More GigE Vision, Camera Link updates

Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 6/1/2010 12:00:00 AM

More updates are coming in the GigE Vision and Camera Link camera interface standards from the AIA (Automated Imaging Association). In January, the association released GigE Vision version 1.2, which provides several improvements including support for nonstreaming devices. By the end of 2010, the AIA expects to have a draft specification of GigE Vision 2.0, which will include formal support for 10 GigE. The next update to Camera Link will be Camera Link 1.3, which the AIA hopes to release before November; a more thorough revision, Camera Link 2, is just getting underway and is not expected to be completed until 2011.

The main focus of GigE Vision 1.2 is the ability to control GigE Vision-enabled devices other than cameras—in particular nonstreaming devices such as strobe lights—over the same switched network, said Eric Carey, chair of the AIA's GigE Vision standard committee and director of R&D for Dalsa. These devices can be attached to the network with the same switch that connects GigE Vision cameras, and they will be automatically recognized by the network's computers. The ability to control all these devices with a common control protocol will help simplify software development.

"Because of customer feedback we've received from vendors, we also want to increase the robustness of GigE Vision systems," Carey said. "The PC that's connected to a GigE Vision camera can crash or experience other problems that interrupt the application. With version 1.2, logic hooks in the primary application that controls the camera allow a second PC to take control of the camera if the first PC goes offline" (figure).

If the primary PC controlling a GigE Vision camera goes offline, Version 1.2 of the standard lets a second PC take control to prevent the vision system from shutting down. Courtesy of Dalsa.

Version 1.2 also includes unconditional streaming. In version 1.0 the camera expects to get a message from the application every few seconds and shuts down the connection if that message stops coming. But in some applications, streaming must continue, Carey said. In version 1.2, this function can be disabled so the camera streams images even if the primary control application has died or the PC has shut down.

At present, the GigE Vision committee is considering five main features for inclusion in version 2.0, said Carey. First is formal support for 10 GigE and link aggregation. Although for practical reasons most GigE Vision 1.0-compliant products do not support link speeds higher than 1 Gbps, version 1.0 does not prevent those higher speeds. The committee will explicitly state this in the 2.0 spec. In addition, version 2.0 will more clearly define how link aggregation can be used for GigE Vision devices.

Next is support for JPEG, JPEG 2000, and H.264 data compression. The third feature, data-flow-control management, prevents congestion when there's a big burst of data. The last two features are a real-time trigger to help synchronize multiple cameras and a frame-packing mechanism for smaller images to reduce packet overhead, in turn reducing the CPU image-processing load.

"We hope to have a draft of GigE Vision 2.0 by the end of this year, but the full specification will probably be ready around the middle of 2011," said Carey. Two minor features for version 2.0 are a generic method of identifying pixel formats and a method for adding new ones, since there are sometimes inconsistencies in how pixel formats are named, plus an appendix containing information that doesn't fit easily anywhere else, such as how to connect GigE Vision devices to the more ruggedized Ethernet cables.

As it prepares the next generation of Camera Link, version 2, the AIA continues to make incremental improvements to the original standard, said Jeff Fryman, the AIA's director of standards development. Camera Link 1.2 included the Power over Camera Link interface and the 26-pin mini-Camera Link connector. "The 1.3 extension, which we hope to finalize prior to November, will include Camera Link Light, a smaller connector with a 14-pin configuration and a different cable, and ‘deca,' or 10-tap, mode," he said. This extension will also include electrical design, performance, and test requirements for cables, including an eye-mask and a bit-error-rate test.

Although Camera Link cable has a 10-m nominal distance, it can carry signals more than 10 m at 40 MHz, but less than 10 m at 85 MHz. "Ten years ago, everyone was using 40-MHz or slower cameras, so distance wasn't an issue," he said. "Now we know the cable is too long for faster speeds."