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346 13 Storytelling through Lighting, a Computer Graphics Perspective

Figure 13.8 Near tangency creates usual tension, focusing our attention on the gap.

attention to itself and becomes a point of emphasis through tension. This tension is created by the feeling of unpredictability caused by the lone element not belonging to the larger group or exhibiting the expected behavior (Figure 13.9).

If this emphasis is undesirable, finding a way to link the element to the larger group may help minimize attention. Using an edge of a shadow to point to the isolated element is one way to link it to the group. N. C. Wyeth used this technique in the painting in Figure 13.10. The man's hat would create too much emphasis if it were not linked to his body by the shadow of his walking stick.

Emphasis through Linear Elements

Edges and contours do not really exist as physical entities, but are illusions created by the borders or intersections of shapes. The human eye is very sensitive to change and can find even very subtle distinctions, which it mentally connects to create an edge or contour. This connection process forces the eye to travel; it is an active

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13.3 Directing the Viewer's EyeThe Study of Composition

Figure 13.9 Emphasis through isolation.

Figure 1 3.10 N. C. Wyeth's Blind Man with Walking Stick uses a shadow edge to point to the man's hat in order to reduce the emphasis created by isolation.

348 13 Storytelling through Lighting, a Computer Graphics Perspective

Figure 13.1 1 Emphasis through perspective angles.

process and is therefore dynamic. The careful placement and emphasis of edges play an important role in leading a viewer's eye through a composition, directing it to the intended subject. A practical example of how lighting can be used to control the placement and emphasis of edges might be the angle of a shadow, highlighting the edge of an object, accentuating the difference between two adjoining planes, or even deliberately allowing an edge to blend with the background.

Linear perspective is the process of taking a 3D space and projecting it onto a view plane, representing the spatial relationship of objects changing over distance, as they appear to the eye. In the CG world, the computer does this for us automatically; in the live-action world, the camera does the job. The result of either is a 2D illusion of the original 3D space. The illusion is partially maintained by lines (edges) that appear to point to one or more vanishing points. The eye travels along the edges and terminates at a vanishing point. As a result, an on-screen vanishing point creates a strong focal point and can easily lead the eye toward or away from the intended subject. If a vanishing point is creating unintended emphasis, it may be necessary to minimize it and attract the eye more strongly using another point of emphasis. In Figure 13.11, it is easy to see how strongly the eye is pulled to the shape that is near the vanishing point.

The painting in Figure 13.12 by Mary Cassatt is an interesting example of using linear elements to direct the eye. The edges of the boat bow, as well as the man's arm and oar, are used to create an artificial vanishing point to lead our eye to the intended focal point, the baby.

A line may also be implied by positioning a series of points so that the eye tends automatically to connect them. The eye has to work a little harder to make the connection, and as a result an implied line is more dynamic than an actual one. A row of ants is a nice example (see Figure 13.13). An implied line can also be created by movement. As an object travels from point A to point B, an imaginary line is created by its path. A line can also be implied by objects that create a mental connection. The eyeline of a character is a good example. If a character looks toward

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13.3 Directing the Viewer's EyeThe Study of Composition

Figure 13.12 Mary Cassatt's painting The Boating Party uses elements to direct the eye. (Photograph courtesy of the Board of Trustees, National Gallery of Art, Washington)

an object, the viewer will also look. These lines are very dynamic because the eye and brain are working on several levels to make the connection. A subtle example of a linear element is the perceived axis through an object. A tall, thin man standing has a vertical axis, while a recumbent man has a horizontal one.

Emphasis through Shape

The brain tends to characterize edges and shapes as either rectilinear or curvilinear. Most images are not composed of strictly one or the other. By creating an image with primarily one type, the other type becomes a point of emphasis. In the simple example in Figure 13.14, the triangle stands out from the field of circles because its shape is unusual in this context. There are very few examples of perfectly straight lines in nature. This is probably why we find curvilinear shapes to be more appealing than rectilinear ones.

Shapes that enclose or frame other shapes draw and contain our eye. A subject that is staged within a door frame will attract more attention than he would if he were staged against a plain wall. A target is an exaggerated example of this visual tendency.

