Huai-Yu Wu

Edge-Directed Single-Image Super-Resolution Via Adaptive Gradient Magnitude Self-Interpolation

Super-resolution from a single image plays an important role in many computer vision systems. However, it is still a challenging task, especially in preserving local edge structures. To construct high-resolution images while preserving the sharp edges, an effective edge-directed super-resolution method is presented in this paper. An adaptive self-interpolation algorithm is first proposed to estimate a sharp high-resolution gradient field directly from the input low-resolution image. The obtained high-resolution gradient is then regarded as a gradient constraint or an edge-preserving constraint to reconstruct the high-resolution image. Extensive results have shown both qualitatively and quantitatively that the proposed method can produce convincing super-resolution images containing complex and sharp features, as compared with the other state-of-the-art super-resolution algorithms.

Global and local isometry-invariant descriptor for 3D shape comparison and partial matching

In this paper, based on manifold harmonics, we propose a novel framework for 3D shape similarity comparison and partial matching. First, we propose a novel symmetric mean-value representation to robustly construct high-quality manifold harmonic bases on nonuniform-sampling meshes. Then, based on the manifold harmonic bases constructed, a novel shape descriptor is presented to capture both of global and local features of 3D shape. This feature descriptor is isometry-invariant, i.e., invariant to rigid-body transformations and non-rigid bending. After characterizing 3D models with the shape features, we perform 3D retrieval with a up-to-date discriminative kernel. This kernel is a dimension-free approach to quantifying the similarity between two unordered featuresets, thus especially suitable for our high-dimensional feature data. Experimental results show that our framework can be effectively used for both comprehensive comparison and partial matching among non-rigid 3D shapes.

Fast image upsampling via the displacement field.

In this paper, we present a fast image upsampling method within a two-scale framework to ensure the sharp construction of upsampled image for both large-scale edges and small-scale structures. In our approach, the low-frequency image is recovered via a novel sharpness preserving interpolation technique based on a well-constructed displacement field, which is estimated by a cross-resolution sharpness preserving model. Within this model, the distances of pixels on edges are preserved, which enables the recovery of sharp edges in the high-resolution result. Likewise, local high-frequency structures are reconstructed via a sharpness preserving reconstruction algorithm. Extensive experiments show that our method outperforms current state-of-the-art approaches, based on quantitative and qualitative evaluations, as well as perceptual evaluation by a user study. Moreover, our approach is very fast so as to be practical for real applications.

Region-based image segmentation with local signed difference energy

Intensity inhomogeneity often causes considerable difficulties in image segmentation. To tackle this problem, we propose a new region-based level set method. The proposed method considers the local image information by describing it as a novel local signed difference (LSD) energy, which possesses both local separability and global consistency. The LSD energy term is integrated into an objective energy functional, which is minimized via a level set evolution process. Extensive experiments are performed to evaluate the proposed method, showing improvements in both accuracy and efficiency, as compared with the state-of-the-art approaches.

Manifold Regularized Local Sparse Representation for Face Recognition

Sparse representation-(or sparse coding)-based classification has been successfully applied to face recognition. However, it can become problematic in the presence of illumination variations or occlusions. In this paper, we propose a Manifold Regularized Local Sparse Representation (MRLSR) model to address such difficulties. The key idea behind the MRLSR method is that all coding vectors in sparse representation should be group sparse, which means holding the two properties of both individual sparsity and local similarity. As a consequence, the face recognition rate can be considerably improved. The MRLSR model is optimized by the modified homotopy algorithm, which keeps stable under different choices of the weighting parameter. Extensive experiments are performed on various face databases, which contain illumination variations and occlusions. We show that the proposed method outperforms the state-of-the-art approaches and provides the highest recognition rate.

