The evaluation of radiographs must be considered with preference given to not only the observer to the physical factors as well. In the study, optimal density was discussed using sensory tests and statistics. The rank of optical merit was determined by nine radiotechnologists using eight radiographs of the skull phantom. First, the order of distance was worked out between the ranking of the visual merit and each tentative virtual point. Second, the value of Spearman's correlation coefficient was calculated by using the ranking of visual merit and the order of distance and finally the distribution figure was drawn. According to these results, virtual density area was differnet from optimal density on the radiographs.
