Text quality metrics for visual display units .2. An experimental survey

This paper discusses several experiments aimed at evaluating the image quality of visual display units (VDUs). A number of quality metrics are presented, i.e. scaled preference, based on numerical ratings and paired comparisons; search velocity in a letter-search task; and two metrics derived from eye movement recordings. The former two metrics are found to be practical. The latter metrics, which are hard to determine, turn out to correspond with search velocity. With varying luminance contrast the scaled preference correlates closely with search velocity. With increasing resolution, however, this is true up to a moderate bandwidth, beyond which search velocity and the eye movement metrics saturate, while scaled preference continues to increase. Small quality differences across various commercially available VDUs are reflected by both search velocity and visual comfort. The results are consistent within subjects. Scaling differences across subjects can be understood by allowing for a subject-dependent weighting of underlying perceptual attributes like sharpness and brightness contrast. It is shown that visual comfort and performance are supplementary metrics that are both useful for modelling VDU image quality. (C) 1997 Elsevier Science B.V.