A laser three-dimensional correlation imaging method and device based on the principle of Sachs imaging

Abstract

The present invention relates to a laser three-dimensional correlation imaging method and device based on the Schaffer imaging principle. An amplitude modulator performs amplitude modulation on a uniform light beam emitted by a laser light source with a preset code, and images the light on the object to be measured through a transmitting lens. The reflected signal of the object to be measured is imaged on a planar array detector through a light receiving lens in a manner that satisfies the Schaffer imaging principle, and the planar array detector records the target reflection information; the laser light source, the amplitude modulator, and the planar array detector are synchronously triggered and controlled by a synchronous signal generator to work simultaneously; the information recorded by each pixel of the planar array detector is subjected to a second-order correlation operation with the pre-set code to obtain a series of tomographic images, and the Schaffer imaging relationship and the tomographic image are combined to realize the three-dimensional image reconstruction of the object to be measured. The present invention uses a modulated light source to detect objects, adopts correlation operations to obtain object graphics, and adopts Schaffer imaging to detect object information in parallel, which can greatly improve the imaging rate and realize three-dimensional real-time imaging.

Description

Technical Field

[0001] The invention relates to a laser three-dimensional correlation imaging method and an imaging device based on the Schaffer imaging principle, belonging to the technical field of optical imaging. Background Art

[0002] Two-dimensional imaging loses the depth information of objects and has gradually failed to meet people's needs. For example, in the fields of satellite measurement, autonomous driving, remote sensing detection, medical imaging, etc., laser three-dimensional imaging with richer data information occupies an important position. The three-dimensional laser radar based on the time of flight method emits a high-intensity pulsed laser to detect the object and then returns, collects the echo signal with an avalanche diode (ADP), and determines the distance of the object based on the time difference between the transmitted and received signals. If you want to improve the accuracy, you must use a high-frequency timing clock, which has great hardware requirements. There are two detection methods for this method: scanning imaging and staring imaging. Among them, the scanning method is difficult to achieve high frame rate real-time imaging, and there are requirements for the scanning device; the staring method is limited by the size of the ADP array, and it is difficult to improve the imaging field of view and resolution. Among the three-dimensional imaging methods other than the TOF method, the streak tube laser radar and the Shashi three-dimensional imaging method both require scanning devices, which cannot achieve high frame rate real-time imaging, and the former has a complex device and limited working band, and the latter's detection accuracy is affected by the beam broadening. The image information acquisition efficiency and imaging resolution of the above-mentioned three-dimensional imaging methods are limited by the Nyquist sampling theorem and the diffraction limit of the optical imaging system, respectively, and there are major technical bottlenecks.

[0003] The three-dimensional laser correlation imaging radar developed based on thermal light field correlation imaging (see reference: Gong W, Zhao C, Yu H, et al. Three-dimensional ghost imaging lidar via sparsity constraint [J]. Scientific reports, 2016, 6(1): 1-6.) is a staring imaging mode. It uses a single-pixel detector to receive the target echo signal by regulating the light field fluctuation and using a computational reconstruction method to obtain the image information of the target. At present, there are three-dimensional laser correlation imaging modes that use narrow pulse spatial modulation laser illumination and echo signal intensity detection mode, and long pulse spatiotemporal two-dimensional modulation laser illumination and echo signal heterodyne detection mode. It uses a single-pixel detector with time resolution to obtain three-dimensional image information of the target scene. Not only can the image information acquisition efficiency break through the limitation of Nyquist sampling theorem, but also can break through the limitation of the diffraction limit of the optical system on spatial resolution. However, reconstruction requires multiple samplings, which affects the imaging rate, and the imaging field of view is limited, so it is impossible to achieve large field of view, high frame rate, and high resolution three-dimensional imaging. Summary of the invention

[0004] In view of the shortcomings of the existing three-dimensional imaging technology, the present invention provides a laser three-dimensional correlation imaging method and an imaging device based on the Schaffer imaging principle, which can greatly improve the imaging rate and imaging field of view.

