The first part of the image processing chain is illumination, and it is one of the most sensitive parts. Investing more money in an optimized illumination system will reduce both programming and image analysis costs. Illumination can be separated into dark and bright field, continuous lights, and flashed lights. Flashed lights are often used with area scan cameras. For line scan cameras, the illumination must be very constant in brightness.
Optimum illumination can be achieved by using different parts of the spectrum or polarization, as well as collimated light, diffuse light, or a mixture of both. A mixture of collimated and diffuse light is often necessary for inspection of metal parts. Typical illumination systems make use of LEDs, halogen lamps, metal halide lamps, lasers, and fluorescent lights with low and high frequencies. Each of these illumination sources has its advantages and disadvantages. The right choice is the key to high quality image capture and accurate image analysis.
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