The 100 or so Pixar Animation Studios employees had good reason to be giddy, and you could understand why they were more than a little nervous too. For more than four years, the animators, sound designers, editors and artists from every other Pixar department had plugged away on "Up," and on an early morning in April, they were finally about to see how their animated movie had turned out.

The movie itself -- Pixar's 10th animated film -- is narratively ambitious, a story about a 78-year-old widower's highly unusual road trip with a chubby young boy that, throughout its making, teetered on becoming sentimental and episodic. Although the movie is filled with comic bits, "Up" also features scenes of complex human emotion -- including the grief of a miscarriage -- that are rarely explored in family films. Parent studio Disney really needed the film to work commercially too: In earnings released recently, Disney's profits fell 46 percent, largely because of underperforming movies such as "Confessions of a Shopaholic" and " Jonas Brothers: The 3D Concert Experience."

To add one more level of pressure to the Pixar team, just a few days before that April screening at George Lucas' bucolic Skywalker Ranch, the Cannes Film Festival had selected "Up" to launch the festival, the first time for an animated film.

If producer Jonas Rivera and writer-director Pete Docter, two of Pixar's earliest employees, were sweating bullets when they introduced "Up" to their Pixar colleagues, they didn't show it. "This is the first time that we've got everything together," Rivera said. Added Docter just before the house lights dimmed: "Thank you guys for making the movie."

Despite all the end-of-the-journey gratitude, "Up," which premiered in Cannes and arrives in theaters Friday, wasn't quite finished. Docter and Rivera had just a few more days to tweak the sound mix, and had reserved one day for composer Michael Giacchino ("Ratatouille") to record a new bit of music if necessary.

As soon as the screening ended, Docter, Rivera, Giacchino, executive producer John Lasseter and a dozen members of Pixar's brain trust met over lunch to discuss what they had just seen. By the time the team finished dessert, they had decided "Up" needed a new piece of music, and the choice they made revealed much about the film's creative ambitions.

As "Up's" poster and trailer make clear, the film's central image is a house, tethered to thousands of balloons, soaring into the sky. When 78-year-old Carl Fredricksen's ( Ed Asner) residence took flight at the Skywalker screening, Giacchino's score was big and dramatic, the kind of music that typically accompanies an action sequence.

"What we had I think works," said Docter. "But I didn't feel like we were quite capturing it." Specifically, the music wasn't magical, poetic. The house's taking off needed to play more like a mystical metaphor -- Fredricksen's trying somehow to join his late wife, Ellie, in the heavens -- and less like a prison break.

"There's something about the lyricism of the floating house that appealed to me from Day One," said Docter, a tall man whose 10-year-old daughter, Elizabeth, provided young Ellie's voice. With a new piece of music, Docter said several days later, the scene played closer to how he always imagined it should. "Now, it's almost like he's waltzing with Ellie as the house takes off."

"Up" represents several Pixar firsts. In addition to the studio's first trip to Cannes, "Up" also marks a new move into producing and releasing a film in 3-D. It's a format that has worked well for competitor DreamWorks Animation's "Monsters vs. Aliens," and Pixar is now remaking its first two "Toy Story" films (in addition to next year's "Toy Story 3") in the immersive technology.

The film's more material departures are harder to detect. It's the first Pixar feature to have as its central character a senior citizen, and because Fredricksen is based on friends and relatives of the filmmakers, "Up" might well be considered the studio's most personal film. "I think so too," said Bob Peterson, "Up's" co-director and co-writer, who also lends his voice to one of the film's dogs. "It's an homage to our grandparents, and that makes it personal."

Before Pixar Animation's "Up" became a movie, it was a single image: a grouchy old man with balloons.

Docter, 40, who has a writing credit on last year's Oscar-winning "WALLE " but hasn't directed a movie since 2001's "Monsters, Inc.," then added another element: What if those balloons raised the man's house into the skies?

