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376 13 Storytelling through Lighting, a Computer Graphics Perspective

Backlight (for separation from background and setting of mood). Also referred to as rim, hair, or separation lights, backlights were traditionally used in black-and-white cinematography for foreground separation. In color cinema, they are needed less for separation but are still heavily used.

A true backlight is traditionally placed behind the subject so that it is pointing directly at the camera, resulting in a thin rim of light around the edge of the subject. Backlights are also placed at higher angles to highlight hair and clothing. Back crosslighting is frequently used to put a rim on both sides of the subject. A soft backlight can look natural even if it has no obvious motivation. A hard backlight, unless a visible practical light motivates it, may look unnatural.

Backlighting is easy to achieve in live action, often with one light. However, many shading algorithms ignore light that strikes the back of an object and do not try to simulate the halo effect that results from a backlight hitting a surface that is not mirror smooth. Without special shaders that comprehend backlighting, creating this effect in CGI requires a bit of cheating and patience. It helps to have roughness controls on the specular highlight of each light source, so that the backlights can have as broad a highlight as possible. Exact light placement can be tricky to control, especially with moving or multiple characters, multiple sources, and wide-angle lenses.

Kicker (for surface modeling and character enhancement). A kicker light is an optional light usually used to define the nonkey edge of a subject. This light typically works from a three-quarters-back position and is placed nearer to the floor than the backlight. It can be soft and diffuse or hard and specular, depending on need and the intended lighting style.

A kicker light is a more general name for a variety of lights that perform slightly different functions. The three main types are a kicker, a liner, and a glow light. When used to create sheen (specular light), on a cheek for instance, they are frequently referred to as a kicker light. When far enough forward to contribute more diffuse light, they are sometimes referred to as a liner light. A glow light is a little farther forward still and is softer, nonspecular, and shadowless.

Specials (to accent an area for either subject or background). A special is any type of light that is used for background and set lighting, or for highlighting an area on the subject.

Bounce lights (to simulate radiosity effects). In the live-action world, light is often bounced off of a reflective surface onto a subject as a soft light source. In computer graphics lighting, an extra light would need to be created, and unless a radiosity renderer is used, extra lights usually need to be added to simulate the light that normally bounces off nearby surfaces. These lights are usually localized, nonspecular, low-intensity, and colored to mimic the surface they are reflecting.

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13.7Revealing Character Personality and Situation

Shaping and Controlling Light

Of equal importance to the placement and direction of light are shaping and controlling it-illuminating the intended subject without spilling into unwanted areas. It is sometimes also desirable to create a defined light shape, either to mimic a logical source or for dramatic or compositional purposes. Many of the techniques used to control and shape light synthetically can be similar to those of live action because the problems are also similar. These problems include controlling the light's size, shape, distribution, isolation, and coverage over distance.

It is often desirable to break up large or even surfaces with varying light and shadow. Sometimes this can be achieved with deliberate, recognizable shadows from actors or props and sets; other times, a more subtle overall variation will be appropriate. Barndoors, the four flaps attached to the sides of a light, can be used to shape and trim a source. The use of freestanding flags to block lights can be used to shape light at various distances from the source, which allows control over the hardness or softness of the shaping. A cucaloris (or cookie), a rigid board with squiggly holes cut into it, can be used in front of a light to create a more random, organic light pattern. Gobos can be used to restrict bounce light. A good computer lighting toolkit will offer a variety of light types and shapes along with sizing and soft barndoor controls. Further light shaping can be accomplished with the use of blocker flags, slides, and cookies, as well as variable light attenuation over distance.

Computer lighting has several benefits that do not exist in live action. Lights and flags can exist anywhere in space without interfering with the camera or subject. It is also possible to illuminate a subject and not have the light affect other characters or the background; negative intensity lights can be used to softly subtract illumination; and shadows can be independently colored, blurred, and given an arbitrary density value. The apparent softness of a light can be independent of its distance from the scene and resulting shadows do not necessarily have to be projected from the source point of the light.

