The end result was a huge database consisting of frames of video with people's joints marked. Twenty percent of the data was used to train the system's brain to recognize movements. Engineers kept the rest in a "ground truth" database used to test the Natal's accuracy.
Choosing the best algorithm and sifting out the essential data are central to the art of machine learning. To test Natal's ability to recognize poses, engineers show it an image from the ground truth and then generate a digital pixel map in which the greater the computer's certainty is of a pixel being correctly placed on the body, the brighter the pixel is. Engineers test hypotheses about how to improve the performance, trying to fine-tune weak areas without regressing strong ones. The more accurately the system can recognize gestures, the more fun it will be to play the game.
Of course, Microsoft is not the only gaming company exploring gestural interfaces. Rival console-maker Sony in May demonstrated a prototype Interactive Communication Unit (ICU) with stereo video cameras and depth sensors at the Vision 2009 trade fair in Stuttgart, Germany, according to New Scientist. Sony developed ICU with the help of Atracsys, LLC, a Swiss firm that specializes in optical-tracking technology. Although Sony makes the popular PlayStation game console, the company says it is planning to promote its new technology only within the advertising industry rather than in the gaming market at this time. Rival Nintendo has not revealed any plans to allow its Wii system to function without the need for Wiimote.
Still, the controller should not disappear altogether, says Hiroshi Ishii, head of the Tangible Media Group at the Massachusetts Institute of Technology Media Lab. "I'm a strong believer of having something tangible in your hand," he says. Wiimote devices, moreover, provide haptic feedback, such as vibration or resistance that makes the action more realistic. Even for activities like Natal's soccerlike Ricochet game demo, he points out, a player might miss the simulated feeling of connecting with a physical object that a controller provides.
But Peter Molyneux, creative director of Microsoft Game Studios Europe, looks forward to a new breed of computer entertainment, because eliminating game controllers opens up more creative possibilities. "Natal is forcing me as a designer to think of this as a relationship between the player and a piece of technology," he says. "We're trying to make something that feels as if it's alive."