Sparse Representation For Image Prediction

Signal Processing, 2015

Motivated by the fact that the signals tend to have a representation biased towards their own classes, we propose a novel Sparse Representation-based Classifier (SRC) named Class Specific Sparse Representation-based Classifier (CSSRC), which incorporates the class information in the representation learning. Unlike the conventional SRC algorithms, CSSRC defines each class as a group and then impels these groups to compete for representing the test sample. To achieve such property, CSSRC imposes a L 1-norm constraint to the classes for compulsively selecting the most relevant classes and introduces a L 2-norm constraint to the samples belonging to the same class for making sure that all homogeneous samples can be sufficiently exploited for representation. Since CSSRC is a typical structure sparse representation issue, it can be efficiently solved by the convex optimization. Seven popular visual and audio signal databases are employed for evaluation. The results demonstrate its effectiveness in comparison with the state-of-the-art classifiers.

Ijcv, 1996

We study the problem of how to detect \interesting objects" appeared in a given image, I. Our approach is to treat it as a function approximation problem based on an over-redundant basis, and also account for occlusions, where the basis superposition principle is no longer valid. Since the basis (a library of image templates) is over-redundant, there are in nitely many ways to decompose I. We are motivated to select a sparse/compact representation of I, and to account for occlusions and noise. We then study a greedy and iterative \weighted L p Matching Pursuit" strategy, with 0 < p < 1. We use an L p result to compute a solution, select the best template, at each stage of the pursuit.

2012

Sparse representations account for most or all of the information of a signal by a linear combination of a few elementary signals called atoms, and have increasingly become recognized as providing high performance for applications as diverse as noise reduction, compression, inpainting, compressive sensing, pattern classification, and blind source separation. In this dissertation, we learn the sparse representations of high-dimensional signals for various learning and vision tasks, including image classification, single image super-resolution, compressive sensing, and graph learning. Based on the bag-of-features (BoF) image representation in a spatial pyramid, we first transform each local image descriptor into a sparse representation, and then these sparse representations are summarized into a fixed-length feature vector over different spatial locations across different spatial scales by max pooling. The proposed generic image feature representation properly handles the large in-class variance problem in image classification, and experiments on object recognition, scene classification, face recognition, gender recognition, and handwritten digit recognition all lead to state-of-the-art performances on the benchmark datasets. We cast the image super-resolution problem as one of recovering a highresolution image patch for each low-resolution image patch based on recent sparse signal recovery theories, which state that, under mild conditions, a high-resolution signal can be recovered from its low-resolution version if the signal has a sparse representation in terms of some dictionary. We jointly learn the dictionaries for high-and low-resolution image patches and enforce them to have common sparse representations for better recovery. Furthermore, we employ image features and enforce patch overlapping constraints to improve prediction accuracy. Experiments show that the algorithm leads to surprisingly good results. Graph construction is critical for those graph-orientated algorithms designed for the purposes of data clustering, subspace learning, and semi-supervised learning. We model the graph construction problem, including neighbor selection and First, I would like to express profound gratitude to my adviser Professor Thomas Huang for all the guidance, advice, and support he has given me during my Ph.D. study at UIUC. For the last five and half years, I have been inspired by his vision and passion to research, his attention and curiosity to details, his dedication to the profession, his intense commitment to his work, and his humble and respectful personality. During this most important period in my career, I thoroughly enjoyed working with him, and what I have learned from him will benefit me for my whole life. I also would like to give my thanks to Professor Yi Ma for his suggestions and support for the last several years. I was deeply impressed and inspired by his passion and insights into research. I also feel very lucky to have had the chance to work with Dr. Kai Yu as a summer intern at NEC Laboratories America. From him, I learned not only techniques and skills but also his precious research insights. I am also very thankful to Professor Narendra Ahuja and Professor Zhi-Pei Liang for their advice and comments. I am fortunate to have them as my thesis committee members. During my Ph.D. study over the last five years, it has been a great honor for me to collaborate with Hasegawa-Johnson at UIUC, Professor Shuicheng Yan at

In this paper, application of sparse representation (factorization) of signals over an overcomplete basis (dictionary) for signal classification is discussed. Searching for the sparse representation of a signal over an overcomplete dictionary is achieved by optimizing an objective function that includes two terms: one that measures the signal reconstruction error and another that measures the sparsity. This objective function works well in applications where signals need to be reconstructed, like coding and denoising. On the other hand, discriminative methods, such as linear discriminative analysis (LDA), are better suited for classification tasks. However, discriminative methods are usually sensitive to corruption in signals due to lacking crucial properties for signal reconstruction. In this paper, we present a theoretical framework for signal classification with sparse representation. The approach combines the discrimination power of the discriminative methods with the reconstruction property and the sparsity of the sparse representation that enables one to deal with signal corruptions: noise, missing data and outliers. The proposed approach is therefore capable of robust classification with a sparse representation of signals. The theoretical results are demonstrated with signal classification tasks, showing that the proposed approach outperforms the standard discriminative methods and the standard sparse representation in the case of corrupted signals.

