CN107610183B - Calibration method of fringe projection phase height conversion mapping model - Google Patents
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Abstract
The invention discloses a fringe projection phase height conversion mapping model and a calibration method, wherein the fringe projection phase height conversion mapping model comprises the following steps: the calibration target is placed in the junction area of the camera view field and the projector projection area, the calibration target image is shot, the projection stripes are emitted, and the image is shot at the same time; placing the calibration target at another position, wherein the calibration target has a different posture from the previous position, and repeating the steps; acquiring enough images; extracting the coordinate information of the feature point image, calculating the absolute phase value of the corresponding feature point by using an interpolation method, and calibrating a camera; and converting the coordinate values of all the characteristic points to CCS, and calculating each parameter in the phase height conversion mapping model by using the information of the characteristic points. The invention solves the problems of weak applicability, strict requirements on the relative poses of the camera and the projector, high complexity of a model algorithm, complex calibration process, accumulated errors and the like in the calibration technology.
Description
Technical Field
The invention relates to an optical three-dimensional detection technology, in particular to a calibration method of a fringe projection phase height conversion mapping model.
Background
The system calibration technology has great influence on the accuracy, speed and system composition of the fringe projection three-dimensional measurement system, and the existing calibration technology can be divided into two types: a calibration technology based on stereoscopic vision and a phase height conversion technology.
Inspired by binocular vision systems, many researchers have studied and improved stereoscopic vision-based calibration techniques. In order to realize three-dimensional measurement, internal parameters of the projector and the camera and a rotation matrix and a translation vector between the internal parameters and the rotation matrix need to be calibrated and calculated. Zhang and Huang propose a calibration method where the projector can "shoot" the image like a camera. This method calibrates the projector by projecting a series of horizontal and vertical stripes and establishes the spatial relationship of the projector and camera. Li et al use a predistortion to project fringes that eliminate the effects of projector lens distortion. To further improve the measurement accuracy, Li and Zhang propose an algorithm to estimate the optimum projection angle of the projector. Recently, Chen et al proposed a self-calibration method to achieve online calibration of fringe projection measurement systems. Calibration techniques based on stereoscopic vision are only applicable where the projector is a Liquid Crystal Display (LCD) or a digital micro-lens array (DMD) because of the need to project various patterns to calibrate the projector and calculate the spatial relationship of the projector and camera. However, in some cases, such as moire fringe projection systems, fiber optic interference projection systems, and scanning strobe fringe projection systems, this technique is no longer applicable because the projectors in these systems cannot be viewed as "inverted" cameras.
The other branch is the phase height conversion scaling technique. This model does not consider calibrating the projector, but directly establishes the phase and height relationship through a mathematical model. Therefore, it is not restricted by the kind of projector. Inspired by interpolation, Leandry et al propose a polynomial mapping model to establish phase and height mapping relationships. In order to achieve high measurement accuracy, the degree of the polynomial is required to be not less than 4, so that the measurement process is time-consuming and is not suitable for a real-time measurement system. Lu et al propose a phase height conversion method based on geometric constraints of fringes. This method has high measurement accuracy and robustness, but also has the disadvantage of being computationally expensive. Du et al established a mapping relationship between phase and height using a camera pinhole model in combination with ray tracing theory, and Huang improved the accuracy of this model by considering the distortion of the camera lens. The corresponding calibration method requires gauge blocks and reference surfaces of different heights, thus limiting their application range. In addition, the number of model parameters in the literature is 34, and the calculation amount is large. Tavares et al have developed a phase difference to height mapping using experimental experience. Zhang et al establishes a one-to-one mapping formula of world coordinates and phase differences by a polynomial mapping method. The method in the literature is essentially a pixel level calibration method using a look-up table method (LUT). These methods rely on the exact phase value of each pixel in the phase map and therefore require the calibration plate to be moved sufficiently and the calibration process is time consuming. In addition, both models require a reference plane to calculate the phase difference, which can cause error accumulation.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, provides an improved phase height conversion mapping model and a calibration method for a fringe projection three-dimensional measurement system by establishing a virtual camera coordinate system and analyzing the conversion relation of fringe information between the camera coordinate system and a projector coordinate system, and solves the problems of weak applicability, strict requirements on the relative poses of a camera and a projector, high complexity of a model algorithm, complex calibration process, error accumulation and the like in the calibration technology.
The purpose of the invention can be realized by the following technical scheme.
