Practical Image Based Lighting

In this paper, we present a user-friendly and practical method for seamless integration of computergenerated images (CG) with real photographs and video. In general, such seamless integration is extremely difficult and requires recovery of real-world information to simulate the same environment for both CG and real objects. This real-world information includes camera positions and parameters, shapes, material properties, and motion of real objects. Among these, one of the most important is lighting. Image-based lighting that is developed to recover illumination information of the real world from photographs has recently become popular in computer graphics. In this paper we present a practical image-based lighting method that is based on a simple and easily constructable device: a square plate with a cylindrical stick. We have developed a user-guided system to approximately recover illumination information (i.e. orientations, colors, and intensities of light sources) from a photograph of this device. Our approach also helps to recover surface colors of real objects based on reconstructed lighting information. 1 Motivation Compositing, which can be defined as the integration of computer-generated images (CG) and liveaction photographs, has been an essential part of movie making. Currently, there exists a number of large special effects companies specializing mainly in compositing. For successful compositing it is crucial to seamlessly integrate real and CG components. It is well known that such a seamless integration requires solving a set of extremely difficult problems. Most of these problems are related to recovering the following real world information: (1) Illumination information to simulate the same lighting environment for both CG and real objects, (2) camera positions and parameters and, (3) shapes, material properties, and motion of real objects. The special effects companies solve these problems by employing a large number of computer graphics experts and mathematicians. The compositing (or integrating) of computer-generated images (CG) with real photographs can be an important part of the architectural design process. Such composited images can show how a new structure will change the existing landscape before actually building the structure. We have observed that some architects and architectural firms have already started to use composited images. The quality 1 Examples of such special effects companies and samples of movies they have contributed are Industrial Light and Magic (ILM) (Jurassic Park, Terminator, Flubber, Jumanji, Pearl Harbor, Artificial Intelligence and Star Wars), Rythm and Hues (Babe, Men in Black, Cats and Dogs, Harry Potter and Lords of the Rings), Digital Domain (Titanic, What Dreams May Come and The Fifth Element), Sony Pictures Imageworks (Hollow Man, Stuart Little and Godzilla).