Oscar-winning filmmaker Ang Lee says his latest offering "Life Of Pi", a 3D adventure drama, has been the most difficult film of his career.

"Undoubtedly this was the most difficult film of my career. It took me three and a half years and 3, 000 crew members to complete the project. It was a herculean task to make an engaging story, which is only about a young boy on a lifeboat with few animals, " Lee told reporters here Wednesday.

He is currently in India to promote the movie, which features Indian actors Suraj Sharma, Tabu and Irrfan.

Releasing Nov 23, the movie is based on the novel of the same name by Canadian writer Yann Martel.

Lee says most of the computer graphics imagery (CGI) of the film was done in India.

"The CGI of the film was time consuming. It approximately took us about six months to complete the tiger. Most of the CGI was done in places such as Mumbai and Hyderabad", said the filmmaker, known for movies like "Brokeback Mountain" and "Crouching Tiger, Hidden Dragon".