What are the special effects?
In the field of cinema, special effects is an expression for the techniques used to artificially create or modify objects or characters.
1-MECHANICAL EFFECTS
Special effects can be divided into several categories. The simplest are the "mechanical effects". They include everything that is physically created on the set, while the scene is filmed normally: so we use models for explosions, walls that collapse, gunshots. Such effects go back to the very beginning of cinema and some were borrowed from theatrical performances.
2-OPTICAL EFFECTS
The second category consists of optical effects. They include all the cinematic deformations that can be done with a camera or a special treatment of the film at certain stages of its exhibition. The simplest of these techniques is the overprint, which consists of two images superimposed on a single negative. If the effect is achieved by printing two negatives afterward on a single photo, this is the technique of "double printing". There are other optical effects, such as fades, crossfades, and irises. In the fades in closing, the image darkens little by little, until the frame becomes completely black. The fade in the opening is in the opposite direction. The fades can be made by the camera by closing and opening the diaphragm or by closing and opening the gap of the shutter in front of the film in the camera. In the crossfades, a fade is performed in opening and closing and, after rewinding the film on the duration of the fade in closing, a new take is made. The second image then appears through the first. In "wipes" (or shutters), one image is gradually substituted for another by a game on the mobile separation line.
All these effects were borrowed from photography or magic lantern techniques, from the early years of cinema. The movements backward were also obtained from 1899 by passing the film upside down. But today, these effects, which still exist, are achieved through an optical printer. This mechanism separating the negative from the positive film does not leave them in contact during printing. The negative is projected frame by frame by a lens system in order to discover the surface of the image to achieve the pose. This leaves room for the different caches or filters that will be introduced between the two films to transform the image in the desired direction.
3-ASSEMBLY EFFECTS
The technique of making objects appear or disappear or turning them, stopping the camera and replacing them with another object, then rotating again and pasting the two pieces of film together in an invisible way, also goes back to very early cinema. This process was first performed by the Edison Company in the film The Execution of Mary, Queen of Scots (1895), but was often associated with Georges Méliès, who used it in his fantasy films.
4- THE CACHES
At the base, a black cache (in English: "matte") is placed in front of the lens, or inside the camera, to hide part of the scene that is filmed. Another scene is then filmed on the surface of the frame that was masked using a back-cover. It covers exactly the surface that was hidden for the first exposure. Such effects go back to the beginnings of cinema. They allow to multiply the same character (or actor) on the same plane or to introduce an element outside the original decoration.
5 - TRAVELING MATTE (OR MOBILE COVERS)
To film a moving actor in front of background also in motion shot separately, we perfected the caches in tracking shot. With this system, moving actors are filmed in front of a blank screen of the appropriate color. Then, the image of the actor is used to create a moving silhouette that can hide part of the background already filmed when the two shots are finally assembled during editing. In color films, we generally use a blue screen that is placed behind the actors.
To achieve the same effect, in the 1930s and 1940s, a simpler method was used which was transparency or background projection. With this system, the background scenes had to be filmed first, then projected onto a translucent screen using a specific projector, synchronized with the camera that was filming the actors playing in front of the scenery thus provided. Since 1969, another method has been used: the frontal projection, which allows the actors to evolve in front of a special screen (made of a material called Scotchlite) whose peculiarities allow the only useful light rays to be reflected towards the objective.
6- INFOGRAPHY
During the last years, the most important progress is due to the computer, which was able to control all the movements of the camera, and to the more and more important use of the animation by Computer graphics.
The use of computer-generated images in feature films has grown considerably in recent years; they took advantage of the increased power of computers. Computer animation is usually done by modeling objects that are then animated, by determining their contours numerically in three dimensions and by determining the trajectories they are supposed to follow. A program then calculates the area that the model will occupy on each image of the film. The area is then drawn and colored ("color rendering") the way it would appear under proper lighting in the sequence. The result is then viewed on the computer screen. The image is transferred to the film using the numbers corresponding to the color of each point in order to direct the appropriate laser light that is scanned onto each image of the negative to produce the final image that will be seen in the film.
Infographic is also used in the shooting of special effects, in order to modify filmed images, for example, to remove the traces of threads used to suspend models. In this case, the film that has been shot is scanned, frame by frame, into digital images in the computer. Then a conventional image editing software modifies the image as desired. Finally, the modified image is transferred to film in the same way as for computer animation.
