In the summer of 1890, Vincent Van Gogh, age 37, shot himself with a revolver in the fields outside Auvers-sur-Oise in France.

This is how Loving Vincent, an extraordinary animated film, begins. On a starry night, a crescent moon glows and the small town outside Paris becomes visible through billowing clouds. What makes this opening, and the film itself, so astonishing? The sequence, and everything that follows, is rendered completely in moving brushstrokes; every frame in this film is an oil painting.

At a time when animation is done mostly digitally, Loving Vincent directors Hugh Welchman and Dorota Kobiela have gone the other way. At about 10 frames a second their movie is made up of roughly 65,000 individual works of art. It’s an unprecedented achievement that could only have been accomplished by the most passionate of Van Gogh lovers.

“It all started with my wife, before she was my wife,” says co-director Hugh Welchman. His wife is co-writer and director of the film Dorota Kobiela. She is also a painter and animator. “She’s re-read the letters of Van Gogh since she was a teenager. She read it again when she was 28, and his story hit her hard.”

The Dutch artist’s 820 letters are beautifully written, detailed and illustrated and offer an insight into his psyche rivalled only by the paintings he left behind. When Kobiela met Welchman, she introduced him to Van Gogh’s writing.

“His struggle and determination in the face of repeated failure, depression, loneliness and heartbreak was inspiring,” says Welshman. “He was so strong, passionate and tenacious – so fiercely intelligent.”

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They decided to illustrate Van Gogh’s story in the most appropriate way.

“You can’t really tell Vincent’s story without his paintings,” says Welchman. “He painted everything around him: his shoes, his bedroom, the view from his bedroom, his food, the person serving his food, his letters, the person delivering the letters … we could assemble a vision of a world as he saw it from his body of work.”

Using a process called rotoscope animation – a process by which artists paint over frames of live-action footage – 125 painters in 20 countries spent two years creating what is best described as a living painting.

In Loving Vincent’s case, each frame was painted then photographed before an artist painted the next frame over the top. Sometimes that involved moving just one detail. Sometimes it involved starting again. In some ways the process has more in common with stop-motion than with traditional animation, except instead of moving puppets on a set these artists move paint across a canvas. Seeing things as if through Van Gogh’s eyes can be disorientating, but the overall effect is mesmerising.

What began as a short film grew to a feature, from 5000 paintings to 65,000. Famous actors joined the project including two-time Academy Award nominee Saoirse Ronan (Brooklyn, Atonement) and Tony Award nominee Chris O’Dowd (Bridesmaids, This is 40).

“It needed to be a combined performance between the actor and the painter,” says Welchman. “We had to hire painters and train them in both animation and in Vincent’s style.”

Nothing in the film contradicts known facts. The plot lives in the gaps around characters based on real people, many of whom appeared in Van Gogh’s paintings.

“There are gaps in the record, mainly around a lot of the other characters,” says Welchman.

Their protagonist is Armand Roulin, a blacksmith who later became a policeman. Roulin’s parents and siblings appeared in a series of famous portraits painted by Van Gogh in 1888 and 1889. For the purpose of the film, the directors styled Roulin as a reluctant investigator who becomes emotionally involved in Van Gogh’s story as he questions those who knew the artist in his final months.

“These people made statements after his death that contradict each other,” says Welchman. “We know some must be lying.”

The film unfolds like an Agatha Christie novel as Roulin assembles the final days of Van Gogh’s life through the recollections of the locals. Secrets are kept. Exaggeration is made. Guilt is rife.

The film’s present day – after Van Gogh has died – is rendered entirely in the artist’s vivid post-impressionist style. Dreamlike and rhythmic, brushstrokes coil and ripple across the screen, occasionally settling on the composition of one of the artist’s paintings. For flashback scenes, the illustrations are monochrome black-and-white.

The contrast divides truth from fiction.

Loving Vincent is screening nationally now. Watch the trailer here.