Previous foveal/peripheral display systems have typically combined the foveal and peripheral views optically, in a single eye, in order to provide simultaneously both high resolution and wide field of view from a limited number of pixels. While quite effective, this approach can lead to cumbersome optical designs that are not well suited to head-mounted displays. A simpler approach may be possible in the form of a dichoptic vision system, wherein each eye receives a different field of view (FOV) of the same scene, at different resolutions. One eye would be presented with highresolution narrow-FOV foveal imagery, while the other would receive a much wider peripheral FOV. Binocular overlap in the central region would provide some degree of stereoscopic depth perception. It remains to be determined, however, if such a system would be acceptable to users, or if binocular rivalry or other adverse side-effects would degrade visual task performance compared to conventional head-mounted binocular displays. In this paper, we describe a preliminary dichoptic foveal/peripheral vision system and suggest methods by which its usability and performance can be assessed. This effort was funded by the U.S. Air Force Research Laboratory Human Performance Wing under SBIR Topic AF093-018.

In order for night vision goggles (NVGs) to be effective in aircraft operations, it is necessary for the cockpit lighting and displays to be NVG compatible. It has been assumed that the cockpit lighting is compatible with NVGs if the radiance values are compliant with the limits listed in Mil-L-85762A and Mil-Std-3009. However, these documents also describe a NVG-lighting compatibility field test procedure that is based on visual acuity. The objective of the study described in this paper was to determine how reliable and precise the visual acuity-based (VAB) field evaluation method is and compare it to a VAB method that employs less expensive equipment. In addition, an alternative, objective method of evaluating compatibility of the cockpit lighting was investigated. An inexpensive cockpit lighting simulator was devised to investigate two different interference conditions and six different radiance levels per condition. This paper describes the results, which indicate the objective method, based on light output of the NVGs, is more precise and reliable than the visual acuity-based method. Precision and reliability were assessed based on a probability of rejection (of the lighting system) function approach that was developed specifically for this study.

While vast numbers of image enhancing algorithms have already been developed, the majority of these algorithms have not been assessed in terms of their visual performance-enhancing effects using militarily relevant scenarios. The goal of this research was to develop a visual performance-based assessment methodology and apply it to assess three Retinex algorithms. The image enhancing algorithms used in this study are the two algorithms described in Funt, Ciurea, and McCann as McCann99 Retinex and Frankle-McCann Retinex, and the multiscale Retinex with color restoration (MSRCR) algorithm. This paper discusses the methodology developed to acquire objective human visual performance data as a means of evaluating various image enhancement algorithms. The basic approach is to determine whether or not standard objective performance metrics, such as response time and error rate, are improved when viewing the enhanced images versus the baseline, non-enhanced images. Four observers completed a visual search task using a spatial-forced-choice paradigm. Observers had to search images for a target (a military vehicle) hidden among foliage and then indicate in which quadrant of the screen the target was located. Response time and percent correct were measured for each observer. Future directions and the viability of this technique are also discussed.

When night vision goggle (NVG) image intensifier tubes ((ITs)-Ts-2) are replaced during maintenance, the output luminances of the two channels must not exceed a ratio of 1.5 (brighter channel luminance divided by the dimmer channel luminance) in order to meet the current allowed binocular luminance disparity specification. Two studies were performed to investigate the validity of this requirement. The first study estimated thresholds of binocular luminance disparity detection for observers looking through NVGs. For eight observers, the 25% corrected-for-chance probability of detecting an ocular luminance difference, yielded an average ratio of 1.43 indicating that the current 1.5 specification is perhaps too loose. The second study investigated the Pulfrich phenomenon, a pseudo-stereo effect that can be induced by presenting luminance imbalances to the eyes. This study created NVG luminance imbalances using neutral density (ND) filters and then investigated whether or not the various imbalance levels were sufficient to cause the Pulfrich phenomenon to be perceived. Results indicated an imbalance ratio of 1.10 was insufficient to cause the effect to be seen, but a ratio of 1.26 was sufficient (p less than or equal to 0.0003) for the effect to be seen, at least part of the time. Based on these results, it is apparent the allowed binocular luminance disparity ratio should probably be tightened to at least 1.3 with a goal of 1.2.

