《数字照明与渲染》第三版 - Jeremy Birn

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"Digital Lighting and Rendering, 3rd Edition 是一本由 Jeremy Birn 编著的专业渲染技术书籍，主要探讨数字照明与渲染技术。该书虽然排版质量不高，但作为学习资源仍然非常有价值。本书适用于对3D图形、游戏开发、电影制作等领域感兴趣的读者，以及希望提升渲染技巧的专业人士。" 在《Digital Lighting and Rendering》第三版中，作者 Jeremy Birn 深入讲解了关于数字领域中的光照和渲染的各个方面，涵盖了从基础理论到高级技术的广泛内容。以下是本书可能涵盖的一些关键知识点： 1. **渲染基础**：书中可能会介绍渲染的基本概念，包括渲染引擎的工作原理、渲染过程中的计算模型以及不同类型的渲染算法。 2. **光照理论**：深入探讨光的物理性质，如颜色、强度、方向和类型（点光源、聚光灯、环境光等），以及如何在数字环境中模拟这些特性。 3. **材质与纹理**：讨论不同材质的视觉效果和它们在渲染中的应用，如镜面反射、漫反射、折射和透明度，以及纹理映射技术。 4. **阴影和光照效果**：介绍如何创建逼真的阴影，包括软阴影、全局光照和区域阴影的计算方法。 5. **光照与色彩理论**：解释色彩在视觉效果中的作用，以及如何通过色彩搭配和照明设计来营造特定氛围。 6. **高级渲染技术**：可能涉及次表面散射、体积光照、焦散、光线追踪、抗锯齿等复杂渲染技术。 7. **后期处理与合成**：讨论图像后期处理的重要性，包括色彩校正、景深效果、运动模糊以及与其他元素的合成技巧。 8. **实时渲染与预渲染的区别**：对比在游戏和动画制作中实时渲染和电影级预渲染的区别及其应用场景。 9. **软件应用**：可能会提供关于流行渲染软件（如 RenderMan、Arnold、V-Ray 等）的实例和工作流程，帮助读者理解如何在实践中应用所学知识。 10. **案例研究**：通过实际项目案例分析，展示如何将理论知识应用于实际工作，以解决具体问题。 11. **技术发展与趋势**：可能涉及当前渲染领域的最新进展，如基于物理的渲染、GPU加速渲染、机器学习在渲染中的应用等。这本书不仅适合初学者建立扎实的理论基础，也对有经验的从业者提供了提升技能的宝贵资源。通过学习，读者可以掌握创建高质量、逼真图像和场景的能力，从而在视觉效果领域取得专业成就。

[Figure 1.4] After the cheat, the statue appears better lit by the candlelight.

The objects in the background (a vase and some plates with incense sticks on them) are bright enough

that they attract attention to themselves. I went into each of their shaders, darkened their colors, and

reduced the brightness of the specular highlights on them. This is another cheat, but it makes them look

as if they are farther back from the candlelight, and it helps the Buddha pop out into the foreground

more. Figure 1.5 shows the scene with background objects darkened and the Buddha appearing more

prominent in the shot.

A pool of light on the floor that appears to have come from a window may actually come from a light

above the set. An actress running into a dark forest may have her face fully lit when in reality she

would have been in darkness. Even the walls of the set are sometimes mounted on wheels (this is

called a wild wall) so that they can be moved out of the way or rotated independently from other

walls.

So why do lighting designers cheat? Why not just make the lighting be as accurate and true-to-life as

possible? The short answer to these questions is that lighting and cinematography are arts, not just

sciences. A more in-depth answer starts with understanding the visual goals that a lighting designer is

trying to achieve when lighting a scene.

Visual Goals of Lighting Design

There is more to lighting a scene than simply running a simulation of real-world parameters. Lighting

is also designed to achieve certain visual goals that help a viewer better appreciate a scene. How

well you accomplish these goals determines how your lighting enhances or detracts from a shot.

Making Things Read

Much like photography, cinematography, and painting, 3D rendering is a process of producing two-

dimensional images that depict three-dimensional scenes. Making things read means producing

images that the audience can interpret as 3D spaces and arrangements of solid objects. To give your

renderings solidity and presence, and to fully communicate the three-dimensional form of an object or

character to an audience, you need to define your models with careful lighting. Some people call this

process modeling with light because it is your lighting that lets the viewer perceive an object’s 3D

form. Defining a character with light is one of the main focuses of Chapter 5.

Making Things Believable

Computer graphics can be rendered in many different visual styles. Some projects require

photorealism (images that can be mistaken for a photograph), while other projects are stylized in

different ways or designed to create more illustrated or cartoon-like looks. Whether or not the visual

style you adopt is photorealistic, your lighting still needs to be believable to the audience.

A believable image is at least internally consistent, with lights that are balanced in a way that would

be motivated in real life. For example, if a beam of direct sunlight is entering a room, the viewer

expects the sunlight to be brighter than the light of a table lamp. Even in a cartoon, basic expectations

of weight and balance still exist. In fact, sometimes getting small details right in your lighting can

even help “sell” a scene that otherwise would be impossible to believe.

Often the key to creating believable lighting is studying real life. Before beginning a project, try to

study how light behaves in situations similar to what you will be rendering. In visual effects work,

studying the live-action footage (the images filmed with a real camera) can show you a great deal

about how a subject should appear in an environment. For projects created entirely in 3D graphics,

collect reference images that you can study to see how color and light appear in a real scene. No

matter how you obtain them (whether you photograph the reference images yourself, find them on a

photography website, or grab still frames from rented movies), you will find your collection of

reference images useful throughout your project; you can use them while pitching your lighting plans

to a director or art director, and later compare them with your renderings as you adjust your lighting.

