Information Technology Reference
In-Depth Information
for standard fonts, tables might be stored permanently within a
printer or display. In such cases, an image or text file would not
need to contain the font table at all, because the font table would al
ready be in the application that would be working with the file.
Only references to the font table would be needed for complete im
age processing.
Shape Tables: Generalizing on the idea of color and font tables,
one might store information about common shapes (e.g., circles,
rectangles, ovals, lines) in a table called a
shape table
. As with font
tables, collecting such shape information in one place saves little
space if an image uses each shape only once. However, if the same
shapes are used repeatedly in a picture, then use of a table allows
each shape to be defined just once, and each instance of the shape in
the picture can be indicated just by giving the table entry plus the lo
cation where the shape appears.
Shapes and Colors: When fonts or shapes are defined in tables,
it is possible to designate one color for each occurrence of a letter or
shape. If, for example, you want circles along a horizontal line in
your image to appear in the colors of the rainbow, you can refer to
both a shape table and a color table for each circle. As long as the
computer knows the location of each circle, it can fill in the rest of
the shape and color information by consulting the tables. This ap
proach requires rather little information to draw many geometric el
ements and, thus, potentially condenses your image's file size. In this
setting, a full recording of a letter or shape might involve the shape
(from a font or shape table), a location, and a color (either using
redgreenblue intensities or specifying an entry in a color table).
Drawing Commands: In describing the shape of an object in a
shape table, one approach is to store a pixelbypixel description of
the object. Although this can work well, such descriptions can re
quire considerable storage, and the shapes themselves may not scale
to a larger size very well. Thus, as an alternative approach, a picture
might instead be constructed by drawing it using basic commands,
just as an artist draws a picture or paints a scene using a pencil or
brush and some basic movements. For example, one could draw a
house by sketching various elements (walls, doors, windows),
adding color by instructing “this wall should be tan,” and so on.
Further, individual elements, such as a wall, door, or window, could
be drawn by starting at one place, moving up, then to the right, then
down, and then back to the start.
