A method for achieving structured light three-dimensional measurement using a scattering lens

Abstract

This invention relates to the field of structured light 3D measurement technology. Currently, small field-of-view 3D measurement using structured light mainly relies on stereomicroscopes or long working distance lenses, which are large, complex, expensive, and have fixed working distances. This invention provides a method for achieving structured light 3D measurement using a scattering lens. The front end of a lensless camera uses a scattering lens as the lens to acquire structural fringes. Through scattering lens calibration, point spread function (PSF) correlation stitching, and structured light 3D measurement system calibration, structured light 3D measurement is achieved. The device of this invention is simple and small in size, and can be applied to the field of small field-of-view structured light 3D measurement. By utilizing the correlation between the PSFs of the scattering lenses, the field of view stitching is achieved, thereby overcoming the limitation of the memory effect range of the scattering lens and realizing large field-of-view imaging with the scattering lens.

Description

Technical Field

[0001] This invention relates to the field of structured light three-dimensional measurement technology, and more specifically, to a method for realizing structured light three-dimensional measurement using a scattering lens. Background Technology

[0002] Structured light 3D measurement based on the principle of optical triangulation is a method for 3D contour reconstruction using phase information. This method boasts advantages such as high robustness, high precision, non-destructive nature, and high efficiency, and is widely used in various fields including medical testing, cultural relic preservation, and reverse engineering. With the continuous development of technology, components are becoming increasingly miniaturized and precise, making rapid and efficient 3D inspection of these devices particularly important. Due to the small size of the measured object, compared to traditional structured light 3D measurement systems, small field-of-view structured light 3D measurement systems require additional optical design to reduce the field of view. This is typically achieved using stereomicroscopes or telecentric lenses to reduce the projection and imaging field of view. Among these methods, stereomicroscopes have high magnification, resulting in a relatively small field of view and depth of field, and system calibration is difficult and expensive. Telecentric lenses, due to their working principle, have a fixed working distance and imaging field of view; the larger the field of view, the larger the volume and the higher the price. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for achieving three-dimensional structured light measurement using a scattering lens. This invention applies a scattering lens to three-dimensional structured light measurement, enabling the measurement of microscopic objects using structured light.

[0004] To achieve the above objectives, the present invention provides the following technical solution:

[0005] A method for achieving structured light 3D measurement using a scattering lens is disclosed. The front end of a lensless camera utilizes a scattering lens as the lens to acquire structured fringes. Through scattering lens calibration, point spread function (PSF) correlation stitching, and calibration of the structured light 3D measurement system, structured light 3D measurement is achieved. The method includes the following steps:

[0006] Step 1. Measure the memory effect range of the scattering lens: First, project a point light source at the center of the projection surface. After passing through the scattering lens, the point spread function is collected by a lensless camera. Then, project a crosshair to obtain the speckle of the crosshair passing through the scattering lens. Deconvolve the obtained speckle with the point spread function to recover the crosshair. The range where the crosshair intensity is higher than 0.5 is the memory effect range of the scattering lens.

[0007] Step 2. Scattering lens calibration: Divide the projection area of ​​the projector according to the memory effect range of the scattering lens. Project point light sources into the center of each segmented area using the projector. The camera collects the speckle patterns corresponding to these point light sources after passing through the scattering lens, and obtains the point spread function of the scattering lens for different positions on the projection surface.

[0008] Step 3. Determine the stitching position: Based on the correlation between the point spread functions at different positions of the scattering lens, determine the relative positions of each point light source in the projection on the camera target surface;

[0009] Step 4. Use a computer to generate a fringe pattern, project it onto a reference plane using a projector, and complete the fringe speckle acquisition and fringe stitching.

[0010] Step 5. Structured light 3D measurement: Perform 2D imaging according to steps 3 and 4, and then recover the 3D information of the object by performing system calibration, fringe acquisition, phase unwrapping, and 3D point cloud restoration in structured light 3D measurement.

[0011] Furthermore, in step 4, the method for generating the stripe pattern can be chosen from the following options:

[0012] Option A: Divide the complete fringe into segments and project them sequentially to achieve three-dimensional measurement of structured light using a scattering lens;

[0013] Option B: Achieve three-dimensional measurement of structured light using a scattering lens by projecting complete fringes in a single pass.

[0014] Furthermore, the specific steps of Plan A are as follows:

[0015] Step A1. For each frame of segmented stripes projected by the projector, the lensless camera captures the stripe speckle once to obtain the stripe speckle in different segmented regions.

[0016] Step A2. According to the segmentation of the projection surface, deconvolve the PSF of the point light source in each segmented region with the fringe speckle at its corresponding position to recover the fringe of different segmented regions. Move and stitch these fringe to the relative positions obtained in step 3 to obtain all the fringe information of the projection surface.

