High-precision video SAR moving target detection method based on information geometric theoryTechnical Field
The invention relates to the technical field of SAR moving target shadow detection, in particular to a high-precision video SAR moving target detection method based on an information geometric theory.
Background
The video SAR has the capability of continuously monitoring the change of a target area, and has wide application in the fields of military decision making, smart cities, traffic supervision and the like. In video SAR systems, the doppler modulation of moving object echoes is very sensitive to the movement of the object due to the high carrier frequency of the radar. Even small movements can cause large shifts and defocusing of moving object imaging in the SAR image, but shadows left by the moving object can reflect the actual position and state information of the moving object in the SAR image sequence. Therefore, shadows of moving objects are more easily observed in a video SAR image sequence, and detection with moving object shadows is a more direct and efficient means than in conventional SAR systems.
Currently, in the conventional video SAR moving target shadow detection technology, there are three main types of methods, namely a moving target detection method based on difference, a constant false alarm detection (CFAR) based device and a threshold segmentation based method.
According to the detection method based on the difference, firstly, a background image is estimated through a plurality of continuous video SAR images, then the background image and the current image to be detected are subjected to difference operation to obtain a binary image of the foreground, then the motion information of the previous frame and the motion information of the next frame are extracted through an inter-frame difference algorithm, and the binary image obtained through the difference between the motion information and the background are subjected to AND operation, and finally, the previous step of result is subjected to morphological processing to extract a shadow region of a motion target. Although the differential-based detection method is effective, the method has some limitations that firstly, the background modeling algorithm has higher requirements, the background is subject to hysteresis due to the fact that a plurality of previous frame estimation is used, and secondly, the inter-frame differential algorithm only compares the difference between two frames and ignores the information of the overlapped part of the two frames, so that the phenomena of hollowness and bilateral in a shadow area of a moving object are easy to occur, and the condition of missed detection or false alarm is caused.
The CFAR-based detection method can effectively avoid the limitation, the CFAR can select a proper area in the background noise of the video SAR image, and a proper detection threshold is determined according to the noise statistical characteristics in the area. When the target area exceeds this threshold, the target is considered detected. However, in a multi-target environment, multiple target signals may be included in the reference area, which may reduce the detection performance of the method, while in a non-uniform noise environment, the performance of the CFAR may be affected.
The detection method based on threshold segmentation can binarize the video SAR image by using an image threshold segmentation method (such as an OTSU method, a minimum error method and the like) to obtain a moving target shadow region in the image. However, the threshold segmentation method is based on the histogram information of the image, and ignores the spatial information and the edge information of the video SAR image, so that the problems of missed detection and over-high false alarm are easy to occur.
Disclosure of Invention
In order to solve the problems, the invention aims to provide a high-precision video SAR moving target detection method based on an information geometric theory, solve the technical problems of the defects of the traditional video SAR moving target shadow detection method, and improve the detection probability of the video SAR moving target shadow on the premise of ensuring the detection precision.
In order to achieve the above object, the technical scheme of the present invention is as follows:
The invention provides a high-precision video SAR moving target detection method based on an information geometric theory, which comprises the following steps:
s1, performing shadow enhancement and background suppression on a video SAR image sequence;
s2, extracting an ROI region based on an information geometric theory;
s3, effectively removing false ROI areas through error detection inhibition.
Further, the step S1 includes the following steps:
s11, calculating an initial subspace { U, V } of the video SAR image sequence by using a principal component analysis algorithm;
S12, setting the number of mixed gaussians, and modeling a data matrix X formed by a video SAR image sequence based on a low-rank representation model of the mixed gaussians, namely:
Wherein,Representing a set of all gaussian component weights,Representing a set of all gaussian component variances;
S13, updating a low-rank matrix U-VT by using an online subspace learning technology, and subtracting the low-rank matrix U-VT from an original video SAR image to obtain a foreground image containing video SAR moving target shadows;
s14, removing strong scattered point object imaging contained in the foreground image by using an alternate direction multiplier algorithm to obtain a video SAR image sequence subjected to shadow enhancement and background suppression, namely an enhanced image.
