Short answers, pulled from the story.
Earl Hurd and John Bray invented the cel animation process in 1914. This innovation allowed static elements like backgrounds to remain fixed while only moving characters were redrawn on transparent celluloid sheets.
Hanna-Barbera became the first American studio to implement computer ink-and-paint systems following a 1979 commitment to technology. Marc Levoy led the Hanna-Barbera Animation Laboratory from 1980 to 1983 developing these systems for domestic production starting in 1984.
The television adaptation Sazae-san abandoned cel animation finally on the 29th of September 2013 after retaining traditional cels until the 6th of October 2013. This marked the end of an era for Western cartoons as Cartoon Network's Ed, Edd n Eddy switched to digital animation in 2004.
Rotoscoping emerged as a method invented by Max Fleischer in 1915 where animation traces actual film footage of actors frame-by-frame. Live-action prints register on paper while another sheet overlays them for tracing under lightboxes to produce results that look hand-drawn yet possess remarkably lifelike motion.
Bill Plympton's Hair High released in 2004 stands as the last animated film to use traditional cels before widespread adoption of software packages. Disney's Beauty and the Beast ballroom sequence integrated 3D CGI backgrounds seamlessly with traditional animation starting in 1989.