Why The Diving Bell and Butterfly will show us visions of an inner world

Cut down by a stroke, J Bauby created a novel merely by blinking. Nicola Christie discovers how his life translated to the screen

It's the Il Postino or the Life is Beautiful runner at the Oscars; the small, special film that nobody quite saw coming. It started life 11 years ago as a book entitled Le Scaphandre et le Papillon, translated into English as The Diving Bell and The Butterfly – a slim book of memoirs written by a man called Jean-Dominique Bauby, known to his friends as Jean-Do. Jean-Do was the editor of the French fashion bible Elle during the 1980s. At the age of 43, without warning, he experienced something similar to a massive stroke, leaving him entirely paralysed with the exception of his left eyelid. The Diving Bell and the Butterfly is the book he dictated with his left eyelid; a series of blinks – estimated at approximately 200,000 – that capture life inside the spirit of somebody entirely alive, but trapped inside the body of a dead weight.

"It is an extraordinary story, incredibly moving," says the Oscar-winning screenwriter Ronald Harwood, who was given the challenge to turn Diving Bell into a film. Five years ago, the producer Kathleen Kennedy, a regular collaborator of Steven Spielberg's, called Harwood to say that she had purchased the rights and would he be interested in having a go at the screenplay. Harwood agreed and took himself off to his flat in Paris to get cracking. Only nothing came out. The nature of the book – one long monologue by a person who is entirely commenting and reflecting, not doing – had left him stuck. Until it came to him that the audience would become Bauby. "They would see everything through his eyes," explains Harwood. "Experience life as he did. The camera would do the blinking. Only I'm not technical and I didn't know whether that could be possible."

Enter painter/film-maker Julian Schnabel. An artist known for his experimental work, he might be the one person able to create an alternative way of looking. He wasn't Kennedy or Harwood's choice, but that of the actor Johnny Depp; Depp had originally accepted the part of Jean-Do on the condition that Schnabel direct him, later pulling out because of Captain Jack Sparrow's commitments. But Schnabel was in place and salivating at the prospect of using the camera in new ways.

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"My director of photography, Janusz Kaminski, thought I was crazy at first. Like I took my glasses off and I put them on the camera," he reveals. "So when you move, it's in focus and then out of focus – I used a swing and tilt lens. I thought it was a great opportunity to put whatever I wanted into the structure of a movie. I had the freedom of Jean-Do's imagination. I could go through time, I could do whatever."

In Jean-Do's own words: "My cocoon becomes less oppressive and my mind takes flight like a butterfly. There is so much to do. You can wander off in space or in time, set out for Tierra del Fuego or for King Midas's court. You can visit the woman you love, lie down beside her and stroke her still-sleeping face."

The French actor Mathieu Amalric is the man in charge of pulling off the almost impossible feat of playing a character who has no opportunity to play. Even in Harwood and Schnabel's masterly hands, the style of storytelling meant that Amalric got precious little screentime to actually express himself; we hear his voice, but when we see him, it is mainly as a memory of his former self.

"This was one of the reasons I was so pleased with the breakthrough idea, though," admits Harwood. "Because otherwise you would have to look at him for two hours – that's an awful sight, the stroke look."

Amalric's performance is hugely impressive, an indication of why he's going to be all over the screen this coming year (we'll next see him as the lead in the French thriller Heartbeat Detector and then, in the autumn, as a Bond villain). In Diving Bell he's supported by actors Emmanuelle Seigner, who plays Bauby's ex-wife Celine Desmoulin, and the legendary French actor Jean-Pierre Cassel, who delivers a heartbreaking portrait of Bauby's broken father. For Schnabel, once Depp was out of the picture, the movie had to be done in French.

"I wanted to get the voice and I had to believe it myself," Schnabel explains. "I knew that if I could just go into his world, I could figure it out on the way."

Schnabel took himself off to the hospital where Bauby had been confined, a former naval recovery bay used during the second world war, situated in the French seaside town of Berck; it allows intoxicating rushes of sea and sand to lap onto the screen as well as first-hand accounts from the doctors and nurses who had nursed Bauby. It is here that a team of therapists rallied around their patient to instruct him in a new language; a frequency-generated one, whereby the nurse would call out the letters of the alphabet and Jean-Do would blink when she reached the ones he wanted. The dictation followed an early morning wake-up call allowing Bauby to internally craft, and then memorise, his next piece of text.

"It is an amazing testament to the human spirit," reflects Harwood. "I mean, it's difficult enough to write a book with your hands, but to blink it. I tried blinking to an alphabet, I found it almost impossible."

The result of such a strict regime is a piece of writing so pared down, so essential, that the printed pages have sold hundreds of thousands of copies all over the world; on the first day of publication alone, in France, the entire run of 250,000 copies sold out.

"Writing was the thing that saved him," explains Schnabel. "His interior life came alive because he started to write the book. The book gave him a raison d'être, gave life to him, gave life to his family. Thanks to the book, they feel like he's alive in some way. It's a way of dealing with their grief."

The book has, for many, been a way of dealing with grief, sickness, or dark times, a tool for survival. The film is likely to be received in a similar way, but, with the opportunity for someone to retreat into visual fantasy now as well as verbal, there is perhaps an even more heady opportunity ahead; certainly Schnabel devours the opportunity to smother the viewer in the intoxicating stuff of life – smells, sounds, sensations; scenes on the beach with the wind whipping his children's tangled hair and sending his wife's skirt a-flutter; eating oysters with a lover; speeding along an open highway with the roof down; this is a butterfly, the flight of a man's imagination.

What's interesting is the forms of imagery Schnabel delves in to to deliver this rush, calling on everything from Marlon Brando, to alpine skiers and matadors in the ring. There's also a soundtrack that veers between Bach and Tom Waits, complete with another "survivor", the pianist Paul Cantelon. "He wrote the piano music for the film. He was a child prodigy," explains Schnabel, "and then he got hit by a car when he was 12. He had total amnesia. At the age of 17 he started to get his memory back and he started playing the piano again."

Art can give someone a reason to live. For J Bauby, once he only had art, he discovered that as a butterfly he could lead a richer life than the so-called former real one; it was then, he discovers, that he had been trapped inside a diving bell. "Had I been blind and deaf or did it take the harsh light of disaster for me to find my true nature?" Jean-Do asks early on in the story.

In Diving Bell he has another go at life, and reminds us, if we need it, that we will only have one go ourselves.

'The Diving Bell and the Butterfly' opens on 8 February