"Let me explain something to you Walsh. This business requires a certain amount of finesse." -Jake Gittes, Chinatown

Chinatown (Roman Polanski, 1974) is a film remembered especially for Robert Towne's screenplay, as demonstrated not only by the reverent tone with which it is discussed inside the Hollywood screenwriting nexus1 but in how key lines have entered the wider pop cultural discourse. Yet the ways in which that screenplay was filmed, the ways in which Polanski's film and Towne's screenplay intersect to obscure, obstruct and flaunt information offer enduring lessons on how images can be manipulated and manipulative. Herewith, five observations.

Twenty minutes into Chinatown there is a series of short scenes in which Jake Gittes undertakes surveillance for his client who, despite seemingly knowing full well her husband is having an affair ("a woman can tell") employs him anyway. We watch Gittes as he performs all the generic surveillance techniques we have come to expect from these films, albeit given a 1920s twist. And then: we are presented with a curious image.

We simultaneously watch Jake Gittes watching and what it is he is watching. Gittes and his camera provide the frame for the action he is surveilling: Hollis Mulwray, acting friendly with a young woman who is definitely not his wife. With a characteristic lack of finesse, Gittes slips a bit, tiles from the roof upon which he is precariously perched crashing below. Hollis looks up but Gittes has hidden himself, and the film cuts quickly to the result of his photography: a front page newspaper article, the image we just watched him capture framed in a love heart. The two ways in which the image is framed legitimate not only the image itself but Gittes' interpretation of it. The shot of the shot within Jake's camera lens shows us the photo was captured covertly, it is unstaged and thus given a layer of authenticity. The heart framing tells us what to make of this authentic image: Hollis Mulwray, chief engineer at Water and Power, is having an affair. Case closed, twenty minutes into the movie. Except, of course, he isn't. Both the image Gittes takes and the image of Gittes taking it suppress their truths.

Barely three minutes into Chinatown Jake informs his client Curly that his wife is having an affair. Indeed, the photographic proof is the first thing we see after the opening credits. Consoling a distraught Curly, he reaches for a bottle of alcohol, then quickly, fluidly, pours a drink from another. The moment barely registers: he pours the drink, then sends Curly on his way.

In the screenplay, however, the moment is emphasised. It is held up by the likes of Syd Field as a classic example of subtext in screenwriting.2 In the script Towne describes the image thus: "Gittes quickly reaches into his desk and pulls out a shot glass, quickly selects a cheaper bottle of bourbon from several fifths of more expensive whiskeys."3 We read into this a fairly obvious subtext: Gittes behaves condescendingly towards Curly, considers him unworthy of a higher priced drink. Yet none of this registers in the filmed version of this action. The way it is filmed there is no way of knowing how expensive each bottle is, we watch Gittes hesitate slightly but the image gives us no clue as to why. The image diffuses, and in so doing suppresses, its truth.

Midway through the surveillance referenced in Observation I, Jake returns to his car. We see a piece of paper attached to the windscreen and thanks to our knowledge of crime film narratives there is instant suspense: is this a clue? A threat? The next shot, from Jake's perspective, reveals it to be a pamphlet, urging the reader to "SAVE OUR CITY!!! LA IS DYING OF THIRST". Jake scrunches it up, throws it away.

Having watched the film, however, we see the flyer for what it is: the biggest clue a detective in Jake's position could ever ignore. It is the truth not just of who murdered Hollis Mulwray and why, but an articulation of the very thematic core of the film. It explains everything, explains the driving force behind Chinatown. The image simultaneously flaunts and suppresses its truth.

The very end of the film. Evelyn Mulwray is dead, Noah Cross physically overwhelms his daughter and drags her from the car. Against Jake's unheeded protestations, the police let him do so. Here we have Cross' total domination: as Jake Gittes is doomed to repeat the mistakes of Chinatown, so too Noah Cross is doomed to repeat his sanctioned transgressions. The image depicts the truth: of the screenplay, of the film, of the society within which it was produced.

Despite letting Jake off the hook, telling him, as the film's final and most notable line commands, to "forget it," Chinatown demonstrates to both its protagonist and audience that there is rarely such a thing as an objective image. An obvious statement in retrospect, Roman Polanski's film demonstrates that it is a surprisingly easy lesson to unlearn.