自适应Gabor特征的协同表示人脸识别算法

为了解决人脸识别应用中针对人脸姿态的变化,光照等外部环境变化导致识别率不高,且稀疏表示应用于人脸识别收敛速度慢的情况,提出了一种基于多分量的Gabor特征提取和自适应权重选择的协同表示人脸识别算法(GAW-CRC).特征提取阶段,将Gabor变换的所有特征分量中鉴别能力较差的分量淘汰,剩余分量构建特征字典,分别协同表示对应测试样本的特征分量,将所有剩余分量的识别结果,按照自适应的权重函数加权融合得出最终分类结果.实验证明:算法应用于AR,FERET与Extended Yale B人脸库中,当对应的样本存在人脸角度变化,表情变化和光照条件变化等情况时,能够得到更高的识别率.     

Bimode model for face recognition and face representation

Tensorface based approaches decompose an image into its constituent factors (i.e., person, lighting, viewpoint, etc.), and then utilize these factor spaces for recognition. However, tensorface is not a preferable choice, because of the complexity of its multimode. In addition, a single mode space, except the person-space, could not be used for recognition directly. From the viewpoint of practical application, we propose a bimode model for face recognition and face representation. This new model can be treated as a simplified model representation of tensorface. However, their respective algorithms for training are completely different, due to their different definitions of subspaces. Thanks to its simpler model form, the proposed model requires less iteration times in the process of training and testing. Moreover bimode model can be further applied to an image reconstruction and image synthesis via an example image. Comprehensive experiments on three face image databases (PEAL, YaleB frontal and Weizmann) validate the effectiveness of the proposed new model.     

Learning class-specific dictionaries for digit recognition from spherical surface of a 3D ball

In the literature, very few researches have addressed the problem of recognizing the digits placed on spherical surfaces, even though digit recognition has already attracted extensive attentions and been attacked from various directions. As a particular example of recognizing this kind of digits, in this paper, we introduce a digit ball detection and recognition system to recognize the digit appearing on a 3D ball. The so-called digit ball is the ball carrying Arabic number on its spherical surface. Our system works under weakly controlled environment to detect and recognize the digit balls for practical application, which requires the system to keep on working without recognition errors in a real-time manner. Two main challenges confront our system, one is how to accurately detect the balls and the other is how to deal with the arbitrary rotation of the balls. For the first one, we develop a novel method to detect the balls appearing in a single image and demonstrate its effectiveness even when the balls are densely placed. To circumvent the other challenge, we use spin image and polar image for the representation of the balls to achieve rotation-invariance advantage. Finally, we adopt a dictionary learning-based method for the recognition task. To evaluate our system, a series of experiments are performed on real-world digit ball images, and the results validate the effectiveness of our system, which achieves 100 % accuracy in the experiments.     

基于半耦合稀疏表达的极低分辨率人脸识别

现有基于学习的人脸超分辨率算法假设高低分辨率特征具有流形一致性（耦合字典学习）,然而低分辨率图像的降质过程使得高低分辨率特征产生了“一对多”的映射关系偏差,减少了极低分辨率图像特征的判决信息,降低了超分辨率重建图像的识别率。针对这一问题,引入了半耦合稀疏字典学习模型,松弛高低分辨率流形一致性假设,同时学习稀疏表达字典和稀疏表达系数之间的映射函数,提升高低分辨率判决特征的一致性,在此基础上,引入协同分类模型,实现半耦合特征的高效分类。实验表明：相比于传统稀疏表达分类算法,算法不仅提高了识别率,并且还大幅度降低了时间开销,验证了半耦合稀疏学习字典在人脸识别中的有效性。     

局部联合结构化稀疏表示的单样本人脸识别

针对单样本问题,基于相同类别的人脸变化信息应有相似的稀疏编码这一事实,提出结构化稀疏变化字典学习方法,以得到较好的共享类内变化字典。同时鉴于同一人脸的所有区域应有相同的类标签,通过训练样本与变化字典按坐标分块联合表示查询人脸区域,然后给稀疏系数引入导致结构化稀疏效果的约束条件,实现对应类别字典的自动选择,从而更好地表示查询人脸。提出的人脸表示方法可以在局部识别方法的优势上整合全局信息,使得在AR、Extended Yale B、CMU-PIE人脸库上的表现超过其他单样本识别相关的方法,取得了较好的识别效果。     

