Interactive frame rates for globally illuminated scenes in presence of participating media

Resumen

The realistic image synthesis is a well known field in computer graphics. Traditionally, one of the goals of this research area has been to be able to compare a photograph with its cor- responding image from a virtual scene without noticing any dierence. A good overview of the realistic image synthesis field can be found in references [11, 70, 21, 29, 17]. Addi- tionally, Glassner [21] describes the characteristics of a computer monitor, the human eye system and some psychological features of the observer related to its vision. Note that, in the end, the quality and the credibility of a given image is usually judged by a human being. The physically-based simulation of the light behaviour is a time consuming task even for modern computers. Consequently, some simplifications have normally been applied in order to deal with a computer-friendly problem instead. A common assumption is to restrict the electromagnetic spectrum to its visible part ([0.380 m, 0.780 m] wavelength range), and usually to its three primary colors (RGB). Another important observation is that the wave theory is barely taken into account; in general, the quantum theory of light is solely applied. There are certain phenomena that can only be explained by considering the wave theory, such as diraction and interference. However, this is a common simplification because the contribution of these phenomena to the final image is frequently low in comparison with its computational cost [21]. This thesis is centered in the rendering of scenes including participating media. This term is used to designate, with a common name, phenomena like fog, dusty air, clouds, smoke, etc. and to indicate that it does participate in the process. In 1994, Rushmeier [65] listed some application areas where it is important to take into account the contribution of participating media and proposed some resolution methods:  Checking the visibility of exit signs.  Entertainment and virtual reality.  Military interest: vision under water, atmospheric eects for simulating remote sens- ing, or battlefield smoke plumes.  Applications devoted to drivers' training. The optical eects of participating media such as fog are important to them. Taking into account the presence of participating media in a scene involves an increment of the complexity of the rendering problem due to several facts:  In a non-participating media environment radiance is constant along the line between two surfaces. This is no longer true in case of including a piece of a participating medium.  Furthermore, a light particle is continuously changing its direction whenever it is traversing a medium.  The computational cost is also augmented if dynamic participating media is being considered. This thesis can be included in the realistic image synthesis field and its main goal is to study and propose ecient algorithms (featuring interactive frame rates or real time performance) for static and dynamic participating media. The thesis is organized as follows: Chapter 2 includes a theoretical background for partic- ipating media, spherical harmonics and Monte Carlo basis, Chapter 3 presents a state of the art including those resolution methods related with the goal of this thesis, Chapter 4 indicates some open problems, the following two chapters explain the proposed two dier- ent approaches; Chapter 5 includes some references and results by applying Monte Carlo techniques whereas Chapter 6 explains a new algorithm to deal with dynamic participating media based on the use of spherical harmonics properties. Finally, Chapter 7 includes the conclusions of the thesis, Chapter 8 the future research direction and Chapter 9 a list with the contributions of the thesis.