Content-based Mesh Research Articles

Point Selection for Triangular 2-D Mesh Design Using Adaptive Forward Tracking Algorithm

Two-dimensional mesh-based motion tracking preserves neighboring relations (through connectivity of the mesh) and also allows warping transformations between pairs of frames; thus, it effectively eliminates blocking artifacts that are common in motion compensation by block matching. However, available uniform 2-D mesh model enforces connec-tivity everywhere within a frame, which is clearly not suitable across occlusion boundaries. To overcome this limitation, BTBC (background to be covered) detection and MF (model failure) detection algorithms are being used. In this algorithm, connectivity of the mesh elements (patches) across covered and uncovered region boundaries are broken. This is achieved by allowing no node points within the background to be covered and refining the mesh structure within the model failure region at each frame. We modify the occlusion-adaptive, content-based mesh design and forward tracking algorithm used by Yucel Altunbasak for selection of points for triangular 2-D mesh design. Then, we propose a new triangulation procedure for mesh structure and also a new algorithm to justify connectivity of mesh structure after motion vector estimation of the mesh points. The modified content-based mesh is adaptive which eliminates the necessity of transmission of all node locations at each frame.

Content-based 3D mesh model retrieval from hand-written sketch

Recently, huge numbers of 3D models (solid, surface, and mesh models) have been archived in CA-X systems for industrial design, engineering, manufacturing and e-commerce. Efficient searching methods for 3D models become important for system users. For this purpose, a content-based 3D mesh model retrieval system from hand- written sketch is proposed in this paper. In the system, the user puts a query in the form of a 2D hand-written sketch to a 3D mesh model database, and the system automatically returns a set of mesh models whose 2D views are similar to the input sketch. Generic Fourier Descriptor and Local Binary Pattern which are features invariant to rotation, translation and scaling of 2D images are used to measure dissimilarities between a query sketch and images generated from 3D models. The effectiveness of the retrieval system is evaluated through case studies on industrial design process.

Contextual encoding in uniform and adaptive mesh-based lossless compression of MR images

We propose and evaluate a number of novel improvements to the mesh-based coding scheme for 3-D brain magnetic resonance images. This includes: 1) elimination of the clinically irrelevant background leading to meshing of only the brain part of the image; 2) content-based (adaptive) mesh generation using spatial edges and optical flow between two consecutive slices; 3) a simple solution for the aperture problem at the edges, where an accurate estimation of motion vectors is not possible; and 4) context-based entropy coding of the residues after motion compensation using affine transformations. We address only lossless coding of the images, and compare the performance of uniform and adaptive mesh-based schemes. The bit rates achieved (about 2 bits per voxel) by these schemes are comparable to those of the state-of-the-art three-dimensional (3-D) wavelet-based schemes. The mesh-based schemes have been shown to be effective for the compression of 3-D brain computed tomography data also. Adaptive mesh-based schemes perform marginally better than the uniform mesh-based methods, at the expense of increased complexity.

Affine motion compensation using a content-based mesh

A content-based approach to the design of a triangular mesh is presented, and its application to affine motion compensation is investigated. An image is first segmented into moving objects, which are then approximated with polygons. Following this, a triangular mesh is generated within each polygon, thus ensuring that no triangle straddles multiple regions. Translation and affine motion parameters are determined for each triangle, using bi-directional motion estimation. Results for three test sequences demonstrate the advantages offered by the proposed mesh design method, and by the use of affine motion compensation.

Mesh-based video objects tracking combining motion and luminance discontinuities criteria

A new content-based mesh design algorithm for video objects segmentation and tracking is proposed. The algorithm moves the mesh nodes along motion or luminance discontinuities in order to fit the objects boundaries. The motion inside adjacent triangular cells is estimated by competitive forward–backward matching. This approach allows the displacements of the nodes without the remeshing of occlusion regions: uncovered background nor background to be covered. The mesh is deformed under the minimization of an objective function. This function includes a motion energy, a spatial boundary energy and a temporal regularization energy. The motion energy is effective in textured regions while the boundary energy mainly operates in homogeneous one according to a boundary distance map. The temporal regularization energy keeps the objects tracking stable along the sequence due to its object-based approach. Experimental results with both synthetic and real-world sequences prove the efficiency of the proposed approach and the cooperative action of the three energy terms.

