阅读说明：本技术 一种基于梯度光强的多频外差面结构光三维重建方法 (Multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity ) 是由 刘飞 吴延雪 吴高旭 杨时超 杨恬 傅渤雅 袁依琳 于 2020-11-21 设计创作，主要内容包括：本发明公开了一种基于梯度光强的多频外差面结构光三维重建方法,步骤包括：1)搭建结构光测量系统；2)对整个结构光测量系统进行标定；3)确定m组待生成的结构光条纹图不同的频率；4)生成m组基于梯度光强的投射图像；5)将投射图像通过投射到被测物体表面,采集图像经过被测物体调制后总采集图像；6)计算出总采集图像的梯度光强；7)计算每组采集图像的包裹相位,获得最高频率包裹相位；8)计算出最高频率采集图像的整数条纹级数；9)计算最高频率采集图像对应的绝对相位,进行三维重建；本发明具有简单易操作,实时性强的优点,适用于高速三维重建技术。(The invention discloses a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity, which comprises the following steps of: 1) building a structured light measuring system; 2) calibrating the whole structured light measuring system; 3) determining different frequencies of m groups of structural light stripe patterns to be generated; 4) generating m groups of projection images based on gradient light intensity; 5) projecting the projection image to the surface of a measured object, and modulating the collected image by the measured object to obtain a total collected image; 6) calculating a total captured image The gradient light intensity of (a); 7) calculating the wrapping phase of each group of collected images to obtain the highest frequency wrapping phase; 8) calculating the integer fringe series of the highest frequency acquisition image; 9) calculating an absolute phase corresponding to the highest frequency acquisition image, and performing three-dimensional reconstruction; the invention has the advantages of simple and easy operation and strong real-time propertyThe method has the advantages of being suitable for a high-speed three-dimensional reconstruction technology.)

1. A multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity is characterized by comprising the following steps:

1) building a structured light measuring system; the structured light measurement system comprises the industrial camera (1), a projector (2), an operation terminal (3) and a measured object (4); the projector (2) and the industrial camera (1) are connected to the operation terminal (3) in a communication way; the industrial camera (1) and the projector (2) are respectively arranged on the front side of the measured object (4);

2) adjusting the positions of the industrial camera (1) and the projector (2), calibrating the whole structured light measurement system after the positions are adjusted, and storing calibration parameters;

3) determining m groups of different frequencies f of the structural light stripe pattern to be generated at the operation terminal (3)_i，(i＝1,2,...,m)；

4) The operation terminal (3) generates m groups of multi-frequency structure light stripe images based on gradient light intensity, and the m groups of multi-frequency structure light stripe images are recorded as projection images

5) The operation terminal (3) projects an imageThe projector (2) is used for projecting to the surface of a measured object (4) respectively, images are collected through the industrial camera (1), m groups of collected images modulated by the measured object (4) are obtained, and the m groups of collected images are recorded as total collected imagesAnd output to the operation terminal (3);

6) the operation terminal (3) calculates a total acquisition imageGradient intensity of light I_ij'(x,y)。

7) The operation terminal (3) is based on total collected imagesGradient intensity of light I_ij' (x, y) calculating the wrapped phase for each set of acquired imagesObtaining highest frequency inclusion phaseBit

8) The operating terminal (3) is based on a multi-frequency heterodyne phase unwrapping method and the wrapping phases of the m groups of collected images computed in the step 7) corresponding to different frequenciesCalculating integral fringe series k of the highest frequency acquisition image₁；

9) The operation terminal (3) collects the integer fringe series k corresponding to the image with the highest frequency₁And highest frequency wrapped phaseCalculating the absolute phase phi corresponding to the highest frequency acquisition image₁(x, y), absolute phase φ₁The formula for the calculation of (x, y) is:

10) the operating terminal (3) collects the absolute phase phi of the image according to the highest frequency₁(x, y) and the calibration parameters obtained in the step 2) calculate the three-dimensional coordinate data of the surface point of the measured object (4), and complete the three-dimensional reconstruction of the measured object (4).