Visual performance through night-vision devices (NVDs) is a function of many parameters such as target contrast, objective and eyepiece lens focus, signal/noise of the image intensifier tube, quality of the image intensifier, night-vision goggle (NVG) gain, and NVG output luminance to the eye. The NVG output luminance depends on the NVG sensitive radiance emitted (or reflected) from the visual acuity target (usually a vision testing chart). The primary topic of this paper is the standardization (or lack thereof) of the radiance levels used for NVG visual acuity testing. The visual acuity chart light level might be determined in either photometric (luminance) units or radiometric (radiance) units. The light levels are often described as “starlight,” “quarter moon,” or “optimum” light levels and may not actually provide any quantitative photometric or radiometric information. While these terms may be useful to pilots and the users of night-vision devices, they are inadequate for accurate visual performance testing. This is because there is no widely accepted agreement in the night vision community as to the radiance or luminance level of the target that corresponds to the various named light levels. This paper examines the range of values for “starlight,” “quarter moon,” and “optimum” light commonly used by the night vision community and referenced in the literature. The impact on performance testing of variations in target luminance/radiance levels is also examined. Arguments for standardizing on NVG-weighted radiometric units for testing night-vision devices instead of photometric units are presented. In addition, the differences between theoretical weighted radiance and actual weighted radiance are also discussed.

Light scattered from helmet visors and aerospace transparencies is known to reduce visual performance. One popular measurement technique, maintained by the American Society for Testing and Materials, is ASTM D 1003. It is a standard procedure used to measure haze inherent in transparent materials, which is defined as the percent of the total transmitted light that is scattered. However, research has shown that visual acuity measured through several different types of helmet visors does not correlate well with visor haze. This is most likely due to the fact that the amount of light scattered from a transparent material depends heavily on the light illuminating the transparency and on the viewing geometry, behavior that ASTM D 1003 does not characterized. Scattered light causes transparent parts to appear luminescent and imparts a veiling luminance when superimposed over a target, reducing target contrast and inducing a visual performance loss. This paper describes an experiment in which threshold target background luminance, the luminance at which a target was barely visible, was measured for a number of observers viewing a Landolt C target through several levels of veiling luminance. Threshold luminance was examined for predictable behavior with respect to veiling luminance.

There are several parameters that are used to characterize the quality of a night vision goggle (NVG) such as resolution, gain, field-of-view, visual acuity, etc. One of the primary parameters is visual acuity or resolution of the NVG. These two terms are often used interchangeably primarily because of the measurement methods employed. The objectives of this paper are to present: (1) an argument as to why NVG visual acuity and resolution should be considered as distinctly different parameters, (2) descriptions of different methods of measuring visual acuity and resolution, and (3) the results of a blind test by several agencies to measure the resolution of the same two NVGs (four oculars).

This paper examines the light transmission, absorption, reflection, and scattering characteristics of military helmet visors used for see-through helmet-mounted displays (HMDs). HMDs used for the within-visual-range (WVR) counter-air mission normally use the inner surface of the helmet visor to reflect the HMD image to the pilot's eye. This approach is popular because it minimizes any optical structures that interfere with the pilot's vision, while also maximizing see-through to the ambient scene. In most cases, a reflective coating, which increases the cost of the helmet visor significantly, must be applied to the inner surfaces in order to achieve enough contrast between the HMD image and the external light passing through the visor. Recently, with the development of high luminance miniature cathode-ray-tubes (CRTs), it has been possible to eliminate the reflective coatings on neutral density helmet visors having a see-through range of 13-35%. This paper examines the light management properties of both types of visors. The paper stresses measurement techniques that produce repeatable results and what these results might imply about visual performance under operational lighting conditions.

Modem fighter aircraft windscreens and canopies are typically made of curved, transparent plastic for improved aero-dynamics and bird-strike protection. Since they are curved these transparencies often refract light in such a way that a pilot looking through the transparency will see a target in a location other than where it really is. This effect has been known for many years and methods to correct the aircraft head-up display (HUD) for these angular deviations have been developed and employed. The same problem occurs for helmet-mounted display/trackers (HMD/Ts) used for target acquisition. However, in this case, the pilot can look through any part of the transparency instead of being constrained to just the forward section as in the case of the HUD and his/her head position can be anywhere in a rather large motion box.To explore the magnitude of these aiming errors several F-15, F-16, F-18, and F-22 transparency systems were measured from a total of 12 different eye positions centered around the HMD Eye (the HMD Eye was defined to be a point 1.25 inches to the right of the aircraft Design Eye). The collection of eye points for assessing HMT/D aiming accuracy were: HMD Eye, 3 inches left and right of HMD Eye, 2 inches above HMD Eye, and 2 inches forward of HMD Eye plus all combinations of these. Results from these measurements along with recommendations regarding means of assessing "goodness" of correction algorithms are presented.

