LOS ANGELES: Calling all superheroes, sci-fi fans and genre lovers of all kinds: Comic-Con is here.

The annual pop-culture celebration kicks off Wednesday night with a preview of the San Diego Convention Center's showroom floor: 460,000 square feet of TV, film and video game displays, along with toys, art and comic books for sale. Four days of panels, presentations, screenings and autograph signings begin on Thursday.

What started as a comic-book convention with 300 participants in 1970 has grown into a corporate-heavy media showcase that draws more than 130,000 attendees. Netflix, Warner Bros., Fox, HBO and Marvel Studios are among the companies hosting large-scale presentations with top-name talent. But while Hollywood has raised Comic-Con's profile, comic book enthusiasts say it keeps edging out the book buyers and sellers at the heart of the event.

"I think the biggest story about Comic-Con this year is that Chuck Rozanski and Mile High Comics isn't attending... He is THE guy in terms of retail comics and he cannot afford to do the setup that he would usually do because he just doesn't get the sales that he used to get at Comic-Con," said Harry Knowles, founder of the fan site Ain't It Cool News and a Comic-Con regular since 1971. "The sadness that's going on is the people that really made Comic-Con worth going to from the very beginning are being squeezed out by the entire corporate structure of Hollywood, of the industry that is creating so much awesome stuff for us to obsess about."

Among the fan obsessions on view this year: "Stranger Things 2" and "Marvel's The Defenders" from Netflix, which also promises a surprise screening Thursday night; HBO's "Game of Thrones" and "Westworld"; "Justice League" and "Blade Runner 2049" from Warner Bros., along with an anticipated appearance by Steven Spielberg showcasing his adaptation of "Ready Player One."

Comic-book discoveries are no longer the main attraction at Comic-Con.

"Marvel and DC still use Comic-Con to make announcements" about characters and story lines, said Adam Parker, book manager at Meltdown Comics in Los Angeles. "There's still Artists Alley. There are still panels of writers and artists talking about the next plans for Batman or what Marvel is doing next. That all still exists, it's just grown so much more beyond that."

Jamie Newbold, who's been attending Comic-Con since 1972 and selling comic books there for more than 20 years, said that as big entertainment companies have seized on the convention's fan base, the cost of exhibit space on the showroom floor has become prohibitive for small vendors.

The owner of Southern California Comics in San Diego still plans to bring about 15,000 books to the convention, but he used to take triple that.

"I have a lot of friends who do what I do, and when they look around and see the booths on either side of them are corporate booths, they're big businesses, and we're just little guys from LA or Colorado or New Orleans," Newbold said. "It would be nice for us to see some form of compensation to keep us there since we're the seeds that sprouted this massive tree."

His wish? That Comic-Con would make its 50th anniversary a celebration of rare and vintage comic books.

Jud Meyers, co-founder of Blastoff Comics in Los Angeles, remembers when comic book sellers dominated the convention center showroom. Now big studio and video game exhibits are front and center, with booksellers are in the back.

"I don't think we can blame Hollywood," he said. "Dedicated comic book stores are at a low we've never seen... The comic book world is not just about comic books."

He noted that fans can experience comic book heroes through movies, games and cosplay, which is hugely popular at Comic-Con.

"It's not that people want to read about superheroes," he said. "It's that they want to be them."

Costuming is the main draw for Victoria Weinert of Los Angeles, who will be dressing up Disney while at Comic-Con. She created her own version of a vintage Disneyland cast member's outfit, complete with a park map printed on its full skirt, for last week's Disney's fan convention, D23.

"I go to cosplay. I go to meet new friends," she said of Comic-Con. "I like the cosplay community because it's a small family."

Knowles, also a producer of the 2011 documentary "Comic-Con Episode IV: A Fan's Hope," said Comic-Con isn't a battle between Hollywood and comic books.

"It's not about who's out to win Comic-Con," he said. "The people who are going to win Comic-Con are the ones who paid for tickets to arrive to Comic-Con. They're going to have the greatest time ever."