Methods and application for photorealistic rendering and lighting of ancient buildings

Within the field of cultural heritage restoration, experts are interested in the visual analysis of data describing status and history of ancient monuments. The use of computers together with image synthesis techniques can support the visual analysis and comparison of restoration simulation. The results of these computations are usually distributed over many sites that can be viewed by VRML and Java technology, which are well-suited for describing and visualizing geometrical models and data interaction over the Internet. Unfortunately, the poor quality of VRML real time rendering is a bottleneck for any analysis based on accurate image synthesis methods. Another problem in reproducing images with photorealistic rendering derives from the adaptation mechanisms of the human visual system. We describe a method and its implementation for providing high quality photorealistic image synthesis of ancient building materials, considering also a final adaptation stage able to simulate the lighting and color adaptation phases of a human observer. In this method, a network based Java application manages geometric 3D models of ancient buildings to provide an editing interface and to manage high quality photorealistic snapshots. Simple 3D VRML data are enhanced with radiometric data derived by gathering measurements on the actual material taken from the site to reproduce. In the example presented in this paper, we have used measurements taken from the ancient Roman Aosta Theatre. A server-based optimized rendering application computes photorealistic images on radiometric data, that are subsequently applied as input to an algorithm simulating the human visual system perception. This latter phase is able to emulate the human local lightness, and chromatic adaptation mechanisms. The enhanced interaction with high quality images of the model through the Java application, allows a visual qualitative evaluation of restoration hypotheses. It also provides a tool that is able to show the final appearance of the model under assigned lighting conditions, as observed by a human being “inside” the virtual environment.