Edge enhancement method and apparatus for dot matrix devices

Apparatus for enhancing the output of a print or display device which produces a digitized image in dot matrix format, comprising:

• means for generating a set of gradient masks each of which represents a plurality of edge segment transition conditions and includes a matrix of axb cells each cell of which is assigned a numerical weight corresponding to the relative lightness or darkness of the corresponding pixel of an image having an edge segment passing through a center pixel of the matrix;
• means for generating a bit data signal including a plurality of data bits representative on a pixel by pixel basis of a bit map image to be printed or displayed;
• storage means for temporarily storing a predetermined number of consecutive bits in a predetermined number of consecutive lines of said bit map image;
• means for selecting subsets of said bits forming a sample matrix of axb bits, the central bit of each sample matrix being a candidate for modification;
• means for convolving each said sample matrix with each said gradient mask to detect those sample matrix having an edge segment passing through their central bit, said edge segment being defined as a series of adjacent aligned data bits of the same data state forming a straight line having a single slope, and to determine the direction of a gradient change;
• means for generating a set of reference bit patterns each of which includes a sub-pattern of bits corresponding to one possible combination of bits of the same data state aligned in one or more edge segments, said pattern including an axb matrix of bits, a first predetermined number of bits disposed adjacent one side of said matrix, and a second predetermined number of bits disposed adjacent another side of said matrix;
• means for comparing each said sample matrix having an edge segment passing through its central bit, a predetermined number of adjacent previously evaluated bits, and a predetermined number of adjacent yet to be evaluated bits to each pattern of at least a sub-set of said set of reference bit patterns;
• means for generating, for each match found to a reference pattern including a predetermined type of segment transition, a modification signal for modifying the central bit of said sample matrix dependent upon the type of transition detected;
• and
• means responsive to said modification signal for causing the print or display apparatus to develop a corresponding output.