Self-adaptive control method for gating SPAD in non-vision field imaging

Abstract

The invention provides a self-adaptive control method for a gated SPAD in non-vision-field imaging, and aims to solve the problems that when the gated SPAD is used for non-vision-field target imaging, selection of door width and position needs to be manually adjusted and depends on operation experience, and target signal loss, non-target signal interference and the like can be caused by fixed door width and position. A triangulation positioning principle and a small amount of feature point echo information are utilized to provide a self-adaptive control method for a gated SPAD. According to the invention, adaptive door width and position setting can be carried out on any single detection point; under the condition of multi-point scanning, the gate width and position setting of all scanning points can be realized only through a small amount of feature point echo information; dependence on prior information when a gating SPAD is set and non-target signal interference in the imaging process are effectively reduced.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric detection and imaging, and in particular relates to an adaptive control method for gated SPAD in non-line-of-sight imaging. Background Art

[0002] Traditional optical imaging technology uses detectors to acquire scenes of interest within the field of view and perform imaging. With the rapid development of laser imaging technology and the improvement of detector accuracy, non-line-of-sight (NLOS) imaging technology has achieved optical detection and visualization of hidden objects outside the line of sight, breaking the inherent physical constraint that light propagates in a straight line. It has broad application prospects in post-disaster rescue, autonomous driving, smart medical care and other fields.

[0003] However, due to multiple diffuse reflections of photons during non-line-of-sight detection and imaging, a large amount of signal loss occurs, and the target information is easily submerged in environmental noise. How to improve the signal-to-noise ratio of the target signal has become the main difficulty in the field of non-line-of-sight imaging. Gated single-photon avalanche diodes (SPADs) have played an important role in the development of the non-line-of-sight field due to their excellent detection capabilities in low-light environments.

[0004] However, when gated SPADs are actually used for target signal detection, the selection of gate position and width often requires manual adjustment and relies on operating experience. This method is not only inefficient, but also inaccurate. At the same time, in the process of imaging data acquisition, existing methods often require the preset of gating parameters based on prior knowledge such as intervening surface information and hidden target range, and the intervening surface information needs to be collected for calibration. However, due to the different optimal gate widths and positions of each point, the preset gating parameters will result in the inability to completely eliminate non-target signal interference or target signal loss, and the need to collect complete intervening surface information, which is time-consuming and has poor real-time performance. In general, the current methods using gated SPADs have not completely solved the problem of gating parameter setting, which has hindered the practical application of non-field of view target imaging. Summary of the invention

[0005] When using a gated SPAD to image a non-line-of-sight target, the selection of a gate width and a position needs to be manually adjusted and depends on operating experience, and fixing the gate width and position may lead to problems such as target signal loss and non-target signal interference. The present invention provides an adaptive control method for a gated SPAD in non-line-of-sight imaging. According to the characteristics of a large intensity of an intermediate surface echo signal during non-line-of-sight detection and imaging data acquisition, with the aid of the echo signal generated by the intermediate surface, the triangulation positioning principle and a small amount of feature point echo information, the gate width and position setting of any single detection point can be adaptively performed; in the case of multi-point scanning, the gate width and position setting of all scanning points can be achieved through only a small amount of feature point echo information; the reliance on prior information when setting the gated SPAD and the interference of non-target signals during the imaging process are effectively reduced.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for adaptively controlling a gated SPAD in non-line-of-sight imaging comprises the following steps:

[0008] Step 1: Use the free mode or fixed gate mode of the gated SPAD to collect echo signals of certain feature points;

[0009] Step 2: Calculate the gating parameters of each feature point using the echo signal;

[0010] Step 3, calculating the gating parameters of all scanning points by using the gating parameters of the above feature points;

[0011] Step 4: Adaptively set the parameters of the gated SPAD according to the gating parameters of all scanning points, and collect the echo signals of all scanning points;

[0012] Step 5: Use the echo signals of all scanning points to complete the imaging of non-line-of-sight targets.

