Representation-based Classification Method Research Articles

Locality-Constraint Discriminative Nonnegative Representation for Pattern Classification

Representation-based classification methods (RBCM) have recently garnered notable attention in the field of pattern classification. Diverging from conventional methods reliant on ℓ1 or ℓ2-norms, the nonnegative representation-based classifier (NRC) enforces a nonnegative constraint on the representation vector, thus enhancing the representation capabilities of positively correlated samples. While NRC has achieved substantial success, it falls short in fully harnessing the discriminative information associated with the training samples and neglects the locality constraint inherent in the sample relationships, thereby limiting its classification power. In response to these limitations, we introduce the locality-constraint discriminative nonnegative representation (LDNR) method. LDNR extends the NRC framework through the incorporation of a competitive representation term. Recognizing the pivotal role played by the estimated samples in the classification process, we include estimated samples that involve discriminative information in this term, establishing a robust connection between representation and classification. Additionally, we assign distinct local weights to different estimated samples, augmenting the representation capacity of homogeneous samples and, ultimately, elevating the performance of the classification model. To validate the effectiveness of LDNR, extensive comparative experiments are conducted on various pattern classification datasets. The findings demonstrate the competitiveness of our proposed method.

A fast dictionary-learning-based classification scheme using undercomplete dictionaries

In dictionary-learning-based classification methods, a given data point is classified based on its representation over one or possibly more learned dictionaries. The goal is to find dictionaries that minimize the classification error. Previous works aimed to train dictionaries with representation and classification powers by using overcomplete dictionaries and sparse coding. These approaches are computationally expensive and do not scale readily to problems with high dimensional data. This paper presents a dictionary-learning-based classification method with the primary goal of classification and not representation. We propose to train multiple undercomplete dictionaries (one for each class of the problem). Each dictionary approximates the given test data, and the one with the lowest reconstruction error determines the class. Singular value decomposition (SVD) is used to obtain a straightforward algorithm for the resulted optimization problem. Simulation results show that our method achieves a higher accuracy compared with a number of successful sparse representation based classification methods, while having a significantly lower computational cost.

Recognition of Continuous Face Occlusion Based on Block Permutation by Using Linear Regression Classification

Face occlusion is still a key issue in the study of face recognition. Continuous occlusion affects the overall features and contour structure of a face, which brings significant challenges to face recognition. In previous studies, although the Representation-Based Classification Method (RBCM) can better capture the differences in different categories of faces and accurately identify human face images with changes in light and facial expressions, it is easily affected by continuous occlusion. For face recognition, there is a situation where face error recognition occurs. The RBCM method frequently learns to cover the characteristics of face recognition and then handle face error recognition. Therefore, the elimination of occlusion information from the image is necessary to improve the robustness of such models. The Block Permutation Linear Regression Classification (BPLRC) method proposed in this paper includes image block permutation and Linear Regression Classification (LRC). The LRC algorithm belongs to the category of nearest subspace classification and uses the Euclidean distance as a metric to classify images. The LRC algorithm is based on one of the classification methods that is susceptible to outliers. Therefore, block permutation was used with the aim of establishing an image set that does not contain much occlusion information and constructing a robust linear regression model. The BPLRC method first modulates all the images and then lists the schemes that arrange all segments, enters the image features of various schemes into linear models, and classifies the result according to the minimum residual of the person’s face image and reconstruction image. Compared to several state-of-the-art algorithms, the proposed method effectively solves the continuous occlusion problem for the Extended Yale B, ORL, and AR datasets. The proposed method recognizes the AR data concentration scarf to cover the accuracy of human face images to 93.67%. The dataset recognition speed is 0.094 s/piece. The arrangement method can be combined not only with the LRC algorithm, but also other algorithms with weak robustness. Due to the increase in the number of blocks and the increase in the calculation index of block arrangement methods, it is necessary to explore reasonable iteration methods in the future, quickly find the optimal or sub-best arrangement scheme, and reduce the calculation of the proposed method.

Kernelized discriminative–collaborative representation-based approach for pattern classification

In representation-based classification methods, Gaussian function is adopted for realizing the nonlinear representation of samples. However, there are some problems. The definition of Gaussian kernel includes exponential operation, which causes the parameters to be sensitive and consumes exponential computational time. In addition, the performance of pattern classification may be dropped with noise (outliers). To solve these problems, a new Euclidean Kernel is designed to replace Gaussian Kernel. Moreover, a new weight and an uncorrelated sparsity constraint are introduced to enhance within-class representation consistency and between-class representation discrepancy. Then, we propose a kernelized discriminative–collaborative representation-based approach for pattern classification by incorporating the cooperative and competitive representation. The proposed model fully excavates the intrinsic factors of the samples and presents promising performance and better interpretability. Finally, extensive experiments are conducted in comparison with other popular methods on different types of databases, and these experiments verify that the designed approach performs better than its competitors.

