Hand shape contour tracking method based on directional gradient extremum

Hand contours are hard to be extracted correctly when hand images are illuminated by a unsymmetrical light. Therefore, this paper proposes a contour tracking algorithm based on the directional maximal gradient value according to the characteristic that values of edge pixels turn sharply in the vertical direction of an edge. The algorithm firstly finds the starting point of hand contour, then depending on some searching rules, it calculates the gradient values of candidate points in a local region, chooses the point whose gradient value is maximal in the candidate set of local region and tracks it point by point to get the final contour. Tracking experiments are carried out on both the hand image database formed by ourselves and the HandImage database from Hong Kong University of Science and Technology(HKUST). Experimental results indicate that the accuracy of contour tracking is 100% in ourselves' database, and 85.8% in the database from HKUST. Moreover, the accuracy of contour tracking in the images eligible to our refined condition from HKUST database is 99.4%. These data show that the algorithm can directly track out the accurate, consecutive and integral hand contour in gray-level picture and it is suitable especially for the contour extraction of hand images affected by the unsymmetrical illumination.