Television, it is understood, is a writer’s medium.

It is taken as an article of faith in the creative community that the writers room is the wellspring of every plot twist, every line of dialogue and every ounce of mood, tone and setting that defines a weekly television series.

The new president of the Directors Guild of America, Paris Barclay, would like us to recognize that this is not entirely true. It’s a bold assertion for a working TV helmer, but it is born of experience and a deep appreciation for the art of collaboration.

“It is impossible to tell most of the time how much to ascribe what you see to the writer,” Barclay says. “It’s impossible to know the alchemy of what happened through all the performances that were filmed — they go through so many different stages. You cannot always assume it’s exactly what the writer imagined. It’s the biggest fallacy out there.”

The director is the crucial bridge between the actor and the camera, Barclay opined during a recent Television Critics Assn. press tour panel that came a month after his election as DGA prexy.

True to form, Barclay didn’t hold back for the sake of niceties with the other guilds, WGA or SAG-AFTRA.

“Knowing what’s happening between the actor and the director is the secret,” he says, noting that while actors sometimes come to the role fully formed, “other times we have to give it to them.

“A good script is great. It really helps. But even if the script is not good, we can come in and save the baby. The director’s job is like being an obstetrician. Or I like to say it’s genetic engineering. I like to get in there while the baby is still in utero and get some new genes in there. I try to get it slightly re-engineered to my liking.”

Barclay may be guilty of bragging, but he’s not complaining. He loves the give and take with writers and actors, and he loves the range of material he works with today.

He’s probably the only director in Hollywood who could pull off episodes of “Sons of Anarchy,” “Smash,” “Glee” and “The New Normal” in a 12-month period (landing an Emmy nom this year for one of his two “Glee” segs, “Diva”).

“This is a damn good time to be a director in television,” he says.

“In this brave new world, we’re making little movies. I always want to think of it as something we’re doing for the bigscreen — it’s that important and it’s that good. I want to be in the business of making something emotionally deep, cinematically interesting and creatively challenging.”

Barclay’s versatility with drama across the intensity spectrum — one of his recent “Sons of Anarchy” episodes had a father being forced to watch as his daughter was burned alive — and comedy has made him a leading light of TV’s new breed of director-producer hyphenates with increasing muscle in the TV biz. As Barclay notes, during the three-season run of HBO’s “In Treatment,” he was the constant force as exec producer while the writers changed every year.

“I’m an excellent cook,” Barclay says of his ability to work in a range of genres. “It’s one of the best skills that can prepare you for being a director. I can work with whatever the recipe is. Whether I’m making a souffle or I’m making a steak, I know enough about cooking to make a great dinner.”

Barclay’s ascent to being the public face of the DGA, and the guild’s first African-American president, is the latest milestone in an unpredictable career. His path to the entertainment industry began in grade school in Illinois, when he impressed by writing and starring in his own musical, “Time for Living,” about a warlock.

Although his family was of humble means, his good grades and skill at football got him into an exclusive Indiana prep school, La Lumiere, which led him to Harvard.

After graduating in 1979 with a degree in English, he arrived in New York City with the intent of working in theater, but he wound up working in advertising as a copywriter. He branched out into directing commercials, and then musicvideos in the heyday of MTV.

The narrative flair he demonstrated in the musicvid for rapper LL Cool J’s “Mama Said Knock You Out” caught the attention of writer-producer John Wells, among others in Hollywood. Wells gave Barclay a shot at directing an episode of the (extremely) short-lived 1992 CBS cop drama “Angel Street.” By the end of the decade, Barclay was riding the wave of edgy new dramas and had notched back-to-back Emmy drama directing wins for “NYPD Blue.”

The entree to TV series provided by Wells was the crucial break for Barclay. He’s been working with the DGA for years as an officer and as the head of its African-American Steering Committee to open more doors for up-and-coming black helmers. (Dee Rees, helmer of the 2011 Sundance film festival fave “Pariah,” has been shadowing Barclay on “Sons of Anarchy” this summer.)

But there’s only so much the DGA can do. The responsibility for scouting and recruiting new talent at all levels rests with those who do the hiring, including showrunners. He’s frustrated that even with the explosion of original series production across the TV dial, the employment figures for minority and female directors remain stubbornly low. He cites HBO and Warner Bros. as biz heavyweights that have notable diversity initiatives. But more needs to be done.

“We can’t make people become members of the DGA,” Barclay says.“Only the studios can. There’s just no excuse today for them not to look for (diversity). The pool of working directors has not grown at the same rate as the number of productions. What we’ve tried to do is beat down the doors and say ‘You’ve got to look at more people, you’ve got to interview more people.’ It won’t happen until the studios start hiring them.”