Further, the step S2 includes the following steps:
S21, forming a neighborhood system by all pixels in the neighborhood of the enhanced image at the coordinate pixel, and constructing statistical distribution describing the point;
s22, calculating geometrical distances in a JS divergence description Gaussian statistical manifold for mode analysis, and capturing local information features in an image;
S23, traversing each pixel of the image to obtain a corresponding JS divergence matrix of the enhanced image, and calculating joint probability distribution JPDF;
s24, performing threshold selection by using a minimum cross entropy algorithm, and extracting the ROI region of the enhanced image.
Further, the step S21 includes the following steps:
S211, forming a neighborhood system by all pixels in N x N neighborhood of the enhanced image at the (x, y) pixels, calculating the mean mu and variance sigma of all pixels in the neighborhood system, and describing the statistical distribution of the neighborhood system by using Gaussian distribution:
s212, taking the gray intensity value at the current (x, y) pixel as a mean value mu ', giving a minimum variance sigma', and constructing a statistical distribution describing the point:
further, the step S22 includes the following steps:
s221, a statistical model S= { P (x|theta) |theta epsilon theta } is formed by a probability distribution family formed by parameters theta= (mu, sigma)T, and S forms a micro Gaussian statistical manifold under a certain topological structure;
S222, calculating JS divergence, describing geometric distances among different probability distributions in the Gaussian statistical manifold by adopting the JS divergence, and analyzing modes;
S223, normalizing the value of the JS divergence, and explaining the geometric relationship between the pixel gray value of the current position and the neighborhood system distribution of the pixel gray value on a Gaussian statistical manifold to help capture local information features in an image.
Further, the JS divergence calculation formula in S222 is as follows:
Wherein,Is the average of two distributions, KL (pq) is defined as:
Further, the step S23 includes the following steps:
s231, traversing each pixel of the image to obtain a corresponding JS divergence matrix of the enhanced image;
S232, setting nij as the joint occurrence number between the gray value and JS scattering, and dividing each element in nij by the total pixel number of the enhanced image to obtain normalized joint probability distribution JPDF.
Further, the step S3 includes the following steps:
s31, calculating a gradient image of the current frame, and eliminating an error ROI region by using the gradient image;
S32, performing multi-frame false alarm suppression by using a data association algorithm.
Further, the step S31 includes the following steps:
S311, detecting the edge of the image by adopting a Sobel operator, and calculating the gray level relative change of the original video SAR image to obtain a gradient image of the current original SAR image;
S312, introducing the gradient image, calculating the superposition area of the gradient image and the ROI, and eliminating the ROI with the superposition area larger than the threshold value.
Further, the step S32 includes the following steps:
s321, extracting the mass center position of each ROI area and the corresponding time frame number as a feature vector;
s322, setting a space distance threshold TI and a time threshold TT, and associating detection points in a time threshold frame through the two thresholds to identify a possible real target;
S323, the detection point with stronger consistency in a plurality of frames is regarded as an effective target, and the detection point which accords with certain association times and the spatial variation of the centroid can be reserved.
By adopting the technical scheme, the invention has the following advantages:
1. The invention provides a high-precision video SAR moving target detection method based on an information geometric theory, which enhances the representation of the shadow of a moving target and simultaneously effectively inhibits strong scattered point objects and low scattering areas in the background by carrying out the operations of shadow enhancement and background inhibition on a video SAR image sequence.
2. The invention provides a high-precision video SAR moving target detection method based on an information geometric theory, which calculates the geometric distance between the current pixel position and the neighborhood system distribution thereof based on the information geometric theory, reveals the change of a local structure, forms joint probability distribution with gray value distribution, completes the extraction of an ROI region by utilizing minimum cross entropy, and greatly improves the detection performance of moving target shadows.
3. The invention provides a high-precision video SAR moving target detection method based on an information geometric theory, which utilizes dynamic information between edge information and multiple frames to effectively remove false ROI areas and improve the detection precision of moving target shadows.
Drawings
FIG. 1 is a flow chart of a high-precision video SAR moving target detection method based on information geometry theory;
FIG. 2 is a flow chart of ROI region extraction according to the present invention;
FIG. 3 (a) is an original video SAR image of the present invention;
FIG. 3 (b) is an enhanced image of the present invention;
FIG. 4 is an extracted ROI area of the present invention;
Fig. 5 is a detection result of a moving object per frame of the present invention.
