Today, printed circuit boards require more color vision solutions because the color of a component helps to identify each part. Plugs and connectors are color coded, and at the same time, the board is tracked using a black-and-white barcode. “These applications used to be done with a high-resolution monochrome camera, but now, you need to be able to sense color to make sure the right component and connector are in the right place,” Kinney explains. “The barcode will usually be located at the edge of the frame. If you use a single-chip color camera, you have to be concerned about color shading and halos at the edge of the image, and it’s made worse if you use cheap optics.”
Color aberrations come in two flavors: axial, where the different wavelengths of light cause each color to focus on a different focal plane or distance from the optic, as well as transverse or longitudinal distortion, where a magnification causes different colors to focus on different points on the same focal plane even when they originate from the same point in front of the camera. Both effects can reduce contrast or produce halo effects in the image. While an electronics manufacturer will likely want the fastest possible frame rate and therefore ask for a high-resolution, high-frame-rate single-color camera solution such as JAI’s SP-20000 with 20 megapixel (MP) CMOSIS full-frame sensor (43.3 mm diagonal), the designer needs to be aware of potential lateral distortion and correct the problem through optical or software methods.
For colorimetric applications that require absolute color measurements (what is the exact red value) versus relative color measurements (which of these reds is the most saturated), three CCD chips offer better color accuracy. Precision dichroic coatings with sharp responses separate colored light better than color dyes used in single-chip Bayer filter solutions, allowing less color crosstalk between pixels. The use of low F-number prisms maximizes light throughput and maintains the color information with high spatial accuracy needed to give good results at the pixel level. However, three-CCD-chip cameras have their own design challenges, too.
refer to:http://www.visiononline.org/vision-resources-details.cfm/vision-resources/Is-Your-Machine-Vision-System-Color-Blind/content_id/4333
