Proposal of a zoom and focus control method using an ultrasonic distance-meter for video-based eye-gaze detection under free-head conditions

To develop noncontact free-head video-based eye-gaze detection devices, there is a need for a zoom and focus control system which controls a zoom lens, so that the sharp eye´s image appears in the same size irrespective of back and forth head movements against the camera. In this study, such a zoom and focus control system using an ultrasonic distance meter was developed. On the front of the zoom lens, a 45-deg tilt transparent glass plate was installed to reflect ultrasound. Thus, the sound traveling axis and the camera axis were made coaxial. This made it possible to stably measure the distance from the camera to its subject, i.e., the eye. Also, a method using a striped panel and a custom-made image processor was proposed to calibrate the relationship between the distance and the focus and zoom control voltages. In the experiment, the head was moved back and forth in a range of 50-70 cm from a camera rotation center, and the zoom and focus was controlled in real time by using the information from the distance meter and the calibrated relationships. The result showed quick and precise control concerning both the zoom and focus