Capturing and Simulating Physically Accurate Illumination in Computer Graphics

Anyone who has seen a recent summer blockbuster has witnessed the dramatic increases in computer-generated realism in recent years. Visual effects supervisors now report that bringing even the most challenging visions of film directors to the screen is no longer a question of what’s possible; with today’s techniques it is only a matter of time and cost. Driving this increase in realism have been computer graphics (CG) techniques for simulating how light travels within a scene and for simulating how light reflects off of and through surfaces. These techniques—some developed recently, and some originating in the 1980’s—are being applied to the visual effects process by computer graphics artists who have found ways to channel the power of these new tools. RADIOSITY AND GLOBAL ILLUMINATION One of the most important aspects of computer graphics is simulating the illumination within a scene. Computer-generated images are two-dimensional arrays of computed pixel values, with each pixel coordinate having three numbers indicating the amount of red, green, and blue light coming from the corresponding direction within the scene. Figuring out what these numbers should be for a scene is not trivial, since each pixel’s color is based both on how the object at that pixel reflects light and also the light that illuminates it. Furthermore, the illumination does not only come directly from the lights within the scene, but also indirectl