Product Focus: Low cost frame grabbers offer subtle variances

Costing less than $1000 each, commercial color frame grabbers handle cost-effective image capture.

Feb 1st, 2000
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Costing less than $1000 each, commercial color frame grabbers handle cost-effective image capture.

By Andrew Wilson,Editor at Large

Currently, more than 20 companies offer color frame grabbers for the PCI bus. Costing less than $1000 per unit, these low-price frame grabbers do not generally provide the technical capabilities of their high-performance counterparts. But, in applications such as microscopy, machine vision, and medical imaging, where broadcast-standard resolution can be tolerated, they deliver a cost-effective means of image capture.

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RIGHT. FIGURE 1. In the design of its Image/VGA-400 frame grabber and display controller, MuTech has integrated a frame grabber and a 64-bit, 3-D accelerated VGA display controller onto a single-slot PCI board. This board can digitize and display NTSC, PAL, or S-Video images inside a resizable video window on the computer's VGA monitor.

At first glance, the specifications of such frame grabbers seem similar. Not surprisingly, most digitize standard color-television formats, such as NTSC, PAL, and SECAM, use off-the-shelf video digitizers (see table on p. 30). Such requirements mandate the use of low-cost color cameras with analog outputs that have been primarily manufactured for broadcast-quality applications.

In such cameras, digital signals from the camera's CCD are first encoded and output as NTSC, PAL, SECAM, or S-Video analog signals. These signals are often digitized by the frame grabber and separated into RGB components. However, this encoding/decoding process decreases the signal-to-noise ratio (S/N) of the video signal, resulting in a loss of resolution. Although the resolution of such cameras is often specified in terms of lines (for example, 525 for NTSC and 625 for PAL) or VGA resolution (for example, 640 x 480 pixels), it depends mainly on the S/N from the camera and on the fidelity of the frame grabber.

On-board VGA

To reduce the cost of color image-processing systems, some vendors have incorporated VGA display controllers on their frame grabbers. This eliminates the need to incorporate a separate VGA display controller in the PC system, freeing a PCI slot and reducing system cost. In such designs, the frame grabber has control of the system VGA display, and the PC display can be combined with incoming video data.

In the design of its Image/VGA-400 frame grabber and display controller, MuTech Corp. (Billerica, MA) has integrated a frame grabber and a 64-bit, 3-D accelerated VGA display controller onto a single-slot PCI board (see Fig. 1). In addition, NTSC, PAL, and S-Video images can be digitized and displayed inside a resizable video window on the computer's VGA monitor.

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RIGHT. FIGURE 2. Integral Technologies FlashPoint 128 board can digitize composite and S-Video inputs in both PAL and NTSC formats as well as component RGB or YUV video. For image display, the board's SuperVGA Windows accelerator can display video images full-screen or in a resizable window.

Text and graphics can be written into VGA memory and, by using a color key, overlaid nondestructively on top of live video. Chroma keying is also supported so that a background can be underlaid behind a video scene. And, because the Image/VGA-400 uses a VGA controller, resolutions, with a live video window, of up to 1024 x 768 x 16 bits and 800 x 600 x 24 bits are supported.

Other companies, such as Coreco Inc. (St. Laurent, Quebec, Canada), Integral Technologies Inc. (Indianapolis, IN), Willow Peripherals (East Hampton, NY), and VisiCom (San Diego, CA), also support VGA controllers on their frame grabbers. However, companies such as Imaging Technology Inc. (Bedford, MA) do not support on-board VGA on its frame grabbers. The company does offer a range of products, including PC-Comp, a PCI-based color frame grabber.

Pull the trigger

Apart from considering whether to choose a frame grabber with on-board VGA, systems developers must fully understand the application for the board. In many machine-vision applications, for example, images must be acquired after some external event has taken place. This acquisition requires that the external event be capable of triggering the frame grabber to capture images. Because many color frame grabbers have not been developed for machine-vision applications, they do not provide external triggering. Of those that do, even fewer frame grabbers offer both triggering and on-board VGA display capabilities.

Although it must be used with a host VGA display controller card, the Pixci SV4 PCI-based imaging board from Epix Inc. (Buffalo Grove, IL) allows NTSC, PAL, or S-Video image sequences to be captured at full or reduced frame rates onto the PCI bus. These images can be stored in host computer memory or passed to other devices on the PCI bus such as disk controllers or VGA adapters. Depending on the VGA adapter used, the imaging board can display 24-bit RGB color images or 8-bit monochrome images. Full-screen, scaled, or cropped images can be placed anywhere on the VGA screen. To synchronize the board with external events, the Pixci SV4 uses four input and four output TTL trigger signals that are controlled by the host PC.

The FlashPoint 128 board from Integral Technologies also can be used to digitize composite and S-Video inputs in both PAL and NTSC formats as well as component RGB or YUV video (see Fig. 2). For image display, the board's SuperVGA Windows accelerator allows video to be displayed full-screen or in a resizable window (video in a window) and can be software-adjusted (hue, brightness, saturation, contrast, offset, and gain) to the desired levels through programmable control of the video decoder. For machine-vision applications, the board also provides general-purpose TTL input/output triggers and features optically isolated output triggers for a flash interface.

