視覚評価における検出能の観察距離依存性

抄録

The detection performance of human observers has been used widely in the evaluation of imaging systems. In observer performance experiments, the detectability is affected by various factors such as object size, viewing distance, illumination, selected observer, order of reading samples and so forth. For the viewing distance, there are two situations where firstly observers are allowed to choose a suitable viewing distance and secondly they are not allowed to do so and must use a fixed viewing distance. The purpose of this paper is to assess whether the detectability of observer performance experiments is dependent on the viewing distance. The contrast-detail (C-D) diagram described the relationship between the threshold contrast in visually detectable by a human observers and viewing distance (20-200cm) using four different radiographic systems. Our results indicated that detectability by detection performance increased when observers adopted a short viewing distance for small objects and long viewing distance for large objects. It is possible that the selected viewing distance changes the evaluation of screen/film systems. Therefore, it is better that the designer of the experiment does not institute the fixed viewing distance.