Forrest Gump is undoubtedly one of America’s most loved movies. Tom Hanks is such a brillant actor! Chromakey technology was made use of for the film. They used archival footage of many famous moments in American history and used it to simulate Tom Hank’s character in it. Special effects artist Larry Butler developed the chroma key process for the film The Thief of Baghdad for which he won an Academy Award. Back then, chroma keying was a chemical process performed on film negatives. Today it is all done digitally.
Tom Hanks was first shot against a blue screen, along with reference markers so that he could line up with the archival footage. The voices of the historical figures weren’t originally from the footage, they were hired voice doubles. To ensure that the voices matched while the people spoke, special effects was used to alter the mouth movement.
Above is an example of a blue screen. Besides using chroma keying for the historical scenes, there was a character, Lt. Dan (Gary Sinise) who had amputated legs in the movie. The actor wore a pair of long blue socks, and they just keyed out the blue and that’s how they made the legs vanish. Industrial Light and Magic was hired to make this sequence. Aren’t they amazing!!!