Abstract. We present an approach to figure/ground organization using mirror symmetry as a general purpose and biologically motivated prior. Psychophysical evidence suggests that the human visual system makes use of symmetry in producing three-dimensional (3-D) percepts of objects. 3-D symmetry aids in scene organization because (i) almost all objects exhibit symmetry, and (ii) configurations of objects are not likely to be symmetric unless they share some additional relationship. No general purpose approach is known for solving 3-D symmetry correspondence in two-dimensional (2-D) camera images, because few invariants exist. Therefore, we present a general purpose method for finding 3-D symmetry correspondence by pairing the problem with the two-view geometry of the binocular correspondence problem. Mirror symmetry is a spatially global property that is not likely to be lost in the spatially local noise of binocular depth maps. We tested our approach on a corpus of 180 images collected indoors with a stereo camera system. K -means clustering was used as a baseline for comparison. The informative nature of the symmetry prior makes it possible to cluster data without a priori knowledge of which objects may appear in the scene, and without knowing how many objects there are in the scene.  According to most studies of human vision, the first step in visual perception is determining whether there are objects in front of the observer: where they are and how many there are. This step (visual function) is called figure-ground organization (FGO). 1 The computer vision community refers to this problem as object discovery. As with all natural visual functions of human observers, FGO operates in three-dimensional (3-D) space, as opposed to the two-dimensional (2-D) retinal image. It follows that it is natural to think about visual mechanisms underlying FGO as based on 3-D operations. However, the fact that the input to the visual system is one or more 2-D retinal images encouraged previous researchers to look for a theory of FGO based on 2-D operations. This is how the human vision community studied FGO. Consider the prototypical example of Edgar Rubin's vase-faces stimulus. 2 In this 2-D stimulus, there are two possible interpretations depending on which region is perceived as a "figure" as opposed to the "ground." Similar bistable stimuli have been used during the last several dozen years of FGO research in human vision. 3,4 This research provided a large body of results, but few theories and computational models. Furthermore, the proposed models are usually not suitable for real retinal or camera images representing 3-D scenes. This paper breaks with this tradition and looks for 3-D operations that can establish the correct 3-D FGO.
In previous work, we investigated using mirror symmetry with two-view geometry to perform figure/ground organization REF .
Figure-ground organization based on three-dimensional symmetry
Journal of Electronic Imaging
Engineering Computer Science