CN112666625A

CN112666625A - Rapid imaging device and method for millimeter wave security inspection

Info

Publication number: CN112666625A
Application number: CN201910985867.XA
Authority: CN
Inventors: 陈志强; 李元景; 吴万龙; 赵自然; 沈宗俊; 郑磊; 程航
Original assignee: Tsinghua University; Nuctech Co Ltd
Current assignee: Tsinghua University; Nuctech Co Ltd
Priority date: 2019-10-16
Filing date: 2019-10-16
Publication date: 2021-04-16

Abstract

The present application provides a fast image forming apparatus and a method thereof, the fast image forming apparatus including: an autofocus module configured to determine an effective imaging area of an object under examination; and a three-dimensional tomography module configured to perform a plurality of times of tomography on the effective imaging region obtained based on the autofocus module, and obtain a final image based on tomography results obtained by the plurality of times of tomography.

Description

Rapid imaging device and method for millimeter wave security inspection

Technical Field

The invention relates to the field of image imaging of security check instruments, in particular to a rapid imaging device and a rapid imaging method for millimeter wave security check.

Background

At present, in the field of security inspection image imaging, a millimeter wave near-field broadband holographic three-dimensional wavenumber domain imaging method is mainly adopted for imaging. However, in the existing millimeter wave near-field broadband holographic three-dimensional wavenumber domain imaging method, the three-dimensional wavenumber domain data needs to be resampled by Stolt interpolation in the imaging process, and the distance direction non-fuzzy range is also required to be larger than the whole imaging range where a target may appear, so that the existing imaging method has the disadvantages of large imaging range, large operation amount and poor real-time performance. Accordingly, there is a need for an improved fast image forming apparatus and method thereof that can solve such problems.

Disclosure of Invention

[ solution ]

To solve the disadvantages of the related art, a fast imaging apparatus and a fast imaging method are proposed.

In a first aspect of the present application, there is provided a fast imaging apparatus, which may include: an autofocus module configured to determine an effective imaging area of an object under examination; and a three-dimensional tomography module configured to perform a plurality of times of tomography on the effective imaging region obtained based on the autofocus module, and obtain a final image based on tomography results obtained by the plurality of times of tomography.

In the first aspect, the autofocus module may be further configured to: arbitrarily extracting two-dimensional data S (k) with fixed frequency point from three-dimensional wave number domain matrix_x，k_y，k_i) Wherein k is_iRepresenting a frequency point; selecting a best focus plane based on the extracted two-dimensional data; and expanding the imaging area based on the determined optimal focus level to obtain an effective imaging area.

In the first aspect, the autofocus module may be further configured to divide the preset imaging area into a number of focal planes; based on the extracted two-dimensional data S (k)_x，k_y，k_i) Calculating an amplitude integral value for each of a number of focal planes using the following formula

And

and selecting the focusing plane corresponding to the minimum amplitude integral value from the calculated amplitude integral values of the focusing planes as the optimal focusing plane.

In the first aspect, the autofocus module may be further configured to: and expanding the threshold distance back and forth on the basis of the optimal focusing level, thereby obtaining an effective imaging area.

In the first aspect, the three-dimensional tomography module may be further configured to: dividing an effective imaging area into a plurality of focusing layers; performing tomography for each of a plurality of focal planes; and combining the resulting tomographic images for each focal plane into a final image.

In the first aspect, the three-dimensional tomography module may be further configured to: selecting a focus plane from a plurality of focus planes and constructing a reference function based on the selected focus plane

Wherein z + R₀Representing a distance of the selected focal slice from the sampling aperture; performing matched filtering on the three-dimensional wave number domain by using a reference function so as to correct nonlinear components in the characteristic frequency of the target echo on the imaging layer; carrying out broadband accumulation on the three-dimensional wave number domain data subjected to matching filtering along the beam direction; and obtaining an imaging result for the selected one focal plane based on the broadband accumulation result.

In the first aspect, the three-dimensional tomography module may be further configured to: determining whether an imaging result is obtained for each of a plurality of focal planes, wherein: in the case of yes, combining the resulting tomographic images for each focal plane into a final image; or, in the case of no, selecting a focus plane from the plurality of focus planes that has not been selected before for processing to obtain an imaging result for the focus plane.

