Lighting is critical to an MVS in that it allows for accurate image capture. Broadband sources, fiberoptic illuminators, or lasers can be used as light sources. The wavelength can be from the IR to the UV to the X-ray regions. Light can be provided in the shape of a ring, a line, a point, or multiple points, or it can cover an area (1) and can be continuous or pulsed (flashes). The latter is used for rapidly moving objects. There are three basic lighting configurations, depending on the features to be highlighted (4,6):

1. Front lighting (front light), in which objects are lit from the top or front of the object but possibly at an angle. This is used for extracting surface features.

2. Back lighting (backlight), in which the light is placed below or behind the object, providing an outline of it. This is suitable for nontransparent objects where high contrast is needed and is usually coupled with a binary-image sensor device.

3. Structural or multidimensional lighting, in which light is directed at various angles so as to extract a two- or three-dimensional image. These may be used to measure a dimension or find shape defects in an object.

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