Advanced Imaging


Advanced Imaging Magazine

Updated: July 8th, 2008 05:26 PM CDT

How To... Use PCIe Applications in Machine Vision


PCI Express is the peripheral bus now being adopted by next-generation PCs, servers and industrial computers. It provides a scaleable, high-bandwidth, point-to-point pathway between peripheral cards and the computing core while retaining application software compatibility with previous generations. For machine vision systems, the architecture and higher bandwidth of PCI Express yield major increases in achievable frame rate and image size as well as simplifying the implementation of multi-channel capability.

The high speed and dedicated bandwidth available to Dalsa's frame-grabber boards because of their native PCIe interface enables users to address a wider variety of machine vision applications than earlier PCI devices. One beneficial application is the use of high-speed line-scan imaging for web inspection. Under the 32-bit addressing limit of PCI, line-scan systems needed to artificially break the image into frames of a size that would fit into the 2-Gigabyte addressable memory space. This framing activity interrupts the data flow and complicates the image processing used in the inspection process by introducing arbitrary image boundaries. The 64-bit compatibility designed into Dalsa's native PCIe interface allows virtually unlimited frame sizes, permitting the web inspection to proceed on a more continuous basis.

Another application that benefits from PCIe's attributes is multi-angle inspection. Such systems use multiple cameras to examine an object from several directions simultaneously. This multiple view allows a system to inspect all surfaces of an object without requiring the object to be manipulated. A conventional PCI-based system that offers multiple image-capture channels, however, must share the system bandwidth among the channels. This sharing quickly becomes a bottleneck, lowering the inspection system's throughput.

A PCIe-based system can employ multiple frame-grabber boards and provide each with a link to system memory. Because the bandwidth of a PCIe link is dedicated to the data transfer it carries, each frame grabber in the system can operate at its full speed without affecting the others. This, in turn, allows the inspection system to provide maximum throughput.

Dalsa aims to exploit additional features of PCIe, such as its independent, bi-directional bandwidth. This bi-directional capability is poised to help simplify co-processing in machine vision systems. As Gigabit Ethernet cameras began making inroads into general purpose machine vision applications, the need to offload from the host CPU the task of converting the GigE Vision packets into usable images became increasingly evident. A Bayer color GigE camera sending data at 100Mbytes/sec., for example, requires the host computer to spend tremendous amounts of valuable CPU clock cycles simply converting and decoding images into usable formats.

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