“Continuous tone representation of three-dimensional objects illuminated by sky light” by Nishita and Nakamae

  • ©Tomoyuki Nishita and Eihachiro Nakamae




    Continuous tone representation of three-dimensional objects illuminated by sky light



    Natural lighting models to date have been limited to calculation of direct sunlight. However, this paper proposes an improved model for natural lighting calculations that adequately considers both direct sunlight and scattered light caused by clouds and other forms of water vapor in the air. Such indirect natural light is termed skylight and can be an important factor when attempting to render realistic looking images as they might appear under overcast skies.In the proposed natural lighting model, the sky is considered to be a hemisphere with a large radius (called the sky dome) that acts as a source of diffuse light with nonuniform intensity. In order to adequately take into account the nonuniform intensity of such skylight, the sky dome is subdivided into bands. The light intensity within individual bands can be assumed to be transversely uniform and longitudinally nonuniform and therefore the total luminance emanating from each band can be calculated more accurately.The proposed method significantly improves the realism of natural lighting effects. Its advantages are particularly apparent when simulating lighting under an overcast sky or when rendering surfaces that fall within a shadow cast by an obstruction lit by direct sunlight.


    1. Gardner G.Y. : Simulation of Natural Scenes Using Textured Quadri~ Surfaces, Computer Graphics, Vol.18, No.3(1984) pp.ll-20.
    2. Gardner, G. : Visual Simulation of Clouds, Computer Graphics, Vol.19, No. 3(1985 ) PP. 297- 303.
    3. Cook, R.C.: Shade Tree, Computer Graphics, Vol. 18, No. 3 (1984) pp.223-23!.
    4. Aono, M. and Kunii,L. : Botanical Tree Image Generation, IEEE CG and A~ Vo!.4, No.5 (1984) pp. i0-29.
    5. Fournier,A. ,Fussel!,D. ,and Carpenter L. , Computer Rendering of Stochastic Models, Comm. ACM, Voi.25, No.6 (1982) pp.371-384.
    6. Blinn, J.F. and Newell, M.E.: Texture and Reflection in Computer Generated Images, Comm. ACM, Vol.19, No.i0(1976) pp.5~2-546.
    7. Cook,R.L. and Torrance,K.E.” A Reflectance Model for Computer Graphics, ACM Trans. on Graphics, Vol.l, No.i(1982) pp.7-24.
    8. Nishita,T.~ 0kamura,l. and Nakamae,E.: Shading Models for Point and Linear Sources, ACM Trans. on Graphics, VoI.&, No.2(1985) pp.124-146.
    9. Nishita,T. and Nakamae ,E. Half-Tone Representation of 3-D Objects Iluminated by Area Sources or Polyhedron Sources, IEEE, Proc. of COMPSAC(1983 ) pp.237-241.
    10. Goral,C.M., Torrance, K.E., Greenberg,D.P. and Battaile,B. : Modeling the Interaction of Light Between Diffuse Surfaces, Computer Graphics, Vol.18, No.3 (1984) pp.66-75.
    11. Nishita,T. and Nakamae,E. : Continuous Tone Representation of Three-Dimensional Objects Taking Account of Shadows and !nterreflection, Computer Graphics, Vol.19, No.3(1985)pp.23-30.
    12. Cohen,M.F. and Greenberg,D.P.: The Hemi-cube: a Radio~sity Solution for Complex Environments, Computer Graphics, Vol. 19, No. 3 (1985) pp.31-41.
    13. Nishita,T. and Nakamae,E.: An Algorithm for Half-Tone Representation of Three-Dimensional Objects, Information Processing in Japan, Vol.14 (1974) pp. 93-99.
    14. iES Daylighting Comittee : Recommended Practice of Daylighting, Lighting Design & Application, Vol.9, No.2(1979) pp. 45-58.
    15. CiE Technical Comittee 4.2: Standardization of Luminance Distribution on Clear Skies, CIE Publication, No. 22, Comission International de i’Eclairaze, Paris (1973) pP.7.
    16. Nakamae, E. and Nishita, T. : An Algorithm for Hi dden line E1 imi nat ion of Po lyhe dra, Information Processing in Japan, Vol.12 (1972) pp~134-141.
    17. Nakamae, E., Harada, K. , Ishizaki, T. and Nishita ~T. : A Montage Method ; The Overlaying of The Computer Generated Images onto a Background Photograph, Computer Graphics, Vol. 20, No. 3 (1986).

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