Millimeter wave security inspection imaging self-focusing method

Abstract

The invention discloses a millimeter wave security inspection imaging self-focusing method. The method comprises the following steps: S1, selecting a reference focusing distance for millimeter wave data for imaging; s2, finding out a maximum value point in the imaged image and carrying out region growth; s3, segmenting each sub-graph after region growth; s4, performing maximum and minimum value optimization on the variance of the subgraph by taking the imaging distance as a variable; s5, selecting the imaging distance with the maximum sub-image variance as a target imaging distance for imaging, and obtaining a focused imaging sub-image; and S6, fusing the sub-images into the original image to obtain a full-focusing millimeter wave image. According to the self-focusing method provided by the invention, the problem of adaptive focusing of the millimeter wave image can be solved, multiple target objects in different distance dimensions can be focused at the same time, and subsequent image processing of a millimeter wave security inspection system is facilitated.

Description

Technical Field

[0001] The invention patent relates to the field of millimeter wave imaging technology, and specifically to a self-focusing method for millimeter wave security inspection imaging. Background Art

[0002] Millimeter-wave security imaging technology has great application prospects due to its non-ionizing radiation safety, excellent clothing penetration, and high imaging resolution.

[0003] The technical principle of millimeter-wave security imaging is to transmit millimeter-wave broadband signals to the target, then coherently receive the echo signals reflected by the target, and obtain high-resolution imaging results by accurately inverting the phase information in the echo signals.

[0004] Traditional millimeter-wave security inspection imaging algorithms mainly include back-projection algorithms and wavenumber domain algorithms, which can achieve focused imaging of a single target object with a known focal length, but cannot achieve clear imaging of a target with an unknown focal length, nor can they achieve fully focused imaging of different target objects at different focal lengths. However, in actual security inspection applications, the location and quantity of hidden objects are often unpredictable.

[0005] Therefore, it is necessary to provide a millimeter-wave security inspection imaging self-focusing method to solve the above problems. Summary of the invention

[0006] The purpose of this patent is to provide a self-focusing method for millimeter-wave security inspection imaging to improve the imaging quality of millimeter-wave security inspection images.

[0007] The technical solution adopted by the present invention is: A millimeter wave security inspection imaging self-focusing technology, comprising: The original echo data obtained by the millimeter wave security inspection imaging hardware system is imaged at a reference focal length to obtain a non-focused millimeter wave security inspection image; Find the maximum point of the non-focused millimeter-wave security inspection image and use it as the seed point for region growing to obtain a binary image of the image; Segment the binary image to obtain different coordinate regions with potential targets; Segment the original echo data using regional coordinates; The segmented sub-data is imaged, and the variance of the image is optimized with the focal length as a variable; Select the focal length with the largest variance of the sub-image as the optimal imaging distance to obtain the focused sub-image, and use this method to obtain the focused imaging sub-images of all target objects; The sub-image is fused into the original image to obtain a fully focused millimeter-wave image.

[0008] It can be seen from the above technical solution that the method provided by the present invention can focus on and image target objects at any distance, and can also simultaneously focus on and image different targets at different distances in the same imaging image, thereby improving the quality of millimeter-wave security inspection images and facilitating subsequent image processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] In order to more clearly illustrate the technical solution of the present invention, the following briefly introduces the drawings used to describe the specific embodiments. The drawings are only used to illustrate the specific embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0010] Figure 1 A flow chart of a millimeter wave security inspection self-focusing method provided by an embodiment of the present invention.

[0011] Figure 2 A set of visual result graphs of the millimeter-wave self-focusing algorithm provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0012] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0013] This specification provides a millimeter-wave security inspection imaging self-focusing method, which segments the original image, then optimizes the image variance of different sub-images to obtain the optimal imaging distance, then focuses on each target separately, and finally obtains a fully focused millimeter-wave image of all target objects through image synthesis.

[0014] Figure 1 1 is a flow chart of the millimeter wave security inspection imaging self-focusing method provided by the embodiment. Figure 1 As shown, the self-focusing imaging method provided in this embodiment includes steps S1-S6.

[0015] S1: Image the original echo data to obtain a non-focused millimeter-wave security inspection image.

[0016] In this step, the millimeter wave security inspection imaging wave number domain algorithm is used to image the original echo data. The image obtained by the traditional wave number domain algorithm is unfocused, so the imaged image is a defocused image of the target.