In a second aspect of the present application, there is provided a fast imaging method, which may include: determining an effective imaging area of a detected object; and performing a plurality of times of tomography based on the effective imaging region, and obtaining a final image based on tomography results obtained by the plurality of times of tomography.

In the second aspect, determining the effective imaging region of the object to be inspected may include: arbitrarily extracting two-dimensional data S (k) with fixed frequency point from three-dimensional wave number domain matrix_x，k_y，k_i) Wherein k is_iRepresenting a frequency point; selecting a best focus plane based on the extracted two-dimensional data; and expanding the imaging area based on the determined optimal focus level to obtain an effective imaging area.

In a second aspect, selecting a best focus plane may comprise: dividing a preset imaging area into a plurality of focusing layers; based on the extracted two-dimensional data S (k)_x，k_y，k_i) Calculating an amplitude integral value for each of a number of focal planes using the following formula

And

In the second aspect, obtaining the effective imaging area may include: and expanding the threshold distance back and forth on the basis of the optimal focusing level, thereby obtaining an effective imaging area.

In the second aspect, performing the plurality of times of tomography based on the effective imaging region and obtaining the final image based on the tomography results obtained by the plurality of times of tomography may include: dividing an effective imaging area into a plurality of focusing layers; performing tomography for each of a plurality of focal planes; and combining the resulting tomographic images for each focal plane into a final image.

In a second aspect, tomographic imaging for each of a plurality of focal planes may comprise: selecting a focus plane from a plurality of focus planes and constructing a reference function based on the selected focus plane

In the second aspect, the method may further include: determining whether an imaging result is obtained for each of a plurality of focal planes, wherein: in the case of yes, combining the resulting tomographic images for each focal plane into a final image; or in the case of no, selecting a focus plane which has not been selected before from the plurality of focus planes for processing to obtain an imaging result for the focus plane.

In a third aspect of the present application, a non-transitory computer-readable medium is provided, comprising computer program code recorded thereon and executable by a processor, the computer program code, when executed by the processor, causing the processor to perform the fast imaging method according to the second aspect.

In a fourth aspect of the present application, there is provided an auto-focusing method, which may include: dividing a preset imaging area into a plurality of focusing layers; based on the extracted two-dimensional data S (k)_x，k_y，k_i) Calculating an amplitude integral value for each of a number of focal planes using the following formula

And

In a fifth aspect of the present application, a non-transitory computer-readable medium is provided, comprising computer program code recorded thereon and executable by a processor, the computer program code, when executed by the processor, causing the processor to perform the auto-focusing method according to the fourth aspect.

[ technical effects ]

Aiming at the problem of interpolation operation, the three-dimensional tomography is used for replacing three-dimensional wave number domain imaging, the tomography thought is utilized for layer-by-layer reconstruction, the three-dimensional cycle process of interpolation operation in the wave number domain method can be replaced by the one-dimensional cycle process in the space distance dimension, and the situation that the k is in the process of k is avoided_zThe dimensionality resampling greatly reduces the operation amount, shortens the signal processing time, completely avoids the calculation error caused by the finite length of the interpolation kernel or the approximate introduction of the interpolation kernel, and improves the inversion imaging precision.

Aiming at the problem of the invalid region, the method for reconstructing the three-dimensional image by using the automatic focusing can roughly judge the position of the effective imaging region by using the automatic focusing method, and then develops a proper distance range by using the position as a reference layer to reconstruct the three-dimensional image, thereby effectively avoiding calculating redundant parts and doubling the calculated amount of the three-dimensional tomography method.

The method combines the three-dimensional tomography method with the automatic focusing method, and can obviously reduce the operation workload, thereby obviously shortening the imaging time.

Drawings

The above and other aspects, features and advantages of particular embodiments of the present disclosure will become more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a millimeter wave near-field broadband holographic imaging geometry.

Fig. 2 shows a flow chart of discrete digital signal processing using the concept of three-dimensional wavenumber domain imaging.

A cross-sectional view of the effective coverage of the echo signals in the three-dimensional beam spectrum is shown in figure 3.

Fig. 4 shows an image range and an effective image range under the wave number domain method.

Fig. 5 shows a flow chart for discrete digital signal processing using the idea of three-dimensional tomography.

Fig. 6 shows a graph of the relationship between the reference distance and the amplitude integration value of the focusing result in the autofocus method.

A flowchart of the autofocus processing is shown in fig. 7.

