No, not the upcoming Ben Stiller version, but the 1947 Secret Life of Walter Mitty (Norman Z. McLeod, Samuel Goldwyn/RKO). Adaptation is probably too strong of a word, since about the only thing that the film takes from the James Thurber story is the premise of a daydreamer who's a somewhat hen-pecked milquetoast in reality.
However, with barely 2000 words in the source, the screenplay for the feature film needed to invent a more sustained narrative. It ends up what I've been calling a light comedy (along the lines of The Hucksters or The Senator Was Indiscreet) with a parade of genre parodies: war film, plantation drama, Boris Karloff spy film....
And the narrative conceit is that Mitty is a writer for a comics and true-romance publisher, and like other light comedies from the 40s, the film playfully reference taste culture battles of the day.
Even though it is a Goldwyn film, McLeod brings (or even was hired to bring) an MGM sensibility to the project, and the film alternates between camp and spectacle numbers, often centers on Danny Kaye's musical performances.
I can't say the cinematography is of great interest, but the production design does have a chromatic intensity that was often downplayed in more dramatic material.