While high quality can never be inspected into a product, you can achieve it by judicious inspection of the processes and materials that make up the product–and swiftly undertake any corrective action. But high quality is not the only goal. Cost reductions are always key objectives. Today, these are being realized by higher levels of integration, resulting in more and more functions being performed in smaller and smaller components.
Inspecting smaller items with greater precision in less time naturally calls for automation. Ideally, inspections could be performed by machines that constantly observe, assess, quantify and report unacceptable deviations from established limits and automatically correct processes. For electronic products, automated inspection could be used to assess the dimensional accuracy, the placement and alignment of components, or the placement and adequacy of solder paste.
Today’s machine vision systems perform these tasks very well, and more systems are being placed in service every day. But there are many electronic component-handling and processing operations for which a custom vision system solution may be ideal.
Fortunately, the elements of such systems are available and relatively inexpensive. They are: a video camera, a frame grabber, a PC and appropriate software. Frame grabbers accept scanned video signals and convert these into successive image frames, each comprised of a set of stored pixel values.
A typical configuration and application are shown in Figure 1. In this case, the requirement is to assess voids and burns in the epoxy of IC packages and quantify plating defects and lead alignment. Four inspection stations are used; all data is processed on two boards and the throughput is 5,000 units/h.
Camera Considerations
Cameras used for industrial applications in the United States commonly provide data in the RS-170 video format, the encoding standard for 60-Hz black and white television signals; and in Europe in the 50-Hz CCIR format. Many nonstandard industrial video sources also exist, providing line scan, area scan, high-resolution and nonvisual, such as infrared and SEM, images. Most of these images are captured in monochrome, some in color, and they are delivered to the frame grabber in either analog or digital form.
While analog outputs are most prevalent, the trend is toward increased use of cameras providing digital outputs. “For electronic inspection, the RS-170-based imaging solutions suitable for die, lead and package inspection two years ago are insufficient today,” said Jeffrey Wilson, Vice President for Sales and Marketing at BitFlow.
“Every time package density quadruples, the areal density of the appropriate imaging technology must quadruple just to stay even. For demanding inspection applications, only digital input will do. “Digital cameras perform the A/D conversion right at the camera head, minimizing noise and signal deterioration along the transmission line to the frame grabber,” he said.
“Just as important, the explicit timing signals produced by digital cameras ensure that the A/D conversion timing for each pixel is right on the money,” Mr. Wilson continued. “With better noise and timing specs, many digital cameras are capable of higher performance, providing quicker sensor readout, more bits per pixel, more pixels per line and more lines per frame.”
Many electronic image-analysis applications also require gray-scale evaluations. “There are two kinds of gray-scale responses to deal with: radiometric or radiant source intensity; and record medial density or optical density, such as in an X-ray film transparency,” explained John Newitt, Applications Engineer at Image Technology Methods Corp. “Since these two imaging parameters are the inverse log of one another, different scaling correction provisions are needed.”
Software look-up tables (LUTs) are often used in frame grabbers to perform these corrections, but they can only correct over a small portion of the range, according to Mr. Newitt. “The corrections should be performed in the analog portion of the camera, prior to digitization, to achieve a highly accurate full-scale readout with constant precision,” he said.
Frame-Grabber Features
Camera Interface
Some frame grabbers accommodate diverse camera inputs by providing programmable circuitry on the board. Others employ custom modules, usually in the form of daughterboards, matched to individual camera types.
Plug-in daughterboards, available in a variety of designs with camera-matching cables, give you the capability to interface to many of today’s analog and digital cameras. But software support for the various cameras is also required, and the frame grabber video input circuit must be programmed with the right scaling and offset factors.
“Our Camera Configurator, a Windows-based utility, lets you configure the camera driver and interface parameters, immediately grab images and see the effects,” said Chuck Hafemann, Marketing Manager at Imaging Technology. “Once satisfied with the results, you can automatically generate the necessary configuration file and embed it into the application.”