[0005] In order to solve the deficiencies of the prior art, the technical solution of the present invention is to provide a laser three-dimensional correlation imaging device based on the Schaff imaging principle, which includes a laser, an amplitude modulator, a transmitting lens, an object to be measured, a light receiving lens, a planar array detector and a computer;

[0006] The amplitude modulator modulates the amplitude of the uniform light beam emitted by the laser with a preset code, and the emitting lens images the modulated light field on the object to be measured, and the reflected light of the object is imaged on the array detector in the form of Sachs imaging after passing through the light receiving lens; the output ends of the amplitude modulator and the array detector are simultaneously connected to a computer that performs second-order correlation operations and Sachs distance calculations, and the laser light source, amplitude modulator and array detector are simultaneously triggered and controlled by a synchronization signal generator to work simultaneously. A second-order correlation operation is performed on the light intensity recorded by each pixel on the array detector and the preset code, and the spatial information of a series of tomographic surfaces is extracted. The distance is calculated in combination with Sachs imaging, and the three-dimensional spatial information of the object to be measured is extracted through traversal.

[0007] The present invention provides a laser three-dimensional correlation imaging device based on the Schaffer imaging principle, wherein the preset code of the amplitude modulator is K randomly generated 0 / 1 binary distribution non-overlapping speckle images, and the corresponding spatial positions of the K randomly generated speckle images are superimposed to form a uniform light distribution. The Schaffer imaging method refers to the intersection of the light receiving lens plane, the array detector plane and the main optical axis plane of the transmitting lens, and different pixels of the array detector detect objects at different distances in an angle-resolved manner.

[0008] The technical solution of the present invention also includes a laser three-dimensional correlation imaging method based on the Schaffer imaging principle, using the above-mentioned imaging device, including the following steps:

[0009] ①Encoding preset of amplitude modulator

[0010] The encoding method preset by the amplitude modulator is that the generated K random speckle images with 0 / 1 binary distribution have no overlap, and the corresponding spatial positions of the K random speckle images are superimposed to present a uniform light distribution;

[0011] ② Object information collection based on the principle of Schaffner imaging

[0012] The amplitude modulator with preset coding performs 0 / 1 amplitude modulation on the uniform light beam emitted by the laser to obtain a modulated light source, which is imaged to the object to be measured through the transmitting lens to generate a three-dimensional measurement space within the depth of field; the reflected signal of the object to be measured passes through the light receiving lens, is collected in parallel by the area array detector using the Schar imaging method, and is recorded by the calculator; the laser, amplitude modulator and area array detector are synchronously triggered and controlled by a synchronous signal generator to work simultaneously;

[0013] ③ Extraction of spatial and distance information of object tomography surface

[0014] (a) The light intensity signals collected and recorded by all pixels on the array detector are sequentially subjected to second-order correlation operations with a preset encoding method to obtain spatial information of a series of tomographic surfaces, where the resolution of the tomographic surface is the number of pixels of the amplitude modulator;

[0015] (b) according to the spatial position of the pixel on the area array detector, the Schaffer imaging relationship is used to calculate the Schaffer detection distance of the pixel, and the spatial information characteristics of the tomographic surface obtained by the second-order correlation operation based on the light intensity signal recorded by the pixel are combined to calculate the distance information of the corresponding tomographic surface;

[0016] ④ Traverse all the pixels on the array detector, match the spatial information and distance information of a series of tomographic surfaces one by one, and obtain a three-dimensional reconstructed image of the object to be measured.

[0017] In the technical solution of the present invention, the method for performing the second-order correlation operation on the computer is: using an amplitude modulator to generate a Bernoulli distribution The random speckle of different sizes is used as the measurement matrix. The image of the random speckle is reflected by the object to be measured. The area array detector of pixels is collected as a signal matrix. The light intensity collected by each pixel of the area array detector is subtracted from the product of the light intensity of N pixels in the measurement matrix, and an N-pixel picture is obtained, which is the spatial information of the corresponding tomographic surface. The spatial information of M tomographic surfaces with a pixel size of N is obtained by traversing the pixels of the area array detector.

