A DVD documentary on Film Noir I watched over the Labor Day Weekend informed that the genre is defined by deep shadows; strong angles; a wedding of style and content; a visualization of non harmonic space; stylized (angled) views of abstract concepts; presence of femme fatale; a mythic way of dealing with music as another character; music that evokes rain, dark, fear, lonely, ticking clock; flashback dreamy structure, laconic voice overs, peculiar narrative devices.
The only area of contention I found as I viewed this: That the hero must be drawn into the evil. That would make Robert Mitchum in Out of the Past a film noir hero [which he is] but not Humphrey Bogart in The Maltese Falcon. The Film Noir commentators included some sick puppies. I don’t think even the French who came up with the term Film Noir meant it to be more than a depiction of color scheme .. in any case, I don’t think they would stipulate that the hero has to be a loser.