Psycho is not a film noir.

Psycho is not film noir. Psycho is a thriller, or a psychological suspense film, but it is not a film noir, for many reasons.

1)Subject - the subject is psychological in nature, and is about a crazy murderer. This is not normal fare for a noir. There's a direct relationship between the killer and the victim, which is also rare in noirs. Noirs usually deal with a shady person, or gang, and deals with crime, usually. Murders may happen, but they're not the sole reason for the "evil" character.

2)Cinematography - This may be where people get the idea that psycho is a noir. Many of the shots in psycho borrow from the film noir genre, using light and dark, intersecting shadows, off-center subjects, odd angles, etc. But that was also just Hitchcock's style, you can find that in many of his films.

3)The Antihero - Usually in noir, but not always, there is an anti-hero, or a reluctant hero. A dirty, possibly corrupt person who will do whatever it takes to do "the right thing". Bogey was excellent at playing these parts, and Sam Spade is the quintessential anti-hero. There's no such person in Psycho, Sam Loomis certainly isn't one, and everyone else is a victim. Also, in most film-noirs, there are no squeaky clean characters, or if they are, they are offed pretty quickly, or are seen as a point of derision and scorn.(Laszlo in Casablanca pops into my head)

4)Focus - the focus in Psycho is on the murderer, and the murdering, and keeping the suspense high. In a noir, there may be suspense, but it is rarely the main focus of the film. When Sam Spade is looking down the barrel of Kasper Gutman's gun, there's tension there, but not the same tension as when Vivian Leigh is about to get stabbed in the shower.

The Hitchcock film that I would have a hard time choosing between film noir and suspense is "Rear Window". There's no hero, the filming is right, the focus is almost right, but the subject is still the murder, and the tension of the final scenes.