Abstract. When color is implemented in helmet-mounted displays (HMDs) that are eyes-out, see-through displays, visual perception issues become an increased concern. A major confound with HMDs is their inherent see-through (transparent) property. The result is color in the displayed image that combines with color from the outside (or in-cockpit) world, producing an image with additive color. As luminance of the HMD imagery is reduced, the color separation between the HMD imagery and the background is also reduced. It is because of this additive effect that luminance contrast is so vitally important in developing HMD standards for color symbology. As a result, this paper identifies luminance requirements for full-color HMDs based upon two lines of investigation. The first is based on a study of white symbology against natural static backgrounds, where the quality of symbology was judged to be a function of not only the background luminance but also of the background complexity as well. The second is based on an evaluation of the complexity inherent in natural backgrounds and from this investigation, a predictive curve was found that describes the complexity of natural backgrounds as a function of ambient luminance. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.[DOI: 10.1117/1.OE.56.5.051404] Keywords: luminance; helmet-mounted display; head-up display; color vision; human factors; scene complexity; symbology; natural backgrounds.Paper 161505SSP received Sep. 26, 2016; accepted for publication Jan. 11, 2017; published online Jan. 31, 2017.
IntroductionFor symbology to be viewed in a see-through helmetmounted display (HMD) or head-up display (HUD), the luminance of the symbology must be sufficient to distinguish it from the see-through background. This is true whether or not symbology is displayed on a monochromatic or full-color display. When the contrast of the transparent symbology is sufficiently high, the symbology appears as an overlay on the ambient scene. In order for an HMD or HUD to be usable in an operational environment, the luminance requirements must take into consideration the type of displayed imagery (e.g., symbology, situational maps, target sights), the tasks (e.g., targeting, navigation, obstacle avoidance), the operational setting (e.g., day/night, terrain features), additional hardware (e.g., visors, windscreens, laser protection), and other considerations. For a color HMD, symbology color overlaid on an ambient scene should consider luminance and color contrast, which requires information about the spectral content of the landscape or ambient scene. However, optical designers must consider all terrain features when designing a see-through optic as the military can be deployed to any geographical location around the globe; this fact may simplify the development of luminance requirements for see-through, fullcolor HMD...