How Green Screen Worked Before Computers

http://tomscott.com -   / tomscott   - For those of us who grew up in the age of CGI, green screen is just "a thing that computers do". But how did effects like this work before the age of pixels? With the help of some suitably shiny graphics, here's a quick summary. Thank you to Matt Gray - http://mattg.co.uk -   / unnamedculprit   - for sterling work getting the camera and lighting right!