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Machine vision: Communication interface in the system

Communication interfaces mediate the transmission of image data between the camera and the machine vision system. When choosing a suitable interface (or cameras communicating via a certain interface), the maximum throughput of the interface, the maximum possible cabling length, the number of cameras that can be used at the same time, the possibility of connecting devices via Plug & Play or certainly the important ability to capture and transmit data must be taken into account. in real time. The following is an overview of the most commonly used interfaces. We will describe their advantages and disadvantages and suitability for selected machine vision applications.

Camera Link

Camera Link is an interface that was developed specifically for the needs of image transmission. Uses serial-parallel data transfer. The simplest configuration (Base) has three multiplexed 8-bit parallel channels (usually used for RGB), appropriate channels for control and synchronization signals, and an auxiliary serial interface for camera setup. There are also Medium and Full configurations with double and triple data transfer capacity. The theoretical communication speed of the CameraLink interface is 2.38 Gb / s, corresponding to a data channel width of 297.5 MB / s.

Due to the fact that this interface has been used for a long time, it is simple and at the same time very reliable. The great advantage of this interface is very high data throughput. The possibility of power supply and communication with the camera via one cable is also interesting.

On the contrary, one of the shortcomings is that it is necessary to install a communication adapter (frame graber), as the PC usually does not have CameraLink among the standard interfaces. The price of the device for CameraLink communication is higher than for other interfaces. It is also not possible to connect or disconnect the device during operation (Plug & Play). Even the working distance is not too great – the maximum cable length is 10m. This interface is most often used in applications with high-speed or line scan cameras. Check for more here.

High Speed ​​Ethernet

GigE, High Speed ​​Ethernet, IEEE 802.3ab (a variant for metallic lines) refers to Gigabit Ethernet, which works on the same principles as Standard Ethernet. The widely accepted GigE Vision transmission standard has been developed for image data transmission.

The big advantage is that PCs normally have this interface and there is no need to buy and install any additional hardware. It is possible to connect multiple cameras at the same time, which can communicate and capture images at the same time. The signal can also be converted to wireless and thus transmit data over long distances. The maximum cable length is 100m. The transmission speed is sufficient for most machine vision applications, reaching from 10MB / s to 1000 MB / s both on twisted pair and on optical fiber. The price of the interface and cabling is low due to its expansion.

One of the few disadvantages is the higher CPU load. Unlike USB3, Plug & Play is less reliable. These cameras are suitable for most common machine vision applications where extremely high speed is not required and a higher CPU load is not a problem.


USB is a serial interface, initially intended as an alternative to RS-232 for connecting local devices to a PC. The advantage of the USB3 standard is the easy Plug & Play connection of the device and its high throughput. Although it does not match the speed of the CamLink interface, 350MB / s is sufficient for most industrial applications. As with GigE, the USB3 Vision protocol has been developed, making it easy to use cameras in real-time applications and improving compatibility between systems and cameras from different manufacturers. It is not excluded to connect multiple cameras to one system. The cost of CCTV systems based on this interface is relatively low, as is the cost of cabling.

The only downside is perhaps only the small maximum cable length, standard only 5m. However, this does not preclude the use of cameras with a USB3 interface in industry, but also in scientific research applications.

IEEE1394 – FireWire

It is a serial interface, the most well-known modifications of which are IEEE 1394a with a speed of up to 400 Mb / s and IEEE 1394b with a speed of up to 800 Mb / s. This interface is now more widely used in commercial video cameras. It is rather abandoned in the industry, it is replaced by high-speed modifications of USB3, which have already exceeded its parameters. The price of the interface and cabling is higher than with USB3, for communication it is necessary to have the appropriate frame graber in the computer, which is not usually standard equipment.

This interface can therefore be recommended only in ready-made machine vision systems, where its replacement would mean large financial or time investments.

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