Seth Rosenblatt/CNET

SAN DIEGO -- Digital comics went boom last year, driven by as many reasons as there are varieties of Kryptonite. But defying the trend set by movies, music, and TV when they went digital, print comics sales in North America recently have been estimated at jumping nearly 18 percent since last year. How the heck did that happen?

Driven by a saturation of iPads and other tablets among people with disposable income, a massive line-wide reboot by DC Comics that encouraged other publishers to fully "go digital," and the obvious sales benefits of being able to buy a comic book wherever you want, when you want, the reasons for digital comics' success aren't hard to understand. The print resurgence is another matter (which we'll in a moment).

Comixology, the largest distributor of digital comics, is publicly reporting sales estimates that dwarf the print resurgence on percentages. The company's CEO, David Steinberger, told CNET that it grossed $19 million in fiscal year 2011, but it expects a gross of $70 million in FY2012. "It's not slowing down," he said. "Everything is pointing towards a continuing growth market."

Measuring comics sales is an imperfect science, since publishers rarely, if ever, report sales figures. However, that doesn't mean that observers haven't been able to turn the science of analyzing print sales figures into an art form. The Comics Chronicles is known for providing reasonable estimates of print sales figures, and the estimated numbers it just released for June 2012 -- if accurate -- are stunningly impressive for print.

"Orders by Direct Market comics shops in North America are up more than 18 percent year-to-date through June, by contrast with last year, when they were down by 8 percent. Retailers have already ordered more material through June -- nearly $223 million in retail dollars -- than they did in last year through July [original emphasis]," wrote the site's creator and author John Jackson Miller.

"I really think it's about two different customers," said Todd Martinez, the sales and licensing coordinator for Image Comics in a conversation at the Image booth here on the Comic-Con show floor. Image is currently enjoying a massive critical and sales resurgence, with its Walking Dead title claiming "between 350,000 and 360,000" preorders for this week's issue 100, a high-water mark not reached in print comics since 2009's "Spider-Man" issue that featured President Obama.

"We're offering such great product right now, with books by Brian K. Vaughn (writer on 'Lost, Y: The Last Man') and Ed Brubaker (writer on 'Batman,' 'Captain America,' and 'Criminal'), and Grant Morrison's upcoming 'Happy' that the market is attracting people who aren't traditional comics readers."

A former retailer with decades of experience at the Berkeley, Calif., comics shop Comic Relief, Martinez said that one of Image's more successful digital use-cases has been using the monthly issues as a feeder to sell print versions of the trade paperback collections.

Martinez, and in fact every publisher CNET spoke with for this story, refused to cite specific sales numbers, and few would agree to go on the record with even sales percentages.

Martinez's take on the situation mirrors those at DC Entertainment, which publishes "Batman," "Superman," and "Wonder Woman." DC is currently seeing sales that over the past year have brought it into close competition for issues sold and dollars earned with its biggest corporate rival, "Iron Man" and "Spider-Man" publisher Marvel. DC's books have dominated the Top 10 list since it rebooted all of its comics last September with same-day digital publishing, new No. 1 issues, and a revamped universe -- not unlike the J.J. Abrams "Star Trek" movie.

"We didn't know what to expect two years ago when we started publishing digitally," said Hank Kanalz, senior vice president of digital for DC, in a conversation at DC's open-plan press booth. As the susurrus of the crowd echoed behind us, Kanalz explained that although sales ramped up when DC went day- and date-digital, they've picked up recently.

DC Entertainment

"In the past three months, we've had an 80 percent increase in app downloads and in-app purchases," Kanalz said. This is in part, he explained, because of $0.99 sales of older books recently converted to digital, of digital-first books like "Batman: Arkham Unhinged" and "Smallville": Season 11, and because of the accessibility and portability of digital.

Jim Lee, co-publisher of DC Entertainment, concurred. At San Diego Comic-Con 2011, he described digital sales as a string of dental floss, compared to print's sheet of paper. That's changed, he said. "Digital sales is a meaningful number now," Lee said, although he wouldn't get more specific than that when asked. He added that there's a direct correlation between print and digital.

When DC relaunched its books, Lee explained, "We trimmed the fat from the line," meaning that DC cut down the number of monthly books it publishes, "and we put everything back on the shipping schedule." The line has had only one late book since the relaunch, he said with a chuckle: "Mine." Lee is the artist on "Justice League."

They also pointed to the benefits of print books, including the collectibility and tangibility. "Even though I'm a big proponent of digital, I still buy my "Justice League" run in print to be complete," said Kanalz.

The value of a print book that readers want to own has proven to be a major selling point for Matt Kindt, the creator of a new book from Dark Horse Comics called "Mind MGMT." The comic has gotten lots of critical accolades with only two issues published, and part of the appeal, Kindt said, is that his book is best read in-hand. "The story isn't between the covers, it's the entire thing you're holding." Mind MGMT presents an immersive, world-building tale, complete with story details in the margins, and related "fake" advertisements on the inside of the covers. "I am working on digital content for MGMT...but [currently] the best experience is buying the book off the shelf."

Marvel Comics

Not everybody believes that this year's print resurgence has much weight to it. Mark Waid, a fan-favorite and award-winning comics author, is currently putting the vast majority of the weight of his talents behind digital with a site called Thrillbent, but he still writes a large number of print comics. He was also one of the few who was willing to call shenanigans on the estimates by Comic Chron and others. "I've seen no evidence from retailers that those numbers bear out," he said. "If they do, that's great, but it's incumbent on the publishers to not create a 'bank scare.'"

The problem, he says, is the Direct Market system that relies on Diamond Comics Distributors, a company that has a virtual monopoly in North America for distributing comics from publishers to your local comic book shop. "There are so many grenades bouncing around on deck that if we lose even 5 percent of the stores, it could force Diamond under."

He also criticized Comixology for re-creating the Diamond system with digital comics. "Comixology is just another Diamond," he said. "From my perspective, we're in a closed ecosystem. We have to stop being a typewriter factory."

Whether from genuine enthusiasm or wishful thinking, it was extremely difficult to find anybody who could back Waid's interpretation with facts, or even revised estimates.

Whether the reported numbers are legitimate or not, DC's Jim Lee says that comics retail shops and digital storefronts will thrive. "A digital comic isn't the same as print. How we maximize both is our goal," he concluded.