The physics of the Kinect

The Microsoft Kinect is a peripheral for the Xbox 360 that does away with the need for a conventional controller - instead the player's body and voice become the controller.

The Kinect sensor consists of:

• 640×480 pixel visible light camera
• 640×480 pixel infrared camera
• Four-microphone sound sensing array
• Class I infrared (780nm) laser diode

iFixit teardown of Kinect

The major advantage of the Kinect is that it works in 3D. Previous console vision systems (such as the PlayStation's EyeToy) were only able to detect changes in one plane; they only processed two-dimensional data. The Kinect features a depth sensor with a 1 in 2048 resolution* and can provide high-resolution three-dimensional data in realtime to the XBox 360.

The Kinect's depth sensor uses "structured light" created by a beam of infrared laser light passing through a diffraction grating. This projects a grid of 50000 infrared dots across the playing area. These infrared dots are visible on many cameras with a "night vision" mode.

By comparing how the dot pattern looks, and how it should look, the Kinect can measure the distance between the sensor and the player - producing a "depth map" in the process.

Images from Matthew Fisher. Objects in red are closest to the screen; colours then move through the spectrum to purple objects that are furthest away.

Unlike Sony, who have cracked down on anyone trying to hack the PlayStation; Microsoft have been very open to Kinect hackers; including the team from Cox Lab at Harvard who have developed a portable Kinect-based 3D camera.

* It has been shown that the depth resolution is non-linear and that the further an object is from the sensor the less information is available about its true distance.