Synchronization
Image data capture, conversion and some processing must be performed synchronously. Camera frame capture may be initiated from the frame grabber or the camera may provide the required sync trigger. Alternatively, the frame grabber may extract the sync information from the video signal (Figure 2).
Image Processing Hardware
Analog video signals are digitized and one or more frames are stored in high-speed buffer memory. Signal conditioning is commonly used to enhance the quantized image. For example, any data captured with the Mm Tech frame grabber is usually passed to a contrast-enhancement and noise-reduction software module to improve the quality of the incoming image and to eliminate extraneous data.
Digital image processing can be performed solely by software or at higher speed with dedicated processing hardware. The application determines which technique is better, and many companies provide products serving either need.
“Some of our Image Capture motherboards accommodate various image-acquisition modules but use the host processor for image processing,” explained Mr. Hafemann. “This architecture takes advantage of the high-performance processors, such as the Pentium and Alpha chips, and allows many machine vision applications to be implemented at low cost.
“Our Pipeline Vision Processor motherboards interface with the pipeline of any of our specialized computational modules. This provides the highest possible image processing performance for the most demanding applications,” Mr. Hafemann concluded.
Frame-grabber and image-processing circuitry may be combined on a single board, implemented with a motherboard and application-specific daughterboards or contained on two boards, depending on the desired processing sophistication. The simplest–and almost always provided–processing element is the input LUT.
The input LUT maps any data value to any other value in real time. It can be used to perform thresholding; addition, subtraction, multiplication or division by a constant; and video inversion.
Input LUTs use the digital data values of the pixels as an input or index into the table. Each index value has a corresponding output value, with the output values or mapping correspondence, predetermined at the time the LUT is defined. Image data can be passed repeatedly through different LUTs to accomplish multistep image processing.1
Image Display
Most frame grabbers contain circuitry which converts the digital pixel data into an RS-170- or CCIR-compatible signal for display. This lets you view the stored or processed image on a separate monitor to check acquisition or processing.
For monochrome frame grabbers, the image display hardware may include an output LUT that accepts data from the frame-store memory. The pixel value from memory becomes an index into the table. If desired, the table maps this data into relative amounts of red, green and blue, which lets you apply artificial color to monochrome images.1
Transferring Data to the PC
The degree to which the memory and computational power of the PC can be used to provide real-time image and display processing depends on the data interchange medium between the card and the PC. When most of the image processing is performed on the plug-in board, the 8- or 16-bit ISA bus may be adequate. But to make greater use of the inherent power of the PC, many companies, such as BitFlow, Imaging Technology, Mm Tech and Data Translation, provide frame grabbers that interface via the VESA local bus or the PCI bus.
The VESA local bus can transfer 32-bit data at 33 MHz, resulting in a transfer rate of 132 MB/s. The PCI bus handles 32- and 64-bit data; and in a 33-MHz 64-bit system, data can be exchanged between the frame grabber and the PC at a 264-MB/s rate. This is fast enough to handle even full-motion true color video.
For frame grabbers configured as stand-alone units, the PC interconnection may be provided via the parallel port or SCSI. Analogic, for instance, has given its new DASM-VIP a SCSI interface. This fast port is available on most PCs and workstations, and this implementation doesn’t take up valuable internal card slots in the host PC.
Essential/Desirable Attributes
When considering an entire equipment category, such as frame grabbers, the diversity of applications make it difficult to differentiate between essential and desirable features. However, a general consensus for electronic inspection applications was summarized by Scott Zellmer, Vice President of ImageNation, and Aleksandar Stefanovic, Digital Design Engineer at ASPRO Technologies.
“It is essential that frame grabbers grab in real time (1/30 s), quantize video into at least 256 gray-scale levels, provide for low noise, digitize accurately (low sampling jitter) and allow fast, random access to the captured image,” said Mr. Zellmer.
“Multiple video inputs, multiplexed under software control; video output; multiple frame memory buffer; external triggering and sync capability; and support for multiple boards in one system and frame/field mode, if not essential, rank among the highly desirable features for frame grabbers,” added Mr. Stefanovic.
