Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 146

Fig. 10.1 In this image, the blue lines represent seams in the object as they appear in the UV editor
( right ) and the object itself ( left )

10.1.2 Undistorted Textures

An undistorted texture is one where all of the square pixels in the texture map are
rendered as perfect squares on the object (Fig. 10.2 ). Distorted UVs always force at
least some of the pixels in a map into non-square shapes. They can be non-square
rectangles, trapezoids, parallelograms, rhomboids, or triangles.
Distorted textures are undesirable for three reasons. The fi rst is that they are inef-
fi cient. A distorted pixel uses more space than an undistorted one, or causes its
neighbors to use more space by forcing them to fi ll in any gap made by a narrow
edge. The second reason is that distorted maps can be diffi cult to fi x in a 2D paint
program, because it is very diffi cult to paint in a way that matches the distortion on
a map. To make it worse, the distortion is caused by non-square pixels and it is not
possible to paint with non-square pixels in a 2D paint program. A 3D paint tool
allows artists to project paint onto distorted texture coordinates, but this is a more
time-consuming way to paint than working in 2D. The last reason is that distorted
textures are likeness errors. A model with serious distortion in any visible map
should be fi xed prior to delivering the fi le.

10.1.3 Effi cient Textures

An effi cient texture makes good use of the UV space it covers (Fig. 10.3 ) . This
means that very little of the map is wasted. The process of packing texture coordinates
to get the best usage of available UV space can be compared to the manufacture
of clothing. It is important for clothing manufacturers to get the most out of their
cloth. They accomplish this by arranging paper cutouts of their pattern in such a
way that all the pieces will fi t on the smallest piece of cloth possible.