[0017] Furthermore, the specific steps of Plan B are as follows:

[0018] Step B1. The projector projects a complete stripe once, and the lensless camera captures a complete stripe speckle image;

[0019] Step B2. According to the projection surface segmentation, deconvolve the point spread function (PSF) of the point light source in each segmented region with the same speckle map of the complete fringe of the projection surface to recover the fringe information within the memory effect range of each PSF. Move and stitch these fringe information according to the relative positions obtained in step 3 to obtain the complete fringe information of the projection surface.

[0020] Furthermore, the scattering lens can be frosted glass, a scattering film, or an artificially made scattering medium.

[0021] Furthermore, the angle between the principal optical axes of the lensless camera and the digital light projector is less than 30°.

[0022] In summary, the invention has the following beneficial effects:

[0023] (1) This invention utilizes the optical memory effect of a scattering lens and uses an anticonvolution algorithm for imaging. The scattering lens is based on speckle anticonvolution of the optical memory effect for imaging. It has the advantages of simple device, small size, high cost performance and adjustable working distance, and can be applied to the field of small field of view structured light three-dimensional measurement.

[0024] (2) This invention utilizes the correlation between the point spread functions of scattering lenses to achieve the effect of field stitching, thereby solving the limitation of the memory effect range of scattering lenses and realizing large field imaging of scattering lenses.

[0025] (3) The scattering lens used in this invention is frosted glass, scattering film and various artificial scattering media; the scattering lens has high cost performance, adjustable working distance, small size and is easy to integrate.

[0026] (4) The system calibration, phase unwrapping and three-dimensional point cloud recovery methods in traditional structured light three-dimensional measurement methods can all be applied to the present invention to realize the three-dimensional measurement of objects. Attached Figure Description

[0027] Figure 1 A schematic diagram of a device for achieving three-dimensional structured light microscopy measurement using a scattering lens.

[0028] In the diagram, 1. Reference plane; 2. Scattering lens; 3. Aperture stop; 4. Lensless camera; 5. Telecentric lens; 6. Projector. Detailed Implementation

[0029] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0030] like Figure 1 As shown, this invention discloses a method for achieving three-dimensional structured light measurement using a scattering lens. The front end of the lensless camera 4 uses a scattering lens 2 as the lens to acquire structural fringes. Through scattering lens calibration, point spread function (PSF) correlation stitching, and calibration of the structured light three-dimensional measurement system, structured light three-dimensional measurement is achieved. Specifically, the method includes the following steps:

[0031] Step 1. Measure the memory effect range of the scattering lens: First, project a point light source at the center of the projection surface. After passing through the scattering lens 2, the point spread function is collected by the lensless camera 4. Then, project a crosshair to obtain the speckle of the crosshair passing through the scattering lens. Deconvolve the obtained speckle with the point spread function to recover the crosshair. The range where the crosshair intensity is higher than 0.5 is the memory effect range of the scattering lens 2.

[0032] Step 2. Scattering lens calibration: Divide the projection area of ​​the projector 6 according to the memory effect range of the scattering lens 2. Use the projector 6 to project point light sources at the center of each divided area. The camera collects the speckle patterns corresponding to these point light sources after passing through the scattering lens 2, and obtains the point spread function of the scattering lens for different positions on the projection surface.

[0033] Step 3. Determine the stitching position: Based on the correlation between the point spread functions at different positions of the scattering lens 2, determine the relative positions of each point light source in the projection on the camera target surface; the point spread functions at different positions in Step 2 are correlated, and the positional relationship between the point light sources is obtained based on the correlation between the point spread functions.

[0034] Step 4. Due to the limited range of the memory effect of the scattering lens, a fringe pattern of the same size as the projected area cannot be obtained without fringe stitching. However, by acquiring and stitching the fringe pattern, a fringe pattern of the same size as the projected area can be obtained. After determining the position of the point light source in Step 3, the fringe pattern is generated by computer and projected onto the reference plane 1 through the projector 6, completing the fringe speckle acquisition and fringe stitching. The method for generating the fringe pattern can be chosen from the following options:

[0035] Option A: Divide the complete fringe into segments and project them sequentially to achieve three-dimensional measurement of the scattering lens using structured light; the specific steps are as follows:

[0036] Step A1. For each frame of segmented stripes projected by the projector 6, the lensless camera 4 captures the stripe speckle once to obtain the stripe speckle in different segmented regions.

[0037] Step A2. According to the segmentation of the projection surface, deconvolve the PSF of the point light source in each segmented region with the fringe speckle at its corresponding position to recover the fringe of different segmented regions. Move and stitch these fringe to the relative positions obtained in step 3 to obtain all the fringe information of the projection surface.