Frame-grabber capabilities, however, should not be considered in a vacuum. The capabilities of each part of the system–the camera, data interfaces, computational power and software–must be taken into consideration when selecting image system components to assure compatibility and provide a cost-effective implementation.
For example, speed and accuracy are usually the most sought-after factors in electronic inspection systems. But speed involves both the image capture speed and data transfer speed, since the image data must be transferred to a processing engine before being overwritten by the next image. You can achieve accuracy only if precise image information is collected and the data does not become contaminated by jitter, noise or computational inaccuracies.
If you want to configure you own system, expert help and advice is available. Since the frame grabber is sitting between the camera and the image processing hardware and software, many frame-grabber suppliers can provide the advice and configuration assistance you may need.
References
1. “Choosing Imaging Boards and Software–Tutorial,” Data Translation 1995 Product Handbook, Data Translation, pp. 258-267.
Imaging Analysis Products
Machine Vision Board Provided
With MS Windows Software
The GPB-2 High-Speed Image Processor occupies only one slot in an AT-compatible PC and has plug-in modules for camera-input and display optimization. Images are saved and simultaneously processed. All required computational operations are performed at 30 frames/s. A library contains >300 built-in functions. The GPB-2 has a 40-ns/pixel (25-MHz) processing speed, includes 12 memory buffers (512 x 512 x 8 b) and accepts four multiplexed camera inputs. Daughterboards perform dual-operand table look-up, arbitrary geometric transformation, high-speed image manipulation and normalized correlation. $7,500. Sharp Digital Information Products, Inc., (714) 261-6224.
Windows NT Support Available
For Frame Grabber Family
The Raptor Framegrabber family provides fast data transfer via the VESA or the PCI local bus and operates under MS DOS, Windows 3.x or NT. They accept up to 8k lines/frame and 32k pixels/line, and pack pixels as 8-, 16- or 32-bit data. Boards feature a 33-MB/s access rate and two 256 x 8 LUTs. Analog inputs are processed with 8-bit digitization to 40 MHz and digital inputs with data rates to 120 MB/s. Drivers are provided for several imaging packages. From $1,800. BitFlow, Inc., (617) 932-2900.
Image Processor Provides
Real-Time Enhancements
The ARGUS-20 processor is designed to enhance low-contrast and low-light images from video cameras. Features include 1,024-point horizontal resolution, color video input, a SCSI interface and quantitative image-analysis capabilities. Real-time edge sharpening can extract or contrast edges within an enhanced image. An image divider shows relative differences between real-time input and a previously recorded image. Real-time zooming magnifies by 200% or 400%. ARGUS-20 is controlled from several image-processing programs, such as Photoshop and Optimas. $9,500. Hamamatsu Photonic Systems, (908) 231-1116.
PCI Bus Handles Continuous
Image Transfer at 34 MB/s
The M-Vision 1000 Gray-Scale Video System is a PCI-bus compatible frame grabber supporting variable scan-rate RS-170/CCIR and digital cameras with 8- or 10-bit resolution. Dual-ported memory can be read by the host CPU at rates to 50 MB/s and transferred to the VGA display card at ~30 MB/s. Features include composite/separate H/V sync, external trigger, an external pixel clock, a low-jitter phase-lock loop and multiple frame-grab control modes. DOS and Windows utilities grab and save images in several formats. From $2,000. Mm Tech Corp., (617) 935-1770.
DSP Video Image Processor
Transfers Data Via SCSI
The DASM-VIP Video Image Processor combines a 24-bit SCSI frame grabber with a DSP image processor. It acquires, processes and displays color and monochrome images. Digital sync-lock circuitry virtually eliminates pixel jitter. Video images can be displayed as single frames or as a sequence of real-time frames. The 33 MFLOP TMS320C31 DSP relieves the host computer of image-processing tasks. DSP application programs perform a range of operations, including frame averaging, edge detection and filtering. From $2,995. Analogic Corp., (508) 977-3000.
