Low-artifact laser reflection tomography image reconstruction method and system

Abstract

The invention provides a low-artifact laser reflection tomography image reconstruction method and system. The invention relates to the field of computational imaging. According to the system, a time division multiplexing structure is adopted to respectively collect laser reference waveforms of each angle of a target and echo signal waveforms of each angle of each target, and discrete digital storage is carried out; the real-time correlation waveform of each angle echo signal is obtained by introducing correlation calculation of a laser reference waveform and a target echo signal waveform, filtering back projection image reconstruction is carried out based on the real-time correlation waveform of each angle echo signal, and a low-artifact and high-resolution tomographic image of a target is obtained. According to the invention, through the waveform realization method of time division multiplexing acquisition and correlation operation, the noise of the laser echo waveform is effectively suppressed, the target characteristic waveform is reserved with high precision, and the problem of suppression of the strong noise of the low signal-to-noise ratio laser echo signal waveform is solved.

Description

Technical Field

[0001] The present invention belongs to the field of computational imaging technology, and in particular relates to a low-artifact laser reflection tomography image reconstruction method and system. Background Art

[0002] In the field of computational imaging, reflection tomography lidar technology is a laser-based active detection method. Reflection tomography lidar technology obtains multi-angle range echo information of the target and uses the corresponding reconstruction algorithm to achieve a two-dimensional contour image of the target. Generally, the image resolution of reflection tomography lidar technology is mainly determined by the pulse width of the outgoing laser light source, the system detection bandwidth and the signal-to-noise ratio of the echo waveform. It is an effective technical means to achieve long-distance super-resolution imaging.

[0003] At present, the traditional laser reflection tomography image reconstruction method is to use the filtered back projection method to filter and reconstruct the measured waveforms at each angle. Due to the influence of the detector itself and external environmental factors (factors such as the detector's working principle, response bandwidth, sensitivity, and many photoelectric noises), the measured waveform data of the echo signals at each angle have waveform distortion and large base noise, resulting in serious artifacts in the image reconstructed by the traditional filtered back projection algorithm, which restricts the image clarity and affects the resolution; under weak signal-to-noise ratio conditions, the original waveform information is easily submerged by noise, causing the reconstructed image contour to be submerged in the artifact noise; when using a pulse light signal to trigger the data acquisition module and receive the echo signal, each photodetector module is used to detect the trigger reference signal and the laser echo waveform signal. The two photodetector modules have differences in response sensitivity, bandwidth, and noise, which leads to distortion of the measured laser trigger waveform and signal echo waveform, affecting the image reconstruction accuracy and resolution, and the system is complex and costly. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a low-artifact laser reflection tomography image reconstruction method and system.

[0005] The first aspect of the present invention discloses a low-artifact laser reflection tomography image reconstruction system, the system comprising a laser, a beam splitter, a transmitting optical component, a receiving optical component, a beam combiner, a photodetector, a collector and a control processor; wherein,

[0006] The control processor is electrically connected to the laser and is used to control the laser to emit pulsed laser;

[0007] After the pulse laser is split by the beam splitter, a reference beam and a signal beam are formed;

[0008] The reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to output the time domain waveform of the reference light, thereby triggering the collector to collect the digital waveform to obtain the laser reference waveform;

[0009] The photodetector has the capability of responding to time domain signals with large bandwidth and high speed;

[0010] The signal light is emitted through the transmitting optical component and is reflected by the target to form a target echo signal;

[0011] After the target echo signal is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal, which is then digitally collected by the collector triggered by the reference signal to obtain the target echo signal waveform;

[0012] The control processor is also electrically connected to the collector to read the laser reference waveform and target echo signal waveform of the same outgoing pulse laser, and then calculate the relevant waveform of the target echo signal in real time, and use the relevant waveform of the target echo signal to calculate the target reconstructed image.

[0013] Optionally, the laser is a narrow pulse laser.

[0014] Optionally, the combiner is a 1×2 multimode fiber combiner, which includes a fiber reference end, a fiber signal end and a fiber output end, and the length difference between the fiber signal end and the fiber reference end is greater than or equal to a laser pulse width flight time distance.

[0015] Optionally, a launch optical assembly is used to compress the laser beam divergence angle.

