A superimposed coding phase unwrapping method based on phase quantization
Through the phase-valued superposition coding phase unwrapping method, the superposition coding stripes and wrapped phase binarization are used to solve the problems of phase jump error and high computational complexity in the traditional method, and an efficient and simplified phase unwrapping process is achieved.
Patent Information
- Application Number
- CN202211474123.X
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2022-11-22
- Publication Date
- 2025-10-17
- Estimated Expiration
- 2042-11-22
AI Technical Summary
Existing temporal phase unwrapping methods are affected by factors such as environmental noise, numerical errors, and limited defocus, resulting in phase jump errors and requiring additional projection of coded stripes, which increases computational complexity and limitations.
The superposition coding phase unwrapping method based on phase valueization is adopted. By generating a black and white stripe image, two groups of order stripes offset by half a cycle are obtained by superposition coding stripes and wrapped phase binarization. Phase unwrapping is performed to simplify the calculation process and reduce additional coding projection.
The utilization rate of the wrapped phase is improved, the algorithm complexity is simplified, the additional coding projection is reduced, the computational burden is lowered, and the accuracy and efficiency of phase unwrapping are improved.
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Figure CN115790451B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application belongs to the field of optical measurement, and particularly relates to a superimposed coding phase unwrapping method based on phase quantization. BACKGROUND
[0002] Phase unwrapping technology is one of the hot issues in the field of optical measurement. Through years of research by numerous scholars, there are many mature phase unwrapping algorithms, which are generally divided into two categories, namely spatial phase unwrapping and time phase unwrapping. The former uses the spatial rules and adjacent phase relationships of the pixel points in the wrapped phase image to unwrap the phase. Although only one wrapped phase is needed for phase unwrapping, this method has low accuracy and strict algorithm conditions, and cannot measure objects with discontinuous surfaces, which has many limitations. The latter needs to project different frequency coding stripes in addition to the wrapped phase for auxiliary phase unwrapping. The phase is unwrapped by calculating the phase of the same pixel points on all coding stripes in time sequence. This method avoids spatial measurement errors, although the number of projected amplitudes is increased, the unwrapping conditions are simple, and objects with complex and discontinuous surfaces can be measured. Therefore, most of the industrial measurement field adopts time phase unwrapping algorithm.
[0003] Multi-frequency method, phase coding and Gray code are the three mainstream time phase unwrapping methods. Although the multi-frequency method can obtain the phase from sinusoidal stripes of different frequencies by using heterodyne principle, it is limited by the frequency selection and needs to project three times the sinusoidal stripes. The phase coding and Gray code are both methods of embedding the information of step level stripes into different types of coding stripes through phase calculation and binary calculation, such as single period phase shift stripes and Gray code stripes. The level value of phase unwrapping is obtained by analyzing the modulated coding stripes, and then the unwrapped phase is obtained.
[0004] The traditional phase unwrapping method will cause the misalignment of the fringe order and the wrapped phase due to the influence of environmental noise, quantization error and limited defocusing, and will introduce phase jump error. In order to eliminate the phase jump error, Lv S, Sun Q, Yang J, et al. An improved phase-coding method for absolute phase retrieval based on the path-following algorithm [J]. Optics and Lasers in Engineering, 2019, 122: 65-73. proposed a path tracking algorithm, which determines the truncation point of the phase, and uses the information of the adjacent points around the truncation point to correct the phase unwrapping error of the traditional phase coding, but this method is only limited to the measurement of smooth surface objects; then, Cai B, Yang Y, Wu J, et al. An improved gray-level coding method for absolute phase measurement based on half-period correction [J]. Optics and Lasers in Engineering, 2020, 128: 106012. proposed a half-period correction code word determination method to determine the fringe order of the wrapped phase, but this method needs to calculate the positive and negative masks, and the computational complexity is high; Zheng D, Da F, Ke M Q, et al. Phase-shifting profilometry combined with Gray-code patterns projection: unwrapping error removal by an adaptive median filter [J]. Optics Express, 2017, 25(5): 4700-4713. corrected the phase unwrapping error by using an adaptive median filter, which needs to iterate different size median filters, and the algorithm runs slowly, and the real-time correction ability is weak. The above methods can eliminate the phase error to a certain extent, but they need to use spatial region information, have certain limitations, and the operation is complex.
