Superheroes have become big moneymakers for Hollywood in recent years, but their success on the silver screen has had little impact on sales at Treasure Valley comic book stores.

While summer blockbusters like "Iron Man," "The Incredible Hulk" and the record-setting Batman movie "The Dark Knight" bring in a few new customers after hitting theaters, owners of the Valley's half-dozen independent comic shops said the slight bump in business is short-lived.

"Usually it will spike for a couple of months, then taper off," said Tim Doyle, co-owner of Outpost 12, 3890 W. State St., Boise.

And the spike, Doyle said, is typically limited to products related to the latest comic-inspired movie.

"I've seen a noticeable increase with comics and graphic novels pertaining to the movies - probably a 20 percent increase in those particular titles - but not really comics in general," he said.

Carol Morelock, owner of the Paper Back Place and Comic Book Co., 7011 W. Fairview Ave., Boise, said the films, to her surprise, have had no measurable influence on sales.

"I was amazed. I thought with all these movies coming out, people would want to find out how they started," she said.

Nonetheless, the films are important to the comic book industry, said Brent Frankenhoff, editor of Comics Buyer's Guide, the industry's longest-running trade publication.

Earlier this month, Frankenhoff attended Comic-Con International - which draws 125,000 people to San Diego each year and is widely recognized as the largest comic book convention in the world - and noticed an increased presence of fans and people from the film and television industries, which aggressively mine comics for story ideas.

The movie and TV fans, Frankenhoff said, got exposed to comics in a big way, and ended up digging the scene.

"There certainly has been some crossover," he said.

That's good news for an industry that hit a high point in the late 1980s and early 1990s - like sports cards, comics took a dive once the market got saturated by speculative production and investment - and didn't find its footing again until the turn of the century.

Sales have been on a steady rise since. In 2007, the year of "Ghost Rider," "Spider-Man 3" and "Fantastic Four: Rise of the Silver Surfer," annual sales were up 9 percent, to $429.9 million.

Single-copy comic books remain dominant, but sales of trade paperbacks, graphic novels and hardcover books, which often anthologize complete story lines from the serials, increased 18 percent last year.

Comic book shops are stocking more of these items, as well as action figures, T-shirts and other related merchandise, in an attempt to court and retain new customers.

Traditionally, hard-core collectors have kept the industry afloat during down times.

"Ninety percent of our customers are here every week," said Shawn Phelps, manager of Captain Comics, 710 S. Vista Ave., Boise. "That core group keeps us going."

But there is growing evidence that a more casual fan, influenced by the high visibility of movie tie-ins and other branding strategies, is getting into comics.

Comic-Con, which has evolved from a comic book convention into a full-bore pop-culture extravaganza, sold out of presale admission tickets this year for the first time in its 39-year history.

Locally, organizers for Fandemonium, a convention for comic book, science fiction, animation and gaming enthusiasts, are expecting 700 attendees Friday through Sunday at the Nampa Civic Center. The inaugural Fandemonium, in 2004, drew 250 people.

Some new readers are getting into comics not because of the format, but because of the writers or subject matter.

Stephen King and "Buffy the Vampire Slayer" creator Joss Whedon are among the growing number of established writers making forays into comics.

Presidential hopefuls John McCain and Barack Obama will star in their own comic books this fall.

"Big names are getting into comics, and they're bringing their fan bases with them," Phelps said.

How it all translates to success for the independent comic shop owner in the 21st century is still being figured out.

A major challenge facing proprietors is an aging customer base, composed of "almost all guys in their early 20s up to their 40s," Phelps said.

Children are getting introduced to comic book characters through the movies, but it often stops there.

"Younger kids are seeing the movies, but they aren't necessarily reading the comics," said Ken Henningsen, owner of Arch Enemy Comics, 1553 N. Milwaukee St., Boise.

Beyond movie theaters, major comic book publishers like Marvel and DC are attempting to reach younger audiences in other obvious places - video games and the Internet - but the verdict is still out on their success.

Even so, the local comic shop remains an American institution, and a financially viable one at that, shop owners said.

Seventy percent of Morelock's sales at Paper Back Books are comics, which she has been selling for 27 years. Henningsen, meanwhile, has been in the game for only two years, but Arch Enemy turned a profit by its second month and has stayed in the black since.

"It's enough to make a nice living off it and do something I enjoy," said Henningsen, who hopes to expand the shop once his lease expires in three years.

The key for the shops is capitalizing on the heroic opportunities presented by the likes of "The Dark Knight," said Frankenhoff, the Comic Buyer's Guide editor.

"Sustainability is a tough one to crack," he said. "A lot of it depends on how well the comics connection is promoted. It takes the retailer's motivation - a case of merchandise related to the movie, handing out flyers at theaters. What efforts are they making to bring in that traffic? They need to be out there aggressively marketing."

Chad Dryden: 672-6734