Photographic Assessment of Dark Spots in Night Vision Device Images

Abstract

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.