The legibility of HMD symbology as a function of background local contrast

As the Army increases its reliance upon helmet mounted displays (HMD), it is paramount that HMDs are developed that meet the operational needs of the warfighter. In see-through HMDs, symbology is overlaid or added to the see-through background. For the symbology to be seen and understood, the symbology must have sufficient contrast to stand-out from the background and be clearly recognized. In an earlier paper, we showed that the quality of see-through symbology was greatly influenced by the complexity of natural backgrounds. Complexity was characterized by the standard deviation of small patches (patches subtending about 1.5°). A better assessment of scene complexity as a function of local contrast is required for the development of HMD luminance specifications. Here we evaluate the small patch luminance and complexity of natural scenes in an attempt to quantify the luminance requirements for HMDs.