350 13 Storytelling through Lighting, a Computer Graphics Perspective

Figure 13.13 A Bug's Life-Implied line created by a row of ants.

(©Disney Enterprises, Inc. and Pixar Animation Studios.) See also color plate 13.7 3.

Figure 13.14 Emphasis through shape.

Emphasis through Size

Size is an obvious way to manipulate emphasis because larger objects tend to attract more attention (Figure 13.15, left). But when an object becomes large enough to break the image frame (Figure 13.15, right), our attention is directed to the smaller of the two shapes because we can see it more clearly.

Emphasis through Recognition

Humans are intrigued by other humans. When we sec another person, our brains immediately begin to work to determine whether we know the person. Despite a familiar walk or physical build, we are often unsure whether we recognize someone until we see his face. If we do not recognize him, we often look anyway to become

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13.4 Creating Depth

Figure 13.15 Emphasis through size.

familiar with the new person. If two characters are standing side by side, one facing the camera and the other one facing away, we will spend most of our time looking at the character whose face we can see, even if the other character has the dialog. We don't learn much from the back of someone's head. We need the mouth and especially the eyes to observe what the person might be thinking or feeling. The less we can observe, the less trusting we are of the person's intentions. Compare the two Woody images in Figure 13.16. Both are smiling the same smile, but which would you rather encounter in a dark alley late at night?

Humans have such a strong interest in themselves that they even like to attach human-like appearance, behavior, emotion, and intelligence to animals and inanimate objects. The animation business has been built around this attraction to anthropomorphosis. Talking animals are a perennial favorite, as well as classic hybrid charactacters such as mermaids, centaurs, and genies.

Emphasis through Motion

A static image has static points of emphasis and all principles of emphasis apply, but the cinematic image has the added bonus of being able to create emphasis through the illusion of motion. Motion can be implied by movement of the camera, movement of the subjects, or by redirecting the eye of the viewer from one area of the screen to another. The eye can be redirected within a single shot or across the cut from one shot to the next. An in-depth discussion of the principles of cinematic motion are beyond the scope of this chapter. Please browse the Further Reading section for suggested reading.

13.4 Creating Depth

The film medium is a 2D surface through which light is projected. Any feeling of depth, space, or volume achieved is merely an illusion. This implied depth must be created; it does not happen automatically simply because the subject matter is 3D. A 3D world can be staged and/or lit to look flat. If the major planes in the scene

352 13 Storytelling through Lighting, a Computer Graphics Perspective

Figure 13.16 Toy Story-Woody fully lit (left) and with his eyes in shadow (right). (©

Disney Enterprises, Inc.)

are staged to be parallel to the image plane, the scene will look flat compared to one with the planes converging toward a vanishing point. Lighting can minimize or accentuate surfaces to alter the illusion of depth and volume. How the illusion of depth is handled in a film is a major component of its visual structure and style.

The painting by Berthe Morisot in Figure 13.17 (top) is a nicely composed and rendered image, however, it is staged and lit to look very flat. This creates a particular visual style. The image from A Bug's Life in Figure 13.17 (bottom) was staged and lit to impart as much visual depth to the image as possible for the location, which creates a very different visual style.

The motion picture image is a window into a world where viewers make intuitive comparisons to determine what they are seeing. Some of these comparisons are easy. If an object is bigger than another, it is probably nearer. If an object overlaps another, it is decidedly closer. At this point, the comparisons start to become more complicated. Does the object appear small because it is a small object or because it is far away? The brain looks for other monocular and binocular clues to establish size and distance, but the clues can be misleading. As an example, a long telephoto lens tends to condense distance, making faraway objects appear very near. Focus

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13.4 Creating Depth

Figure 13.1 7 An example of flat stage lighting (top) in Berthe Morisot's The Sisters. (Gift of Mrs. Charles S. Carstairs. Photograph © Board of Trustees, National Gallery of Art, Washington.) A Bug's Life-An example of deep staging and lighting (bottom). (© Disney Enterprises, Inc. and Pixar Animation Studios.) See also color plate 13.17.

and depth of field are also important clues but are dependent on the lens focal length and aperture used. Aerial perspective is helpful, but it can vary depending upon atmospheric conditions. The brain also uses the angle between a light source and where its shadow falls to help determine object-to-object proximity. The viewer uses all of these static comparisons to organize the image and to establish depth. In a motion picture shot, motion parallax due to camera or object motion is a vital depth cue.