Frame Grabber Features
Multiple Capture Modes
Imager BW Plus is a single-board (16-bit ISA) monochrome frame grabber for PC-ATs and compatibles. It accepts RS-170 or CCIR signals. A 256 x 8 input LUT RAM facilitates real-time image manipulation, such as thresholding, contrast enhancement, video reversal and implementation of nonlinear A/D conversion, prior to data storage. The on-board frame buffer (1,024 x 768 x 8) stores one full resolution frame. With the memory and interface controller, various capture modes can be selected. From $485. ASPRO Technologies, Ltd., (905) 712-2131.
All-Digital Synchronization
Assures Low Sampling Jitter
The CX100 Video Frame Grabber, a precision image-capture ISA-bus board, is compatible with monochrome video in NTSC or CCIR formats. The image transfer rate is 1 MB/s. Hardware-controlled field or frame grab, software-adjustable offset and gain, and automatic LUT load are supported. Input and output LUTs facilitate gamma correction, contrast and brightness adjustment, and thresholding in real time. Overlay RAM allows text and graphics to be superimposed on the video or a captured image. $495. ImageNation Corp., (503) 641-7408.
Image-Capture VESA-Bus Board
Uses Host-Based Processing
The IC-VL Image Capture VESA Local Bus Card is an entry-level member of the company’s Modular Vision Computer 150/40 family. It can be equipped with any acquisition module from the MVC 150/40 family, accommodating analog input to 50 MHz, digital input to 40 MHz, color input with real-time color space conversion such as RGB to HSI, and RS-170/CCIR. A comprehensive camera interface software library is provided and industry-standard imaging software such as Optimas and Image-Pro is supported. From $2,195. Imaging Technology, Inc., (800) 333-3035.
Test Set Determines
Digitizer/Video Performance
The WAVETEST™ Model 271 Frame Grabbing Digitizer and Video Test Set is a hand-held test generator for determining linearity, stability, spurious response and band-pass characteristics of digitizers. Analog waveforms are provided for qualifying digitizer performance by histogram pattern testing. Outputs are compared with idealized patterns to quantify distortion and nonlinearity. When used in conjunction with the TESTAB™ camera calibration test tablet, a comprehensive test facility is provided for determining combined camera and digitizer performance. $750. Image Technology Methods Corp., (617) 894-1720.
Frame Grabber Achieves
High Display Rate Via PCI Bus
The DT3155 Monochrome PCI Frame Grabber is MS Windows ’95 plug ‘n play compatible. It uses the PC system display and RAM to achieve real-time image display and data storage. Software support is provided by Global Lab Image and DT-Open Layers Frame Grabber SDK for Windows. Digital Clock Sync™ locks to video signals within one frame time, enabling the DT3155 to accommodate asynchronous video devices. Pixel jitter of ±5 ns assures precise measurements. The unit provides 8 bits of gray-scale resolution. $995. Data Translation, (800) 525-8528.
Image Processing Program Uses
LabVIEW Application Builder
Ultimage™ for Windows is an image processing and analysis tool operating under Windows 3.1 and National Instrument’s LabVIEW’s Application Builder. The Application Builder helps create virtual instruments with embedded run-time engines that operate as stand-alone applications. Ultimage tools include contour detection, convolution, nonlinear filters, geometrical transforms, thresholding and color-space conversions. A library with more than 400 image acquisition, enhancement and display functions handles 1- to 32-bit images. More than 60 shape and density measurements are performed per object. $2,300. Graftek Imaging, (800) 959-3011.
Off-the-Shelf Components
Yield Performance at Low Cost
The Pulsar PCI Frame Grabber captures data from standard and nonstandard cameras and achieves sustained transfer rates of up to 45 MB/s. It has 4-MB of on-board memory and an integrated display capability providing 1,600 x 1,200 resolution. The board digitizes 8-bit data at up to 45 MHz or 10-bit data at up to 30 MHz. A 16-bit TTL data interface accepts digital-camera inputs. Up to 4 input channels are available to accommodate multiple cameras. $1,995. Matrox Electronic Systems Ltd., (800) 361-4903.
Copyright 1995 Nelson Publishing Inc.
July 1995
