New Techniques For Global And Detailed Shape Matching And Their Applications
Shape matching is an important problem and arises in many applications of image processing, pattern recognition, and computer vision. Shape matching problems in different applications usually have their own distinct characteristics and cannot be solved uniformly. In this dissertation, two new global matching techniques are proposed for registration of rotationally symmetric shapes, and two new iterative matching schemes are proposed for detailed shape matching. The applications of the proposed new matching schemes are also investigated. Due to the inapplicability of the definition of the conventional principal axis to rotationally symmetric shapes high-order principal axes are first defined to specify the orientations of rotationally symmetric shapes. An analytic formula like that for conventional principal axis, in terms of high-order momeut functions is derived for computing the directions of high-order principal axes. Alternatively, the concept of fold-expanded shape is proposed for computing the directions of rotationally symmetric shapes. A fold-expanded shape is generated by expanding one fold of a rotationally symmetric shape to the full angle span of 2n. After computing the conventional principal axis of a fold-expanded shape, the fold priucipal axis is then defined accordingly to specify the orientation of the rotationally symmetric shape. The application of these new global matching techniques for recognition and detection of rotationally symmetric shapes is performed and good results have been obtained. As for detailed shape matching, the proposed new iterative matching schemes are based on the premise of one-to-one or many-to-one mapping as well as the mutually-best match strategy for deciding correspondences. Two iterative procedures, one no-discrete and the other discrete type, for updating similarity measures between feature entities is developed. Siinila.r entities in a shape are considered to compete with one another for their best matches during the iterations. As a result, useful information can be derived from the competition to update the match link strengths so that the interference among the feature entities is reduced. By updating the match link strengths iteratively, the match relationships will reach a stable stale finally. The discrete type of iterative matching scheme is suitable for inherent simpler iiiatcliiiig problems. These ma.tching schemes are compared with the well-known relaxation matching technique and several advantages over the latter are identified. The proposed new iterative matching schemes are general matching techniques, and can be applied to solve any matching problem provided that the assumption of one-to-one or one- to-zero match mapping is appropriate. In this dissertation study, they are applied to three appliications, namely, stereo line segment correspondence, and off-line and on-line handwrit- ten Chinese character recognition. In stereo line segment correspondence, geometric con- straints are derived for pruning impossible matches of line segments. Simple line segment attributes, including lengths, orientations, and locations, are used to define a similarity mea- sure function. With the initial similarity measures, the first proposed iterative matching scheme is applied to find correspondences. In the off-line Chinese character recognition application, a stroke-segment similarity measure function, like that for stereo line segmentcorrespondence, is defined first, and the first proposed iterative matching scheme is againapplied to determine the stroke-segment correspondences. Based on the similarity values oftlie stroke-segment correspondences as well as the structural relationships among the corre-spondences, a character similarity measure is defined In the on-line character recognition, tlieproposed discrete type of matching scheme is used to guarantee real-time responses. Withthe initial similarity measures, defined by simple attributes of line segments such as lengths,orientations and locations, the proposed discrete iterative matching scheme is applied tofind the correspondences. Experimental results show that the proposed itcrative matchingschemes are effective and produce good matching results in these applications.
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