Kodak Kodachrome slides (transparencies) were a very popular way to process color film. From Wikipedia: “A 35mm Kodachrome transparency, like other 35mm transparencies on films of comparable ISO rating, contains an equivalent of approximately 20 megapixels of data in the 24 mm x 36 mm image. In 2010 the last roll of this film was processed. “Kodachrome film can no longer be processed in color, but it can be processed in black and white by some labs that specialize in obsolete processes and old film processing.”