A method for fast three-dimensional measurement using a scattering lens

Abstract

The present application relates to the field of structured light fast three-dimensional measurement and imaging technology, and the imaging method of optical lens is used to image the target through isotropic medium, but the optical lens is expensive and easy to be damaged in the measurement process, resulting in that the three-dimensional measurement system needs to be re-adjusted and built, the present application provides a method for realizing fast three-dimensional measurement by using scattering lens, the front end of lens-free camera uses scattering lens as lens to collect stripes, the scattering lens calibration and structured light three-dimensional measurement system calibration are used, the method of Fourier transform profilometry is used to realize the structured light fast three-dimensional measurement of moving objects through a frame of stripe speckle, the structured light fast three-dimensional measurement is realized by using single stripe speckle, the Fourier profilometry is applied to the structured light three-dimensional measurement based on scattering lens, and the fast three-dimensional measurement of small objects is realized.

Description

Technical Field

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

[0002] Structured light rapid 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. In real life, most objects are in motion, making rapid 3D measurement of moving objects particularly important. In traditional structured light rapid 3D measurement systems, the camera needs to acquire images through an optical lens. The imaging method using optical lenses follows the "what you see is what you get" principle, allowing imaging of the target through isotropic media. However, optical lenses are expensive and easily damaged during measurement, necessitating a complete reconfiguration of the 3D measurement system. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a method for rapid three-dimensional measurement using a scattering lens. This invention applies Fourier profilometry to three-dimensional measurement based on structured light using a scattering lens, thereby enabling rapid three-dimensional measurement of minute objects.

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

[0005] A method for rapid 3D measurement using a scattering lens is proposed. The lensless camera front end uses a scattering lens as the lens to acquire speckle patterns. After calibration of the scattering lens and a structured light 3D measurement system, the method utilizes Fourier transform profilometry to achieve rapid structured light 3D measurement of a moving object using a single frame of speckle patterns. The method specifically includes the following steps:

[0006] Step 1. Scattering lens calibration: First, project a point light source at the center of the projection surface, and then collect the point spread function (PSF) of the scattering lens using a lensless camera;

[0007] Step 2. Memory effect range measurement: Project the crosshairs using a projector to obtain the speckle pattern of the crosshairs after passing through the scattering lens. Deconvolve the speckle pattern of the crosshairs after passing through the scattering lens with the point spread function (PSF) from Step 1 to obtain the recovered crosshairs. The range where the crosshair intensity is higher than 0.5 is the memory effect range of the scattering lens. The memory effect range is also the maximum area of ​​the object that the scattering lens 3D measurement system can recover. Then, generate a sine fringe pattern of the same size as this area.

[0008] Step 3. Calibration of the scattering lens 3D measurement system: Within the depth of field of the projector, the reference plane is moved to different depth positions, and the sinusoidal fringes from Step 2 are projected onto the reference plane to collect the fringe speckle at different depths of the reference plane.

[0009] Step 4. Reference plane calibration fringe recovery: The fringe speckle acquired in step 3 is deconvolved with the point spread function (PSF) obtained in step 2 to obtain the fringe pattern required for the calibration of the scattering lens three-dimensional measurement system;

[0010] Step 5. Construct a phase height lookup table: Use Fourier profilometry to obtain the wrapping phase of the reference planes at different depths obtained in Step 4. Calculate the phase distribution results corresponding to the reference planes at different depths by de-phase calculation of the wrapping phases. Construct a phase height lookup table using the phase distribution results and the corresponding depth planes.

[0011] Step 6. Object deformation fringe acquisition: Restore the reference plane to the initial position when performing step 3, fix the object to be tested on the reference plane, project the fringe from step 2 onto the object to be tested, and acquire the speckle pattern of the deformation fringe of the object to be tested using a lensless camera.

[0012] Step 7. Object Deformation Stripe Recovery: Perform deconvolution operation on the fringe speckle of the object deformation stripe acquired in Step 6 and the point spread function (PSF) obtained in Step 1 to obtain the object deformation stripe map.

[0013] Step 8. 3D shape restoration of the object: The deformation fringe pattern of the object to be tested obtained in Step 7 is used to obtain the wrapping phase of the object using the Fourier profilometry method. The wrapping phase is then calculated by spatial phase decomposition to obtain the phase distribution result of the object. The phase distribution result is then substituted into the phase height lookup table to obtain the height distribution of the object, thus realizing rapid 3D measurement using structured light from a scattering lens.

[0014] Furthermore, the scattering lens is made of frosted glass, a scattering film, or an artificially made scattering medium.

[0015] Furthermore, in step 3, the reference plane is moved to different depth positions, at least four different depth positions.

[0016] In summary, the invention has the following beneficial effects:

[0017] (1) This invention utilizes the optical memory effect of a scattering lens and uses a deconvolution algorithm for imaging; it uses a thin scattering lens to replace the existing complex and expensive optical lens, which performs imaging based on speckle deconvolution of the optical memory effect to achieve fringe acquisition.

