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Some explanations of the device base it on a simple echo of light: "The camera transmits invisible near-infrared light and measures its “time of flight” after it reflects off the objects. Time-of-flight works like sonar: If you know how long the light takes to return, you know how far away an object is." (wired.com). Is it so easy? On other hand, the developers, Primesense, speak about "a sophisticated parallel computational algorithm to decipher the received light coding". And they claim to avoid noise from ambiance light and to be able to obtain a resolution of 1cm at 2 meters.

A motivation to ask this here in physics is that some other questions were asking for measurement of light speed with household devices.

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From the comments, it seems that the device from 3DV was a time-of-flight, but the one from PrimeSense is a scanner. eurogamer.net/articles/digitalfoundry-primesense-article?page=2 – arivero Jan 28 '11 at 19:13

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No. It does not measure time of flight. Kinect is, deep down, a structured light scanner, meaning that it projects an infrared pattern (so invisible for us). According to the underlying technology firm PrimeSense, the structured light code is drawn with an infrared laser. This pattern is then read by an infrared camera and the 3D information is reconstructed from the distortions of the pattern. This results in a depth channel which is made available through USB.

If you want to see the pattern, you may have some luck by turning off all the lights in the room, turn on the kinect, and try to use your cellphone camera. Generally, these camera sensors are sensitive to IR, which appears as green. You may verify if this is the case by trying the same with a TV remote and pressing the buttons. The LED should turn green.

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+1 The tales in the "wired" link are lies? – Georg Jan 25 '11 at 22:18
@Georg : it appears so – Stefano Borini Jan 25 '11 at 22:30
I think Stefano is right, +1. The system may use lots of data beyond that, including the information from the microphone array, but it doesn't do any timing. It evaluates "snapshots" and may vary the IR light. – Luboš Motl Jan 26 '11 at 6:30
I read (around 1980) about a system of Zeiss using IR reflection to measure distances of some hundred meters with a resolution of cmters. Then, and again in the 90ties I thought about to tinker something like that, to use it on less than 3 meters. I looked for appropriate and affordable parts wich allowed the time resolution necessary, and saw this was impossible in the 90ties and today still is maybe. Such a time of flight thing needed a mode locked laser and a multiplier as a receiver. This is possible for "a ray" not for a lot of pixels. – Georg Jan 26 '11 at 10:57
The history from @sigoldberg1 seems correct too, MS bought a company using a time of flight camera but at the end they went with PrimeSense. – arivero Jan 28 '11 at 19:17
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Here is further confirmation that the Kinect uses structured light measurement.

Presentation covering time of flight and Kinect's structured light range imaging

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