That large swash of red across the screen isn’t something in your eye. It’s Fat Albert, Bill Cosby’s durable comic creation, starring in his own movie.

Fat Albert and Cosby’s other childhood buddies came to life in the comedian’s 1960s stand-up routines and were immortalized in Cosby’s best-selling record albums. But a generation of kids knew Fat Albert and Old Weird Harold and the rest of the gang from a lesson-teaching cartoon TV series that ran in the 1970s.

The movie version of “Fat Albert” is closely, and somewhat strangely, tied to the cartoon (which was co-written by Cosby). One afternoon a sad teenage girl (Kyla Pratt) is watching the cartoon on TV. She sheds a tear, which magically allows the animated characters to come into her house through the television screen, where they are played by real actors.

It takes a while to get used to this notion. After all, some of those cartoon characters looked pretty weird. It’s one thing for Dumb Donald (Marques Houston) to go around in a knit cap that covers half his face in a cartoon, and another to see him walking the real streets of north Philadelphia. (Well, “real” being the back lot of Paramount Pictures.)

For a while, the movie gets its laughs the same way “The Brady Bunch Movie” did, via time-warp humor. After all, the Cosby kids are trapped in a perpetual ’70s vibe; their outfits and lingo are decidedly old-school, and they don’t recognize cell phones or hip-hop.

Then, as in the old show, Fat Albert (Kenan Thompson) finds ways of solving people’s problems. He also attracts the attention of a popular girl (Dania Ramirez), which has him wondering whether he really wants to go back to the cartoon. But how could he fit in the real world? After all, he’s never even changed his red sweater.

So Fat Albert decides to talk to his creator. That’s right. He goes to Bill Cosby’s house, and the man himself gives Fat Albert some advice.

“Fat Albert” has enough cheerful moments to make you like the characters. All the young actors playing the ex-cartoons are in on the joke, especially Bucky (Alphonso McAuley) and Mushmouth (Jermaine Williams).

It’s a very clean-cut, inoffensive movie, but it might not have enough slapstick to keep the kiddy audience in their seats. The mild humor is carried by a talented actor (much padded out) in the lead role.

Kenan Thompson has been a regular on “Saturday Night Live” for a couple of years, and as a kid had a series on Nickelodeon. Maybe that accounts for his having such savvy comic instincts at such a young age. Whatever the reason, he’s a funny guy, and “Fat Albert” is lucky to have him animating (so to speak) its otherwise predictable action.