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

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Optical Performance 103 luminance domain encompasses those display parameters identified with the overall sensitivity of the user to illumination levels. The temporal domain addresses display parameters associated with the observer’s sensitivity to changing levels of light intensity. [Baron (1994) adds two additional domains: Depth (3D) and noise.] Table 5.2. FPD FOMs. Spatial Spectral Luminance Temporal Pixel resolution (HxV) Pixel size and shape Pixel pitch Subpixel configuration Number of defective (sub)pixels Spectral distribution Color gamut Chromaticity Peak luminance Luminance range Grey levels Contrast (ratio) Uniformity Viewing angle Reflectance ratio Halation Refresh rate Update rate Pixel on/off response rates In general, these FOMs can be used for image quality evaluation for HMDs since the final image is that of the source image modified by the transfer function of the relay optics. However, there are a few additional FOMs which relate to the system as a whole. The FOMs selected for discussion here are not all inclusive but represent the most critical ones needed to effectively evaluate image quality. However, even for simple HMDs, these FOMs can fail to allow a user to judge between two competitive designs which significantly differ in scope and function (Baron, 1994). In the following FOM discussions, the FOM will be developed in relationship to the overall HMD design. The interrelationship between FOMs will be discussed. In addition, the operational values of the FOM for the currently fielded ANVIS and IHADSS, and in- development HIDSS HMDs will be provided along with recommendations for minimum or maximum specifications.
104 Contrast Clarence E. Rash and William E. McLean Contrast refers to the difference in luminance between two (usually) adjacent areas. There is often confusion associated with this term due to the multiple FOMs used to express contrast (Klymenko et al., 1997). Contrast, contrast ratio, and modulation contrast are three of the more common formulations of luminance contrast. Further confusion may result from the terminology, because different names are used for the two luminances involved in the definitions. Sometimes the luminances are identified according to their relative values and, therefore, labeled as the maximum luminance (L max ) and minimum luminance (L min ). However, if the area at one luminance value is much smaller than the area at the second luminance, the luminance of the smaller area sometimes is referred to as the target luminance (L t), and the luminance of the larger area is referred to as the background luminance (L b). The more common mathematical expressions for luminance contrast include: C = (L t - L b) / L b for L t > L b (Contrast) Equation 5.1a = (L b - L t) / L b for L t < L b Equation 5.1b = (L max - L min) / L min = (L max / L min) - 1 Equation 5.1c C r = L t / L b for L t > L b (Contrast ratio) Equation 5.2a = L b / L t for L t < L b Equation 5.2b = Lmax / Lmin Equation 5.2c Cm and = (Lmax - Lmin ) / (Lmax + Lmin) (Modulation contrast) Equation 5.3a = | (L t - L b )| / (L t + L b) | Equation 5.3b In the preceding equations, modern conventions are adopted which preclude negative contrast values. [Classical work with the concept of contrast did not concern itself with which had the larger luminance value, the target or the background and, therefore, allowed negative contrast values (Blackwell and Blackwell, 1971); Blackwell, 1946.] The values for contrast as calculated by Equations 5.1a and 5.1c can range from 0 to � for
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Helmet-Mounted Displays: Design Iss
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The views, opinions, and/or finding
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vi Contents 4. Visual Coupling Clar
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viii Contents References ..........
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x Ben T. Mozo, Research Physicist U
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xii Foreword began its phenomenal e
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xiv Preface Acknowledgments The aut
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Introductory Overview 1 Clarence E.
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Introductory Overview 5 Figure 1.2.
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Introductory Overview 7 The trend f
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Introductory Overview 9
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Introductory Overview 11 aviator to
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Introductory Overview 13 1970's. Ta
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Introductory Overview 15 Image sour
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Introductory Overview 17
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Table 1.3. HMD performance figures-
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Introductory Overview 21 direct vie
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Introductory Overview 23 Figure 1.9
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Introductory Overview 25 Figure 1.1
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Introductory Overview 27 Ercoline,
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Introductory Overview 29 II, Procee
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Introductory Overview 31 Armstrong
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34 Clarence E. Rash, Melissa H. Led
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40 Liquid crystal Clarence E. Rash,
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Page 70 and 71: Optical Designs 3 William E. McLean
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Page 116: DESIGN ISSUES PART TWO
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154 Clarence E. Rash and William E.
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168 Number of SOG = � log (C r) /
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Visual Performance 6 William E. McL
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Visual Performance 171 observer is
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seen. Visual Performance 173 Figure
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Visual Performance 175 perception.
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Visual Performance 177 with monovis
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Visual Performance 179 individuals
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Visual Performance 181 0 to -5.25 d
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Visual Performance 183 Report No. 9
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Biodynamics 7 B. Joseph McEntire He
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Biodynamics 187 behavior of this de
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Figure 7.2. Head anatomical coordin
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Biodynamics 191
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Biodynamics 193 al., 1972), and man
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Biodynamics 195 Figure 7.5. Vertica
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Biodynamics 197 disability and fata
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Biodynamics 199 been fabricated int
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Biodynamics 201 Ty pic al acc ele r
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Biodynamics 203 exceed the mechanic
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Biodynamics 205 complexity and comp
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Type Reference helmet Foam in place
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Biodynamics 209 the fitting problem
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Biodynamics 211 adjustment buckle,
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Biodynamics 213 down. The helmet ma
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Biodynamics 215 Desert Shield/Deser
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Biodynamics 217 Donelson, S. M., an
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219 Fort Rucker, AL: U.S. Army Aero
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220 Ben T. Mozo Figure 8.1. Noise l
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222 Ben T. Mozo available in the ne
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224 Ben T. Mozo Protectors”(ANSI,
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226 Ben T. Mozo language. Tests of
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228 Ben T. Mozo Figure 8.6. Speech
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230 Ben T. Mozo the communications
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232 Ben T. Mozo Item Mass (grams) C
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Ribera, J. E., and Mozo, B. T. Unda
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236 Joseph R. Licina operational us
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238 Joseph R. Licina Standard MIL-S
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240 Joseph R. Licina On electro-opt
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242 Joseph R. Licina For HMDs with
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244 Joseph R. Licina 1994b) that wi
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246 Joseph R. Licina Table 9.2. Hea
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248 Joseph R. Licina provided a 93.
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250 Joseph R. Licina and buckles, a
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252 Joseph R. Licina authorized to
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254 Joseph R. Licina a nuclear flas
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256 Joseph R. Licina requirements:
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HMD PERFORMANCE ASSESSMENT PART THR
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262 Clarence E. Rash, John C. Mora,
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Glossary 11
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270 making stereoposis possible. Bi
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272 John C. Mora and M elissa H. Le
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NOTES ON CONTRIBUTORS Melissa H. Le
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Notes on Contributors 281 Research
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284 Index Breakaway force (see Fran
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286 Index movement, 55, 80, 84, 90,
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288 Index 198, 204, 205, 208, 210,
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290 Index Microphone, 15, 186, 224,
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292 Index Speech intelligibility (S
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