[0005] To this end, Zhang Q, Su X, Xiang L, et al.3-D shape measurement based on complementary gray-code light[J].Optics and Lasers in Engineering, 2012, 50(4):574-579. proposed a complementary gray code phase error correction method, two groups of complementary orders offset by half a period were formed by gray code stripes, and the order was exchanged near the phase error to reduce error errors; Yu S, Zhang J, Yu X, et al.Unequal-period combination approach of gray code and phase shifting for 3-D visual measurement[J].Optics Communications, 2016, 374(1):97-106. proposed a method of combining gray code with different period phase shift, which reduces decoding errors by optimizing the stripe period; Liu Lu, Pan Yanjuan, Xi Dongdong, et al.Phase unwrapping error correction method of phase encoding fringe projection profilometry[J].Application Optics, 2020, 41(5):1002-2082. proposed a phase error correction method with additional binary stripes, which uses the half-period misalignment between the introduced binary stripes and the phase encoding stripes to calculate the complementary order to reduce the phase error of the phase encoding.
[0006] Although the above three methods effectively reduce the phase error, they need to project additional encoding stripes, which sacrifices the efficiency of stripe utilization, and the decoding is complex and has weak universality. SUMMARY
[0007] In view of the shortcomings of the prior art, the purpose of the present application is to provide a superimposed encoding phase unwrapping method based on phase quantization to solve the problems in the background art.
[0008] The purpose of the present application can be achieved by the following technical solutions:
[0009] A superimposed encoding phase unwrapping method based on phase quantization, comprising the following steps:
[0010] According to the hardware parameters of the three-dimensional measurement system built, the pixel width W, the pixel height H and the stripe period T of the projected image are confirmed, and then according to the pixel width W and the stripe period T, the pixel width W1 of each period in the image is confirmed, W1=W / T, and N-step phase shift stripes are generated;
[0011] According to the distribution rule of the step code value and the pixel width W1, the superimposed coding stripe with auxiliary phase unfolding is designed, each period of the superimposed coding stripe is uniformly valued, and a black and white stripe image is generated;
[0012] According to the designed projection stripe, the projection stripe is projected to the measured object through a projector, and the modulated projection stripe is collected by a camera and transmitted to a computer;
[0013] The wrapped phase is extracted from the modulated phase shift stripe image by using the phase shift algorithm, and the order stripe k1 is extracted from the modulated coding stripe image by using the superposition principle;
[0014] According to the obtained wrapped phase, the value of the wrapped phase is valued as a binary stripe, and another group of stripe orders k2 is determined by superimposing the binary stripe through the order k1.
[0015] The wrapped phase is unwrapped by using the complementary order stripes, and the absolute phase of the measured object is obtained by using the phase unfolding algorithm.
[0016] Preferably, the calculation process of the order stripe k1 is as follows:
[0017]
[0018] Preferably, the binary calculation process of the wrapped phase is as follows:
[0019]
[0020] Preferably, the superimposed calculation process of generating the order k2 is as follows:
[0021] k2=k1+I.
[0022] Preferably, the phase unfolding calculation process is as follows:
[0023]
[0024] The present application has the following beneficial effects:
[0025] 1. The method of the present application replaces the additional stripes of multiple projections by binaryzing the wrapped phase, and combines the designed superimposed coding stripe, obtains two groups of order stripes which are offset by half a period from each other by stripe superimposition calculation, and unwraps the phase by using complementary orders.
[0026] 2. In the process of obtaining the order, the coding stripe can obtain the step order by digital superimposition operation, the algorithm is simple, and does not need cumbersome calculations such as radix operation, mapping array or phase calculation, and the binary method of the wrapped phase is used to assist in correcting the jump error, improve the utilization rate of the wrapped phase, and reduce the projection of additional coding. BRIEF DESCRIPTION OF DRAWINGS
[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, for those skilled in the field, other drawings can also be obtained based on these drawings without any creative effort.