The amount of scattered light, or haze, typically increases as transparent materials age, wear, become dirty, or become scratched from cleaning. Light scattered from scratched aircraft transparencies, such as windscreen, head-up-display combiners, and helmet visors, can potentially reduce pilot visual performance and reduce target detection range. Presented in this paper are the results of an investigation of light scattered from transparencies exhibiting different levels of wear and surface damage. Two methods of measuring scattered light are compared. Visual performance under conditions of white light scatter relevant to the use of helmet-mounted displays in the cockpit is also examined.

Use of night vision goggles (NVGs) for military applications has grown steadily over the past 30 years. Each successive NVG model represents some kind of improvement in terms of size, weight, ruggedness, gain, noise, spectral sensitivity, field-of-view or resolution. The primary focus of this paper is the determination of NVG resolution. Many methods have been devised to measure the resolving power of NVGs and each method has with it an associated variance or accuracy of measurement. This variance is most likely caused by several sources including observer visual capability (since most methods involve visual observations and judgement to assess NVG resolution). The main purpose of this paper is to present the different methods that have been used to assess NVG resolution and to determine to what extent observer visual capability limits the accuracy of NVG resolution measurement. This study uses a methodology that measures an observerOs psychometric function when viewing through NVGs (percent correct detection as a function of spatial separation) to determine their visual acuity using probit analysis.

Visible defects in night vision device (NVD) images, arising from image intensifier (I 2 ) tube defects and dirt on the deviceOs optics, can become more than cosmetic blemishes. They can act as visual distractions and may be large enough to mask critical information pilots need to conduct normal night vision operations. This paper is concerned with the assessment of NVD dark spots. Current methods of assessing dark spots examine only the image intensifier tube, ignoring spots due to dirt and dust introduced during night vision device assembly. Current methods are limited in the size of spot that can be counted and do not address the issue of spot contrast. This paper discusses a photographic method for classifying, locating, and counting dark spots in an assembled night vision device. Also documented in this paper is an experiment to determine an observerOs ability to classify round dark spots, conducted as part of an effort to determine the accuracy of the photographic test procedure. To quantify the defects, they were classified by size and then counted. Inspectors used a comparison key as an aid in categorizing dots by size. The defect specification should not exceed the classifiers' visual discrimination capabilities. This study directly examined the dot size classification performance of observers using dots of 3, 4, and 6 minutes of arc (MOA) in diameter.

Night vision goggles (NVGs) are used for night flying in many military aircraft in the US Army, Navy, and Air Force. NVGs are seen as a means of improving flying safety by providing aircrew with a direct view of the outside world scene thereby improving situation awareness. However, NVGs cannot operate effectively in a cockpit environment unless the interior lighting is NVG compatible. NVG compatible means the lighting is sufficient for the aircrew to view their instruments with their unaided vision but the lighting does not interfere with the NVG's view of the outside world. There are several ways to achieve NVG compatibility by using plastic and glass filters, and by changing light sources to eliminate near infra-red light from the cockpit. One less desirable technique for achieving NVG compatible lighting is to use chemical lightsticks to flood-light the cockpit instrumentation. This paper presents a number of issues associated with using "chemsticks" as a means of achieving NVG compatibility including spectral effects, temporal effects, and temperature effects. It is concluded that chemsticks are marginal as a means of achieving NVG compatibility. Also, if they are used, then pilots and associated support personnel need to be informed of the chemstick's limitations and characteristics to assure safe NVG flight operations.

