Method of accurately locating the fractional position of a template match point

An improved method of accurately determining a position of a given object on a two-dimensional grid having an x axis and a y axis within a field of view in a machine vision system, without the use of enhanced resolution apparatus, utilizing an improved method of calculating a sub-pixel maximum value, said sub-pixel maximum value calculation comprising the steps of:

• searching all grid points values on said two-dimensional grid and identifying a grid point having a maximum grid point value;
• considering all grid point values of all grid points neighboring said grid point having said maximum grid point value and selecting neighboring grid points on said x and Y axes having next highest grid point values;
• defining a quadrangle having four sides,
• a first side of said quadrangle having endpoints defined by said grid point having said maximum grid point value and said grid point on said x axis having said next highest grid point value,
• a second side of said quadrangle having endpoints defined by said grid point having said maximum grid point value and said grid point on said y axis having said next highest grid point value,
• a third side of said quadrangle having endpoints defined by said grid point having said next highest grid point value on said x axis and a grid point having an x value equal to an x value of said grid point having said next highest grid point value on said x axis and a y value equal to a y value of said grid point having a next highest grid point value on said y axis, and
• a fourth side of said quadrangle having endpoints defined by said grid point having said next highest grid point value on said y axis and a grid point having an y value equal to a y value of said grid point having said next highest grid point value on said y axis and an x value equal to an x value of said grid point having a next highest grid point value on said x axis;
• computing a one-dimensional, fractional maximum along each side of said quadrangle;
• computing a first line connecting said one-dimensional maxima computed on a first pair of opposite sides of said quadrangle and a second line connecting said one-dimensional maxima computed on a second pair of opposite sides of said quadrangle;
• and
• calculating a sub-pixel coordinate location for said sub-pixel maximum having an x coordinate and a y coordinate corresponding to an intersecting point of said first and said second lines.