[0028] Figure 1 is a flow chart of the method of the present application;
[0029] Figure 2 is a schematic diagram of the superimposed coding principle in the present application;
[0030] Figure 3 is a schematic diagram of the superimposed coding stripe in the present application;
[0031] Figure 4 is a phase error correction image profile in the present application;
[0032] Figure 5 is a schematic diagram of the physical measurement stripe expansion in the present application;
[0033] Figure 6 is a schematic diagram of the point cloud reconstruction of the object measurement in the present application. DETAILED DESCRIPTION
[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without any creative effort fall within the scope of the present application.
[0035] Please refer to Figures 1 to 6 The superimposed coding phase expansion method based on phase quantization shown in the figure comprises the following steps:
[0036] Step 1: According to the hardware parameters of the three-dimensional measurement system built, confirm the pixel width W, pixel height H and stripe period T of the projection image. According to the pixel width W and stripe period T, confirm the pixel width W1 of each period in the image W1=W / T, and generate N-step phase shift stripes.
[0037] Step 2: According to the distribution rule of the step code value and the pixel width W1, design the superimposed coding stripes for computer aided phase expansion, uniformly assign “0” or “1” to each period, and generate black and white stripe images.
[0038] The superimposed coding stripe acquisition process is as follows:
[0039] The method assigns black and white stripes to the coded images by partitioning, for example, 2n stripe levels, n coded images are needed to embed level information coding processing, each coded image is divided into 2n period intervals. Taking the first coded image as an example, the second and n+2 period intervals are assigned to white stripes with value "1", and the white stripe set of the first coded image is collectively shifted right by 1 period interval to form the second coded image, and the remaining coded images are sequentially followed, until the n-1th coded image. The nth coded image needs to assign the first n periods to black stripes with value "0", and the last n periods to white stripes with value "1".
[0040] Step three, according to the projection stripes designed in step one and step two, the projection stripes are projected to the measured object through the projector, and the modulated projection stripes are collected by the camera and transmitted to the computer;
[0041] Step four, the wrapped phase is extracted from the modulated phase shift stripe image by using the phase shift algorithm, and the level stripe k1 is extracted from the modulated coded stripe image by using the superposition principle;
[0042] The operation of superimposed coded stripe generating level k1 is:
[0043]
[0044] Wherein, k1 is the level stripe to be obtained, i is the number of superimposed stripes designed for projection, I i is the i-th coded superimposed stripe, I n is the n-th superimposed stripe;
[0045] Step five, according to the wrapped phase obtained in step four, the value is taken as a binary stripe, and another group of stripe levels k2 is determined by superimposing the binary stripe with level k1;
[0046] The binary process of the wrapped phase is:
[0047]
[0048] Wherein, I is the binary stripe to be obtained, is the wrapped phase obtained.
[0049] The superposition process of generating level k2 is:
[0050] k2=k1+I
[0051] Wherein, k2 is the level stripe to be obtained, k1 is the first group of level stripes obtained, and I is the binary stripe after the value of the wrapped phase is taken.
[0052] Step six, phase unwrapping operation is performed on the wrapped phase through two sets of complementary order fringes, and the absolute phase of the measured object is obtained through the phase unwrapping algorithm.
[0053] The phase unwrapping process is as follows:
[0054]
[0055] Wherein, φ is the absolute phase to be obtained, is the wrapped phase, k1 is the first set of order fringes, and k2 is the second set of order fringes.
[0056] Based on the above steps, that is, the proposed superimposed coding phase unwrapping method based on phase quantization, the wrapped phase is binarized instead of the additional fringes of multiple projections, and the superimposed coding fringes designed in the application are combined to obtain two sets of order fringes offset by half a period from each other through fringe superposition calculation, and phase unwrapping is performed through complementary order. In the process of obtaining the order, the coding fringes can obtain the step order through digital superposition operation, the algorithm is simple, and there is no need for cumbersome calculations such as radix operation, mapping array or phase calculation, and the method of binarizing the wrapped phase is used to assist in correcting the jump error, improve the utilization rate of the wrapped phase, and reduce the additional projection of the coding.
