Many many years ago, foreign films (primarily from Hollywood and in English?) were becoming popular in Hong Kong, but the general populace was either too illiterate or didn't speak or read English. Dubbing in Cantonese was inexistent back then (I guess the studios didn't distribute the films to the Hong Kong movie theatre chains or distributors with dialogue and sound effects on separate sound tracks, like they can today thanks to object-based encodings); subtitling was also useless or inexistent (maybe due to lack of technology, and also due to poor literacy levels). So the movie theatres hired film interpreters. The film interpreter would literally stand next to the silver screen during the screening, and verbally explain, in Cantonese, what the actors were saying or relevant English text displayed on screen.
Obviously that wasn't very scalable.
As technology progressed and as the population's literacy and education improved, it became feasible to put subtitles or dub the films in Cantonese. So the job of the film interpreter became obsolete.
Nowadays, the verb (解畫, to interprete a film) has been hijacked to mean something else: to defuse a misunderstanding that was a result of ambiguous or careless wordings in speech between two parties.