Standards converters provide mix-and match imaging

Andrew Wilson, Editor

Developers of machine vision and image processing systems are faced with a myriad of choices when choosing which camera to computer interface to use. In the machine vision industry, older digital standards such as FireWire are being superseded by the USB 3.0 Vision standard. For high-speed imaging, the legacy CameraLink standard now faces some very strong competition from CoaXPress (CXP), while other standards such as GigE are touted for their low-cost, and long distance capabilities.

Needless to say, the trend to move to digital standards is also apparent in the broadcast industry where, although legacy RS-170-type analog broadcast standards are still used in many applications, they are now being replaced by serial digital interface (SDI) standards for transmitting uncompressed high-definition video signals.

All of these standards, of course, have their own advantages and disadvantages in terms of speed, cable length, triggering capability, latency, jitter and power-over interface capability. Numerous comparisons of these standards are available on-line from sources such as Basler (Ahrensburg, Germany; www.baslerweb.com), Point Grey (Richmond, BC, Canada; www.ptgrey.com) and Raptor Photonics (Co. Antrim, Northern Ireland; www.raptorphotonics.com). These can be found at http://bit.ly/1nqpTok, http://bit.ly/1dQEYae and http://bit.ly/1jO59qj respectively.

While individual cameras and frame grabbers may be tailored for one particular camera to computer interface, it is often necessary to leverage the benefits of one standard while deploying cameras or frame grabbers based on a different interface.

In the past, for example, LVDS frame grabbers were used with LVDS cameras. Today, however, many cameras are based on the CameraLink or CoaXPress (CXP) standard and developers may wish to incorporate these cameras into systems using their legacy LVDS frame grabbers. In other applications, image data from such CameraLink or CXP cameras may need to be transmitted over long distances using either the GigE Vision or fiber interfaces. Developers looking to incorporate high-performance cameras into broadcast or studio-based systems may also require the performance of CameraLink or CoaXPress cameras while retaining the flexibility of broadcast-based standards.

Because of this, a number of companies have developed converter products that allow developers to mix and match cameras and frame grabbers with different interfaces. In this way, legacy products based on older standards can be used with more recent interfaces, preserving the developer's investment while leveraging the power of newer peripherals. At the same time, some of these converters can overcome some of the limitations – such as the limited networking capabilities and distance limitations of existing standards.

To interface CameraLink cameras to RS-422 and LVDS frame grabbers, for example, Vivid Engineering (Shrewsbury, MA USA; www.vividengineering.com) offers its CLT-353R and CLT-353L Camera Link Translators that convert CameraLink to RS-422 and LVDS, at a 32 MHz max pixel clock rate (RS-422) and 85 MHz (LVDS). Similarly, Imperx (Boca Raton, FL USA; www.imperx.com) offers a number of such converters in its Adapt A-Link series that are designed to convert Base CameraLink to LVDS, LVDS to Base Camera Link and DVI to Camera Link.

For those wishing to deploy the latest CXP cameras with existing CameraLink cameras, or CameraLink cameras with CXP frame grabbers, Tecphos (Falcon, CO USA; www.tecphos.com) has developed a Camera Link to CXP converter/ CXP to CameraLink converter. While such converters are useful, they cannot be used to overcome the distance limitations of standards such as CameraLink.

While repeaters can be used to accomplish this task, leveraging the power of Gigabit Ethernet or fiber allows developers to extend the camera to converter distance, support network architectures and eliminate the need for a PC-based frame grabber. For this reason, companies such as Pleora (Kanata, Ontario, Canada; www.pleora.com) and GigaLinx (Hod Hasharon, Israel; www.gigalinx.net) have developed converters that allow Camera Link cameras to be interfaced to Gigabit Ethernet networks.

While process and machine monitoring and security and surveillance systems that require cameras to be positioned at distances from the host computer can deploy such converters, harsh environments may require the use of digital to fiber converters. A review of these converters can be found on-line at: http://bit.ly/1jx6cIf.