# Low-Rank Tensor Patching Based on Convolutional Sparse Coding for Communication Data Repair

Authors: Yi Hu; Yuyi Yao; Zhen Cheng
Journal: Mobile Information Systems
 (2022)

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## Abstract

The study aimed to solve the common problem that hardware limitations and degradation make the data obtained in reality usually incomplete and improve the quality of communication transmission. In this paper, we propose a new low-rank tensor complementation model LRTC-CSC, which is based on tensor kernel parametrization (TNN), preserves the low-rank structure of information while restoring the detail features, and finally solves the problem using the efficient alternating direction multiplier method (ADMM). Based on the low-rank nature of the tensor, adding convolutional sparse coding (CSC) can well represent the characteristics of the high-frequency part of the information to handle the details while recovering the global information. The experimental results show that the training set of this paper saves much time compared with other models in several metrics by using only ten images of similar color for each data. At the same time, the data recovery effect is much higher than the novel TV canonical prior. In particular, the LRTC-CSC model is 5.18 dB higher than the LRTC-TV model in terms of PSNR value for image recovery at a 70% missing rate. The LRTC-CSC model proposed in this paper is more accurate and efficient for communication data restoration.


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## Body

## 1. Introduction

With the rapid development of information technology, a large amount of communication data has appeared on the Internet, and the means of communication have significantly changed. Among them, image resources occupy an important position in daily life because they contain more vivid images and convey the information to be expressed more clearly and distinctly. They have become one of the most essential information transmission media due to their abundant quantity and complex data storage structure. Information includes three-dimensional color images, multispectral images, hyperspectral images, and videos [1]. Traditional means of communication can no longer meet the demand for fast and accurate transmission of many pictures. The advantages of fiber-optic transmission technology make it occupy an increasingly important position in communication methods.Fiber-optic transmission technology in various forms can meet the needs of people for various forms of information access. Fiber-optic transmission systems are characterized by extensive frequency bands and high communication capacity than traditional wire-based information transmission methods. In transmitting information, the transmission rate is greatly improved compared to the traditional copper wire. The transmission rate of single-wavelength optical fibers can reach between 3 Gbps and 10 Gbps [2]. The fiber-optic transmission system is the essential information transmission and is the most important. The degree of information loss reflects the degree of excellence of the information transmission system [3]. At the same time, optical fiber has unique advantages over coaxial cables, microwave systems, and satellite communications. It can significantly improve the image transmission quality and is an ideal transmission medium.Due to the influence of equipment, transmission methods, and storage methods, high-dimensional data such as images can be mutilated and blurred, containing noise in acquisition and storage. It is supposed that the information receiver follows the traditional vector or matrix representation to recover the presentation. In this case, it will lead to a large loss of information and cannot accurately portray the intrinsic structure and characteristics of the observed data [4–7]. In turn, the quality of the transmitted sample data is degraded, and the image transmission data are severely distorted. Then, it is used to complete the missing item data which is an urgent problem. Currently, tensor completion and recovery are commonly used to solve this problem.As a higher-order extension of matrix, the tensor is an important data format for multi-dimensional data applications, which can better express the complex structure of high-dimensional data [8]. Complementary and recovery of matrices use only two dimensions of data information, which is difficult for complex data processing [9–11]. Therefore, the low rank (LR) tensor-based approach is more effective when dealing with high-dimensional data than the low-rank matrix-based approach. To perform tensor complementation, the most critical point is the tensor decomposition and the rank solution.In a paper published by Candès and Recht in 2009 [12], a matrix complementation model based on minimizing kernel parametrization was proposed, and it was shown that the matrix can be complemented with high probability under certain conditions. At present, optimization algorithms based on minimizing the kernel parametrization to solve the matrix complementation model are emerging, such as the singular value thresholding (SVT) algorithm proposed by Cai et al. [13]. In addition, for matrices of large size, to solve the matrix complementation problem faster and more efficiently, Ma et al. [14] proposed the FPCA (fixed point continuation with approximate SVD) algorithm based on the linearized approximate point algorithm and the Bregman iterative algorithm.Low-rank matrix decomposition-based methods are based on the direct decomposition of large observation matrices into the product of several small-scale low-rank matrices. Wen et al. [15] proposed a fast and efficient method LRMaFit (low-rank matrix fitting) based on a model of matrix decomposition using a nonlinear over-relaxation algorithm, in which the rank of the tensor can be dynamically adjusted. To further improve the performance of low-rank tensor decomposition-based methods, researchers have proposed a series of methods, such as OptSpace [16, 17], GROUSE [18], and ScGrassMC [19].Currently, tensor complementation can provide rich applications for data such as image or video restoration [20–22], hyperspectral data recovery [23], or nuclear magnetic resonance image data recovery [24–26]. In recent years, the research area of low-rank tensors has been extended to numerical analysis, computer vision, machine learning, signal and image processing, etc. [27–31]. Therefore, it is worthwhile to pay attention and explore how to perform efficient and accurate tensor complementation to recover the information of each dimension of the incomplete tensor.Although the low-rank constraint has the above advantages, it is still difficult to recover all the tensor information. It is because relying only on the low-rank property of the tensor itself for complementation tends to ignore some important detailed information, making the lower bound of the distance between the recovered result and the original tensor always remain near a fixed value, making it challenging to optimize further. After the introduction of physical regularities such as TV and framelet, although the local features can be spatially smoothed and constrained, for some tensor data with too high missing rates, the information available for the observations is very limited, which often leads to the inevitable unsatisfactory results of the recovered tensor. Studies have combined deep learning models with tensors, such as using CNN as a common term. Such methods have achieved good results in recovering the tensor by using a data set trained in advance as prior information, but CNN needs to be trained in advance with tens of thousands of samples, which is time-consuming and not suitable for extensive generalization studies.Signoretto et al. [32] applied the benchmark Olivetti face data set for face image complementation. They called the pure complementation problem a hard complementation problem, and their spectral regularization framework can handle both pure complementation and multi-task situations. Geng et al. [33, 34] used the higher-order orthogonal iteration (HOOI) method to model face images for face complementation, recognition, and facial age estimation. To address the problem of missing values during data collection, they used the expectation maximization (EM) method to interpolate missing terms and demonstrated the superior performance of their multilinear subspace analysis method for age estimation. Bazerque et al. [35] applied a probabilistic parallel approach to corrupted brain MRI images by integrating a priori information in a Bayesian framework, and the method was able to enhance smoothing and predictive power. Similarly, Liu et al. [36] proposed a complementary method combining tensor trace parametrization and tensor decomposition and validated the effectiveness of their proposed algorithm on brain MRI data sets.Candès and Recht’s paper [12] proposed a matrix complementary set model based on a minimization kernel parameterization, Cai et al. proposed the SVT algorithm [13], and Ma et al. [14] proposed the FPCA algorithm based on the linearized approximation point algorithm and the Bregman iteration algorithm. However, these algorithms involve singular value decomposition (SVD) of the matrix in the solution process, which can lead to low computational efficiency and limited applications on large-scale data. The LRMaFit method proposed by Wen et al. [15], and a series of methods such as OptSpace [16, 17], GROUSE [18], and ScGrassMC [19] are nonconvex models; therefore, the results obtained by solving them are not necessarily globally optimal and may be locally optimal. Miles and Geng et al. [33, 34] model face images, and Bazerque et al. [35] and Liu et al. [36] verify the effectiveness of their proposed algorithms on brain MRI data sets. However, CNNs require tens of thousands of samples to be trained in advance, which is time-consuming and not suitable for extensive generalization studies.Based on the experience of these predecessors, this paper innovates the methodology to obtain better results and wider application. In this paper, we propose to use convolutional sparse coding (CSC) as a common term to recover the details of the incomplete tensor, then combine it with the underlying LRTC model to recover the global structure information and details of the original tensor in the process of completing the missing values, and finally obtain a result that is very close to the original tensor. In addition, CSC requires pretrained dictionaries with only a small number of samples of the same type, which significantly saves recovery time.An effective alternating direction multiplier method (ADMM) is introduced to solve the optimization problem. The HaLRTC model is dependent on SNN, and LRTC-TV model is referred to as SNN with TV regularity, as well as the LRTC-TNN model based on TNN with CSC regularity is selected for comparison experiments with the LRTC-CSC model based on TNN with CSC regularity to demonstrate the superiority of the algorithm in this paper.By conducting experiments on six 256 × 256 × 3 color images, 181 × 217 × 30 MRI data, and 144 × 176 × 150 video data, the results prove the effectiveness and superiority of the algorithm in this paper, and the model proposed in this paper is better than other models in terms of recovery effect. The results show that the model with a regular prior (either CSC regular or TV regular) is better than its counterpart with only low-rank constraint and demonstrates that TNN can approximate the tensor rank better than SNN. The general flow of the research in this paper is shown in Figure1.Figure 1
Technical route and workflow.This paper is organized as follows:Section1 introduces the research background and illustrates the research significance of low-rank tensor complementarity in data restoration problems. The literature review analyzes the strengths and weaknesses of existing models and introduces the superiority of this paper’s innovative model for two hot research issues: data restoration effectiveness and time.Section2 introduces three data sets and modeling methods involved in this paper, and proposes a low-rank tensor complementation method based on convolutional sparse coding.Section3 shows the numerical analysis of the model proposed in this paper with the three models HaLRTC, TTN, and TV and gives outcome evaluation indicators.Section4 shows the experimental results of comparing the LRTC-CSC model proposed in this paper with HaLRTC, TTN, and TV on three different data sets.In Section5, the results and convergence analysis show that the communication data restoration technique planned in this paper is significantly better than other methods and is feasible, which has important implications for communication restoration.


