Film Noir - Visual Motifs

Film noir is typically defined as "a style or genre of cinematographic film marked by a mood of pessimism, fatalism, and menace". However, film noir is an intricate topic that is still difficult to give a clear meaning to. However, it is mostly agreed upon that visual style is the consistent thread that unites the very diverse films that together comprise the phenomenon of film noir. Characteristic moods of film noir include: claustrophobia, despair, paranoia, and so on - all which are expressed through a films style.
When shooting a film, lighting is important because it helps set the mood of the film. For film noir, low-key lighting is popularly used. This is because low-key lighting creates areas of high contrast with rich, black shadows. This aids in setting the noir "mood". This technique of lighting and diffusion removes any element of softness or vulnerability from the film.
As for directional style in film noir, we often see off-angled, peculiar compositions of figures that are placed regularly in the film. This creates a feeling of unstableness- that anything in the film can drastically change at any given moment. The visually unstable environment created by the "dark mirror" of film noir gives the characters no moral base to be able to confidently operate.
Between low-angle shots, low-key lighting, and the dark, rich shadows accompanied by bizarre framing - we see these visual motifs regularly in films exhibiting film noir.