Passive vision systems have a limited resolution and robustness because the number of depth points is limited to the number of recognizable features. Some 3D scenes will not contain many features, leading to missed objects; for example a white object placed in front of a white wall.
Structured light systems effectively project an array of features. Our fully integrated VCSEL dot projector modules can project up to 15k high contrast dots, enabling high-resolution 3D data to be derived for even featureless scenes. The presence of the defined pattern also considerably reduces the computational load imposed by the software, as it offers many features to facilitate matching of the two images. Near infrared wavelengths are used, combined with a corresponding filter on the camera, to avoid interference from ambient light. For example, this approach is behind the user face recognition being implemented in smartphones.
At a minimum, a structured light system comprises a single camera and dot projector. Again, the maximum detectable depth range is proportional to the baseline (B) distance between them, and the image sensor resolution. This is, for example, the technology behind face recognition in smart phones.
Active stereovision systems combine two cameras with a dot projector, to give enhanced accuracy and robustness.