Glossary for Geospatial Science

vignetting:  Darkening at the edges and corners of an optical image.  Vignetting occurs because lenses are physically unable to pass as much light to the fringe of an optical field as they do to its center.  Several techniques compensate for vignetting, but it is almost always present to some degree.  For color rasters, vignetting means that the color of a feature at the edge or corner of an image may not match the color of that same feature in the center.