visual effects

What visual effects are

Visual effects, commonly abbreviated VFX, are images that are created or manipulated beyond what a camera recorded live and then integrated into a film so that they appear to belong to the photographed scene. The defining feature is that the imagery is produced or altered away from the moment of live capture — typically in post-production — and combined with recorded footage in a way meant to be indistinguishable from it. Elements that would be impractical, unsafe, or impossible to film directly, such as vast environments, crowds, historical settings, or fantastical creatures, are built by other means and joined to the live-action material.

Because the goal is seamless integration, visual effects work is closely bound to the photographic properties of the shots it augments: the added imagery must match the perspective, motion, lighting, and grain or noise of the footage, and its appearance is finalized alongside the film’s color-grading. The techniques share much of their craft with animation, which likewise constructs images frame by frame, but visual effects are distinguished by their aim of blending with photographed reality rather than presenting an avowedly drawn or modeled world.

Distinguished from practical and computer-generated effects

Visual effects are conventionally distinguished from practical or special effects, which are physical and achieved on set during filming — mechanical props, animatronics, pyrotechnics, weather rigs, prosthetic makeup, and miniatures photographed in camera. Special effects exist in front of the lens at the time of shooting; visual effects are added or completed afterward. Many productions combine the two, capturing a practical element live and then extending or refining it with visual effects.

Visual effects are also broader than computer-generated imagery (CGI). CGI refers specifically to imagery synthesized by computer, and it is one means of producing visual effects among several; conversely, many long-established visual effects methods, such as painted backdrops and photochemical compositing, involve no computer at all. CGI is therefore best understood as a subset of the techniques that visual effects draw upon rather than a synonym for the field.

Principal techniques

A matte painting is a painted or, later, digitally rendered image of a setting that is combined with live action so that the depicted environment appears real; traditionally it was executed on glass or a large panel and photographed together with the actors. Optical printing rephotographs one or more strips of film through a device that projects them into a camera, allowing separate images to be layered, repositioned, or transformed; it was for decades the standard photochemical means of combining elements.

Compositing is the general operation of combining multiple image sources into a single frame, whether photochemically or digitally. Chroma key, known in production as green screen (or blue screen), is a compositing method in which a subject is filmed against a uniformly colored backdrop; that color is then made transparent so another image can be placed behind the subject. Motion capture records the movement of a performer or object — often via markers tracked by cameras — and applies that motion to a digital model, so that a computer-generated character can move with the nuance of a live performance. CGI synthesizes imagery directly by computer, modeling objects, surfaces, lighting, and motion to render elements that were never photographed.

From optical to digital

For most of the medium’s history, visual effects were achieved by optical and photochemical means: matte paintings, in-camera tricks, models, and multiple exposures combined on an optical printer. These methods manipulated the film itself, and each additional layer of rephotography tended to accumulate loss of image quality. From the late twentieth century the work shifted to digital methods, in which footage is scanned or captured as data on an image-sensor and manipulated on computer workstations.

Digital compositing removed the generational quality loss of repeated optical printing and, together with advances in CGI and motion capture, greatly widened the range of achievable imagery. The underlying aim — to add or alter elements so convincingly that the join is not perceived — remained constant, but the digital pipeline largely replaced the optical printer and the photochemical matte as the standard means of realizing it.