One of the major problems in scene analysis is segmentation of a scene. In this paper a particular gray-level based segmentation technique is used to partition one particular scene. The same scene is then segmented into the material classes that comprise it by using the explicit information about the existing materials. A comparison of the two sets of results is made. A set of probabilities of detection based on various information about material boundaries is then derived. This set quantifies the limitations of gray-level based segmentation schemes in detecting the material boundaries, and can be used as a measure for comparing various segmentation techniques.