel, and the multi-frequency phase-shifted fringe image is taken by the light field camera, and the average brightness of the phase-shifted fringe image is calculated. Due to the vignetting effect of the micro-lens, the brightness of the center of the micro-lens is caused. Higher, and weaker at the edges, so the central pixel of the microlens can be determined by a peak detection algorithm. Since the physical parameters of the light field camera are determined after the manufacture is completed, it is only necessary to calibrate the central parameters of the microlens once. Calibrate the pose relationship between the light field camera and the double-layer planar modulator Use the light field camera to shoot the calibration mirror and the checkerboard pattern displayed on the internal reflection modulator of the calibration mirror with the same size as the calibration mirror, and extract the subset of each light field image For the aperture image, the pixel coordinates of the sub-aperture image are replaced by the pixel coordinates under the center of the microlens, and finally the two-dimensional plane checkerboard calibration method is used for calibration. The pose relationship between the camera and the double-layer planar modulator is obtained by mirroring the checkerboard in the calibration mirror with respect to the calibration mirror, and the pose relationship between the double-layer planar modulators can be obtained through parameter conversion.

Compared with the calibration method mentioned above, the present invention has the following advantages due to the adoption of the above technical scheme:

The invention is easy to operate, the user only needs to place the calibration mirror in the field of view of the camera, and the camera can capture the checkerboard image projected by the double-layer optical plane modulator from the mirror reflection of the calibration mirror, and use the two-dimensional checkerboard calibration after one shot Calibration can be completed.

The invention is easier to integrate into the measurement environment, improves the calibration efficiency, and can be applicable to two measurement modes of the deflectometry system at the same time. It fills the blank of the pose relationship in the light field camera mode of the calibration light field deflectometry system at home and abroad, and provides a basis for the light field deflection measurement system to measure highly reflective objects.

Description of drawings

The present invention will be described in further detail below in conjunction with the accompanying drawings and embodiments:

Fig. 1 is the calibration mirror schematic diagram of the present invention

Fig. 2 is a schematic diagram of calibration of cameras (common camera and light field camera) of the present invention

Fig. 3 is the flow chart of common camera calibration algorithm of the present invention

Fig. 4 is a schematic diagram of the microlens center of the calibration light field camera of the present invention

Fig. 5 is a flow chart of the light field camera calibration algorithm of the present invention

Detailed ways

The following preferred embodiments will further illustrate the present invention in conjunction with the accompanying drawings.

Embodiment one:

Referring to Fig. 1, a kind of deflectometry measuring system calibration mirror is used for calibrating the pose relationship of the deflectometry system, including a reflector, and it is characterized in that: the mirror surface of the reflector is composed of checkerboard mirror surface 1 It is composed of two parts in parallel with the mirror surface 2, that is, the checkerboard is depicted on a part of the mirror surface of a plane mirror, so that it has the function of calibrating the chessboard and reflection; it is suitable for calibrating the relationship between the camera and the double-layer optical plane modulator and the double-layer optical plane modulator. The relationship between layer light planar modulators.

Embodiment 2: This embodiment is the same as Embodiment 1, and the special feature is: refer to Fig. 2 to Fig. 5 .

Referring to Fig. 2, the pose relationship between the calibration camera and the double-layer planar modulator, the present invention has two situations for the pose relation between the camera 5 and the double-layer planar modulator (3, 4), ordinary camera mode and light field Camera mode, the corresponding calibration algorithm is divided into common camera calibration algorithm and light field camera calibration algorithm. Camera 5 may represent both a normal camera and a light field camera.

