Writer-director Mark Romanek’s “One Hour Photo” is a film that develops as slowly as an old-fashioned Polaroid. Clocking in at under two hours, the film spends most of its time painstakingly unraveling the psychology of Seymour Parrish (Robin Williams), who lives the family life vicariously through the photos he develops.

The patience of “One Hour Photo,” and its dignified reluctance to become an all-out slashfest, are the films strongest points. Romanek forsakes slick production and horror film gore, letting mood and tension carry his film to an atypical climax.

The film’s tight form mirrors Williams’ subtle but engrossing performance. Gone are the actor’s familiar comedic gestures, what remains are the smallest of movements and sudden twitches of mitigated rage — Williams is a meek man falling apart at the seams, feigning ignorance of the strangeness of his life and actions in a calming voice-over. His textured performance makes the film fascinating and disturbing, like a car accident at which you can’t help but stare, that stirs your sympathy while making you writhe in disgust.

Seymour Parrish lives and works in a sterile world. In his voice-over — actually a confession to the police — Williams details the inner mechanisms of his life: where he works and who he is, which are largely the same thing.

For 11 years, “Sy” has worked at a photo developing center at Savmart, a thinly disguised version of Walmart. The store glares from the screen like a fluorescent tube light, where customers shop in suburban anonymity. Sy quietly explains how he creates a sense of self-importance, by convincing himself that his job is not a “job for a clerk.” His further theorizing on the importance of family photos and their relationship to the photo developer may be interesting, but William’s nervous tics make it obvious that his is a false optimism.

Sy becomes obsessed with the Sorkin family, a brood that seems perfect in every way — economically, socially and genetically. Sy memorizes not only their address but also the most intimate details of the past several years in their lives. He offers avuncular advice to young son Jake after following him home from soccer practice. He passes himself as a Deepak Chopra reader to woo mother Nina’s companionship. Sy becomes an unexpected stalker while attempting to find happiness, initially failing to realize that the Sorkins have their own troubles, presented briefly and a bit too abruptly to the audience.

Romanek, in his first major feature film, builds tension like an expert, although occasionally he overindulges in Seymour’s bizarre idiosyncrasies. This same tendency, however, leads Romanek to pay great attention to detail and create a pervasive, creepy mood. The aisles of the Savmart are in impeccable order; the fluorescent lights buzz ominously; the photo developing machine clicks and whirs for several seconds on screen, echoing the mechanical inhumanity of Sy’s existence.

Cinematographer Jeff Cronenweth, of “Fight Club” fame, further enhances the film’s mood with his lighting, drawing sharp contrast between the Sorkins’ Technicolor world and the pale, diseased realm of Sy’s photo center. In fact, Williams is always lit to look sickly except when he is on the verge of madness and collapse, when he sits in a devilish red darkroom.

Cronenweth’s work particularly shines in his long, steady shots of Williams. The slow zooms on Sy seem almost like photographs themselves — Cronenweth thus revives the photographic sensibility of old Hollywood, creating a true “moving picture.” Cronenweth also frames some scenes-within-scenes, creating a virtual framed photo on the screen. For example, as Sy peers into the Sorkins’ window, Cronenweth recalls “American Beauty” cinematographer Conrad Hall and shoots the family dinner from outside, so that the window acts as a frame.

Both Romanek and Cronenweth allow the film’s form to follow its function, which is precisely why the mood of “One Hour Photo” never falters. Even Sy’s most bizarre fantasies — such as using the Sorkins’ bathroom — seem eerie, while in another film they might have sparked some derisive laughter.

The selling point of “One Hour Photo,” however, remains Williams’ performance. He deftly trades comic inanity for a complete lack of emotion and social grace, something he attempted to do less successfully with “Insomnia.” Although his character is largely repulsive, he is also quite empathetic, allowing the audience to see parallels between Sy and the Sorkins, who all live superficially and find refuge in photographic smiles.