Nevertheless, while the team once thought that AI offered all the solutions, a new question soon arose. Audience members asked: "Where's the original flavor?"

After restoring the images to their original state, they soon began to realize that people still needed some nostalgia. For example, old series made by Hong Kong-based company TVB usually have yellowing images, but many viewers complained that its retro ambience had vanished after the color cast was corrected, Jiang says.

"People then said our restored version looked like a camera filter has been added," Pei says with a bitter smile. "We then had to go back and adapt our methods."

More complicated algorithms were later developed to carry out a tailored plan for each type of series, including those by TVB, Chinese mainland productions from the 1980s and Taiwan productions of the 1990s. Some techniques in hands-on restorations were introduced later too, as Pei confesses even the best AI cannot handle every case.

"People's tastes are more highly developed," Jiang says. "We just want to give people the same feeling watching them on digital devices today as they had on small TV screens years ago."

More than 300 TV series have been restored since November, and Pei says all their data has gradually helped to build up a database, which will further improve the algorithms.

In March, the restored edition of 2003's Legend of the Dragonslayer Sword was released online through Youku. Unexpectedly, it soon climbed into the top 10 list of most-viewed drama series on the platform, with all the others being new productions.

Jiang points out that many adaptations of old classics are now being made following the rise of online streaming media platforms.

"But they are often heavily criticized," he says. "I don't know whether it is because the performances are so poor. However, if we can make the original productions look just like new ones through restoration, people can at least have more choice."

The 1980s classic The Bund produced by TVB, a story set in Shanghai in the 1930s starring Chow Yunfat, has so far been the most time-consuming restoration work, but Jiang says it's worth it.

"George Lucas spent many years restoring old Star Wars films he made himself," Jiang says. "It's almost like a remake. We're also looking to create a classic Chinese production, which needs just as much of our energy."

Speaking of the future, Pei says there is no end to their work. "People get used to watching TV productions shot in 4K resolution today. However, once 8K becomes common, viewers might consider 4K shows 'unwatchable' again. Today's work will still need restoration one day."