The race for the ultimate interface

Camera Link is emerging as a key interconnect-technology for linking digital cameras and frame grabbers. The technology enables manufacturers to transmit large amounts of image data over a compact, flexible cable, and several vendors now offer Camera Link products, including Data Translation and Pulnix America.

Developed through an initiative led by Pulnix (Sunnyvale, CA; http://www.pulnix.com) and based on the Channel Link technology from National Semiconductor (Santa Clara, CA; http://www.national.com), Camera Link has become a recognized standard for high-end machine-vision applications. A key advantage is the technology's universal interface, which allows users to swap cameras without having to reconfigure hardware or software; it also eliminates the need for custom cables for different cameras.

Mike Roberts, GM of imaging and machine vision at Data Translation (Marlboro, MA; http://www.datx.com), explains, "The main advantages of using Camera Link are the simple interoperability between the camera and the frame grabber and the high data-transfer-rates, allowing higher pixel-depth and resolution."

At the heart of a Camera Link product is a Channel Link LVDS (low-voltage differential-signaling) chipset. Camera Link products use the chipsets to transmit 28 bits of data at 2.38 Gbits/s, sending digital data through a cable of five wrapped pairs of wire, four for camera control and one for a clock signal. Before Channel Link chipsets emerged, transmitting 28 bits of data at high rates of speed required 28 wrapped pairs of wire, making for bulky cables with little flexibility and limiting the maneuverability of the camera.

Making the switch to Camera Link can seem expensive. The individual products are competitively priced, but you need to purchase a fully integrated system to use the technology. Purchasing a camera, a frame grabber, software, and a cable simultaneously means incurring high costs. According to Roberts, "These are the types of issues faced while trying to put forward a standard of this nature. . . but this is just a short-term hurdle."

Camera and frame-grabber manufacturers see Camera Link as a cost-effective means for building products with performance capabilities not available with other technologies. "With RS-644 LVDS, multiple chipsets are needed to handle the traffic requirements that one Channel Link chipset can handle. This and the significant reduction in cable size greatly saves on costs of materials, making Camera Link a cost-effective solution for high-end performance," says Steve Kinney, Committee Chairperson of the Automated Imaging Association (AIA; http://www.machinevisiononline.org).

So why not run out and get Camera Link products right away? "It all depends upon the needs of the user. For some applications that do not require high bandwidth and real-time transmission rates, IEEE 1394 with transmission rates of 400 Mbits/s or USB which runs at 480 Mbits/s are suitable alternatives to Camera Link," says Kinney.

As camera and frame-grabber manufacturers continue to develop Camera Link products, you might ask, "Will IEEE 1394 and USB soon be considered archaic forms of machine-vision interfacing?" According to Don Lake, director of marketing at Pulnix America, "Camera Link is specifically designed for high-performance, high-bandwidth applications and certainly usable for lesser applications, but USB, IEEE 1394, and even the standard NTSC television analog connectivity will continue to succeed in their own respective markets."