AppleInviteOn Tuesday, Apple will hold a media event its headquarters in Cupertino, Calif. for a big announcement. True to form, the company has only said that an event will be taking place, along with a smattering of satellite international media events happening after the initial announcement.

That said, the rumor mill has been churning for what many observers see as a key event for Tim Cook and his executive team. Everyone has this event pegged as Apple’s iPhone announcement for 2013, which means that we’ll be seeing the unveiling of Apple’s strategy for competing with Samsung and other smartphone manufacturers for the next year. There’s a lot of pressure on Apple to make a bold move to continue its growth as a smartphone maker.

If the rumors are right, Cook is hoping that a pair of new iPhone models will be a good start, at least.

The first, which everyone is calling the iPhone 5S, seems to be an expected upgrade to the iPhone 5 chassis, similar to the 4S and 3GS before it. The 5S is rumored to feature a fingerprint sensor in the phone button, though how the sensor integrates with the rest of iOS remains to be seen. The 5S is expected to be available in gold and silver, in addition to the now-standard white and black. If past trends in S model iPhones hold with the 5S, it’ll also feature a processor upgrade and improvements to the camera.

Tuesday should also feature the unveiling of a new, lower-cost iPhone many are calling the iPhone 5C, after a few images of packaging bearing that moniker emerged from China. It’s not clear how accurate those photos are, however. The 5C is expected to have a footprint similar to the iPhone 5 and 5S, but feature a plastic shell instead of the metal and glass construction of the 5’s chassis.

The 5C is expected to come in a variety of colors, much like the iPod Touch, iPod Nano and iPod Shuffle before it. While the exact number of colors is unknown, it seems fair to assume that the 5C will launch in five colors, especially given the current options available to purchasers of the iPod Touch. The company’s multi-colored event invite, promising to “brighten everyone’s day,” supports this theory.

No matter what it’s called, a lower-cost iPhone would give Apple a chance to make inroads in China, India and other international markets where cell companies don’t subsidize the cost of a phone. Apple’s Chinese revenue dipped significantly last quarter, while Samsung and Chinese domestic manufacturers continue to grow. Furthermore, if Amazon is planning on releasing a completely free smartphone, as was reported last week, the 5C could be a key part of Apple’s strategy in dealing with it.

In addition to the hardware announcements, Apple is expected to announce the final release date for iOS 7, the latest major update for the company’s mobile operating system, that features a new design aesthetic spearheaded by Jony Ive. If patterns hold, it will be released to the public a couple days before the new iPhone goes on sale.

AllThingsD’s Peter Kafka reported last week that Apple also plans to announce updates to the software powering its Apple TV set-top box, including a feature that integrates with its AirPlay technology to allow visiting guests to play media that they’ve purchased through the iTunes Store on somebody else’s Apple TV.

All of that said, there’s still a lot we don’t know about what’s being announced on Tuesday. Most of the leaks have come from Apple’s suppliers, which means that while we know a decent amount about the physical capabilities of the next iPhones, we don’t know how those capabilities will be translated into features just yet. For that, we’ll probably have to wait until Tuesday morning.

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