Trippy English Countryside Fantasy

The 1960s audiences who saw Mary Poppins probably thought they were hallucinating. Mixing animation and live-action…? How could they even…?

There'd been a few examples of cartoons mixed with real stuff before—Gene Kelly danced with a cartoon mouse, dressed up as a sailor, in 1944's Anchors Aweigh—but Mary Poppins served up an extended sequence. The magical secret, of course, was the "sodium vapor process," sometimes called yellowscreen—forerunner of the green screen. It actually earned Mary Poppins an Oscar for Best Special Effects.

Also, interestingly enough, Disney owned the only camera capable of filming with the sodium vapor process, and wouldn't rent it out to anyone else. It was like the recipe for secret sauce—you're not just going to leave that lying around. The process itself involved the actors performing in front of a white screen, illuminated by orange sodium vapor lights. This allowed you to add in animated footage, super-imposed behind the actors. (Source)

Also, Mary Poppins was filmed on…film. The idea of digitally filming a movie was just a twinkle in someone's Mom's eye back in 1964—computers, at the time, were still giant, clunky machines that filled up entire rooms, but with less power than your average Mac. So it was filmed in Technicolor on 35mm film. (Source)

But whatever works. Those cartoon penguin waiters still look pretty good, even today.