Method for expressing image acquisition time of high-speed camera by sine optical signal array

Abstract

The invention relates to a method for expressing an image acquisition moment of a high-speed camera by using a sine optical signal array, which realizes high-precision expression of the image acquisition moment by arranging an m * n sine optical signal array in a view field of the high-speed camera by using a phase shift technology and a period difference strategy. The frequency of each row of signals is the same, the phase difference is 2pi / n in sequence, and the period of each row is gradually reduced by integer multiples to form a multi-period nested structure. And through wrapped phase calculation and periodic difference analysis, the time precision is improved step by step, and finally, the time value corresponding to the minimum periodic signal is taken as the acquisition time. The method has the advantages of long time expression period, high precision, simple device and the like, and is suitable for long-time, high-speed and high-resolution shooting measurement scenes.

Description

TECHNICAL FIELD

[0001] The application relates to a high-speed camera field, in particular to a method for expressing image acquisition time of a high-speed camera by using a sinusoidal light signal array. BACKGROUND

[0002] The image acquisition time of the existing high-speed camera is generally determined by the following four methods: 1. the time stamp output by the built-in hardware of the camera when the image is acquired is taken as the image acquisition time; 2. the time of a trigger signal (triggered by software or hardware) is taken as the image acquisition time by referring to an external trigger source time; 3. the computer clock time when the image is captured is taken as the image acquisition time by referring to the system time of the high-speed camera control software; and 4. the image acquisition time is calculated according to the frame rate and frame number of the camera. Due to the response delay of the hardware or software, the above four methods often result in inconsistent time interval errors of the image acquisition time of a single high-speed camera and inconsistent start-up errors of the initial image acquisition time of multiple high-speed cameras. The fundamental reason for the above-mentioned image acquisition time errors is the independent acquisition of image information and time information, and it is difficult to strictly unify the time of the two types of acquisition hardware. SUMMARY

[0003] The application provides a method for expressing the image acquisition time of a high-speed camera by using a sinusoidal light signal array, which can realize high time expression accuracy, long time expression period and does not affect the image acquisition of a high-speed motion scene.

[0004] The application is implemented by the following technical scheme:

[0005] The application relates to a method for expressing the image acquisition time of a high-speed camera by using a sinusoidal light signal array, which comprises the following steps:

[0006] S1, a light signal generating device is used to generate an m*n light point array in a non-interest area, i.e. a non-motion scene area, in the imaging field of view of the high-speed camera, and the brightness of each light point changes in a sinusoidal manner, wherein m represents the number of rows (m>=3), and n represents the number of columns (n>=3).

[0007] The sinusoidal change refers to that the brightness change frequency of the n light points in each row of the array is the same, and the phase is sequentially different by 2pi / n, that is, the initial phase of the i-th column sinusoidal light signal is ; the period of the j-th row light point is , wherein T1 is the period of the first row sinusoidal light signal, T2 is the period of the second row sinusoidal light signal, k j is a positive integer, and the larger j is, the larger k j is.

[0008] The light signal generating device adopts, but is not limited to, an LED, a laser, or other devices that can generate a sinusoidal light signal.

[0009] The high-speed camera does not limit the specific number on the premise that all high-speed cameras can observe the sinusoidal light signal.

[0010] S2, image the imaging field of view by a high-speed camera, and extract the gray scale information of the m*n sinusoidal light signal array in the image, wherein the gray scale change of the light point in the jth row and the ith column is , i=1, 2, 3, …, n, j=1, 2, 3, …, m, a is the background gray scale, and b is the gray scale amplitude.

[0011] S3, use a phase shift technique to solve the wrapped phase of the sinusoidal light signal in the first column of each row in the gray scale change signal of step S2 .

[0012] The phase shift technique includes a three-step camera, a four-step phase shift, a five-step phase shift, a twelve-step phase shift, and other multi-step phase shift techniques; the number of phase shift steps is equal to the number of columns of the array of light points.

[0013] S4, according to the phase difference between the first column of the second row and the first column of the first row in the gray scale change signal of step S2, calculate the absolute time t2 represented by the second row sinusoidal light signal, specifically: , wherein: , is the phase of the first column of the second row sinusoidal light signal, is the phase of the first column of the first row sinusoidal light signal, is the wrapped phase of the first column of the second row sinusoidal light signal, is the wrapped phase of the first column of the first row sinusoidal light signal.