[0018] In the technical solution of the present invention, the method for calculating the tomographic surface distance information using the tomographic surface spatial information and the pixel position is as follows: the longitudinal distance from the point on the tomographic surface to the center of the image is obtained according to the tomographic surface spatial information, the corresponding Schaber detection distance and sampling angle are calculated using the pixel position on the area array detector, the distance difference between the tomographic surface and the Schaber detection distance is obtained from the longitudinal distance and the sampling angle, and the distance information of the tomographic surface is thereby obtained.

[0019] The imaging device provided by the present invention changes the original uniform light field into a modulated light field in terms of system structure, uses a planar array detector without time resolution capability, and receives information of objects at different distances in parallel in an angle-resolved manner, thereby eliminating the need for a complex scanning structure. In terms of imaging method, the image resolution is determined by the transmitting end (the image resolution of the reconstructed object is determined by the amplitude modulator), and a planar array detector with a large number of pixels is used to expand the imaging field of view. Through the combination of correlation imaging and Schafer imaging, real-time imaging of three-dimensional objects is achieved with an extremely low sampling number, thereby greatly improving the imaging field of view and imaging rate.

[0020] Compared with the prior art, the present invention has the following technical effects:

[0021] 1. Compared with laser three-dimensional correlation imaging based on the time-of-flight method, the planar array detector described in the present invention does not require time resolution capability and adopts a parallel detection method, which can achieve real-time three-dimensional imaging with a large field of view under the condition of extremely low sample number.

[0022] 2. Compared with streak tube laser radar, the present invention does not require slits or mechanical scanning, and can obtain three-dimensional image information of the target under the condition of staring detection, and has a wide working band range and low cost.

[0023] 3. Compared with the existing Schaffner laser three-dimensional imaging method, the present invention does not have a mechanical scanning structure, and the number of laser irradiation pulses required for the same imaging field of view is less. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the structure of a laser three-dimensional correlation imaging device based on the Schaffer imaging principle provided by an embodiment of the present invention;

[0025] Figure 2 It is a principle diagram of calculating the tomographic distance information of an object by using Sachs imaging in a laser three-dimensional correlation imaging method based on the Sachs imaging principle provided by an embodiment of the present invention;

[0026] Figure 3 and Figure 4 They are respectively schematic diagrams of a laser three-dimensional correlation imaging method based on the Schaffer imaging principle and a schematic diagram of an object to be detected and three-dimensional information of an extracted object in a device thereof provided by an embodiment of the present invention;

[0027] In the figure: 1 is the laser light source; 2 is the amplitude modulator; 3 is the transmitting lens; 4 is the object to be measured; 5 is the receiving lens; 6 is the planar array detector with high resolution; 7 is the computer; 8 is the object plane; 9 is the tomographic surface; 10 is the spatial information of the tomographic surface; 11 is the tomographic surface with a distance of 35.2 meters; 12 is the tomographic surface with a distance of 35.1 meters. DETAILED DESCRIPTION

[0028] The technical solution of the present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0029] Example 1

[0030] See attached Figure 1 , is a schematic diagram of the structure of a laser three-dimensional correlation imaging device based on the Schaffner imaging principle provided in this embodiment. Figure 1 It can be seen that the imaging device includes a laser light source 1, an amplitude modulator 2, a transmitting lens 3, an object to be measured 4, a light receiving lens 5, a plane array detector 6 and a computer 7. The amplitude modulator 2 performs amplitude modulation on the uniform light beam emitted by the laser 1 with a pre-set code, and images it on the object to be measured through the transmitting lens 3, generating a series of tomographic surfaces within the depth of field, and its resolution is determined by the number of pixels of the amplitude modulator 2; the reflection signal of the object to be measured 4 is collected in parallel by the plane array detector 6 in the form of Schar imaging through the light receiving lens 4, and objects at different distances are detected in an angle-resolved manner, and different pixel positions correspond to tomographic surfaces at different distances, realizing three-dimensional real-time imaging at a low sampling number; the output ends of the amplitude modulator 2 and the plane array detector 6 are simultaneously connected to the computer 7 that performs correlation operations and Schar distance calculations, and the laser 1, the amplitude modulator 2 and the plane array detector 6 are simultaneously triggered and controlled by a synchronization signal generator to work simultaneously. The computer 7 performs a second-order correlation operation on the light intensity recorded by each pixel on the array detector 6 and the preset code, extracts the spatial information of a series of tomographic surfaces, combines the spatial information characteristics of the tomographic surfaces with the Schaffer imaging to calculate the distance, traverses all the pixels on the array detector 6, and matches the spatial information of a series of tomographic surfaces and the distances one by one, so as to obtain a three-dimensional spatial image of the object to be measured.

