Visual CRT sharpness estimation using a fiducial marker set

A visual estimation technique has been developed to quickly, yet quantitatively, determine the sharpness quality of CRT displays. While high-resolution camera measurement equipment accurately characterizes display sharpness, the equipment cost is high and the measurements are time consuming to perform. Previously reported visual sharpness assessment techniques are either qualitative or the quantitative measures do not possess adequate sensitivity. The rating scheme investigated in this study provides a practical solution for tracking monitor sharpness in a clinical environment. The target consists of a high frequency, high contrast pattern with an embedded, magnified fiducial marker set based upon a Gaussian model for the CRT spot. The magnification of the marker set allows the reference to remain nearly invariant to the actual sharpness of the display. In this study, three commercially available diagnostic displays were evaluated, each at two luminance levels and seven static focus settings. High-resolution CCD camera measurements were acquired for each display and setting combination. The visual sharpness estimate target was then displayed and scored by observers. High correlation was found between the visual ratings and the photometric measurements. More importantly, the sensitivity of the target produced observer ratings, which distinguish between the measured CRT spot sizes at different focus levels.