Issue 75 of the Star Wars beacon, the official Star Wars newsletter, has as its main feature an interview with CG Supervisor David Meny about the creation of the Kaminoan clone factories.
Here is the story:
As Obi-Wan tours the Kaminoan cloning facility, he sees an immense hatchery of fetal clones suspended in glassy jars affixed to disc-like pods. This sequence incorporated live action and miniature elements, but the centerpieces of the environment -- the hatchery pods -- were entirely digital creations.
"Because the hatchery pieces were really comprised of five basic components that are repeated numerous times throughout the shots, computer graphics were a really good solution for creating this scene," says David Meny, Computer Graphics Supervisor at ILM.
The "real" elements of the shot included bluescreen photography of actor Ewan McGregor, a miniature corridor environment, and a miniature of the far dome interior. The glassy forest of hatchery pods outside the corridor was all digital.
"The main challenge in this sequence was realizing an environment that has so many glass elements with so many reflections and refractions. Also, there's a large number of models that you have to render, because in each of these jars there's a fetus with significant detail and motion," says Meny.
Each hatchery "tree" consisted of five repeated pieces: a fetus, a jar, a pod, a base, and a tube. "Because of the depth of the shot, we needed some pods that would stand-up very close to the camera and some that could be seen way in the background. We created multiple resolutions of the models to put the detail where we needed it, but not incur the expense of rendering that detail when we didn't expect to see it."
Within each jar was a fetal clone. ILM crafted two models to suggest different stages of clone development. The animators created one long sequence of motion for the fetus model, which was than offset throughout the jars for the illusion of individual performances.
Once the visual characteristics of the models were finalized, the shot began to be assembled layer by layer. For this shot, this was necessary since the visual and lighting complexity of the environment would be impossible to render in one pass. Some of the most complex layers alone required 12 hours per frame to render.
"We break it down to as many rendering layers as we can manage reasonably," says Meny. "In this shot, there's about 120 rendered layers that are then combined in the composite. The main reason in doing that is it gives you a lot more control to change things. If a certain part of the shot isn't working, you only have to re-render a subsection of that," says Meny.
With the outside hatchery assembled complete with lighting and atmospheric haze, one final addition gave the shot an added hint of realism. Since there was no reflective glass on the bluescreen stage during Ewan McGregor's shoot, ILM had to trick a reflection of Obi-Wan on the inside of the glass corridor. "The compositor had to cheat it using elements from other shots, and slip-sync them to give you a sense there's a reflection in the glass. The final composite is pretty subtle, and we hide it behind the principal element of Obi-Wan."