[0031] During the operation of the device, the laser light source 1, the amplitude modulator 2 and the array detector 6 are synchronously triggered and controlled by a synchronous signal generator (not shown in the figure) to work simultaneously: the specific steps are as follows:

[0032] (1) Laser 1 emits a uniform beam which is modulated by amplitude modulator 2 in a preset coding manner, generating a number of pixels that obeys the Bernoulli distribution: The random speckle of (the number of pixels of the amplitude modulator 2) is imaged to the object 4 to be measured through the transmitting lens 3, forming a three-dimensional measurement space within the depth of field. The number of pixels of a series of tomographic surfaces in the three-dimensional measurement space is equal to the number of pixels of the amplitude modulator 2, that is, the imaging resolution is determined by the transmitting end and is not affected by the receiving end;

[0033] (2) The plane where the light-collecting lens 5 is located, the plane where the area array detector 6 is located, and the plane of the principal optical axis of the transmitting lens 3 intersect each other, wherein the inclination angle between the plane of the principal optical axis of the transmitting lens 3 and the plane where the light-collecting lens 5 is located is , the inclination angle between the plane where the light collecting lens 5 is located and the plane where the array detector 6 is located is β, forming a Schaber detection. Different from the ideal Schaber imaging condition where the array detector 6 can only detect a two-dimensional plane and needs a scanning device to assist in completing three-dimensional reconstruction, due to the beam broadening, the array detector 6 directly detects a three-dimensional space at this time, and achieves the same imaging field of view as the Schaber three-dimensional imaging method with a smaller number of laser irradiation pulses;

[0034] (3) The area array detector 6 receives and records the light intensity distribution information of the reflected light from the object to be measured 4 along with the position of the area array detector. According to the Sandberg imaging, the pixels at different positions on the area array detector 6 detect the tomographic planes at different distances from the object. The more pixels the area array detector 6 has, the larger the measurement field of view and the more tomographic planes there are. That is, the reflected signal of the object to be measured 4 is collected in parallel by the area array detector 6 without time resolution capability through the light collecting lens 5 in the Sandberg imaging mode. Without the need for any additional device, the distance information of the object is obtained in the angle resolution mode, thereby realizing large field of view three-dimensional staring imaging with low cost and extremely wide working band.

[0035] (4) Computer 7 controls the array detector 6 The light intensity collected by each pixel is sequentially compared with the preset encoding method (the amplitude modulator is Point-to-point correlation operation is performed on M pixels to obtain M pictures with N pixels, which are the spatial information of M tomographic planes in the three-dimensional measurement space. Compared with the situation that the three-dimensional correlation imaging technology can only extract the spatial information of one tomographic plane in a single measurement, this method can reconstruct the object to be measured with a very low sampling number.

[0036] (5) The longitudinal distance from the point on the tomographic surface to the midpoint is calculated based on the spatial information characteristics of the tomographic surface. Combined with the corresponding pixel position, the pixel detection distance and sampling angle are calculated by Schaffer imaging to obtain the distance of the tomographic surface. All pixels on the array detector 6 are traversed to extract the three-dimensional information of the target to be measured.

