The main objective of this paper is to study the performance of a Know
ledge-based Object REcognition system that Learns (KOREL). Other objec
tives of this paper include, firstly, identifying information about ed
ge-junction objects that is particularly useful in recognizing objects
in two-dimensional (2D) images. An edge-junction object is an object
that can be recognized by the arrangement of its junctions and by whet
her each edge is curved or straight. Secondly, this paper presents met
hods to acquire (learn) this information automatically and to use it i
n object recognition. Thirdly, whereas most previous systems aimed at
identifying one or a few target objects, the research reported here ad
dresses a more challenging problem, namely, recognizing any edge-junct
ion objects known to the system. The number of objects to be recognize
d might be large, their appearances in the images might be slightly di
fferent from those previously encountered, and they might be partially
occluded. KOREL represents characteristic views of a three-dimensiona
l (3D) object by models derived from 2D images. Three-dimensional obje
cts in a scene are then recognized by matching a 2D image of the scene
against object models. KOREL recognizes an object primarily by abstra
cting its structure, with representations of less comprehensive struct
ures indexing representations of more comprehensive structures. Exact
matching is not required, so occlusion and imperfect data are accommod
ated.