Margin embedding net for robust margin collaborative representation-based classification

Collaborative Representation-based Classification method (CRC) shows great potential in classification task. However, redundancies in both features and samples limit the application of CRC seriously. The existing works only solve one of them and ignore the other, which leads to performance degradation. To address this problem, we explore collaborative representation mechanism and propose a classification method termed Robust Margin Collaborative Representation-based Classification (RMCRC) which uses a few but more representative robust marginal samples to eliminate redundancy between samples. As the performance of RMCRC is related to robust marginal samples and class separability assumption closely, we further propose a feature extraction method termed Margin Embedding Net (MEN) for RMCRC. In MEN, virtual samples are generated by a generative model to enhance effectiveness of robust marginal samples and generalizability of RMCRC. Then, an embedding network with triplet loss is used to eliminate the redundancy in features and ensure the assumption is satisfied. Specifically, we construct triplet according to the collaborative representation. Hence, MEN fits RMCRC very well. Extensive experimental results validate effectiveness of proposed method.

Face Recognition Based on SRC Combined with Sparse Embedding Dimensionality Reduction

<p>Sparse representation-based classification (SRC) method has achieved good recognition results and shown strong robustness for face recognition, especially when the face image is affected by illumination variations, expression changes and occlusion. SRC method simply uses the training set as a dictionary to encode test samples. However, the high-dimensional training face data usually contain a large amount of redundant information, which will increase the complexity of this method. Therefore, the image dimensionality reduction procedure is separately performed by most of the existing methods before SRC is launched, but this may not be able to make full use of the discriminative information of the training samples. In this paper, based on the efficient SRC method, a sparse embedding dimensionality reduction strategy is combined with to achieve a face recognition method. For the proposed method, a projection matrix is used to project high-dimensional data into a low-dimensional space. At the same time, a discriminative coefficient constraint term in the objective function is introduced to reduce the classification residual of the sample through the distance relationship between all coefficients. Then the label information of the sample is used to iteratively update the projection matrix and coefficient representation. Finally, the test samples are projected into the low-dimensional space for classification. A large number of experimental results on three widely used face datasets show that the proposed method improves the discrimination of face images in low-dimensional space and can achieve better face recognition results.</p> <p> </p>

A class-specific mean vector-based weighted competitive and collaborative representation method for classification

Collaborative representation-based classification (CRC), as a typical kind of linear representation-based classification, has attracted more attention due to the effective and efficient pattern classification performance. However, the existing class-specific representations are not competitively learned from collaborative representation for achieving more informative pattern discrimination among all the classes. With the purpose of enhancing the power of competitive and discriminant representations among all the classes for favorable classification, we propose a novel CRC method called the class-specific mean vector-based weighted competitive and collaborative representation (CMWCCR). The CMWCCR mainly contains three discriminative constraints including the competitive, mean vector and weighted constraints that fully employ the discrimination information in different ways. In the competitive constraint, the representations from any one class and the other classes are adapted for learning competitive representations among all the classes. In the newly designed mean vector constraint, the mean vectors of all the class-specific training samples with the corresponding class-specific representations are taken into account to further enhance the competitive representations. In the devised weighted constraint, the class-specific weights are constrained on the representation coefficients to make the similar classes have more representation contributions to strengthening the discrimination among all the class-specific representations. Thus, these three constraints in the unified CMWCCR model can complement each other for competitively learning the discriminative class-specific representations. To verify the CMWCCR classification performance, the extensive experiments are conducted on twenty-eight data sets in comparisons with the state-of-the-art representation-based classification methods. The experimental results show that the proposed CMWCCR is an effective and robust CRC method with satisfactory performance.

Pairwise Elastic Net Representation-Based Classification for Hyperspectral Image Classification

The representation-based algorithm has raised a great interest in hyperspectral image (HSI) classification. -minimization-based sparse representation (SR) attempts to select a few atoms and cannot fully reflect within-class information, while -minimization-based collaborative representation (CR) tries to use all of the atoms leading to mixed-class information. Considering the above problems, we propose the pairwise elastic net representation-based classification (PENRC) method. PENRC combines the -norm and -norm penalties and introduces a new penalty term, including a similar matrix between dictionary atoms. This similar matrix enables the automatic grouping selection of highly correlated data to estimate more robust weight coefficients for better classification performance. To reduce computation cost and further improve classification accuracy, we use part of the atoms as a local adaptive dictionary rather than the entire training atoms. Furthermore, we consider the neighbor information of each pixel and propose a joint pairwise elastic net representation-based classification (J-PENRC) method. Experimental results on chosen hyperspectral data sets confirm that our proposed algorithms outperform the other state-of-the-art algorithms.

