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What is Motivation in CG lighting

Today I will be writing about motivation in CG lighting means in Animation Field....
So let me start that and this is an article from the book Digital Lighting and rendering by Jeremy Birn and he is the most famous CG lighting artist in the world.

What is Motivation?

When you go to lighting in Animation, before you add a light to your scene, you should know its motivation. Motivation is the cause or original source for each light in your scene.

You probably wouldn't begin to animate a character without knowing what the character was doing or trying to do, or paint a texture map without knowing what material you were trying to create- and yet many people add lights to their scenes in just this sort of random manner, without thinking about what kind of light they are trying to depict, and what kind of light they are trying to depict.

Motivation should inform every decision you make in adjusting your lights. Once you know a lights motivation, you know what qualities of real light you are trying to to depict, and what kind of light sources you should study or think about when creating an appearance in 3D.

What is off screen Space?

Off screen space is the area that isn't visible in your shot, such as the space above the camera. The illumination, shadows, and reflections you see in a photograph are often motivated by off screen sources, rather than by light sources that are visible within the frame. An important part of your job in designing lighting for any scene is to imagine what exists in off screen space, So that you can light your scene with lights that appear to be motivated by real light sources.

If the light coming from off screen space in a photograph can provide less information then how do we make the lighting in our 3D scenes appear just as distinctive to communicate the same thing? The answer starts with studying the visible qualities of light from each kind of light source.

Qualities of light

We recognize different sources of illumination by the different qualities of light they add to the scene. The main qualities of light that we notice in a picture are color,  brightness, softness, throw pattern, and angle.

* Every type of light source has a distinctive color temperature, which, when combined with the white balance of the camera, determines the color of the light. Chapter 8, "The Art and Science of Color," has charts of real light sources' color temperatures.

* Brightness, like color, is all relative to how the camera is adjusted this time based on the exposure settings of the camera. Chapter 6, "Cameras and Exposure," describes a real camera's exposure process, and how to make sure your own renderings are exposed properly.

* Softness is a function of several settings on a light. The penumbra of a spotlight sets the softness of the edge of its cone. The decay or drop-off of a light sets how it fades away with distance. Most importantly, soft shadows create the impression of soft, diffused light while crisply defined shadows indicate hard light. Figure 1.1 showed the hard-edged shadows of the chess pieces lit by direct sun, and the much softer shadows cast by the cloudy sky. Chapter 3, "Shadows and Occlusion," discusses several approaches to rendering hard and soft shadows.

* Throw pattern, or the shape of a light, is another noticeable quality of light. Figure 1.1 showed the pattern of the light filtered through Venetian blinds as the throw pattern of sunlight that has passed through a window. Chapter 2, "Lighting Basics and Good Practices," discusses projecting cookies from your lights to simulate different throw patterns.

* A light's angle tells you where it is coming from. For example, a late afternoon sun will come from a lower angle than light in the middle of the day. To a lighting designer, angle also helps determine the visual function of a light, such as whether it functions as a key light, a kicker, or a rim. Aiming lights at the correct angle to achieve different visual functions is described in Chapter 5, "Lighting Creatures, Characters, and Animation."

Almost any adjective you use to describe light could be considered a quality of light. I sometimes consider animation, such as whether a light is flickering or consistent, to be a quality of light. I have heard other people describe the level of contrast as a quality of light, although I consider the amount of contrast in an image to be a function of the brightness and softness of the lights in the scene.

The one thing that ties all of these qualities of light together is that you can study them in real life, and work to imitate them with the lights in your 3D scene. Knowing which kinds of light you want to study in real life starts with imagining what kinds of light sources are motivating your scene's illumination.

Direct and Indirect Light

Direct light shines directly from an original source, such as a lightbulb or the sun, to an object that it illuminates. Indirect light is light that has reflected or bounced off one surface already, before it indirectly illuminates other objects. For example, if a floor lamp aims light at the ceiling, then the circle of light on the ceiling is direct light. The light that has reflected off the ceiling to softly illuminate the rest of the room is indirect light.

Direct light sources are usually the motivation for most of the brighter lights in your scene, but indirect light, such as light that has bounced off the ground or a wall, is also a motivation for light that can fill in or illuminate parts of your scene. Chapter 4, "Lighting Environments and Architecture," explains how to set up extra lights to simulate indirect light bounces in an environment, as well as global illumination functions that automate the simulation of indirect light.


the whole source you will get from the book Digital Lighting and Rendering written by Jeremy Birn
Want to buy this book click here