Correlation of spot characteristics with perceived image quality

A project is described whose primary objective was to determine how much a spot must change in size on a projection CRT (cathode ray tube) before an observer could detect the change. This number is important in estimating the impact of CRT electron gun improvements on observed PTV (projection TV) performance. In order to quantify this subjective ability, the authors designed a focus survey experiment. The focus quality of a spot (i.e. spot size, shape, etc.) is significantly affected by focus voltage, therefore this measurable quantity becomes the numerical link between the subjective perception of the observer and a statistical analysis. The perceived spot size increment on a typical production 46-in projection TV having 330 TV lines of resolution by an average observer from a distance of 10 ft is PSSI₅₀=0.04 mm, PSSI₉₀=0.14 mm