## 2. Methodology

### 2.1. Data Set Introduction

This paper uses three data sets obtained by optical fiber sensing as the test set: color image, magnetic resonance imaging (MRI), and video image data. We use Python to process data sets.(1)
Color image: color image is a kind of three-dimensional data, including red, green, and blue (RGB) color images. In this paper, the color image data are obtained through optical fiber sensing, and six pictures with the size of 256× 256 pixels are selected as the test set. The data set is from the website of the University of Southern California. The data are shown in Figure 2.(2)
MRI data: in this paper, magnetic resonance imaging is obtained by optical fiber sensing. MRI data often include more than ten or hundreds of bands than color image data. In this paper, MRI data with the size of 181× 217 × 30 are selected as the test set of the experiment. These data are from the OASIS website (the Open Access Series of Imaging Studies). The images imaged in each band of the data set can be obtained by calculating the front slice of the tensor. The extracted front slice data image is shown in Figure 3.(3)
Video data: this paper obtains video data through optical fiber sensing. This paper selects the data set with a size of 144× 176 × 150 as the test set of this paper. Considering the calculation capacity and speed, aiming at the mat file of 144 × 176 × 150 as and considering the calculation performance of existing computers, this paper only selects 30 frames of video data as the test set of the experiment. The data set is from the website of Arizona State University. Each framed picture is the front slice of each order of the tensor. The 30 frames of image data are shown in Figure 4.Pictures are stored in an ordered multi-dimensional matrix, which is divided into grayscale pictures by color, the pixel values of the pictures are stored in a two-dimensional array, and the pixel values of the three-channel colors of the pictures are stored in a three-dimensional array for color pictures. Take the picture size of 64× 128 × 3 as an example, and the computer uses 24576 numbers to store a picture. If the number of images is small, a series of operations can be carried out using the picture matrix as the image feature, but the amount of data in the actual application scene is very large. If all kinds of operations are carried out directly using the image storage matrix as the image feature, it will occupy a lot of storage and computing resources, which is very wasteful and unreasonable. Similarly, not all the information stored in such huge data is necessary for the computer. There is a certain amount of redundant information, and the dimension of image data can be reduced through certain dimensionality reduction methods. Therefore, it is very necessary to select image features and train them.Figure 2
Color picture test set.Figure 3
MRI data of 30 bands.Figure 4
Frame video data.


### 2.2. Low-Rank a Priori

Low-rank tensor completion (LRTC) can be regarded as the generalization of low-rank matrix completion, and matrix completion can be regarded as the process of two-dimensional tensor completion. The derivation of this paper starts with the well-known optimization problem of matrix completion. The low-rank matrix completion model is as follows [37]:(1)minX：rankX,s.t.XΩ=MΩ,where M∈Rm×n is a partially observed matrix; Ω is the observed element index set; and X∈Rm×n is the estimation matrix we want to get.However, equation (1) is a problem that can only be solved in super-polynomial time, and its difficulty is that the solution of matrix rank is nonconvex. To solve this problem, Fazel and Boyd [38] proposed using rank constrained iterative estimation of missing values. Another popular and effective method is to use norm to approximate. Therefore, under certain conditions, equation (1) can be written as(2)minX：X∗,s.t.XΩ=MΩ,where X∗ represents the trace norm of the matrix X.Low-rank tensor completion is difficult, but it can be extended to tensor completion through matrix completion based on matrix low-rank completion. Although there are many methods to complete the low-rank tensor, they are all modified based on equation (1). Therefore, the low-rank tensor completion model can be expressed as(3)minX：X∗,s.t.XΩ=TΩ,where TΩ is an intermediate variable.For the solution of equation (3), a simple method is to expand the tensor into a matrix to solve the complement model of the matrix. However, this method only obtains a low rank for tensor mode and cannot recover the tensor well [39]. Therefore, it is necessary to consider a method to obtain the low rank of all tensor modes. Recently, Zhang et al. [40] established the definition of kernel norm as the norm of a tensor rank substitute, so that the objective function can be further expressed as(4)minX：1n3circX∗,s.t.XΩ=TΩ.Here,circX refers to the circular domain function.Some optimization methods can solve equation (4). This objective function is based on the low-rank a priori of TNN, which can perfectly complete the global information of the image.


