Visual data detection, modeling and enhancement

This thesis presents new methods and algorithms for fast face detection, statistical data modeling and image enhancement. Face detection is an important basic technique for a variety of image processing tasks. To improve its applicability, we study fast detection techniques. An efficient framework of multiscale sequential detection is developed to achieve accurate detection with very low complexity. Three useful techniques are employed to speed up the detection: wavelet image modeling with histograms, discriminative feature selection and sequential Bayesian detection. In particular, we introduce several discriminant analysis methods to separate complex class distributions. The technique of error analysis is proposed to select discriminative features adaptively. With adaptive feature selection, a detection based tracking algorithm is also developed. In the second part of the thesis, we present a new paradigm for appearance modeling. A nonlinear generative model is introduced to characterize manifold distributions of deformable patterns. In this model, the visual data is represented with an augmented set of deformable local components. The random deformation is described by probability models. The techniques of basis selection and progressive density estimation are proposed to obtain a data driven representation as well as a manifold distribution model. We use the nonlinear model to characterize handwritten digits and facial expression, construct pose manifolds and derive a layered representation for video data. The last part of the thesis addresses two problems of image quality enhancement: wavelet domain image interpolation and error concealment. A linear composite MMSE estimator is proposed for image interpolation, where a parametric edge model is used to infer the detailed wavelet coefficients, and local statistics are used to minimize the estimation error. For error concealment, we introduce a directional smoothness measure to evaluate the structural consistency around image edges. A block-based concealment algorithm is developed to reconstruct damaged areas and assure consistent edge structures.