[0037] In the laser three-dimensional correlation imaging method based on the Sachs imaging principle provided in the embodiment of the present invention, the method for extracting the spatial information of the object through the second-order correlation operation is:

[0038] The amplitude modulator 2 performs 0 / 1 amplitude modulation on the uniform light beam emitted by the laser in a pre-set coding mode, and the image is formed at the object to be measured 4 through the transmitting lens 3. The reflected signal of the object is collected by the array detector 6 in the form of Schaffer imaging through the receiving lens 5. In this process, the object to be measured 4 is set to X (N*1, N is the number of pixels of the object, which is determined by the number of pixels of the amplitude modulator 2), the coding mode pre-set by the amplitude modulator 2 is the measurement matrix A (K*N), and the light intensity distribution received by the pixels of the array detector 6 is the signal matrix Y (K*1). According to the correlation imaging theory, we have

[0039] (1)

[0040] in, is the image of the object to be measured; is the similarity ratio between the speckle field imaged by the transmitting lens 3 to the object 4 to be measured and the measurement matrix in the traditional imaging process; is the similarity ratio between the speckle field collected by the area array detector 6 and the speckle field reflected by the object during the sand imaging process; K is the number of sampling times; I is the unit matrix of K*1; represents the average value; Represents the random fluctuations of the speckle field of the measurement matrix.

[0041] Therefore, using Figure 1 The schematic diagram of the structure of the Schaffer laser three-dimensional correlation imaging device shown in the figure only needs to substitute the light intensity distribution Y recorded by the array detector 6 and the preset encoding method A into the formula (1), and the spatial information of the target to be measured can be extracted under certain imaging conditions. The amplitude modulator 2 and the number of pixels are The planar array detector 6 obtains M images with N pixels through the above calculation, which are the spatial information corresponding to the M tomographic planes.

[0042] See attached Figure 2 , is a schematic diagram of a laser three-dimensional correlation imaging method based on the principle of Scharnauer imaging provided in this embodiment, which uses Scharnauer imaging to calculate the distance information of the tomographic surface of an object. Figure 2 It can be seen that when the object plane 8 and the plane of the light-collecting lens 5 are not parallel, the device can also clearly image the object on the object plane 8 by tilting the plane of the area array detector 6 at a certain angle so that the object plane 8, the plane of the light-collecting lens 5 and the area array detector 6 intersect with each other. Figure 2 The z direction is the laser emission direction. According to the different positions of the detection pixels on the area array detector 6, the corresponding distances in the z direction are:

[0043] (2)

[0044] in, is the distance from the midpoint of the light-collecting lens 5 to the z-axis, is the angle between the plane of the light-collecting lens 5 and the z-axis, is the angle between the plane of the array detector 6 and the plane of the light-collecting lens 5, is the distance from the midpoint of the light-collecting lens to the array detector 6

[0045]

[0046] Wherein, f is the focal length of the light receiving lens 5;

[0047] is the pixel distance on the area array detector 6;

[0048]

[0049] in, is the total number of pixels of the array detector 6, is the pixel index of the area array detector 6, is the pixel width.

[0050] The spatial information 10 (black dots in the figure) of the tomographic surface 9 extracted by the association operation is used to calculate the longitudinal distance from the spatial information 10 (black dots) of the tomographic surface to the center of the image. ,according to , the distance on the z-axis is obtained by formula (2): and pixel sampling angle , then the distance of the tomographic surface 9 on the z axis is for:

[0051] (3)

[0052] See attached Figure 3 and 4 , Figure 3 The object to be measured in the laser three-dimensional correlation imaging method and the device thereof based on the Schaff imaging principle provided in this embodiment is composed of a capital letter G on the tomographic plane 11 at a distance of 35.2 meters and a capital letter I on the tomographic plane 12 at a distance of 35.1 meters; Figure 4 The figure is a schematic diagram of extracting the three-dimensional information of an object in the present invention, and the Z direction represents the distance information. The spatial information of a series of tomographic surfaces is extracted according to formula (1), and the distance information of the corresponding tomographic surfaces is calculated according to formula (3). The pixels of the array detector are traversed, and the spatial information and distance information of a series of tomographic surfaces are matched one by one. The three-dimensional reconstruction result is obtained at an extremely low sampling rate (4096 pixels are sampled 50 times, about 1%). Figure 4 shown.