[0013] Furthermore, the method for selecting some feature points in step 1 is: when the scanning area is a polygon, each vertex of the polygon is selected as a feature point.

[0014] Furthermore, the method for calculating the gating parameters of each feature point in step 2 is:

[0015] First, the starting point and end point of the intermediate surface echo signal are obtained, which are expressed as , , then the gated SPAD parameters are set to: The starting point is set to , the width is ,in, Indicates the total number of discrete points of the collected signal. represents the remainder function, Indicates the conversion factor between the acquisition signal time and discrete points.

[0016] Furthermore, the implementation method of step 3 is as follows:

[0017] Assume that the collection area is If the quadrilateral is a quadrilateral, the upper left, upper right, lower left and lower right vertices are selected as feature points, and the starting position of the intermediate surface echo between the feature points is obtained according to step 2. , , , , the end point of the intermediate surface echo , , , , the peak position of the intermediate surface echo , , , .

[0018] Furthermore, the scanning point in step 3 Intermediate surface echo starting point The calculation formula is:

[0019] ;

[0020] Among them, the intermediate parameters , intermediate parameters ; is the horizontal scanning point number, is the longitudinal scanning point number, .

[0021] Furthermore, the scanning point in step 3 Intermediate surface echo end position The calculation formula is:

[0022] ;

[0023] Furthermore, the scanning point in step 3 Intermediate surface echo peak position The calculation formula is:

[0024] ;

[0025] Furthermore, the step 3 scanning point Intermediate echo width The calculation formula is:

[0026] ;

[0027] Scan Point The gated SPAD parameters are set to: Starting point ,width .

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The present invention can perform adaptive door width and position setting for any single detection point;

[0030] (2) In the case of multi-point scanning, the present invention can realize the door width and position setting of all scanning points only through the echo information of a small number of feature points;

[0031] (3) The present invention effectively reduces the reliance on prior information when setting the gated SPAD and the interference of non-target signals during the imaging process. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a schematic diagram of non-line-of-sight target imaging using an adaptive control method;

[0033] Figure 2 1 is an original signal diagram of the intermediate surface echo of four characteristic points in the scanning area collected in the embodiment, wherein (a) is an intermediate surface echo signal diagram of the upper left vertex, (b) is an intermediate surface echo signal diagram of the upper right vertex, (c) is an intermediate surface echo signal diagram of the lower left vertex, and (d) is an intermediate surface echo signal diagram of the lower right vertex;

[0034] Figure 3 1 is a diagram showing the calculation result of the position and width of the intermediate surface echo signal of the first characteristic point collected in the embodiment, wherein (a) is a diagram showing the intermediate surface echo signal after cyclic displacement of the first characteristic point, (b) is a schematic diagram showing the calculation of the starting point of the intermediate surface echo using the left half signal, (c) is a schematic diagram showing the calculation of the end point of the intermediate surface echo using the right half signal, and (d) is a schematic diagram showing the calculation result of the position and width of the intermediate surface echo signal at this point;

[0035] Figure 4 1 is a graph of the calculation results of the position and width of the intermediate surface echo signal of the characteristic points of the scanning area collected in the embodiment, wherein (a) is the intermediate surface echo signal recognition result of the upper left vertex, (b) is the intermediate surface echo signal recognition result of the upper right vertex, (c) is the intermediate surface echo signal recognition result of the lower left vertex, and (d) is the intermediate surface echo signal recognition result of the lower right vertex;

[0036] Figure 5 1 is a comparison diagram of the calculation of the position and width of the echo signal actually collected at a certain point using the adaptive control method and the triangulation positioning method in the embodiment, wherein (a) is a comparison diagram of the calculation results, and (b) is a comparison diagram of the calculation results in detail;

[0037] Figure 6 The results of front view, top view and side view of non-viewing target imaging in the embodiment using the adaptive control method for data acquisition;