An exemplary flow chart for determining the best focus plane is shown in fig. 8.

A flow chart of the fast imaging method is shown in fig. 9.

A schematic block diagram of a fast imaging apparatus is shown in fig. 10.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the drawings are illustrative only and should not be construed as limiting the invention.

As used herein, the singular forms "a", "an", "the" and "the" may include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may also be present. Further, "connected" or "coupled" as used herein may include wirelessly connected or wirelessly coupled. As used herein, the term "and/or" includes all or any element and all combinations of one or more of the associated listed items.

It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the prior art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

FIG. 1 shows a millimeter wave near-field broadband holographic imaging geometry. Reference numeral 101 denotes a planar sampling aperture, wherein the spatial aperture is z ═ -R₀The size of the aperture is D_x×D_yThe position coordinates of the single-station radar are (x ', y', -R)₀) And (x, y, z) represents the position of any scattering point in the target area, so that the distance from any scattering point to the single-station radar is

The scattering coefficient of any scattering point in the target area is represented by sigma (x, y, z), the frequency of a narrow-band signal emitted by the system is f, c represents the propagation speed of the electromagnetic wave in free space, namely the speed of light, and k is 2 pi f/c, which is the wave number corresponding to the emission frequency. According to the dispersion relation of the electromagnetic wave, the wave number k and the wave number domain component k of the transmitted signal_x、k_y、k_zSatisfy the relation:

then

For a continuous target consisting of numerous scattering points, the interference signal collected by the single-station radar is the integral of the echoes of the numerous scattering points. The amplitude of the target area echo received by the sampling aperture is modulated by the scattering coefficient of the target point, the phase is modulated by the round-trip path of the scattering point and the antenna array element, and the echo is subjected to coherent receptionAn expression can be written as:

after obtaining the sampling signal, the prior art adopts a three-dimensional wave number domain imaging method, and the calculation formula is as follows:

wherein,

a reference function is represented.

Fig. 2 shows a flow chart of discrete digital signal processing. The specific steps of the millimeter wave near-field bandwidth holographic three-dimensional wavenumber domain imaging method will be described below with reference to fig. 2.

1) At step 201, a sampling aperture receives echoes of a target region to obtain echo signals.

2) The obtained echo signals are subjected to a spatial two-dimensional fourier transform with respect to the azimuth and elevation dimensions, transformed into the three-dimensional wavenumber spectral domain at step 202.

3) At step 203, a reference function is constructed with the imaging region center plane as a reference plane. When the millimeter wave near-field bandwidth holographic three-dimensional wavenumber domain imaging method is used for imaging, the imaging region is integrally imaged, so the constructed reference function is the reference function for the integrally imaged region.

4) At step 204, the transformed three-dimensional wavenumber domain data is multiplied by the constructed reference function, thereby match filtering the wavenumber domain data. During three-dimensional discrete signal processing, because a distance blurring effect exists in a distance dimension, it is required to ensure that imaging targets are located in the same non-blurring distance window, otherwise, all imaging targets cannot be focused and imaged. In the imaging geometry, the center of the imaging region is typically set as the origin, so the default choice is to use the distance of the sampling aperture from the origin as the originDistance parameter in reference function, Z_ref＝R₀。

5) At step 205, a Stolt interpolation operation is performed on the matched and filtered wave number domain data, which is a key step of the wave number domain imaging method, and resampling of the wave number domain data is completed in a three-dimensional wave number domain space by using an interpolation operation. Wherein Stolt interpolation has two layers of implications: firstly, echo signal wave number domain data are converted from (k) through Stolt coordinate_x，k_yK) transformation of the coordinate system to (k)_x，k_y，k_z) A coordinate system, which eliminates the phase coupling of the azimuth direction and the distance direction from the perspective of the SAR; and secondly, the originally non-uniformly distributed sampling data is changed into uniformly distributed sampling data through interpolation so as to meet the requirement of three-dimensional fast Fourier inverse transformation on the sampling data.