Referring to Fig. 3, the common camera calibration algorithm displays a standard checkerboard with the same size as the checkerboard mirror 1 on the double-layer planar modulator (3, 4) in time-sharing, and is photographed by the camera and has a checkerboard at the same time. Mirror 1 and reflecting mirror 2 reflect the checkerboard pattern displayed by the double-layer planar modulator, and then the calibration is completed by a two-dimensional planar checkerboard calibration method. After calibration, after parameter conversion, the position and attitude relationship of the checkerboard mirror 1 and the checkerboard in the checkerboard mirror under the camera coordinate system can be obtained; from the mirror image theory, the actual two-layer planar modulator (3,4) checkerboard and Reflecting mirror 2 is symmetrical with respect to checkerboard mirror 1, so the pose relationship between camera 5 and double-layer planar modulator (3, 4) can be obtained by mirroring the checkerboard in mirror 2 with respect to checkerboard mirror 1; when the double-layer After the calculation of the pose relationship between the optical planar modulators (3, 4) and the camera 5 is completed, the pose relation between the two-layer planar modulators (3, 4) can be obtained through parameter transformation. From the above, it can be known that the pose relationship between the camera and the double-layer planar modulator and the pose relationship between the two-layer planar modulators can be obtained in one shot.

Referring to FIGS. 4 and 5 , the light field camera calibration algorithm first needs to calibrate the parameters of the light field camera. The light field camera parameter calibration here mainly refers to the center position of the microlens. In the subsequent calibration experiments, it is mainly used to extract the sub-aperture image composed of the central pixels of the light field microlens. The multi-frequency phase-shift fringe image displayed on the display 7 is captured by a light field camera, the average brightness of the phase-shift fringe image is calculated, and the central pixel of the microlens is determined by a peak detection algorithm. Calibrate the pose relationship between the light field camera and the double-layer planar modulator (3, 4) Use the light field camera to shoot the checkerboard pattern with the same size as the calibration mirror displayed on the internal reflection modulator of the checkerboard mirror surface 1 and mirror surface 2, The sub-aperture image of each light field image is extracted, and the pixel coordinates of the sub-aperture image are replaced by the pixel coordinates under the center of the microlens. Finally, the two-dimensional plane checkerboard calibration method is used for calibration. The pose relationship between the camera and the double-layer planar modulator is obtained by mirroring the checkerboard in the checkerboard mirror surface 1 with respect to the mirror surface 2, and then the pose relationship between the double-layer planar modulators can be obtained.

The working process and principle are as follows:

Referring to Figure 3, when calibrating an ordinary camera, it is divided into: taking pictures, calibrating, mirroring, and parameter conversion. It is necessary to take multiple checkerboard pictures of the calibration mirror 6 in different postures. The pictures of the checkerboard mirror surface 1 and the reflection mirror surface 2 must be within the field of view of the camera. According to the two-dimensional checkerboard calibration method, the internal and external parameters of the camera 5 are obtained. According to the obtained internal and external parameters of the camera, the position and attitude relationship of the checkerboard in the camera coordinate system can be calculated, and the mirror image of the checkerboard in mirror 2 with respect to checkerboard mirror 1 can be determined to determine the double-layer planar modulator (3,4) The position and attitude relationship in the camera coordinate system. According to the position and attitude relationship of the double-layer optical plane modulator in the camera coordinate system obtained by solving in , and according to the parameter conversion, the positional relationship between the double-layer optical plane modulators can be determined.

Refer to Figure 4, calibrate the center of the microlens of the light field camera, and display a multi-frequency phase shift fringe image on the display. The light field camera shoots, calculates the average brightness of the captured image, and then detects it according to the peak detection method. The peak point is the center point of the microlens .

Referring to Figure 5, when calibrating a light field camera, it is divided into: taking pictures, extracting sub-aperture pictures, calibrating, mirroring, and parameter conversion. It is necessary to take multiple checkerboard pictures of the calibration mirror 6 in different postures. The checkerboard pictures in the checkerboard mirror surface 1 and the mirror surface 2 must be within the field of view of the camera. The pixels at the center point of the microlens are extracted to form the calibration mirror aperture image, and the The pixel coordinates of the center of the microlens corresponding to the different pixels of the aperture image, determine the internal and external parameters of the light field camera according to the two-dimensional checkerboard calibration method, and calculate the checkerboard in the checkerboard mirror surface 1 and the mirror surface 2 in the camera coordinate system The following coordinate information is mirrored by the checkerboard in mirror surface 2 with respect to checkerboard mirror surface 1, and the position and posture relationship of the double-layer planar modulator (3, 4) in the camera coordinate system can be determined. According to the position and attitude relationship of the double-layer optical plane modulators (3, 4) in the camera 5 coordinate system obtained from the solution in , and according to the parameter conversion, the positional relationship between the double-layer optical plane modulators (3, 4) can be determined.