[0016] The second aspect of the present invention discloses a low-artifact laser reflection tomography image reconstruction method, which is implemented by a low-artifact laser reflection tomography image reconstruction system as described in any one of the above items;

[0017] The method comprises:

[0018] S1, the control processor controls the laser to emit pulsed laser; wherein the pulsed laser is split by the beam splitter to form a reference beam and a signal beam;

[0019] S2, the reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to the output of the time domain waveform of the reference light, which in turn triggers the collector to collect digital waveforms to obtain the laser reference waveform of the current target angle;

[0020] S3, the signal light is emitted through the transmitting optical component and is reflected by the target at the current target angle to form a target echo signal at the current target angle;

[0021] S4, after the target echo signal of the current target angle is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal of the current target angle, and then the collector triggered by the reference signal performs digital waveform acquisition to obtain the target echo signal waveform of the current target angle;

[0022] S5, controlling the processor to read the laser reference waveform of the current target angle and the target echo signal waveform of the current target angle, and then calculating the real-time correlation waveform of the echo signal of the current target angle, and filtering the real-time correlation waveform of the echo signal of the current target angle;

[0023] S6, repeat S1-S5 n times, and sequentially and equally space the real-time correlation waveform filtering results of the echo signals at each angle of the target rotation angle of Δφ, and then calculate the target reconstructed image; wherein Δφ·n=360°.

[0024] Optionally, in step S5, the real-time correlation waveform p(r, φ) of the target echo signal is obtained by calculation according to the following formula:

[0025]

[0026] Where r is the distance from the target to the rotation center at the current target angle φ; p ref is the laser reference waveform of the current target angle; p sig It is the target echo signal waveform of the current target angle.

[0027] Optionally, in step S5, the actual waveform of the real-time correlation waveform of the current target angle echo signal after filtering for:

[0028]

[0029] Among them, φ i is the target angle corresponding to the current real-time correlation waveform, and are the forward and inverse Fourier transforms, and k is the filter function.

[0030] Optionally, in step S6, the target reconstructed image g(x,y) is:

[0031]

[0032] Among them, x and y are the two-dimensional coordinates of the target reconstructed image.

[0033] In summary, the solution proposed by the present invention has the following technical effects:

[0034] By introducing the real-time output laser waveform and performing aliasing correlation with the laser echo waveform, the noise of the laser echo waveform is effectively suppressed through correlation operation, the target characteristic waveform is retained with high precision, and the strong noise suppression problem of the low signal-to-noise ratio laser echo signal waveform is solved. At the same time, the problem of high image artifact interference in the traditional laser reflection tomography image reconstruction method is solved;

[0035] By introducing a time-division multiplexing optical path in the low-artifact laser reflection tomography image reconstruction system, a single photodetector is used to time-divisionally detect the outgoing laser pulse waveform and the laser pulse echo waveform, thereby solving the problem of differences in output signal waveforms caused by differences in bandwidth and sensitivity of multiple detectors. A more accurate correlation waveform can be obtained, and the imaging accuracy of the system can be improved. At the same time, the system can be simplified, the system integration and stability can be improved, and the system cost can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] Figure 1 is a structural diagram of a low-artifact laser reflection tomography image reconstruction system according to an embodiment of the present invention;

[0038] Figure 2 is a flow chart of a low-artifact laser reflection tomography image reconstruction method according to an embodiment of the present invention;

[0039] Figure 3 Reconstruct the image by traditional filtered back-projection for cross-shaped targets;

[0040] Figure 4 This is a reconstructed image obtained by a low-artifact laser reflection tomography image reconstruction method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0042] The first aspect of the present invention discloses a low-artifact laser reflection tomography image reconstruction system, which adopts a time-division multiplexing structure to respectively collect the echo signal waveforms of the target at each angle and the outgoing laser waveform at the current angle, and perform discrete digital storage; by introducing the correlation calculation of the measured outgoing laser pulse waveform and the laser echo signal, the accurate correlation waveform of the laser echo signal is obtained, and the filtered back-projection image is reconstructed based on the correlation waveform of the laser echo signal to obtain a low-artifact, high-resolution tomography image of the target.