[0018] (2) The present invention utilizes the Fourier profilometry method to achieve rapid three-dimensional measurement of structured light using a single stripe speckle pattern.

[0019] (3) This invention uses a multi-depth plane calibration method to construct a phase height lookup table;

[0020] (4) The scattering lens used in this invention is metric frosted glass, scattering film and various artificial scattering media; the scattering lens used in this invention has high cost performance, adjustable working distance, small size and easy integration. It has the advantages of simple device, small size, high cost performance and adjustable working distance, and can be well applied in the field of rapid three-dimensional measurement of structured light. Attached Figure Description

[0021] Figure 1 A schematic diagram of a device for achieving rapid three-dimensional measurement using a scattering lens.

[0022] In the diagram, 1. Reference plane; 2. Scattering lens; 3. Aperture stop; 4. Lensless camera; 5. Telecentric lens; 6. Projector. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0024] like Figure 1 As shown, this invention discloses a method for rapid three-dimensional measurement using a scattering lens. A lensless camera 4 uses a scattering lens as its front end to acquire fringe patterns. After calibration using the scattering lens and a structured light three-dimensional measurement system, the method employs Fourier transform profilometry to achieve rapid structured light three-dimensional measurement of a moving object using a single frame of fringe speckle. The specific steps include:

[0025] Step 1. Scattering lens calibration: First, project a point light source at the center of the projection surface, and then collect the point spread function (PSF) of the scattering lens 2 by the lensless camera 4.

[0026] Step 2. Memory effect range measurement: Project the crosshairs using the projector 6 to obtain the speckle pattern of the crosshairs passing through the scattering lens 2. Deconvolve the speckle pattern with the point spread function (PSF) from Step 1 to obtain the recovered crosshairs. The range where the crosshair intensity is higher than 0.5 is the memory effect range of the scattering lens 2. The memory effect range is also the maximum area of ​​the object that the scattering lens 3D measurement system can recover. Then, generate a sine fringe pattern of the same size as this area.

[0027] Step 3. Calibration of the scattering lens 3D measurement system: Within the depth of field of the projector 6, the reference plane 1 is moved to different depths, and the sinusoidal fringes from step 2 are projected onto the reference plane 1. The fringe speckle at different depths of the reference plane 1 is collected, and the plane is moved to at least 4 different depths.

[0028] Step 4. Reference plane calibration fringe recovery: The fringe speckle acquired in step 3 is deconvolved with the point spread function (PSF) obtained in step 2 to obtain the fringe pattern required for the calibration of the scattering lens three-dimensional measurement system.

[0029] Step 5. Construct a phase height lookup table: Use Fourier profilometry to obtain the wrapping phase of the reference planes at different depths obtained in Step 4. Calculate the phase distribution results corresponding to the reference planes at different depths by dephase calculation of the wrapping phase. Construct a phase height lookup table using the phase distribution results and the corresponding depth planes.

[0030] Step 6. Object Deformation Fringe Acquisition: Return the reference plane 1 to its initial position as in Step 3, fix the object to be tested on the reference plane 1, project the fringes from Step 2 onto the object to be tested, and use the lensless camera 4 to acquire the speckle pattern of the object's deformation fringes.

[0031] Step 7. Object Deformation Stripe Recovery: Perform deconvolution operation on the speckle pattern of the deformed stripes of the object under test collected in Step 6 and the point spread function (PSF) obtained in Step 1 to obtain the deformed stripe pattern of the object under test.

[0032] Step 8. 3D shape restoration of the object: The deformation fringe pattern of the object to be tested obtained in Step 7 is used to obtain the wrapping phase of the object by Fourier profilometry. The wrapping phase is calculated by spatial phase decomposition to obtain the phase distribution result of the object. The phase distribution result is substituted into the phase height lookup table to obtain the height distribution of the object, thus realizing rapid 3D measurement using structured light from the scattering lens 2.

[0033] The scattering lens 2 is made of frosted glass, a scattering film, or an artificially made scattering medium.

[0034] The phase recovery algorithm used in this invention is Fourier contouring, and the phase unwrapping algorithm used is spatial phase unwrapping.

[0035] Rapid 3D Measurement of Scattering Lenses Based on Fourier Profilometry

[0036] A point light source of appropriate pixel size is generated at the center of the projection surface of the projector. This point light source is projected onto the reference plane, and the point spread function (PSF) generated by the point light source through the scattering lens is collected by the camera.

[0037] The computer generates stripes according to formula (1).

[0038] I p (x p ,y p ) = a p (x p ,y p )+b p (xp ,y p cos(2πf) p x p (1)

[0039] 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 f represents the modulation intensity. p Indicates the fringe frequency;

[0040] The above stripe I p (x p ,y p The image is projected onto a reference plane by a projector. The reference plane is moved within the projector's working distance, and the camera captures the position h of the reference plane. i Speckle pattern at (i = 1, 2, 3, 4) i (i = 1, 2, 3, 4); the collected speckle patterns S i (i = 1, 2, 3, 4) are deconvolved with the point spread function (PSF) to obtain the fringe pattern I at position hi (i = 1, 2, 3, 4) of the reference plane. i (i = 1, 2, 3, 4).