[0038] Figure 7 These are the front, top, and side views of non-field of view target imaging results using the traditional fixed gate width method for data acquisition in the embodiment. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0040] When using a gated SPAD for non-line-of-sight detection or imaging, manually adjusting the gate position and width can easily lead to target signal loss and human error in operation. When performing non-line-of-sight imaging, presetting the gate width and gate position based on prior information of the intermediate surface can easily lead to problems such as target signal loss and non-target signal interference, affecting imaging accuracy. Therefore, automatically adjusting the gating parameters of the gated SPAD is crucial for target recognition and target imaging. The present invention provides an adaptive control method for a gated SPAD in non-line-of-sight imaging, such as Figure 1 As shown, the method comprises the following steps:

[0041] Step 1: Use the free mode or fixed gate mode of the gated SPAD to collect echo signals of certain feature points;

[0042] Step 2: Calculate the gating parameters of each feature point using the echo signal;

[0043] Step 3, calculating the gating parameters of all scanning points by using the gating parameters of the above feature points;

[0044] Step 4: Adaptively set the parameters of the gated SPAD according to the gating parameters of all scanning points, and collect the echo signals of all scanning points;

[0045] Step 5: Use the echo signals of all scanning points to complete the imaging of non-line-of-sight targets.

[0046] Specifically, the method for selecting some feature points in step 1 is: when the scanning area is a polygon, each vertex of the polygon can be selected as a feature point.

[0047] Specifically, in step 2, the method for calculating the gating parameters of each feature point is:

[0048] First, the starting point and end point of the intermediate surface echo signal are obtained, which are expressed as , , then the gated SPAD parameters are set to: The starting point is set to , the width is .in, Indicates the total number of discrete points of the collected signal. represents the remainder function, Indicates the conversion factor between the acquisition signal time and discrete points.

[0049] Specifically, in step 3, it is assumed that the acquisition area is If the quadrilateral is a quadrilateral, the upper left, upper right, lower left and lower right vertices are selected as feature points, and the starting position of the intermediate surface echo between the feature points is obtained according to step 2. , , , , the end point of the intermediate surface echo , , , , the peak position of the intermediate surface echo , , , . Then scan point , is the horizontal scanning point number, is the longitudinal scanning point number, , Intermediate surface echo starting point No. Line start position The calculation formula is:

[0050] (1)

[0051] No. End of row position The calculation formula is:

[0052] (2)

[0053] Scan point Intermediate surface echo starting point The calculation formula is:

[0054] (3)

[0055] Let the intermediate parameters , intermediate parameters , then the scanning point Intermediate surface echo starting point It can be expressed as:

[0056] (4)

[0057] Similarly, scan point Intermediate surface echo end position The calculation formula is:

[0058] (5)

[0059] Scan Point Intermediate surface echo peak position The calculation formula is:

[0060] (6)

[0061] Scan Point Intermediate echo width The calculation formula is:

[0062] (7)

[0063] Scan point The gated SPAD parameters are set to: Starting point ,width .

[0064] Example:

[0065] Taking a non-viewing area imaging experiment as an example, this experimental embodiment includes the following steps:

[0066] Step 1: Use the free mode or fixed gate mode of the gated SPAD to collect echo signals of certain feature points.

[0067] In this embodiment, the scanning area is Therefore, the four vertices of the rectangle are selected as the acquisition feature points. First, the gated SPAD fixed gating mode is used to collect the echo signals of the four feature points, and the raw data is collected as follows: Figure 2 As shown, Figure 2 (a) is the echo signal diagram of the intermediate surface at the upper left vertex. Figure 2 (b) is the echo signal diagram of the intermediate surface at the upper right vertex. Figure 2 (c) is the echo signal diagram of the intermediate surface at the lower left vertex. Figure 2 (d) is the echo signal diagram of the intermediate surface at the lower right vertex.

[0068] Step 2: Calculate the gating parameters of each feature point using the above echo signal.

[0069] Taking the first characteristic point as an example, the total length of the signal is (nanoseconds), the signal is discretized into 5000 points, then , This embodiment uses a triangulation positioning method to obtain the starting point of the intermediate surface echo signal between the feature points, and the steps are:

[0070] First, find the maximum value of the echo signal in the collected signal, which is 3198 points. Then, shift the signal 698 points to the left to move it to 2500 points in the middle of the signal. Divide the signal into two halves from the maximum value. Use the following formula to calculate the starting and ending positions of the middle surface echo signal for the two halves.

