The global market for tablet computers is growing faster than expected, with Apple Inc.’s (Nasdaq: AAPL) iPad widening its lead as consumers’ top choice, according to market researcher International Data Corp.

Worldwide shipments of tablets this year will be 107.4 million units, up from an earlier projection of 106.1 million, IDC said Thursday in a statement.

Worldwide shipments should reach 142.8 million next year and 222.1 million by 2016, the group said.

“Demand for media tablets remains robust, and we see an increasing interest in the category from the commercial side,” said Tom Mainelli, research director for Mobile Connected Devices at IDC. “We expect pending new products from major players, increasingly affordable mainstream devices, and a huge marketing blitz from Microsoft around Windows 8 to drive increased consumer interest in the category through the end of the year.”

However, IDC is not including Windows 8 or Windows RT tablets in the research. They are included in IDC’s separate PC Tracker forecast.

Beginning next quarter, IDC said all tablets will be included in the Media Tablet Tracker report.

“We’re looking forward to rolling the Windows-based tablets into our tablet forecast in order to give customers a complete view of tablet slates all in one place,” Mainelli said.

“Our current thinking, based upon early pricing expectations for these products, is that Windows-based tablets will be largely additive to our existing media tablet market forecast,” he added. “We don’t expect Windows-based tablets to necessarily take share from Apple and Android, but will grow the overall tablet market.”

IDC also had bad news for Apple competitors: Its forecast moves a bigger percentage of future sales toward Apple iOS.

IDC predicted iOS will increase its marketshare in 2012 to 62.5 percent, up from 58.2 percent in 2011.

Android’s share is expected to drop from 38.7% in 2011 to 36.5% in 2012.

Third-place Blackberry’s share will slip to 1 percent from 1.7 percent.

“After a very strong launch of new products in March, Apple’s iPad shows few signs of slowing down,” Mainelli said. “The addition of the Retina Display and 4G capabilities to the third-generation products clearly enticed many current owners to upgrade.

“And Apple’s decision to keep two iPad 2s in the market at lower prices—moving the entry-level price down to $399—seems to be paying off as well. If Apple launches a sub-$300, 7-inch product into the market later this year as rumored, we expect the company’s grip on this market to become even stronger.”

Lenovo, the world’s No. 2 PC manufacturer, is rolling out tablets designed to compete with the iPads, especially in its home market of China where Apple dominates.

(Bloomberg news contributed to this report.)