[0043] Specifically, the system includes a laser, a beam splitter, a transmitting optical component, a receiving optical component (receiving telescope), a beam combiner, a photodetector, a collector (such as a high-speed acquisition card) and a control processor (such as an industrial computer); wherein,

[0044] The control processor is electrically connected to the laser and is used to control the laser to emit pulsed laser;

[0045] After the pulse laser is split by the beam splitter, a reference beam and a signal beam are formed;

[0046] The reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to output the time domain waveform of the reference light, thereby triggering the collector to collect the digital waveform to obtain the laser reference waveform;

[0047] The photodetector has a large bandwidth and high-speed response to time domain signals, and the bandwidth is at least sufficient to respond to the laser pulse width waveform;

[0048] The signal light is emitted through the transmitting optical component and is reflected by the target to form a target echo signal;

[0049] After the target echo signal is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal, which is then digitally collected by the collector triggered by the reference signal to obtain the target echo signal waveform;

[0050] The control processor is also electrically connected to the collector to read the laser reference waveform and target echo signal waveform of the same outgoing pulse laser, and then calculate the relevant waveform of the target echo signal in real time, and use the relevant waveform of the target echo signal to calculate the target reconstructed image.

[0051] Optionally, see Figure 1 , the laser is a narrow pulse laser. The beam combiner is a 1×2 multimode fiber beam combiner, which includes a fiber reference end, a fiber signal end, and a fiber output end, and the length difference between the fiber signal end and the fiber reference end is greater than or equal to a laser pulse width flight time distance. The emitting optical component is a laser beam expander, which is used to compress the laser beam divergence angle.

[0052] The working process of the system is as follows: the narrow pulse laser emits high-energy narrow pulse laser; after passing through the beam splitter, it enters the laser beam expander to further compress the laser beam divergence angle and radiate the target in front; the beam splitter allows most of the energy to be transmitted into the laser beam expander, and a very small part of the energy is reflected into one end of the 1×2 multimode beam-combining optical fiber (optical fiber reference end), which is responded by the high-speed detector to output an electrical signal, which is used to trigger the high-speed acquisition card and collect the output pulse waveform as the laser reference waveform; the receiving telescope receives the scattered laser signal of the target in front and couples it into the other end of the 1×2 multimode beam-combining optical fiber (optical fiber signal end); the echo signal at the optical fiber signal end is responded by the same high-speed detector, and the echo waveform is collected by the high-speed acquisition card as the laser signal waveform; the length of the optical fiber signal end of the 1×2 multimode optical fiber combiner is greater than that of the optical fiber reference end, and the length difference is not less than the flight time distance of a laser pulse width; the laser reference waveform and signal waveform of the same output pulse laser are digitally stored by the industrial control computer, and the industrial control computer calculates the relevant waveform of the laser echo signal in real time while coordinating and controlling the narrow pulse laser and the high-speed acquisition card, so as to realize high-precision laser reflection tomography image reconstruction.

[0053] In this embodiment, by introducing a time-division multiplexing optical path in the low-artifact laser reflection tomography image reconstruction system, a single photodetector is used to time-divisionally detect the outgoing laser pulse waveform and the laser pulse echo waveform, thereby solving the problem of differences in output signal waveforms caused by differences in bandwidth and sensitivity of multiple detectors. A more accurate correlation waveform can be obtained, and the imaging accuracy of the system can be improved. At the same time, the system can be simplified, the system integration and stability can be improved, and the system cost can be reduced.

[0054] The second aspect of the present invention discloses a low-artifact laser reflection tomography image reconstruction method, which is implemented by a low-artifact laser reflection tomography image reconstruction system as described in any one of the above items;

[0055] See also Figure 2 , the method comprising:

[0056] S1, the control processor controls the laser to emit pulsed laser; wherein the pulsed laser is split by the beam splitter to form a reference beam and a signal beam;

[0057] Optionally, the laser emits a narrow laser pulse, which is divided into two paths by a beam splitter. One path has strong energy and is transmitted into a laser beam expander to irradiate a target in front. The other path is relatively weak and is coupled into one end (fiber reference end) of a 1×2 multimode fiber combiner. The high-speed photodetector responds to the output of the time domain waveform of the current emitted pulse and triggers a high-speed acquisition card to perform digital waveform acquisition.

