There’s a delicate line to be walked when adapting a best-selling book into a movie, especially when your intended audience is young and impressionable.

There’s a delicate line to be walked when adapting a best-selling book into a movie, especially when your intended audience is young and impressionable.

The biggest chunk of readers of Jeff Kinney’s wildly successful “Wimpy Kid” series are between 10 and 13. They have devoured the first four books, and no doubt have fully formed pictures of the middle school-age characters in their heads (that go far beyond the stick figure drawings that accompany the text).

That’s the way it should be: an imagining of these characters, raw edges and subtleties intact. Of course, everything changes when a film is made. Rules are thrown out the door; nothing is left to the imagination; there’s now one indelible vision of these characters.

And in the case of “Diary of a Wimpy Kid” making the jump to the screen, any hint of subtlety is gone. Though there are some good performances from the young actors, they are – with only a couple of exceptions – way too over-the-top.

But first the semi-good news. The film’s “hero” is Greg Heffley, a full-of-himself 12-year-old who’s just entering middle school and is the picture of self-confidence. He’s normal, he tells us in voiceover, and everyone around him is a moron. This wisecracker has big plans to become popular and get ahead in the world, but he has a few lessons to learn about loyalty and friendship along the way. Played by Zachary Gordon with a great deal of enthusiasm and, late in the film, some well placed self-doubt, he’s a complicated character who some young viewers are going to root for, but others will find rather distasteful.

Then there are Greg’s cohorts in the story. The character of Rowley (Robert Capron) is supposed to be a good-hearted dummy. The character of Fregley (Grayson Russell) is the kind of freaky, wimpy kid no one wants to have lunch with. The character of Patty (Laine MacNeil) is a nasty shrew in the making. It would appear that director Thor Freudenthal (best known for directing packs of pooches in “Hotel for Dogs”) had each of these young actors simply turn it up, let their characters’ traits run wild. So Rowley comes across as an idiot, Fregley is someone you’d try to have quarantined, and Patty ... well, Patty could stand a switch to decaf.

The most interesting character in the film (the best actor as well) is Angie (Chloe Moretz), the “arty” girl who’s first seen reading a copy of Allen Ginsberg’s “Howl” and who tries to open Greg’s eyes to what’s going on at school. Unfortunately, the script keeps her part down to a few cameos. The same goes for Greg’s parents, played by Steve Zahn and Rachael Harris, who aren’t much more than shadows who’ve come to pick up a paycheck.

The film does stick to the story of Greg and Rowley being friends, then having that friendship challenged by selfish, cowardly acts. And there’s a strong message that this is without a doubt the wrong way to behave.

But the writers and director just don’t have a grip on things. They let scenes go on too long without the benefit of a good payoff (You might want to check your watch at the start and end of the interminable Halloween sequence), and they’ve reduced the emotional content to such utter simplicity, that even 12-year-olds in the audience are going to lose interest.

But, for those who are easily pleased, and who like things in basic black and white, maybe the film will be a fun escape. It has at least one other thing going for it that the book’s fans are going to crave: There’s plenty of cheese.

DIARY OF A WIMPY KID (PG for rude humor and language). Cast includes Zachary Gordon, Robert Capron. 1 1/2  stars out of 4.