Correlation and image moment approaches to analyze the Glagolitic script carved in stone tablets

In relatively recent paleographic studies, a new type of the Glagolitic script, namely triangular type, was introduced as being older than the rounded type (commonly considered as the oldest known type) with possible mixing of letter types in the early period of Glagolitic writing. That hypothesis, drawn from the so-called generative model, has been lacking of a quantitative analysis. Here, we report on such an analysis in which the forms of the original letters carved in two among oldest stone tablets are compared to the models of the triangular and rounded letters. To calculate similarity measures, two different approaches were used. In the first approach, we use the standard correlator systems that are fast but sensitive to various letter deformations. The second approach, via calculating Fourier–Jacobi image moments, is rather slow but possesses invariance to input image deformations. To accelerate the entire recognition and classification process of the later approach, we introduced so-called sensitivity vector consisting of those moments that are robust to rotational and scale change deformations of input image. Although different in details, both approaches indicate presence of a mixture of both letter types supporting thus one of the hypothesis claims.