Devotion to an artist can lead to obsession, which is the only explanation for “Loving Vincent,” the extraordinary film on Vincent van Gogh by Dorota Kobiela and Hugh Welchman. In plot, it’s a sort of detective story, a dramatized investigation of the painter’s slow death by gunshot wound on July 29, 1890, in Auvers-sur-Oise, where he had repaired to paint. Was it caused by a suicide attempt that accomplished its goal, but only gradually, as is generally believed? Or was it manslaughter, perhaps even murder?

The narrative is told in the form of an inquiry by Armand Roulin (Douglas Booth), the dissolute son of the postmaster (Chris O’Dowd) in Arles, who had been a friend to the artist and had found an undelivered letter to van Gogh’s brother Theo. He asks his son to hand-carry it, but Arnaud arrives only after Theo’s death, so he decides to look into the circumstances of Vincent’s demise himself.

Arnaud’s investigation involves questioning a variety of locals in Auvers, among them Dr. Gachet (Jerome Flynn), an art lover who signed the death certificate; his daughter Marguerite (Saoirse Ronan), whom Vincent exhibited feelings for; Adeline (Eleanor Tomlinson), the daughter of the innkeeper with whom Van Gogh stayed; and Mazery (Bill Thomas), a quirky doctor who disputes Gachet’s conclusion that the wound was self-inflicted. He also interviews Pere Tanguy (John Sessions), the paint supplier who provided the pastels Vincent used, and who describes the young Vincent’s life in Paris. In what amount to flashbacks—and excerpts from Vincent’s letters to Theo (the usual signature line in which is the film’s title)—the artist himself is played by Robert Gulaczyk.

Frankly, this plot-driven aspect of the film is its least successful element. Arnaud’s queries result in some questions—essentially the ones that Steven Naifeh and Gregory White Smith raised in their 2011 biography—that challenge the generally-accepted finding of suicide. That’s all well and good. The problem lies rather in the script, which is riddled with clunker lines of dialogue, and the acting, which is at times very irritating. The main culprit is Booth, who turns Armand Roulin into an aggressive, impudent—and often tipsy and disagreeable—fellow.

He does look like Armand, however—or at least the Armand that van Gogh painted in his 1888 portrait, in which he wears the bright yellow coat as he does here. Moreover, Booth is not simply photographed playing him. His performance has been painted over, frame by frame, by an army of more than a hundred artists working over seven years, in van Gogh’s signature style. The same is true of every other character in the film, who are shot in poses resembling the artist’s paintings, along with the backgrounds. Thus van Gogh’s paintings appear to “come to life” in the hands of the directors and their platoon of contemporary painters.

The technique is a form of rotoscoping, but a much more sophisticated version of the process than has ever been employed before. The effect is like the one imagined by Albinus, the protagonist of Vladimir Nabokov’s “Laughter in the Dark,” who imagines the possibility of animating art masterpieces to make them move. “What a tale might be told,” Nabokov wrote, “the tale of an artist’s vision, the happy journey of eye and brush, and a world in that artist’s manner suffused with the tints he himself had found!” Albinus’ dream was scoffed at by animation experts, one of whom opined that such a film would bore most people to death, but Kobiela and Welchman have effectively pulled it off, and visually it’s hardly dull. Experts will undoubtedly try to identify the van Gogh works that are being referenced in each of the segments—a cascade of vibrantly colored “present day” images and shimmering black-and-white “past” ones—of “Loving Vincent,” but the rest of us can simply luxuriate in the flow.

It’s a pity that the more conventional aspects of the film—the writing and acting—don’t match the extraordinary quality of its visual execution. But the sheer beauty of the individual frames goes far to compensate for the narrative bumps along the way.

Be certain, by the way, to stay for the final credits, in which all the cast members are matched up with the canvases in which they were depicted by van Gogh. They only reinforce the obsessiveness of the entire mad, marvelous enterprise.