An enhanced sparse representation-based intelligent recognition method for planet bearing fault diagnosis in wind turbines

Fault diagnosis techniques are vital to the condition-based maintenance strategy of wind turbines, which enables the reliable and economical operation and maintenance for wind farms. Due to the complex kinematic mechanism and modulation characteristic, planet bearing is the most challenging component for fault diagnosis in wind turbine drivetrains. To address this challenge for planet bearing fault diagnosis, we propose an enhanced sparse representation-based intelligent recognition (ESRIR) method, which involves two stages of structured dictionary designs and intelligent fault recognition. In the first stage, the structured dictionary designs are achieved with the overlapping segmentation strategy, which exploits the strong periodic self-similarity and shift-invariance property in planet-bearing vibration signals to enhance the representation and discrimination power of ESRIR. In the second stage, the intelligent fault recognition of planet bearings is implemented with the sparsity-based diagnosis strategy utilizing the minimum sparse reconstruction error-based discrimination criterion. Finally, the applicability of ESRIR for planet bearing fault diagnosis has been validated with the wind turbine planetary drivetrain test rig, demonstrating that ESRIR yields the superior recognition accuracy of 100% and 99.9% for diagnosing three and four planet-bearing health states, respectively. Comparative studies show that ESRIR outperforms the deep convolution neural network and four classical sparse representation-based classification methods on the recognition performances and computation costs.

Discriminative Dictionary Learning-Based Sparse Classification Framework for Data-Driven Machinery Fault Diagnosis

Data-driven machinery fault diagnosis is important for smart industrial systems to guarantee safety and reliability. However, the conventional data-driven fault diagnosis methods rely on the expert-designed features, which greatly affect the diagnosis performances. Inspired by the sparse representation-based classification (SRC) methods which can learn discriminative sparse features adaptively, we propose a novel discriminative dictionary learning based sparse classification (DDL-SC) framework for data-driven machinery fault diagnosis. The DDL-SC framework can jointly learn a discriminative dictionary for sparse representation and an optimal linear classifier for pattern recognition, which bridges the gaps between two separate processes, dictionary learning and classifier training in traditional SRC methods. In the learning stage, to enhance the discriminability of dictionary learning, we introduce the discriminative sparse code error along with the reconstruction error and classification error into the optimization objective. In the recognition stage, we employ sparse codes of testing signals with respect to the learned discriminative dictionary as inputs of the learned classifier, and promote the recognition performance by connecting a binary hard thresholding operator with the classifier predictions. The effectiveness of DDL-SC is evaluated on the planetary bearing fault dataset and gearbox fault dataset, indicating that DDL-SC yields the recognition accuracies of 99.73% and 99.41%, respectively. Besides, the comparative studies prove the superiority of DDL-SC over several state-of-the-art methods for data-driven machinery fault diagnosis.

Discriminative non-negative representation based classifier for image recognition

During the past decade, representation based classification method has received considerable attention in the community of pattern recognition. The recently proposed non-negative representation based classifier achieved superb recognition results in diverse pattern classification tasks. Unfortunately, discriminative information of training data is not fully exploited in non-negative representation based classifier, which undermines its classification performance in practical applications. To address this problem, we introduce a decorrelation regularizer into the formulation of non-negative representation based classifier and propose a discriminative non-negative representation based classifier for pattern classification. The decorrelation regularizer is able to reduce the correlation of representation results of different classes, thus promoting the competition among them. Experimental results on benchmark datasets validate the efficacy of the proposed discriminative non-negative representation based classifier, and it can outperform some state-of-the-art deep learning based methods. The source code of our proposed discriminative non-negative representation based classifier is accessible at https://github.com/yinhefeng/DNRC .

Generalized and Discriminative Collaborative Representation for Multiclass Classification.

