The International Journal of Virtual Reality, 2011, 10(4):43-51 45 Abstract — In shadow volume, the most expensive computation is silhouette detection. In this paper, the triangular algorithm (TA) and visible-non-visible (VnV) algorithm that are famous algorithms to detect the outline of occluder are renewed. In this paper, we proposed a hybrid algorithm based on TA and VnV, namely Hybrid Silhouette Detection (HSD) algorithm. HSD is an improved algorithm that can recognize silhouette for generating real-time shadow volume. Our algorithm involves detecting silhouette and decreases the cost of implementation for shadow volume rendering. The last shadow volume algorithm using stencil buffer is rewritten and an algorithm for shadow volume using HSD with respect of culling invisible parts of scene is proposed. An accurate mathematical comparison between TA, VnV and HSD algorithms is undertaken. The obtained results confirm superiority of our proposed algorithm in terms of processing and rendering time. Our algorithm can be used in virtual environment to increase the frame per second and to enhance the realistic of games programming. Index Terms—silhouette detection, shadow volume, visibility culling, real-time rendering I. INTRODUCTION Nowadays computer games and effects of computer graphics play most important roles in the living. Shadows have most important contribution to make a virtual scene, realistic. In video games, shadows give the gamers feeling that they imagine they play in realistic world and they can enjoy as much as possible. Although the number of algorithms to create shadow is huge, they are suffering from low Frame per Second (FPS). Real-time is occurring immediately. The real time word is used for some different features. For example, real-time shadows are that respond to input immediately. They are used for such tasks as navigation, in which the computer must react to a steady flow of new information without interruption. Real time shadows in real-time applications such as computer games and virtual environment are more important to create realistic scenes so that the users will feel realistic in the scenes. In practice, the rendering performance and the quality of shadows generated are important considerations in the selection of shadow algorithm. Manuscript Received on June 18，2011. E-mail: shahinkey@yahoo.com Shadow volume that has been proposed by Crow [1] in 1977 is one of the famous algorithms that still in use to create real-time shadow in computer games. Shadow volume is based on silhouette detection because in this algorithm only part of occluder, which has contribution on shadow generation, is outlining of occluder not all parts. How to recognize the outline of the occluder can improve the speed of algorithm. To find out outline of object, silhouette detection is so important because it can reduce the cost of implementation and it is the main item to improve an algorithm, which needs silhouette detection. Silhouettes are the especial parts of a 3D object outline which only those parts are important to create shadow at different time of rendering. Silhouette detection plays an important phase to create shadow volume. Silhouette detection is visual and view point base. To generate shadow, especially shadow volume, silhouette detection plays a crucial role to detect the boundary of occluder. II. PREVIOUS WORKS Silhouette detection is a function that converts a 3D world to 2D. In 1987 Richards, Koenderink, and Hoffman [2] were the first researchers who proposed how recognize the silhouette of arbitrary objects. Saito and Takahashi, in 1990, used geometric buffer for silhouette detection. G-buffer was based on Z-buffer which produced by adding some geometric data. Hertzmann[3], proposed an algorithm in irregularity surface with lake of continuity and silhouette based on combine of normal map and depth mapping. The hybrid algorithm changes the face of object in using Z-buffer. Raskar and Cohen [4] introduced a method for silhouette detection by changing the front face and back face of the polygon. In 1999, Gooch et al. [5] used a similar method combined with previous ones to recognize the silhouette. In 2000, Northup and Markosion [6] proposed an algorithm, although it is difficult to find starting points of each coherence, it is very simple. In the Northup’s algorithm, spatial coherence is so impressively. Pop et al. [7] introduced a method for the on-line silhouette finding using frame coherence. For some consequent different viewpoints, in construct to compute the whole silhouettes each time, they tried to calculate the different changes in the silhouette of a polyhedral model between sequence frames. In the each model they transformed the normal vectors to dual line segments and transformed the viewpoint to a dual plane. The Hybrid Silhouette Detection for Real-Time Shadow Volume Hoshang Kolivand and Mohd Shahrizal Sunar UTM ViCubelab, Department of Computer Graphics and Multimedia，Faculty of Computer Science and Information System, Universiti Teknologi Malaysia，81310, Johor, Malaysia