Three-dimensional (3D) imaging systems are increasingly being used in a wide variety of applications such as, for example, industrial production, video games, computer graphics, robotic surgeries, consumer displays, surveillance videos, 3D modeling, real estate sales, autonomous navigation, and so on.
Existing 3D imaging technologies may include, for example, the time-of-flight (TOF) based range imaging, stereo vision systems, and structured light (SL) methods.
In the TOF method, distance to a 3D object is resolved based on the known speed of light—by measuring the round-trip time it takes for a light signal to travel between a camera and the 3D object for each point of the image. The outputs of pixels in the camera provide information about pixel-specific TOF values to generate a 3D depth profile of the object. A TOF camera may use a scannerless approach to capture the entire scene with each laser or light pulse. In a direct TOF imager, a single laser pulse may be used to capture spatial and temporal data to record a 3D scene. This allows rapid acquisition and rapid real-time processing of scene information. Some example applications of the TOF method may include advanced automotive applications such as autonomous navigation and active pedestrian safety or pre-crash detection based on distance images in real time, to track movements of humans such as during interaction with games on video game consoles, in industrial machine vision to classify objects and help robots find the items such as items on a conveyor belt, and so on.
In stereoscopic imaging or stereo vision systems, two cameras—displaced horizontally from one another—are used to obtain two differing views on a scene or a 3D object in the scene. By comparing these two images, the relative depth information can be obtained for the 3D object. Stereo vision is highly important in fields such as robotics, to extract information about the relative position of 3D objects in the vicinity of autonomous systems/robots. Other applications for robotics include object recognition, where stereoscopic depth information allows a robotic system to separate occluding image components, which the robot may otherwise not be able to distinguish as two separate objects—such as one object in front of another, partially or fully hiding the other object. 3D stereo displays are also used in entertainment and automated systems.
In the SL approach, the 3D shape of an object may be measured using projected light patterns and a camera for imaging. In the SL method, a known pattern of light—often grids or horizontal bars or patterns of parallel stripes—is projected onto a scene or a 3D object in the scene. The projected pattern may get deformed or displaced when striking the surface of the 3D objet. Such deformation may allow an SL vision system to calculate the depth and surface information of the object. Thus, projecting a narrow band of light onto a 3D surface may produce a line of illumination that may appear distorted from other perspectives than that of the projector, and can be used for geometric reconstruction of the illuminated surface shape. The SL-based 3D imaging may be used in different applications such as, for example, by a police force to photograph fingerprints in a 3D scene, inline inspection of components during a production process, in health care for live measurements of human body shapes or the micro structures of human skin, and the like.