Forward–Backward Mean-Shift for Visual Tracking With Local-Background-Weighted Histogram

Object tracking plays an important role in many intelligent transportation systems. Unfortunately, it remains a challenging task due to factors such as occlusion and target-appearance variation. In this paper, we present a new tracking algorithm to tackle the difficulties caused by these two factors. First, considering the target-appearance variation, we introduce the local-background-weighted histogram (LBWH) to describe the target. In our LBWH, the local background is treated as the context of the target representation. Compared with traditional descriptors, the LBWH is more robust to the variability or the clutter of the potential background. Second, to deal with the occlusion case, a new forward-backward mean-shift (FBMS) algorithm is proposed by incorporating a forward-backward evaluation scheme, in which the tracking result is evaluated by the forward-backward error. Extensive experiments on various scenarios have demonstrated that our tracking algorithm outperforms the state-of-the-art approaches in tracking accuracy.

Adaptive εLBP for background subtraction

Background subtraction plays an important role in many computer vision systems, yet in complex scenes it is still a challenging task, especially in case of illumination variations. In this work, we develop an efficient texture-based method to tackle this problem. First, we propose a novel adaptive eLBP operator, in which the threshold is adaptively calculated by compromising two criterions, i.e. the description stability and the discriminative ability. Then, the naive Bayesian technique is adopted to effectively model the probability distribution of local patterns in the pixel level, which utilizes only one single eLBP pattern instead of eLBP histogram of local region. Our approach is evaluated on several video sequences against the traditional methods. Experiments show that our method is suitable for various scenes, especially can robust handle illumination variations.

Consistent Correspondence between Arbitrary Manifold Surfaces

We propose a novel framework for consistent correspondence between arbitrary manifold meshes. Different from most existing methods, our approach directly maps the connectivity of the source mesh onto the target mesh without needing to segment input meshes, thus effectively avoids dealing with unstable extreme conditions (e.g. complex boundaries or high genus). In this paper, firstly, a novel mean-value Laplacian fitting scheme is proposed, which aims at computing a shape-preserving (conformal) correspondence directly in 3D-to-3D space, efficiently avoiding local optimum caused by the nearest-point search, and achieving good results even with only a few marker points. Secondly, we introduce a vertex relocation and projection approach, which refines the initial fitting result in the way of local conformity. Each vertex of the initial result is gradually projected onto the target models surface to ensure a complete surface match. Furthermore, we provide a fast and effective approach to automatically detect critic points in the context of consistent correspondence. By fitting these critic points that capture the important features of the target mesh, the output compatible mesh matches the target meshs profiles quite well. Compared with previous approaches, our scheme is robust, fast, and convenient, thus suitable for common applications.

Layer-Wise Floorplan Extraction for Automatic Urban Building Reconstruction

Urban building reconstruction is an important step for urban digitization and realisticvisualization. In this paper, we propose a novel automatic method to recover urban building geometry from 3D point clouds. The proposed method is suitable for buildings composed of planar polygons and aligned with the gravity direction, which are quite common in the city. Our key observation is that the building shapes are usually piecewise constant along the gravity direction and determined by several dominant shapes. Based on this observation, we formulate building reconstruction as an energy minimization problem under the Markov Random Field (MRF) framework. Specifically, point clouds are first cutinto a sequence of slices along the gravity direction. Then, floorplans are reconstructed by extracting boundaries of these slices, among which dominant floorplans are extracted and propagated to other floors via MRF. To guarantee correct propagation, a new distance measurement for floorplans is designed, which first encodes floorplans into strings and then calculates distances between their corresponding strings. Additionally, an image based editing method is also proposed to recover detailed window structures. Experimental results on both synthetic and real data sets have validated the effectiveness of our method.

Mean-Shift object tracking with a novel back-projection calculation method

In this paper, we propose a mean-shift tracking method by using the novel back-projection calculation. The traditional back-projection calculation methods have two main drawbacks: either they are prone to be disturbed by the background when calculating the histogram of target-region, or they only consider the importance of a pixel relative to other pixels when calculating the back-projection of search-region. In order to solve the two drawbacks, we carefully consider the background appearance based on two priors, i.e., texture information of background, and appearance difference between foreground-target and background. Accordingly, our method consists of two basic steps. First, we present a foreground-target histogram approximation method to effectively reduce the disturbance from background. Moreover, the foreground-target histogram is used for back-projection calculation instead of the target-region histogram. Second, a novel back-projection calculation method is proposed by emphasizing the probability that a pixel belongs to the foreground-target. Experiments show that our method is suitable for various tracking scenes and is appealing with respect to robustness.