Face detection is a computer technology being used in a variety of applications that identifies human faces in digital images. Face detection also refers to the psychological process by which humans locate and attend to faces in a visual scene.
Definition and related algorithms
Face detection can be regarded as a specific case of object-class detection. In object-class detection, the task is to find the locations and sizes of all objects in an image that belong to a given class. Examples include upper torsos, pedestrians, and cars.
Face-detection algorithms focus on the detection of frontal human faces. It is analogous to image detection in which the image of a person is matched bit by bit. Image matches with the image stores in database. Any facial feature changes in the database will invalidate the matching process.
Firstly, the possible human eye regions are detected by testing all the valley regions in the gray-level image. Then the genetic algorithm is used to generate all the possible face regions which include the eyebrows, the iris, the nostril and the mouth corners.
Each possible face candidate is normalized to reduce both the lightning effect , which is caused by uneven illumination; and the shirring effect, which is due to head movement. The fitness value of each candidate is measured based on its projection on the eigen-faces. After a number of iterations, all the face candidates with a high fitness value are selected for further verification. At this stage, the face symmetry is measured and the existence of the different facial features is verified for each face candidate.
Facial motion capture
Some recent digital cameras use face detection for autofocus. Face detection is also useful for selecting regions of interest in photo slideshows that use a pan-and-scale Ken Burns effect.
Modern appliances also use smile detection to take a photograph at an appropriate time.
Face detection is gaining the interest of marketers. A webcam can be integrated into a television and detect any face that walks by. The system then calculates the race, gender, and age range of the face. Once the information is collected, a series of advertisements can be played that is specific toward the detected race/gender/age.
An example of such a system is OptimEyes and is integrated into the Amscreen digital signage system. The most recent innovation in the field was by, Miami Beach based, AdMobilize. Their AdBeacon, became the world's first 'plug and measure real time analytics device', allowing for any retailer to get the same facial detection technology large advertisers are using. They've also coined the term pay-per-face.
Other examples include Visage Technologies' SDK which gives marketing researchers face detection information, including analysis, such as gender detection, emotion recognition and age detection and freeware applications such as OpenFace and similar.