Query-expanded collaborative representation based classification with class-specific prototypes for object recognition

Linear representation based classifiers (LinearRCs) assume that a query image can be represented as a linear combination of dictionary atoms or prototypes with various priors (e.g., sparsity), which have achieved impressive results in face recognition. Recently, a few attempts have been made to deal with more general cases (e.g., multi-view or multi-pose objects, more generic objects, etc.) but with additional requirements. In this paper, we present a query-expanded collaborative representation based classifier with class-specific prototypes (QCRC_CP) from the general perspective. First, we expand a single query in a multi-resolution way to cover rich variations of object appearances, thereby generating a query set. We then condense the gallery images to a small amount of prototypical images by maximizing canonical correlation in a class-specific way, in which the implicit query-dependent data locality discards the outliers. Given the query set, we finally propose a multivariate LinearRC with collaborative prior to identify the query according to the rule of minimum normalized residual (MNR). Experiments on four object recognition datasets (FERET pose, Swedish leaf, Chars74K, and ETH-80) show that our method outperforms the state-of-the-art LinearRCs with performance increases at least 3.1%, 3.8%, 10.4% and 3.1% compared to other classifiers.     

Discriminative sparse representation for face recognition

Recently Sparse Representation (or coding) based Classification (SRC) has gained great success in face recognition. In SRC, the testing image is expected to be best represented as a sparse linear combination of training images from the same class, and the representation fidelity is measured by the ?₂-norm or ?₁-norm of the coding residual. However, SRC emphasizes the sparsity too much and overlooks the spatial information during local feature encoding process which has been demonstrated to be critical in real-world face recognition problems. Besides, some work considers the spatial information but overlooks the different discriminative ability in different face regions. In this paper, we propose to weight spatial locations based on their discriminative abilities in sparse coding for robust face recognition. Specifically, we learn the weights at face locations according to the information entropy in each face region, so as to highlight locations in face images that are important for classification. Furthermore, in order to construct a robust weights to fully exploit structure information of each face region, we employed external data to learn the weights, which can cover all possible face image variants of different persons, so the robustness of obtained weights can be guaranteed. Finally, we consider the group structure of training images (i.e. those from the same subject) and added an ?_2,1-norm (group Lasso) constraint upon the formulation, which enforcing the sparsity at the group level. Extensive experiments on three benchmark face datasets demonstrate that our proposed method is much more robust and effective than baseline methods in dealing with face occlusion, corruption, lighting and expression changes, etc.     

基于双密度双树复小波变换多字典的人脸特征稀疏分类方法

基于超完备字典的人脸稀疏表示方法的难点是其字典构成。针对此问题,首先采用双密度双树复小波变换(DD-DT CWT)提取人脸图像不同尺度的高频子带,然后根据能量平均分布最大原则选择能量较大的部分子带构成对应尺度的超完备字典。同时,将测试样本相应的人脸DD-DT CWT子带特征看成超完备字典中原子的线性组合,并组合多字典上的稀疏表示进行识别。在AR人脸图像库上进行了实验,结果表明该方法是一种有效的人脸特征表示及分类方法。     

Image super-resolution via two coupled dictionaries and sparse representation

In image processing, the super-resolution (SR) technique has played an important role to perform high-resolution (HR) images from the acquired low-resolution (LR) images. In this paper, a novel technique is proposed that can generate a SR image from a single LR input image. Designed framework can be used in images of different kinds. To reconstruct a HR image, it is necessary to perform an intermediate step, which consists of an initial interpolation; next, the features are extracted from this initial image via convolution operation. Then, the principal component analysis (PCA) is used to reduce information redundancy after features extraction step. Non-overlapping blocks are extracted, and for each block, the sparse representation is performed, which it is later used to recover the HR image. Using the quality objective criteria and subjective visual perception, the proposed technique has been evaluated demonstrating their competitive performance in comparison with state-of-the-art methods.     