2. A multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity as claimed in claim 2, wherein in step 4), the frequency f of a single fringe is_iCorresponding to a group of structural light stripe images; each set of the structured light stripe images comprises two structured light stripe imagesAnd2m structural light stripe images are projected in total, and the 2m structural light stripe images are recorded as projection imagesEach set of structured light stripe images has the following expression:

in the formulae (2) to (3),representing the gray value size of the (x, y) point in the 1 st projection image corresponding to the single fringe frequency;representing the gray value size at the (x, y) point in the 2 nd projection image in the group corresponding to the single fringe frequency; a. the^pRepresenting the DC component of the image, B^pA magnitude representing an image; phi is a_i(x, y) is the absolute phase in the image.

3. A multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity as claimed in claim 2, wherein in step 6), the frequency f of a single fringe is_iThe gradient light intensity of the corresponding group of collected images has the following expression:

I_i1'(x,y)＝-B^csinφ_i(x,y)dφ_i (4)

I_i2'(x,y)＝B^ccosφ_i(x,y)dφ_i (5)

in formulae (4) to (5), I_ij' (x, y) represents the gradient light intensity value at the (x, y) point in the j acquired image in the group corresponding to the single fringe frequency; b is^cGray scale modulation representing the acquired image; d phi_iIs the differentiation of the phase in the acquired image; .

4. A multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity as claimed in claim 3, wherein in step 7), the calculation formula of the wrapped phase of each group of the collected images corresponding to a single fringe frequency is as follows:

5. the method according to claim 1, wherein the method comprises a step of performing three-dimensional reconstruction on the multi-frequency heterodyne surface structured light based on gradient light intensity, and a step of performing three-dimensional reconstruction on the multi-frequency heterodyne surface structured light based on gradient light intensity by using a method comprising the following steps: the optical axes of the industrial camera (1) and the projector (2) are crossed, the projection areas are mutually overlapped, and the measured object (4) is just positioned in the common field of view of the industrial camera (1) and the projector (2).

Technical Field

The invention belongs to the field of three-dimensional measurement of surface structured light, and particularly relates to a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity.

Background

With the continuous development of modern science and technology, the application requirements of reconstruction technology in the three-dimensional measurement method in various industries are continuously increased. The main idea of the technology is to obtain the three-dimensional shape information of the object to be measured by a certain technical method and reconstruct a three-dimensional model of the object. In recent years, three-dimensional reconstruction techniques are increasingly used in the fields of industrial detection, medical treatment, cultural relic restoration and the like.

According to different implementation forms, the three-dimensional measurement technology can be mainly divided into the following steps according to whether the three-dimensional measurement technology is in contact with a measured object or not: contact and contactless. Contact three-dimensional measurement techniques have a high degree of accuracy but are destructive because they require contact with the surface of the object being measured. Compared with contact measurement, non-contact measurement has the advantages of no destructiveness, high efficiency, large working distance and the like. Among many non-contact three-dimensional measurement technologies, three-dimensional visual reconstruction based on surface structured light has the characteristics of high precision, simple operation, strong real-time performance and the like, wherein the surface structured light three-dimensional reconstruction Technology based on Multi-frequency Heterodyne Phase-shifting Technology is emphasized by many researchers, and is a research hotspot in the field of visual reconstruction.

For the higher and higher speed requirements in the three-dimensional measurement technology, the multi-frequency heterodyne phase shift technology still has some problems, in order to acquire accurate phase information of a measured object from a collected image, the conventional multi-frequency heterodyne phase shift technology generally needs to project a series of phase shift images with different frequencies to calculate a wrapping phase, and the multi-frequency heterodyne principle is utilized to perform phase expansion calculation, so that the number of projected fringe images is increased, the time for collecting the images is increased, the possibility of interference on the measurement process is increased, and the speed of three-dimensional reconstruction of structured light is reduced. The application of the multi-frequency heterodyne phase shift technology in the high-speed and high-precision real-time structured light three-dimensional reconstruction technology is limited by a large number of images to be projected.

