Eyes off, screen off

By Kimberly Patch, Technology Research News

If a computer screen is on, but no one is watching, it still consumes energy.

Researchers from Duke University have devised a detector that determines if a person is present and looking at a computer screen, and keeps the screen on only when it is being watched.

The key to making a practical power-saving detector was making sure that the device itself used very little energy, said Angela Dalton, a researcher at Duke University. "There had to be very low power sensors, and algorithms that could be simplified enough that the system did not use more energy in overhead than it saved," she said.

The researchers' prototype uses a wireless motion sensor and a WebCam. When the motion sensor is triggered, indicating that someone is present, the WebCam turns on and takes pictures, and the pictures are analyzed by a face detection algorithm to determine if anyone is looking at the display.

The system, dubbed FaceOff, consumes almost no power when waiting for the motion sensor to trigger, and the camera consumes between 1 and 1.5 watts when it is running, said Dalton. In an initial study, the system achieved energy savings as high as 30 percent, she said.

The system uses off-the-shelf parts, and could be optimized to consume even less power, said Dalton. Tiny cameras that can be embedded into computer systems and consume as little as 20 milliwatts, or thousandths of a watt, could further increase energy savings, according to Dalton.

Face recognition software that triggers a screen saver is available commercially as an extra in security applications that identify authorized users, but these packages don't go so far as to track gaze.

The Duke prototype "shows the feasibility of using low-power sensors to better match system input-output behavior to user behavior, and by doing so reduce overall system energy consumption," said Dalton.

With the increasing availability of cheap, low-power sensors, numerous mobile devices could use this kind of technique to reduce energy consumption and thus extend battery life, according to Dalton. Mobile devices with built-in sensors, including cameras, microphones, light sensors, and global positioning system receivers are becoming available. "Mobile devices could leverage the sensors beyond their obvious uses to determine user intention and context, and match the system behavior," she said.

The researchers' work is a twist on traditional system-level energy management, which has historically been tied to turning components off when they are not engaged. Input-output devices, however, might be needed by the user even if the computer is not carrying out a process. At the same time, computer displays account for a relatively high percentage of computer power use.

A 17-inch cathode ray tube monitor, for instance, draws between 60 and 120 watts, and even flat panel monitors draw between 15 and 25 watts.

Practical energy-saving sensor systems could be implemented in two to three years, according to Dalton.

Devices are capable of performing the necessary computation, and the types of sensors the systems will require currently are available, she said. "The main hurdle [is] user studies to determine usability, usage scenarios, and user interface requirements."

The researchers' next step is to perform a comprehensive user study to better characterize the scenarios in which the technique is useful, said Dalton. The researchers are also planning to experiment with how often to sample the users gaze, to, for example, make the system more responsive when motion is detected and decrease or halt image sampling when no motion is detected, according to Dalton. And they are planning to incorporate a light sensor into the prototype so the display brightness can be adjusted to save power.

Dalton's research colleague was Carla S. Ellis. They presented the work at the Usenix HotOS IX: 9TH Workshop on Hot Topics in Operating Systems in Lihue, Hawaii, May 18 to 21, 2003. The research was funded by the National Science Foundation (NSF).

Timeline:   2-3 years
Funding:   Government
TRN Categories:  Human-Computer Interaction
Story Type:   News
Related Elements:  Technical paper, "Sensing User Intention and Context for Energy Management," presented at Usenix HotOS IX: 9TH Workshop on Hot Topics in Operating Systems, Lihue, Hawaii, May 18-21, 2003, and posted at www.usenix.org/events/hotos03/tech/full_papers/dalton/dalton.pdf


July 30/August 6, 2003

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