# Forced perspective through depth perception

Forced perspective is a technique used in film, photography and other art that alters perceived object size and distance. The technique takes advantage of the visual cues humans use to perceive depth such as angular size, aerial perspective, shading, and relative size. Using tools to counter and manipulate these cues, artists can move the visual plan of an object at will.

## Angular size

Consider two objects of equal size placed at different distances from an audience. Increasing the object's distance from the audience makes the 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.[1]

### Calculating angular size

Angular Size, distance and object size.

The formula for calculating angular size is as follows:

$\theta=2\tan^{-1}\left(\frac{h}{2D}\right)$

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.[2]

## Manipulating perspective in art

Humans use a variety of techniques beyond angular size to perceive depth. 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 other 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.

### Techniques employed

• Solely manipulating angular size by moving objects closer and farther away cannot fully trick the eye. Objects that are farther away from the eye have a lower luminescent contrast due to atmospheric scattering of rays. Fewer rays of light reach the eye from more distant objects. Using the monocular cue of aerial perspective, the eye uses the relative luminescence of objects in a scene to discern relative distance. Filmmakers and photographers combat this cue by manually increasing the luminescence of objects father away to equal that of objects in the desired plane. This effect is achieved by making the more distant object more bright by shining more light on it. Because it is known that luminance decreases by ½d (d is distance from the eye), artists can calculate the exact amount of light needed to counter the cue of aerial perspective.[3]
• Similarly, blurring can create the opposite effect by giving the impression of depth. Selectively blurring an object moves it out of its original visual plane without having to manually move the object.[4]
• A perceptive illusion that may be infused in film culture is the idea of Gestalt psychology, which holds that people often view the whole of an object as opposed to the sum of its individual parts.[5]
• Another monocular cue of depth perception is that of lighting and shading. Artists also use lighting to establish shadows. Shading in a scene or on an object allows the audience to locate the light source relative to the object. Making two objects at different distances have the same shading gives the impression that they are in similar positions relative to the light source, and therefore, they are apparently much closer than they are in actuality.[6]
• A simpler technique employed by artists is that of manipulating relative size. Once the audience becomes acquainted with the size of an object in proportion to the rest of the objects in a scene, a photographer or filmmaker can replace the object with a larger or smaller replica to change another part of the scene's apparent size. This is done frequently in movies. For example, to aid in the appearance of a person as a giant next to a "regular sized" person, a filmmaker might have a shot of two identical glasses together, then follow with the person who is supposed to play the giant holding a much smaller replica of the glass and the person who is playing the regular-sized person holding a much larger replica. Because the audience has seen that the glasses are the same size in the original shot, the difference in relation to the two characters allows the audience to perceive the characters as different sizes based on their relative size to the glasses they are holding.[7]
• A monocular cue easily taken advantage of by painters is the trend for the color of objects in the distance to be shifted more towards the blue end of the spectrum, while closer objects' colors are shifted toward the red end of the spectrum. A painter can give the illusion of distance by adding blue or red tinting to the color of the object he is painting.[7]

### Examples of forced perspective

#### In film

Most recently, forced perspective has been employed to create dwarfs and giants in film series such as Harry Potter and The Lord of the Rings. For example, the Hobbit Frodo in the Lord of the Rings, and Hagrid the half-giant in Harry Potter.

In reality, there is only a 5-inch height difference between the two actors, Frodo being 5′6″ and Gandalf being 5′11″, but the altered angular size of the actors allows for a much more drastic difference.

Consider this photo of Harry Potter (Daniel Radcliffe, 5′5″) and Rubeus Hagrid (Robbie Coltrane 6′1″). Forced perspective techniques allow for the illusion that Hagrid is much larger than Harry in the movie than he is in reality.

#### In art

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.

#### In photography

Consider this photo that utilizes the technique of forced perspective to place a man into a coffee cup. Manipulating angular size allows the man to appear small enough to fit in the coffee cup. This is done by placing the coffee cup much closer to the camera than the man is to the camera.

The shading and shadows have been manipulated to make the two objects appear to be the same distance from the light source. They also appear to have the same orientation to the shared light source. This has been achieved by using multiple light sources to alter shadows and luminescence. Increasing the luminescence of the man counteracts the dimming effect of increased distance.

Finally, the man and the cup have a very similar level of focus/blur, meaning that they are brought into the same visual plane.