3D Animation Workshop: Lesson 12: Getting Started With Surfacing | 2 | WebReference

3D Animation Workshop: Lesson 12: Getting Started With Surfacing | 2

Lesson 12 - Getting Started With Surfacing - Part 2

To speak of an object's diffuse color really only begins to make sense when we consider some different possibilities of color.

What if the color of an object is not due to the reflection of light from another source, but rather from light given off by the object itself. In other words, what about luminous objects, such as neon signs, or even the computer screen you're looking at right now?

Here is the same sphere with no diffuse color, and its luminous color set to red.

Not very interesting, is it? And perhaps not what you would expect. To speak of "luminous color" has a sultry sound, but in 3-D surfacing it simply mean the assignment of a color to an object that is completely independent of light sources. Thus in this case, although we still have the same lighting as before, the effect is only of a flat disk, and the 3-D effect is completely lost.

Let's add back some diffuse color into the picture and see what happens.

The sphere is now responding to the light again and the shadowing reveals the 3-D shape. If we compare it to our original red sphere, with full diffuse color but no luminous color, we learn something valuable.

Without the luminous color added, the shaded area of the sphere is darker. Thus the luminous color can be used (and most typically IS used) to bring color into shadowed areas when the object already has a diffuse color. This kind of thinking typifies the way in which 3-D often diverges from the real world. In the real world--on a photo shoot for example--additional lighting would be added to the shadowed area if necessary. And the same could be done in with our sphere here. We could have added another small light from below, or more likely have brought up the ambient lighting. But we could also do something that was impossible in the real world--cause the object to give off color independent from the light sources. This may be much easier or more useful than the other alternatives, because adding or changing the lighting might have consequences elsewhere in the scene.

Diffuse color is reflected light. But there is another type of reflected light that is extremely important to 3-D surfacing. Compare the following sphere with the one above.

Diffuse color is determined by the sphere. But the new highlight is the color of the light itself, in this case the white spotlight. This kind of reflection is called SPECULAR REFLECTION, and is extremely important to 3-D graphics because it provides critical visual clues about the shape of the object, its orientation toward the lights, and perhaps most important, the kind of material of which it is apparently made.

The specularity of a surface is controlled by setting both the intensity of the reflection and degree of its spread across the surface, and these factors working together make for a very broad range of effects. Consider the following examples.

Very few natural surfaces have no specularity at all, and the right amount of highlight, even where barely visible, is convincing. The human eye is highly attuned to reading highlights and is drawn instinctively toward them.

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Created: June 16, 1997
Revised: June 16, 1997

URL: http://webreference.com/3d/lesson12/part2.html