The process of remastering old movies in 4K resolution involves scanning the original film reels using a high-resolution scanner. These scanners can capture each frame of the film at a much higher resolution than was previously possible, allowing for the creation of a digital copy with a resolution of up to 4K. This is possible because the celluloid film used in the production of old movies actually records images at a much higher resolution than could be reproduced on traditional formats like DVD or Blu-ray.
However, simply scanning the film reels is not enough to create a high-quality 4K version of an old movie. The digitized footage must also undergo a process called restoration, which involves repairing any damage to the film and removing any imperfections such as dirt, scratches, or flickering. This is often a painstaking and time-consuming process, but it is necessary in order to produce a final product that is true to the original film and looks great on modern 4K televisions. Despite the challenges, studios have been able to successfully remaster many classic films in 4K, providing viewers with a new way to experience these beloved movies.