[0058] S2, the reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to the output of the time domain waveform of the reference light, which in turn triggers the collector to collect digital waveforms to obtain the laser reference waveform of the current target angle;

[0059] S3, the signal light is emitted through the transmitting optical component and is reflected by the target at the current target angle to form a target echo signal at the current target angle;

[0060] S4, after the target echo signal of the current target angle is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal of the current target angle, and then the collector triggered by the reference signal performs digital waveform acquisition to obtain the target echo signal waveform of the current target angle;

[0061] Optionally, the fiber length at the other end of the 1×2 multimode fiber combiner (fiber signal end) is greater than the fiber reference end length, and is no less than the transmission distance of a laser pulse width in the fiber; the receiving telescope receives the target current angle echo signal, and couples it into the fiber signal end of the 1×2 multimode fiber combiner, and is then responded to by the same high-speed photoelectric detector and outputs the scattered laser time domain waveform of the target current angle, which enters the high-speed acquisition card for digital acquisition;

[0062] The same high-speed photodetector responds to the outgoing laser pulse waveform p in different time periods based on the optical path time division multiplexing method. re f and target scattered echo signal waveform p sig , and the same acquisition channel of the high-speed acquisition card performs p re f and p sig Digital discrete sampling and storage of electrical signals. Based on the time-division multiplexing optical path, the same detector for photoelectric detection can eliminate the waveform differences caused by the different bandwidths and sensitivities of different high-speed photoelectric detectors, making it easier to calculate accurate related waveforms in step three; at the same time, a single-channel acquisition card can be used to detect two electrical signals (p re f and p sig ) to improve system integration and reduce costs.

[0063] Optionally, in step S5, the real-time correlation waveform p(r, φ) of the target echo signal is obtained by calculation according to the following formula:

[0064]

[0065] Where r is the distance from the target to the rotation center at the current target angle φ; p ref is the laser reference waveform of the current target angle; p sig It is the target echo signal waveform of the current target angle.

[0066] Optionally, in step S5, the actual waveform of the real-time correlation waveform of the current target angle echo signal after filtering for:

[0067]

[0068] Among them, φ i is the target angle corresponding to the current real-time correlation waveform, and are forward and inverse Fourier transforms, k is the filter function, and the Ramp-Lak filter is generally selected.

[0069] The traditional filtering back projection algorithm is based on the echo signal waveform p sig Filtering is performed. In the present invention, the echo signal related waveform p(r,φ) calculated in step S5 is subjected to filtering processing in the classical filtering back projection algorithm to obtain the actual waveform of the echo signal related waveform at the current angle after filtering. The noise of the laser echo waveform is effectively suppressed, the target characteristic waveform is retained with high precision, and the problem of suppressing strong noise of the low signal-to-noise ratio laser echo signal waveform is solved.

[0070] S5, controlling the processor to read the laser reference waveform of the current target angle and the target echo signal waveform of the current target angle, and then calculating the real-time correlation waveform of the echo signal of the current target angle, and filtering the real-time correlation waveform of the echo signal of the current target angle;

[0071] S6, repeat S1-S5 n times, sequentially obtain the real-time correlation waveform filtering results of the echo signals of each angle with an equally spaced target rotation angle of Δφ, and then calculate the target reconstructed image; wherein Δφ·n=360°.

[0072] Optionally, in step S6, the target reconstructed image g(x,y) is:

[0073]

[0074] Among them, x and y are the two-dimensional coordinates of the target reconstructed image.

[0075] In summary, the solution proposed by the present invention has the following technical effects:

[0076] The laser reflection tomography image is reconstructed by using the correlation waveform data of the echo signal. Since this technical means introduces the correlation operation of the measured outgoing laser pulse waveform and the echo waveform of the pulse, the signal correlation waveform carrying the target feature information is obtained. The image reconstruction is realized based on the filtered back projection method of the correlation waveform. It is a new and important optimized image reconstruction algorithm in the field of computed tomography.

[0077] By introducing the real-time outgoing laser waveform and performing alias correlation with the laser echo waveform, the noise of the laser echo waveform is effectively suppressed through correlation operation, the target characteristic waveform is retained with high precision, and the problem of suppressing strong noise of the laser echo signal waveform with low signal-to-noise ratio is solved;

[0078] This method uses the filtered back-projection method of the laser echo signal correlation waveform to achieve the direct reconstruction output problem of low-artifact images, improve the image resolution and contour clarity, and further improve the display of image features, especially under low signal-to-noise ratio echo conditions. The imaging results are shown below. Figure 3 and Figure 4 , Figure 3 For a cross-shaped target, the traditional filtered back-projection image is reconstructed. Figure 4 The image was reconstructed for this application. After comparison, this application effectively reduced the background artifact noise.

