Slumdog Millionaire director Danny Boyle says he filmed the "very subversive" and yet loveable tale of a slum kid who hijacks a game show to present a vibrant Mumbai in all "its horrors and incredible joys".

Boyle, whose latest film "Slumdog Millionaire" has opened here to rave reviews from American critics, says he had not initially read Indian diplomat Vikas Swarup's novel "Q&A", but when he saw Simon Beaufoy's screenplay based on it, he was floored.

"It was the depiction of Mumbai, a vibrant city of vivid contrasts that attracted me, " the British filmmaker, known for his cult classics "Trainspotting", "28 Days" and "Shallow Grave", told in a telephonic interview.

"And this character from the slums of Mumbai who is accused of cheating to win the 'Who Wants to be a Millionaire?' show. But people don't know he has a completely different agenda - to find his ladylove through the show."

"In a way it's 'very subversive' - a slum kid taking a shot at a mind game and winning it - but I loved it, " said Boyle.

So Simon Beaufoy and he went off together to Mumbai to make sure it was all authentic, the very characters, situations and the setting depicted in the screenplay of the film commissioned by Channel 4 TV in London.

"I wanted to tell the story of the slum kid who hijacks the show... wanted to present the maximum society. Wanted to portray... to try to present Mumbai in all its colours, " Boyle said. But "I did not want to do it through a Westerner's eye. I wanted to do it through the character."

The perfect blend of pathos, humour and action that has made US critics go gaga over this film was "not really a judgement call, " the director said. "Such extremes do exist because of the city's intrinsic nature as a whole."

"In many ways it was different from a filmmaker's usual perspective. Those are not relevant as Mumbai is beyond that kind of rigid divisions with all its horrors and incredible joys, " he said.

"Also, when you go in the slums you find they are not really like the places one would imagine in the West, " Boyle said. "They are just places where people live. These people are not lying about waiting to die out there. They are industrious, vivacious people living life very very fully."

Boyle said they zeroed in on Madhur Mittal to play the older Salim, the lead character's brother through auditions. As it turned out, "Madhur was very terrific." But try hard as they did, they could not find in India the right person to fit the role of Jamal Malik, the protagonist.

"I wanted a guy who would blend. But all those who came, they all looked like hero-types, " he said. Then he looked at "this guy in London, Dev (Patel) who is on British television show 'Skins' and he has a bit of a profile."

"But Dev has a very protective mother who wanted to tag along everywhere. But in the end, as it turned out she was a very happy mom, " he said.

"Things were great" with Bollywood star Anil Kapoor, who plays the game show host. "He was a bit nervous at first. It was his first English film, I suppose. His English is excellent. He also does a lot of research to give credence to his role and assures people, " said Boyle.

"It was also wonderful for me. I could not communicate with the crew, as a lot of them didn't speak English. So Anil would talk to them. He would stir them and enthuse them."

But he had to work hard to persuade Irrfan Khan to play the detective who interrogates the slum kid, said Boyle who found the actor "wonderful."

"Initially he thought it was a small role. But I told him 'you are the one who makes the most progress' with the kid when he is brought to the police on suspicion of cheating. It's the inspector who gets to unravel the story and in a way the tale hangs on him."

"Filming at the fabled Taj Mahal was an extraordinary experience, " said Boyle. "It's overwhelming, incredibly romantic. There are lots of restrictions... understandably so given that filmmakers in the past have not been respecting the structure and its heritage."

"We were able to get round the problem with the use of a still camera and shooting with a second unit to avoid unwanted attention, " he said.

Boyle was equally ecstatic about working with Indian composer A.R. Rahman. He is "terrific to work with. He is so talented. He is amazing, " the filmmaker gushed.

"When I first talked to him, he did not know whether he was going to do it. But when I showed him the film, he loved it. He is a fusion of what's disco, hip hop and rap. He has a very 'jagged' preference, not even, " said Boyle. "I loved that most."

Before filming "Slumdog...", Boyle said he watched three recent Indian films, "Satya", "Company" and "Black Friday" recommended to him. He found them to be "three exceptional films."

"They do have a slightly stretched Bollywood style, " but what he liked most about them was the "enormous dynamism of story telling."