Special Effects

OPTICAL EFFECTS

Many optical effects are produced in camera, among them irising in and irising out (an effect that relies on literally manipulating the camera's iris, a technique already well established when Billy Bitzer (1872–1944) shot Broken Blossoms for Griffith in 1919 and blanking out areas of the field of view to emulate binoculars, telescopes, keyholes, gun sights, and similar shapes. Double exposure can be achieved in camera as well as in postproduction, by the simple expedient of rewinding the film and shooting over it again.

Many more effects relied on the optical printer, a device used to print from the master negative to the positive for editing. Dissolves from one shot to another and fades to black, for example, could be achieved by running two strips of negative through the printer simultaneously. Passing a matte (in this case a thin sheet of opaque material) across the interface of the two filmstrips, exposing first one area and then the area previously masked by the matte, produced wipes, whose variety can be best seen displayed in RKO's Flying Down to Rio (1933). Different areas of the filmstrip can be printed with different images, a technique used extensively in the documentary Woodstock (1970). Crucially, optical printing can be used to match shots from disparate sources: for example, a landscape with characters reacting matched with a sky filled with billowing clouds (produced by spilling specially mixed pigments into a tank of translucent oil) for the arrival of the aliens in Independence Day (1996). The optical printer was also a crucial device in titling, where the lettering was filmed separately on a rostrum, and then printed over the photographic plate. Likewise, optical printing provided the base for such innovations as the mixture of cartoon with rotoscoped live action in Ub Iwerks's (1901–1971) early Alice animations, such as Alice the Toreador (1925), Alice Rattled by Rats (1925), and Alice the Whaler (1927).

Indeed, animation has remained a consistent source of effects within live action cinema, including such landmarks of animation as the city of the Krell in Forbidden Planet (1956) and the painterly effects of Waking Life (2001). The full integration of animation techniques into features had to wait, however, for the development of three-dimensional digital animation. Pioneer attempts like Disney's Tron (1982) and the genesis effect in Star Trek: The Wrath of Khan (1982) intimated what might be possible. The financial success of the first Star Wars (1977) indicated what could be achieved with almost exclusively analogue effects. By 1988, Industrial Light and Magic, the effects shop established by George Lucas to work on Willow (released that year, the film in which he pioneered the digital morph), would provide over a thousand shots for Robert Zemeckis's Who Framed Roger Rabbit? (also released that year). Certain techniques have remained fairly constant, notably the use of key frame animation to establish the most important moments (frequently the beginning and end) of an animated gesture. Others were the fruit of laborious research, such as the problem of soft objects (which explains the preponderance of billiard balls in early digital animation) and z -buffering (getting objects to touch without penetrating each other on the z or depth axis of the image, as opposed to the x and y axes of two-dimensional images). Celebrated in early examples such as the watery pseudopod in James Cameron's (b. 1954) The Abyss (1989), digital animation swiftly reached for less self-conscious, more embedded functions in movies, achieving a notable success in Cameron's Titanic in 1997, where the distinctions between set, model, and animation were all but invisible to contemporary audiences.

Early vector animation composed creations out of algebraic descriptions of curves. The popular NURBS (Non-Uniform Rational B-Splines) uses such vectors to define sections of the surface of a creature rendered initially in wire frame view, a lattice of interconnecting lines. The areas bounded by these lines (polygons) can be programmed to relate to neighboring polygons, so that if one stretches, another may contract to make up for the move. More recently, animators have moved toward subdivision modeling, in which a crude figure is gradually refined by adding and subtracting polygons to provide detail. Industry wisdom has it that "reality begins at 1 million polygons," a mathematical response to the idea that a typical frame of 35mm film has approximately that many grains of silver compounds. Wire frame was for some years the basic view designers had during production, since the frames required relatively little processing time. Once the movements were approved, the frames would have surfaces applied to them. These may be generated digitally, typically by the process of ray-tracing, which allows for both surface color and texture and for different lighting conditions. Alternatively, they may have a "skin" applied, a surface texture derived from photography, as in the case of the digital Harrier jumpjet in True Lies (1994). Especially for close-up shots, animators will frequently add bitmap effects, such as the paint effects available in Adobe Photoshop, to add extra detail or to provide digital "dirt." One attraction of three-dimensional modeling is that once built, a creature can be reused numerous times. A three-dimensional model is a dataset, and can be recycled not only in films but, for example, as a Computer-Aided Design and Manufacture (CADCAM) file, as was the case with the Buzz Lightyear character in Toy Story (1995), subsequently mass produced as a toy.

