Collaborative Representation based Classification for Face Recognition

By coding a query sample as a sparse linear combination of all training samples and then classifying it by evaluating which class leads to the minimal coding residual, sparse representation based classification (SRC) leads to interesting results for robust face recognition. It is widely believed that the l1- norm sparsity constraint on coding coefficients plays a key role in the success of SRC, while its use of all training samples to collaboratively represent the query sample is rather ignored. In this paper we discuss how SRC works, and show that the collaborative representation mechanism used in SRC is much more crucial to its success of face classification. The SRC is a special case of collaborative representation based classification (CRC), which has various instantiations by applying different norms to the coding residual and coding coefficient. More specifically, the l1 or l2 norm characterization of coding residual is related to the robustness of CRC to outlier facial pixels, while the l1 or l2 norm characterization of coding coefficient is related to the degree of discrimination of facial features. Extensive experiments were conducted to verify the face recognition accuracy and efficiency of CRC with different instantiations.Comment: It is a substantial revision of a previous conference paper (L. Zhang, M. Yang, et al. "Sparse Representation or Collaborative Representation: Which Helps Face Recognition?" in ICCV 2011

Integrating simplified inverse representation and CRC for face recognition

© Springer International Publishing Switzerland 2015. The representation based classification method (RBCM) has attracted much attention in the last decade. RBCM exploits the linear combination of training samples to represent the test sample, which is then classified according to the minimum reconstruction residual. Recently, an interesting concept, Inverse Representation (IR), is proposed. It is the inverse process of conventional RBCMs. IR applies test samples’ information to represent each training sample, and then classifies the training sample as a useful supplement for the final classification. The relative algorithm CIRLRC, integrating IR and linear regression classification (LRC) by score fusing, shows superior classification performance. However, there are two main drawbacks in CIRLRC. First, the IR in CIRLRC is not pure, because the test vector contains some training sample information. The other is the computation inefficiency because CIRLRC should solve C linear equations for classifying the test sample respectively, where C is the number of the classes. Therefore, we present a novel method integrating simplified IR (SIR) and collaborative representation classification (CRC), named SIRCRC, for face recognition. In SIRCRC, only test sample information is fully used in SIR, and CRC is more efficient than LRC in terms of speed, thus, one linear equation system is needed. Extensive experimental results on face databases show that it is very competitive with both CIRLRC and the state-of-the-art RBCM

Collaborative Learning of Fine-grained Visual Data

Problem: Deep learning based vision systems have achieved near human accuracy in recognizing coarse object categories from visual data. But recognizing fine-grained sub-categories remains an open problem. Tasks like fine-grained species recognition poses further challenges: significant background variation compared to subtle difference between objects, high class imbalance due to scarcity of samples for endangered species, cost of domain expert annotations and labeling, etc. Methodology: The existing approaches, like transfer learning, to solve the problem of learning small specialized datasets are still inadequate in case of fine-grained sub-categories. The hypothesis of this work is that collaborative filters should be incorporated into the present learning frameworks to better address these challenges. The intuition comes from the fact that collaborative representation based classifiers have been earlier used for face recognition problems which present similar challenges. Outcomes: Keeping the above hypothesis in mind, the thesis achieves the following objectives: 1) It demonstrates the suitability of collaborative classifiers for fine-grained recognition 2) It expands the state-of-the-art by incorporating automated background suppression into collaborative classification formulation 3) It incorporates the collaborative cost function into supervised learning (deep convolutional network) and unsupervised learning (clustering algorithms) 4) Lastly, during the work several benchmark fine-grained image datasets have been introduced on NZ and Indian butterflies and bird species recognition