The sparse representation-based classification algorithm has been used for human face recognition. But an image database was restricted to human frontal faces with only slight illumination and expression changes. Cropping and normalization of the face needs to be done beforehand. This paper uses a sparse representation-based algorithm for generic image classification with some intra-class variations and background clutter. A hierarchical framework based on the sparse representation is developed which flexibly combines different global and local features. Experiments with the hierarchical framework on 25 object categories selected from the Caltech101 dataset show that exploiting the advantage of local features with the hierarchical framework improves the classification performance and that the framework is robust to image occlusions, background clutter, and viewpoint changes.

The goal in sparse coding is to seek a linear basis representation where each image is represented by a small number of active coefficients. The learning algorithm involves adapting a basis vector set while imposing a low-entropy, or sparse, prior on the output coefficients. Sparse coding applied on natural images has been shown to extract wavelet-like structure [9, 4]. However, our experience in using sparse coding for extracting multi-scale structure in object-specific ensembles, such as face images or images of a gesturing hand, has been negative. In this paper we highlight three points about the reliability of sparse coding for extracting the desired structure:´½µ using an overcomplete representation´¾µ projecting data into a low-dimensional subspace before attempting to resolve the sparse structure and´¿µ applying sparsity constraint on the basis elements, as opposed to the output coefficients.

Sparse representations with learned dictionaries have been successful in several image analysis applications. In this paper, we propose and analyze the framework of ensemble sparse models, and demonstrate their utility in image restoration and unsupervised clustering. The proposed ensemble model approximates the data as a linear combination of approximations from multiple weak sparse models. Theoretical analysis of the ensemble model reveals that even in the worst-case, the ensemble can perform better than any of its constituent individual models. The dictionaries corresponding to the individual sparse models are obtained using either random example selection or boosted approaches. Boosted approaches learn one dictionary per round such that the dictionary learned in a particular round is optimized for the training examples having high reconstruction error in the previous round. Results with compressed recovery show that the ensemble representations lead to a better performance compared to using a single dictionary obtained with the conventional alternating minimization approach. The proposed ensemble models are also used for single image superresolution, and we show that they perform comparably to the recent approaches. In unsupervised clustering, experiments show that the proposed model performs better than baseline approaches in several standard datasets.

2018

We consider the problem of classifier design via sparse representation based on a constrained subspace model. We argue that the data points in the linear span of the training samples should be constrained in order to yield a more accurate approximation to the corresponding data manifold. For this purpose, the constrained set of data points is formulated as a union of affine subspaces in the form of affine hulls spanned by training samples. We argue that the intrinsic dimension of the affine subspaces should be equal to that of data manifold. Thus, a classifier based on this model has a high classification accuracy similar to that of the conceptual NM (Nearest Manifold) classifier. Based on this model, we connect the dots of some classical classifiers including NN (Nearest Neighbor), NFL (Nearest Feature Line), NS (Nearest subspace) and the recently emerged state-of-the-art SRC (Sparse Representation Classifiers) and interpret the mechanism of SRC and Yang's variant of the SRC using the constrained subspace perspective. Experiments on the Extended Yale B database for image classification corroborate our claims and demonstrate the possibility of a proposed classifier called NCSC-CSR which has higher classification accuracy and robustness.

Computing Research Repository, 2008

In this paper an extension of the sparse decomposition problem is considered and an algorithm for solving it is pre- sented. In this extension, it is known that one of the shifted versions of a signal s (not necessarily the original signal itself) has a sparse representation on an overcomplete dictionary, and we are looking for the sparsest representation among

2012 IEEE International Conference on Acoustics, Speech and Signal Processing (ICASSP), 2012

The success of sparse reconstruction based classification algorithms largely depends on the choice of overcomplete bases (dictionary). Existing methods either use the training samples as the dictionary elements or learn a dictionary by optimizing a cost function with an additional discriminating component. While the former method requires a good number of training samples per class and is not suitable for video signals, the later adds instability and more computational load. This paper presents a sparse reconstruction based classification algorithm that mitigates the above difficulties. We argue that learning class-specific dictionaries, one per class, is a natural approach to discrimination. We describe each training signal by an error vector consisting of the reconstruction errors the signal produces w.r.t each dictionary. This representation is robust to noise, occlusion and is also highly discriminative. The efficacy of the proposed method is demonstrated in terms of high accuracy for image-based Species and Face recognition and video-based Action recognition.