Creating and Editing Texture Coordinates (UVs) - An Introduction to Computer Graphics for Artists - page 153

Fig. 10.10 Forcing maps into power of two or square shapes signifi cantly adds to their size with-
out increasing their effective resolution

10.2.5.2 Inconsistent UV Scale

When adjacent polygons have different pixel to unit scales used for their respective
UVs, they have an inconsistent UV scale . Inconsistently scaled textures are easily
spotted at lower resolutions because the contrast between any two resolutions makes
the lower resolution maps appear to be excessively crude, and the higher resolution
maps appear excessively smooth. For example, imagine the corner of a building,
where one side uses a 256 pixel square map and the other uses a 1,024 pixel square
map. Both walls are the same size. Where they meet, you will see the individual pixels
of the lower resolution map clearly where they meet the higher resolution map.
If both maps were 256 pixels square, you may still see the pixels, but they wouldn't
draw attention to themselves as they do when contrasted with higher resolution
textures. Inconsistent scale is most evident with adjacent polygons, but can also be
found in non-adjacent polygons if the disparity is great enough. To solve this, some
artists globally increase the resolution of their maps. By doing this, they use up their
allotted texture space more quickly and have fewer maps to work with overall, leading
to less textural variety in the scene.

10.2.5.3 Reference Cube

For mapping objects that must be proportionately consistent, a reference cube may
be employed. A reference cube is an object that is selected as a size reference along
with any objects you wish to map. By selecting the cube along with the object you
wish to project coordinates onto, the software is forced to scale the projection
matrix to fi t the reference cube. If all of the objects in a scene have their UVs
projected in reference to the same reference cube, their coordinates will automati-
cally be the same scale. Some software allows for equivalent control by typing in
absolute dimensions for the mapping volume. For the purpose of explanation, the
cube is used here. In both cases, the principle is the same.
A reference cube should always be large enough to contain all objects that
must have proportionate texture coordinates. It may be larger than all your scene