Form similarity via Levenshtein distance between ortho-filtered logarithmic ruling-gap ratios

Geometric invariants are combined with edit distance to compare the ruling configuration of noisy filled-out forms. It is shown that gap-ratios used as features capture most of the ruling information of even low-resolution and poorly scanned form images, and that the edit distance is tolerant of missed and spurious rulings. No preprocessing is required and the potentially time-consuming string operations are performed on a sparse representation of the detected rulings. Based on edit distance, 158 Arabic forms are classified into 15 groups with 89% accuracy. Since the method was developed for an application that precludes public dissemination of the data, it is illustrated on public-domain death certificates.