Market analysis firm IDC has released its figures for tablet shipments during the second quarter of 2012 — and, unsurprisingly, Apple continues to be the dominant player, accounting for 68 percent of the market. Still, IDC is bullish on Apple’s competitors, noting that the tablet market as a whole grew 66 percent over the same quarter a year ago, and four of the five top tablet vendors worldwide saw their unit shipments increase year over year.

Asus and Samsung in particular saw year-to-year percentage increases in sales that exceeded even Apple’s sale’s growth. Samsung shipped 117.6 percent more tables in the second quarter of this year than it did during the second quarter of last year; for Asus, that figure was 115.5 percent. But neither company’s shares hold a candle to Apple, with Samsung’s tablet shipment sales for the quarter amounting to 14 percent of Apple’s, and Asus just 5 percent.

IDC’s figures for market share have been criticized for mixing apples and oranges. First, they directly compare figures from Apple on iPads it has actually sold with figures and third-party estimates from other manufacturers on the number of tablet products that have shipped. The difference can be crucial, since products shipped to retailers may linger in inventory for some time, or even wind up getting returned to the manufacturer. IDC also counts so-called “media tablets” like the Barnes & Noble Nook and Nook Tablet alongside full-fledged like the iPad and the Motorola Xoom. Some would argue lower-end devices should be considered media players rather than tablets, while others argue virtually all flat, rectangular devices with a screen five inches or larger that don’t have “phone” in the name should count as a tablet.

Nonetheless, even IDC’s expansive view of the tablet market gives an idea of how dominant the iPad has been in the category. This chart, derived from the last year of IDC figures summarizing the tablet market, compares sales of Apple’s iPad to reported and estimates shipments of essentially anything that’s not an iPad:

The “Android et al” category includes both tablets running Android and Android-based devices like the Kindle Fire, as well as devices like BlackBerry PlayBook and the now-defunct HP TouchPad. According to IDC’s figures, the only quarter in the last year where the non-iPad market managed to gain ground on the iPad was the fourth quarter of 2011. That bump is almost entirely due to the Amazon Kindle Fire, which IDC estimated shipped some 4.7 million units during the quarter — although Amazon has never disclosed actual sales figures.

IDC forecasts the iPad will see considerable competition during the second half of 2012, with the launch of the generally well-reviewed Google Nexus 7 expected to put a dent in iPad sales. Microsoft will also be entering the market with its new Surface tablets, while Amazon is expected to deliver a refresh to the Kindle Fire.