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

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Clarence E. Rash and William E. McLean
Farrell and Booth (1984) define image quality as the extent to which a
displayed image duplicates the information contained in the original scene
in a form suitable for viewing and interpreting. [It should be noted that
near-IR and IR images are not normally viewed images.] To the user,
image quality determines his ability to recognize and interpret information.
For our purpose, we shall confine our discussion to the system’s final
image, which is defined by the image source and display optics. Numerous
image quality FOMs have been developed and used to evaluate the physical
quality of the image produced on a display with the goal of gauging user
performance with the display. Task (1979) provides an excellent summary
of a number of FOMs which commonly are used for evaluating image
quality in CRTs. These are listed in Table 5.1, categorized as geometric,
electronic, and photometric.
Table 5.1.
CRT display system FOMs.
Geometric Electronic Photometric
Viewing distance
Display size
Aspect ratio
Number of scan lines
Interlace ratio
Scan line spacing
Linearity
Bandwidth
Dynamic range
Signal to noise ratio
Frame rate
Luminance
Grey shades
Contrast ratio
Halation
Ambient illuminance
Color
Resolution
Spot size and shape
MTF
Luminance uniformity
Gamma
FP technologies are being used as alternate HMD image sources.
Klymenko et al. (1997) have categorized FOMs for FPDs into four
domains: spatial, spectral, luminance, and temporal (Table 5.2). These
image domains parallel analogous human visual performance domains. The
spatial domain includes those display parameters associated with angular
view (subtense) of the user and coincide with the user’s visual acuity and
spatial sensitivity. The spectral domain consists of those parameters
associated with the user’s visual sensitivity to color (wavelength). The