This article presents a generalized collaborative representation-based classification (GCRC) framework, which includes many existing representation-based classification (RC) methods, such as collaborative RC (CRC) and sparse RC (SRC) as special cases. This article also advances the GCRC theory by exploring theoretical conditions on the general regularization matrix. A key drawback of CRC and SRC is that they fail to use the label information of training data and are essentially unsupervised in computing the representation vector. This largely compromises the discriminative ability of the learned representation vector and impedes the classification performance. Guided by the GCRC theory, we propose a novel RC method referred to as discriminative RC (DRC). The proposed DRC method has the following three desirable properties: 1) discriminability: DRC can leverage the label information of training data and is supervised in both representation and classification, thus improving the discriminative ability of the representation vector; 2) efficiency: it has a closed-form solution and is efficient in computing the representation vector and performing classification; and 3) theory: it also has theoretical guarantees for classification. Experimental results on benchmark databases demonstrate both the efficacy and efficiency of DRC for multiclass classification.

A Hierarchical Discriminative Sparse Representation Classifier for EEG Signal Detection.

Classification of electroencephalogram (EEG) signal data plays a vital role in epilepsy detection. Recently sparse representation-based classification (SRC) methods have achieved the good performance in EEG signal automatic detection, by which the EEG signals are sparsely represented using a few active coefficients in the dictionary and classified according to the reconstruction criteria. However, most of SRC learn a linear dictionary for encoding, and cannot extract enough information and nonlinear relationship of data for classification. To solve this problem, a hierarchical discriminative sparse representation classification model (called HD-SRC) for EEG signal detection is proposed. Based on the framework of neural network, HD-SRC learns the hierarchical nonlinear transformation and maps the signal data into the nonlinear transformed space. Through incorporating this idea into label consistent K singular value decomposition (LC-KSVD) at the top layer of neural network, HD-SRC seeks discriminative representation together with dictionary, while minimizing errors of classification, reconstruction and discriminative sparse-code for pattern classification. By learning the hierarchical feature mapping and discriminative dictionary simultaneously, more discriminative information of data can be exploited. In the experiment the proposed model is evaluated on the Bonn EEG database, and the results show it obtains satisfactory classification performance in multiple EEG signal detection tasks.

Automatic Assessment for Severe Self-Reported Depressive Symptoms Using Speech Cues

Patients with severe depressive symptoms are exposed to high suicidal risk. Since assessing depressive symptoms is either implicated by variability among subjects and clinicians or by time-consuming procedures, it is difficult to do objectively and effortlessly. There is a need for automatic approaches to estimate them. Previous investigations on speech-based severity’s categorical assignment predominantly focused on distinguishing depressive disorders from healthy. This article presents an automatic assessment system of severe self-reported depressive symptoms (SSDSs) to classify speakers with severe depressive symptoms from normal and not so severe ones. First, modulation-domain spectral centroid mean (MSCM) features characterizing severe depressive symptoms are extracted. Subsequently, aiming at the problems of limited and imbalanced training data, we establish variance-weighted sum-to- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> constraint ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${H}$ </tex-math></inline-formula> is an adjustable parameter) collaborative representation-based classification (VWSC-CRC) method to exploit interclass separability between SSDS and non-SSDS. The proposed system (MSCM–VWSC-CRC) was evaluated on the small and imbalanced data set from AVEC2013 by dominant metrics, such as F1-score and area under the precision–recall curve (AU-PRC), as well as auxiliary indices, including specificity, recall (sensitivity), precision, accuracy, and area under the receiver operating characteristic curve (AU-ROC) as needed. The results exhibit a clear advantage over three important systems in the literature. The gains of this article are likely to lay the substantive groundwork to assist clinicians in automatically screening subjects with severe depressive symptoms so as to facilitate the diagnosis of the corresponding psychological disorders.

Block-wise weighted sparse representation-based classification

We present a block-wise weighted sparse representation-based classification (BW-SRC) method, an extension of sparse representation-based classification (SRC), useful when the input features can be treated in a block-wise manner. We apply the method, which extracts features (coefficients) embedded in a supervised scheme on three known datasets. We show that, depending on the blocks of features used, our method outperforms linear dictionary learning and sparse coding methods without learning a dictionary. As an additional advantage of our method, the input feature blocks are automatically given an interpretation based on their importance for their ease of representation.

Multiplication fusion of sparse and collaborative-competitive representation for image classification

Representation based classification methods have become a hot research topic during the past few years, and the two most prominent approaches are sparse representation based classification (SRC) and collaborative representation based classification (CRC). CRC reveals that it is the collaborative representation rather than the sparsity that makes SRC successful. Nevertheless, the dense representation of CRC may not be discriminative which will degrade its performance for classification tasks. To alleviate this problem to some extent, we propose a new method called sparse and collaborative-competitive representation based classification (SCCRC) for image classification. Firstly, the coefficients of the test sample are obtained by SRC and CCRC, respectively. Then the fused coefficient is derived by multiplying the coefficients of SRC and CCRC. Finally, the test sample is designated to the class that has the minimum residual. Experimental results on several benchmark databases demonstrate the efficacy of our proposed SCCRC. The source code of SCCRC is accessible at https://github.com/li-zi-qi/SCCRC .