Disclosure of Invention

The technical scheme adopted for achieving the purpose of the invention is that the method for three-dimensional reconstruction of the multi-frequency heterodyne surface structured light based on gradient light intensity comprises the following steps:

1) and (5) building a structured light measuring system. The structured light measurement system comprises an industrial camera, a projector, an operation terminal and a measured object. The projector and the industrial camera are communicably connected to the operation terminal. The industrial camera and the projector are respectively arranged on the front side of the measured object.

2) And adjusting the positions of the industrial camera and the projector, calibrating the whole structured light measuring system after the position adjustment is finished, and storing calibration parameters.

3) Determining different frequencies f of m groups of structured light stripe patterns to be generated at the operation terminal_i，(i＝1,2,...,m)。

4) The operation terminal generates m groups of multi-frequency structural light stripe images based on gradient light intensity, and the m groups of multi-frequency structural light stripe images are recorded as projection imagesj＝1,2。

5) The operation terminal projects an imageRespectively projecting the images to the surface of a measured object through a projector, acquiring the images through an industrial camera, obtaining m groups of acquired images modulated by the measured object, and recording the m groups of acquired images as total acquired imagesAnd output to the operation terminal.

6) The operation terminal calculates a total acquisition imageGradient intensity of light I_ij'(x,y)。

7) The operation terminal is based on total acquisition imageGradient intensity of light I_ij' (x, y) calculating the wrapped phase for each set of acquired imagesObtaining highest frequency wrapped phase

8) The operating terminal is based on a multi-frequency heterodyne phase unwrapping method and the wrapping phases of the m groups of collected images computed in the step 7) corresponding to different frequenciesCalculating integral fringe series k of the highest frequency acquisition image₁。

9) The operation terminal acquires an integer fringe series k corresponding to an image at the highest frequency₁And highest frequency wrapped phaseCalculating the absolute phase phi corresponding to the highest frequency acquisition image₁(x, y), absolute phase φ₁The formula for the calculation of (x, y) is:

10) the operation terminal acquires the absolute phase phi of the image according to the highest frequency₁(x, y) and the calibration parameters obtained in the step 2) calculate the three-dimensional coordinate data of the surface points of the measured object, and complete the three-dimensional reconstruction of the measured object.

Further, in step 4), a single fringe frequency f_iCorresponding to a group of structured lightA striped image. Each set of the structured light stripe images comprises two structured light stripe imagesAnd2m structural light stripe images are projected in total, and the 2m structural light stripe images are recorded as projection imagesEach set of structured light stripe images has the following expression:

in the formulae (2) to (3),indicating the gray value magnitude at the (x, y) point in the 1 st projection image in the set for a single fringe frequency.Indicating the gray value magnitude at the (x, y) point in the 2 nd projection image in the set for a single fringe frequency. A. the^pRepresenting the DC component of the image, B^pRepresenting the magnitude of the image. Phi is a_i(x, y) is the absolute phase in the image.

Further, in step 6), a single fringe frequency f_iThe gradient light intensity of the corresponding group of collected images has the following expression:

I_i1'(x,y)＝-B^csinφ_i(x,y)dφ_i (4)

I_i2'(x,y)＝B^ccosφ_i(x,y)dφ_i (5)

in formulae (4) to (5), I_ij' (x, y) indicates the gradient intensity value at the (x, y) point in the j-th acquired image in the group corresponding to the single fringe frequency. B is^cRepresenting a grey scale modulation of the acquired image. d phi_iTo acquire the differential of the phase in the image.

Further, in step 7), the calculation formula of the wrapped phase of each group of acquired images corresponding to the single fringe frequency is as follows:

further, the optical axes of the industrial camera and the projector are intersected, the projection areas are mutually overlapped, and the measured object is just positioned in the common field of view of the industrial camera and the projector.

The technical effects of the invention are undoubted, and compared with the traditional multifrequency heterodyne phase shift technology, the invention has the beneficial effects that:

1. according to the method, a series of phase shift images with different frequencies are not required to be projected, the wrapping phase can be calculated by only two acquired images, the number of the projected images is greatly reduced, the acquisition time and the calculation speed are greatly improved, and the measurement efficiency is remarkably improved.