The invention relates to a calibration method of a fringe projection phase height conversion mapping model, which comprises the following steps:
firstly, placing a calibration target in an area at the junction of a camera view field and a projector projection area, shooting a calibration target image by a camera, then emitting projection stripes by the projector, and shooting an image by the camera;
placing the calibration target at another position in the junction area of the camera view field and the projector projection area, wherein the calibration target has different postures from the previous one, and repeating the step one;
step three, repeating the step two until enough images are acquired;
extracting image coordinate information of the feature points, calculating absolute phase values of the corresponding feature points by using an interpolation method, and calibrating the camera;
step five, converting the coordinate values of all the feature points into a camera coordinate system CCS, and utilizing the information (Z) of the feature pointsC(ii) a u v phi), calculating each parameter in the fringe projection phase height conversion mapping model;
wherein, the fringe projection phase height conversion mapping model is as follows:
wherein the content of the first and second substances,
kij＝b3pij+b4qij
[u v]Trepresenting image coordinates without distortion correction; [ u "v"]TIs the transformed image coordinates; dot O in projector coordinate system PCSPRepresenting a luminous point, XPThe axis being parallel to the direction of phase change of the projected fringes, YPDirection of phase change of the axially perpendicularly projected fringes, ZPThe axis is perpendicular to the phase plane of the projected fringes and the coordinates of any point in the projector coordinate system PCS are denoted as [ X [ ]P YP ZP]TIn the projector coordinate system PCS, the spatial points on the same light have the same phase and are all phi, and the spatial points are at the same height ZPUp, phase value from phi0Change to phi1Corresponding to XPThe range of variation is [ XP(φ0),XP(φ1)](ii) a w is a scale factor; t isPIs a translation vector, TP＝[tX tY tZ]T；[fu fv]TRepresents the focal length of the lens, [ u ]o vo]TIs the image center coordinate; s is the distortion factor of the image coordinate axes.
In order to reduce algorithm complexity and realize real-time measurement, a look-up table LUT method is used for definition
Fringe projection phase height conversion mapping model ZcThe method is simplified as follows:
compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the invention provides an improved phase height mapping model aiming at a fringe projection measurement system by establishing a virtual camera coordinate system and analyzing the conversion relation of projection fringe information between a projector coordinate system and a camera coordinate system, and provides a novel calibration method aiming at the model. Compared with the mapping model and the calibration method aiming at the fringe projection measurement system, the model provided by the invention has no strict requirements on the relative poses of the projector and the camera, the algorithm complexity of the calibration model is low, the rapid and accurate three-dimensional measurement can be realized, and the corresponding calibration method is simple and efficient. The phase height mapping model and the calibration method provided by the invention have the advantages, so that the phase height mapping model and the calibration method can be applied to field calibration.
Drawings
FIG. 1 is a schematic view of a projector coordinate system PCS;
FIG. 2 is a schematic diagram of a virtual camera coordinate system CCS' and a camera coordinate system CCS;
FIG. 3 is a calibration schematic of a fringe projection phase-height conversion mapping model;
FIG. 4 is a calibration field map using a fringe projection phase height transform mapping model;
FIG. 5 is a schematic view of an object measured using the present model;
FIG. 6 is a schematic diagram of feature point reconstruction information used for calibration;
fig. 7 is a diagram showing the results of three-dimensional measurement using the present model.
Detailed Description
The invention is further described below with reference to the accompanying drawings.
As shown in FIG. 1, a projector coordinate system PCS is established in which a dot O is locatedPRepresenting a luminous point, XPThe axis being parallel to the direction of phase change of the projected fringes, YPDirection of phase change of the axially perpendicularly projected fringes, ZPThe axis is perpendicular to the phase plane of the projected fringes. Thus, arbitrary in the projector coordinate system PCSThe coordinates of a point may be expressed as [ X ]P YP ZP]T. As can be seen from fig. 1, in the projector coordinate system PCS, the phases of the spatial points on the same light ray are the same and are all phi. At the same height ZPUp, phase value from phi0Change to phi1Corresponding to XPThe range of variation is [ XP(φ0),XP(φ1)]. For slave OPAny emitted light can obtain the formula (1):
XP＝wZP(φ-φ0)+XP(φ0) (1)
where w is a scale factor. The coordinate transformation formula from the camera coordinate system CCS to the projector coordinate system PCS is:
[XP YP ZP]T＝TP+RP[XC YC ZC]T (2)
wherein R isPIs a rotation matrix, TPIs a translation vector, [ X ]C YC ZC]TAre the coordinates in the camera coordinate system,
here, a virtual camera coordinate system CCS' is defined to have the same attitude as the projector coordinate system PCS and the same position as the camera coordinate system CCS, as shown in fig. 2 and equation (3).
