Jon Favreau has been dreaming about The Jungle Book since he was a kid.

"I remember Mowgli actually popping up in a dream of mine when I was young, and he was riding around in my parents' car in Manhattan. It was a strange dream, but it is an early memory, so I know it must've been an important film to me," the cheerful director laughs.

"And of course I remember being very excited about the music, and I remember the idea of Mowgli and Baloo being buddies, and Baloo being really protective of him. And I liked the fact that Mowgli was always getting into trouble, you know, he felt like a real kid to me," he explains.

So when Disney got in touch to ask if the Iron Man director would consider helming a new version of the film (based on the Rudyard Kipling stories first published in the 1890s) three years ago, he was both excited and nervous.

"I wanted to make sure I honoured at least the images and music and memories that I had from when I was younger, even though we were updating it, and doing a tonally different version of it. I tried to include some of that for people of my generation who have memories of the original, and who have certain expectations based on them."

That tonal difference is an interesting point, with the film having a distinctly darker, more dramatic outlook than the 1967 Disney original or the cartoon version from 1992, which stems from both the writing and the incredible advancement in animation techniques that makes the animals hyper-real, and seamlessly blends the real-life Mowgli (played by Neel Sethi) into the computer-generated jungle world.

"We didn't want to just make a G-rated kids movie, this one is PG and you know, you've gotta know your kid - if they see the trailer and think it's too much for them, then that's a good indicator.

"But what you get with these photo-real animals is a much more exciting, thrilling experience, and I think we also found a way to incorporate what people remember from the old movie with the relationships between the characters and some of the music and so on. That was the balancing act."

The visual world which they've created for the film is very impressive - it lies somewhere between real and animated, like Avatar or Life of Pi, but is so consuming when viewed on the big screen, you forget all about the painstaking process behind it.

Some of that was done by Weta Digital, who have previous primate experience with the likes of King Kong and the Planet of the Apes reboots.

"They did a whole block of the film which deals with the monkeys and the gigantapithicus, which is the giant orangutang character that Christopher Walken plays, King Louie, and boy it was great working with them. They had so many ideas, and the imagination that they brought to the table, and how to bring a fun tone to the action and adventure elements, I was very happy to collaborate with them."

Interestingly, the man who was King Kong, Andy Serkis, is directing in his own motion capture version of The Jungle Book starring Christian Bale, Cate Blanchett and Benedict Cumberbatch.

Of course to make any computer generated film have resonance with an audience, it still needs an emotional centre. Here, that comes in the form of Neel Sethi, who does an excellent wide-eyed job as Mowgli. He makes you believe he's really leaping around the jungle, and singing songs with Baloo the bear, even though the film was shot in Los Angeles studios in front of blue screens.

"He was a smart kid, very sharp, and the trick is that you don't dumb down your conversation. If you just say 'Ok here's where the camera is, and this is what we're trying to do, and you act like it's not going to be a problem, kids are pretty good at adapting."

They tried to make it a fun experience for Sethi too, having his family around, and giving him the Favreau says that the new version of the film is darker than the cartoon version from 1992.

opportunity to do as many stunts as possible.

"Because we were doing so much blue screen, he could do a lot of stunts, and if he was ever climbing or jumping we could have pads under him or people in blue suits spotting him, so he got to really act with a lot of reckless abandon, like a kid on a playground, except we could make it look like the jungle.

"And we made sure there were always other actors on set, and Sometimes we had puppeteers - we had the Jim Henson studios design puppets and supply puppeteers so that he could interact with these animals [instead of a tennis ball on a stick], and there's always that look in his eye like he's experiencing something for the first time."

Of course having a voice cast that includes Ben Kingsley (Bagheera the black panther), Lupita Nyongo (Raksha the Indian wolf), Idris Elba (Bengal tiger Shere Khan), Scarlett Johannson (huge python Kaa), Christopher Walken (King Louie, the gigantopithecus orangutan), and Bill Murray as Baloo, gives the film wonderful character too. It was a dream cast for Favreau.

"Bill Murray, I didn't know if I would get anywhere near him, because I've reached out to him in the past and you know, he's an elusive figure. But I sent him a letter, got some things to him, showed him some visuals, and when I got the call back I knew it was good, because he wouldn't have called if he wasn't interested.

"He's been an idol of mine since I was young, before I even knew I wanted to be in this business, and he was a real treat. He improvised a lot, he had ideas, he was really encouraging, and very obliging, doing it as much and as many times as I wanted, it was so great to work with him."

Despite the amount of CGI involved, Favreau was also determined to make sure the film was injected with the real personalities of the actors involved.

"We did have the actors work together as much as we could, you know, we had Neel work with Bill, we had Christopher Walken with Bill. We had all these different actor combinations, and then we videoed, with several cameras, all the performances, so that we could animate the characters based on their acting choices, and their body language and facial expressions.

"So there were a lot of steps involved, but hopefully that all disappears when you're watching it, and you're lost in the story."

Very few of the actors have seen the film yet, so Favreau is looking forward to seeing their reaction, particularly given how challenging it was to describe an overall picture of the film before it was finished with all the elements in place.

"There was a lot of me trying to explain what it would look like and how it would feel when it was finished, but it's hard to explain for sure. You know 'it looks like real animals, but they're not, and they're talking, and there's music, but it's not like a cartoon'. It was hard for me to explain what we were going to be able to achieve. But I have to say after working for two to three years on it, I had a lot of time to play with it, and get it just right, and I'm very proud of how it turned out."

Voices from the jungle

Idris Elba:

"Shere Khan reigns with fear. He terrorises everyone he encounters because he comes from a place of fear."

Sir Ben Kingsley:

"Bagheera is Mowgli's adoptive parent. His role in Mowgli's life is to educate, to protect and to guide. My Bagheera is military - he's probably a colonel. He is instantly recognisable by the way he talks, how he acts and what his ethical code is."

Scarlett Johansson:

"Kaa seduces and entraps Mowgli with her storytelling. She's the mirror into Mowgli's past. The way she moves is very alluring, almost coquettish."

Christopher Walken:

"King Louie is huge - 12 feet tall. But he's as charming as he is intimidating when he wants to be."

Giancarlo Esposito:

"Akela is a fierce patriarch of the wolf pack. He believes the strength of the pack lies in what each and every wolf offers. He's a great leader, a wise teacher."

Lupita Nyong'o:

"She is the protector, the eternal mother. The word Raksha actually means protection in Hindi. I felt really connected to that, wanting to protect a son that isn't originally hers but one she's taken for her own."

Who: Jon Favreau, director
What: The Jungle Book
Where and when: Opens in cinemas on Thursday April 21