A cross-sectional view of the effective coverage of the echo signals in the three-dimensional beam spectrum is shown in figure 3. Since the echo data is uniformly sampled in x 'and y', it is Fourier transformed and then sampled at k_xAnd k_yAbove is also uniform sampling. With vertical dotted lines at k_xAnd k_yUniform sampling space in dimension, then at k_x，k_yAnd k_zIn the coordinate system of (1), the sampling points of the three-dimensional wave number spectrum are distributed on a concentric sphere with a radius of 2k at equal intervals along the horizontal direction, and are distributed on an arc with a radius of 2k at equal intervals along the horizontal direction in the section shown in the figure, and the dots in the figure represent echo signals s (k)_x，k_y，k_z) Distribution in space. For three-dimensional inverse fast Fourier transform, k is divided by a horizontal dotted line_zDimension is divided into uniform sampling space, and sampling data at the intersection of the dotted line cross is obtained by resampling from the existing sampling data at the round point through an interpolation technology so as to meet the condition of k_zThe requirement of uniform sampling in dimension. The sector area in the figure represents the effective coverage range of the echo signal on the section of the wave number spectrum, and in the three-dimensional wave number spectrum, the effective range of the echo signal is a spherical cover layer with a certain thickness.

6) At step 206, the three-dimensional wavenumber spectral signals are transformed into the three-dimensional spatial domain by three-dimensional inverse fast fourier transform (3D-IFFT), thereby obtaining a three-dimensional distribution map of the scattering intensity with the target fully focused (step 207).

The above describes the principle of the millimeter wave near-field broadband holographic three-dimensional wavenumber domain imaging method, but the disadvantages are: the method has the advantages of large operation amount and poor real-time performance, and is mainly caused by the following two reasons:

1: the broadband holographic wave number domain imaging method in the prior art can effectively reconstruct a three-dimensional image of a target according to a reflected echo, but three-dimensional wave number domain data needs to be resampled by Stolt interpolation in the reconstruction process. Through analyzing the operation amount of the wave number domain imaging method, the interpolation operation amount is at least in the same order of magnitude as the operation amount of the broadband holographic wave number domain main body imaging method, and for a sinc interpolation kernel with higher interpolation precision, the operation amount is even far larger than the operation amount of the main body imaging method.

2: since the sampled signal data is discrete, discrete digital signal processing can produce periodicity, resulting in the production of unambiguous ranges. In the prior imaging art, in order to ensure full focus imaging of the target, the range of distance-wise blur-free must be larger than the entire imaging range in which the target may appear, typically above 1 m. In practice, however, since millimeter waves cannot penetrate the human body, echo signals are only generated by the body surface near the side of the scanning aperture and the effective imaging subject that can be irradiated by the radar. Although the human body surface and the effective imaging subject carried with it are not on the same focal plane, their distribution range in the distance dimension is limited, and usually does not exceed 0.3 m. As such, in the prior art imaging results, the region from the scanning aperture to near the surface of the human body, and the region behind the human body contain only invalid images due to coupling leakage, background clutter, and system noise (see the other regions within the image range of the wavenumber domain method in fig. 4 that process the valid image region are all invalid image regions). These regions are referred to as redundant portions in the reconstructed three-dimensional image, and are not necessarily included in the image reconstruction range (refer to fig. 4).

In order to solve the interpolation operation problem in the existing millimeter wave near-field broadband holographic three-dimensional wavenumber domain imaging method, three-dimensional tomography is used for replacing three-dimensional wavenumber domain imaging.

In three-dimensional tomography, the imaging range is divided into a plurality of focal planes, then two-dimensional imaging of the focal planes is performed at one selected focal plane at a time, and finally the imaging result of the full scene range is obtained based on the imaging at each plane.

When the calculation is performed by using three-dimensional tomography, the calculation formula is as follows:

The operations at

steps

501 and 502 are similar to

steps

201 and 202 in fig. 2 and will not be described repeatedly here.

At step 503, an imaging range is set and several focal planes are divided along the distance within the imaging range.

Illustratively, the imaging range is predefined or preconfigured by the system or the user.

Illustratively, the imaging range may be the wave number domain method image range shown in fig. 4, but is not limited thereto.

The focus level may be arbitrarily divided by the user according to the needs. Furthermore, the division of the focus plane may be implemented using any technical means known to those skilled in the art or developed in the future.

At step 504, a focus plane is selected from the number of focus planes.

Illustratively, each focus plane may be selected sequentially or the focus planes may be selected according to any rule.

At step 505, a reference function for the selected focal plane is constructed based on the signal frequency and the distance of the selected focal plane to the aperture

Where z represents the position of the selected focal slice at the distance up, and z is signed. For example, when the selected focal plane is to the left of the origin, then z is a negative value; when the selected focal plane is to the right of the origin, z is positive at this time.

