For much of the 20th century, contact sheets (also called proof sheets) were vital to the practice of photography. The rising popularity of roll film encouraged more and more exposures; the best frame would be chosen later. The photographer first saw positive images on the contact sheet, which was marked up for printing and served as a lasting reference. Digital technology has put an end to that era: the photographer now sees the image instantly, and systems of storage, retrieval, and editing have become increasingly sophisticated.