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An article on Industrial Cameras (3)

 According to different measurement principles, mainstream 3D cameras generally have three options: time-of-flight method, structured light method, and binocular stereo vision. The brief introduction is as follows:

(1) The flight time is literally translated from Time of Flight, referred to as ToF. The principle of ranging is to continuously transmit a modulated light pulse of a specific frequency (generally invisible light) to the object to be observed, and then receive the light pulse reflected back from the object, and calculate the flight (round trip) time of the light pulse. The distance of the measured object from the camera.

(2) The structured light method is to use a specially designed pattern (such as discrete spot, stripe light, coded structure light, etc.) designed in advance to project the pattern onto the surface of the three-dimensional object and observe the three-dimensional physical surface using another camera. The distortion of the image. If the structured light pattern is projected on the surface of the object as a plane, then the observed pattern of structured light in the imaged image is similar to the projected pattern, without distortion, but with a certain scale change depending on the distance. However, if the surface of the object is not flat, then the observed structured light pattern will have different distortions due to the different geometries of the surface of the object, and will vary according to the distance, according to the known structured light pattern and observed. The deformation can calculate the three-dimensional shape and depth information of the measured object according to the algorithm.

(3) Binocular stereo vision method The human eye imaging principle is obtained by calculating the parallax of the same object in the space of two cameras to obtain the distance of the object from the camera. The algorithm is also calculated according to the triangular relationship.

These three 3D vision schemes have advantages and disadvantages in detecting distance, accuracy, and detection speed, and are suitable for different application scenarios, and are currently in the three countries. The advantage of the structured light scheme is that the technology is mature, the depth image resolution can be made relatively high, but it is easily affected by the light, and the outdoor environment is not suitable for use; the ToF scheme has good anti-interference performance, wider viewing angle, and the lack of depth image resolution is lower. Mainly used for simple obstacle avoidance and visual navigation, not suitable for high precision occasions. The cost of the binocular solution is the lowest compared to the first two schemes, but the depth information depends on a pure software algorithm. This algorithm is highly complex and difficult, and the processing chip requires high computational performance. At the same time, it also inherits the shortcomings of ordinary RGB cameras: it is not suitable in dimly lit environments and when the features are not obvious. Of course, these three programs also have some mutual integration trends in the development process, such as active binocular + structured light, and complement each other, so that 3D cameras can adapt to more scenes. There are also occasions where it can be used at the same time. For example, the basic confirmation of the front of the smart phone will use structured light for face recognition, but the rear is used for augmented reality (AR) applications, and both structured light and ToF solutions have application opportunities.

Throughout the development of machine vision, it has mainly experienced the process from black and white to color, from low resolution to high resolution, from static to dynamic, and from 2D to 3D. Industrial cameras as the core hardware, the iterative changes in technology are also following the corresponding development. With the diversification of industrial automation and machine vision applications, the industrial camera market has also risen with the fierceness of the machine market. Although high-end, high-speed and other high-end industrial camera technologies are still mainly in the hands of foreign manufacturers, including Keyence, Cognex, Basler, AVT, Teledyne DALSA. However, with the continuous accumulation and breakthrough of domestic camera manufacturers' technology, domestic industrial camera brands have begun to gradually replace imports from the low-end market, such as Daheng Image and Huarui Technology. We believe that with the global manufacturing center shifting from Europe and America to Asia, China's upgrading and transformation process from manufacturing to manufacturing countries, in the context of market and policy, this is a breakthrough and head-on for China's industrial camera manufacturers. A good time to catch up.