It is well known in certain circles that Rainbow Media chief exec Joshua Sapan collects art not from Christie’s or Sotheby’s but from the trash.

Art school leavings, curbside detritus — these are the sculptures and paintings that line the walls of his Penn Plaza office, Shelter Island vacation home and 3,700-square-foot apartment on the Upper East Side. Rescuing these hundreds of pieces from the dustbin of history offers Sapan a thrill no auction can match. “I’m attracted to the ecology of it,” he says.

But what strikes a visitor even more about his modest-sized office is how crammed it is with devices spanning a century of showbiz, everything from wood-paneled radios to late-model laptops.

The menagerie speaks to the rise of Sapan, 56, from a film buff renting 16mm prints from the back of his station wagon at the U. of Wisconsin to running a multimedia company. Sapan is up on tech and societal trends but also a published poet who can vividly recall scenes from Japanese existentialist film “Woman in the Dunes.” His eclectic tastes, personable style and drive to build brands have combined to take Rainbow to new heights.

Emmy wins for “Mad Men” and “Breaking Bad” continue to resonate and have given AMC some of that turn-of-the-century HBO mojo. The film world has taken note lately of IFC Films, whose video-on-demand strategy has found traction as it aims to offer consumers 100 films a year.

“Televisions are getting a lot bigger and also a lot smaller,” Sapan says, noting the proliferation of both mobile devices and flatscreen sets. “These proclamations about ratings declining and audiences diminishing are missing the point. The opportunities for content now are much greater because of all of the venues that are available.”

Seven-day Nielsen ratings, which take into account DVR viewings after the initial airdates, favor AMC and IFC in particular. Because Rainbow is owned by major cable operator Cablevision, the company has another incentive to use VOD as an additional tool to win brand loyalty.

“The perception of a brand’s value matters more than ratings,” Sapan says, noting how AMC’s recent success has brought a flood of new material. “They have so much more importance now that there are so many channels.”

Similarly, IFC, on his watch, has spent years persuading a roster of internationally acclaimed filmmakers that their festival darlings benefit from a day-and-date VOD push along with a theatrical run.

“Che,” acquired in Toronto, is the peak of that sales pitch. The Wild Bunch two-parter directed by Steven Soderbergh, which reportedly cost more than $60 million, was acquired for a tiny fraction of that. It will enjoy a “road show” theatrical bow reminiscent of Sapan’s four-walling days in Wisconsin, but will be on VOD the same day.

Clad in jeans and a gunmetal-gray dress shirt, Sapan visibly enjoys analyzing the evolution of his business since his stint as a young exec at pay cabler Uptown, essentially Gotham’s version of the Z Channel. Tall and thin, his thick brown eyebrows waver animatedly when he tosses off self-deprecating lines (“I need to be careful with what I say so I don’t shame myself with candor”).

Two subjects Sapan unhesitatingly dodges are the prospect of renewing “Mad Men,” possibly via a long-term deal with creator Matt Weiner, and whether Rainbow could be sold. Sapan’s uber-bosses, Charles and James Dolan, said recently they are reviewing all Cablevision assets with a possible spinoff or sale in mind.

That move followed the acquisition of the Sundance Channel and the Newsday newspaper. Also in the Rainbow stable are the IFC channel, women’s channel We and Voom, a suite of 15 nascent high-definition channels whose creation Sapan oversaw in 2005.

Any strategic moves are undoubtedly on hold in the current economy, however.

Sapan came aboard as prexy of Bravo and AMC in 1987, when Bravo was a pay channel with 200,000 subscribers and American Movie Classics belied its name by rerunning “Jaws 3-D.” He came to the channels from a seven-year run at Showtime, where he met his wife, longtime exec Ann Foley who recently left the biz to spend more time with their 12- year-old daughter and 14-year-old son.

After Wisconsin, the New York native worked as UA-Columbia Cable as a volunteer. “I knew from an early age that I wanted to go into television,” he says. “There was never any doubt.” There was division in the household as to the medium, though. Sapan’s dad made smallscreen ads, while his stage actress mother hated TV.

Always a lover of classic movie theaters even as he climbed the TV ladder, Sapan used his own funds to buy the Greenport Theater on Long Island’s North Fork a few years ago. Built in 1939, it has been expanded to four screens and a gallery for art, discarded or not.

Walking out his office into the hallway, he pauses by an old-fashioned, brass-framed mail chute, one of the few remnants of the made-over building’s 1923 bones.

“I always wonder how that’s still here,” he marvels when a visitor takes note of the chute. “I’ll be standing in this modern space and then be fascinated when a piece of mail drops down. I can’t believe people still use that thing!”