2. The method improves the periodicity of the projected fringe image, can effectively improve the precision of three-dimensional reconstruction, and ensures both the reliability and the precision compared with the traditional multi-frequency heterodyne phase shift method.

3. The method realizes the measurement efficiency and the measurement precision only by the algorithm under the condition of not changing hardware, has the advantages of simplicity, easy operation and strong real-time performance compared with the traditional multi-frequency heterodyne technology, and is more suitable for the high-speed three-dimensional reconstruction technology.

Drawings

FIG. 1 is a schematic view of a measurement system of a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity;

FIG. 2 is a schematic flow chart of a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity according to the present invention;

fig. 3 is a schematic diagram of a fringe image generated by the gradient light intensity-based multifrequency heterodyne surface structured light three-dimensional reconstruction method of the present invention.

In the figure: an industrial camera 1, a projector 2, an operation terminal 3, and an object to be measured 4.

Detailed Description

The present invention is further illustrated by the following examples, but it should not be construed that the scope of the above-described subject matter is limited to the following examples. Various substitutions and alterations can be made without departing from the technical idea of the invention and the scope of the invention is covered by the present invention according to the common technical knowledge and the conventional means in the field.

Example 1:

the embodiment discloses a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity, which is suitable for various frequency heterodyne measurement methods, and is specifically implemented by the following steps, referring to fig. 1 and fig. 2:

1) and (5) building a structured light measuring system. The structured light measurement system includes an industrial camera 1, a projector 2, an operation terminal 3, and a measured object 4. The projector 2 and the industrial camera 1 are communicably connected to the operation terminal 3. The industrial camera 1 and the projector 2 are respectively arranged on the front side of the object to be measured 4. The optical axes of the industrial camera 1 and the projector 2 are intersected, the projection areas are mutually overlapped, and the measured object 4 is just positioned in the common field of view of the industrial camera 1 and the projector 2.

2) And adjusting the positions of the industrial camera 1 and the projector 2, calibrating the whole structured light measurement system after the position adjustment is finished, obtaining the three-dimensional coordinate-phase relation of the projector 2 and the industrial camera 1, and storing calibration parameters.

3) Determining different frequencies f of m groups of sinusoidal grating stripe images at the operation terminal 3_i(i ═ 1, 2.. multidot.m). In this embodiment, three conventional fringe frequencies and a heterodyne phase unwrapping method based on a mole sequence are selected, and the number m of fringe frequencies is determined to be 3. According to the related research, three different heterodyne frequencies are preferred to unwrappe the phase, the frequencies being: f. of₁＝70、f₂＝64、f₃59. In this embodiment, three groups of images at different frequencies need to be acquired, and each group of images has two vertical stripe grating images. The width of each image to be projected is set to be 1024, and the height is set to be 768.

4) The undetermined parameters in the structured light fringe grating expression set and generated according to the embodiment are respectively as follows:

A、B(1)

in equations (1) to (2), a is a dc component of an image, B is an amplitude of the image, Φ (x, y) is an absolute phase in the image, p is a pitch, and p is W/f, which represents a total number of pixels in one fringe period. Then corresponds to p_i(i 1, 2.. said., m), the expression of the light intensity at a set of vertical striped gratings (x, y) of the pitch is:

according to the preset f in the step 3)₁＝70、f₂＝64、f₃Three sets of stripe raster images may be generated, each set containing two vertical stripe images. The six structural light stripe images generated corresponding to the present embodiment are shown in fig. 3.

5) The projector 2 projects the six structural light stripe images generated in the step 2 to the object to be measured 4, and simultaneously, the industrial camera 2 synchronously collects the stripe images after the height of the object is modulated, and the six collected images are stored in the control terminal 3.

