Marion Cajori’s documentary “Chuck Close,” which begins a two-week engagement December 26 at Film Forum, opens with the 67-year-old eponymous artist seated in front of a camera, taking photos of himself. He fusses over details of light and shadow, symmetry, angle; he complains that his face is too fat. After his assistants pin various prints up on the wall, he chooses one he thinks is just right. But that doesn’t make it a Chuck Close self-portrait — just the beginning of one.

There’s nothing groundbreaking about Cajori’s thorough rendering of Mr. Close, arguably the world’s greatest living portraitist, but the filmmaker, an art-world documentarian who died in 2006 shortly after completing this film, is commendably devoted to exploring the artist’s creative process.

The funny thing about Mr. Close’s process is that it’s as fascinating as it is mind-numbingly tedious. His outsize mug shots — painstakingly adapted, one hand-painted pixel at a time, from blown-up photographs — are products of the kind of labor generally reserved for machines these days, or at least outsourced to Asia. But they are also a testament to an immense talent, one the film is eager to explore.

Mr. Close paints his enormous grids one square at a time, filling each one with a solid color on his first pass over the canvas. He adds squares, triangles, and blobby shapes in subsequent stages, each resembling a brightly colored fish egg. Eventually, they coalesce into a remarkably life-like image of a human face. The photographic detail of his portraits is undermined by the obvious fact — at least upon close inspection — that they are handmade, and the way each one shimmers between a figurative whole and an orderly arrangement of discrete units that Mr. Close calls “art marks” is the key tension in his work.

Laying bare the illusion of representation was, of course, a primary preoccupation of 20th-century art, and the film enlists an A-list group of Mr. Close’s colleagues (many of whom he has painted) to weigh in on his contributions to that effort over the past four decades. The composer Philip Glass, who compares the subject to Marcel Duchamp and John Cage, explains that Mr. Close’s works contain the story of their own creation. The painter Brice Marden says that the expressive molecular patterns that make up Mr. Close’s paintings help carry them “beyond the image.” The formative pop artists Andy Warhol and Roy Lichtenstein come up in conversation, but everyone, including Mr. Close himself, seems put off by their android-like tendencies. As Mr. Marden points out, there’s a tangible human struggle going on underneath Mr. Close’s meticulously assembled surfaces.

Without being too pushy about it, the film suggests that Mr. Close’s struggle began at age 11, when his father died. At one point it proposes that the instability in his work — the constant breaking down and reforming of the image, which magically takes place during Cajori’s elegant slow zooms — is a reflection of that tragedy. The metaphor gains strength from another pivotal moment in the artist’s life, a 1988 spinal blood clot that left him temporarily unable to paint and has confined him to a wheelchair ever since.

Though he claims to have been influenced by such grand-gesture painters as Jackson Pollock and Willem de Kooning, Mr. Close dabs at the canvas without bravado and whistles to pop tunes as he works. Watching this likeable painter in his studio is surprisingly fun, thanks to the ever-changing soundtrack and the magical transformation that takes place on the canvas during the course of three months. Cajori’s keen visual sense helps, too — her framing is excellent, and the camera whips from Mr. Close’s palette to the canvas with a puppy-dog curiosity. Late in the film, there’s even a brush-cam — admittedly, a bit of a gimmick — that takes the viewer on a roller-coaster ride of Mr. Close’s workspace.

But the biggest reason the studio scenes are rewarding is because Cajori’s film manages to integrate them into the larger puzzle of the art-making process. Casual fans may question whether Cajori really needed nearly two hours to do it, but she knowingly explores Mr. Close’s predecessors, peers, and personal life with a deft sense of balance.

And although a dry, tacked-on epilogue incorporating a 1997 MoMA retrospective dulls the impact of what would have made a fine closing shot, it does reinforce the primeval, albeit evasive, force of Mr. Close’s totemic headshots. Since the early 1970s, the artist has played a significant role in the return of figurative painting, but his multilayered work does not necessarily bring the world into focus. As Robert Rauschenberg says, viewing it is “like going into an Egyptian tomb and you don’t read hieroglyphics.”

Begins a two-week engagement at Film Forum on December 26 (209 W. Houston St., between Sixth Avenue and Varick Street, 212-727-8110).