基于稀疏表示的快速l2范数人脸识别方法

多数稀疏表示方法需要原子数目远远大于原子维数的大规模冗余字典,并采用l1-范数最小化方法来计算稀疏系数。为了降低算法复杂度,本文提出一种基于稀疏表示的快速l2-范数人脸识别方法。通过提取融合特征和缩小字典规模来改善字典结构,增强l2-范数的稀疏性,从而在保证识别性能的前提下大幅提高算法运行速度。实验表明,与其他稀疏表示方法相比,本文方法可以显著降低算法复杂度,同时可以保持良好的人脸识别率和排除干扰人脸的能力。     

Subspace evolution analysis for face representation and recognition

This paper develops a novel framework that is capable of dealing with small sample size problem posed to subspace analysis methods for face representation and recognition. In the proposed framework, three aspects are presented. The first is the proposal of an iterative sampling technique. The second is adopting divide-conquer-merge strategy to incorporate the iterative sampling technique and subspace analysis method. The third is that the essence of 2D PCA is further explored. Experiments show that the proposed algorithm outperforms the traditional algorithms.     

Bidirectional representation for face recognition across pose

Conventional representation methods try to express the test sample as a weighting sum of training samples and exploit the deviation between the test sample and the weighting sum of the training samples from each class (also referred to as deviation between the test sample and each class) to classify the test sample. In particular, the methods assign the test sample to the class that has the smallest deviation among all the classes. This paper analyzes the relationship between face images under different poses and, for the first time, devises a bidirectional representation method-based pattern classification (BRBPC) method for face recognition across pose. BRBPC includes the following three steps: the first step uses the procedure of conventional representation methods to express the test sample and calculates the deviation between the test sample and each class. The second step first expresses the training sample of a class as a weighting sum of the test sample and the training samples from all the other classes and then obtains the corresponding deviation (referred to as complementary deviation). The third step uses the score-level fusion to integrate the scores, that is, deviations generated from the first and second steps for final classification. The experimental results show that BRBPC classifies more accurately than conventional representation methods.     

Multi-resolution dictionary collaborative representation for face recognition

Pattern Analysis and Applications - In this paper, a multi-resolution dictionary collaborative representation(MRDCR) method for face recognition is proposed. Unlike most of the traditional sparse...     

基于稀疏表示的分块人脸识别算法

最近基于原型（Prototype）加变差（Variation）表示模型的稀疏表示方法被有效用于人脸识别。由于该算法是基于整个人脸来考虑的,忽略了人脸局部特征对整个识别过程的影响。为了解决这个问题,引入了分块处理的思想,运用Borda计数的方法对每个子模块按照残差大小进行投票,根据最终的投票结果对人脸进行分类判别。在AR人脸库上的实验结果表明该方法与其他方法相比,在对具有部分遮挡和光照变化人脸的识别上具有更好的效果。     

Local sparse representation projections for face recognition

How to define the sparse affinity weight matrices is still an open problem in existing manifold learning algorithm. In this paper, we propose a novel supervised learning method called local sparse representation projections (LSRP) for linear dimensionality reduction. Differing from sparsity preserving projections (SPP) and the recent manifold learning methods such as locality preserving projections (LPP), LSRP introduces the local sparse representation information into the objective function. Although there are no labels used in the local sparse representation, it still can provide better measure coefficients and significant discriminant abilities. By combining the local interclass neighborhood relationships and sparse representation information, LSRP aims to preserve the local sparse reconstructive relationships of the data and simultaneously maximize the interclass separability. Comprehensive comparison and extensive experiments show that LSRP achieves higher recognition rates than principle component analysis, linear discriminant analysis and the state-of-the-art techniques such as LPP, SPP and maximum variance projections.     

基于特征化字典的低秩表示人脸识别

针对现有低秩表示（LRR）算法中全局与局部人脸特征信息融合不足的问题,提出了一种新的人脸识别算法——基于特征化字典的低秩表示（LRR-CD）。首先,将每张人脸照片表示成一个个特征化字典的集合,然后同时最小化基于训练样本的低秩重构特征系数以及与之相对应的类内特征差异。为了获得高效且具有高判别性的人脸图像的特征块重构系数矩阵,提出了一种新的数学公式模型,通过同时求解训练样本中相对应的特征块以及对应的类内特征差异词典的低秩约束问题,尽可能完整地保留原始高维人脸图像中的全局和局部信息,尤其是局部类内差异特征。另外,由于对特征块中信息的充分挖掘,所提算法对于一般程度上的面部遮挡和光照等噪声影响具有良好的鲁棒性。在AR、CMU-PIE和Extended Yale B人脸数据库进行多项对比实验,由实验结果可知LRR-CD相较于对比的稀疏表示（SRC）、协从表示（CRC）、低秩表示正规切（LRR-NCUT）和低秩递归最小二乘（LRR-RLS）算法在平均识别率上有2.58~17.24个百分点的提高。实验结果表明LRR-CD性能优于与之对比的算法,可以更高效地用于人脸全局和局部特征信息的融合,且具有优良的识别率。     

