The various scanning sessions of the Parthenon and its works of art.

Debevec's 3D modeling techniques are based on using CG primitives — boxes, wedges and other geometric shapes — with photographic images in a way that the computer can figure out the 3D re-construction of the photo. His photogrametric technique — Facade — makes computer graphics primitives snap to the edges in photographs, so the computer can use perspective geometry to quickly create a full three dimensional structure of the scene. Once the computer recreates the geometry, the photographs are projected onto the model as texture maps. Debevec wants to create a whole environment, but unlike a virtual setting like the storybook appearance of the Polar Express, he has a different goal. "Our work is focused to make it look real, as real as photographs." But in 3D modeling, getting the right geometric representation of an object or scene won't make it photorealistic. Lighting is an inescapable factor in making CG images believable.

Debevec learned lighting while taking photographs of architecture. He noticed the different effects in varying amounts of sun and shade. Photos and computer images have a limited range of colors and pixel values while most film scenes have a wide range of varying light conditions. Realistic lighting not only relies on direct lighting sources such as the sun, but includes the reflective properties of objects. Debevec knew he needed better tools. "These 8-bit pixel values really weren't good for representing anything brighter than what a monitor could display or dimmer than where things start to look muddy. It became painfully obvious that the range of light in the real world is far greater than this." Debevec worked to capture the full range of light by taking a series of photographs with variations of exposure that when put together in a final image, balanced the levels of brightness and mimicked lighting in the real world. This work with High Dynamic Range Imagery (HDRI) contributes to making CG images look absolutely real. The technique is used to record the illumination on a set and then light a digital character, that when added to the scene, would actually be lit with the light that was really on set.

This August at the SIGGRAPH 2004 Conference, Debevec's cutting-edge computer graphics technology will be showcased in his latest short film, The Parthenon. The film premieres at the prestigious Electronic Theater Computer Animation Festival at the Los Angeles Convention Center. Using the best archaeological sources available, The Parthenon takes the viewer on a two-and-a-half minute virtual journey through both the digitally reconstructed temple and a photorealistic recreation of the Duveen Gallery of the British Museum, home to a majority of the Parthenon sculptures.

The crowning monument of the Athenian Acropolis in Greece, the Parthenon was dedicated to the goddess Athena in 438 BC and remains one of the world's greatest architectural achievements. Its sculptural decorations included marble statues in its triangular pediments, high relief metopes above its outer columns and a low-relief frieze that circled the inner colonnade of the temple. Over the years, it has been battered by time and wars, damaging or destroying some of these details. Most were removed in the early 1800s when the British Lord Elgin had them shipped to England. They remain on display at the British Museum despite requests from Greece for their return.

In the film, Debevec and his ICT research group use technology to virtually return the Parthenon's sculptures to their former places. To achieve this simulation, ICT developed two custom scanning processes — one for the sculptures, one for the architectural ruins. The team traveled to Switzerland's Basel Skulpturhalle, a museum that houses high-quality casts of all the Parthenon sculptures and fragments scattered throughout Europe, including the ones in London, Athens and Paris. More than 2,000 scans of the collection were captured using a newly developed ultrafast 3D scanning system that allowed highly detailed geometry to be recorded with a standard desktop video projector and digital video camera. These were then assembled into millimeter-accurate models of the friezes, metopes and pediment sculptures.