Helmet-Mounted Displays: - USAARL - The - U.S. Army

Optical Performance 129
Figure 5.9. Representative model output for a CRT
display using P28 phosphor (70-msec
persistence) and having a vertical frame
rate of 33 msec (Rash and
Becher,1983).
msec is typical. This value is defined by the pixel access time (relatively
short, ~65 �sec), crystal’s response speed, and other LCD physical
properties such as the dependence of cell capacitance on drive voltage and
temperature (Bitzakidis, 1994; Leroux, 1989).
In a similar fashion to CRT phosphor response, the slow transition
between luminance values will degrade modulation transfer in dynamic
images on AMLCDs. Consider the example of a black vertical bar moving
across a white background where the luminance changes are completed
after addressing the pixels twice (Bitzakidis, 1994). The display pixels can
be categorized as:
a) Background pixels, which remain white for two fields.
b) Overlap-area pixels between the presentations of the bar at different
fields, which remain black for two fields.
c) Pixels which change from white to black (the leading edge of the
bar).
d) Pixels which change from black to white (the trailing edge of the
bar).