Road Trip the Light Fantastic

Imagine a big, round ball with a highly polished mirror for a surface. Imagine it floating magically above the ground, reflecting everything around it?both earth and sky?in all directions. Then, take the image on the surface of the ball, turn it inside out and scan it into a computer. You now have a fairly good approximation of how Mike Callaway and Mark Banas, of Chicago's Bending Light Studios, use high dynamic range imagery (HDRI) to seamlessly integrate completely digital objects?in this case, computer-generated Toyota SUVs?into a conventionally photographed scene, producing an image that is, to most observers, 100 percent realistic.

Callaway and Banas recently turned their CGI and retouching skills to a project for Saatchi & Saatchi L.A. Automobile manufacturers often need to create advanced prototypes of cars not yet in production, for both auto show displays and advertising. Because these prototypes can be extremely expensive?sometimes running to several million dollars?manufacturers have long wanted to substitute CGI versions of the prototypes for the real thing in print ads. The purpose of this project was primarily to show Saatchi and its client Toyota that it could be done convincingly.

HDRI is a relatively new technology: Until 2000 or so, it was used primarily by computer scientists and computer researchers. Now, however, affordable HDRI technology is available on the desktop. "The idea is to capture the entire dynamic range of a scene," Callaway says, "and not just in one exposure. You grab a whole range of luminosities and layer those together to make one dynamic image."

This HDRI image is then used to virtually create the world that will be reflected in the reflective surface of a CGI object. "When you aim a camera at something, whatever that something is, it's being lit by light sources nearby. And the object?to a greater or lesser degree?is going to reflect the scene around it. But when you have a 3-D object created in a computer, there's no world it can reflect; it's just a digital object floating in a void," Callaway explains. "What the HDRI image gives it is an environment that it can reflect."

In this case, Banas shot both the HDRI images and the landscapes they would use as the backgrounds. For the HDRI images, he positioned the camera at the spot in the scene where the car would have been sitting, then shot a panoramic image that goes all the way up, all the way down and all the way around?essentially producing a sphere.

Banas then created the HDRI image using off-the-shelf camera equipment. For the Toyota images, which included approximately ten different setups, he used a Canon 20D digital camera. He swept the tripod-mounted camera from ground to sky in all directions, and shot a broad range of exposures for each part of the scene, sometimes as many as 15 for each section.

"You want to get all of that information into the image, changing exposures to get full shadows, mid-tones and highlights. And all of those exposures are then layered into the HDRI sphere, so you have complete control over exactly what the CGI object is reflecting and complete control over the degree of reflectance," says Banas. "We generally don't need to use the lighting features in the 3-D program, as the HDRI image provides the lighting for us."

Banas combined the images using a program called Stitcher, from software developer Realviz, running on a Mac. When the HDRI images were done, he handed them to Callaway, who created the CGI of the car.

"We take copious notes on every scene," says Callaway, "and we work closely with the photographer, because we have to know everything about the camera that shot the background. We have to know how far it was from the spot where the object will be placed, how high the camera was off the ground, focal length of the lens, exposure, all those things. And we use that information to then re-create the shoot virtually, inside the computer."

Toyota's engineers provided Callaway with wireframe CAD files of each prototype. "CAD files can be huge," he says, "because they're often incredibly detailed, down to the screws and bolts, which adds considerably to the rendering time if we don't take those features out. These files had already been translated, though, from CAD to a more generic format that was easier for us to work with."

The next step was to set up the virtual scene. "We set up the virtual camera to match the real-world camera," says Callaway, "and set up the background to match the real-world background. Then, we place the wireframe and start surfacing it, deciding what's going to be rubber, what's going to be paint, what's going to be glass and so on." Bending Light has extensive libraries of digitized paint colors and surfaces. "We spent a lot of time with car-paint swatches, and also worked with the different surfaces and different types of finishes, getting them to react to the CGI lighting the same way a car's finish would react to real-world lighting."

Once Callaway had imported the HDRI image, he began tweaking the virtual reflections in the surface of the car. He set up the virtual scene using Maya and used mental ray software to do the actual rendering. He then brought the Saatchi art directors in, giving them low-resolution renders for their approval. Images were imported into Photoshop for final compositing, tweaking and color correction, then Callaway did the final render. The image of a virtual car in a virtual world was complete.

Callaway concludes, "We've been able to do this type of thing for a while, but for most of that time, it was a very painful process. It's only recently that technology has gotten the process to a level I can honestly call 'seamless.' We can put CG products into photographic backgrounds, we can put photographed objects onto CG backgrounds. Photography is really just the starting point now?for artists or art directors or anyone who wants to make whatever image their mind has come up with a reality, CGI is the ultimate tool." Remember when they used to say that about Photoshop? Bending Light

Address: 200 North Dearborn St., Suite 1502, Chicago, IL 60601

Phone: (312) 357-6554

Web: www.bendinglight.com

Contact: Michael Callaway

E-mail: mike@bendinglight.com



Equipment: Bending Light uses a combination of Macintosh G5 PowerPCs with 4 gb of RAM and PCs for CAD/CAM and CGI applications. Software includes Adobe Photoshop CS2, Maya and LightWave 3-D programs, mental ray for rendering and various computer-aided design and engineering applications.



Sample Clients: Sony, McDonald's, Chevron, Disney, Pixar, Wrigley's Gum, Frito-Lay, Skill/Bosch, Victoria's Secret, Waldorf Astoria, American Film Institute, Blockbuster Video.