[0038] Option B: Achieving 3D measurement of structured light using a scattering lens by projecting complete fringes in a single pass. The specific steps are as follows:

[0039] Step B1. Projector 6 projects a complete stripe once, and lensless camera 4 captures a complete stripe speckle image;

[0040] Step B2. According to the projection surface segmentation, deconvolve the point spread function (PSF) of the point light source in each segmented region with the same speckle map of the complete fringe of the projection surface to recover the fringe information within the memory effect range of each PSF. Move and stitch these fringe information according to the relative positions obtained in step 3 to obtain the complete fringe information of the projection surface.

[0041] Step 5. Structured light 3D measurement: Perform 2D imaging according to steps 3 and 4, and then recover the 3D information of the object by performing system calibration, fringe acquisition, phase unwrapping, and 3D point cloud restoration in structured light 3D measurement.

[0042] The scattering lens 2 is made of frosted glass, a scattering film, and an artificially made scattering medium.

[0043] The angle between the principal optical axes of the lensless camera 4 and the digital light projector 6 is less than 30 degrees.

[0044] This invention belongs to the interdisciplinary field of structured light 3D measurement, scattering optics, and computational imaging. The proposed method differs from traditional structured light 3D measurement in the process of camera acquisition of fringes. There are two fringe projection schemes during the acquisition process, with the following different implementation schemes:

[0045] Option A: Divide the complete fringe into segments and project them sequentially to achieve three-dimensional measurement of structured light using a scattering lens.

[0046] The projection surface of projector 6 is divided into n parts. A point light source of appropriate pixel size is generated at the center of each segmented region. These segmented regions are projected sequentially onto reference plane 1. The point spread function (PSF) generated by the point light source passing through the scattering lens 2 is collected by lensless camera 2. i (i = 1, 2... n); Calculate the PSF based on the correlation between the two-point diffusion functions of the scattering lens. i (i=1,2...n) and PSF n / 2 The relative positions between these two points can be used to obtain the relative positions of the corresponding point light sources, thus obtaining the positional distribution of the point light sources on the camera target surface; the computer generates sinusoidal fringes according to formula (1):

[0047] I p (x p ,y p ) = a p (x p ,y p )+b p (x p ,y p cos(2πf) p x p +2πm / N) (1)

[0048] Among them, (x p ,y p ) represents the projector pixel coordinates, in pixel coordinates (x p ,y p At ) location, I p (x p ,y p ) represents the grayscale value of the stripes, a p (x p ,y p ) represents background intensity, b p (x p ,y p () represents the modulation intensity, fp represents the fringe frequency, N represents the average number of times the projected fringe moves within one period, m = 1, 2...N, N≥3;

[0049] The fringes are divided into n parts, then projected onto a reference plane 1 by a projector 6, and the speckle pattern S of the fringes on the reference plane is captured by a lensless camera 4. i (i = 1, 2...n); collect the striped speckle patterns S i (i = 1, 2...n) are respectively associated with PSF i (i = 1, 2... n) The speckle pattern and the point spread function are deconvolved to obtain the reference plane fringe pattern I. i (i = 1, 2...n);

[0050] The obtained I i (i = 1, 2... n) By splicing the displacements according to the relative position distribution, a complete fringe pattern I on the reference plane can be obtained. C Based on the process of scattering lens calibration and stripe acquisition by lensless camera 4, combined with system calibration, phase extraction, phase unwrapping, and phase height conversion in traditional structured light 3D measurement, the 3D appearance measurement of objects can be realized.

[0051] Option B: Achieving 3D Measurement of Scattering Lens Structured Light Using Complete Fringes in a Single Projection

[0052] The projection surface of the projector is divided into n parts. A point light source of appropriate pixel size is generated at the center of each segmented region. These segmented regions are projected sequentially onto a reference plane. The point spread function (PSF) generated by the point light source passing through a scattering lens is collected using a lensless camera 4. i (i = 1, 2... n); Calculate the PSF based on the correlation between the point spread functions of the scattering lenses. i (i=1,2...n) and PSF n / 2 The relative positions between them are used to obtain the position distribution of the point light source on the camera target surface; the computer generates sinusoidal fringes I according to formula (1). p (x p ,y p), stripe I p (x p ,y p The speckle pattern S on the reference plane is directly projected onto the reference plane using a projector, and then captured by a camera. The captured complete speckle pattern S is compared with the PSF. i Perform deconvolution operation on (i = 1, 2, ..., n) to obtain the reference plane fringe pattern I. i (i = 1, 2...n).

