Active sensors are the most reliable equipment to obtain accurate geometries of any objects including faces. An active sensor system typically consists of a light emitter (e.g., laser or projector) and a light receiver (camera). The reason that it is called an active sensor is because it actively emits lights. There are different types of active sensors including laser scanners, structured light systems, and structured light stereo systems. So far, the laser scanners are the most commonly used and most accurate active sensors. Recently, structured light systems have started to gain interest because they are capable of capturing continuous motions. Active sensors are popular tools for researchers to obtain ground truth data or to capture example faces or facial expressions as training data.

Laser scanners

So far, laser scanners are the most accurate and reliable equipment to obtain face geometry. It works by projecting a laser onto the face (or any object to be scanned), and a camera is used to detect the laser light on the face. The distance can then be determined based on the pixel location of the detected laser light. Laser scanners usually do not work well on shiny surfaces, and they do not work well on dark materials such as hair.