Rendering - Physically-Based Rendering

Global Illumination-Perception: Tone Reproduction Operator

Accurate simulation of radiometric scene properties does not guarantee that the final images will have a realistic visual appearance. Current display devices are limited in a number of ways, including spatial resolution, temporal resolution, absolute and dynamic range, and color gamuts. In addition, the observer of the physical scene and the observer of the display may be in very different visual states, which can affect how they perceive the visual information before them.

A better understanding of the spatial, temporal, chromatic, and three-dimensional properties of vision can lead to even more realistic and efficient graphics algorithms. Our research framework in this area is based on the idea of a tone reproduction operator, introduced by Tumblin [TUMB93], which incorporates the physical transfer properties of the display device and the visual states of the scene and display observers. Using this visual model to determine the mapping from simulated scene radiances to display radiances that produce a perceptual match between the scene and the displayed image, we can produce images predictive of what observers in the simulated scene would see. This allows the images to be used quantitatively in areas such as illumination engineering, transportation and safety design, and visual ergonomics.

Current global illumination algorithms spend a great deal of time computing unimportant and imperceptible scene features. Algorithms can be substantially accelerated by using error metrics that correctly predict the perceptual thresholds of scene features. The establishment of these techniques will not only allow realistic visual display, but will also provide a feedback loop to improve the efficiency of the global illumination computations.