[0053] I i (i = 1, 2... n) By performing displacement stitching according to the position distribution of the point light source, a complete fringe pattern I on the reference plane can be obtained. C Based on the process of scattering lens calibration and camera stripe acquisition, combined with system calibration, phase extraction, phase unwrapping, and phase height conversion in traditional structured light 3D measurement, it is possible to achieve 3D appearance measurement of objects.

[0054] Taking traditional structured light 3D measurement as an example, the system calibration method, phase unwrapping algorithm, and error compensation algorithm in traditional structured light 3D measurement can all be used in the method proposed in this invention.

[0055] The scattering lens can be metric frosted glass, scattering film, or various artificial scattering lenses, all of which can be used in this invention to realize three-dimensional measurement using structured light from scattering lenses.

[0056] Due to the optical memory effect of scattering lenses, the area of ​​a single image formed by a scattering lens is relatively small. This invention proposes to utilize the correlation between point spread functions to obtain the relative positions between each point spread function. The small-area fringes recovered using these point spread functions are then moved and stitched together according to these positions to obtain complete fringes on the projection surface.

[0057] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for achieving three-dimensional measurement of structured light using a scattering lens, characterized in that: The front end of the lensless camera (4) uses a scattering lens (2) as a lens to collect structural fringes. Through scattering lens calibration, point spread function (PSF) correlation stitching and structured light three-dimensional measurement system calibration, structured light three-dimensional measurement is realized, which specifically includes the following steps: Step 1. Measure the memory effect range of the scattering lens: First, project a point light source at the center of the projection surface. After passing through the scattering lens (2), the point spread function is collected by the lensless camera (4). Then, project the cross line to obtain the speckle of the cross line passing through the scattering lens. Deconvolve the obtained speckle with the point spread function to recover the cross line. The range where the cross line intensity is higher than 0.5 is the memory effect range of the scattering lens (2). Step 2. Scattering lens calibration: Divide the projection area of ​​the projector (6) according to the memory effect range of the scattering lens (2), and use the projector (6) to project point light sources at the center of each segmented area. The camera collects the speckle corresponding to these point light sources after passing through the scattering lens (2) to obtain the point spread function of the scattering lens for different positions on the projection surface. Step 3. Determine the stitching position: Based on the correlation between the point spread functions at different positions of the scattering lens (2), determine the relative positions of each point light source of the projection on the camera target surface; Step 4. Use a computer to generate a fringe pattern and project it onto a reference plane (1) using a projector (6), and complete the fringe speckle acquisition and fringe stitching; Step 5. Structured light 3D measurement: Perform 2D imaging according to steps 3 and 4, and then recover the 3D information of the object by performing system calibration, fringe acquisition, phase unwrapping, and 3D point cloud restoration in structured light 3D measurement.

2. The method for achieving structured light three-dimensional measurement using a scattering lens according to claim 1, characterized in that: In step 4, the method for generating the stripe pattern can be chosen from the following options: Option A: Divide the complete fringe into segments and project them sequentially to achieve three-dimensional measurement of structured light using a scattering lens; Option B: Achieve three-dimensional measurement of structured light using a scattering lens by projecting complete fringes in a single pass.

3. The method for achieving structured light three-dimensional measurement using a scattering lens according to claim 2, characterized in that: The specific steps of Scheme A are as follows: Step A1. The projector (6) projects a frame of segmented stripes for each frame, and the lensless camera (4) collects stripe speckle once to obtain stripe speckle in different segmented regions. Step A2. According to the segmentation of the projection surface, deconvolve the PSF of the point light source in each segmented region with the fringe speckle at its corresponding position to recover the fringe of different segmented regions. Move and stitch these fringe to the relative positions obtained in Step 3 to obtain all the fringe information of the projection surface.

4. The method for achieving structured light three-dimensional measurement using a scattering lens according to claim 2, characterized in that: The specific steps of scheme B are as follows: Step B1. The projector (6) projects a complete stripe once, and the lensless camera (4) captures a complete stripe speckle image; Step B2. According to the projection surface segmentation, deconvolve the point spread function (PSF) of the point light source in each segmented region with the same speckle map of the complete fringe of the projection surface to recover the fringe information within the memory effect range of each PSF. Move and stitch these fringe information according to the relative positions obtained in step 3 to obtain the complete fringe information of the projection surface.

5. A method for achieving structured light three-dimensional measurement using a scattering lens according to any one of claims 1 to 4, characterized in that: The scattering lens (2) is made of frosted glass, a scattering film, and an artificially made scattering medium.

6. The method for achieving structured light three-dimensional measurement using a scattering lens according to claim 1, characterized in that: The angle between the main optical axes of the lensless camera (4) and the digital light projector (6) is less than 30°.

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