[0041] to I i For (i = 1, 2, 3, 4), a fast Fourier transform is performed to obtain the corresponding frequency domain spectral distribution, filtering out the fundamental frequency component. Then, an inverse Fourier transform is performed to obtain the truncated phase, and the phase P is obtained using a spatial phase expansion algorithm. i (i = 1, 2, 3, 4), phase P i (i = 1, 2, 3, 4) and h i (i = 1, 2, 3, 4) Perform a quadratic fitting to construct a phase height lookup table H p .

[0042] Move the reference plane to position h1, fix the object on the reference plane, and set stripe I. p (x p ,y p The image is projected onto the object using a projector, and the speckle pattern of the object's deformed stripes is captured by a camera. O ; Collected speckle pattern I'O Deconvolution operations were performed with the point spread function (PSF) to obtain the deformation fringe pattern I of the object. O Object deformation fringe pattern I O A fast Fourier transform is performed to obtain the corresponding frequency domain spectral distribution, and the fundamental frequency component is filtered out. Then, an inverse Fourier transform is performed to obtain the truncated phase, and an appropriate phase expansion algorithm is selected to obtain the object phase P. O The phase P of the object O Substitute into the phase height lookup table H p In the process, the height information H of the object is obtained. O This enables rapid three-dimensional measurement using structured light through scattering lenses.

[0043] The scattering lens 2 can be frosted glass, a scattering film, or an artificial scattering lens, all of which can be used in this invention to realize three-dimensional measurement using structured light from the scattering lens.

[0044] In the calibration process of the scattering lens 3D measurement system of this invention, the reference plane is moved at least four times. The more times it is moved, the more accurate the 3D information of the object recovered by the scattering lens 3D measurement system will be. In this invention, the lensless camera can be a CCD camera or an sCMOS camera.

[0045] 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 rapid three-dimensional measurement using a scattering lens, characterized in that: The lensless camera (4) uses a scattering lens as a lens to collect fringe patterns. After calibration by the scattering lens and the structured light 3D measurement system, the Fourier transform profilometry method is used to achieve rapid 3D measurement of moving objects using structured light through a single frame of fringe speckle. The specific steps include: Step 1. Scattering lens calibration: First, project a point light source at the center of the projection surface, and then collect the point spread function (PSF) of the scattering lens (2) by the lensless camera (4); Step 2. Memory effect range measurement: Project the crosshairs using a projector (6) to obtain the speckle of the crosshairs passing through the scattering lens (2). Deconvolve the speckle of the crosshairs passing through the scattering lens with the point spread function (PSF) in step 1 to obtain the recovered crosshairs. The range where the crosshair intensity is higher than 0.5 is the memory effect range of the scattering lens (2). The memory effect range is also the maximum area of ​​the object that the scattering lens three-dimensional measurement system can recover. Then generate a sine fringe pattern of the same size as this area. Step 3. Calibration of the three-dimensional measurement system of the scattering lens: Within the depth range of the projector (6), the reference plane (1) is moved to different depth positions, and the sinusoidal fringes in step 2 are projected onto the reference plane (1) to collect the fringe speckle at different depths of the reference plane (1); Step 4. Reference plane calibration fringe recovery: The fringe speckle acquired in step 3 is deconvolved with the point spread function (PSF) obtained in step 2 to obtain the fringe pattern required for the calibration of the scattering lens three-dimensional measurement system; Step 5. Construct a phase height lookup table: Use Fourier profilometry to obtain the wrapping phase of the reference planes at different depths obtained in Step 4. Calculate the phase distribution results corresponding to the reference planes at different depths by de-phase calculation of the wrapping phases. Construct a phase height lookup table using the phase distribution results and the corresponding depth planes. Step 6. Object deformation fringe acquisition: restore the reference plane (1) to the initial position when performing step 3, fix the object to be tested on the reference plane (1), project the fringe of step 2 onto the object to be tested, and the lensless camera (4) acquires the speckle of the deformation fringe of the object to be tested. Step 7. Object Deformation Stripe Recovery: Perform deconvolution operation on the fringe speckle of the object deformation stripe acquired in Step 6 and the point spread function (PSF) obtained in Step 1 to obtain the object deformation stripe map. Step 8. Object 3D shape restoration: The deformation fringe pattern of the object to be measured obtained in step 7 is used to obtain the wrapping phase of the object by Fourier profilometry. The wrapping phase is calculated by spatial phase decomposition to obtain the phase distribution result of the object. The phase distribution result is substituted into the phase height lookup table to obtain the height distribution of the object, thus realizing the rapid 3D measurement of structured light using the scattering lens (2).

2. The method for rapid three-dimensional measurement using a scattering lens according to claim 1, characterized in that: The scattering lens (2) is frosted glass, a scattering film, or an artificially made scattering medium.

3. The method for rapid three-dimensional measurement using a scattering lens according to claim 1, characterized in that: In step 3, the reference plane (1) is moved to different depth positions, at least 4 different depth positions.

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