"We found something that worked really well for a long time. And when nothing else was working, we would use that sequence to pitch to people and they would say, 'Wow, I want to see this movie,'" Docter said. As visually striking as the image might be, it wasn't clear how it and the senior citizen inside fit into a larger story, which explains why "Up" took four years to make it to the screen.

"In the very first draft ... he just wanted to join his [late] wife up in the sky," Docter said. "It was almost a kind of strange suicide mission or something. And obviously that's [a problem]. Once he gets airborne, then what? So we had to have some goal for him to achieve that he had not yet gotten."

Added Peterson: "Originally, he was not going anywhere. He was just going into the sky because he had always associated his wife with birds."

That didn't sound like a Pixar movie -- it sounded like a film out of the surrealism movement. So Docter, Peterson and Rivera tried to figure out what they were really trying to communicate.

As the story took shape, it became clear that Fredricksen felt not only a little angry, but also unfulfilled. He had enjoyed a long romance with his wife, but they hadn't been able to have kids, (a fact touched on in a highly emotional, dialogue-free, four-minute montage of their lives), and their childhood dreams of traveling to the distant land of Paradise Falls had died when she did. But those were episodes, not narrative. "Up" needed something more.

So now real estate developers are encroaching on Fredricksen's last remaining patch of comfort, his home, and a pesky 8-year-old Wilderness Explorer named Russell (voiced by newcomer Jordan Nagai) is knocking on his door, trying to collect a help-a-senior-citizen merit badge.

Taking flight, in other words, wouldn't be such a bad idea. But even if he (along with Russell, who happened to be on Fredricksen's porch at the moment of liftoff) was finally able to get to Paradise Falls, was that it? What would they find there?

When Russell and Fredricksen land in Paradise Falls, they encounter a once-famous explorer whom Fredricksen and his wife had idolized as kids. The exotic land is populated with strange birds and talking dogs, but the real surprise is Charles Muntz (Christopher Plummer), who has gone the way of Col. Kurtz in "Heart of Darkness" and becomes "Up's" villain. Fredricksen suddenly has to become Russell's protector and, in a strange way, the two (along with a slow-witted but faithful dog) become something of a family. "A guy ties thousands of balloons to his house and floats away to South America to go to Paradise Falls," Rivera said. "That's what happens, those are the plot points," Rivera said. "But that's not what it's about. What is it about? It's about adventure; it's about life. It's about learning that the most important things are not external. They're internal."

To solve that question -- What are the most important things in life? -- the "Up" team turned to its oldest acquaintances and relatives, mining their memories for stories and videotaping their homes for reference, figuring out how you can be cantankerous and warmhearted at the same time. The influences included Rivera's grandfather, the legendary Disney animator Joe Grant (who died in 2005) and Disney costume designer Alice Davis.

What the filmmakers decided was that the most meaningful trips didn't have to be in a balloon-propelled dwelling. They could be picnics in the park, watching clouds drift by, visits to an ice-cream store.

"He's always thought of adventure as travel and exotic places and animals no one has ever seen and all of this far-out stuff," Docter said of Fredricksen. "And in the end he comes around to realize that the real adventures in life are the small things that we do with our family and friends."

"Up," for all of its novelty, was returning to some of the same simple, universal ideas that anchor all Pixar movies, stories that always seem to transcend the perceived limitations of what they are about. A talking rat who cooks? A robot who packs up garbage? A man with balloons? Strip away the elaborate (if sometimes unconventional) narrative devices, and you begin to see relatable truths that give the movies heart. WALLE just wants to hold hands. "Ratatouille" is about becoming the person you were born to be. The importance of family? Watch "Finding Nemo."

What "Up" was trying to say, in other words, was not so different from what has happened to Pixar itself: that growing older can be a beautiful thing.

Is 'Up' good?

Find out what Tribune critic Michael Phillips thinks Friday in Live!/Movies.