Character thinning apparatus

Claim 1

Character rewriting apparatus for use in recognizing binarized characters made up of points on a matrix of regular rows and columns, comprising: machine means for applying a compound operator in predetermined cycles to each point of the binarized character on a first matrix, said compound operator having an operative center surrounded by a sub-matrix of points defining an operative area fitting said first matrix; and machine means for rewriting, in each one of said predetermined cycles ones of said character points to which said compound operator is applied into corresponding positions on a second matrix in accordance with a predetermined compound test criterion applied by said compound operator, said compound operator comprising a set of operators, each operator of said set being applied to all of the four orientations in which said operator fits said first matrix, each operator being adapted to apply, in each of said four orientations, a predetermined binary logic function, for each one of said operators, to the binary values of the character points found in coincidence with the sub-matrix points, said compound test criterion being defined so that a character point at the operative center is omitted by said machine means on second matrix if any one of the binary logic functions so applied is satisfied, wherein a binary logic function being satisfied is defined as when those points in the operator defined herein as black or as white are all in coincidence with character points or background points respectively; each operator of said set of operators having sides of three operator points parallel to said rows and columns, said compound operator comprising: (a) all operators of a first kind having at least two but not more than five black points forming a chain of adjacent black points occupying not more than two adjacent sides of the operator, and (b) all operators of a second kind having at least five but not more than seven black points forming a chain of adjacent black points occupying three sides of the operator, all remaining points in the operators of both kinds being white, and the operators of the second kind having an additional external adjacent black point when applied in at least two of the adjacent orientations in which said operator sub-matrix fits said matrix points, said additional black point being located on the center of the side remote from the side having a central white point.