Claims

1. A laser three-dimensional correlation imaging device based on the Schaffhausen imaging principle, characterized in that: It comprises a laser (1), an amplitude modulator (2), a transmitting lens (3), an object to be measured (4), a light receiving lens (5), a planar array detector (6) and a computer (7); the amplitude modulator (2) with a preset code performs 0 / 1 amplitude modulation on the uniform light beam emitted by the laser (1); the transmitting lens (3) images the modulated light field on the object to be measured (4); the reflected light of the object passes through the light receiving lens (5) and is imaged on the planar array detector (6) in a manner satisfying the Schaffer imaging principle; the laser (1), the amplitude modulator (2) and the planar array detector (6) are synchronously triggered and controlled by a synchronization signal generator to work simultaneously; the output ends of the amplitude modulator (2) and the planar array detector (6) are connected to a computer (7) that performs a second-order correlation operation; the computer (7) performs a correlation operation on the light intensity recorded by each pixel input by the planar array detector (6) and the preset code input by the planar array detector (6) to obtain a series of spatial information of tomographic planes, and then calculates the distance information corresponding to each tomographic plane according to the Schaffer imaging principle to obtain a three-dimensional image of the object to be measured; The Schaffer imaging principle is that the plane of the light-collecting lens (5), the plane of the array detector (6) and the optical axis plane of the transmitting lens (3) intersect with each other, and each pixel of the array detector (6) detects objects at different distances in an angularly resolved manner.

2. The laser three-dimensional correlation imaging device based on the Schaffer imaging principle according to claim 1 is characterized in that: The preset code of the amplitude modulator is K randomly generated 0 / 1 binary distribution non-overlapping speckle images, and the corresponding spatial positions of the K randomly generated speckle images are superimposed to present a uniform light distribution.

3. A laser three-dimensional correlation imaging method based on the Schaffer imaging principle, characterized in that: The imaging device according to claim 1 comprises the following steps: ①Encoding preset of amplitude modulator The amplitude modulator (2) is preset to encode in a manner such that the generated K random speckle images with a 0 / 1 binary distribution have no overlap, and the corresponding spatial positions of the K random speckle images are superimposed to present a uniform light distribution; ②Information collection of the object to be tested based on the principle of Sachs imaging The amplitude modulator (2) with preset coding performs 0 / 1 amplitude modulation on the uniform light beam emitted by the laser (1) to obtain a modulated light source, which is imaged to the object to be measured (4) through the emitting lens (3), thereby generating a three-dimensional measurement space within the depth of field range; the reflected signal of the object to be measured (4) is collected in parallel by the area array detector (6) through the light receiving lens (5) by the method of Schaff imaging, and is input into the computer (7) to record the light intensity signal; the laser (1), the amplitude modulator (2) and the area array detector (6) are synchronously triggered and controlled by a synchronous signal generator to work simultaneously; ③ Extraction of spatial and distance information of the tomographic surface of the object to be measured (a) the computer performs a second-order correlation operation on the light intensity signals collected and recorded by each pixel input by the area array detector (6) and the preset codes input by the amplitude modulator (2) in sequence, thereby obtaining spatial information of a series of tomographic surfaces, wherein the resolution of the tomographic surface is the number of pixels of the amplitude modulator (2); (b) according to the spatial position of the pixel on the area array detector (6), the detection distance of the pixel on the optical axis is calculated through the Schaffer imaging relationship, and the spatial information characteristics of the tomographic surface obtained by the second-order correlation operation based on the light intensity signal recorded by the pixel are combined to calculate the distance information of the corresponding tomographic surface; ④ Traverse all the pixels on the array detector (6), match the spatial information and distance information of a series of tomographic surfaces one by one, and obtain a three-dimensional reconstructed image of the object to be measured.

4. The laser three-dimensional correlation imaging method based on the Schaffer imaging principle according to claim 3 is characterized in that: The area array detector (6) collects the reflection signals of the object to be measured in parallel in the manner of Schafer imaging, and extracts the three-dimensional information of the object to be measured through second-order correlation operation and Schafer imaging distance calculation.

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