On-board processing

Systems developers looking to perform high-performance image-processing functions such as image filtering, Fourier analysis, and color analysis can use low-cost color frame grabbers. However, because little or no image-processing capabilities in the form of LUTs, CPUs, and DSPs are built into most low-cost color frame grabbers, these processing functions must be performed by the host PC. This setup limits processing speed and, therefore, the number of applications that such boards can be used to address. However, if image processing does not have to be performed at real-time rates, such boards do represent a low-cost option.

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RIGHT. FIGURE 3. The Bandit integrated PCI frame grabber and VGA card from Coreco can zoom a live video window by arbitrary factors in both x and y directions. Additional images can be zoomed or reduced allowing system developers to fill the entire screen with live video or create icon-sized live video images.

Those boards that incorporate on-board VGA often use the function of the graphics display controller to perform graphics overlays, bit-block transfers (BitBLTs), and line-drawing capabilities. For example, in the design of its VGA-CTV NTSC or PAL PCI video frame-capture board, Willow Peripherals uses an on-board VGA controller for functions such as BitBLT, line draw, and hardware cursor. To provide system developers with 1024 x 768-pixel resolution and color depth of the VGA display, the board incorporates 2 Mbytes of display memory.

In addition to using an on-board VGA controller for display functions, the Bandit integrated PCI frame grabber and VGA card from Coreco can zoom a live video window by arbitrary factors in both x and y directions (see Fig. 3). Additional images also can be zoomed or reduced, allowing system developers to fill the entire screen with live video or to create icon-sized live video images. Moreover, the Bandit's architecture supports video mirroring and inversion, enabling digitized images to be inverted (top becomes bottom) or mirrored (right becomes left) on the display at video rates. According to Coreco, both mirroring and inverting the image can occur at the same time and require no processing by the host PC.

Whereas many low-cost color frame-grabber boards use integrated graphics controllers to perform rudimentary display functions, the VigraVision board from VisiCom uses field-programmable gate arrays (FPGAs). These arrays allow system developers to perform sophisticated image-processing operations (see Fig. 4). Combining color image capture, FPGA-based image processing, and on-board graphics display, the board can be configured with a variety of FPGA devices, allowing system developers to implement customer-specific, real-time image-processing functions. Using the Xilinx (San Jose, CA) XC4000 series of FPGAs, the board can be configured on the fly to perform such functions as spatial filtering, frame averaging, motion detection, and image resampling with bilinear interpolation. For image display, the board's integrated S3 Virge display controller accommodates noninterlaced displays with resolutions to 1600 x 1200 pixels at 75-85 Hz.

Expanded support

Before purchasing low-cost frame-grabber boards, system developers should determine whether the board supplier offers other higher-performance frame grabbers that are software-compatible with their low-cost products. For, as often happens, should the requirements of the machine-vision or image-processing system change in mid-development, the system developer may have to abandon both the board—and worse—the more expensive software development effort.

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RIGHT. FIGURE 4. The VigraVision board from VisiCom uses FPGAs that allow system developers to perform sophisticated image-processing operations. Combining color image capture, programmable FPGA-based image processing, and on-board graphics display, this board can be configured with a variety of FPGA devices that allow system developers to implement customer-specific, real-time image-processing functions.

To accommodate such possibilities, Matrox Electronic Systems Ltd. (Dorval, Quebec, Canada) offers it's Meteor-II frame grabber in three versions: the Meteor-II board for NTSC/PAL and composite RS-170/CCIR signals from video cameras and VCRs; the Meteor-II/Multi-Channel version for capturing images from standard or variable analog monochrome or component RGB frame-scan sources; and a digital version for capturing images from digital frame and linescan sources including multi-tap configurations (see Fig. 5). All three boards include the company's VIA chip, a custom ASIC that is used for region-of-interest capture, independent horizontal and vertical subsampling, and reformatting operations for reconstructing images from multitap cameras in real time.

All of the color frame grabbers discussed can be purchased for less than $1000, but the features found on each one are subtly different. While many offer triggering, on-board display, and some image-processing functions, the software support provided by each frame grabber can vary widely. In considering the purchase of a less than $1000 color frame grabber, system developers should carefully consider the software support offered by the manufacturer.

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Representative list of frame grabbers and suppliers (table)

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Representative list of frame grabbers and suppliers (table con't)

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RIGHT. FIGURE 5. The Matrox Meteor-II frame grabber is offered in three versions. For digitizing NTSC/PAL and composite RS-170/CCIR from video cameras and VCRs, system developers can choose the Meteor-II. For capturing images from standard or variable analog monochrome or component RGB frame-scan sources, the Meteor-II/Multi-Channel version is available. Lastly, a digital version can capture images from digital-frame and linescan sources including multitap configurations.

To support its products, for example, Matrox offers the Matrox Imaging Library (MIL)—a programming library with functions for image capture, statistics, filtering, morphology, blob analysis, gauging, calibration, bar- and matrix-code reading, OCR, and graphics. Another company, Integral Technologies, offers ImagePro Plus software from Media Cybernetics (Silver Spring, MD) with its Flashpoint128 color frame grabber.

Before considering which frame grabber to choose, system developers should carefully study the image-processing task that needs to be performed, the hardware specifications of the frame grabber, and, more important, whether the manufacturer offers easy-to-use development tools or software packages so that applications can be developed in a timely manner.

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