In January 1980, Martha Cooper was a New York Post photographer assigned to cover a supposed riot in a Washington Heights subway station.

When she arrived, “I asked the cops what happened,” Cooper tells The Post. “They said these kids had been dancing and spinning on their heads, and started fighting over who had won.” The “riot” was a breakdancing contest; Cooper had stumbled upon the new hip-hop culture filtering through the city.

Now, in honor of hip-hop’s beginnings, the Museum of the City of New York is hosting the new exhibit “Hip-Hop Revolution.” Besides Cooper’s, the show features photos by Janette Beckman and Joe Conzo.

Open Monday to Sunday, 10 a.m. to 6 p.m. The Museum of the City of New York, Fifth Avenue at 103rd Street; mcny.org. Admission $14.

After seeing that the “riot” she was supposed to cover in Washington Heights wasn’t happening, Cooper was intrigued to hear the police description of the dancing they had witnessed.

“After they were released, I asked the kids to show me what they had been doing, and this was it. No one I knew had ever heard of it before and, as far as I know, this is the earliest picture of anyone break dancing. And it was shot for the New York Post.”

Cooper says of this dancer, “I didn’t know the boy at the time, but, more than 20 years later, I used this picture again in a book called ‘

The Hip Hop Files

,’ and he contacted me.

“His name is Christopher Sawyer and he’s now a dance instructor in New York.” Sawyer, 44, has toured with Mariah Carey and been in Whitney Houston videos.

Beckman shot Flavor Flav and Chuck D for the now-defunct music weekly Melody Maker in 1987, and found them to be much more agreeable than their reputation suggested.

“I was warned ahead of time that they might not like me,” she says. “But Chuck was very polite and Flavor was so funny — cracking jokes all the time. He’s also holding what I like to think is one of his first clocks. I don’t think he wore them before this shoot, but it went on to become his signature look.”

Beckman’s relationship with the Beastie Boys started way back when producer Rick Rubin was still their DJ. It wasn’t just turntables he was packing back then, either.

“I have no idea why, but Rick had a gun with him that day. I actually have another picture of him posing with it in one hand, and a Blimpie cup in another!”

By the early 1980s, the first wave of b-boys had their own apprentices. Richard “Crazy Legs” Colón of the Bronx-based Rock Steady Crew rapidly became a local celebrity and inspired ‘Lil’ Crazy Legs (pictured here) to take his name and imitate his dance moves.

Queens native James Todd Smith (a k a LL Cool J, second from left) was hip-hop’s first big heartthrob and, as Beckman found when she photographed him and his friends on Great Jones Street, ladies really did love him.

“You can’t see it here, but I remember he had this red mark on his neck, which was probably a love bite! He was a very handsome man — and still is!”