“Shockproof,” director Douglas Sirk’s 1949 masterpiece, originated in the typewriter of Samuel Fuller, and is the sole rung shared by two revered cinema originals on their otherwise unrelated climb up the a ladder to commercial success in the 1950s.

Cornily, sincerely, and briskly zipping along for 80 minutes on the wings of Fuller’s tabloid storytelling verve (unmistakably evident despite meddlesome studio interference) and kept buffed to showroom-quality smoothness by Sirk’s elegant camera style and compositional genius, “Shockproof” is a minor film vehicle with major virtues.

Though aware that fraternization is verboten, two-fisted but bighearted parole officer Griff Marat (Cornel Wilde) falls hard for gorgeous murder parolee Jenny Marsh (Wilde’s then real-life wife Patricia Knight). What Griff doesn’t know is that Jenny’s underworld boyfriend, Harry Wesson (John Baragrey), isn’t as far out of the picture as Jenny claims. When Griff takes Jenny home to meet his mother, Jenny’s crazy love for Harry begins to fade.

In his marvelously emphatic and colloquial memoir “A Third Face,” New York-born copyboy-turned-screenwriter-turned World War II infantry dogface Sam Fuller described the postwar search for work in Hollywood that would lead to his “Shockproof” credit.

Fuller’s prodigious combat experience drove him to pitch scripts with the punch-to-the gut truth of his pre-war years covering the NYC waterfront and his soul-shattering walk across Europe with the 1st Infantry Division.

Studio executives listened respectfully as Fuller pitched films with titles like “Murder: How to Get Away With It,” and “Crime Pays.” But Fuller’s back-alley reality was judged too real for the public’s fragile morals, and Fuller was shown the door all over Hollywood.

The script that would become “Shockproof,” was originally called “The Lovers,” and was, Fuller said in a late ’60s interview, “about a woman who, in order to get her lover back, marries someone else.” An independent producer bought “The Lovers” and brought it to Columbia, where Sirk, then under contract to the studio, accepted the assignment of directing it.

“There was something great in Fuller’s ending,” Sirk himself (the two men never actually met) recalled decades later in Jon Halliday’s “Sirk on Sirk.” But Columbia’s brain trust didn’t see it that way and enlisted staff writer (and future adapter of “Valley of the Dolls”) Helen Deutsch to de-claw Fuller’s spitting, arched-back tale.

Pioneer programmer Ray Privett offers “Shockproof” as the first in a series of films chosen by members of an online auteur theory discussion group called “a_film_by.” Championed by filmmakers and “a_film_by” regulars Bilge Ebiri and Dan Sallit, “Shockproof” is a perversely smart example of the kind of director-vs.-screenwriter dynamic that often revved up Hollywood B-movies of the ’40s.

Even with both horns removed by Deutsch’s rewrite, the story charges from scene to scene courtesy of Fuller’s unmistakable ear for dialogue. Speculating on the roots of criminal recidivism, for instance, Griff and a colleague break it down succinctly — “It’s heredity! It’s environment! It’s a joke!”

But “Shockproof” clearly belongs to Sirk. The latter third of the film’s unblinking view of marriage as a kind of bond of guilt has the same precision queasiness of the director’s influential ’50s frozen hothouse melodramas like “Imitation of Life.” And, like several of his ingenious late ’40s peers, Sirk made the most of his meager budget by shooting much of “Shockproof,” on actual L.A. locations, including the oft-filmed Bradbury Building and the now vanished downtown neighborhood of Bunker Hill.

Thanks to the tireless efforts of Sony Pictures Repertory’s Michael Schlesinger, dozens of Columbia films that are, like “Shockproof,” unavailable on DVD have been resurrected on local repertory screens in the past decade. This characteristically pristine new print shows off both Sirk’s supernaturally pure film sense and the reliably brilliant photography of unsung Columbia staff cinematographer Charles Lawton, Jr. Each shot, full to the bursting with set dressing bric-a-brac, sub-frames, and intersecting lines, subtly points a moral finger at Griff, Jenny, Harry, and ultimately at love itself.

Through January 30 (155 E. 3rd St., between Avenues A and B, 212-591-0434).