13.7Revealing Character Personality and Situation

The quality, color, and direction of light can give the audience impressions about the personality or character of the subject. They can also say something about the dramatic situation, or emotional state of mind, in which the subject currently finds himself. When a character is narrating a scene, he can describe his thoughts and how he sees the world; visual representation of his thoughts is not necessary. Most of the time, however, we require the use of our imagination to decipher the motivations and feelings of the characters by observing their actions, watching them emote, listening to them interact with other characters, and surveying their surroundings. It would be confusing to listen to a movie with the picture turned off; we rely so much on our vision to tell us what is happening, which is why we "watch" television or go to "see" a movie:

378 13 Storytelling through Lighting, a Computer Graphics Perspective

Visual clues are an aid for the viewer to help him understand the story more quickly or completely, getting him emotionally involved with the characters and their predicaments. Visual clues are tangible elements, such as location, sets, props, wardrobe, time of day, time of year, that are almost taken for granted but without which the viewer would have no context. Is it Elizabethan England in the dead of winter, high noon on the chaparral, or a humid summer night in New Orleans?

Besides establishing context for scenes, visual clues can also impart an emotional impression to the viewer by employing symbolism. My online computer dictionary describes symbolism as "expressing the invisible or intangible by means of visible or sensuous representations" and as "artistic imitation or invention that is a method of revealing or suggesting immaterial, ideal, or otherwise intangible truth or states." Some of this is absorbed on a conscious level (the good guys wear white hats, right?), while much of it is subliminal.

Light itself expresses symbolism-life, freedom, clarity, hope, enlightenment, truth, and guidance. Darkness represents the opposing forces. The source type can also express emotion. Candles, for instance, are associated with happy occasions such as weddings and social dinners, as well as contemplative locations such as church. They are also nostalgic because they remind us of times before electricity. Warm, soft, flickering candlelight is sensuous, flattering, seductive, and romantic. Windows and doorways represent transitions. Our hopes "fly out the window," and "opportunity knocks" on, and comes in through, the doorway. How something is portrayed relative to a subject can also have an effect. The past is "behind us," while the future is "in front of us."

Light placement and direction can impart emotional significance as well. Hard underlighting is commonly used to signify an evil or criminal character or situation. Soft underlighting can look very sensual. Lighting from directly overhead can look dreary when the subject is looking down but spiritual, uplifting, and hopeful as the subject looks up toward the light. Completely illogical lighting is often used in dream sequences or hallucinations-the more illogical, the better. The images of Woody in Figure 13.34 show that lighting can dramatically alter the form, and the resulting visual personality, of a character.

In the image of Hopper in Figure 13.35, great care was taken in staging to keep a wall of fire behind Hopper in his close-ups. This is a good example of using staging and lighting to reveal the personality of the character and to also heighten the tension of the scene.

Whether we realize it or not, we attach symbolic meanings and react emotionally to virtually everything. Some reactions are innate, others are dependent on our culture, and still others are uniquely personal. As lighting designers (and visual storytellers), we can take advantage of these emotional reactions in how we choose to portray characters in a scene. The best way to learn how to do this is to study films (with the sound off) to experience how you are emotionally affected by what you see.

Figure 13.34 Toy Story-Lighting direction, quality, and shaping are powerful tools to change the visual personality of a character. (© Disney Enterprises, Inc.) See also color plate 13.34.

Figure 13.35 A Bug's Life-An example of staging and lighting used to reveal personality of a character and to heighten tension. (© Disney Enterprises, Inc. and Pixar Animation Studios.) See also color plate 13.35.

13.8Continuity

It would be wonderful if there were enough time to craft each shot as its own masterpiece, capable of surviving scrutiny on a gallery wall. But there isn't enough time, and sometimes it is also not appropriate. A complex composition takes time to study, and the eye can take its time meandering to various points of emphasis. A thirty-frame shot needs to direct the eye quickly. The audience does not have time

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to guess where to look; the shot needs to have immediate impact. Often, most of the subtleties are unnoticed.

The desire to craft each shot as a masterpiece also needs to be balanced with the necessity of a consistently lit sequence. It is very important to constantly check the lighting progress on other shots being lit in a sequence, especially if adjacent shots are being lit by other people. Lighting will inevitably and necessarily vary from shot to shot, but the overall feeling of the shot should be consistent with its sequence and especially with its adjacent shots. Sometimes this means that lights need to be brighter, darker, warmer, cooler, or even repositioned to achieve a unified feeling as camera angles change. Two characters standing side by side may even need different lighting to make it feel like they are being lit by the same source.

