Resolution
The pixels stored in computer memory, although they are derived from regions of
finite area in the original scene (see Sections 5.1 and 7.5), may be thought of
as mathematical points having no physical extent. When displayed, the space
between the points must be filled in. This generally happens as a result of the
finite spot size of a cathode-ray tube (CRT). The brightness profile of a CRT
spot is approximately Gaussian and the number of spots that can be resolved on
the display depends on the quality of the system. It is relatively
straightforward to obtain display systems with a resolution of 72 spots per
inch (28.3 spots per cm.) This number corresponds to standard printing
conventions. If printing is not a consideration then higher resolutions, in
excess of 30 spots per cm, are attainable.