Perceptual image quality measures of VDUs tested in comparative multi-display experiments

The sensitivity of two perceptual image quality measures - comfort judgement and search velocity - was investigated in multi-display experiments in which commercially available terminal displays were evaluated. In a pilot study the influence of image polarity and near vision correction on these two measures was investigated for two subjects. For a constant value of the peak: luminance a better performance was found for dark characters on a bright background. Also, the effect of near vision correction was reflected by the performance measure. Using the same method in the main experiment, ten subjects evaluated eight terminal displays. Both quality measures were found to be sufficiently sensitive to discriminate the relatively small quality variations of the evaluated displays. However, the strength of the correlation between scaled comfort and performance was subject-dependent. From the subjects' reports we learned that the comfort differences between subjects are due to a subject-dependent weighing of a number of image quality parameters in the total judgement value. The effect of subjective comfort appearing to be less sensitive than search velocity is probably due to the summation of opposite effects.