Scaling Subjective Impressions of Quality

Abstract

To assure that the 600 dpi Heidelberg Digimaster 9110 Network Imaging System would deliver best-in-class image quality, extensive image measurement and assessment—including customer surveys and benchmarking—was conducted throughout the engineering and design phases. This process continues for every machine as it rolls through the final assembly area.A significant contributor to the Digimaster 9110's superior image quality was the development of meaningful image quality specifications and requirements. To develop these specifications, well-designed scaling surveys were of paramount importance. These surveys are the keystones to demonstrating the veracity of virtually all objective image quality measures. Unless an objective measure of quality can be carefully correlated with observers' subjective impressions of quality, the metric's usefulness is limited. That is, without establishing a correlation to visual quality, how is one to know if a new toner formulation, for example, produces a meaningful improvement in line sharpness? This paper discusses the relative utility of the four basic types of scales: nominal, ordinal, interval, and ratio. Methods for determining these scales are given along with fundamentals for designing single- and multiplestimulus scaling experiments. Specific examples are included showing how correlation with the subjective impression of quality was established for several metrics of black text image quality.