Software that recognizes and rates smiles was demonstrated recently at an exhibition in Tokyo, where attendees competed to outsmile one another.

The smile-checking technology is the latest addition to Omron Corporation's OKAO Vision software suite, which detects faces in images and can determine the person's gender and approximate age, or verify his or her identity from a database of faces. The smile ­software is Omron's first foray into facial-expression detection and analysis, a field that could revolutionize how humans interact with machines, and with each other.

Omron, a Japanese electronics company, won't say if it plans to commercialize its smile software, which was on show at Japan's Combined Exhibition of Advanced Technologies. But spokesman James Seddon says that it could be used in digital cameras to help capture people's broadest smiles, in market research and customer-service training, and even by mental-health professionals to evaluate patients. Sony uses similar technology in some of its newest digital cameras so that they snap pictures when people are smiling their best.

Omron's smile-measurement software picks up the hallmarks of a smile--such as narrowed eyes, an open mouth, creases around the mouth, and wrinkles turning downward around the eyes--and uses an algorithm to assess the extent of the smile and rate it on a percentage scale. The analysis is performed in real time and only takes about 44 milliseconds using a Pentium 4 3.2-gigahertz PC, Seddon says. The smile software works on images of faces as small as 60 pixels wide.

Omron engineers used about 10,000 images of human faces--some with spontaneous smiles, some with posed smiles, and others sporting different expressions--to train the software to evaluate smiles.

Omron's smile-recognition technology is part of the company's OKAO Vision software suite. The face-recognition component of the software analyzes patterns of light and dark in an image to determine if it includes a face. Because it's based on contrast, Seddon says that the system performs well when dealing with poorly lit images.

Once OKAO Vision has registered a two-dimensional version of a face, it overlays a 3-D mask that allows the software to evaluate the face, even if the subject's head is turned or she's looking away from the camera.