NEW YORK (Reuters) - Gay cowboy drama "Brokeback Mountain" may have been considered a risky film to make, but director Ang Lee said his new movie, "Life of Pi," a 3D exploration of faith about a boy stranded on a boat with a Bengal tiger, is his riskiest yet.

The film, which was released in U.S. theaters this week, is adapted from Yann Martel's best-selling novel of the same name and was once considered impossible to make.

Oscar-winning Taiwanese director Lee, 58, took on the laborious task of using computer-generated imagery to bring the sensational plot to the big screen, taking a year and a half just to edit the film together.

The director talked to Reuters about the film's themes, technical barriers and casting an unknown actor in the lead.

Q. Why was "Life of Pi" considered unfilmable?

A. "Because you cannot make the tiger do everything you want to do, you have to use digital. A digital animal, up until two years ago, was not totally realistic yet, let alone in 3D, and then water is pretty difficult."

Q. Was this your most difficult filming experience yet?

A. "Oh yes. And it was also the longest...there was the technical difficulty and then it is a big movie. And it was across continents, I finally decided to shoot most of it in Taiwan, but we also had to go to India to shoot for two to three weeks. Because you can't fake Pondicherry, and Munnar. And then we have scenes in Canada."

Q. But Brokeback Mountain was a risky film too?

A. "No, that wasn't for me. At least when I made it, I thought it was strictly arthouse and few people would see it. And it's a lot cheaper (to make). So I didn't care...And then I got nervous, 'Oh they are going to lynch me, making a gay cowboy movie, that will go into a shopping mall.'"

Q. It was only after you made it you realized that?

A. "Yes, I was afraid. I was looking around when I walked, when I would go home, to see if anybody was following me. Once it hit the shopping mall I was nervous, actually. My brother is a distributor in Taiwan and I told him not to buy it. He hates me to this day, he is still babbling about it."

Q. Why choose unknown Suraj Sharma to play Pi?

A. "I wanted someone authentic, and no bad habits, that means you have to train them from the start. "

Q. Why did you replace Tobey Maguire and reshoot his scenes with the little-known Rafe Spall?

A. "It was a small part, and he is a big movie star. He is a good old friend of mine and he would do this for nothing, for me. But he is not doing anything (in the role), he is just sitting there listening most of the time. It becomes a little distracting I think."

Q. How does the film explore spirituality?

A. "To me, faith can be elusive, but .. As a Taoist would say, 'That's the apple's truth.' The source of all the material comes from nothingness, illusion is working more on things you can prove. That's the principle, the essence of life, it is actually an illusion, not immaterial. That's worth pursuing. So illusion is not nothing. In a way, that is the truth."

"Sometimes I feel (illusions) are more of life's essence, I can trust them more than real life that is full of deceit and covering up."

Q. Did exploring faith encourage you to make this?

"The book is fascinating, it talks about faith. But it didn't make me believe in God or anything...I didn't go to church or a temple after that. When I started making the movie, you do feel faith embody you and carry you through. But when I picked the subject, and chose to do the book, it was actually more storytelling in my mind. The value of storytelling. How people share a story. Because a story has structure, it has a beginning, middle and end. It seems to have meaning, where life has not."

Q. Do you practice any religion?

A. "No, my mother is a baptized Christian, so she made me go to church every Sunday, and I prayed four times a day until I was 14. And at lunchtime kids at school would giggle at my praying...I stopped praying. And two weeks later, nothing happened to me, so I didn't pick it up again."

"I am not particularly religious. But I think we do face the question of where God is, why we are created and where does life go, why we exist. That sort of thing. And it is very hard to talk about it these days, because it cannot be proven. It is hard to discuss it rationally."

Q. Do you consider yourself spiritual?

A. "I hate to think life is just facts and laws. And I am a filmmaker, I am a sensitive person, I like to think it is spiritual, so I like people to be more in that way. I think life without spirit is in the dark, it is absurd. Call it illusion or call it faith, whatever you call it, we have emotional attachment to the unknown. We yearn to find out. That is human nature. It can be, in a way, unrequited love, we don't know. I don't have a particular God I pray to, except sometimes a movie god." (laughs)