Method of pattern positioning for automatic verification of seal imprint

Abstract

AbstractIn automatic computer verification of seal imprints accurate positioning of an examined seal imprint over a registered imprint is of great importance. This paper proposes a method which positions an examined seal imprint in relation to a parallel shift and rotation by using the centroid of its frame figure and the pixels on a circle of a certain radius from the centroid. Since this method achieves positioning by using local features of the examined seal imprint, rapid positioning is possible. In the presence of small defects in the imprint frame this method has the advantage that the centroid of the seal imprint is accurately obtained and is not affected by distortion of the imprint frame. In a positioning experiment based on this method 240 actual seal imprints were used. All imprints were positioned within a ±0.1‐mm parallel shift error and more than 99% of the seal imprints were positioned within ±1.76° rotation angle errors. A verification experiment was conducted using a seal imprint verification system which incorporated the principles of this method. As a result, the verification error which was caused by the positioning error was found to be 0.83%. The experimental results show that the proposed positioning method is efficient for automatic verification of seal imprints.