### 2.3. CSC Regular

#### 2.3.1. Plug-and-Play Framework

Equation (4) considers the recovery of the tensor’s global information with the tensor’s low rank, ignoring the recovery of the details. Due to the loss of a large amount of detailed information, many composite algorithms have additional a priori information to optimize and improve the lost detailed information. Therefore, in addition to relying on the low-rank prior information of tensor, additional regular priors are often added to the LRTC model to improve the detail of local features.To solve the nondifferentiable problem of many regularization operators, some approximate algorithms have appeared in recent two decades to solve the problem of regularized image denoising. The plug-and-play (PNP) framework has become a hot topic [41]. Research shows that any ready-made denoising method can be directly used as a priori, rather than the steps in the solution to calculate the proximal operator of the specified regularization [42]. In the process of solving, there are usually the following subproblem:(5)ProxΦy=argminXρ2x−y22+λΦx,where Pro refers to a function in Python, ρ=n3n4…nN (nN is the pixels of Nth dimensional tensor), and λ>0 is the trade-off parameter.Takingy as a noisy image, the above problem can be regarded as a denoising problem. Given the regularization formula, Φx here is a corresponding denoiser to deal with the denoising problem. This paper adds convolutional sparse coding based on the LRTC model as regular a priori.


#### 2.3.2. Convolutional Sparse Coding

With the development of optical fiber sensing technology, using optical fiber sensing to obtain image resources has become a way of information transmission. However, the image obtained by optical fiber sensing may be damaged in acquisition. The emergence of sparse coding (SC) has achieved great success in image restoration. In 2010, Zeiler et al. [43] proposed convolutional sparse coding (CSC) based on traditional sparse coding. Convolutional sparse coding uses a set of filters (also known as dictionaries) to convolute with their corresponding feature maps, and the convolution sum between them replaces the general linear representation. CSC decomposes the input image into n sparse feature maps through n filters rather than representing a vector sparsely through a linear combination of dictionaries.CSC has been used in many projects to extract features from images for object recognition [44], but the performance of CSC in tensor completion has not been explored. The high-frequency part often contains more important details than the low-frequency part. Therefore, it is a feasible choice to optimize the high-frequency part alone. In this paper, CSC is regarded as a priori. Instead of decomposing the signal vector into the product of dictionary matrix and coding vector, CSC represents the image as the convolution sum of feature map and corresponding filter, that is,(6)argminX^1ρblkdiagX^∗+12X^−X^k+1+Q^kF2,where X^ is the Fourier transform of X along three dimensions and blkdiagX is the block diagonal matrix. In the CSC model, the size of each feature map is almost the same as X. The reconstructed X is obtained by summing the convolution output. Compared with linear representation, convolution dictionary can obtain translation invariant features and improve the model’s efficiency.


#### 2.3.3. Dictionary Pretraining

In this paper, the convolution dictionary is trained. To determine the best number of filters, this paper selects ten fruit pictures as the training set for pretraining, as shown in Figure5.Figure 5
Fruit training set.In this paper, several dictionaries with different filter numbers are trained with the training set, and then these dictionaries are used in Lena, pepper, and starfish test sets. The experimental results are shown in Figure6. It can be seen from Figure 7 that the number of filters with the best performance is 32. Therefore, this paper chooses to use the training set to train a dictionary containing 32 filters. Figure 8 shows the visual effects of three trained dictionaries.Figure 6
Complementary results of different algorithms with the missing rate of 70%.Figure 7
PSNR and SSIM values recovered by dictionaries with different filter numbers on the test set when the missing rate is set at 80%.Figure 8
(a) 32 filters trained with the fruit training set. (b) 32 filters trained with other MRI training sets. (c) Using Suzie data set to select 10 frames of images to train 32 filters. (a) Fruit. (b) MRI. (c) Suzie.
(a)(b)(c)


### 2.4. Establishment of the LRTC-CSC Model

This paper attempts to use the low-rank a priori and convolution dictionary to learn the a priori interaction model, to give full play to their respective advantages. By combining TNN regular term with CSC regular term, the new model proposed in this paper is LRTC-CSC.(7)arg.minXXTNN+λΦX,s.t.XΩ=TΩ,where ΦX is the canonical a priori of CSC and λ is the trade-off parameter. Constraint XΩ=TΩ can be written as(8)minPx=0,XΩ=TΩ,￥,other.Therefore, objective function equation (7) can be rewritten as follows:(9)arg.minXXTNN+λΦX+PX.


## 2.1. Data Set Introduction

This paper uses three data sets obtained by optical fiber sensing as the test set: color image, magnetic resonance imaging (MRI), and video image data. We use Python to process data sets.(1)
Color image: color image is a kind of three-dimensional data, including red, green, and blue (RGB) color images. In this paper, the color image data are obtained through optical fiber sensing, and six pictures with the size of 256× 256 pixels are selected as the test set. The data set is from the website of the University of Southern California. The data are shown in Figure 2.(2)
MRI data: in this paper, magnetic resonance imaging is obtained by optical fiber sensing. MRI data often include more than ten or hundreds of bands than color image data. In this paper, MRI data with the size of 181× 217 × 30 are selected as the test set of the experiment. These data are from the OASIS website (the Open Access Series of Imaging Studies). The images imaged in each band of the data set can be obtained by calculating the front slice of the tensor. The extracted front slice data image is shown in Figure 3.(3)
Video data: this paper obtains video data through optical fiber sensing. This paper selects the data set with a size of 144× 176 × 150 as the test set of this paper. Considering the calculation capacity and speed, aiming at the mat file of 144 × 176 × 150 as and considering the calculation performance of existing computers, this paper only selects 30 frames of video data as the test set of the experiment. The data set is from the website of Arizona State University. Each framed picture is the front slice of each order of the tensor. The 30 frames of image data are shown in Figure 4.Pictures are stored in an ordered multi-dimensional matrix, which is divided into grayscale pictures by color, the pixel values of the pictures are stored in a two-dimensional array, and the pixel values of the three-channel colors of the pictures are stored in a three-dimensional array for color pictures. Take the picture size of 64× 128 × 3 as an example, and the computer uses 24576 numbers to store a picture. If the number of images is small, a series of operations can be carried out using the picture matrix as the image feature, but the amount of data in the actual application scene is very large. If all kinds of operations are carried out directly using the image storage matrix as the image feature, it will occupy a lot of storage and computing resources, which is very wasteful and unreasonable. Similarly, not all the information stored in such huge data is necessary for the computer. There is a certain amount of redundant information, and the dimension of image data can be reduced through certain dimensionality reduction methods. Therefore, it is very necessary to select image features and train them.Figure 2
Color picture test set.Figure 3
MRI data of 30 bands.Figure 4
Frame video data.


