Using analogies stretching from the Wright Brothers' first flight to ancient cave paintings, Jeffrey Katzenberg, George Lucas and James Cameron took the stage at CinemaCon to tell exhibitors that the 3D revolution has only just begun.

But the three had a word of caution for filmmakers looking to pad the grosses by converting films to 3D late in the process.

"I’m concerned about things that erode the market. Bad 3D is one of them," Cameron said.

Katzenberg echoed Cameron, labeling the conversions – like last spring's "Clash of the Titans" – "disappointing" and noting that "the 3D done to date has lowered the high bar."

Cameron said that true conversion should take between six to eight months, not six to eight weeks. The "Avatar" director said that only about 20 movies were worthy of being converted to 3D. Among those will be his own "Titanic," sailing into theaters in 2012, and "Star Wars," which will come to our galaxy the same year.

Key to helping 3D come of age, they stressed, has been movie theaters' conversion to digital.

"Where we are in digital is like 1900 in celluloid," Lucas said.

The filmmaking panel represented the industry's velvet-glove approach: a trio of thoroughbreds trotted out to entice those stragglers still hesitant to spend the money to make the leap to digital.

Lucas said that once an exhibitor make the initial capital investment for digital conversion, which can be about $100,000 per screen, their cash outlay is pretty much over.

"Three-D is like color, it's not like sound. Digital is like sound. Digital changes everything. Sound changed everything, color just made it better," Lucas said.

They stressed that despite the mounting threat of VOD and the chaotic windowing situation, there is still a place for movie theaters.

"Movie theaters will never, ever go away," Lucas said. "We love the movie theater. I make my movies for the movie theater. I don't mind it going on other platforms, but if you want to see it in the best way possible, you've got to see it in a movie theater."

Not that they don't believe there are new frontiers are left to conqueror. In this Cameron's case, it's the decidedly more wonkish topic of frame rates. The "Titanic" auteur said he wants to see frame rates accelerate from 24 frames per second up to rates of 48 to 60.

He said he plans to make the next two "Avatar" sequels at higher frame rates.

"If the 3D puts you into the picture, the higher frame rate takes the glass out of the window," Cameron said.