[0014] S5, according to the rough absolute phase of the first column of the jth row sinusoidal light signal, calculate the absolute time represented by the jth row sinusoidal light signal, specifically: , wherein: the accurate absolute phase of the first column of the jth row sinusoidal light signal , the number of phase wrapping times of the first column of the jth row sinusoidal light signal , the rough absolute phase of the first column of the jth row sinusoidal light signal , is the absolute time solved by the second row sinusoidal light signal obtained in step S5, is the period of the jth row sinusoidal light signal.

[0015] Preferably, to ensure that the number of phase wrapping times L is accurate, the error of t2 solving should be less than T j .

[0016] S6, loop step S5, use the absolute time tj , solve the absolute time of the subsequent row sinusoidal light signal, until the absolute time t of the mth row sinusoidal light signal is obtained m At this time, since the period of the mth row sinusoidal light signal is the smallest, the time accuracy of the solution is the highest. Therefore, t m is the time finally solved by the method.

[0017] Preferably, the absolute time t m is not greater than the time length of the sinusoidal light signal array expression , wherein: is the rounding operation, T1 is the period of the gray scale change of the first row sinusoidal light signal in the gray scale change signal of step S2, and T2 is the period of the second row sinusoidal light signal.

[0018] The m*n is a sorting mode of the sinusoidal light signal form in the array, and does not represent that the sinusoidal light signal array is arranged in the form of a matrix.

[0019] Technical effects

[0020] The present application adopts sinusoidal light signal array time light encoding / decoding, cooperates with the phase shift technology, significantly improves the accuracy of the sinusoidal light signal expression time, and utilizes the periodicity difference of the sinusoidal light signal to prolong the period of the sinusoidal light signal expression time. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is the flow chart of the present application;

[0022] Figure 2 is the schematic diagram of the embodiment scene;

[0023] Figure 3 is the sinusoidal light signal array sorting schematic of the embodiment;

[0024] Figure 4 is the time expression verification result of the embodiment. DETAILED DESCRIPTION

[0025] As shown in Figure 1 , the present embodiment relates to a method for expressing the image capturing moment of a high-speed camera by using a sinusoidal light signal array, which comprises the following steps:

[0026] S1, using a laser to project a laser dot array with sinusoidal brightness change in a non-interesting area, i.e. a non-motion scene area, in the imaging field of view of a high-speed camera.

[0027] The actual projection form of the laser dot array is as shown in Figure 2 For the convenience of discussion, the laser dot array is rearranged as Figure 3The 3x4 form is shown, the frequency of the 4 laser spots in each row is the same, the phase difference is π / 2, the period of the first row laser is T1, the period of the second row laser is T2, and (ΔT > 0); the period of the third row laser is T3, and .

[0028] S2, the high-speed camera images the non-interesting area and the interesting area in the imaging field of view, and extracts the gray scale information of each laser spot in the image. The gray scale information of each laser spot in the laser dot array , wherein: i=1, 2, 3, 4, j=1, 2, 3, a is the background gray scale, and b is the gray scale amplitude.

[0029] S3, the wrapped phase of the first column of the sinusoidal light signal of each row is solved by using the four-step phase shift technique, specifically: , wherein: is the wrapped phase of the gray scale information of the jth row laser spot, between [0, 2π].

[0030] S4, the absolute time expressed by the second row sinusoidal light signal is calculated, specifically including:

[0031] 4.1 The phase difference between the phase of the first column of the sinusoidal light signal of the second row and the phase of the first column of the sinusoidal light signal of the first row , according to the length definition of the time expression , the absolute time expressed by the second row sinusoidal light signal is ,

[0032] 4.2 Express as the difference between the wrapped phase of the first column of the sinusoidal light signal of the second row and the wrapped phase of the first column of the sinusoidal light signal of the first row , specifically: , wherein: is the wrapped phase of the first column of the sinusoidal light signal of the second row, is the wrapped phase of the first column of the sinusoidal light signal of the first row;

[0033] 4.3 According to the phase difference and the periods of the first row and the second row , , the absolute time expressed by the second row sinusoidal light signal is inversely solved to obtain .

[0034] S5, the absolute time expressed by the third row sinusoidal light signal is calculated, specifically including:

[0035] 5.1 Calculate the rough absolute phase of the first column of the sinusoidal light signal of the third row ​;

[0036] 5.2 Calculate the phase wrapping times of the sine light signal in the first column of the third row ;

[0037] 5.3 Calculate the accurate absolute phase of the sine light signal in the first column of the third row ;

[0038] 5.4 Calculate the absolute time expressed by the sine light signal in the third row .

