The Importance of Resolution in CG - An Introduction to Computer Graphics for Artists - page 92

Table 7.3 Bit-depth, resolution, and fi le size
Bit depth X resolution Y resolution Pixel resolution Size (KB)
1 128 128 16,384 2
2 128 128 16,384 4
4 128 128 16,384 8
8 128 128 16,384 16
16 128 128 16,384 33
24 128 128 16,384 49
32 128 128 16,384 66
64 128 128 16,384 131
Note: The Xbox 360 uses texture compression on maps. This partially compensates for using
32-bit maps for all textures

7.5 Bit Depth

The bit depth of a texture map infl uences its size in bytes, but not its resolution in
pixels. Bit depth is the number of bytes of data used to store each color. The lower
the bit depth, the smaller the number of colors represented in a single map. A one
bit map can contain two colors (black or white), a 2 bit map can represent 4 colors,
a 4-bit map can contain up to 16 colors, and so on. The Xbox 360 requires 32-bit
maps, which can represent millions of colors as well as a separate channel for 256
levels of transparency. High bit-depth images are used for extremely complex
maps, but they are also frequently used unnecessarily, when lower bit-depth maps
would do. Because the memory imprint of different bit-depth images can be orders
of magnitude different, it is prudent to determine what bit-depth is needed for
the texture in question before using a high bit-depth map. If, for instance, a 32 bit-
depth map is used to represent 16 colors, the majority of the bits in the image
are wasted. Unless your render platform requires a 32-bit texture, you may want to
use a lower bit depth map. Depending on the type of map, there may be no loss of
quality (Table 7.3 ).

7.6 Minimum Resolution

Two vertices are required to describe either end of a straight line. A fl at, unbroken
rectangular wall requires no more than four points. There are reasons why either
of these objects, the line or the wall might have more vertices, but these are the
minimums. You should get in the habit of always trying to answer the question,
“What is the minimum?” before proceeding on a project. Knowing the answer to
this question will help you decide what your resolution scale should be. The resolu-
tion scale defi nes the level of curve detail, structural detail that will or will not be
included, and which part types will be included in your model.