Claims (4)

1. a kind of application process of light field deviation art measuring system calibration mirror, is carried out using light field deviation art measuring system calibration mirror Operation, light field deviation art measuring system calibration mirror are used for the position orientation relation for demarcating light field deviation art system, including a reflection Mirror, the minute surface of the speculum are in parallel and are formed by gridiron pattern minute surface (1) and mirror surface (2) two parts, i.e., carved gridiron pattern It is drawn in a part for a plane mirror minute surface, makes it have calibration gridiron pattern and reflection function；Suitable for calibration for cameras The relation between relation and double-deck optical plane modulator between double-deck optical plane modulator；It is characterized in that this method is used to mark Determine the position orientation relation of camera and double-deck optical plane modulator, the position orientation relation of camera (5) and double layer planar modulator (3,4) has two Situation --- general camera pattern and light-field camera pattern, corresponding calibration algorithm are divided into general camera calibration algorithm and light field to kind Camera calibration algorithm；The general camera calibration algorithm is：By on double layer planar modulator (3,4) timesharing show and chessboard Lattice minute surface (1) portrays standard gridiron pattern of the gridiron pattern with size, and is had gridiron pattern minute surface at the same time by camera (5) shooting (1) and the chessboard grid pattern that shows of mirror surface (2) double layer planar modulator it is, then complete by two dimensional surface gridiron pattern standardization Into calibration；After calibration, by Parameter Switch, gridiron pattern can be obtained in gridiron pattern minute surface (1) and mirror surface in camera coordinates Position and attitude relation under system；Mirror image calculating is carried out on gridiron pattern minute surface (1) to mirror surface (2) and can be obtained by camera (5) and double layer planar modulator (3,4) position orientation relation, when double-deck optical plane modulator (3,4) with respect to camera (5) pose close After the completion of system calculates, the position orientation relation between double layer planar modulator (3,4) is just can obtain by parameter transformation；From the above one Secondary shooting just can obtain the position orientation relation between the position orientation relation and double layer planar modulator of camera and double layer planar modulator.

A kind of 2. application process of light field deviation art measuring system calibration mirror according to claim 1, it is characterised in that institute Stating light-field camera calibration algorithm is：The center of light-field camera microlens array, light field lenticule center pixel composition are determined first Sub-aperture image be used for demarcate position orientation relation.

A kind of 3. application process of light field deviation art measuring system calibration mirror according to claim 2, it is characterised in that institute Stating the algorithm at the center of definite microlens array is：Display is shot by light-field camera（ 7）The multifrequency phase shift striped of display Image, calculates its average phase-shift stripe pattern brightness, the center pixel of lenticule is determined by peak detection algorithm, peak point is just It is lenticule central point.

A kind of 4. application process of light field deviation art measuring system calibration mirror according to claim 3, it is characterised in that institute State calibration light-field camera position orientation relation：Gridiron pattern minute surface (1) and mirror surface (2) internal reflection modulator is shot using camera (5) The chessboard grid pattern having with calibration mirror with size of upper display, extracts the sub-aperture image of every width light field image, sub-aperture figure The pixel coordinate of picture is replaced with the pixel coordinate under its lenticule center, finally using two dimensional surface gridiron pattern standardization into rower It is fixed；The position orientation relation of camera and double layer planar modulator reflects gridiron pattern on gridiron pattern minute surface (1) mirror by mirror surface (2) As obtaining, and then the position orientation relation between double layer planar modulator (3,4) can be obtained.