[0057] In the description of the present specification, the description of the terms "one embodiment", "example", "specific example" and the like means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are contained in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.
[0058] The basic principles, main features and advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only illustrative of the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the claimed present application.
Claims
1. A superposition coding phase unwrapping method based on phase valueization, characterized in that: The following steps are involved: Step 1: Based on the hardware parameters of the built 3D measurement system, determine the pixel width W, pixel height H, and fringe period T of the projected image. Then, based on the pixel width W and fringe period T, determine the pixel width W1 of each period in the image, where W1 = W / T, and generate N-step phase-shifted fringes. Step 2: Based on the distribution of the staircase code value and the pixel width W1 in step 1, design the superimposed coding stripes for auxiliary phase unwrapping, assign a uniform value to each cycle, and generate a black and white stripe image; Step 3: Project the projection fringes designed in Steps 1 and 2 onto the object to be measured, and collect the modulated projection fringes and transmit them to the computer; Step 4: extract the wrapped phase from the modulated phase-shifted fringe image using a phase shift algorithm, and extract the order fringe k1 from the modulated coded fringe image using the superposition principle; Step 5: Convert the wrapped phase obtained in step 4 into binary fringes, and determine another set of fringes with order k2 by superimposing the binary fringes with order k1. Step 6: Perform phase unwrapping operation on the wrapped phase by complementing the two groups of order fringes, and obtain the absolute phase of the object under test by using the phase unwrapping algorithm; The acquisition process of the superimposed coding stripes in step 2 is as follows: By dividing the coded image into intervals and assigning black and white stripes, the n coded images are embedded with level information encoding. Each coded image is divided into 2n periodic intervals, and white stripes with a value of "1" are assigned to the second periodic interval and the n+2th periodic interval. Then, the white stripes of the first coded image are collectively shifted to the right by one periodic interval to form the second coded image. The remaining coded images are similarly shifted until the n-1th coded image. For the nth coded image, the first n periods need to be assigned black stripes with a value of "0", and the last n periods need to be assigned white stripes with a value of "1".
2. The superposition coding phase unwrapping method based on phase valueization according to claim 1, characterized in that: The calculation process of the secondary stripe k1 in step 4 is as follows: Among them, k1 is the level fringe to be obtained, i is the number of superimposed fringe amplitudes of the designed projection, and I i is the superimposed stripe of the i-th code, I n The nth superimposed stripe.
3. The superposition coding phase unwrapping method based on phase valueization according to claim 2, characterized in that: The binarization calculation process of the wrapped phase in step 5 is as follows: Among them, I is the binary stripe to be obtained, is the obtained package phase.
4. The superposition coding phase unwrapping method based on phase valueization according to claim 3, characterized in that: The superposition calculation process for generating the level k2 in step 5 is as follows: Among them, k2 is the order fringe to be obtained, k1 is the first group of order fringe obtained, and I is the binary fringe after the wrapped phase value is converted.
5. The superposition coding phase unwrapping method based on phase valueization according to claim 4, characterized in that: The phase unwrapping calculation process in step 6 is as follows: in, is the absolute phase to be obtained, is the wrapped phase, k1 is the first group of order fringes, and k2 is the second group of order fringes.
6. A superposition coding phase unwrapping system based on phase valueization, the system being used to implement the superposition coding phase unwrapping method based on phase valueization according to claim 1, characterized in that: The system comprises: The projection image module is used to confirm the pixel width of each period in the image and generate N-step phase-shifted fringes; The stripe image module is used to uniformly assign values to each period of the superimposed coded stripes to generate a black and white stripe image; An acquisition module is used to collect the modulated projection fringes and transmit them to a computer; An extraction module is used to extract level stripes k1 from the modulated coded stripe image by using the superposition principle, and determine another group of stripe levels k2 by superimposing the binary stripes on the level k1; The phase unwrapping module is used to obtain the absolute phase of the object under test through the phase unwrapping algorithm.