[0079] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. Although the present invention has been described in detail with reference to the above embodiments, it should be understood by those skilled in the art that the technical solutions described in the above embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-artifact laser reflection tomography image reconstruction system, characterized in that: The system includes a laser, a beam splitter, a transmitting optical component, a receiving optical component, a beam combiner, a photoelectric detector, a collector and a control processor; wherein, The control processor is electrically connected to the laser and is used to control the laser to emit pulsed laser; After the pulse laser is split by the beam splitter, a reference beam and a signal beam are formed; The reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to the output of the time domain waveform of the reference light, thereby triggering the collector to collect the digital waveform to obtain the laser reference waveform; wherein, The bandwidth of the photodetector is at least sufficient to respond to the laser pulse width waveform; The signal light is emitted through the transmitting optical component and is reflected by the target to form a target echo signal; After the target echo signal is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal, which is then digitally collected by the collector triggered by the reference light to obtain the target echo signal waveform; The control processor is also electrically connected to the collector to read the laser reference waveform and target echo signal waveform of the same outgoing pulse laser, and then calculate the relevant waveform of the target echo signal in real time, and use the relevant waveform of the target echo signal to calculate the target reconstructed image.

2. The low-artifact laser reflection tomography image reconstruction system according to claim 1, characterized in that: The laser is a narrow pulse laser.

3. The low-artifact laser reflection tomography image reconstruction system according to claim 1, characterized in that: The combiner is a 1×2 multimode fiber combiner, which includes a fiber reference end, a fiber signal end and a fiber output end, and the length difference between the fiber signal end and the fiber reference end is greater than or equal to a laser pulse width flight time distance.

4. The low-artifact laser reflection tomography image reconstruction system according to claim 1, characterized in that: The launch optics are used to compress the laser beam divergence angle.

5. A low-artifact laser reflection tomography image reconstruction method, characterized in that: The method is implemented by a low-artifact laser reflection tomography image reconstruction system according to any one of claims 1 to 4; The method comprises: S1, the control processor controls the laser to emit pulsed laser; wherein the pulsed laser is split by the beam splitter to form a reference beam and a signal beam; S2, the reference light is transmitted to the photodetector through the beam combiner, and the photodetector responds to the output of the time domain waveform of the reference light, which in turn triggers the collector to collect digital waveforms to obtain the laser reference waveform of the current target angle; S3, the signal light is emitted through the transmitting optical component and is reflected by the target at the current target angle to form a target echo signal at the current target angle; S4, after the target echo signal of the current target angle is received by the receiving optical component, it is transmitted to the photodetector through the beam combiner, and the same photodetector responds to output the time domain waveform of the target echo signal of the current target angle, and then the collector triggered by the reference light performs digital waveform acquisition to obtain the target echo signal waveform of the current target angle; S5, controlling the processor to read the laser reference waveform of the current target angle and the target echo signal waveform of the current target angle, and then calculating the real-time correlation waveform of the echo signal of the current target angle, and filtering the real-time correlation waveform of the echo signal of the current target angle; S6, repeat S1-S5 n times, sequentially obtain the real-time correlation waveform filtering results of the echo signals of each angle with an equally spaced target rotation angle of Δφ, and then calculate the target reconstructed image; wherein Δφ·n=360°.

6. A low-artifact laser reflection tomography image reconstruction method according to claim 5, characterized in that: In step S5, the real-time correlation waveform p(r, φ) of the target echo signal is obtained by calculation according to the following formula: Where r is the distance from the target to the rotation center at the current target angle φ; p ref is the laser reference waveform of the current target angle; p sig It is the target echo signal waveform of the current target angle.

7. A low-artifact laser reflection tomography image reconstruction method according to claim 6, characterized in that: In step S5, the actual waveform of the real-time correlation waveform of the current target angle echo signal after filtering for: Among them, φ i is the target angle corresponding to the current real-time correlation waveform, and are forward and inverse Fourier transforms, k is the filter function, and Ramp-Lak filter is generally selected.

8. The low-artifact laser reflection tomography image reconstruction method according to claim 7, characterized in that: In step S6, the target reconstructed image g(x,y) is: Among them, x and y are the two-dimensional coordinates of the target reconstructed image.

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