Individually handcrafted creatures may be too time-consuming, expensive, or processor-heavy for larger scale projects. Disney's The Lion King (1994) used a technique developed in scientific computing to analyze flocking behavior in order to animate the wildebeest stampede. Each wildebeest was given a small list of behaviors that it applied repeatedly, such as "run in the same direction as the others" and "always try to get to the inside of the group." Referred to as recursive (to describe the complex behavior emerging from the repeated application of a small rule set), this basic artificial life technology allowed the wildebeest effectively to animate themselves. Similar techniques have been used with larger numbers of "agents" with a broader range of behaviors in Disney's follow-up The Hunchback of Notre Dame (1996) for carnival crowds including a hundred or so different characters, each with a special attribute such as juggling, dancing, or carousing. Massive (Multiple Agent Simulation System in Virtual Environment), developed for The Lord of the Rings trilogy, extends these principles significantly. Massive uses motion-capture elements to provide its agents with vocabularies of up to two hundred movements. Each agent has collision-detection, and each emits a signal allowing other agents to identify whether it is friend or foe. Controls allow animators to increase or diminish the amount of "aggression" at any moment, triggering a fight or a riot. Otherwise, the agents are allowed to direct their own actions, guided by tracking algorithms that direct them toward a particular goal, such as a pass through a valley. Agents are animated at one of three levels, according to their size relative to the camera, with maximum detailing applied with subdivision modelling only to those closest. Many Massive agents are

entirely digital, but many, such as the animated horses attacking the "oliphaunts" in The Lord of the Rings: The Return of the King , also use photographic elements, while others, such as many of the "hero" (close-to-camera) "orcs" were given features derived from digital scans of performers in prosthetic makeup and full costume. To cut render times for sequences employing up to a hundred thousand agents, the Massive renderer begins with the agents closest to the screen, so that only those visible behind that agent need to be rendered at all, although the others are still in some sense visible to the program, which tracks their movements while they are obscured from the virtual lens.

Certain aspects of digital postproduction still pose challenges. The most familiar elements of the world, including eyes and skin, are considered the most difficult to render successfully. The most complex and successful experiments on skin tone include subsurface refraction of light, using complex three-dimensional models with not only skin but blood vessels, muscles, and bones. Major three-dimensional models are articulated on virtual skeletons, with virtual muscles, and with algorithms governing the sliding of skin over muscle and bone. Eyes, so deeply associated with emotion, must also be given great depth by the use of layers of animation, each of which responds differently to virtual light. Such effects must then be matched with the live-action lighting conditions, with movement in the lit environment as well as their angle to the camera, and in relation to anything in the environment that might be reflected in their eyes. One solution to the problems posed by lesser challenges like water and fire is the use of sprites, practical elements, some filmed on location (like the stormy seas of Master and Commander: The Far Side of the World ) and others created in studios, applied to three-dimensional geometry. In analogue days, such effects might be achieved in optical printers (a flamethrower shot was passed through the optical printer fifty times to provide the burning skies of Voyage to the Bottom of the Sea , 1961). Such sprites may then "track" other digital or photographic elements through software that instructs, for example, the sprite of a boat's wake to follow the boat, as in Troy (2004).

Other aspects are automations or more effective variants of traditional techniques. Editors have long been responsible for brushing out unwanted elements in a shot, either literally painting them out or using garbage mattes to hide them, replacing the matted area with a "beauty pass," a clean plate of the location without actors or equipment. These processes are now done digitally. The process of grading, during which photographic laboratories print the edited film to changing specifications in order to match the light and color responses, has also been overtaken by digital grading, a technology that, however, allows far more than supporting the use of filters for day-for-night shooting. Digital grading can be used to apply a color palette to an entire movie or sequence, and can be applied differentially to different areas of the image. This tool is useful not only for balancing exposures in scenes where one area is brightly lit and another in shadow, nor simply for highlighting detail in an actor's face; it is an essential tool for combining plates from disparate sources, especially when compositing may involve as many as fifty plates in a single frame.

Motion control files are extremely significant at this juncture, as is information on the types of lens used. Digital mattes, unlike their physical correlates, need to provide three-dimensional information if there is any camera movement, where a move would reveal another facet of the backdrop. A sky applied to a sequence may derive from "scenic" location shoots or be painted, but it must match the lighting on all the other plates—for example, casting cloud shadows or opening into brilliant sunshine on cue. The crisp detail of digital animations may need to have motion blur applied to make it more credible as the photographed object of a camera lens, and even such accidental artifacts as lens flares (an effect of sunlight bouncing inside the refracting elements of an actual camera lens) are often added digitally to give a

greater sense of the presence of a real camera on the virtual or hybrid set. Pyrotechnic effects may be scaled to match the scene, in which case the effects of their light on the immediate environment needs to be considered. Animatronics, water effects (sometimes shot at speeds over a hundred frames per second), puppets, digital effects, miniatures, and live action, many of them shot in multiple passes under different lights, must be blended together as seamlessly as possible. Excessive detailing may need to be toned down to produce a more coherent plane of vision, while providing for the effects of scale and of the interaction between layers. When major film projects may take two to three years to develop from storyboard (often digital animatic) to release, the problem of infinite "tweakability" enters, not least since each change to the master edit requires a change to scoring and sound effects, whose synchronization with the image must be perfect to convince an audience of its authenticity. Not surprisingly, the digital storage for feature films is now measured in terabytes.