Andromeda Galaxy M31 and its small companions M32 (lower center), and M110 (upper right). The image was made by combining three separate frames derived from photographic plates taken in 1979 at the Burrell Schmidt telescope of the Warner and Swasey Observatory of Case Western Reserve University (CWRU). In order to provide color information, photographic plates were coated with different emulsions, which are sensitive to different regions of the spectrum, in conjunction with filters which only let pass part of the full range of wavelengths. Three plates having three different combinations of emulsion and filter were digitized with Kitt Peak's PDS plate densitometer, a high resolution, photometrically stable, scanner. The three frames approximate the primary colors red, green and blue, from which it was possible to create this estimate of a true color picture. Plates are less accurate for measuring light intensities, but they can still be of benefit for imaging large areas at one time.