## 2.2. Low-Rank a Priori

Low-rank tensor completion (LRTC) can be regarded as the generalization of low-rank matrix completion, and matrix completion can be regarded as the process of two-dimensional tensor completion. The derivation of this paper starts with the well-known optimization problem of matrix completion. The low-rank matrix completion model is as follows [37]:(1)minX：rankX,s.t.XΩ=MΩ,where M∈Rm×n is a partially observed matrix; Ω is the observed element index set; and X∈Rm×n is the estimation matrix we want to get.However, equation (1) is a problem that can only be solved in super-polynomial time, and its difficulty is that the solution of matrix rank is nonconvex. To solve this problem, Fazel and Boyd [38] proposed using rank constrained iterative estimation of missing values. Another popular and effective method is to use norm to approximate. Therefore, under certain conditions, equation (1) can be written as(2)minX：X∗,s.t.XΩ=MΩ,where X∗ represents the trace norm of the matrix X.Low-rank tensor completion is difficult, but it can be extended to tensor completion through matrix completion based on matrix low-rank completion. Although there are many methods to complete the low-rank tensor, they are all modified based on equation (1). Therefore, the low-rank tensor completion model can be expressed as(3)minX：X∗,s.t.XΩ=TΩ,where TΩ is an intermediate variable.For the solution of equation (3), a simple method is to expand the tensor into a matrix to solve the complement model of the matrix. However, this method only obtains a low rank for tensor mode and cannot recover the tensor well [39]. Therefore, it is necessary to consider a method to obtain the low rank of all tensor modes. Recently, Zhang et al. [40] established the definition of kernel norm as the norm of a tensor rank substitute, so that the objective function can be further expressed as(4)minX：1n3circX∗,s.t.XΩ=TΩ.Here,circX refers to the circular domain function.Some optimization methods can solve equation (4). This objective function is based on the low-rank a priori of TNN, which can perfectly complete the global information of the image.


## 2.3. CSC Regular

### 2.3.1. Plug-and-Play Framework

Equation (4) considers the recovery of the tensor’s global information with the tensor’s low rank, ignoring the recovery of the details. Due to the loss of a large amount of detailed information, many composite algorithms have additional a priori information to optimize and improve the lost detailed information. Therefore, in addition to relying on the low-rank prior information of tensor, additional regular priors are often added to the LRTC model to improve the detail of local features.To solve the nondifferentiable problem of many regularization operators, some approximate algorithms have appeared in recent two decades to solve the problem of regularized image denoising. The plug-and-play (PNP) framework has become a hot topic [41]. Research shows that any ready-made denoising method can be directly used as a priori, rather than the steps in the solution to calculate the proximal operator of the specified regularization [42]. In the process of solving, there are usually the following subproblem:(5)ProxΦy=argminXρ2x−y22+λΦx,where Pro refers to a function in Python, ρ=n3n4…nN (nN is the pixels of Nth dimensional tensor), and λ>0 is the trade-off parameter.Takingy as a noisy image, the above problem can be regarded as a denoising problem. Given the regularization formula, Φx here is a corresponding denoiser to deal with the denoising problem. This paper adds convolutional sparse coding based on the LRTC model as regular a priori.


### 2.3.2. Convolutional Sparse Coding

With the development of optical fiber sensing technology, using optical fiber sensing to obtain image resources has become a way of information transmission. However, the image obtained by optical fiber sensing may be damaged in acquisition. The emergence of sparse coding (SC) has achieved great success in image restoration. In 2010, Zeiler et al. [43] proposed convolutional sparse coding (CSC) based on traditional sparse coding. Convolutional sparse coding uses a set of filters (also known as dictionaries) to convolute with their corresponding feature maps, and the convolution sum between them replaces the general linear representation. CSC decomposes the input image into n sparse feature maps through n filters rather than representing a vector sparsely through a linear combination of dictionaries.CSC has been used in many projects to extract features from images for object recognition [44], but the performance of CSC in tensor completion has not been explored. The high-frequency part often contains more important details than the low-frequency part. Therefore, it is a feasible choice to optimize the high-frequency part alone. In this paper, CSC is regarded as a priori. Instead of decomposing the signal vector into the product of dictionary matrix and coding vector, CSC represents the image as the convolution sum of feature map and corresponding filter, that is,(6)argminX^1ρblkdiagX^∗+12X^−X^k+1+Q^kF2,where X^ is the Fourier transform of X along three dimensions and blkdiagX is the block diagonal matrix. In the CSC model, the size of each feature map is almost the same as X. The reconstructed X is obtained by summing the convolution output. Compared with linear representation, convolution dictionary can obtain translation invariant features and improve the model’s efficiency.


