CG Basics - An Introduction to Computer Graphics for Artists - page 26

Fig. 2.21 When images are applied to polygons, they become textured polygons

Table 2.6 Shader types
Shader type Lambert (dull) Phong (plastic) Blinn (metallic)

Diffuse (color) X X X

Transparency X X X

Bump X X X

Specularity X X

Refl ectivity X X

2.4.2.2 Materials

Materials are represented by shaders . Shaders can be extremely complex (more
on that in Sect. 11.3 ). At their simplest, they defi ne how readily light is absorbed
by the shader and its color. The most commonly used values are shown in
Table 2.6 .

2.4.2.3 Textures

In the early years of computer graphics, CG objects did not have texture maps.
Texture maps simulate a higher level of color and structural detail by projecting an
image onto the faces of a CG object. The idea of mapping textures onto objects was
introduced by Edwin Catmull in 1974 (Blinn and Newell 1976 ). Since that time,
many methods for aligning images with the faces of an object have been invented,
and maps have been used to represent many different types of information beyond
surface color. Texture maps are kept in separate fi les from geometry, called image
fi les. These fi les can be in almost any format or size, as long as it is compatible
with the renderer being used.
Textures are attached to shaders to control the many channels of information
used by a shader to adjust its appearance. For instance, a texture map attached to the
color channel of a shader can be used to apply a label to a cereal box (Fig. 2.21 ).
A texture applied to the specularity channel could make the box appear to be wet
or shiny.