Detailed Description
In the following detailed description of the embodiments of the present invention, reference is made to the accompanying drawings, in which it is to be noted that, in this document, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
Fig. 1 shows a flow chart of a high-precision video SAR moving target detection method based on the information geometric theory, and the high-precision video SAR moving target detection method based on the information geometric theory is wholly divided into three parts, wherein the method comprises the following steps:
s1, performing shadow enhancement and background suppression on a video SAR image sequence;
wherein, S1 comprises the following specific steps:
s11, calculating an initial subspace { U, V } of the video SAR image sequence by using a principal component analysis algorithm;
S12, setting the number of mixed gaussians, and modeling a data matrix X formed by a video SAR image sequence based on a low-rank representation model of the mixed gaussians, namely:
Wherein,Representing a set of all gaussian component weights,Representing a set of all gaussian component variances;
S13, updating a low-rank matrix U-VT by using an online subspace learning technology, and subtracting the low-rank matrix U-VT from an original video SAR image to obtain a foreground image containing video SAR moving target shadows;
S14, removing strong scattered point object imaging contained in the foreground image by using an alternate direction multiplier algorithm to obtain a video SAR image sequence subjected to shadow enhancement and background suppression, namely an enhanced image for short.
S2, extracting an ROI region based on an information geometric theory;
Wherein, the following steps are specifically shown in fig. 2:
S21, forming a neighborhood system by all pixels in the neighborhood of the enhanced image at the coordinate pixel, and constructing statistical distribution describing the point;
Wherein, S21 comprises the following specific steps:
S211, forming a neighborhood system by all pixels in N x N neighborhood of the enhanced image at the (x, y) pixels, calculating the mean mu and variance sigma of all pixels in the neighborhood system, and describing the statistical distribution of the neighborhood system by using Gaussian distribution:
s212, taking the gray intensity value at the current (x, y) pixel as a mean value mu ', giving a minimum variance sigma', and constructing a statistical distribution describing the point:
s22, calculating geometrical distances in a JS divergence description Gaussian statistical manifold for mode analysis, and capturing local information features in an image;
wherein, S22 comprises the following specific steps:
S221, a probability distribution family formed by parameters theta= (mu, sigma)T can form a statistical model S= { P (x|theta) |theta ∈theta }, S forms a micro Gaussian statistical manifold under a certain topological structure, and compared with Euclidean space and Euclidean distance measurement, the statistical manifold and the measurement based on the geodesic distance can reflect the geometric position and the similarity of each point;
S222, calculating by adopting Jensen-Shannon divergence (JS divergence), describing geometric distances among different probability distributions in the Gaussian statistical manifold by adopting the JS divergence, and analyzing modes;
Wherein,Is the average of two distributions, KL (p||q) is Kullback-Leibler divergence (KL divergence), defined as:
S223, normalizing the value of JS divergence to 0-255, on Gaussian statistical manifold, JS divergence provides a non-Euclidean 'distance' measure, the geometrical relationship between the pixel gray value of the current position and the neighborhood system distribution can be explained on manifold, the change of local structure can be revealed, and the capturing of local information features in an image can be facilitated, wherein the features are 'target areas' different from the background.
S23, traversing each pixel of the image to obtain a corresponding JS divergence matrix of the enhanced image, and calculating joint probability distribution JPDF;
S23 comprises the following specific steps:
s231, traversing each pixel of the image to obtain a corresponding JS divergence matrix of the enhanced image;
S232, setting nij as the joint occurrence number between the gray value and JS scattering, and dividing each element in nij by the total pixel number of the enhanced image to obtain normalized joint probability distribution JPDF.
S24, based on the obtained joint probability distribution JPDF, calculating JPDF = { jpdfij, i, j=0, 1, & gt, and extracting the ROI area of the enhanced image by using a minimum cross entropy algorithm, wherein the optimal gray value threshold TG of L-1 and the JS divergence threshold TJS.
