The cost of custom cables and the broad range of digital transmission formats were the driving force behind the development of the Automated Imaging Association (AIA) standard for high-speed transmission of digital video. The AIA standard is known as Camera Link, which defines the cable, connector, and signal functionality between the camera and the frame grabber. Any camera that complies with the Camera Link specification should work with any frame grabber that is also Camera Link-compliant.
Throughput: Camera Link, a high-speed serial digital bus designed specifically for machine vision cameras, offers the highest throughput of any camera bus. Camera Link provides a three-tiered bandwidth structure (base, medium, and full) to address a variety of applications. Base-configuration cameras acquire at up to 255 MB/s (3 bytes × 85 MHz), though most cameras use roughly 100 MB/s or less (1 or 2 bytes × 50 MHz or less). A typical base-configuration camera might acquire 1 Mpixel images at 50 frames/s or more. Medium- and full-configuration cameras acquire at up to 510 MB/s and 680 MB/s, respectively. A typical full-configuration camera can acquire 1,280 × 1,024 images at 500 frames/s, or larger 4 Mpixel images at more than 100 frames/s. Score: 5
Cost-effectiveness: Because Camera Link is designed for medium- to high-performance image acquisition, the cameras are generally more expensive than lower performance cameras. Also, Camera Link requires a frame grabber that can handle the high data rates described above. These cameras are more expensive than USB, IEEE 1394, or Gigabit Ethernet adapters. Score: 1
Cable length: The Camera Link standard replaces expensive, custom cables with a single, low-cost standard cable with fewer wires. Special components on the camera are used to serialize 28 parallel TTL signals into four high-speed differential pairs, which are transmitted across the cable. A similar component is used on the frame grabber to deserialize the data stream into parallel TTL signals. This reduces cable size and cost and increases noise immunity and maximum cable length.
The Camera Link specification defines a maximum cable length of 10 m. Camera Link uses a standardized cable that is relatively inexpensive and works with any Camera Link-compliant camera and acquisition device. Base-configuration cameras require only one cable. Medium- and full-configuration cameras require two cables. Score: 3
Standardized interface: The Camera Link specification defines a standard cable, connector, signal format, and serial communication API for configuring cameras. However, unlike IEEE 1394 and GigE Vision, the communication between the camera and PC is not defined by the standard. This means that every Camera Link camera requires a special camera configuration file to explain to the software how to acquire images from the camera, how to communicate with the camera, and which features can be modified. You can compare cameras and download camera files at ni.com/cameras. Score: 3
Power over cable: Camera Link offers an option known as Power over Camera Link (PoCL) for providing power to cameras over a cable. Several Camera Link-compliant NI frame grabbers work with this feature. Score: 3
CPU usage: Camera Link cameras require the use of frame grabbers, which transfer the image data to memory using DMA channels that do not burden the computer’s CPU. Because of this, Camera Link image acquisition uses very little of the system CPU. Score: 5
I/O synchronization: Although serial signals are defined on the cable pinout, the specific serial commands for setting exposure, gain, and offset, for example, are not defined by the specification. The frame grabber driver software must be configured to accommodate a particular camera’s serial commands. Control signals are also provided on the Camera Link cable for triggering and timing, but many manufacturers offer separate connectors for advanced triggering capabilities. Although the limited scope of the Camera Link specification does not provide plug-and-play compatibility, it gives camera and frame grabber companies an opportunity to differentiate their products by adding features or enhancing functionality. Overall, Camera Link offers the most I/O flexibility and capability. Because of their more demanding synchronization requirements, most linescan cameras use Camera Link. Score: 5