354 13 Storytelling through Lighting, a Computer Graphics Perspective

Figure 13.18 A Bug's Life-Reversing the usual value cues by making more distant objects brighter. (© Disney Enterprises, Inc. and Pixar Animation Studios.) See also color plate 13.18.

13.4.1 Linear Perspective

We have already discussed linear perspective as it relates to emphasis. It is also an important element for implying depth. If all of the planes in a scene are parallel to the image plane, the scene appears very flat. Sometimes this effect is desirable if it supports the visual structure defined for the story. By rotating the planes off parallel, the plane edges converge toward one or more vanishing points. A two-point perspective appears to have more depth than one; three-point seems even deeper; beyond three points depth seems to stop accumulating.

13.4.2 Value

A bright value will attract our eye more than a darker one. This is especially true in a darkened theater because the bright value has more contrast with the surrounding environment. The darker values also tend to recede into the darkened environment, while the lighter ones tend to pop instead. Therefore, lighter values tend to feel nearer most of the time. Contrast also provides spatial cues for depth perception. Areas of greater contrast appear to advance into the foreground, while areas of lesser contrast tend to recede.

A value progression from the area nearest the camera to the area farthest away can help to exaggerate the perception of distance. A short hallway can look much longer if it is lit so that the light falls off before the end of it. Reversing this progression so that the light gets brighter as surfaces gain distance from the camera will draw the viewer into the frame. (See Figure 13.18.)

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13.4Creating Depth

13.4.3Color

Depth can also be enhanced with color. In general, warm colors tend to feel nearer than cool colors. One reason may be that we are familiar with the cooling effect of aerial perspective. A warm subject over a cool background will impart more apparent depth than a subject and background with the same color temperature. The reverse situation is also true, however. It is the chromatic separation of planes that increases the illusion of depth.

13.4.4 Atmosphere

The use of atmospheric effects can enhance both depth and mood. Except for a windy day or immediately following a rainstorm, some dust and water particles hang in the air that reflect, refract, and scatter light. Smoke and fog machines are heavily used in live-action cinema to heighten natural effects.

Atmospheric effects are noticeable over distance where they create aerial perspective by minimizing local color saturation and contrast. In the computer, simply adding a percentage of a fog color into the shading calculation for each pixel based upon surface distance from the camera can create aerial perspective. For more complicated, three-dimensional effects, volumetric light shaders can be used.

To create a natural-looking aerial perspective, keep in mind that atmosphere that is backlit will appear to brighten objects over distance, while frontlit atmosphere will appear to darken objects over distance. The color of the atmosphere also changes depending upon the camera angle relationship to the light source and depending upon what the atmospheric particles consist of. Dense atmosphere or fog will tend to make objects blend with the background as they recede over distance, as shown in Figure 13.19.

Atmospheric effects are usually employed to enhance the feeling of depth or space in an environment. They can also be used to limit depth if the atmosphere is thick enough to obscure objects. Limiting depth in this way can have a profound emotional effect on the viewer in the right context. Imagine yourself driving on a winding, unfamiliar road in very dense fog. How do you feel? You probably feel tense because the situation feels unpredictable. You can't see where you are, and you aren't sure where the road is going to turn or what might pop up in front of you. This feeling of apprehension adds drama to the foggy chase scene in A Bug's Life in which Dot is running from the grasshoppers (Figure 13.20).

Atmospheric effects are also used on a smaller local scale to create shafts of light projected through openings, which can help to impart a nice feeling of space (see Figure 13.1).

13.4.5 Resolution

Surface texture gives the audience cues as to how close they are to the object surface, because texture becomes less apparent as the object moves farther away.