A Fast Display Method of Sky Colour Using Basis Functions

Computer graphics recently have began being used for visual environmental assessment or architectural designs. Displaying the sky as a background is indispensable in generating photorealistic images for such applications. In this paper, we propose a fast display method of the sky color by expressing the intensity distribution of the sky using basis functions, even if the sun position and/or the camera position are altered. In the proposed method, cosine functions are used as basis functions. The sun altitude is altered at certain intervals and the distributions of the sky color for each sun altitude is precalculated and stored efficiently using basis functions. The color of the sky in the view direction of an arbitrary sun position can be obtained from the stored distributions and displayed quickly.