Advanced Imaging - September 1997
FPGAs Provide Image Processing Alternative
by Sheldon Liebman
Over 10 years ago, Xilinx Corporation introduced the first generation of Field Programmable Gate Arrays, or FPGAs. These chips were designed to allow hardware manufacturers to include simple control logic in their products without having to include custom circuits. The concept behind the FPGA is fairly straightforward - you can program the chips to perform a variety of functions and new code can be loaded into them at any time, changing the characteristics to perform another function.
Although the original FPGAs were relatively simple devices, this class of chip has grown in size and complexity to the point that today, complex algorithms can be implemented using FPGAs. Univision Technologies, located in Burlington, MA, has become a leader in adapting this technology for use in image processing applications.
Approximately three years ago, Univision introduced the first member of their Falcon family of boards, which combine an SVGA display with frame grabbing and image processing functions. That first card used three small FPGAs to control different aspects of the product. One was used as a multiplexer to direct data through the frame grabber on the Falcon, the second acted as a DMA controller and the third was used to synchronize to different camera formats. Image processing was performed through the use of an optional DSP.
According to John Smith, Principal Engineer at Univision, people have been suggesting since FPGAs were first introduced that they could be used for complex algorithms like image processing. These suggestions were for very simple processes and were not commercialized. After the introduction of the original Falcon product, however, Smith wanted to investigate the possibility of putting some real image processing functions on the FPGA and was given the green light to try it. Based on the results of his initial experiments, Univision decided to go to market with the idea.
The original goal was to eliminate the DSP chip for simple image processing applications. If the tasks could be accomplished by the FPGA, an OEM customer could save thousands of dollars on a single board and significantly more than that over the life of an OEM product.
Univision initially identified two OEM customers who could take advantage of this opportunity and both jumped at the chance to try this new approach. The first was JEOL USA, a leading manufacturer of scanning and transmission electron microscopes, semiconductor inspection tools and analytical instruments.
One of JEOL's products, Xvision Plus, is a computerized control for the microscopes that includes high-resolution image acquisition, processing, storage and database management. It was introduced approximately two years ago using the Falcon-PCI without a DSP.
"One of the requirements for the Xvision Plus," states Robert O'Donnell, Electron Optics Systems Manager at JEOL, "was that it had to support recursive frame averaging in real-time." This process removes noise and creates a sharper, higher resolution image. To meet this goal, Univision and JEOL worked closely to program and debug the FPGA based on JEOL's spec. "As a result," adds O'Donnell, "we are the only company that produces a true 1K x 1K recursive averaged image."
The other company Univision identified was American Science and Engineering of Billerica, MA. By taking advantage of the way that FPGA technology can be customized to each application, AS&E has started improving their x-ray based vision systems.
The company serves two principal markets - detection of contraband for Customs agencies and security for both high-risk government facilities and executive offices of Fortune 500 companies. The first product that AS&E adapted to use the Falcon's FPGA is their Model 66Z for MailSearch and LobbySearch applications.
For AS&E, Univision programmed the FPGA to perform a new edge enhancement algorithm and zoom function. Using a 7x7 convolution, this high-pass filter enhancement highlights areas of the image with high spatial frequency components, such as circuit boards, wire bundles, guns and knives and other inorganic materials. Another function of the system is used to identify organic materials such as plastic explosives and flammable liquids. With the new product, the ability to identify these materials is enhanced.
As the processing power of the FPGAs increased, Univision designed a second generation of the Falcon product, which was introduced earlier this year. The Falcon-XL is supported by Univision's image processing library. Implementing the image processing functions of the Falcon Toolbox on a Xilinx series 4000 FPGA eliminates the need for a DSP in many types of image processing applications. With the introduction of this new, more powerful family of FPGAs, Smith was confident that the processing power now existed to perform general purpose image processing in real-time.
For example, the Xilinx 4025 may be configured to contain over 100 16-bit adders. "Running at 40 MHz, it is capable of performing 4 billion adds a second," explains Smith, "which is pretty powerful." In a paper Smith wrote for Xilinx, he described the implementation of a 3x3 median filter using an FPGA.
Smith concluded that an FPGA running at 25 MHz could perform the median function easily. Implementing the same function in a DSP would require the chip to be running at over 3000 MHz, which is more than 30 times the speed of a typical 100 MHz general purpose DSP or RISC processor.
Using FPGAs for image processing provides a price/performance level that just can't be matched by the current generation of DSP products. In addition to the power advantage illustrated above, FPGAs result in lower costs. For example, most DSP-based image processors are priced starting at over $5000, while the Falcon-XL lists for only $3695.
Also, since the FPGA is reconfigurable, the life of an FPGA-based product may be longer. New functions can be developed for OEMs that allows them to change the functionality and personality of a Falcon in the field without requiring a hardware upgrade. None of Univision's Falcon customers are planning to do this presently, but when the time comes to upgrade their systems, this may end up as a very pleasant surprise.
In some cases, suggests Smith, the FPGA chip itself can be upgraded to provide additional power without having to redesign the Falcon. "The standard Falcon-XL uses the Xilinx 4010 and 4013 chips," he explains. "But the footprint is shared by the 4020, which has roughly twice the processing power."
Using FPGAs for image processing offer other advantages as well. DSP-based image processors tend to have large heat sinks while the FPGA system does not. According to Smith, a well-designed circuit on an FPGA is not going to use as much power or generate as much heat as a general purpose DSP doing the same task. For OEMs, this can be significant.
AS&E, for example, found that their new system takes less time to set up and test. The cabling is simplified and maintenance is easier using the Falcon. Power issues and bus traffic conflicts in their previous generation product have also been eliminated.
When compared to a DSP-based system, systems built around Univision's Falcons can also be easier to develop for an OEM. Since implementation of the custom functionality is done by Univision, some of the programming tasks are shared between two companies. Once the functions are available, they are simply accessed through additions to Univision's standard Falcon Toolbox, which is a high level programming tool compatible with a number of C compilers. The OEM never needs to worry about programming the FPGA directly.
Based on the success of the current Falcon products, Univision is already working on the next generation of FPGA-based processors that will add color capture and processing. Continued advancements in graphics chip technology are allowing the company to offload some of the pixel processing from the FPGA to the graphics chip. This, says Smith, "frees up some bandwidth in the data path so we can move data in and out for processing more quickly." The new product should be introduced before the end of this year.
Whichever product an OEM chooses to use, however, the concept of FPGA technology as an alternative to DSPs for image processing has been clearly demonstrated by Univision with the products they have introduced already. As OEMs like JEOL and AS&E have discovered, you can get all the functionality you need with more flexibility, lower costs, and simpler systems. It's truly a win-win situation.
Back to Recent L&S Marketing Articles