An active vision system equipped with a high-speed pulsed light-emitting projector and a high-speed image sensor is proposed and applied to lane marker detection in this paper. The proposed system has the capability to suppress image information obtained from the background light and provides only the image information from the signal light emitted by the projector. This is accomplished by synchronizing image capture with the time of signal light emission.
To reduce the power consumption and cost of the system, a relatively low intensity projector is used as the light source. The background illuminance on a bright day can be much higher than that of the signal. To improve the signal-to-background ratio, the signal light is modulated using a pulse width modulation technique. Then, the image is captured using a high-speed camera operating in synchronization with the time the signal light is emitted. Finally, heterodyne lock-in image detection is performed by digital multiplication of the output of the camera and the width of the signal light, and a digital low-pass filter is used for extracting only the low-frequency component of the multiplication result.
A high-speed light-emitting diode projector and camera, together with a field programmable gate array for digital heterodyne lock-in image detection, were developed and installed on a test car. Experimental results of indoor, outdoor and real-world road testing are presented which indicate that the proposed system can successfully eliminate background light shadows from the detected image.