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The objective of this paper is to apply clipping techniques on natural images and to analyze the performance of various clipping algorithms in computer graphics. The clipping techniques used in this paper is Cohen–Sutherland line clipping, Liang–Barsky line clipping, Nicholl–Lee–Nicholl line clipping and Sutherland–Hodgman polygon clipping. The clipping algorithms are evaluated by using the three parameters: time complexity, space complexity and image accuracy. Previously, there is no performance evaluation on clipping algorithms done. Motivating by this factor, in this paper an evaluation of clipping algorithms is made. The novelty of this paper is to apply the clipping algorithms on natural images. It is justified that the above mentioned clipping algorithms outperform well on clipping the natural images. [ABSTRACT FROM AUTHOR]

Curved surface mesh generation is a key step for many areas. Here, a mesh generation algorithm for closed curved surface based on Delaunay refinement is proposed. We focus on improving the shape quality of the meshes generated and making them conform to 2-manifold. The Delaunay tetrahedralization of initial sample is generated first, the initial surface mesh which is a subset of the Delaunay tetrahedralization can be achieved. A triangle is refined by inserting a new point if it is large or of bad quality. For each sample, we also check the triangles that adjoin it whether from a topological disk. If not, the largest triangle will be refined. Finally, the surface mesh is updated after a new point is inserted into the sample. The definition of mesh size function for surface mesh generation is also put in this paper. Meshing experiments of some models demonstrate that the new algorithm is advantageous in generating high quality surface mesh, the count of mesh is suitable and can well approximate the curved surface. The presented method can be used for a wide range of problems including computer graphics, computer vision and finite element method. [ABSTRACT FROM AUTHOR]

This paper deals with the problem of detecting "weak symmetry" in a polygon, which is a special bijective and continuous mapping between the vertices of the given polygon. An application of this work is the automatic reconstruction of 3D polygons symmetric with respect to a plane from free-hand sketches of weakly-symmetric 2D polygons. We formalize the weak-symmetry notion and highlight its many properties which lead to an algorithm detecting it. The closest research work to the proposed approach is the detection of skewed symmetry. Skewed symmetry detection deals only with reconstruction of planar mirror-symmetric 3D polygons while our method is able to identify symmetry in projections of planar as well as nonplanar mirror-symmetric 3D polygons. [ABSTRACT FROM AUTHOR]

With the availability of powerful multimedia editing software, all types of personalized image and video resources are available in networks. Multimedia forensics technology has become a new topic in the field of information security. In this paper, a new source video system identification algorithm is proposed based on the features in the video stream; it takes full advantage of the different characteristics in the rate control module and the motion prediction module, which are two open parts in the MPEG-2 video compression standard, and combines a support vector machine classifier to build an intelligent computing system for video source identification. The experiments show this proposed algorithm can effectively identify video streams that come from a number of video coding systems. [ABSTRACT FROM AUTHOR]

Many problems solved in computer graphics, computer vision, visualization etc. require fast and robust computation of an area of a triangle or volume of a tetrahedron. These very often used algorithms are well known and robust if vertices coordinates of triangles or tetrahedrons are given in Euclidean coordinates. The homogeneous coordinates are often used for the representation of geometric transformations. They enable us to represent translation, rotation, scaling and projection operations in a unique way and handle them properly. Today's graphics hardware based on GPU offers very high computational power using pixel shaders and fragment shaders not only for graphical elements processing, but also for general computation using GPU as well. This paper presents simple methods for the area of a triangle and the volume of a tetrahedron computation if vertices are given in homogeneous coordinates without the need to use the division operation for vertices coordinates transformation from the homogeneous coordinates to the Euclidean coordinates. Area or volume computation is transferred to the cross product computation that is fast, simple, and robust and can be supported in hardware or implemented on GPU that uses vector operations with homogeneous coordinates natively. The presented formula can be used directly for Euclidean representation just setting w equal to 1. [ABSTRACT FROM AUTHOR]

In this paper, we present a new approach to geometrical modeling which allows the user to easily characterize and control the shape defined to a closed surface. We will focus on dealing with the shape's topological, morphological and geometrical properties separately. To do this, we have based our work on the following observations concerning surfaces defined by control-points, and implicit surfaces with skeleton. They both provide complementary approaches to the surface's deformation, and both have specific advantages and limits. We thus attempted to conceive a model which integrates the local and geometrical characterization induced by the control points, as well as the representation of the morphology given by the skeleton. Knowing that the lattice of control points is close to the surface and that the skeleton is centered in the related shape, we thought of a 3-layer model. The transition layer separates the local geometrical considerations from those linked to the global morphology. We apply our model to shape design in order to modify an object in an interactive and ergonomic way, as well as to reconstruction which allows better shape understanding. To do so, we present the algorithms related to these processes. [ABSTRACT FROM AUTHOR]

In this paper we propose two improvements to the beam tracing method, one is to reduce the final redundant-drawing of pixel fragments into the frame buffer, and the other is to use Snell's law instead of the tangent law. It is well known that the ray tracing scheme is one of the most effective methods for high quality CG image synthesis. The beam tracing method was introduced because traditional ray tracing algorithms have a significant calculation cost. In the improved method, the projection screen is recursively divided into non-overlapping coherent region segments based on the coherence of the ray-trace-tree structure of a given scene, and an image can be synthesized after the segmentation process by tracing one or several rays in each region segment. We introduced Snell's law for the refractions of the rays. Therefore, we can reduce the computational cost of ray tracing, eliminate the extra calculations caused by overlapping polygons on a screen, and increase the quality of CG images generated by our proposed method. [ABSTRACT FROM AUTHOR]