We encourage viewing this slideshow in âfull-screenâ mode.
Along a stretch of elevated train tracks on Westchester Avenue in the Bronx, Henry Chalfant encountered the Ghost of Christmas Past in 1977. It was faded, yet stun ning - though it wasn't quite a Dickensian tableau rendered by strokes of a quill.
This apparition covered the entire side of a train, done at night by graffiti artists using swiped cans of Krylon spray paint.
âIt was the âMerry Christmas train' by Lee, Mono and Doc of the Fab 5,â Mr. Chalfant recalled. âIt was parked in the center track layup. I climbed down onto the catwalk to shoot it with my little 50-millimeter lens.â
From moments like that, Mr. Chalfant went on to amass an archive of New York City subway graffiti that is rivaled only by that of Martha Cooper, a noted shooter in her own right and his collaborator on the seminal volume âSubway Art.â During those heady days in the 1970s, as the city went broke and crazy, armies of young people swept through tunnels and yards, leaving behind rolling - albeit illegal - murals on steel ca nvases.
Granted, a lot of it was less than pleasing, and some of it was flat-out bad. Mr. Chalfant caught much of it - from nascent masters like Blade, Crash and Daze, to flash-in-the pan toys. Now, after working on his archives for more than a dozen years, Mr. Chalfant is releasing a series of  interactive iBooks as  âHenry Chalfant's Big Subway Archive,â which co mbines classic train photos, essays and current video interviews with the artists.
It is a capstone to a career spent chronicling urban art and bringing it to a mass audience here and abroad.
âWhat we were doing was using a language among ourselves and talking to each other,â said John Matos, the graffiti artist known as Crash. âHenry brought an intellectual eye to it, and I guess that was needed. He was able to manifest our language to the public so they could see it differently. He brought a clandestine thing out into the open.â
Mr. Chalfant - who also gained fame as the co-director of âStyle Wars,â the definitive documentary of hip-hop's early years - hadn't started out to shoot graffiti. He had moved to New York in 1973 with his wife to pursue a career in sculpture. He had a studio on Grand Street and an apartment on the Upper West Side. As he commuted by subway each day, he couldn't help but see piece s that covered the cars' sides (and doors and windows).
It wasn't until 1976, he said, that he took the Broadway local up to Inwood, where he started photographing the trains outdoors. His interest soon led him to the Bronx, where the 2 and the 5 lines had some of the most active artists around, like Lee Quinones and Steven Ogburn, known as Blade.
His method was simple: he would head to the Bronx in the morning, positioning himself on the uptown platform, with the sun to his back. He was partial to the Intervale Avenue stop, which was high enough to have no buildings in the background, or the East Tremont stop, where he could see the downtown trains approaching as they rounded a wide curve.
Then he would wait. As soon as a train pulled in, he would snap a frame, dash a few steps, take another frame and keep on until he had four or five shots of an entire car. At the end of an outing, he would drop off the film at a quick processing place, where he would get double prints. For about three years he kept up this pace. As the number of prints grew, so did his albums, filled with page upon page of prints of whole cars that in the pre-Photoshop era were âmergedâ using an X-acto blade and cold mount film. (For his new archive series, his negatives were digitally scanned and stitched.)
Mr. Chalfant didn't meet any actual graffiti writers until 1979, when someone told him about the Writer's Bench, inside the lower level of the 149th Street and Grand Concourse station. Though some of the artists wondered if the skinny guy in glasses was a cop, his pictures soon won them over. In time, they started going to his studio.
âWe used to take pictures ourselves using those little 110 cameras at angles or as close as possible,â Mr. Matos said with a laugh. âHenry had the first dead-on pictures of trains. It was like you had a solid, s traight-on clean shot without people or el poles. We had never seen that before. It took my breath away.â
Mr. Chalfant's shooting became more systematic that same year when he bought a motor drive, allowing him to stand at the front end of the platform and squeeze off a sequence as the trains pulled out. Soon, writers were leaving messages on his studio phone alerting him to new pieces. Some even painted, âYo Henry, you gotta catch a picture of thisâ on trains, as they vied for his attention and tried to outdo each other.
âIt was kind of weird,â said Eric Felisbret, the author of âGraffiti New Yorkâ and a former graffiti artist himself. âIn âStar Trek' they have the Prime Directive, where they are not supposed to interfere with the different civilizations they encounter. Henry had no intention of doing that. But his very presence ended up doing just that. It became a little prestigious for him to shoot your work.â
Within a few years, Mr. Chalfant turned his attention to working on âStyle Wars,â which was originally focused more on the B-Boy scene dominated by the Rock Steady Crew. But by the time he and Tony Silver were able to finance the film, Rocky Steady had hit it big in âBeat Streetâ and âFlashdance,â and their manager was demanding equally big bucks. Instead, Mr. Chalfant and Mr. Silver turned their attention to the graffiti writers.
âWith film, you don't know what it is until long after it i s,â Mr. Chalfant said. âMost of the world probably saw âBeat Street' before âStyle Wars.' It had an enormous effect.â
One of those effects was disappointment. Someone involved in âBeat Streetâ saw early footage of âStyle Wars,â which featured a notorious graffiti writer named Cap, who went around writing over everyone's murals. That real person wound up in âBeat Streetâ as the character âSpit.â Mr. Chalfant and Mr. Silver got a check from âBeat Street,â but he is still rankled, because the so-called graffiti in the movie was done by union set designers - and looked it.
âIt was totally upsetting,â Mr. Chalfant said. âIt wasn't real. We knew it wasn't real. But we were outflanked by this inauthentic thing that came out first. I don't care that it's inauthentic. I wanted to be first.â
His documentary was released in 1983, followed by âSubway Artâ with Ms. Cooper the next year. Both the book and the documentary have become part of the urban art canon. The book was reissued in larger, updated form a few years ago, and Mr. Chalfant is working on a restored print of the film.
Some people ask him if he's going to do âSubway Art 2,â but he demurs.
âI've always said, however âinside' I was, I was an outsider,â he said. âI want to see books published by those who experienced it firsthand, like Fuzz One. His book captures the flavor of a crazy wonderful time. It was fun because it was open and free. And because it was open and free, it was dangero us.â
Mr. Chalfant stopped shooting trains around 1983, partly because the vibe was getting a bit menacing thanks to the onset of crack. Soon after that, the city rolled out white trains that were mostly covered with scrawls, although a few groups, like TATS Cru, mounted an underground revival until the city devised ways to quickly buff - erase - trains.
Today, most of the graffiti Mr. Chalfant sees is on precisely painted walls in place like Hunts Point in the Bronx or Five Pointz in Queens. When he shows up at these sites, he is greeted like an elder statesman. But as much as he admires some of the artists working today, it can't match what he caught on the fly decades back.
âTheir work gets close to airbrush painting,â he said. âBut it loses the experimentation that alw ays went on. It's so refined, it reminds me of mannerism in Renaissance painting. It's beautiful, but it loses spontaneity. All the experimentation in the '70s was exciting. People had to work against all these odds: will you get caught? Will you get beaten up? Will you run out of paint? There was always that tension.â
Follow @dgbxny and @nytimesphoto on Twitter.