It is a poor artist who blames his tools for his work. Part of making a scene believable is

compensating for the failures, flaws, and limitations inherent in your hardware or software. Almost

every physical effect discussed in this book, from indirect light bouncing off walls to the translucency

in human skin, can be simulated through careful texturing, lighting, and compositing, even when your

software doesn’t fully or automatically simulate everything for you. When someone sees the picture or

animation that you have lit, they want to see a complete, believable picture, not hear excuses about

which program you used.

Enhancing Shaders and Effects

Frequently in 3D graphics you find it necessary to add lights to a scene to help communicate the

identity of different surfaces and materials. For example, you may create a light that adds highlights to

a character’s eyes to make them look wetter, or puts a glint of light onto an aluminum can to make it

look more metallic. Many effects that, in theory, you could create exclusively by developing and

adjusting surfaces and textures on 3D objects are often helped along during production by careful

lighting you design to bring out the surface’s best attributes. No matter how carefully developed and

tested the shaders on a surface were before you started to light, it’s ultimately your job to make sure

all that is supposed to be gold actually glitters.

Effects elements such as water, smoke, and clouds often require special dedicated lights. The effects

department will create the water droplets falling from the sky on a rainy night, but it’s your job as a

lighting artist to add specular lights or rim lights to make the drops visible. Effects such as explosions

are supposed to be light sources, so you need to add lights to create an orange glow on the

surrounding area when there’s an explosion.

Maintaining Continuity

When you work on longer projects such as feature films, many people are involved in lighting

different shots. Even though the lighting is the work of multiple artists, you need to make sure that

every shot cuts together to maintain a seamless experience for the audience. Chapter 12 discusses

strategies that groups of lighters use to maintain continuity, including sharing lighting rigs for sets and

characters, duplicating lighting from key shots to other shots in a sequence, and reviewing shots in

context within their sequence to make sure the lighting matches.

In visual effects, continuity becomes a more complex problem, because you need to integrate your 3D

graphics with live-action plates. During a day of shooting, the sun may move behind a cloud while

one shot is filmed, and it may be brighter outside when another shot is filmed. Although integrating a

creature or spaceship with the lighting from the background plate may be the key to making your shot

believable, the continuity of the sequence as a whole is just as high a priority, and sometimes you

need to adjust your shot’s lighting to match the lighting in adjacent shots as well.

Directing the Viewer’s Eye

In a well-lit scene, your lighting should draw the viewer’s eye to areas that are important to the story,

animation, or key parts of the shot. Chapter 7 will cover more about how composition and staging

work and what makes a part of the frame attract the viewer’s eye or command attention.

Besides making the intended center of interest visible, good lighting avoids distracting the audience

with anything else. When you are viewing an animated film, the moment something unintended catches

your eye—whether it’s a strange flicker or artifact, a highlight where it doesn’t belong, or a shadow

that cuts across a character—your eye has been pulled away from the action and, worse than that,

your attention has been pulled away from the story. Good lighting can add a lot to a film, but first and

foremost, you must do no harm when it comes to the viewer’s experience of watching the animation.

Emotional Impact

When they are absorbed in the story and watching what happens to the characters in a movie, most of

your audience never consciously sees your lighting; instead they feel it. Helping create a mood or tone

that enhances your audience’s emotional experience is the most important visual goal of cinematic

lighting design.

Chapter 8 focuses on the different moods and associations that color schemes can create for a shot.

While staying within what is motivated and believable, you still have room to achieve a range of

different looks or moods when you are lighting a scene. Is it very starkly lit, with high contrast and

harsh shadows? Is it softly lit, with subtle lighting and soft shadows? Is the scene very colorful with

lots of saturated tones, or is it gloomy and desaturated? Is there a point in the scene when the tone

shifts and something changes? Knowing the story and, of course, discussing the main points of the

scene with the film’s director are the keys to planning the type of mood you will try to achieve.

Achieving the visual goals of good lighting design is an artistic process, grounded in the tradition of

cinematography, which in turn borrows a great deal from painting. Although this book covers a

number of the key technologies that are speeding up or changing the process of lighting, mastering the

craft of lighting a 3D scene is, at its heart, a timeless skill whose value will not go away with any

new button or switch that will be added to future graphics software.

Lighting Challenges

Lighting is an iterative process. Rerendering scenes with better and better lighting, while getting

feedback on your versions, is essential to perfecting your lighting skills. To help you get more

practice with lighting, and to get feedback on your scenes as you light them, you can browse through

an ever-expanding set of “Lighting Challenge” scenes, which are available for download from this

book’s companion website, www.3dRender.com, in a variety of file formats. On the Lighting

Challenges discussion forum, you can see how other artists have lit each scene; see breakdowns of

the lights, the render passes, and other elements of people’s work; and, most important, post versions

of your own work to get feedback.

Even though the Lighting Challenges were conceived as a sort of online lighting contest in which

many people have participated, the wealth of scenes we have generated over the years are ideal for

practicing lighting, whether you are going to post your results on our discussion forum or not. As you

read this book, you’ll notice that I use Lighting Challenge scenes in many of the figures to illustrate

many concepts and techniques. These scenes can be rendered many different ways. Figure 1.6 shows

several of the entries created by different artists using just the first Lighting Challenge scene, a basic

fruit bowl. Feel free to download the scene and take a stab at lighting it yourself.

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《数字照明与渲染》第三版 - Jeremy Birn

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