Extending the Photon Mapping Method for Realistic Rendering of Hot Gaseous Fluids Byungkwon Kang † , Insung Ihm † , Chandrajit Bajaj ‡ † Department of Computer Science Sogang University Seoul, Korea ‡ Department of Computer Sciences University of Texas at Austin Austin, Texas, U.S.A. Abstract With the increased sophistication and use of heated gas, fire, and explosion simulations in computer graphics applications, there is a corresponding impetus to improve the visual realism in the rendering of such simulated phenomena. In visualizing these turbulent fluids, an appropriate incorporation of their incandescent properties into the rendering significantly enhances the realism of visual effects. In this paper, we effectively synthesize the light emission phenomena of hot gaseous fluids by extending the photon mapping global illumination method. In particular, we add two new photon maps to capture the thermal radiation effects. First, we define an emission photon map to store the photons emitted within hot gaseous fluids. Second, we utilize additional flash and flash reflection photon maps, which are effective in creating a visual effect of light that intensively and instantly propagates outside hot gaseous fluids, visually capturing shock waves. Our current technique, while based on the theory of blackbody radiation, is parameterized to enable an animator to generate a wide range of visual effects with fairly intuitive user control. We demonstrate the effectiveness of our new rendering technique and user-controlled generation of visual effects with several example pictures and animations. Keywords: Rendering, gaseous fluids, incan- descence, blackbody radiation, photon mapping, physically based fluid animation. 1 Introduction Among a variety of natural phenomena, hot gaseous fluids, ranging from simple smoke and gas to fire flames and explosions, abound in the real world, and are often indispensable ingredi- ents in the production of computer animations. Many simulation techniques for such fluids have long been developed in the computer graphics community for the purpose of effective visual applications. In particular, recent research ef- forts to exploit numerical simulation methods in computational fluid dynamics have proved very successful. As a result, diverse physically based fluid animation techniques are now rou- tinely applied to create realistic visual effects of hot gaseous fluids. While realistic rendering of simulated fluids is an essential part of a fluid animation process, researchers have focused mainly on generating appealing motions and controlling their shapes. Physically based simulation techniques gener- ally produce their results in the form of volu- metric datasets, describing physical properties of gaseous fluids, such as density, temperature, pressure, and velocity. Obviously, the most de- cisive attribute that affects the appearance of flu- ids in the rendered images is their density. How- ever, the temperature property also becomes im- portant when hot gaseous fluids that give out light are to be rendered. Although volume ren- dering has been studied rigorously, primarily for visualizing the density field, only a few studies of computer animation have seriously dealt with