Digital imagers build high-bandwidth bridges

Two digital imaging standards are rapidly growing out of the massive installed base of analog systems.

Oct 1st, 2002
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Two digital imaging standards are rapidly growing out of the massive installed base of analog systems. One, IEEE 1394, emphasizes networking and scalability, and eliminates the need for a frame-grabber board. The other, camera link, emphasizes bandwidth and synchronization, and, like analog and legacy LVDS (low- voltage differential signaling) digital-imaging standards, requires a frame-grabber board. As the predominantly analog imaging market continues to grow the two new digital-imaging standards are increasing in market share, according to Stanley Shmia, market development manager in the Vision Components Division (Exton, PA) of Basler Vision Technologies (Ahrensberg, Germany). Shmia, whose company manufactures digital cameras exclusively, and other imaging industry executives described IEEE 1394 and camera link as complementary technologies.

"The camera-link cameras and of course the corresponding frame grabbers, as well as 1394 cameras and the corresponding hardware inside the host PC, complement each other in terms of what is required for the machine-vision market," Shmia said. "Camera link offers greater flexibility in terms of the information that you can send between the camera and the frame grabber and offers much greater speed and higher bandwidth than what you have with IEEE 1394."

From the perspective of someone whose company manufactures digital cameras exclusively, Shmia characterized IEEE 1394, also known as FireWire, as a bridging technology between the analog world and the digital world of high-bandwidth camera-link flexibility. A sizeable chunk of his company's market is interested in and pursuing 1394, particularly customers who are using analog or legacy digital cameras and would like to have the state-of-the-art digital advantages such as cleaner signals and no pixel jitter. Customers with line-scan cameras, or cameras running multiple tasks at large bit depths, however, tend to seek out camera link.

From the perspective of a manufacturer of image- camera boards and software, however, Pierantonio Boriero, product-line manager at Matrox Imaging (Dorval, Quebec, Canada) characterized the bridging a little differently. He described camera link as an intermediate step from analog and legacy digital systems to the networking flexibility of 1394. Even though camera link standards simplify and standardize the interconnection, camera link is still essentially a point-to-point connection, Boriero said. But 1394 allows you to actually build a network.

Compulsive controllers

Vendors that use imaging as part of machine control and robotic technologies, such as Adept Technology (Livermore, CA) are highly enthusiastic about 1394 because of the significant simplification and cost reduction that comes with a direct connection, as well as the ability to add nonimaging devices along with the cameras (see figure).

The complexity and cost associated with multiple point-to-point connections (top) is reduced significantly with network connections enabled by IEEE 1394 (bottom).
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"What I think is exciting right now encompasses vision but it's not vision specific," said Joseph Campbell, vice president of Adept Technology. "We are trying to attack the cost infrastructure of control systems." Cost infrastructure components include power supplies, back planes, metal chassis, and cabling, and their costs increase as systems are scaled upward with the addition of robot mechanisms, axes of motion control, processing power, vision-processing cameras and sensors, and so on.

"We are now seeing the benefit of building our network on FireWire, IEEE 1394 standard," Campbell said. "We're starting to see industrial FireWire cameras specifically designed for machine vision that plugs into the network. What goes away is the frame grabber because the FireWire network is delivering image data directly from the camera to the CPU. So if you want to add another camera, you just put another camera on the network."

Campbell's description gives the impression of IEEE 1394 building a metaphorical bridge to new paradigms in robotics and machine control. Taking a step back, however, it becomes clear that the bridges that everyone is talking about are actually parallel lanes all under simultaneous construction on the same bridge. No one will know exactly what the destination looks like until the bridge is complete. But everyone expects to ultimately achieve very high-quality digital imaging and very high-bandwidth transfer of imaging data in multifunctional networks that promise much greater ease of assembly and scaling than is available today.

"Technologically FireWire is a very attractive solution for applications in which the pixel data rate is in the realm of TV rates, basically around 1 Mbytes of pixel data per image or 30 Mbytes per second of continuous video streaming," Boriero said. "That's what the 1394A standard can accommodate today, but 1394B will effectively double that bandwidth.

"At the same time, "image-sensor technology has gone way beyond TV data rates and will continue to do so," he said. "That's where standards like camera link come in. Right now it's probably the hottest standard in terms of industrial and scientific imaging in terms of connecting camera to the PC through a camera link frame grabber." Even though camera link is a point-to-point connection, bandwidths exceed 100 Mbytes per second.

Big pictures

Jerry Fife, product manager for industrial and scientific cameras, both analog and digital, at Sony Electronics (Park Ridge, NJ) corroborated much of what has already been said but also added some perspectives. "On the digital side, Sony's focus has been primarily from the digital solutions point of view to go toward FireWire 1394," he said. "Customers are looking for something more than they were able to get from the traditional analog cameras. The highest resolution we have available on our cameras is 1280 by 960, which is four times the traditional resolution 640 by 480 VGA camera."

In addition, the lanes on the metaphorical digital-imaging bridge are not strictly digital, according to Fife. "In the analog world, we are now up at 60 frames per second at 640 by 480. So the analog world is actually a little faster from that perspective, but I think it's just a matter of time," he said. "Ultimately you'll probably see that kind of speed migrating to 1394 as well."

IEEE 1394 is generating a lot of interest because the bus architecture allows sharing of resources. But multiple camera applications are not the only drivers, Fife said. He typically tells customers that, particularly in lower bandwidth monochrome applications, 1394 makes sense for high-resolution imaging, reducing or simplifying cabling, and for working with smaller, lower-cost, slotless computers.

"It makes a lot of sense if what you're trying to do is reduce or simplify your cabling, and it makes a lot of sense if you want to use it on smaller, lower-cost, slotless computers, like laptops and some of the industrial systems," he said. "There's a plethora of industrial-design computers that are coming to the marketplace that all have 1394 ports built onto them," he said. "You don't have to do anything special or add any additional hardware. You just plug in your 1394 camera and away you go."

Boriero also emphasized the influence of Windows operating-system support in the popularity and spread of 1394, and he mentioned Intel support for a USB 2 standard in new computer systems as a possible competitor. But Fife's response indicates that the USB 2 lane on the metaphorical imaging bridge is likely to be a slow lane for some time to come (see table).

Click here to enlarge image

"There aren't any industrial cameras that support USB 2 yet, and people I know who are designing interface boards and cameras to go on a USB 2 are finding that the sustainable throughput on USB 2 is significantly less than 1394," Fife said. And that gap is already widening as 1394B doubles the bandwidth available through FireWire. "So we are right back to the same place we are today, with more bandwidth available on 1394."

Of course, that is how things look now. Things will probably look a lot different once the bridge is actually completed.

Hassaun A. Jones-Bey, Senior Editor

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