[0039] Since the period of the sine light signal in the third row is the smallest, the time accuracy of the solution is the highest. Therefore, t3 is the time finally solved by the method.

[0040] Through specific simulation experiments, the period T1 of the first row laser is set to 1650us, the period difference AT is set to 50us, the amplitude of the sine gray signal is 50, and the gray noise level is 3 Gaussian noise. The expression time length calculated by the above method is 52800us, and the expression time accuracy is ±1us, as shown in Figure 4 .

[0041] Compared with the prior art, the method designs a sine light signal array encoding time scheme, cooperates with the phase shift technology, decodes the time from the sine light signal array again, and controls the time analysis error within ±1us; the periodicity difference of the sine light signal is used to prolong the period of the sine light signal expression time. In the embodiment, the expression time length is improved from 1650us to 52800us.

[0042] The above specific implementation can be adjusted in different ways by those skilled in the art without departing from the principles and purposes of the present application. The protection scope of the present application is subject to the claims and is not limited by the above specific implementation. Each implementation scheme within the scope is subject to the constraints of the present application.

Claims

1. A method of representing the instant of image capture by a high-speed camera with an array of sinusoidal light signals, characterized in that, The method comprises the following steps: S1, generating an m*n light point array in a non-interesting area in a high-speed camera imaging field of view, i.e. a non-motion scene area, by using a light signal generating device, and the brightness of each light point changes in a sinusoidal manner; S2, image the imaging field of view by a high-speed camera, extract the gray information of the m*n sinusoidal light signal array in the image, wherein the gray change of the light spot in the jth row and the ith column , i=1,2,3,…,n, j=1,2,3,…,m, a is the background gray, and b is the gray amplitude. S3, solving the wrapped phase of the sinusoidal light signal in the first column of each row in the gray scale variation signal by using phase shift technique ; S4, calculating the absolute time t2 represented by the second row sinusoidal light signal according to the phase difference between the first column of the second row and the first column of the first row in the gray scale change signal of step S2, specifically: wherein: , is the phase of the first column sinusoidal light signal of the second row, is the phase of the first column sinusoidal light signal of the first row, is the wrapped phase of the first column sinusoidal light signal of the second row, is the wrapped phase of the first column sinusoidal light signal of the first row; S5, calculating the absolute time represented by the jth row sinusoidal light signal according to the coarse absolute phase of the 1st column sinusoidal light signal of the jth row, specifically: , wherein: the accurate absolute phase of the 1st column sinusoidal light signal of the jth row , the phase wrapping number of the 1st column sinusoidal light signal of the jth row , the coarse absolute phase of the 1st column sinusoidal light signal of the jth row , is the absolute time obtained by solving the 2nd row sinusoidal light signal in step S5, is the period of the jth row sinusoidal light signal; S6. Repeat step S5, using the absolute time t obtained from the sinusoidal optical signal in the j-th row. j Solve for the absolute time of the sinusoidal optical signal in subsequent rows until the absolute time t of the m-th row of sinusoidal optical signal is obtained. m This is the time required to finally solve the problem.

2. The method of claim 1, wherein the sinusoidal light signal array represents the time at which an image is captured by a high speed camera. The sinusoidal variation refers to that the brightness of the n light points in each row of the array varies at the same frequency, and the phase successively differs by 2π / n, i.e. the initial phase of the i-th column sinusoidal light signal is ; Period of the jth row of light points wherein: T1 is the period of the first row of sinusoidal light signals, T2 is the period of the second row of sinusoidal light signals, k j is a positive integer, and the larger j is, the larger k j is, m denotes the number of rows, and n denotes the number of columns.

3. The method of claim 1, wherein the sinusoidal light signal array represents the time at which an image is captured by a high-speed camera, and wherein the sinusoidal light signal array is characterized by, The phase shift technique is a multi-step phase shift technique, and the number of phase shift steps is equal to the number of columns of the light point array.

4. The method of claim 1, wherein the sinusoidal light signal array represents the time at which an image is captured by a high speed camera, and wherein the sinusoidal light signal array is characterized by, To ensure the phase wrapping number L is accurate, the error of t2 should be less than T j .

5. The method of claim 1, wherein the sinusoidal light signal array represents the time at which an image is captured by a high speed camera, and wherein the sinusoidal light signal array is characterized by, The final solution absolute time t m Not more than the time length of the sine light signal array expression Wherein: is an integer operation, T1 is the period of the first row of the sine light signal gray scale change in the gray scale change signal of step S2, and T2 is the period of the second row of the sine light signal.

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