Image recognition method and apparatus utilizing edge detection based on magnitudes of color vectors expressing color attributes of respective pixels of color image

A method of deriving for a selected pixel of a color image that is part of an array of pixels, for each of a plurality of predetermined edge directions, an edge strength value that corresponds to a specific one of a plurality of predetermined edge directions and is indicative of a degree of probability that said selected pixel is located on an edge between regions of respectively different color within said image, with said edge being oriented in said specific edge direction, the method comprising a set of steps performed for each of said edge directions of:

• expressing color attributes of each of said pixels of said color image as a plurality of scalar values representing a color vector within an orthogonal color space;
• obtaining a first weighted vector sum of a first set of pixels which are located adjacent to said selected pixel on one side thereof with respect to said specific edge direction and a second weighted vector sum of a second set of pixels which are located adjacent to said selected pixel on an opposite side from said first set with respect to said specific edge direction, and deriving the vector difference between said first and second weighted vector sums;
• and
• obtaining a modulus of said vector difference,
• and a step of judging the respective moduli thereby obtained respectively corresponding to said predetermined edge directions, to obtain said edge strength value as a largest one of said moduli.

An image recognition apparatus for processing image data of a color image which is represented as respective sets of color attribute data of an array of pixels, to successively operate on each of said pixels as an object pixel in order to determine whether said object pixel is located on an edge within said color image, and thereby derive shape data-expressing an edge image corresponding to said color image, the apparatus comprising:

• color vector generating means for expressing said sets ofcolor attribute data of each of said pixels as respective color vectors, with each said color vector in the form of an array of a plurality of scalar values which are coordinates of an orthogonal color space;
• edge template application means for generating a plurality of edge templates each formed of an array of respectively predetermined numeric values, with said edge templates corresponding to respective ones of a plurality of predetermined edge directions, thereby extracting an array of color vectors as respective color vectors of a sub-array of said pixels, with said sub-array of pixels being centered on said object pixel, and successively applying each of said edge templates to said array of color vectors in a predetermined array 5processing operation, to derive edge vectors respectively corresponding to said edge directions;
• edge pixel determining means for comparing the respective moduli of said derived edge vectors to obtain a value of edge strength for said object pixel, as a maximum value of modulus of said edge vectors, thereby obtaining a possible edge direction for said object pixel as a direction corresponding to an edge vector having said maximum:
• value of modulus, and for judging whether said object pixel is located on an actual edge that is oriented in said possible edge direction, based upon comparing said edge strength of said object pixel with respective values of edge strength derived for pixels disposed adjacent to said object pixel.