Despite their best efforts, lifeguards cannot monitor every swimmer in a loud, busy pool. According to the US Centers for Disease Control and Prevention, an average of six people drown daily in US pools, and drowning is the second leading cause of injury-related deaths in US children. With the help of a computerized lifeguard being installed across North America and Europe, that may change. The Poseidon drowning-detection system backs up lifeguards by monitoring the trajectories of swimmers in the pool. Poseidon comprises a central processor and a network of cameras, including CCDs in the pool that are packaged to resist water and chlorine. Developed by Poseidon Technologies SA of Boulogne, France, the Poseidon machine vision system identifies a swimmer in distress underwater and alerts the lifeguards. The system at the Centre Aquatic Jean Blanchet in Ancenis, France, has already been credited with saving a swimmer's life. Poseidon comprises a series of cameras in and above the pool, which are networked to a central processor on-site. The computer monitors the trajectories of the swimmers in the pool and pages the lifeguards when it detects, for example, a person immobile on the bottom or sinking slowly. Resuscitation of a drowning swimmer should begin within 30 seconds to prevent injury or death; Poseidon gives the staff the coordinates of the swimmer within 10 to 15 seconds of a drowning event. Steve Bagby, president and general manager at the company's US subsidiary, Poseidon Technologies Inc., explained that the system's hardware is off-the-shelf, including 0.5- to 1.0-megapixel, black-and-white CCD cameras from Sony Corp. of Tokyo. "The cameras are pretty standard. They're not very sexy." The company did, however, develop machine vision algorithms to deal with the unique challenges of imaging swimmers underwater. "The biggest problem is the shadows from the natural lighting," Bagby said. The solution was to give the computer stereo vision, which enables Poseidon to discriminate volumes and textures. "A swimmer, unlike a shadow or a light artifact, doesn't have the texture of the background," he explained. Smaller facilities To date, 15 pools have been equipped with Poseidon, including the 82 x 65-ft pool at the North Toronto Community Centre, the first installation in North America. Installations are also planned for facilities in Sarasota, Fla., and in Dedham, Mass. Bagby said that the company plans to bring Poseidon to smaller pools, such as those at hotels and resorts. At this point, an entry-level system carries a price tag of $65,000, prohibitive for pools smaller than half-Olympic-size. "It only makes sense, really, for that size," he said. Better and cheaper computers and cameras will bring down the installation cost and should open up the market for the machine vision system. Until then, the company is scheduled to install another 30 systems in the next four to six months, Bagby said. "In the meantime, we have our hands full."