[0071] (8)

[0072] In the formula, Indicates the starting point of the intermediate surface echo signal after cyclic displacement, is the maximum position of the intermediate surface echo signal after cyclic shift, It indicates the end point of the intermediate surface echo signal after the cyclic displacement. The independent variable representing the discrete points of the signal. , are the distance functions from the left half signal and the right half signal to the auxiliary straight line, respectively, and their calculation formula is:

[0073] (9)

[0074] In the formula, represents the left half signal, express The left half signal amplitude information at express The left half signal amplitude at . represents the right half signal, express The right half signal amplitude information at express The right half signal amplitude at . Calculate the starting and ending positions of the intermediate surface echo signal after cyclic displacement: , .

[0075] Then the signal is reversely shifted back to the original coordinate system. After the reverse cycle displacement, it is the starting point of the intermediate surface echo , After the reverse cycle displacement, the intermediate surface echo signal end position is reached. .

[0076] In order to suppress the interplane echo, the gating parameters are set to the reverse of the interplane echo, and the end point of the interplane echo is used as the starting point of the gating parameters, and the remainder of its width is used as the width of the gate. That is, the gating parameters are set to: starting point ,width The process of using the triangulation positioning method to obtain the starting and ending positions of the intermediate surface echo signal at the feature point is as follows: Figure 3 As shown, Figure 3(a) is the echo signal of the intermediate surface after the first feature point is cyclically shifted. Figure 3 (b) is a schematic diagram of using the left half signal to calculate the starting point of the intermediate surface echo. Figure 3 (c) is a schematic diagram of using the right half signal to calculate the intermediate surface echo endpoint. Figure 3 (d) is a schematic diagram of the calculation results of the position and width of the intermediate surface echo signal at this point.

[0077] Step 3: Calculate the gating parameters of all scanning points using the gating parameters of the above feature points.

[0078] According to step 2, the starting positions of the interfacial echo signals between the four feature points are , , , , the end positions of the intermediate surface echo signals are , , , The calculation results of the position and width of the intermediate echo between the feature points are as follows Figure 4 As shown, Figure 4 (a) is the recognition result of the intermediate surface echo signal at the upper left vertex; Figure 4 (b) is the recognition result of the intermediate surface echo signal at the upper right vertex; Figure 4 (c) is the recognition result of the intermediate surface echo signal at the lower left vertex; Figure 4 (d) is the recognition result of the intermediate surface echo signal at the lower right vertex.

[0079] The gating parameters of all scanning points are calculated by the gating parameters of the above feature points. Gating parameters are set as example.

[0080] First, use formula (1) to calculate the scanning point The starting point of the 4th line of the intermediate surface echo starting point :

[0081] ;

[0082] Then the scanning point is calculated by formula (2) Intermediate surface echo starting point 4th line end position :

[0083] ;

[0084] Then the scanning point is calculated by formula (4) Intermediate surface echo starting point :

[0085] ;

[0086] In the formula, the intermediate parameter , intermediate parameters ;

[0087] Then the scanning point is calculated by the following formula The starting point of the 4th line of the intermediate surface echo end point :

[0088] (10)

[0089] The scanning point is calculated by the following formula Intermediate surface echo end point 4th line end point position :

[0090] (11)

[0091] Then the scanning point is calculated by formula (5) Intermediate surface echo end position :

[0092] ;

[0093] Finally, the scanning point is calculated by formula (7) Intermediate echo width :

[0094] ;

[0095] Scan point The adaptive gating parameters are set as: starting point ,width .

[0096] To verify the accuracy of the calculation results, the points The actual echo signal of the point is obtained by using the triangulation positioning method. The starting position of the intermediate surface echo signal is , Intermediate surface echo end position , the calculation results of the intermediate surface echo at this point are compared with Figure 5 As shown, Figure 5 (a) is a comparison chart of calculation results. Figure 5 (b) is a comparison of the calculation results. The starting point error is 0.17ns, the end point error is 0.06ns, and the width error is 0.11ns, which are all smaller than the gated SPAD jitter. The calculation results can be considered accurate.

