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All PC-based imaging systems incorporate common components, most notably a camera. Chances are that you will also need a device for streaming the image data to your computer’s system memory, a role that is fulfilled by video capture cards, more commonly known as frame grabbers. This article discusses the most common interfaces in use today and how they are used in an imaging system.
Analog and Digital… and Digital
Generally, you will select the camera first before anything else. Although this is step one, it is by no means a simple task. Choosing a camera means determining the needs of your application and surveying the vendors. Among the basics, you must determine the required resolution, speed and sensitivity. Will your image be in the millimeter or micrometer order of magnitude? Will the camera take pictures of objects zipping along a conveyor belt or cells on a microscope’s slide? How much light is needed for acquiring an image? If you buy from a well-known camera manufacturer, the camera model you select will likely be available for different interfaces. It is the interface that will determine your image or video acquisition hardware. The most common standard interfaces in use today are analog, LVDS, IEEE 1394, Camera Link™ and, more recently, Gigabit Ethernet.
Depending on the particulars of your application, you might choose a smart camera. A few short years ago smart cameras descended on the marketplace. While they are not revolutionizing image processing per se, they are a different vehicle for existing algorithm technologies. What smart cameras offer is a new package of delivery; they open opportunities to systems integrators because they are highly-integrated devices with a small footprint. For applications with space restrictions, smart cameras can resolve the issue. Furthermore, devices (smart cameras) with their higher level of integration, might offer lower-cost solutions to the user.
All new image processing technologies can be run on a smart camera, namely geometric pattern recognition and edge-detection, the edge-based image processing techniques that relax optical and illumination requirements and render sub-pixel results. But smart cameras are limited in processing power, and they might not be fast enough to process complex imaging algorithms in a practical way. Due to power consumption issues and heat dissipation, smart cameras cannot be fitted with the same processors as a PC; there is a limit to the types of applications that can be run on a smart camera.
Imaging Hardware’s Capabilities and Caveats
Once your camera and interface are established, you are ready to choose your imaging hardware. This could be a traditional frame grabber, digital video interface card or vision processor. The particulars of your application and of course, your budget, are the deciding factors at this stage.