Since the announcement of photography's invention in 1839, various methods of making photographs have been practiced. Until the advent of digital photography at the end of the twentieth century, all of these methods required three elements: light-sensitive materials that behave predictably in response to light; chemicals that control and fix the action of light to create an image; and a support upon which the image rests. Photographers and others have continually explored and refined these basic requirements in their quest to expand the artistic and technological possibilities of photography.