Modelling of Clouds from a Hemispherical Image

Abstract

This paper presents an image-based method for modelling clouds. Unlike previous image-based approaches, a hemispherical photograph is used as input, enabling to consider an entire sky instead of merely a portion. Our method computes the intensity and opacity of the clouds from the photograph. For this purpose, beforehand, the sun illumination is filtered, the pixels are classified between cloud and sky pixels, and the sky behind the clouds is reconstructed. After having been smoothed, the intensity of the clouds is used to create vertices on a hemisphere, and their radius coordinate is modulated by the intensity value of the corresponding pixel. Finally, the mesh is generated by triangulation of the vertices. Additionally, the use of the opacity of the clouds to simulate their transparency and render them is proposed. The results show that our method can be used to produce a realistic full sky populated with clouds in a very straightforward way for the user.