6) Calculating the gradient light intensity of the acquired image in the step 5). Corresponds to f_iThe expression of the gradient intensity at a set of vertically acquired images (x, y) at a frequency (i ═ 1,2,3) is:

I₁'(x,y)＝-B^csinφ_i(x,y)dφ_i (5)

I₂'(x,y)＝B^ccosφ_i(x,y)dφ_i (6)

in formulae (5) to (6), B^cRepresenting the grey-scale modulation of the vertically acquired image, d phi_iIs the differentiation of the phase in the vertically acquired image. And (3) obtaining gradient light intensity values of the three groups of collected images according to the three fringe frequencies preset in the step (3).

7) And calculating the wrapping phase corresponding to the gradient light intensity of each group of vertically collected images in the step 6). The gradient light intensity values of each group of collected images obtained in this embodiment are:

corresponds to f₁Gradient intensity values of a set of vertically acquired images of (1): i is₁₁'、I₁₂'; corresponds to f₂Gradient intensity values of a set of vertically acquired images of (1): i is₂₁'、I₂₂'; corresponds to f₂Gradient intensity values of a set of vertically acquired images of (1): i is₃₁'、I₃₂'；

The wrapped phases of each set of acquired images can be solved according to the above assumptions:

corresponds to f₁The wrapped phase of a set of vertically acquired images of (a) is:

corresponds to f₂The wrapped phase of a set of vertically acquired images of (a) is:

corresponds to f₂The wrapped phase of a set of vertically acquired images of (a) is:

8) obtaining the highest frequency f through a heterodyne phase expansion algorithm based on a Moore sequence according to the wrapping phases corresponding to each group of vertically acquired images solved in the step 7)₁The phase progression integer part of the set of vertically acquired images corresponding to 70, i.e. the fringe progression k is calculated₁；

9) According to the integer fringe order k obtained in the step 8)₁And the highest frequency wrapped phase obtained in step 7)Calculating the absolute phase phi of the group of vertically acquired images corresponding to the highest frequency₁(x, y), the corresponding calculation formula is:

10) calculating the three-dimensional coordinate data of the surface point of the object to be measured according to the absolute phase information of the highest-frequency acquired image obtained in the step 9) and the three-dimensional coordinate-phase relation of the projector-camera system obtained by calibration in advance, and finishing the three-dimensional reconstruction of the object to be measured.

In the method for three-dimensional reconstruction of the multi-frequency heterodyne surface structured light based on gradient light intensity provided by this embodiment, a set of multi-frequency surface structured light fringe images based on gradient light intensity is generated, and a projector 2 is used to project projection images with different frequencies onto a measured object 4. Firstly, the gradient light intensity of the collected image is calculated, and then the wrapping phase information is obtained through the gradient light intensity. And solving the absolute phase according to the phase unwrapping principle of the multi-frequency heterodyne. The number of the projected images is reduced, the cycle number of the stripe images is increased, and the speed and the precision of three-dimensional reconstruction are improved.

Example 2:

the embodiment provides a basic implementation manner, and is a multi-frequency heterodyne surface structured light three-dimensional reconstruction method based on gradient light intensity, which is suitable for various frequency heterodyne measurement methods, and is shown in fig. 1 and 2, and includes the following steps:

1) and (5) building a structured light measuring system. The structured light measurement system includes an industrial camera 1, a projector 2, an operation terminal 3, and a measured object 4. The projector 2 and the industrial camera 1 are communicably connected to the operation terminal 3. The industrial camera 1 and the projector 2 are respectively arranged on the front side of the object to be measured 4.

2) And adjusting the positions of the industrial camera 1 and the projector 2, calibrating the whole structured light measurement system after the position adjustment is finished, obtaining the three-dimensional coordinate-phase relation of the projector 2 and the industrial camera 1, and storing calibration parameters.

