虽然三维模型的轮廓线在图形交流中起着重要的作用，但由于轮廓线是视点依赖的，当物体在空间运动时，用现有算法从复杂的三维模型中抽取轮廓线需耗费大量时间，为了提高抽取轮廓线的速度，提出了两种新的抽取三维模型轮廓线算法，这两种算法是先利用轮廓线的局部极值特性来获得部分轮廓边，然后利用轮廓线的连通性，通过简单的比较运算，即可获得三维模型的外部轮廓线，实验结果表明，该两种算法都可快速获得三维模型的外围轮廓线，最后还将本算法与相关算法进行了详细的比较分析。

Silhouettes play a very important role in graphics communication. Because silhouettes are view dependent, it is expensive to extract silhouettes for previous techniques when the object is moving in space. This paper presents two algorithms of extracting silhouettes from 3D models. By exploiting the property of local maximum value and connectivity of silhouettes, the methods first identify part of silhouettes, then extract external silhouettes of 3D models by simple comparisons. The first method divides the model into some zones evenly in X and Y direction. Then it calculates the maximum edges of the zones in X and Y direction. These edges are silhouette edges. By searching the neighbor maximum edges of the silhouette edges, it finds the silhouette of the model. The second approach begins from the top edge in Y direction. By comparing the angles between the silhouette edge and its neighbor edges, it obtains the silhouette easily. Experimental results illustrate the efficiency of the methods. The algorithms and previous methods are compared and analyzed at the end of the paper.