Graphics Reference
In-Depth Information
Chapter 10
Creating and Editing Texture
Coordinates (UVs)
10.1
Introduction
Texture coordinates, as described in Sect.
2.4.2.4
,
are used to attach a texture map
to a CG object. Without them, textures cannot be applied to models. Without texture
coordinates and a texture map, most models are not considered fi nished. Texture
coordinates then, are quite important.
Assigning texture coordinates is one thing, doing it well requires more effort. Editing
texture coordinates, like other aspects of CG art, requires artists to balance many
variables at once. The goals of UV editing are simple to describe: to have seamless,
undistorted, and effi cient textures. However, there are numerous possible solutions, all
of which are in some manner less than ideal (John McDonald and Burley
2011
).
10.1.1
Seamless Textures
A
seam
in texture coordinates is similar to a seam in an article of clothing. It is the
boundary of a polygon or group of polygons. With clothing, seams are the boundar-
ies of the cloth a garment is made from. When different boundaries are sewn
together, the seam is usually evident because the pattern on the cloth is discontinu-
ous across the border. Texture discontinuities are undesirable if they interrupt a
continuous surface like the face of a character, but are acceptable if they fall along
natural seam borders like the sides of a box, or the boundary between two pieces of
cloth in a garment (Fig.
10.1
).
In the context of a CG model, the term
seamless
does not literally mean “without
a seam” because all things have boundaries, therefore all things have seams. It means
that artists should avoid making visible seams in inappropriate locations. It also
means that artists should avoid making more seams than necessary. The reason for
the last condition is that it can take extra effort to make textures align across seam
borders. If there is no seam, there is no need to line up texture elements that would
otherwise be split by the seam.
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