For a TV series to become a successful motion picture, it ultimately has to appeal to both fans of the series and the average moviegoer who has never seen a single episode. Could "The Sopranos" exist as a stand-alone movie, without somehow referring to all the back history of the characters and their complicated story lines? Could someone walk in off the street and even begin to unravel the various relationships and references?

When "Dark Shadows" was remade into a movie, the producers took the easy way out: They simply retold the origin of the show's most popular character, vampire Barnabas Collins, as if everything after Barnabas' arrival never happened. Same with the massively successful (and excellent) 1993 movie version of "The Fugitive," starring Harrison Ford. Yet the big-screen debut of "The X-Files" in 1998, while toiling extra hard -- and reasonably successfully -- to create a story that would both work by itself and within the context of the show's mythology, still needed viewers to have at least a working knowledge of the series' increasingly complex (and confused) alien-invasion story line.

The most egregious example of this? That dubious honor must go to David Lynch's "Twin Peaks: Fire Walk with Me," the 1992 movie that served as a prequel to Lynch's briefly popular series of the previous two seasons. Although the movie, vastly underrated at the time of its release, has been generously reappraised over the years, Lynch's own typically obscure style and the many loose ends and inexplicable plot points woven between the movie and the film leave even fans of the series hopelessly baffled.

Even the upcoming, long-awaited "Simpsons" movie, with trailers highlighting its gallery of recurring characters, must be intimidating to the two or three of us who have never seen the series. Then again, the show's iconic status will make the movie a box-office smash even if it's 90 minutes of Bart writing on the classroom blackboard.

Once upon a time there was a science-fiction TV series called "Firefly." Although it got good reviews and attracted a loyal following, that audience was not large enough to keep it from being canned after nine episodes. But that very vocal minority endlessly lobbied for a movie version and finally, in 2005, they got it. The movie, called "Serenity," got good reviews and attracted the show's loyal cult following, but that wasn't enough to make it a hit and it disappeared shortly thereafter. Perception -- in this case, that there was a huge contingent of silent "Firefly" fans out there -- did not translate to reality.

Studio executives, it seems, often live in a cultural bubble: Just because one apparently thought "The Avengers" was cool back when he was watching it as a stoned college student doesn't mean the rest of us want to pay $10 to see a film version of a surreal British import. We even wonder if "Batman Begins" director Christopher Nolan's proposed re-imagining of the ultimate counterculture series, "The Prisoner," could attract any interest. Of course, we have to go back to "Star Trek" -- surely the mother of all such gambits -- for the greatest exception to the rule. But "Star Trek" took a decade to become a movie, and during that time enough people saw the show in syndication to make it bigger than it ever was during its original run (it also had 70 more episodes under its belt than "Firefly") -- an advantage "The Prisoner" lacks.

As we said at the start, the exact factors that make for a successful transition from small screen to big screen are hard to pin down. Every rule has been either broken successfully or proven correct. But chances are that if you give an audience a compelling idea, a neat twist on a timeworn concept or an irresistible set of characters, they'll seek it out whether shown on a TV screen, computer monitor, movie screen or wall.