An Effective Framework for Cloud Modeling, Rendering, and Morphing

In many multimedia applications such as computer games, flight simulation, and spe- cial effects for movies, clouds play an important role. In this paper, we present a variety of techniques for cloud modeling, cloud rendering, and cloud morphing in order to make the visual appearance of clouds in these applications more effective and interesting. For cloud modeling, we propose a polygon sampling technique that enables users to accurately model various types of cloud shapes from a 2D image. Moreover, if a 3D model is available, we provide a tetrahedron sampling method to model the cloud. In cloud rendering, we present two line integral convolution (LIC) techniques. The first technique eliminates the Gaussian blobs caused by the splatting algorithm that is commonly used in conventional cloud ren- dering while the second one produces a sky plane which increases the visual appearance of the cloud rendering. Finally, we present a "greedy" morphing algorithm for the purpose of cloud morphing. This algorithm allows a gradual transition of smooth cloud shapes during the animation process with only a limited number of frames. Our techniques increase the visual realism of the appearance of clouds.

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