Polar-radii graphs: a geometric-invariant, shape-based approach to handwritten character recognition

The problem of variability in handwriting due to geometric distortion of letters by scale, location and rotation is addressed using the polar-radii graph (PRG) scheme. The PRG of a handwritten character is a functional representation that can be used to describe and regenerate the character with accuracy. It shows the relationship between the relative distances from the character´s centroid to points along the outer boundary of the character image as a function of angle. A handwriting recognizer was developed using PRGs as features and was tested using both single and double character handwriting obtained from 500 different writers. The handwritten texts are limited to at most two characters that may or may not be connected. They can be any of the 52 upper and lower case characters of the English alphabet. The test for 26,000 single handwritten characters yielded a recognition rate of 90.22%. The test for 1,500 double characters yielded a recognition rate of 87.08%.