Cameras at work

New to machine vision? Here's a quick primer. A standard machine-vision system consists of five basic parts: the camera, optics, illumination or lighting, the image-acquisition hardware, and the machine-vision software. While some people tend to group optics along with the camera, it really is a stand-alone topic. However, the choice of camera plays a role in the choice of optics and vice versa. The selection of a camera is determined by the object the camera views and the type of image. Most installations use visible- light cameras, but special applications may demand infrared sensitivity. Infrared cameras typically handle heat-mapping applications but also work well when ambient light may vary widely and analysis is sensitive to the change. Though designed for visible spectrum light, many CCDbased cameras also work in the infrared spectrum. The selection of imaging sensor or imager used in the camera is not as critical as it once was. The old vidicon tubes have given way to solid-state imaging by chargecoupled devices (CCD) and complementary metallic-oxide semiconductor (CMOS) technology. While CCDs held sway over CMOS in the past, neither sensor today is superior to the other. Both have strengths and weaknesses that give each advantages in specific situations. CCDs are the venerable workhorse of solid-state imagers, creating the standard for image quality in photographic, scientific, and industrial applications. CMOS imagers are rapidly gaining ground through the integration of processing circuitry on the same chip as the imager and lower power needs. More critical than the choice of imager type is its resolution. Each imager is made up of an XY grid of photosites. Each photosite corresponds to a picture element or pixel, the smallest part of an image. Typical pixel resolution today is 640 480 pixels, but imagers can run from 128 96 to 7,216 5,412 pixels. Cameras with higher resolutions see greater details over larger areas. The trade-off is in the speed of processing the image. Larger images take longer to process, thus vision response slows as image resolution