At step 506, the focus plane is matched filtered using the constructed reference function for the selected focus plane. Specifically, the reference function is multiplied by the three-dimensional wave number spectrum of the broadband echo signal obtained in step 502, and the nonlinear component in the phase-frequency characteristic of the target echo on the imaging slice is corrected, so that the phase-frequency characteristic only contains the linear phase representing the position information of the scattering point.

At step 507, the three-dimensional wavenumber domain after matched filtering is integrated along the wavenumber direction, and for discrete signals, spatial two-dimensional wavenumber spectra of different transmission frequencies are coherently added. Through coherent addition, the wave number domain spectral amplitude of the focusing target is greatly increased, and the wave number domain spectral amplitude of the defocusing target is relatively reduced.

At step 508, the signal is transformed to the spatial domain by a two-dimensional inverse spatial fourier transform, resulting in a fully focused scatter intensity profile of scatter points located on the reference slice.

By this, imaging with respect to the selected slice is completed.

Thereafter, at step 509, a determination is made as to whether all of the focus planes have been traversed. If not, the process returns to step 504 to continue selecting the next focus plane, and the operations of steps 505 through 509 are repeated again for the selected focus plane. If so, the process proceeds to step 510 to obtain an overall imaging result based on the imaging results for each focal plane.

The idea of chromatography is utilized for imaging layer by layer, a three-dimensional cyclic process of interpolation operation in a wave number domain method can be replaced by a one-dimensional cyclic process in a space distance dimension, and k is avoided_zThe dimension resampling greatly reduces the operation amount, shortens the signal processing time, completely avoids the calculation error caused by the finite length of the interpolation kernel or the approximate introduction of the interpolation kernel, and improves the inversion imagingAnd (4) precision.

In order to solve the problem of invalid regions in the existing millimeter wave near-field broadband holographic three-dimensional wavenumber domain imaging method, preferably, an automatic focusing method is used in the method.

The implementation of the autofocus method in this application is to use the amplitude integration value as a function of the image sharpness estimate.

Specifically, echo data s (x, y, f) of any frequency point is selected from the echo data_n) Performing focusing layer division in the non-fuzzy window, and then based on the selected frequency point f_nAt different reference distances Z_refThe focusing process is performed and the amplitude value of the focusing result is integrated. The Amplitude Integral Value (Amplitude Integral Value-AIV) expression can be written as:

specifically, based on the selected frequency point f_nAnd operating an amplitude integral value formula aiming at different focusing layers. When the amplitude integration value is minimum, the reference distance is the optimal reference distance.

Fig. 6 shows a graph of the relationship between the reference distance and the amplitude integration value of the focusing result in the autofocus method. As can be seen from the figure, suppose Z_refThe focusing level of 1 is the best focusing level, the amplitude integral value of the imaging result for the focusing level is the smallest, and the amplitude integral values of the remaining positions increase as the distance between the reference plane and the focusing level increases. The definition function of the amplitude integral value meets the requirements of unbiasedness, unimodal performance, capability of reflecting defocusing polarity and low noise sensitivity. The method can determine the real distance between the target to be measured and the scanning array.

A flowchart of the autofocus processing is shown in fig. 7. At step 701, one two-dimensional data S (k) is arbitrarily extracted from three-dimensional wavenumber domain data obtained via two-dimensional fourier transform_x，k_y，k_i)。

At step 702, based on the extracted S (k)_x，k_y，k_i) Medium frequency point, selectAnd selecting the optimal focusing level.

In particular, an exemplary flow chart for determining best focus adjustment is shown in FIG. 8.

At step 801, an imaging region is divided into several focal planes.

At step 802, a focus plane is selected from the divided focus planes.

At step 803, based on the reference distance for the focus plane and the selected two-dimensional data S (k)_x，k_y，k_i) Middle frequency point k_iThe amplitude integral value is calculated using an amplitude integral value formula.

Thereafter, the process proceeds to

steps

804 and 805. At step 805, the calculated amplitude integration value is stored. In step 804, it is determined whether all of the focus planes have been traversed. In the case of "no", the process returns to step 802 to continue selecting another focus plane, thereby repeating steps 803 to 805; in the case of "yes", the process proceeds to step 702.

