3D Animation Workshop: Lesson 5: Lights, Camera, Render! | 2 | WebReference

3D Animation Workshop: Lesson 5: Lights, Camera, Render! | 2

Lesson 5 - Lights, Camera, Render! - Part 2

The following is a rendering of a sphere. There is no lighting in the scene, and therefore the sphere is completely black. Notice that the background is white. In 3-D graphics applications, the background of a scene is typically assigned a fixed color (or an image) that may have no relationship with the scene.

Now we add a light, actually a couple of lights. A spot light is pointing down on the object from above and behind, reflecting off the surface of the sphere. This simple highlight gives the viewer a completely different reading of the scene.

The object is now perceived of (barely) as a 3-D sphere, and not just a flat circle. The color of the sphere is black, but it is made of a somewhat shiny material, like a billiard ball. The highlight, called a "specular reflection" is white, telling the viewer the light shining on the object is white. To compare, look at a rendering using a yellow spotlight.

The object being black, the only visual clue to its three-dimensional nature is the highlight. Shadows cannot be seen on a black surface. If we change the object's surface to a light blue, the shading across the surface (revealed as darker shades of blue and gray) do much more to reveal the shape.

The color of the spot light has been changed back to white, so that the color of the ball in the rendering reveals its true blue surface color. A little ambient light was also added to fill in the shadows. To understand this process better, let's remove the ambient light and change the color of the spotlight back to yellow.

The effect is exactly what one would get in stage lighting, with a single yellow spot on a blue ball. Without the ambient light, the shadows are stark and black. The net effect of a yellow light on a blue ball is a slightly greenish yellow.

The process of assigning the surface qualities to an object is often called "surfacing" or "shading." The information itself is called a surface, or a shader, and in some programs it is referred to as the object's "material properties." This is a very suggestive term because the surface information contains all the features that cause us to conceive of what an object is made of. We distinguish plastic from metal because of the way these materials reflect light. Thus shading or surfacing is much more than assigning a base color to an object. One of the most important clues to an object's material nature is specular reflectivity--the way it reflects highlights. Here is the blue ball without any specular qualities at all. The spotlight is white as before and ambient light has been used to fill in the shadows.

There is a soft feeling, as though the object were made of chalk, and were this same surface used on a longish cylinder or cube, it would pass for an artist's pastel.

Compare a very bright and pointed highlight, which creates the perception of very shiny plastic, even more like a billiard ball than our earlier example.

If the highlight is quieted a bit and spread out, a glossy, but not shiny, surface is created, as though the ball were painted with a latex paint. A remarkably broad range of possibilities are available by simply controlling the basic color of an object and its specular qualities. As you look around at the world, you will soon discover that specular reflection is the primary visual clue to the perceived material nature of objects.

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Created: Mar. 25, 1997
Revised: Apr. 22, 1997

URL: http://webreference.com/3d/lesson5/part2.html