### 2.3.3. Dictionary Pretraining

In this paper, the convolution dictionary is trained. To determine the best number of filters, this paper selects ten fruit pictures as the training set for pretraining, as shown in Figure5.Figure 5
Fruit training set.In this paper, several dictionaries with different filter numbers are trained with the training set, and then these dictionaries are used in Lena, pepper, and starfish test sets. The experimental results are shown in Figure6. It can be seen from Figure 7 that the number of filters with the best performance is 32. Therefore, this paper chooses to use the training set to train a dictionary containing 32 filters. Figure 8 shows the visual effects of three trained dictionaries.Figure 6
Complementary results of different algorithms with the missing rate of 70%.Figure 7
PSNR and SSIM values recovered by dictionaries with different filter numbers on the test set when the missing rate is set at 80%.Figure 8
(a) 32 filters trained with the fruit training set. (b) 32 filters trained with other MRI training sets. (c) Using Suzie data set to select 10 frames of images to train 32 filters. (a) Fruit. (b) MRI. (c) Suzie.
(a)(b)(c)


## 2.3.1. Plug-and-Play Framework

Equation (4) considers the recovery of the tensor’s global information with the tensor’s low rank, ignoring the recovery of the details. Due to the loss of a large amount of detailed information, many composite algorithms have additional a priori information to optimize and improve the lost detailed information. Therefore, in addition to relying on the low-rank prior information of tensor, additional regular priors are often added to the LRTC model to improve the detail of local features.To solve the nondifferentiable problem of many regularization operators, some approximate algorithms have appeared in recent two decades to solve the problem of regularized image denoising. The plug-and-play (PNP) framework has become a hot topic [41]. Research shows that any ready-made denoising method can be directly used as a priori, rather than the steps in the solution to calculate the proximal operator of the specified regularization [42]. In the process of solving, there are usually the following subproblem:(5)ProxΦy=argminXρ2x−y22+λΦx,where Pro refers to a function in Python, ρ=n3n4…nN (nN is the pixels of Nth dimensional tensor), and λ>0 is the trade-off parameter.Takingy as a noisy image, the above problem can be regarded as a denoising problem. Given the regularization formula, Φx here is a corresponding denoiser to deal with the denoising problem. This paper adds convolutional sparse coding based on the LRTC model as regular a priori.


## 2.3.2. Convolutional Sparse Coding

With the development of optical fiber sensing technology, using optical fiber sensing to obtain image resources has become a way of information transmission. However, the image obtained by optical fiber sensing may be damaged in acquisition. The emergence of sparse coding (SC) has achieved great success in image restoration. In 2010, Zeiler et al. [43] proposed convolutional sparse coding (CSC) based on traditional sparse coding. Convolutional sparse coding uses a set of filters (also known as dictionaries) to convolute with their corresponding feature maps, and the convolution sum between them replaces the general linear representation. CSC decomposes the input image into n sparse feature maps through n filters rather than representing a vector sparsely through a linear combination of dictionaries.CSC has been used in many projects to extract features from images for object recognition [44], but the performance of CSC in tensor completion has not been explored. The high-frequency part often contains more important details than the low-frequency part. Therefore, it is a feasible choice to optimize the high-frequency part alone. In this paper, CSC is regarded as a priori. Instead of decomposing the signal vector into the product of dictionary matrix and coding vector, CSC represents the image as the convolution sum of feature map and corresponding filter, that is,(6)argminX^1ρblkdiagX^∗+12X^−X^k+1+Q^kF2,where X^ is the Fourier transform of X along three dimensions and blkdiagX is the block diagonal matrix. In the CSC model, the size of each feature map is almost the same as X. The reconstructed X is obtained by summing the convolution output. Compared with linear representation, convolution dictionary can obtain translation invariant features and improve the model’s efficiency.


## 2.3.3. Dictionary Pretraining

In this paper, the convolution dictionary is trained. To determine the best number of filters, this paper selects ten fruit pictures as the training set for pretraining, as shown in Figure5.Figure 5
Fruit training set.In this paper, several dictionaries with different filter numbers are trained with the training set, and then these dictionaries are used in Lena, pepper, and starfish test sets. The experimental results are shown in Figure6. It can be seen from Figure 7 that the number of filters with the best performance is 32. Therefore, this paper chooses to use the training set to train a dictionary containing 32 filters. Figure 8 shows the visual effects of three trained dictionaries.Figure 6
Complementary results of different algorithms with the missing rate of 70%.Figure 7
PSNR and SSIM values recovered by dictionaries with different filter numbers on the test set when the missing rate is set at 80%.Figure 8
(a) 32 filters trained with the fruit training set. (b) 32 filters trained with other MRI training sets. (c) Using Suzie data set to select 10 frames of images to train 32 filters. (a) Fruit. (b) MRI. (c) Suzie.
(a)(b)(c)


## 2.4. Establishment of the LRTC-CSC Model

This paper attempts to use the low-rank a priori and convolution dictionary to learn the a priori interaction model, to give full play to their respective advantages. By combining TNN regular term with CSC regular term, the new model proposed in this paper is LRTC-CSC.(7)arg.minXXTNN+λΦX,s.t.XΩ=TΩ,where ΦX is the canonical a priori of CSC and λ is the trade-off parameter. Constraint XΩ=TΩ can be written as(8)minPx=0,XΩ=TΩ,￥,other.Therefore, objective function equation (7) can be rewritten as follows:(9)arg.minXXTNN+λΦX+PX.


## 3. Numerical Experiment

### 3.1. HaLRTC Model

HaLRTC (high-accuracy low-rank tensor completion) model [45] is a classical model proposed by Liu et al. It mainly uses trace norm (SNN) to constrain the rank, and it uses relaxation technology to separate the constraints between variables. It has used the ADMM algorithm to solve problems with the optimal global solution. The objective function is(10)minX,L1,M,Ln∑i=1nαiMi∗,s.t:XΩ=TΩX=Mi,i=1,L,n.After introducing auxiliary variables and rewriting Lagrange multipliery into augmented Lagrange Lp, ADMM is solved.


### 3.2. LRTC-TNN Model

LRTC-TNN model mainly adopts TNN regularization [40] to approximate the matrix rank, and the objective function is(11)minXX∗,s.t:X^−Z^=0.After introducing auxiliary variables and rewriting Lagrange multipliery into augmented Lagrange Lp, ADMM is solved.


### 3.3. LRTC-TV Model

LRTC-TV model [46] introduces the total variation (TV) regularization term to recover the local information of the image. TV regularization follows the anisotropic version, which is easy to optimize, and it is more flexible in applying piecewise smoothing priority to different modes. The model without regularization term degenerates into the HaLRTC model. The objective function is(12)minNλn=1NβnFnZn+1Nn=1NZn∗.After introducing auxiliary variablesQn=FnRn,Mn=Zn, Rn=Zn and Lagrange multipliers Λnn=1N,Φnn=1N and Γnn=1N and rewriting them as augmented Lagrange Lp, ADMM solution is carried out.


### 3.4. Evaluation Indicators

This paper mainly uses peak signal-to-noise ratio and structural similarity as quantitative indicators of good or bad models.


#### 3.4.1. Peak Signal-to-Noise Ratio

Peak signal-to-noise ratio (PSNR) [47] is a widely used objective measurement method for evaluating picture quality. PSNR is often used to measure signal reconstruction quality in fields such as image compression, and since the tensor is three-dimensional data, relative error (RE) is used to define it. The relative error is calculated as(13)RE=X−TFTF.Then, the PSNR is calculated as follows:(14)PSNR=10log10n1n2n3TF2X−TF2,where T denotes the original image, X denotes the recovered image, and TF represents the maximum pixel value of the original image.