[XP YP ZP]T＝TP+[XC' YC' ZC']T(3) Wherein, [ X ]C' YC' ZC']T＝RP[XC YC ZC]T。
Bringing formula (3) into formula (1) gives formula (4):
XC'+tX＝w(ZC'+tZ)(φ-φ0)+XP(φ0) (4)
bringing the camera aperture imaging mold into formula (4), formula (5) can be obtained:
wherein the content of the first and second substances,
in the above formula [ X ]C' YC' ZC']TRepresenting the coordinates in the camera coordinate system CCS'; [ f ] ofu fv]TRepresents the focal length of the lens, [ u ]ovo]TIs the image center coordinate; s is the distortion factor of the image coordinate axes. Expand (3) and let XC'And YC'Are each divided by ZC'And using the camera imaging model, equation (6) can be obtained:
wherein the content of the first and second substances,
expanding the formula (6) by using Taylor series, and obtaining the formula (7),
correcting the distortion of the camera lens, wherein the distortion model of the camera lens is as the formula (8),
wherein, [ u v ]]TRepresenting the image coordinates without distortion correction, [ u [un vun]TRepresenting the corrected image coordinates; e.g. of the type1,e2And e3Representing radial distortionParameter, g1And g2Representing the parameter of the tangential distortion,
representing the distance between the image coordinate point and the center point. To avoid finding the image center coordinate uo vo]TExpanded form (8). At the same time, expansion (7). The results after development of formula (7) and formula (8) can both be represented by formula (9), wherein [ u "v"]TIs the coordinates of the image after the transformation,
taking the distortion of a camera lens into consideration in a camera coordinate system CCS, and bringing the formula (9) into the formula (5) to obtain the novel fringe projection phase height conversion mapping model Z of the inventionC(u, v,. phi.), can be expressed as:
wherein k isij＝b3pij+b4qij. Equation (10) can be considered as a case where the image coordinates in CCS are converted to the image coordinates in CCS' after the camera lens distortion correction.
The parameter in equation (10) can be calculated by equation (11), where N is the total number of feature points extracted from the calibration target. Estimating the minimum of equation (11) is a non-linear optimization process that can be calculated by the Levenberg-Marquardt algorithm.
In general, a good fitting effect can be achieved when the parameter order n in equation (10) reaches 3 or 4. After all parameters are estimated, the height value ZCCan be obtained by the formula (10), and XCAnd YCCan be passed through ZCEquation (8) and camera pinhole imaging model acquisition.
In order to reduce the algorithm complexity and realize real-time measurement, a look-up table LUT method is considered here, and equation (12) is defined:
the novel fringe projection phase height conversion mapping model of the present invention can be simplified as follows:
and the Z _ LUT [ u, v ] of each pixel point is calculated in advance, and the calculation amount during measurement can be obviously reduced. Likewise, the measurement in the X and Y directions can also be performed in such a manner as to reduce the amount of calculation and increase the measurement speed.
The invention discloses a calibration method of a novel fringe projection phase height conversion mapping model, which comprises the following specific steps as shown in figure 3:
firstly, placing a calibration target in any area at the junction of a camera view field and a projector projection area. Firstly, the projector does not need to emit any projection stripes, and the camera shoots a calibration target image for extracting the characteristic points of the calibration target; then, the projector emits the projection stripes while the camera takes images for acquiring the absolute phases of the feature points.
And step two, placing the calibration target at another position in the junction area of the camera view field and the projector projection area, ensuring that the calibration target is different from the previous posture, and repeating the step one.
And step three, repeating the step two until enough images are acquired, wherein the images are 2-10 groups of images generally. In fact, all parameters can be calculated using only 2 sets of images. Nevertheless, typically at least 5 sets of images are required to ensure that sufficient accuracy is achieved.
And step four, extracting image coordinate information of the feature points, calculating absolute phase values of the corresponding feature points by using an interpolation method, and calibrating the camera.
Step five, converting the coordinate values of all the feature points into a camera coordinate system CCS, and utilizing the information (Z) of the feature pointsC(ii) a uv phi), calculating each parameter in the novel fringe projection phase height conversion mapping model.
As shown in fig. 4, the camera, projector and its support are mounted on the optical platform as shown, where the relative pose of the camera and projector is not critical. As in fig. 3 and the process described above, the projector is controlled by the computer to project the projected stripes while the camera is used to capture the calibration target image; extracting a characteristic point image coordinate through image processing, substituting the characteristic point image coordinate and a coordinate under a characteristic point camera coordinate system into the phase height conversion mapping model provided by the invention, and solving parameters; after all the parameters in the model have been calculated, the object to be measured as in fig. 5 is measured using the present model.
According to the above mode, the model and the calibration method thereof proposed by the present invention are experimentally verified, when the nonlinear number n in the model is 4, the reconstruction information of the feature points used for calibration is shown in fig. 6, the result of three-dimensional measurement using the model is shown in fig. 7, and the time taken for measurement is 11 milliseconds.
