of Microprocessors

CONTROL SEQUENCE DISPLAY AND EDITING 353
Bus-oriented computers using the S-lOO bus, Multibus (Intel), Versabus
and VME bus (Motorola), or Q-bus (DEC), have available plug-in raster
graphics display boards that can offer much higher resolutions than
integrated computers. A resolution of 640 X 400 is common and up to
1,280 X 1,024 is available with from 2 to 2 24 colors. Of course, costs can be
quite high, but such units have the resolution required for nearly any
conceivable musical application. For example, three-dimensional spectral
plots, which often look like mountain ranges, need high display resolution to
be useful. Likewise, a conventional score editor benefits greatly from
resolution high enough to permit seeing an entire page of music rather than
just one line at a time.
Color
As with home televisions, color is expected on home computer displays
and, in fact, most connect to color TV sets. A color television, even an
expensive one, makes a very poor computet display because the three color
signals are multiplexed onto one 4-MHz band-limited video signal. The result
is that the displayable (as opposed to addressable) color resolution is often no
better than 100 pixels across the screen due to blurring. Add to that artifacts
of the multiplexing process, such as ghosts and "worms" at sharp edges in the
ima~e, and the result is a very unpleasant display to watch at close range. The
better personal computers provide separate red-b1ue-green color signals to
'Specialized monitors, which gives a much more satisfactory image.
With current color picture tube technology, there are still substantial
defects that make color displays tiring to use for long periods. One of these is
poor convergence, in which the three color images do not perfectly line up,
an effect often seen in the Sunday comics. For example, when white
characters are shown against a dark background, obvious color fringes are
seen around the edges, or in extreme cases, entire characters may be a
rainbow of color. Another problem is moire patterns of "beating" between the
tube's color dot or stripe pattern and individual display pixels. Very expensive
color monitors (upward of $2,000) can minimize these problems by using a
more precise "sectorized" convergence system and fine pitch shadow masks
that may have dot or stripe density up to three times that of entertainment
grade monitors.
Perhaps the best way to appreciate the clarity difference between
monochrome and color displays is to compare them side-by-side showing the
same image. The higher the resolution of the display generator, the more
dramatic the difference is. Monochrome images can be enhanced in many
ways, such as providing gray scale and rippling dashed lines, to highlight
parts of images. If the resolution is high enough, an almost endless vatiety of
shading patterns can be used when gray scale is not available. Apple
Maclntosh software uses this technique extensively.