Identification of military targets and simple laboratory test patterns in band-limited noise

摘要

We investigate the effect of band-limited masking noise and blur on the minimum contrast required to identify a) military targets, b) the standard MRTD and MTDP four-bar test pattern and c) the TOD equilateral triangle test pattern. First, the image containing the test object was spatially blurred by an amount varying from one pixel up to the maximum blur at which the object could still be identified or resolved. This mimics the effect of sensor optics and detector blur on the image of a target at different ranges. Then, band-limited noise was added to the image. The center spatial frequency f_c of the masking noise was varied over 7.0 octaves. Observers had to indicate at which target contrast they were just able to identify the target. The results are a) identification thresholds for all targets are strongly elevated by masking noise of certain spatial wavelengths and much less by coarser or finer noise, showing that identification by human observers is mediated by a relatively narrow visual filter, and b) with increasing blur, maximum masking shifts towards lower noise spatial frequencies in a consistent but non-linear way. Current popular TA models are inconsistent with these results but suggestions for improvement are presented. The laboratory test patterns are appropriate to characterize target acquisition performance with viewing systems that include noise and blur.