Abstract : There are several ASTM Standards that address light transmissivity through transparencies (ASTM Standards F 1316-90D and 1003-61) in the visible spectrum (400 through 700 nm). However, night vision goggles (NVGs) are now being used in aircraft and other applications (e.g., marine navigation, surveillance, personnel carriers) with increasing frequency. These devices amplify both visible and near-infrared (NIR) spectral energy. A transparency may have excellent visible transmissive characteristics but could have poor NIR transmissivity. Overall visual performance (acuity) can be degraded if the observer uses the NVGs while looking through a transparency that has attenuated transmissivity in the NIR region (Pinkus and Task, 1997, see Appendix A). ASTM P94-02, Standard Test Method for Measuring Night Vision Goggle-Weighted Transmissivity of Transparent Materials (see draft in Appendix B) addresses this issue.

Night vision goggles (NVGs) are currently used in a wide variety of military aircraft that were not originally designed for NVGs. Likewise, the windscreens and canopies on these aircraft were not designed with NVGs in mind. Present day windscreens and canopies typically have one or more specialized coatings applied to them. These may be reasonably transparent for visible wavelengths but not so transparent for near infrared light to which the NVGs are sensitive. It was hypothesized that the major mechanism by which aircraft transparencies affect the operation of NVGs is through reduced light levels. This would mean that the key characteristic of interest for determining the effect of an aircraft transparency on the operation of the NVGs would be its transmission coefficient calculated using the spectral sensitivity of the NVGs. This hypothesis was tested by investigating visual acuity performance of trained observers viewing through NVGs for three levels of ambient illumination (1, 2 and 5 times starlight) and three levels of NVG-weighted windscreen transmissivities (58, 76 and 100%). In addition two levels of contrast were included in the study (20 and 70% modulation contrast). Three trained observers determined the orientation of a Landolt C using a two-alternative, forced-choice step paradigm. A luminance-based model was developed to smoothly combine the effects of illumination level and transmission level for each contrast thus supporting the hypothesis. In addition the results demonstrate the significant difference between individual observer's performance level and the increased difficulty, (higher variability) of performance at lower contrast levels.

Modern fighter aircraft windscreens are typically made of curved, transparent plastic for improved aero-dynamics and bird-strike protection. Since they are curved these transparencies often refract light in such a way that a pilot looking through the transparency will see a target in a location other than where it really is. This effect has been known for many years and methods to correct the aircraft head-up display (HUD) for these angular deviations have been developed and employed. The same problem will occur for helmet-mounted displays (HMDs) used for target acquisition only worse due to the fact the pilot can look through any part of the transparency instead of being constrained to just the forward section as in the case of the HUD. To determine the potential impact of these windscreen refraction errors two F-15 windscreens were measured; one acrylic and one multilayer acrylic and polycarbonate laminate. The average aiming error measured for the acrylic was 3.6 milliradians with a maximum error of 9.0 milliradians. The laminated windscreen was slightly worse at 4.1 milliradians average error and 10.5 milliradians maximum. These aiming errors were greatly reduced by employing correction algorithms which could be applied to the aiming information on the HMD. Subtleties of coordinate systems and roll correction are also addressed.

A device is described which is capable of doing dynamic spatial filtering. The filter, which can be changed at TV frame rates, utilizes a liquid crystal light valve (LCLV) in a controlled-reflectivity mode. A filter pattern can be generated by a CRT or by other optical methods and imaged onto the LCLV. The LCLV is placed in the Fourier plane of an optical transform system. The dynamic spatial filter is described in detail, and current experimental results are given.

: Television display systems are currently widely used for many image transmission applications other than home entertainment. For many military and commercial uses the quality of the displayed imagery is critical with respect to its effect on observer performance. This dissertation investigates 19 figures of merit (FOM's) that have been proposed as measures of television image quality. Target detection and target recognition study was implemented to determine which of the 19 FOM's correlated highest with performance. The study employed a 525 line, 60 Hz field rate television display system with 2:1 interlace of fields. Nine different display quality conditions were investigated using all combinations of three contrast ratios (50:1, 50:5 and 50:15) and three video bandwidths (6.0 MHz, 1.0 MHz, and 0.4 MHz). Noise was not varied. Three FOM's stood out as promising indicators of display quality and observer performance. The highest correlating FOM was the log band-limited modulation transfer function area (log BLMTFA) closely followed by the just-noticeable difference area-log (JNDA-log), 1/2 cpd and the JNDA-log, 2 cpd.