Optical sensor systems are frequently used in automobiles and other vehicles to provide images of areas around the vehicle. In some instances, these images are used by various vehicle warning and control systems. In the example of forward looking optical sensor systems, the images provided by the sensor may be used as inputs for collision avoidance, lane departure detection, forward collision warning, side warning, adaptive cruise control, night vision, headlight control, rain sensing systems and others. Typically, a forward looking optical sensor system is located behind the windshield near the rear view mirror to obtain a view of the road ahead which is similar to the driver's view. Optical sensor systems may also be used to view the area behind a vehicle for backing up, trailer towing, rearward collision warning, and rear blind zone warning systems. Additionally, optical sensor systems may be used to determine occupant position for restraint systems, rear seat occupant monitoring, or security and intrusion detection systems. Other examples of optical sensor systems include a rain sensor that optically detects the presence of moisture (e.g. rain drops or condensation) on the windshield, and an ambient light sensor that determines ambient lighting conditions outside the vehicle so, for example, the brightness of a display inside the vehicle can be varied to be readily viewable during various ambient lighting conditions.
The cost of individual sensor systems for each of these vehicle warning or control systems, plus the challenges of efficiently packaging multiple optical sensor systems in a vehicle make it desirable to use a single sensor system to provide images or signals for multiple vehicle warning and control systems. Unfortunately, performance tradeoffs exist when using a single optical sensor system due to light sensitivity, spectrum sensitivity, and field-of-view requirements specific to each vehicle warning and control system. These performance tradeoffs have previously precluded optimum performance for every vehicle warning and control system.
For example, a night vision system may require an optical sensor system with high light sensitivity because of the need to sense contrast of objects at long ranges with very little active illumination. In contrast, a lane departure system may accommodate an optical sensor system with lower light sensitivity because daylight or headlights (at closer ranges) provide sufficient lighting.
Light sensitivity is primarily determined by the pixel size of the optoelectronic device used in the optical sensor system to convert light to an electrical signal; a larger pixel has more area available for photons to strike the pixel and be absorbed. As used herein, an optoelectronic device is a component of an optical sensor system that may be operable to generate a video signal. However, a larger pixel size requires a larger optoelectronic device for equivalent pixel resolution. Light sensitivity for a given pixel size may be improved by increasing the exposure time. However, longer exposure time will decrease the frame rate of the images. Additionally, light sensitivity can be increased by using a larger aperture lens to allow more light to fall on the pixels of the sensor. However, a larger aperture usually requires a larger lens, which increases the packaging size of the optical sensor system.
Different vehicle warning and control systems may also require an optical sensor system with different spectrum sensitivity. For example a tail light detection system may require sensitivity to red light, a lane departure detection system may require sensitivity to yellow light, and a night vision system may require sensitivity to infrared light. There are performance tradeoffs that may be required if a single optical sensor system is used with all three of these vehicle warning and control systems.
Different vehicle warning and control systems may also require an optical sensor system with a different field-of-view. For example, a rain detection system may need a wide field-of-view while an adaptive cruise control system may need a narrower field-of-view. Again, using a single optical sensor system may require performance tradeoffs.