Special effects (often abbreviated as SFX, SPFX, F/X or simply FX) are illusions or visual tricks used in the theatre, film, television, video game, and simulator industries to simulate the imagined events in a story or virtual world. Special effects are traditionally divided into the categories of mechanical effects and optical effects. With the emergence of digital film-making a distinction between special effects and visual effects has grown, with the latter referring to digital post-production and optical effects, while 'special effects' refers to mechanical effects. Mechanical effects (also called practical or physical effects) are usually accomplished during the live-action shooting. This includes the use of mechanized props, scenery, scale models, animatronics, pyrotechnics and atmospheric effects: creating physical wind, rain, fog, snow, clouds, making a car appear to drive by itself and blowing up a building, etc. Mechanical effects are also often incorporated into set design and makeup. For example, prosthetic makeup can be used to make an actor look like a non-human creature. Optical effects (also called photographic effects) are techniques in which images or film frames are created photographically, either 'in-camera' using multiple exposure, mattes or the Schfftan process or in post-production using an optical printer. An optical effect might be used to place actors or sets against a different background. Since the 1990s, computer-generated imagery (CGI) has come to the forefront of special effects technologies.