S3, false ROI areas are effectively removed through error detection suppression (road edge information assistance and inter-frame association).
S3 comprises the following specific steps:
s31, calculating a gradient image of the current frame, and eliminating an error ROI region by using the gradient image;
wherein, S31 comprises the following specific steps:
s311, detecting the edge of the image by adopting a Sobel operator, and calculating the gray level relative change of the original video SAR image to obtain a gradient image of the current original SAR image;
S312, introducing the gradient image, calculating the superposition area of the gradient image and the ROI area, and eliminating the ROI area with the superposition area larger than the threshold TA.
S32, most of the false ROI areas existing at the edge are eliminated, but a small part of the false ROI areas exist, so that the false alarm suppression of multiple frames is performed by using a data association algorithm.
Wherein, S32 comprises the following specific steps:
s321, extracting the mass center position of each ROI area and the corresponding time frame number as a feature vector;
s322, setting a space distance threshold TI and a time threshold TT, and associating detection points in a time threshold frame through the two thresholds to identify a possible real target;
S323, the detection point with stronger consistency in a plurality of frames is regarded as an effective target, and the detection point which accords with certain association times and the spatial variation of the centroid can be reserved.
Finally, high-precision moving target detection of the video SAR can be realized through the three major parts.
In a specific embodiment, the implementation steps are as follows:
S1, performing shadow enhancement and background suppression on an original video SAR image by adopting a low-rank representation model based on mixed Gaussian to obtain an enhanced image sequence, in the example, selecting a 56 th frame video SAR image and an enhanced image as examples are shown in fig. 3 (a) and 3 (b), and comparing the fig. 3 (a) and 3 (b) to show that the shadow of a moving target of the enhanced image is more obvious and the contrast of the moving target shadow with the surrounding is higher, and simultaneously suppressing the background of the original video SAR image so that the extraction operation of a subsequent ROI area of the original video SAR image is not interfered by the background.
S2, setting the neighborhood size of 20 x 20, extracting a JS divergence characteristic matrix of an image by utilizing an information geometric theory, combining the JS divergence characteristic matrix with an image gray value, calculating joint probability distribution JPDF of the image, calculating an optimal gray value threshold TG and a JS divergence threshold TJS by adopting a minimum cross entropy algorithm, and simultaneously, setting the pixel point positions of the threshold TG and the JS divergence threshold TJS smaller than the threshold pixel point positions as the ROI region. And carrying out connected domain statistics on the ROI area, and deleting the connected domains of more than 500 pixels and less than 100 pixels. And recording centroid position information and frame number information of the connected domain, and entering the next step. The overall flow of this step is shown in fig. 2, and an exemplary diagram of the extracted ROI area is shown in fig. 4 in particular, and it can be seen from fig. 4 that almost all the moving object shadow areas are detected.
S3, calculating the gradient amplitude of the current original video SAR image by utilizing a Sobel operator, and generating a gradient image with the gradient amplitude of more than 50. And calculating the superposition area of the gradient image and the ROI area, wherein the superposition area is more than 50% of the area of the ROI area of the gradient image and the ROI area is the error ROI area, and eliminating the error ROI area. And then extracting the centroid position and the time frame number of the ROI area of each frame, and calculating the Euclidean distance between the detection result of the current frame and the detection result of the next frame by frame. If a target is found to be less than the spatial distance threshold (TI =30) from the target in the next frame, then both targets are considered to belong to the same track and marked as the same group, if not, then found in the next frame until the limit of the temporal threshold (TT =5) is exceeded. Finally, counting the association times of each target, and detecting the change between the first centroid position and the last centroid position. If the movement distance is large and the association number is 8 or more, the target is considered to be a valid target. The final detection result of the moving object of each frame is shown in fig. 5, wherein the red frame is the detection frame of the present invention, and the green frame is the real label frame.
Finally, it is pointed out that while the invention has been described with reference to a specific embodiment thereof, it will be understood by those skilled in the art that the above embodiments are provided for illustration only and not as a definition of the limits of the invention, and various equivalent changes or substitutions may be made without departing from the spirit of the invention, therefore, all changes and modifications to the above embodiments shall fall within the scope of the appended claims.