Step 805 and step 804 may be performed simultaneously or in a sequential order. The order of execution of step 805 and step 804 is not limited.

Further, at step 805, the amplitude integration value is stored in association with the focus plane.

At step 702, the amplitude integration values for all focus planes stored in step 805 are compared. As described above with respect to fig. 6, when the amplitude integration value is minimum, the reference distance at this time is the optimum reference distance. Based on this, in step 702, the focus plane with the smallest amplitude integration value is selected as the reference plane by comparison.

Referring back to fig. 7 again, in the case where the optimal reference plane is determined, the process proceeds to step 703 where the imaging area is expanded based on the determined optimal reference plane.

Illustratively, the extended imaging area is determined by the optimal reference plane ± a threshold distance.

Illustratively, the threshold distance may be 15 cm.

Illustratively, the thickness of the expanded imaging area does not exceed the thickness of the detected object.

By using the automatic focusing method, the position of the effective imaging area can be roughly judged by the automatic focusing method, and then a proper distance range is developed by taking the position as a reference layer to reconstruct a three-dimensional image, so that the redundant part can be effectively prevented from being calculated.

For further optimization, the three-dimensional imaging method is combined with an automatic focusing method, so that invalid imaging areas are avoided being calculated while the calculation time is shortened.

A flow chart of the fast imaging method is shown in fig. 9. Wherein the operations in step 901 and step 902 are similar to

steps

201 and 202 described above with reference to fig. 2, steps 903 to 905 are similar to steps 701 to 703 described above with reference to fig. 7, and steps 906 to 913 are similar to steps 503 to 510 described above with reference to fig. 5. For the sake of simplicity, the description will not be repeated here.

By the rapid imaging method, imaging time can be shortened remarkably. The total and interpolated time obtained with the different imaging methods are shown in table 1.

TABLE 1

As can be seen from the table, the 8-point Sinc interpolation wave number domain method has high interpolation precision and large calculation amount; the linear interpolation precision is low, and the operand is small; the imaging region of the broadband three-dimensional tomography method is the same as the wave number domain method; the autofocus tomography method only images the active area near the focal plane. In terms of time consumption, the total time consumption using the broadband three-dimensional chromatography method was 6.9s, whereas the total time consumption using the autofocus chromatography method was only 2.1 s.

In order to execute the above fast imaging method proposed by the present application, the present application also correspondingly provides a fast imaging device.

A schematic block diagram of a fast imaging apparatus is shown in fig. 10. The fast imaging device 1000 comprises an autofocus module 1001 and a three-dimensional tomography module 1002. Among other things, the fast imaging apparatus 1000 may be configured to perform the fast imaging method process described above with respect to fig. 9. In particular, the autofocus module 1001 may be configured to perform the autofocus method processes described above with respect to fig. 7 and 8. The three-dimensional tomography module 1002 may be configured to perform the three-dimensional tomography method processes described above with respect to fig. 5.

Although the various steps are described above with respect to the order shown in the figures, those skilled in the art will appreciate that the various steps may be performed in a different order or that embodiments of the invention may be practiced without one or more of the steps described above.

As can be appreciated from the foregoing, the electronic components of one or more systems or devices can include, but are not limited to, at least one processing unit, memory, and a communication bus or communication means that couples the various components including the memory to the processing unit. The system or device may include or have access to a variety of device-readable media. The system memory may include device-readable storage media in the form of volatile and/or nonvolatile memory such as Read Only Memory (ROM) and/or Random Access Memory (RAM). By way of example, and not limitation, system memory may also include an operating system, application programs, other program modules, and program data.

Embodiments may be implemented as a system, method or program product. Accordingly, embodiments may take the form of an entirely hardware embodiment or an embodiment containing software (including firmware, resident software, micro-code, etc.) that may all generally be referred to herein as a "circuit," module "or" system. Furthermore, embodiments may take the form of a program product embodied in at least one device-readable medium having device-readable program code embodied therein.

A combination of device readable storage media may be used. In the context of this document, a device-readable storage medium ("storage medium") may be any tangible, non-signal medium that can contain, or store a program comprised of program code configured for use by or in connection with an instruction execution system, apparatus, or device. For the purposes of this disclosure, a storage medium or device should be construed as non-transitory, i.e., not including a signal or propagation medium.