可见光-近红外HSV图像融合的场景类字典稀疏识别方法

针对典型自然场景智能观测的需求,为提高稀疏分类器在小样本数据库上的识别精度,提出一种可见光和近红外（NIR）HSV图像融合的场景类字典稀疏识别方法。首先,利用一直应用在计算机视觉显示领域中的图像HSV伪彩色处理技术将近红外图像与可见光图像融合;然后,对融合图像进行通用搜索树（GiST）特征和分层梯度方向直方图（PHOG）特征的提取与融合;最后,结合提出的类字典稀疏识别方法得到场景分类结果。所提方法在RGB-NIR数据库上的实验识别精度达到了74.75%。实验结果表明,融合近红外信息的场景图像的识别精度高于未融合时的识别精度,所提方法能够有效增加稀疏识别框架下场景目标的信息表征质量。     

Learning locality-constrained collaborative representation for robust face recognition

The models of low-dimensional manifold and sparse representation are two well-known concise models that suggest that each data can be described by a few characteristics. Manifold learning is usually investigated for dimension reduction by preserving some expected local geometric structures from the original space into a low-dimensional one. The structures are generally determined by using pairwise distance, e.g., Euclidean distance. Alternatively, sparse representation denotes a data point as a linear combination of the points from the same subspace. In practical applications, however, the nearby points in terms of pairwise distance may not belong to the same subspace, and vice versa. Consequently, it is interesting and important to explore how to get a better representation by integrating these two models together. To this end, this paper proposes a novel coding algorithm, called Locality-Constrained Collaborative Representation (LCCR), which introduce a kind of local consistency into coding scheme to improve the discrimination of the representation. The locality term derives from a biologic observation that the similar inputs have similar codes. The objective function of LCCR has an analytical solution, and it does not involve local minima. The empirical studies based on several popular facial databases show that LCCR is promising in recognizing human faces with varying pose, expression and illumination, as well as various corruptions and occlusions.     

Supervised neighborhood regularized collaborative representation for face recognition

How to represent a test sample is very crucial for linear representation based classification. The famous sparse representation focuses on employing linear combination of small samples to represent the query sample. However, the local structure and label information of data are neglected. Recently, locality-constrained collaborative representation (LCCR) has been proposed and integrates a kind of locality-constrained term into the collaborative representation scheme. For each test sample, LCCR mainly considers its neighbors to deal with noise and LCCR is robust to various corruptions. However, the nearby samples may not belong to the same class. To deal with this situation, in this paper, we not only utilize the positive effect of neighbors, but also consider the side effect of neighbors. A novel supervised neighborhood regularized collaborative representation (SNRCR) is proposed, which employs the local structure of data and the label information of neighbors to improve the discriminative capability of the coding vector. The objective function of SNRCR obtains the global optimal solution. Many experiments are conducted over six face data sets and the results show that SNRCR outperforms other algorithms in most case, especially when the size of training data is relatively small. We also analyze the differences between SNRCR and LCCR.     

A Kernel-based sparse representation method for face recognition

Sparse Representation Method has been proved to outperform conventional face recognition (FR) methods and is widely applied in recent years. A novel Kernel-based Sparse Representation Method (KBSRM) is proposed in this paper. In order to cope with the possible complex variation of the face images caused by varying facial expression and pose, the KBSRM first uses a kernel-induced distance to determine N nearest neighbors of the testing sample from all the training samples. Then, in the second step, the KBSRM represents the testing sample as a linear combination of the determinate N nearest neighbors and performs the classification by the representation result. It can be inferred that the N nearest training samples selected are closer to the test sample than the rest, so using the N nearest neighbors to represent the testing sample can make the ultimate classification more accurate. A number of FR experiments show that the KBSRM can achieve a better classification result than the algorithm mentioned in Xu et al. (Neural Comput Appl doi:10.1007/s00521-012-0833-5).