Datenbank Glossar – CGI
Shading
In the real world, objects are seen in specific ways based on the following:
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The materials they are made of.
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Their surface textures.
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How they are lit and reflect light.
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The environment surrounding them.
In Maya, you provide your surfaces and objects with these characteristics by assigning shading materials to them.
Shading Materials provide instructions to the renderer so it can simulate how the surfaces in your scene react to light and appear in the final image. Shading involves such attributes as color, transparency, shininess, and many others to create a realistic look.
Editing the material attributes associated with shading materials affects how they appear in the rendered image. In this way, Maya provides the option of allowing you to create images as they would appear in the real world or in your imagination.
Lighting
Directors of live-action film use camera and lighting techniques to enhance the visual impact of a scene. Wide, medium, and close up views of the subject, depth of field, high or low key lighting all communicate something about the subject and the scene to the viewer.
Lighting and camera techniques are one of the most crucial aspects to consider when working with artificial characters and objects. The more realistic the lighting and shading appear, the more convincing the scene will appear to the viewer.
A prerequisite to creating effective 3D rendered animation is to study the lighting and camera effects used in live-action film. Your goal is to create the desired scene ambience while keeping the lights and camera view as unobtrusive as possible.
Lighting, (in combination with textures, camera angle etc.) is where your scene has the potential to come alive. But used improperly, light can wash out your scene, make objects appear hard or flat, and destroy all you’ve worked for. But skillfully applied, lighting can make your scene convincing, or if realism is your aim, create (in combination with materials and geometry), a scene that is virtually indistinguishable from real life.
In 3D, lights don’t actually exist as they do in the real world. Lights in 3D are objects that are designed to simulate how lighting works in real life, but in order to obtain the results you’re after, you have to apply a number of settings, not only to the lights, but to the materials. To elaborate, let’s say you turn on a lamp.
Looking at this screenshot, notice the intensity of the light, the color, the softness of the shadow on the wall, the haloing effect around the light source and how that affects the color of the black casing the houses the light (the halo effect changes, depending on the angle at which you view the light and if there atmospheric particles in the air).
Other factors are decay, where the light is strongest at the source and decays or decreases, the further away you move from the source. Other factors, are whether the bulb casing is clear, colored or frosted, whether the light bulb is tungsten, halogen or daylight corrected (this is a tungsten bulb which casts as yellowish-orange light) – the list goes on and on.
Even if you have lighting specifically designed for photography, you’re dealing with issues of light placement, direction and shaping of the light (which you can accomplish with snoots or barn doors), falloff, etc.
In a 3D scene, being aware of lighting conditions is very important. While the aim of this article is to introduce some lighting concepts, it’s not designed to be a complete course. To understand lighting in more detail, it’s helpful to experiment with 3D, but if you’re not familiar with lighting, I encourage you to take a studio lighting course in photography or to read up on lighting setups.
In 3D (depending on the application), if you don’t add lights to a given scene, the entire scene and objects will be rendered as a black frame (as in Maya). In other programs (such as 3DS Max), there is default lighting in a scene which is replaced as soon as you start adding lights. Depending on how you add lights to the scene will determine the effect. In 3D (again depending on the program), some basic lighting components are spotlights, omni lights, directional lights and lights that mimic the effects of the sun.
When designing a workflow in 3D, here are some steps to observe:
1. Plan out how you want your scene to look and how the light sources will interact in your scene.
2. Create the necessary light sources and set the characteristics for the light as necessary (such as hotspot, falloff, color, intensity, attenuation, etc.).
3. Move light sources as necessary in the scene. If precision is important, use tools such as the Transform Type-In (3DS Max) for precise positioning. As you move lights in your scene, it’s a good idea to perform test renderings as you do so, to make sure you’re getting the effect you’re after.
4. Turn on Cast Shadows in your scene and adjust them for the desired effect.
5. Once you’ve applied the above steps, you’re ready to introduce optical light effects such as glows, halos or lens flares.
Note: Use of ambient light is most often used for exterior scenes, when the overall light of the sky creates an even distribution of light. This is not the case with indoor scenes, where multiple lights are in use. In this case, try setting the ambient light to black. If you choose to use ambient light, keep it at a low value such as RGB 6 and no more than 12. One common mistake is to use too much ambient light, which can wash out the scene.
Lighting Guidelines
The type of lighting you’ll need to use depends on a multitude of factors, such as whether you want to simulate a natural or artificially lit scene. In the case of a natural scene, such as in daylight or a night sky, there is only one light source.
With artificial lighting, such as a downtown city street, there are multiple light sources, often in different colors and intensities. Indoor and outdoor scenes also make a big difference. The quality of lighting will interact with your materials and you might have to change the color or intensity.
For more information on lighting
http://www.itchy-animation.co.uk/light.htm
http://www.itchy-animation.co.uk/tutorials/light02.htm
http://www.itchy-animation.co.uk/tutorials/light03.htm
http://www.itchy-animation.co.uk/tutorials/light04.htm
Color
Color is an important element of lighting. When you first consider it, you might think of lighting as white, a natural assumption. But if you start to observe your environment, you’ll find that light casts many different colors, even supposedly “white” light. To see what I mean, have a look at the lighting in your home. If you look at a tungsten light, you’ll probably notice that the color it emits is yellow and with tints of orange. If you go into a department store and look up at the fluorescent lights, you’ll probably see a variety of colors, such as pink, blue and green. All of this affects what you see. In addition, let’s say you’re looking at white clothing. Some clothing will appear whiter than other clothing. This is the result of brighteners that have been added to the fabrics to make them appear to pop, to be whiter than white.
Outside, all sorts of factors come into play such as the angle of light and the time of day, which produces a wide range of color shifts ranging anywhere from pale yellow to red or orange at sunset. Cloudy weather can tint the light into shades of blue and even gray on dull days. However, paradoxically, on overcast days where the entire sky seems to be one gray mass, the sun’s rays are filtered, almost like using a soft box in a photography studio. The result? Bright colors (such as yellow) really pop and appear to be brighter than normal. At the same time, shadows are minimal and soft, unlike a brightly lit day, when shadows will have a much harder edge and will be darker.
