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Forced perspective is a technique that employs optical illusion to make an object appear farther away, closer, larger or smaller than it actually is. It is used primarily in photography, filmmaking and architecture. It manipulates human visual perception through the use of scaled objects and the correlation between them and the vantage point of the spectator or camera.
One example of forced perspective is a scene in an action/adventure movie in which dinosaurs are threatening the heroes. By placing a miniature model of a dinosaur close to the camera, the dinosaur may be made to look monstrously tall to the viewer, even though it is just closer to the camera.
Forced perspective had been a feature of German silent films and Citizen Kane revived the practice.  Movies, especially B-movies in the 1950s and 1960s, were produced on limited budgets and often featured forced perspective shots.
Forced perspective can be made more believable when environmental conditions obscure the difference in perspective. For example, the final scene of the famous movie Casablanca takes place at an airport in the middle of a storm, although the entire scene was shot in a studio. This was accomplished by using a painted backdrop of an aircraft, which was "serviced" by dwarfs standing next to the backdrop. A downpour (created in-studio) draws much of the viewer's attention away from the backdrop and extras, making the simulated perspective less noticeable.
Early instances of forced perspective used in low-budget motion pictures showed objects that were clearly different from their surroundings: often blurred or at a different light level. The principal cause of this was geometric. Light from a point source travels in a spherical wave, decreasing in intensity (or illuminance) as the inverse square of the distance travelled. This means that a light source must be four times as bright to produce the same illuminance at an object twice as far away. Thus to create the illusion of a distant object being at the same distance as a near object and scaled accordingly, much more light is required. When shooting with forced perspective, it's important to have the aperture stopped down sufficiently to achieve proper DOF (depth of field), so that the foreground object and background are both sharp.
Since miniature models would need to be subjected to far greater lighting than the main focus of the camera, the area of action, it is important to ensure that these can withstand the significant amount of heat generated by the incandescent light sources typically used in film and TV production.
Peter Jackson's film adaptations of The Lord of the Rings make extended use of forced perspective. Characters apparently standing next to each other would be displaced by several feet in depth from the camera. This, in a still shot, makes some characters appear much smaller (for the dwarves and Hobbits) in relation to others.
An extensively used technique in The Lord of the Rings: The Fellowship of the Ring was an enhancement of this principle which could be used in moving shots. Portions of sets were mounted on movable platforms which would move precisely according to the movement of the camera, so that the optical illusion would be preserved at all times for the duration of the shot. The same techniques were used in the Harry Potter movies to make the character Hagrid look like a giant. Props around Harry and his friends are of normal size, while seemingly identical props placed around Hagrid are in fact smaller.
The techniques developed center around a nodal point axis, so the camera's panning axis is at the point between the lens and aperture ring where the light travelling through the camera meets its axis. By comparison, the normal panning axis would be at the point at which light would strike the film (or image sensor in a digital camera).
The position of this nodal point can be different for every lens. However, on wide angle lenses it is often found between the midpoint of the lens and the aperture ring.
As with many film genres and effects, forced perspective can be used to visual-comedy effect. Typically, when an object or character is portrayed in a scene, its size is defined by its surroundings. A character then interacts with the object or character, in the process showing that the viewer has been fooled and there is forced perspective in use.
An example used for comic effect can be found in the slapstick comedy Top Secret! in a scene which appears to begin as a close-up of a ringing phone with the characters in the distance. However, when the character walks up to the phone (towards the camera) and picks it up, it becomes apparent that the phone is extremely oversized instead of being close to the camera. Another scene in the same movie begins with a close-up of a wristwatch. The next cut shows that the character actually has a gargantuan wristwatch.
The same technique is also used in the Dennis Waterman sketch in the British BBC sketch show Little Britain. In the television version, oversized props are used to make the caricatured Waterman look just three feet tall or less.
In The History of the World, Part I, while escaping the French peasants, Mel Brooks' character, Jacques, who is doubling for King Louis, runs down a hall of the palace, which turns into a ramp, showing the smaller forced perspective door at the end. As he backs down into the normal part of the room, he mutters, "Who designed this place?"
