Matte Paintings are two-dimensional “backdrops” used to provide an appropriate background scene for a full-size 3D set that can not readily be placed against the desired background. Consider a false-front western town photographed on a sound stage. How can this be viewed against the Rocky Mountains? Or how can the proper background be provided for action on an alien planet? A large painting or photomural can be created and placed behind the set. Or, the set and action can be photographed with a plain blue background (“blue screen”), which is later replaced in post-processing with a desired background, either painted or separately photographed.
Models and Time
Integrating models into a movie so that they appear to be full-size objects moving at “normal” speeds can pose some intriguing problems. A big issue is time. When small models are being photographed, high frame rates can be used to give the miniature the appearance of being full-sized and more massive (and thus subject to normal gravity and momentum). “Most explosions filmed at ILM (Industrial Light and Magic) are shot at speeds in excess of 100 frames per second… Consider the effect of a small explosion that rips apart a miniature spaceship; the entire action may take a half of a second to occur when filmed, but if filmed at 240 frames per second this half-second event becomes a five-second explosion. When accompanied by a powerful sound, it is a convincing event.” (Smith 1981) Since motion at any instant is effectively linear, the frame rate for shooting the movie so that the action appears “normal” needs only to be faster 68 than the usual frame rate by the ratio of the linear dimensions of the modeled object to the dimensions of the model:
When extremely high speeds are needed to achieve the effect desired, there is a technical complication: the faster the camera runs, the more light is needed to expose the film. The miniature landslide shot for Dragonslayer at 250 frames per second required more than 10 times as much light to film as it would have required at normal speeds. … In addition, a miniature shot is more effective when shot at a high f/stop in order to keep both close and distant objects in sharp focus—again the need for a great many lights. Sometimes the lights are so intense and hot that they can only be turned on a second or two before the shot is made, and then must be extinguished the moment the shot is over so the model doesn’t melt!” (Smith 1981)