Class-specific residual constraint non-negative representation for pattern classification

Representation-based classification methods (RBCM) remain one of the hottest topics in the community of pattern recognition, and the recently proposed non-negative representation-based classification (NRC) achieved impressive recognition results in various classification tasks. However, NRC ignores the relationship between the coding and classification stages. Moreover, there is no regularization term other than the reconstruction error term in the formulation of NRC, which may result in an unstable solution leading to misclassification. To overcome these drawbacks of NRC, we propose a class-specific residual constraint non-negative representation (CRNR) for pattern classification. CRNR introduces a class-specific residual constraint into the formulation of NRC, which encourages training samples from different classes to competitively represent the test sample. Based on the proposed CRNR, we develop a CRNR-based classifier (CRNRC) for pattern classification. Experimental results on several benchmark datasets demonstrate the superiority of CRNRC over conventional RBCM as well as the recently proposed NRC. Moreover, CRNRC works better than or comparable to some state-of-the-art deep approaches on diverse challenging pattern classification tasks.

Multivariate copula statistical model and weighted sparse classification for radar image target recognition

We propose in this paper a new method for targets recognition from radar images. To characterize the radar images, we adopt a statistical multivariate modeling using copula in the complex wavelet domain. For the recognition step, we investigate the weighted sparse representation-based classification (WSRC) method. To build the dictionary, the estimated copula parameters are stacked together in a matrix structure. In order to include the locality information of this dictionary for each unknown radar image to recognize, we affect weights for its atoms (columns). That is done by calculating the Kullback–Leibler divergence (KLD) between the multivariate copula parameters of training and test radar images. Finally, the unknown radar image is recognized through the SRC classifier. Several empirical results carried out on the SAR (synthetic aperture radar) and ISAR (inverse synthetic aperture radar) images demonstrate that the proposed method achieves high recognition rates and outperforms the remaining methods.

Weighted discriminative collaborative competitive representation for robust image classification

Collaborative representation-based classification (CRC) is a famous representation-based classification method in pattern recognition. Recently, many variants of CRC have been designed for many classification tasks with the good classification performance. However, most of them ignore the inter-class pattern discrimination among the class-specific representations, which is very critical for strengthening the pattern discrimination of collaborative representation (CR). In this article, we propose a novel CR approach for image classification, called weighted discriminative collaborative competitive representation (WDCCR). The proposed WDCCR designs the discriminative and competitive collaborative representation among all the classes by fully considering the class information. On the one hand, we incorporate two discriminative constraints into the unified WDCCR model. Both constraints are the competitive class-specific representation residuals and the pairs of class-specific representations for each query sample. On the other hand, the constraint of the weighted categorical representation coefficients is introduced into the proposed model for further enhancing the power of discriminative and competitive representation. In the weighted constraint, we assume that the different classes of each query sample should have less contribution to the representation with the small representation coefficients, and then two types of weight factors are designed to constrain the representation coefficients. Furthermore, the robust WDCCR (R-WDCCR) is proposed with l1-norm representation fidelity for recognizing noisy images. Extensive experiments on six image data sets demonstrate the effective and robust superiorities of the proposed WDCCR and R-WDCCR over the related state-of-the-art representation-based classification methods.

Score level fusion in representation-based classification method for face recognition

Recent years have witnessed the success of representation-based classification method (RBCM) in the domain of face recognition. Collaborative representation-based classification (CRC) and linear regression-based classification (LRC) are two representative approaches. CRC is a global representation method which uses all training samples to represent test samples and utilizes representation residuals to perform classification, whereas LRC is a local representation method which exploits training samples from each class to represent test samples. Related researches indicate that the combination of LRC and CRC can fully exploit the representation residuals produced by them, thus improving the performance of RBCM. However, the representation coefficients obtained by CRC usually contain negative values which may result in overfitting problem. Therefore, to solve this problem to some extent, the combination of LRC and non-negative least square-based classification (NNLSC) is proposed in this paper. Experimental results on benchmark face datasets show that the proposed method is superior to the combination of LRC and CRC and other state-of-the-art RBCMs. The source code of our proposed method is available at https://github.com/li-zi-qi/score-level-fusion-of-NNLS-and-LRC .