This special report on the Camera Link interface provides technical information about the standard, explains and promotes the importance and impact of this standard on the machine-vision and image-processing industry, and attempts to keep our readers updated and informed on this major development trend. Written exclusively by technical experts from companies in this industry, all overviews and articles in this report provide key insights into the standard by its originators, prime movers, and supporters. Because of the overwhelming cooperation, support, and editorial response from the industry, this special report will be presented in two parts: Part I is published here; Part II will be published in a subsequent issue.—GK
Until recently, broadcast video standards provided the interface between cameras and frame grabbers. This allowed users, camera vendors, and frame-grabber vendors to design products that met almost everyone's needs. Competition was based mostly on price and features. With analog cameras as the standard interface, the main differentiator was whether processing was done in real time on the frame grabber or the data were transferred in nonreal time to the PC via the AT bus for storage or future processing. Here, competition was at the frame-grabber level.
Concurrent with the introduction of PCI technology, digital cameras based on TTL, PECL, and LVDS interfaces emerged. These cameras yielded higher performance for the camera manufacturers who could take advantage of the digital revolution to support faster and larger formats. Camera manufacturers were able to meet the higher frame and data rates, but now have to worry about compatibility with as many framer grabbers as possible.
Frame-grabber vendors now have to design for the numerous, slightly different, digital interfaces that camera vendors are providing, as well as to convince systems integrators and users of their claims to ease of integration at low cost. Therefore, frame-grabber manufacturers are further differentiated as supporters of native PC (for example, Bitflow, Imagenation, and Integral Technologies) or supporters of coprocessors (for example, Alacron, Coreco, Datacube, and Matrox), further complicating the commercial market (see Table 1).
Since 2000, further standardization of peripheral buses (spurred by OEM PC manufacturers to enable users to easily add peripherals—or even cameras—to their PCs without expert assistance) has had an invigorating effect on the choice of camera interfaces. This has been accelerated by the rapidly increasing CPU and memory data rates commercially available at competitive prices, which present an increasing option of native PC-based-real time or nearly real-time processing at speeds only recently possible (see Table 2)
The ubiquitous USB 1.0 interface is now used for low-speed, low-resolution cameras connected directly to the PC, eliminating the need for a frame grabber. However, the limited distances, speeds, and resolutions of USB 1.0 cameras severely limit their applications in serious machine-vision environments. The high-technology industry expects that the USB 2.0 interface will supplant USB 1.0 platforms as PCs evolve their USB designs, but USB 2.0 may take time to become widespread in the motherboard market.
The IEEE 1394 (FireWire) and newer USB 2.0 standards are fast enough for the original analog camera signal in digital formats as well as for low-to-medium speed, existing digital cameras. Impeding IEEE 1394's utility, however, is the lack of widespread OEM PC support for it in the industrial PC market (as opposed to the consumer portable/Apple environment). The USB 2.0 interface can provide higher data rates, but the same difficulty applies with the additional problem that IEEE 1394 has wider current acceptance. Even with the newest PCI, CPU, and memory technologies, the standard PC may have significant problems doing nearly real-time processing without adding extra processors. After two processors, the cost and shared memory contention potentially make a coprocessor (accelerated) frame grabber substantially less costly and more efficient than the native PC solution. The advantage of using shrink-wrapped software packages is also lost.
Camera Link emerges
The Camera Link standard is based on National Semiconductor's inexpensive Channel Link technology, which boasts superior transmission rates of up to 2.38 Gbits/s (297.5 Mbytes/s) per channel. With a standard connector and pin-outs, Camera Link, as currently defined, uses one to three channels (Base, Medium, or Full configurations, with a recent extension proposed by Basler Vision Technologies), depending on video data format and rate. The Full configuration delivers impressive transmission rates up to 680 Mbytes/s at 66 MHz or 850 Mbytes/s at 85 MHz. Moreover, this technology is highly scalable and limited only by the number of chipsets that frame-grabber makers put on a laminate or the number of frame grabbers an integrator or end user is willing to put in a chassis.
For low- and medium-end cameras, frame-grabber manufacturers and end users are back in the same competitive environment they occupied during the analog era. Camera vendors like the ease of implementing Camera Link and the low power and low cost of Channel Link chipsets. Frame-grabber vendors like the new standard because they don't have to do a lot of hardware design, and the interface is easy to implement. Therefore, IEEE 1394 and USB 2.0 boards, and even single Camera Link boards costing less than $50, will satisfy most native PC processing needs. Customers like the ease of systems integration and the low cost. So, it's pretty much an all-around win.
In the last year, however, semiconductor performance improvements have begun to expand beyond microprocessors and memory to CCD and CMOS sensors. This trend will continue. For example, the performance of high-end CMOS imagers such as the Micron Imaging (formerly Photobit) MV13 (10 bits x 10 taps x 66 MHz) is 833 Mbytes/s, and the MV40 (10 bits x16 taps x 66 MHz) is 1333 Mbytes/s. All these data need a scheme for storage or processing that will tax the most-powerful current multiprocessor and envisioned uniprocessor system in the near future. This includes accelerated frame-grabber manufacturers who bypass the 64-bit/66-MHz PCI bus, as well as CPU memory performance issues.
At present, camera vendors are beginning to manufacture cameras using rates near 1 Gbyte/s. However, they will have to convince frame-grabber manufacturers to support their cameras, and the frame grabbers will require acceleration for use in anything approaching real time in the machine-vision market. Otherwise, such camera manufacturers would quickly have to become makers of "intelligent" cameras, which will require substantial digital hardware design and manufacturing experience and an enormous software effort.
For the foreseeable future, Camera Link will remain the only standard digital camera interface with the potential high performance and scalability needed by medium- and high-end cameras and the low cost needed by the low end of the industrial digital-camera market. Given the past reluctance of most camera manufacturers to expand to processing cameras (and the required extensive software suites), the frame-grabber vendors, systems integrators, and end users will split into two groups: a native PC, low-cost group, keeping pace with the changes in standard PC technology and boxed software, and the remaining users, who will require accelerated frame grabbers or high-end multiprocessor servers with sophisticated data I/O channels. With respect to either group, the continued adoption and enhancement of the Camera Link standard are assured.
Joseph Sgro is chief executive officer at Alacron Inc., Nashua, NH 03060.