The disclosure has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments were chosen and described in order to explain the principles and practical application, and to enable others of ordinary skill in the art to understand the various embodiments of the disclosure for various modifications as are suited to the particular use contemplated.

Claims

1. A fast imaging apparatus comprising:

an autofocus module configured to determine an effective imaging area of an object under examination; and

a three-dimensional tomography module configured to perform a plurality of times of tomography on the effective imaging region obtained based on the autofocus module, and obtain a final image based on tomography results obtained by the plurality of times of tomography.

2. The fast imaging device of claim 1, wherein the autofocus module is further configured to:

arbitrarily extracting two-dimensional data S (k) with fixed frequency point from three-dimensional wave number domain matrix_x，k_y，k_i) Wherein k is_iRepresenting a frequency point;

selecting a best focus plane based on the extracted two-dimensional data; and

expanding an imaging region based on the determined best focus plane to obtain the effective imaging region.

3. The fast imaging device of claim 2, wherein the autofocus module is further configured to:

dividing a preset imaging area into a plurality of focusing layers;

based on the extracted two-dimensional data S (k)_x，k_y，k_i) Calculating an amplitude integral value for each of the number of focal planes using the following formula

And

selecting the focusing plane corresponding to the smallest amplitude integration value from the calculated amplitude integration values for each of the plurality of focusing planes as the best focusing plane.

4. The fast imaging device of claim 3, wherein the autofocus module is further configured to:

and expanding the threshold distance back and forth on the basis of the optimal focusing layer, thereby obtaining the effective imaging area.

5. The fast imaging device of any of claims 1 to 4, wherein the three-dimensional tomography module is further configured to:

dividing the effective imaging area into a plurality of focusing planes;

tomographic imaging for each of the plurality of focal planes; and

the resulting tomographic images for each focal plane are combined into the final image.

6. The fast imaging device of claim 5, wherein the three-dimensional tomography module is further configured to:

selecting a focus plane from the plurality of focus planes and constructing a reference function based on the selected focus plane

Wherein z + R₀Indicating the distance of the selected focal plane from the sampling aperture；

Performing matched filtering on the three-dimensional wave number domain by using the reference function so as to correct nonlinear components in the characteristic frequency of the target echo on the imaging layer;

carrying out broadband accumulation on the three-dimensional wave number domain data subjected to matching filtering along the beam direction; and

obtaining an imaging result for the selected one focal plane based on the broadband accumulation result.

7. The fast imaging device of claim 6, wherein the three-dimensional tomography module is further configured to:

determining whether an imaging result is obtained for each of the plurality of focal planes, wherein:

in the case of yes, combining the resulting tomographic images for each focal plane into the final image; or

In the negative case, a focus plane that has not been selected before is selected from the plurality of focus planes and processed to obtain an imaging result for the focus plane.

8. A method of rapid imaging comprising:

determining an effective imaging area of a detected object; and

a plurality of times of tomography are performed based on the effective imaging region, and a final image is obtained based on tomography results obtained by the plurality of times of tomography.

9. The fast imaging method according to claim 8, wherein the determining an effective imaging region of the inspected object comprises:

selecting a best focus plane based on the extracted two-dimensional data; and

10. The fast imaging method of claim 9, wherein the selecting a best focus plane comprises:

dividing a preset imaging area into a plurality of focusing layers;

And

11. The fast imaging method of claim 10, wherein the obtaining the effective imaging area comprises:

12. The fast imaging method of claim 11, wherein the performing multiple tomography based on the effective imaging region and obtaining a final image based on tomography results obtained from the multiple tomography comprises:

dividing the effective imaging area into a plurality of focusing planes;

tomographic imaging for each of the plurality of focal planes; and

13. The fast imaging method of claim 12, wherein the tomographic imaging for each of the plurality of focal planes comprises:

Wherein z + R₀Representing a distance of the selected focal slice from the sampling aperture;

14. The fast imaging method of claim 13, further comprising:

15. A non-transitory computer readable medium comprising computer program code recorded thereon and executable by a processor, the computer program code, when executed by the processor, causing the processor to perform the fast imaging method according to any one of claims 8 to 14.

16. An auto-focusing method, comprising:

dividing a preset imaging area into a plurality of focusing layers;

And

17. A non-transitory computer readable medium comprising computer program code recorded thereon and executable by a processor, the computer program code, when executed by the processor, causing the processor to perform the auto-focus method of claim 16.