While the present invention has been described in terms of its functions and operations with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise functions and operations described above, and that the above-described embodiments are illustrative rather than restrictive, and that various changes and modifications may be effected therein by one skilled in the art without departing from the scope or spirit of the invention as defined by the appended claims.
Claims (1)
1. A calibration method for a fringe projection phase height conversion mapping model is characterized by comprising the following steps:
firstly, placing a calibration target in an area at the junction of a camera view field and a projector projection area, shooting a calibration target image by a camera, then emitting projection stripes by the projector, and shooting an image by the camera;
placing the calibration target at another position in the junction area of the camera view field and the projector projection area, wherein the calibration target has different postures from the previous one, and repeating the step one;
step three, repeating the step two until enough images are acquired;
extracting image coordinate information of the feature points, calculating absolute phase values of the corresponding feature points by using an interpolation method, and calibrating the camera;
step five, converting the coordinate values of all the feature points into a camera coordinate system CCS, and utilizing the information (Z) of the feature pointsC(ii) a u v phi), calculating each parameter in the fringe projection phase height conversion mapping model;
wherein, the fringe projection phase height conversion mapping model is as follows:
in order to reduce the complexity of the algorithm and realize real-time measurement, a look-up table LUT method is used for defining:
fringe projection phase height conversion mapping model ZcThe method is simplified as follows:
wherein the content of the first and second substances,
kij＝b3pij+b4qij
[u v]Trepresenting image coordinates without distortion correction; [ u "v")]TIs the transformed image coordinates; dot O in projector coordinate system PCSPRepresenting a luminous point, XPThe axis being parallel to the direction of phase change of the projected fringes, YPDirection of phase change of the axially perpendicularly projected fringes, ZPThe axis is perpendicular to the phase plane of the projected fringes and the coordinates of any point in the projector coordinate system PCS are denoted as [ X [ ]PYP ZP]TIn the projector coordinate system PCS, the spatial points on the same light have the same phase and are all phi, and the spatial points are at the same height ZPUp, phase value from phi0Change to phi1Corresponding to XPThe range of variation is [ XP(φ0),XP(φ1)](ii) a w is a scale factor; t isPIs the translation vector, T, of the conversion of the camera coordinate system CCS to the projector coordinate system PCSP＝[tX tY tZ]T；[fu fv]TRepresents the focal length of the lens, [ u ]o vo]TIs the image center coordinate; s is the distortion factor of the image coordinate axes.
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| CN110793464B (en) * | 2019-10-17 | 2021-08-20 | 天津大学 | Large-field-of-view fringe projection vision three-dimensional measurement system and method |
| CN110849268B (en) * | 2019-12-10 | 2021-07-06 | 南昌航空大学 | Quick phase-height mapping calibration method |
| CN111754408A (en) * | 2020-06-29 | 2020-10-09 | 中国矿业大学 | High-real-time image splicing method |
| CN112967342B (en) * | 2021-03-18 | 2022-12-06 | 深圳大学 | High-precision three-dimensional reconstruction method and system, computer equipment and storage medium |
| CN113566709A (en) * | 2021-08-26 | 2021-10-29 | 苏州小优智能科技有限公司 | Calibration method and device of structured light measurement system and electronic equipment |
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102768020A (en) * | 2012-08-03 | 2012-11-07 | 南京理工大学 | Measurement system and method for measuring height of surface of micro object on basis of digital fringe projection technology |
| CN104111039A (en) * | 2014-08-08 | 2014-10-22 | 电子科技大学 | Calibrating method for randomly placing fringe projection three-dimensional measuring system |
| CN106767405A (en) * | 2016-12-15 | 2017-05-31 | 深圳大学 | The method and device of the quick corresponding point matching of phase mapping assist three-dimensional imaging system |
-
2017
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Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102768020A (en) * | 2012-08-03 | 2012-11-07 | 南京理工大学 | Measurement system and method for measuring height of surface of micro object on basis of digital fringe projection technology |
| CN104111039A (en) * | 2014-08-08 | 2014-10-22 | 电子科技大学 | Calibrating method for randomly placing fringe projection three-dimensional measuring system |
| CN106767405A (en) * | 2016-12-15 | 2017-05-31 | 深圳大学 | The method and device of the quick corresponding point matching of phase mapping assist three-dimensional imaging system |
Non-Patent Citations (2)
| Title |
|---|
| Accurate and robust calibration method based on pattern geometric constraints for fringe projection profilometry;PENG LU 等;《applied optics》;20170124;全文 * |
| High-speed real-time 3-D coordinates measurement based on fringe projection profilometry considering camera lens distortion;Shijie Feng 等;《Optics Communications》;20141015;全文 * |
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