It is also easy to get too carried away with continuity. You can get away with more than you might think, but the only way to know for sure is to be able to view the shot in context. The computer lighting environment offers immediate feedback as well as preview and comparison capabilities not found in live action.

Another advantage the CG world has over live action is not having the physical reality of getting all of the day's shots filmed before the light changes significantly. If you have watched the film Liar, Liar, did you happen to notice the big time-of-day shift in the climax? Probably not. In one shot, Jim Carrey is racing down the airport runway, chasing a jet, on one of those motorized stairs, emergency crews in full pursuit. It is broad daylight. He has a crash and flies off of it. We cut to a night shot of the emergency crews attending to him. The cut feels like it has been minutes; the lighting change looks like it has been hours. Nobody notices the lighting change because we expect maybe a slight time shift, but also because it isn't really relevant to the story. The cinematographer may have been begging for another shooting day for the sake of continuity, but the producer was probably happy because the shooting stayed on schedule.

13.9 Film Considerations

Once a shot is lit on the computer, it is rendered and exposed onto film. It is then developed, printed, and projected onto the screen, sometimes with surprising results. Colors and values can sometimes change drastically. Film can only capture a small range of the available light and color gamut of the real world. Film recorders may not even be able to reach the gamut of the film stock. Video monitors vary widely and may not match the final result. However, color-matching software now exists to minimize surprises.

Although it is desirable to get as close as possible at exposure time, the printing process offers great latitude in altering overall color and density (brightness). This process is called timing or grading. The traditional lab timing is applied to individual shots over the entire image and usually cannot vary over time. It is now

Further Reading

possible to do color timing digitally with as much control as a digital film-to-tape transfer session using a DaVinci. This will dramatically change what is possible and the speed with which it can be accomplished. It will be interesting to see how quickly this new process becomes commonplace.

If using the traditional lab timing process, it should be kept in mind that it is much easier to time a print darker than brighter. Brightening a print means that more light is pumped through the negative, which can result in a washed-out "milky" quality.

13.10 Conclusion

The primary purpose of lighting is to support the visual structure established for the story being told. The visual structure is designed top down, from the overall story arcs, the sequences and scenes, down to the individual shots. Visual "rules" for the movie are decided and implemented for all design elements, including the lighting design. Sometimes the rules are complicated, sometimes they are as simple as a particular character who is always lit with underlighting, and sometimes the established rules are intentionally ignored. Having a plan and defining a visual style is the primary outcome of preproduction.

Once a film is in production, the priority of meeting a hard deadline causes the planning processes to shift toward efficiency. Making good decisions and compromises in the heat of production is another part of the art. A good lighting designer knows how to visually reduce a complex scene so that the important story point reads instantly. A good lighting designer also knows when the band-for-the-buck has been reached where continued refinement does not aid the story.

This chapter has presented a wide range of visual tools to explore, the details of which may seem overwhelming. Observation of the physical world and the study of cinematic and artistic interpretations of it are also necessary. Experience from actual lighting shots and learning from spontaneous happy accidents are better than reading any chapter. Get out there and do it!

Further Reading

Matters of Light & Depth by Ross Lowell, 1992, Broad Street Books.

Logic & Design in Art, Science & Mathematics by Krome Barratt, 1980, Design Books.

Painting with Light by John Alton, 1995, University of California Press. Film Lighting by Kris Malkiewicz, 1986, Prentice-Hall Press. Cinematography, 2d ed., by Kris Malkiewicz, 1989, Simon & Schuster Inc.

3d ed., by David A. Lauer, 1990, Holt, Rinehart and Winston Inc.

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Psychology in Action, 2d ed., by Huffman, Vernoy, Williams, and Vernoy, 1991, John Wiley & Sons.

Elements of Film, 3d ed., by Lee R. Bobker, 1979, Harcourt Brace Jovanovich. Introduction to Film by Robert S. Withers, 1983, Barnes & Noble Books.