[0017] S2: Find the maximum point that meets the requirements in the imaging image and use it as the seed point for region growing.

[0018] Due to the imaging characteristics of millimeter waves, the area with the target object in the imaging image after step S1 will have maximum scattering coefficient points. These maximum points are used as seed points for regional growth to obtain a binary image containing the target object area.

[0019] S3: Segment each sub-image after region growth to obtain the coordinate range of the image region with the target object, and then map it to the original echo data.

[0020] The area with a value of 1 in the binary image obtained in step S2 is the area with the target object. The range of the area is determined by the coordinates of the two vertices at the upper left corner and lower right corner of a rectangular box. The range represented by this coordinate can correspond to the data range corresponding to the target object in the original data.

[0021] S4: Optimize the mean and mean square value of the sub-images with imaging distance as the variable.

[0022] The original echo data is cut according to the coordinate range, and each sub-echo data after cutting is imaged. The variance of each sub-image is obtained with the imaging reference distance as a variable. The reference distance when the sub-image variance is the largest is the optimal imaging distance of the target.

[0023] Assume that I(m,n) represents the grayscale value at the image pixel (m,n), Represents the grayscale average of the entire image, specifically expressed as: Then the clarity function Y of the millimeter wave image can be expressed as: Changing the focal length will also change the value of the clarity function Y. The maximum value of Y corresponds to the image with the best focus effect.

[0024] S5: Select the focal length with the largest sub-image variance as the target imaging focal length to obtain a clear imaging image.

[0025] The optimal focal length obtained in step S4 is used to image the original echo data to obtain a clear image of the target object. Then, a sub-image of the target object is cut out according to the coordinate area obtained in step S3.

[0026] S6: Fuse the sub-image into the original image to obtain a fully focused millimeter-wave image.

[0027] So far, we have completed all the steps of the millimeter-wave imaging self-focusing method and achieved full focusing on targets in different focal planes in the original data.

[0028] The above shows and describes the basic principles, main features and advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A millimeter wave security inspection imaging self-focusing method, characterized in that: The steps include: S1: Perform imaging on the original echo data to obtain a non-focused millimeter wave security inspection image; S2: Find the maximum point that meets the requirements in the image and use it as the seed point for region growing; S3: Segment each sub-image after region growth to obtain the coordinate range of the image region with the target object, and then map it to the original echo data; S4: Optimize the variance of the sub-image with the imaging distance as the variable; S5: Select the focal length with the largest sub-image variance as the target imaging focal length to obtain a clear imaging image; S6: Fuse the sub-image into the original image to obtain a fully focused millimeter-wave image.

2. A millimeter wave security inspection imaging self-focusing method as claimed in claim 1, characterized in that: The specific method for performing millimeter wave security inspection imaging on the original image in S1 is a wavenumber domain algorithm.

3. A millimeter wave security inspection imaging self-focusing method as claimed in claim 2, characterized in that: The reference focusing distance of the imaging method is 0.6 m.

4. A millimeter wave security inspection imaging self-focusing method as claimed in claim 1, characterized in that: The specific method of performing region growing on the image in S2 is: S21: Find seed points: Search the image globally for maximum points whose grayscale values ​​are greater than 0.4, and the image grayscale values ​​within a 4×4 range centered on the maximum point are convex; S22: starting from the seed point, region growing is performed in four directions: up, down, left, and right. The region growing judgment standard is that the interpolation of the grayscale values ​​of the two image pixels is not greater than 0.

2.

5. The millimeter wave security inspection imaging self-focusing method according to claim 1, characterized in that: The variance expression used in S4 is: Where I(m,n) represents the grayscale value of the image pixel, M and N represent the size of the image. Represents the average gray value of the entire image, and its expression is: Optimize the function Y.

6. An optimization method according to claim 6, characterized in that: The optimization method is the gradient descent method.

7. The millimeter wave security inspection imaging self-focusing method according to claim 1, characterized in that: The specific method for performing millimeter wave security inspection imaging on the original image in S5 is a wave number domain algorithm, and the imaging distance is the optimal distance obtained in S4.

8. The millimeter wave security inspection imaging self-focusing method according to claim 1, characterized in that: In S6, all fully focused imaging sub-images are cropped into the original image to obtain a clear millimeter wave security inspection image.

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