[0097] Step 4: According to the gating parameters of all scanning points, the parameters of the gated SPAD are adaptively set, and the echo signals of all scanning points are collected.

[0098] This embodiment builds a confocal non-field of view imaging system, and adaptively sets the parameters of the gated SPAD for scanning and acquisition. The scanning device uses a GVS012 dual-axis galvanometer system to achieve scanning in both the X-axis (horizontal) and Y-axis (vertical) directions. The Moku:lab signal generator is used to control the X-axis and Y-axis of the galvanometer to achieve Point array scanning. Collect the echo signals of all scanning points and get transient image.

[0099] Step 5: Use the echo signals of all scanning points to complete the imaging of non-line-of-sight targets.

[0100] This embodiment uses the above The transient image is reconstructed using the light cone transform (LCT) algorithm. The imaging result is as follows: Figure 6 shown.

[0101] In order to evaluate the effect of the adaptive control method, this embodiment uses a fixed gate width method for data acquisition and uses the LCT algorithm for target reconstruction (imaging results are shown in Figure 2). Figure 7 The results are shown in Table 1), and the peak signal-to-noise ratio, structural similarity and other evaluation indicators are used to quantitatively compare the imaging results. The results show that the evaluation indicators of the target imaging results using the adaptive control method for data acquisition are all rising, as shown in Table 1.

[0102] Table 1 Comparison of imaging quality of different methods

[0103]

[0104] The present invention is to explain in detail some of the well-known technologies belonging to those skilled in the art.

Claims

1. An adaptive control method for gated SPAD in non-line-of-sight imaging, characterized in that: The steps include: Step 1: Use the free mode or fixed gate mode of the gated SPAD to collect echo signals of certain feature points; Step 2: Calculate the gating parameters of each feature point using the echo signal; Step 3, calculating the gating parameters of all scanning points by using the gating parameters of the above feature points; Step 4: Adaptively set the parameters of the gated SPAD according to the gating parameters of all scanning points, and collect the echo signals of all scanning points; Step 5: Use the echo signals of all scanning points to complete the imaging of non-line-of-sight targets.

2. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 1, characterized in that: The method for selecting some feature points in step 1 is: when the scanning area is a polygon, each vertex of the polygon is selected as a feature point.

3. The adaptive control method for gated SPAD in non-line-of-sight imaging according to claim 1, characterized in that: The method for calculating the gating parameters of each feature point in step 2 is: First, the starting point and end point of the intermediate surface echo signal are obtained, which are expressed as , , then the gated SPAD parameters are set to: The starting point is set to , the width is ,in, Indicates the total number of discrete points of the collected signal. represents the remainder function, Indicates the conversion factor between the acquisition signal time and discrete points.

4. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 1, characterized in that: The implementation method of step 3 is as follows: Assume that the collection area is If the quadrilateral is a quadrilateral, the upper left, upper right, lower left and lower right vertices are selected as feature points, and the starting position of the intermediate surface echo between the feature points is obtained according to step 2. , , , , the end point of the intermediate surface echo , , , , the peak position of the intermediate surface echo , , , .

5. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 4, characterized in that: The scanning point of step 3 Intermediate surface echo starting point The calculation formula is: ； Among them, the intermediate parameters , intermediate parameters ; is the horizontal scanning point number, is the longitudinal scanning point number, .

6. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 4, characterized in that: The scanning point of step 3 Intermediate surface echo end position The calculation formula is: 。 7. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 4, characterized in that: The scanning point of step 3 Intermediate surface echo peak position The calculation formula is: 。 8. The method for adaptively controlling a gated SPAD in non-line-of-sight imaging according to claim 4, characterized in that: The step 3 scanning point Intermediate echo width The calculation formula is: ； Scan Point The gated SPAD parameters are set to: Starting point ,width .

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