This article proposes a facial expression removal method to recover a 3D neutral face from a single 3D expressional or non-neutral face. We treat a 3D non-neutral face as the sum of its neutral one and the residual. This can be satisfied if the correspondence between 3D vertices of expressional faces and those of neutral faces is established. We propose a non-rigid deformation method to establish the correspondence between 3D faces. Then, according to algebra inequality, the minimization of a neutral face model can be replaced by the minimization of its upper bound, i.e., the errors of an expressional face model and a residual model. Thus, we co-optimize the representation errors of the latter two models and build the relationship between the representation coefficients of the two models. Given an expressional face as the input, its corresponding neutral face can be inferred by the associative representation parameters in these two models. In the testing stage, we use an iterative joint fitting scheme to obtain a more accurate recovery. Extensive experiments are conducted to evaluate our method. The results show that our method obtains considerably better performance than existing methods in terms of average root mean square errors and recognition rates, and also better visual effects.

Sparse principal component analysis (sparse PCA) aims at finding a sparse basis to improve the interpretability over the dense basis of PCA, while still covering the data subspace as much as possible. In contrast to most existing work that addresses the problem by adding sparsity penalties on various objectives of PCA, we propose a new method, sparse PCA via rotation and truncation (SPCArt), which finds a rotation matrix and a sparse basis such that the sparse basis approximates the basis of PCA after the rotation. The algorithm of SPCArt consists of three alternating steps: 1) rotating the PCA basis; 2) truncating small entries; and 3) updating the rotation matrix. Its performance bounds are also given. The SPCArt is efficient, with each iteration scaling linearly with the data dimension. Parameter choice is simple, due to explicit physical explanations. We give a unified view to several existing sparse PCA methods and discuss the connections with SPCArt. Some ideas from SPCArt are extended to GPower, a popular sparse PCA algorithm, to address its limitations. Experimental results demonstrate that SPCArt achieves the state-of-the-art performance, along with a good tradeoff among various criteria, including sparsity, explained variance, orthogonality, balance of sparsity among loadings, and computational speed.

In invasive brain-machine interfaces (BMI), the recorded high-quality neural signals produce a large data volume. This calls for effective compression. In this paper, we focus on extracellular recording of motor cortex. First the characteristics of the signals are studied, one of which is that peaks of DCT coefficients at high frequency may correspond to spike firing patterns. Based on these characteristics, we propose a high-fidelity compression framework for these signals. The DCT coefficients of the signal are divided into two parts according to amplitude, rather than frequency. The Low-Amplitude-Component (LAC) is encoded by a phase called Symbol Encoding, which helps to reduce overall distortion. The High-Amplitude-Component (HAC), containing major information and spikes, is encoded by another phase called Hybrid Encoding. It combines the Huffman encoding and a novel Zero-Length-Encoding. Experiments show that the algorithm achieves a compression ratio of 18% without obvious distortion. Moreover, spikes are reserved more than 92%, outperforming existing work. Our algorithm enables low-cost storage devices to store long-time neural signals.

Establishing a dense vertex-to-vertex anthropometric correspondence between 3D faces is an important and fundamental problem in 3D face research, which can contribute to most applications of 3D faces. This paper proposes a sparse facial deformable model to automatically achieve this task. For an input 3D face, the basic idea is to generate a new 3D face that has the same mesh topology as a reference face and the highly similar shape to the input face, and whose vertices correspond to those of the reference face in an anthropometric sense. Two constraints: 1) the shape constraint and 2) correspondence constraint are modeled in our method to satisfy the three requirements. The shape constraint is solved by a novel face deformation approach in which a normal-ray scheme is integrated to the closest-vertex scheme to keep high-curvature shapes in deformation. The correspondence constraint is based on an assumption that if the vertices on 3D faces are corresponded, their shape signals lie on a manifold and each face signal can be represented sparsely by a few typical items in a dictionary. The dictionary can be well learnt and contains the distribution information of the corresponded vertices. The correspondence information can be conveyed to the sparse representation of the generated 3D face. Thus, a patch-based sparse representation is proposed as the correspondence constraint. By solving the correspondence constraint iteratively, the vertices of the generated face can be adjusted to correspondence positions gradually. At the early iteration steps, smaller sparsity thresholds are set that yield larger representation errors but better globally corresponded vertices. At the later steps, relatively larger sparsity thresholds are used to encode local shapes. By this method, the vertices in the new face approach the right positions progressively until the final global correspondence is reached. Our method is automatic, and the manual work is needed only in training procedure. The experimental results on a large-scale publicly available 3D face data set, BU-3DFE, demonstrate that our method achieves better performance than existing methods.

Obtaining training sets for special hyperspectral data sets or applications seems so time consuming and expensive especially for relatively inaccessible locations. Moreover, current techniques of image processing and pattern recognition are not robust enough to make automated remote sensing interpretation feasible. The Margin Infused Relaxed Algorithm (MIRA) is a new perceptron-like online algorithm with a margin-dependent learning rate; meanwhile, it's also a specific online algorithm that seeks a set of prototypes to represent each class. In this paper, we put emphasis on building an online framework by MIRA, which can naturally combine inputs from human and learn as few labeled data points as possible. Experimental results have proved that the MIRA applied in our method is effective in classification problem and economical of the computation time cost.