Just as expected, Amazon's just-announced Fire Phone features a unique interface that is quite a bit different than what you'll see on pretty much any other smartphone on the market. While the basic interface is very much reminiscent of the Kindle Fire tablets, there are a few new tricks that combine the phone's hardware — particularly the multiple front-facing cameras — and software. The phone's dynamic perspective feature updates 60 times per second to make the interface work. Amazon CEO Jeff Bezos likened it to the move from flat artwork to artwork with geometric perspective which began in the 14th century.

The first demo showed off some pretty wild perspective effects on the lock screen — a nice trick, but not exactly something entirely useful. However, the maps interface takes advantage of the dynamic perspective to show a 3D render of buildings; the demo first showed off the Empire State Building before Bezos moved on to showing how the interface uses different layers to hide and show information on the map like Yelp reviews. Unfortunately, right now it seems more of a gimmick than anything that's a must-have feature, though we imagine developers could take advantage of this and use it in some pretty interesting ways. To foster that, Amazon's releasing a dynamic perspective SDK to help developers build the technology into their apps.

Amazon is getting really good at recognizing heads and faces

Perhaps the most useful application shown off so far is simply tilting the phone to scroll through a web page like The Washington Post or to page through a Kindle book. Of course, we've seen other tilting features before and they've a lot to be desired, but Amazon's demo seems to make these features seem far better than previous attempts. The question will be whether or not the extra processing power and potential battery life drain to run these multiple cameras will be worth it.

The key to making dynamic perspective work is knowing exactly where the user's head is at all times, in real time, many times per second, Bezos said. It's something that the company has been working on for four years, and best way to do it is with computer vision, he went on to note. The single, standard front-facing camera wasn't sufficient because its field of view was too narrow — so Amazon included four additional cameras with a much wider field of view to continuously capture a user's head. At the end of the day, it features four specialized front-facing cameras in addition to the standard front-facing camera found near the earpiece, two of which can be used in case the other cameras were covered; it uses the best two at any given time. Lastly, Amazon included infrared lights in each camera to allow the phone to work in the dark.

The rumors of a "3D interface" for Amazon's upcoming device started gaining steam last fall, when sources revealed that the phone would incorporate four front-facing cameras to track a user's head and use that data to position 3D effects within the interface. Earlier this spring, BGR followed up on its leak of the phone's hardware with more details about a tilt- and gesture-based interface based on four infrared cameras, and TechCrunch corroborated its report from last fall with more details about the company that build the unusual new interface for Amazon.

Patent filings have also revealed that Amazon's been working on such an interface for a long time — a patent from Jeff Bezos himself dating back to 2008 showed just how Amazon's proposed interface might operate.