At present, in theory, manufacturers' design criteria are used to evaluate the image quality of copiers when they are shipped. In fact, however, designers of these familiar devices are not completely aware of the images that users want,and outgoing inspections tend to be conducted on the basis of experience and judgement. In the first report in this series an image was prepared as a basis for evaluation, over 1000 copies of it were collected from different manufacturers'monochrome copiers in the field, and a unit space was constructed from the copies that users judged to be good. In the second report, the unit space constructed in the first report was reconsidered, and a unit space with greater discriminatory power was successfully constructed by improving the precision of the signal levels. In the present study, the feasibility of evaluating color copies by using this unit space was studied. A sample color copy judged to be good was established as a reference point, and the Mahalanobis distance from the reference point was calculated. It was confirmed that a unit space of monochrome images can be used to evaluate color images.
