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

The SQRI is given by
Figure 5.8. MTFA.
Optical Performance 127
Equation 5.15
where M(u) is the MTF of the display, M t(u) is the visual contrast threshold
curve, and u is spatial frequency per unit angle at the eye of the observer.
The integration extends over the range from 0 to maximum spatial
frequency. As with the MTFA, this equation takes into consideration the
spatial frequency description of the display and the human visual system.
Good agreement has been found between the SQRI and subjective measures
of image quality (Barten, 1993, 1991; Westerink & Roufs, 1989).
What has not been emphasized so far is that most MTF curves
encountered are static MTFs, i.e., the modulation in the scene is not
changing. However, while static targets relative to the ground do exist on
the battlefield, in the aviation environment, relative motion obviously is the
more prevalent condition. In addition to the relative target-aircraft motion,
when VCSs are used, sensor gimbal jitter and head motion are present.
When motion is present, the temporal characteristics of the scene
modulation interact with those of the imaging system (e.g., scan rate and
phosphor persistence for CRTs) and the transfer of modulation from the
scene to the final display image can be degraded.
Phosphor persistence is an important display parameter affecting
temporal response in CRT displays. Excessive persistence reduces