Friday, April 29, 2016

Simulating a projector shutter in HUGO 3D

Martin Scorsese's HUGO (2009) is a real compendium of film and animation techniques. In a pivotal scene, the film even simulates the one device that is most often taken for granted but is essential for the illusion of motion in mechanical film projection: the shutter.

If you pull a film strip through the gate of a projector past the lamp, you simply see a fast moving strip in a blur. In order to fool the eye into perceiving motion within the frame (due to persistence of vision) the images on the filmstrip have to stand still for us to register. Then the strip has to be transported without the viewer noticing. This is achieved by an intermittent mechanism consisting of a Maltese cross for transportation and a revolving shutter (see below) that shuts out the light exactly at the time the film strip is transported to the next frame.
(Image from English Wikipedia)

As we all know, a flip book does not need a shutter because the pages flip out of sight (or rather past our focus). Due to its nature, in a book as opposed to consecutive frames on a filmstrip the images stay in place.

In a key scene near the mid-point of HUGO, while Méliès' pre-production art floats around the room due to clumsiness on behalf of the investigating children Hugo and Isabelle, Martin Scorsese shows us two animation sequences based on sheets of paper:
I like to add a time code* so that the scene is easily found within the film and we also see how long each image is on screen.

The Fire-Breathing Dragon
The seven animation drawings slightly aligned.
In the first one of a fire-breathing dragon, Scorsese's film basically simulates the action of flipping (or rather rolling) through a stack of animation drawings. This is the same mechanism as a flip book. But in addition to that, Scorsese simulates a visual shutter:

Whenever an animation drawing is floating away, another piece of paper zooms through the frame (in roughly the same direction, and closer to us in 3D) obscuring the actual transition like a rotating shutter in a film projector. In the video excerpt above you can hear that this is matched by a chattering sound. Note that the animation artists even included a "hold" of two identical drawings (#5 and 6) to accent the animation.

This scene is based on a Méliès drawing (above) for the film LE PALAIS DE MILLE ET UNE NUITS (1905). A variant of this scene is later used in an extensive flashback sequence to show how Méliès shot his films (below).
In the real film, the dragon scene looks slightly different with a less elaborate dragon on display.

The Magical Thaumatrope
The butterfly lady animation in the second part of the video above plays a trick on the setup of a Thaumatrope (see a Thaumatrope in action). When we turn a piece of paper around its horizontal axis, the transition to the next image, i.e. the flipside, is "invisible" because the paper is visually contracted and then expanded. We do not need a shutter to mask the transition.

Because we focus on an object close to the imaginary turning line, we see it long enough to register. This also works so well because of the strong contrast between the moving object (the bright fantasy character) and the muddy background. The impossible "magic" trick here is obviously that, every time the page turns, a new animation frame is visible resulting in a continuous motion whereas a Thaumatrope only combines two images into one.

* The time code refers to the Blu-ray3D version of HUGO.

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