One of the recurring The Kids in the Hall sketches featured Mr. Tyzik, "The Headcrusher", who used forced perspective (from his own point of view) to "crush" other people's heads between his fingers. This is also done by the character Sheldon Cooper in the TV show The Big Bang Theory to his friends when they displease him.
In the making of Season 5 of Red vs. Blue, the creators used forced perspective to make the character of Tucker's baby look small. In the game, the alien character used as the baby is the same height as other characters.
For example, when forced perspective is used to make an object appear farther away, the following method can be used: By constantly decreasing the scale of objects from expectancy and convention toward the farthest point from the spectator, an illusion is created that the scale of said objects is decreasing due to their distant location. In contrast, the opposite technique was sometimes used in classical garden designs and other "follies" to shorten the perceived distances of points of interest along a path.
The Statue of Liberty is built with a slight forced perspective so that it appears more correctly proportioned when viewed from its base. When the statue was designed in the late 19th century (before easy air flight), there were few other angles from which to view the statue. This caused a difficulty for special effects technicians working on the movie Ghostbusters II, who had to back off on the amount of forced perspective used when replicating the statue for the movie so that their model (which was photographed head-on) would not look top-heavy. This effect can also be seen in Michelangelo's statue of David.
An extraordinary forced perspective doorway in Pézenas, France.
The technique takes advantage of the visual cues humans use to perceive depth such as angular size, aerial perspective, shading, and relative size. In film, photography and art, perceived object distance is manipulated by altering fundamental monocular cues used to discern the depth of an object in the scene such as aerial perspective, blurring, relative size and lighting. Using these monocular cues in concert with angular size, the eyes can perceive the distance of an object. Artists are able to freely move the visual plane of objects by obscuring these cues to their advantage.
Increasing the object's distance from the audience makes an object appear smaller, its apparent size decreases as distance from the audience increases. This phenomenon is that of the manipulation of angular and apparent size.
A person perceives the size of an object based on the size of the object's image on the retina. This depends solely on the angle created by the rays coming from the topmost and bottommost part of the object that pass through the center of the lens of the eye. The larger the angle an object subtends, the larger the apparent size of the object. The subtended angle increases as the object moves closer to the lens. Two objects with different actual size have the same apparent size when they subtend the same angle. Similarly, two objects of the same actual size can have drastically varying apparent size when they are moved to different distances from the lens.
The formula for calculating angular size is as follows:
in which θ is the subtended angle, h is the actual size of the object and D is the distance from the lens to the object.
Forced perspective has been employed to create dwarfs and giants in film series such as Hagrid, the half-giant in Harry Potter, and in the special effects of The Lord of the Rings film series to film the dwarves and hobbits.
In reality, there is only a 5-inch height difference between Elijah Wood, 5′6″, and Ian McKellen, 5′11″, the two actors playing Frodo, and Gandalf, however the use of camera angles and trick scenery and props creates the illusion of a much greater difference in size and height.
In his painting entitled Still life with a curtain, Paul Cézanne creates the illusion of depth by using brighter colors on objects closer to the viewer and dimmer colors and shading to distance the "light source" from objects that he wanted to appear farther away. His shading technique allows the audience to discern the distance between objects due to their relative distances from a stationary light source that illuminates the scene. Furthermore he uses a blue tint on objects that should be farther away and redder tint to objects in the foreground.
Forced perspective is extensively employed at theme parks and other such architecture as found in Disneyland and Las Vegas, often to make structures seem larger than they are in reality where physically larger structures would not be feasible or desirable or to provide an optical illusion for entertainment value. Most notably, it is used by Walt Disney Imagineering in the Disney Theme Parks. Some notable examples of forced perceptive in the parks, used to make the objects bigger, are the castles (Sleeping Beauty, Cinderella, and Belle). One of the most notable examples of forced perspective being used to make the object appear smaller is the The American Adventure Pavilion in EPCOT.