This movie was made by painting beautiful pictures on clear sheets of plastic called cels. The backgrounds are gorgeous watercolor paintings.
The original lines were drawn with pens and ink. At extreme resolutions like 4K, you often see microscopic imperfections in the ink lines or dust trapped between the layers. The 720p frame smoothly blends these lines, presenting the art exactly as it was meant to look on a theatrical projector.
This paper examines the visual presentation of Hayao Miyazaki’s 1979 debut feature, Lupin III: The Castle of Cagliostro