#### 3.4.2. Structural Similarity

Structural similarity [48] (SSIM) measures the similarity of two images. The SSIM formula is dependent on three comparative measures between samples x and y: luminance, contrast, and structure. The formulae are as follows:(15)lx,y=2μxμy+c1μx2+μy2+c1,cx,y=2σxσy+c2σx2+σy2+c2,sx,y=σxy+c3σxσy+c3.Generally,c3 = c2/2; μx, μy is the mean of x, y; σx2, σy2 is the variance of x, y and is the covariance of x, y; c1 = (k1L)2, c2 = (k2L)2 are two constants, where k1 = 0.01 and k2 = 0.03 are the default values; and L is the range of pixel values. So, there is(16)SSIMx,y=2μxμy+c12σxσy+c2μx2+μy2+c1σx2+σy2+c2.The range of structural similarity is from −1 to 1. The value of SSIM is 1 when the two images are the same.


## 3.1. HaLRTC Model

HaLRTC (high-accuracy low-rank tensor completion) model [45] is a classical model proposed by Liu et al. It mainly uses trace norm (SNN) to constrain the rank, and it uses relaxation technology to separate the constraints between variables. It has used the ADMM algorithm to solve problems with the optimal global solution. The objective function is(10)minX,L1,M,Ln∑i=1nαiMi∗,s.t:XΩ=TΩX=Mi,i=1,L,n.After introducing auxiliary variables and rewriting Lagrange multipliery into augmented Lagrange Lp, ADMM is solved.


## 3.2. LRTC-TNN Model

LRTC-TNN model mainly adopts TNN regularization [40] to approximate the matrix rank, and the objective function is(11)minXX∗,s.t:X^−Z^=0.After introducing auxiliary variables and rewriting Lagrange multipliery into augmented Lagrange Lp, ADMM is solved.


## 3.3. LRTC-TV Model

LRTC-TV model [46] introduces the total variation (TV) regularization term to recover the local information of the image. TV regularization follows the anisotropic version, which is easy to optimize, and it is more flexible in applying piecewise smoothing priority to different modes. The model without regularization term degenerates into the HaLRTC model. The objective function is(12)minNλn=1NβnFnZn+1Nn=1NZn∗.After introducing auxiliary variablesQn=FnRn,Mn=Zn, Rn=Zn and Lagrange multipliers Λnn=1N,Φnn=1N and Γnn=1N and rewriting them as augmented Lagrange Lp, ADMM solution is carried out.


## 3.4. Evaluation Indicators

This paper mainly uses peak signal-to-noise ratio and structural similarity as quantitative indicators of good or bad models.


### 3.4.1. Peak Signal-to-Noise Ratio

Peak signal-to-noise ratio (PSNR) [47] is a widely used objective measurement method for evaluating picture quality. PSNR is often used to measure signal reconstruction quality in fields such as image compression, and since the tensor is three-dimensional data, relative error (RE) is used to define it. The relative error is calculated as(13)RE=X−TFTF.Then, the PSNR is calculated as follows:(14)PSNR=10log10n1n2n3TF2X−TF2,where T denotes the original image, X denotes the recovered image, and TF represents the maximum pixel value of the original image.


### 3.4.2. Structural Similarity

Structural similarity [48] (SSIM) measures the similarity of two images. The SSIM formula is dependent on three comparative measures between samples x and y: luminance, contrast, and structure. The formulae are as follows:(15)lx,y=2μxμy+c1μx2+μy2+c1,cx,y=2σxσy+c2σx2+σy2+c2,sx,y=σxy+c3σxσy+c3.Generally,c3 = c2/2; μx, μy is the mean of x, y; σx2, σy2 is the variance of x, y and is the covariance of x, y; c1 = (k1L)2, c2 = (k2L)2 are two constants, where k1 = 0.01 and k2 = 0.03 are the default values; and L is the range of pixel values. So, there is(16)SSIMx,y=2μxμy+c12σxσy+c2μx2+μy2+c1σx2+σy2+c2.The range of structural similarity is from −1 to 1. The value of SSIM is 1 when the two images are the same.


## 3.4.1. Peak Signal-to-Noise Ratio

Peak signal-to-noise ratio (PSNR) [47] is a widely used objective measurement method for evaluating picture quality. PSNR is often used to measure signal reconstruction quality in fields such as image compression, and since the tensor is three-dimensional data, relative error (RE) is used to define it. The relative error is calculated as(13)RE=X−TFTF.Then, the PSNR is calculated as follows:(14)PSNR=10log10n1n2n3TF2X−TF2,where T denotes the original image, X denotes the recovered image, and TF represents the maximum pixel value of the original image.


## 3.4.2. Structural Similarity

Structural similarity [48] (SSIM) measures the similarity of two images. The SSIM formula is dependent on three comparative measures between samples x and y: luminance, contrast, and structure. The formulae are as follows:(15)lx,y=2μxμy+c1μx2+μy2+c1,cx,y=2σxσy+c2σx2+σy2+c2,sx,y=σxy+c3σxσy+c3.Generally,c3 = c2/2; μx, μy is the mean of x, y; σx2, σy2 is the variance of x, y and is the covariance of x, y; c1 = (k1L)2, c2 = (k2L)2 are two constants, where k1 = 0.01 and k2 = 0.03 are the default values; and L is the range of pixel values. So, there is(16)SSIMx,y=2μxμy+c12σxσy+c2μx2+μy2+c1σx2+σy2+c2.The range of structural similarity is from −1 to 1. The value of SSIM is 1 when the two images are the same.