Color & Human Response by Faber Birren, 1978, Van Nostrand Reinhold. Design and Composition by Nathan Goldstein, 1989, Prentice-Hall. Composing Pictures by Donald W. Graham, 1970, Van Nostrand Reinhold.

Film Directing Shot by Shot by Steven D. Katz, 1991, Michael Wiese Productions. Film Directing Cinematic Motion by Steven D. Katz, 1992, Michael Wiese Productions. By Design by Vincent LoBrutto, 1992, Praeger.

Story by Robert McKee, 1997, ReganBooks.

Lighting Controls for Computer Cinematography*1

Ronen Barzel

Pixar Animation Studios

This chapter presents a practical light source model that has developed over several years in response to the needs of computer graphics film production, in particular for making CG animated films such as Toy Story. The model gives the CG lighting designer control over the shape, placement, and texture of lights so that the designer's realworld cinematographic talent can be applied to computer images. Chapter 13 discussed what lighting effects are desired; this chapter presents a light source implementation that allows such effects to be conveniently described.

*1 This chapter is adapted from Barzel (1997).

384Lighting Controls for Computer Cinematography

14.1Introduction

Photorealism is an important and much-studied goal in computer graphics imagery and illumination. But photographers and cinematographers know that when it comes to lighting, realism is not the only goal.

As discussed in Chapter 13, the purposes of lighting for cinematography are to contribute to the storytelling, mood, and image composition, and to direct the viewer's eye. The "practical" light sources on a real-world movie set, such as desk or ceiling lamps, are rarely major contributors to the illumination. Instead, various types of lamps and spotlights are placed offcamera in order to create the desired illumination effect. A lighting designer will use whatever techniques, tricks, and cheats are necessary, such as suspending a cloth in front of a light to soften shadows, positioning opaque cards or graded filters to shape a light, focusing a narrow "tickler" light to get an extra highlight, or hiding a light under a desk to fill in dark areas under a character's chin.

This chapter describes a CG lighting model that provides a convenient and powerful encapsulation of control for cinematography. It was developed in response to needs and requests of lighting designers doing computer graphics film production: the features that we describe are those that have proven useful in practice, and almost all lighting effects used in Toy Story were achieved with the available features.

The emphasis of the model is not on realism nor on physically simulating the tools of real-world cinematography. Rather, we take advantage of various sorts of unreality available to us in the CG world in order to get the desired cinematographic effects*2, so, although real-world.effects provide motivation, our lighting model is ultimately based on effects that are useful in computer graphics.

To keep things intuitive, we'll first describe all the features of the lighting model (Section 14.2) and give the implementation notes (including a complete RenderMan shader) later on (Section 14.3). We'll also go over a few examples from Toy Story (Section 14.4). But remember, we talk here mostly about the technology of cinematography; for the artistry of cinematography, see Chapter 13 and its references.

14.2 The Lighting Model

Section 9.6 presented some basic light source shaders that implement a fairly limited model of lighting control. Here, we generalize and introduce controls over many more aspects of each light source: selection, shape, shadowing, texture, dropoff, direction, and properties. We describe and illustrate these capabilities in

*2 In fact, real-world cinematographers would doubtless use CG tricks if they could-for example, have light emanate out of nowhere, cut off alight after a certain distance, or change the direction of shadows.

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14.2 The Lighting Model

Figure 14.1 Cylinder and cube on the floor, torus in midair (left), with a conical key light (right).

Figure 14.2 Selection; same as Figure 14.1, but the torus is unaffected by the key light.

Sections 14.2.1-14.2.7. For clarity, each feature is illustrated in isolation, although the model allows them to be used in any combination. Also, we illustrate with static images, but all parameters can of course be animated.

Figure 14.1 shows a sample scene lit only by fill lights and the same scene with a simple conical key light. Fog is introduced to illustrate the effect of the light throughout space. (The fog is implemented using the technique and shader described in Section 12.6.)

14.2.1Selection

Computer graphics lights can be enabled or disabled on a per-object basis (Figure 14.2). The ability to selectively illuminate objects in a scene is a powerful feature, which has no analog in real-world lighting. In our experience, per-object selection is used frequently, in particular to adjust illumination separately for the characters and the set.