Effects of Pixel Density on Softcopy Image Interpretability

Softcopy viewing systems have been used to display aerial imagery for over 20 years. CRT technology has dominated the market. However, imagery viewing requirements have not been a dominant force in the marketplace. The entertainment industry, the pre-press market, and office automation have generally been responsible for technology advances. More recently, the medical imaging community has helped to drive improvements in CRT technology. Among these improvements are ultra-high resolution monochrome monitors. In the past ten years, displays have moved from 512 by 512 pixel addressability at 50 pixels per inch (ppi) to 1200 by 1680 pixel addressability (100 ppi). In the past two years, displays with addressabilities of 2000 by 2560 (170 ppi) have come on the market. Although these five mega-pixel displays provide more data at higher resolution, there is a question as to how much of the data can be resolved by the human visual system. To address the benefits of improved CRT resolution, 100 and 170 ppi monitors were compared at varying magnification levels (and thus effective resolutions). Trained image analysts viewed imagery on the monitors and provided National Imagery Interpretability Rating Scale (NIIRS) ratings. They also viewed Briggs targets (checkerboard patterns at varying contrast and resolution levels) and provided ratings. Results indicate that interpretability is optimized at pixel densities on the order of 70-80 ppi.