3) Determining m groups of different frequencies f of the structured light stripe pattern to be generated at the operation terminal 3_i，(i＝1,2,...,m)。

4) The operation terminal 3 generates m groups of multi-frequency structure light stripe images based on gradient light intensity according to the m stripe frequencies determined in the step 3), and records the m groups of multi-frequency structure light stripe images as projection imagesj＝1,2。

5) The operation terminal 3 projects an imageRespectively projecting the images to the surface of a measured object 4 through a projector 2, acquiring the images through an industrial camera 1, obtaining m groups of acquired images modulated by the measured object 4, and recording the m groups of acquired images as total acquired imagesAnd outputting the images to the operation terminal 3, wherein each group of the structural light stripe images to be projected corresponds to one group of collected images collected by the industrial camera 1.

6) The operation terminal 3 calculates a total collection imageGradient intensity of light I_ij'(x,y)。

7) The operation terminal 3 is based on the total collected imageGradient intensity of light I_ij' (x, y) calculating the wrapped phase for each set of acquired imagesObtaining highest frequency wrapped phaseTherefore, the wrapping phases of the m groups of collected images are respectively solved, and the calculation results of the wrapping phases of the m groups corresponding to different frequencies are obtained.

8) The operating terminal 3 is based on a multi-frequency heterodyne phase unwrapping method and the wrapping phases of the m groups of collected images computed in the step 7) corresponding to different frequenciesCalculating the integer part of the phase progression, i.e. the integer fringe progression k, of the highest frequency acquired image₁。

According to the heterodyne principle, two high-frequency fringe images can be synthesized into a low-frequency heterodyne fringe image. The pitch (the number of pixel points included in one fringe period T) of m collected images with different frequencies and the last heterodyne fringe image synthesized by the multi-stage heterodyne operation covers the whole image field, that is, the frequency of the last heterodyne fringe image synthesized is 1.

9) The operation terminal 3 acquires the integer fringe series k corresponding to the image with the highest frequency₁And highest frequency wrapped phaseCalculating the absolute phase phi corresponding to the highest frequency acquisition image₁(x, y), absolute phase φ₁The formula for the calculation of (x, y) is:

10) the operation terminal 3 acquires a graph according to the highest frequencyAbsolute phase phi of image₁(x, y) and the calibration parameters obtained in the step 2), and calculating the three-dimensional coordinate data of the surface point of the measured object 4 according to the three-dimensional coordinate-phase relation of the projector-camera system obtained by calibration, thereby completing the three-dimensional reconstruction of the measured object 4.

Example 3:

the main steps of this example are the same as example 2, and further, in step 4), the frequency f of a single stripe_iCorresponding to a set of structured light stripe images. Each set of the structured light stripe images comprises two structured light stripe imagesAnd2m structural light stripe images are projected in total, and the 2m structural light stripe images are recorded as projection imagesEach set of structured light stripe images has the following expression:

in the formulae (2) to (3),indicating the gray value magnitude at the (x, y) point in the 1 st projection image in the set for a single fringe frequency.Indicating the gray value magnitude at the (x, y) point in the 2 nd projection image in the set for a single fringe frequency. A. the^pRepresenting the DC component of the image, B^pRepresenting the magnitude of an image。φ_i(x, y) is the absolute phase in the image.

Example 4:

the main steps of this example are the same as example 3, and further, in step 6), the frequency f of a single stripe_iThe gradient light intensity of the corresponding group of collected images has the following expression:

I_i1'(x,y)＝-B^csinφ_i(x,y)dφ_i (4)

I_i2'(x,y)＝B^ccosφ_i(x,y)dφ_i (5)

in formulae (4) to (5), I_ij' (x, y) indicates the gradient intensity value at the (x, y) point in the j-th acquired image in the group corresponding to the single fringe frequency. B is^cRepresenting a grey scale modulation of the acquired image. d phi_iTo acquire the differential of the phase in the image.

Example 5:

the main steps of this embodiment are the same as those of embodiment 4, and further, in step 7), the calculation formula of the wrapped phase of each group of acquired images corresponding to a single fringe frequency is as follows:

example 6:

the main steps of this embodiment are the same as those of embodiment 2, and further, the optical axes of the industrial camera 1 and the projector 2 intersect, the projection areas overlap with each other, and the object to be measured 4 is exactly located in the common field of view of the industrial camera 1 and the projector 2.