2-D mesh-based video object segmentation and tracking with occlusion resolution

This paper integrates fully automatic video object segmentation and tracking including detection and assignment of uncovered regions in a 2-D mesh-based framework. Particular contributions of this work are (i) a novel video object segmentation method that is posed as a constrained maximum contrast path search problem along the edges of a 2-D triangular mesh, and (ii) a 2-D mesh-based uncovered region detection method along the object boundary as well as within the object. At the first frame, an optimal number of feature points are selected as nodes of a 2-D content-based mesh. These points are classified as moving (foreground) and stationary nodes based on multi-frame node motion analysis, yielding a coarse estimate of the foreground object boundary. Color differences across triangles near the coarse boundary are employed for a maximum contrast path search along the edges of the 2-D mesh to refine the boundary of the video object. Next, we propagate the refined boundary to the subsequent frame by using motion vectors of the node points to form the coarse boundary at the next frame. We detect occluded regions by using motion-compensated frame differences and range filtered edge maps. The boundaries of detected uncovered regions are then refined by using the search procedure. These regions are either appended to the foreground object or tracked as new objects. The segmentation procedure is re-initialized when unreliable motion vectors exceed a certain number. The proposed scheme is demonstrated on several video sequences.

Optimal 2-D hierarchical content-based mesh design and update for object-based video

Representation of video objects (VOs) using hierarchical 2-D content-based meshes for accurate tracking and level of detail (LOD) rendering have been previously proposed, where a simple suboptimal hierarchical mesh design algorithm was employed. However, it was concluded that the performance of the tracking and rendering very much depends on how well each level of the hierarchical mesh structure fits the VO under consideration. To this effect, this paper proposes an optimized design of hierarchical 2-D content-based meshes with a shape-adaptive simplification and a temporal update mechanism for object-based video. Particular contributions of this work are: (1) analysis of optimal number of nodes for the initial fine level-of-detail mesh design; (2) adaptive shape simplification across hierarchy levels; (3) optimization of the interior-node decimation method to remove only a maximal independent set to preserve Delaunay topology across hierarchy levels for better bitrate versus quality performance; and (4) a mesh-update mechanism which serves to update a temporally 2-D dynamic mesh in case of occlusion due to 3-D motion and self-occlusion. The proposed optimized and temporally updated hierarchical mesh representation can be applied in object-based video coding, retrieval, and manipulation.

Hierarchical 2-D mesh representation, tracking, and compression for object-based video

This paper proposes methods for designing, tracking and coding hierarchical two-dimensional (2-D) content-based mesh representations. The design procedure consists of constructing a fine-to-coarse hierarchy of Delaunay meshes, using image- and shape-based criteria for mesh geometry simplification. Hierarchical tracking employs a coarse-to-fine strategy with mesh-based motion vector optimization. We introduce new techniques to maintain the initial mesh hierarchy and topology during tracking by imposing certain constraints at each stage of the procedure. The hierarchical compression technique is based on a nearest neighbor ordering of mesh node points. This ordering serves to identify the mesh boundary nodes as well as establish spatial predictors for differential coding of node coordinates and motion vectors. The proposed hierarchical mesh representation, which has applications in object-based video manipulation, investing, and compression, provides improved tracking performance (compared to a nonhierarchical representation) and allows progressive (scalable) transmission of the object geometry (including shape) and motion information, as well as variable level-of-detail rendering. Experimental results are presented to compare the tracking and compression performance of hierarchical versus nonhierarchical mesh representations and to demonstrate the tradeoff between image quality and mesh bit rate for 2-D mesh-based video object rendering.

Occlusion-adaptive, content-based mesh design and forward tracking

Two-dimensional (2-D) mesh-based motion compensation preserves neighboring relations (through connectivity of the mesh) as well as allowing warping transformations between pairs of frames; thus, it effectively eliminates blocking artifacts that are common in motion compensation by block matching. However, available 2-D mesh models, whether uniform or non-uniform, enforce connectivity everywhere within a frame, which is clearly not suitable across occlusion boundaries. To this effect, we hereby propose an occlusion-adaptive forward-tracking mesh model, where connectivity of the mesh elements (patches) across covered and uncovered region boundaries are broken. This is achieved by allowing no node points within the background to be covered (BTBC) and refining the mesh structure within the model failure (MF) region(s) at each frame. The proposed content-based mesh structure enables better rendition of the motion (compared to a uniform or a hierarchical mesh), while tracking is necessary to avoid transmission of all node locations at each frame. Experimental results show successful motion compensation and tracking.