## 4. Experiment

### 4.1. Color Images

According to the developed model, six color images in the test set were firstly subjected to different degrees of random missing, and the missing ratio (MR) was 70%, 80%, and 90%, respectively. Under the same conditions, the proposed model and the other three models are applied to color image completion.The PSNR and SSIM values of the six color images recovered by different algorithms are given in Table1. It can be seen that the LRTC-TNN method is generally better than the SNN-based HaLRTC method. Compared with the model without regularization, LRTC-TV with TV regularization is a better-recovered model, indicating that the addition of the regularization term is effective in image recovery. The performance of LRTC-TV is second only to the model proposed in this paper. Because the LRTC-CSC model uses a dictionary trained on the fruit data set and has a more considerable lead on color images similar to peppers and fruits, it can recover these two data better. In addition, when the loss rate is 90%, it is difficult for other algorithms to maintain stable SSIM values, but LRTC-CSC is still at a high level.Table 1
Evaluation results of different algorithms for complementary color images.
ImageMR (%)PSNRSSIMHaLRTCTTNTVCSCHaLRTCTTNTVCSCAirplane 256 × 256 × 37025.2125.4926.5530.050.6580.6220.9130.9458022.7022.9124.1327.370.5410.4910.8580.9139019.5419.7620.9623.920.3670.2910.7450.848Peppers 256 × 256 × 37024.0323.5426.8631.720.9340.9700.9690.9868020.7020.5025.5428.310.8230.9500.9450.9759016.9216.7520.2423.960.7590.8910.8710.936Fruits 256 × 256 × 37024.0824.3026.8130.360.8750.8640.9480.9728021.6521.7924.8927.590.8170.7960.9210.9499018.2218.4021.6923.760.7160.6580.8610.901Starfish 256 × 256 × 37023.6824.4126.1829.780.9070.8990.9590.9768020.9121.1723.5526.750.8480.8260.9270.9589017.2017.5420.1922.630.7320.6800.8800.907Lena 256 × 256 × 37025.5925.8627.6932.030.9480.9460.9670.9858022.8223.0325.8429.000.9130.9040.9510.9729019.2619.4722.2925.340.8450.8130.9100.943House 256 × 256 × 37027.3027.8328.4533.000.9230.9150.9560.9748024.2224.5726.5330.720.8610.8410.9320.9609020.6020.6222.5026.490.7280.6640.8610.915Taking airplane images with different deletion rates as an example, we visualized the experimental results as shown in Figure9, and it can be intuitively observed that the model in this paper is better than other models in restoring the same noisy image.Figure 9
Curves of image recovery results of different algorithms at different deletion rates.Figure6 shows the results of color image recovery by four different models with a 70% missing rate, and the details of the image are marked with marker boxes and placed on the image with 2 times magnification. For example, in the case of the airplane, the LRTC-CSC model can clearly show the “F16” marker; for peppers, the model in this paper can recover the details of the pepper vine stalk. This paper shows the superiority of CSC a priori through the actual image recovery effect.


### 4.2. MRI Images

In this paper, MRI image data of 181 × 217 × 30 were brought into the model, and MRI image data were recovered by different algorithms. The visualization of PSNR value and SSIM value recovered by the HaLRTC model, LRTC-TNN model, LRTC-TV model, and LRTC-CSC model under different wavebands is shown in Figure10. It can be seen numerically that the model in this paper is far stronger than other models in recovering MRI image data. The average value of the model in this paper is 4.0–7.5 dB higher than that of other models. However, the HaLRTC model and LRTC-TV model are based on SNN prior algorithm, and their recovery effect is more stable in the first and last images. However, the LRTC-TNN model and LRTC-CSC model are algorithms based on TNN prior, and they have the same trend of change, but the processing effect of front and rear sections is worse.Figure 10
Curves of MRI image recovery results of different algorithms at different wavebands.Same as the color image processing process, this paper used different models to recover MRI image data at 70%, 80%, and 90% missing rates, respectively, and the extracted 30th band of the recovered MRI image data is shown in Figure11. The image recovery effect proves the superiority of the LRTC-CSC model. Although the ability of TNN as a canonical in recovering the last few bands is not strong, its recovery of details is still much higher than that of the LRTC-TV algorithm.Figure 11
Complementary results of different algorithms for the 30th band MRI with 70%, 80%, and 90% missing rate.


### 4.3. Video Images

As with the MRI data, the Suzie data set of size 144 × 176 × 150 is used as the test set for this paper, and 30 consecutive frames are selected to demonstrate the effect of image recovery. The visualized images of PSNR and SSIM values recovered by the HaLRTC model, LRTC-TNN model, LRTC-TV model, and LRTC-CSC model at different frames of the video at a 90% missing rate are shown in Figure12. Although the average PSNR values of this model are 4.0–7.0 dB higher than the other models at 90% missing rate, the data in Figure 12 demonstrate that the LRTC-CSC model is significantly more efficient in detailed processing than the other models. This again proves the merits of the present model.Figure 12
Curves of video image recovery results of different algorithms at different frames.From Figure12, it can be seen that TNN has a clear advantage in processing data with large dimensionality and continuous changes. The model effects are ranked in order of LRTC-CSC, LRTC-TNN, LRTC-TV, and HaLRTC, but TNN has obvious drawbacks when processing the first 1-2 frontal slices and the last 1-2 frontal slices. But in general, the images recovered by TNN are better than those recovered by SNN. In this paper, the recovery effect of video images is demonstrated at a missing rate of 90%, and the effect images of the 5th, 10th, 15th, 20th, 25th, and 30th frames are extracted, which are shown in Figure 13.Figure 13
Complementary results of different algorithms for frames 5, 10, 15, 20, 25, and 30 of the video with a 90% missing rate.


### 4.4. Convergence Analysis

The algorithm in this paper will stop iterating when the relative change of variablesXk−XFk−1/TF<10−5. Numerical experiments show that the LRTC-CSC model has significant performance, and the CSC canonical is applied as a plug-and-play framework to the low-rank tensor complementation model in this paper, which makes the recovery of the model greatly improved.Although the plug-and-play framework has been widely proven to be effective, it is still an open question whether it can carry a convex model with good convergence. To demonstrate the convergence of the numerical algorithm, Figure14 shows the convergence behavior of the color image iterations at MR = 70%. In this paper, the peak signal-to-noise ratio (PSNR) and relative error (RE) curves of the images are used to measure the convergence of the algorithm. The results show that the proposed algorithm can converge well on different images and improve their PSNR.Figure 14
Color image convergence behavior-changing curve.


## 4.1. Color Images

According to the developed model, six color images in the test set were firstly subjected to different degrees of random missing, and the missing ratio (MR) was 70%, 80%, and 90%, respectively. Under the same conditions, the proposed model and the other three models are applied to color image completion.The PSNR and SSIM values of the six color images recovered by different algorithms are given in Table1. It can be seen that the LRTC-TNN method is generally better than the SNN-based HaLRTC method. Compared with the model without regularization, LRTC-TV with TV regularization is a better-recovered model, indicating that the addition of the regularization term is effective in image recovery. The performance of LRTC-TV is second only to the model proposed in this paper. Because the LRTC-CSC model uses a dictionary trained on the fruit data set and has a more considerable lead on color images similar to peppers and fruits, it can recover these two data better. In addition, when the loss rate is 90%, it is difficult for other algorithms to maintain stable SSIM values, but LRTC-CSC is still at a high level.Table 1
Evaluation results of different algorithms for complementary color images.
ImageMR (%)PSNRSSIMHaLRTCTTNTVCSCHaLRTCTTNTVCSCAirplane 256 × 256 × 37025.2125.4926.5530.050.6580.6220.9130.9458022.7022.9124.1327.370.5410.4910.8580.9139019.5419.7620.9623.920.3670.2910.7450.848Peppers 256 × 256 × 37024.0323.5426.8631.720.9340.9700.9690.9868020.7020.5025.5428.310.8230.9500.9450.9759016.9216.7520.2423.960.7590.8910.8710.936Fruits 256 × 256 × 37024.0824.3026.8130.360.8750.8640.9480.9728021.6521.7924.8927.590.8170.7960.9210.9499018.2218.4021.6923.760.7160.6580.8610.901Starfish 256 × 256 × 37023.6824.4126.1829.780.9070.8990.9590.9768020.9121.1723.5526.750.8480.8260.9270.9589017.2017.5420.1922.630.7320.6800.8800.907Lena 256 × 256 × 37025.5925.8627.6932.030.9480.9460.9670.9858022.8223.0325.8429.000.9130.9040.9510.9729019.2619.4722.2925.340.8450.8130.9100.943House 256 × 256 × 37027.3027.8328.4533.000.9230.9150.9560.9748024.2224.5726.5330.720.8610.8410.9320.9609020.6020.6222.5026.490.7280.6640.8610.915Taking airplane images with different deletion rates as an example, we visualized the experimental results as shown in Figure9, and it can be intuitively observed that the model in this paper is better than other models in restoring the same noisy image.Figure 9
Curves of image recovery results of different algorithms at different deletion rates.Figure6 shows the results of color image recovery by four different models with a 70% missing rate, and the details of the image are marked with marker boxes and placed on the image with 2 times magnification. For example, in the case of the airplane, the LRTC-CSC model can clearly show the “F16” marker; for peppers, the model in this paper can recover the details of the pepper vine stalk. This paper shows the superiority of CSC a priori through the actual image recovery effect.


## 4.2. MRI Images

In this paper, MRI image data of 181 × 217 × 30 were brought into the model, and MRI image data were recovered by different algorithms. The visualization of PSNR value and SSIM value recovered by the HaLRTC model, LRTC-TNN model, LRTC-TV model, and LRTC-CSC model under different wavebands is shown in Figure10. It can be seen numerically that the model in this paper is far stronger than other models in recovering MRI image data. The average value of the model in this paper is 4.0–7.5 dB higher than that of other models. However, the HaLRTC model and LRTC-TV model are based on SNN prior algorithm, and their recovery effect is more stable in the first and last images. However, the LRTC-TNN model and LRTC-CSC model are algorithms based on TNN prior, and they have the same trend of change, but the processing effect of front and rear sections is worse.Figure 10
Curves of MRI image recovery results of different algorithms at different wavebands.Same as the color image processing process, this paper used different models to recover MRI image data at 70%, 80%, and 90% missing rates, respectively, and the extracted 30th band of the recovered MRI image data is shown in Figure11. The image recovery effect proves the superiority of the LRTC-CSC model. Although the ability of TNN as a canonical in recovering the last few bands is not strong, its recovery of details is still much higher than that of the LRTC-TV algorithm.Figure 11
Complementary results of different algorithms for the 30th band MRI with 70%, 80%, and 90% missing rate.


## 4.3. Video Images

As with the MRI data, the Suzie data set of size 144 × 176 × 150 is used as the test set for this paper, and 30 consecutive frames are selected to demonstrate the effect of image recovery. The visualized images of PSNR and SSIM values recovered by the HaLRTC model, LRTC-TNN model, LRTC-TV model, and LRTC-CSC model at different frames of the video at a 90% missing rate are shown in Figure12. Although the average PSNR values of this model are 4.0–7.0 dB higher than the other models at 90% missing rate, the data in Figure 12 demonstrate that the LRTC-CSC model is significantly more efficient in detailed processing than the other models. This again proves the merits of the present model.Figure 12
Curves of video image recovery results of different algorithms at different frames.From Figure12, it can be seen that TNN has a clear advantage in processing data with large dimensionality and continuous changes. The model effects are ranked in order of LRTC-CSC, LRTC-TNN, LRTC-TV, and HaLRTC, but TNN has obvious drawbacks when processing the first 1-2 frontal slices and the last 1-2 frontal slices. But in general, the images recovered by TNN are better than those recovered by SNN. In this paper, the recovery effect of video images is demonstrated at a missing rate of 90%, and the effect images of the 5th, 10th, 15th, 20th, 25th, and 30th frames are extracted, which are shown in Figure 13.Figure 13
Complementary results of different algorithms for frames 5, 10, 15, 20, 25, and 30 of the video with a 90% missing rate.


## 4.4. Convergence Analysis

The algorithm in this paper will stop iterating when the relative change of variablesXk−XFk−1/TF<10−5. Numerical experiments show that the LRTC-CSC model has significant performance, and the CSC canonical is applied as a plug-and-play framework to the low-rank tensor complementation model in this paper, which makes the recovery of the model greatly improved.Although the plug-and-play framework has been widely proven to be effective, it is still an open question whether it can carry a convex model with good convergence. To demonstrate the convergence of the numerical algorithm, Figure14 shows the convergence behavior of the color image iterations at MR = 70%. In this paper, the peak signal-to-noise ratio (PSNR) and relative error (RE) curves of the images are used to measure the convergence of the algorithm. The results show that the proposed algorithm can converge well on different images and improve their PSNR.Figure 14
Color image convergence behavior-changing curve.


## 5. Conclusion

This paper focuses on the kernel parametric-based low-rank tensor complementation method and its application in the restoration process of actual visual data. Additional CSC priors are added to recover the details from the images, and the convolutional sparse coding is combined with the traditional low-rank tensor complementation model. It is demonstrated that the CSC prior requires only a small number of training samples, which saves much time compared with other priors. At the same time, the recovery effect is much higher than the novel TV regular prior, especially the PSNR value of the LRTC-CSC model is 5.18 dB higher than that of the LRTC-TV model for MRI image recovery at a 70% missing rate, and the model in this paper is convergent.This paper proposes that convolutional sparse coding is realistic, and its superiority is evident. In the future, the model of this paper can be applied to more fields, and the model can be continuously optimized to achieve better results.



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*Source: 8194834-2022-09-05.xml*