Apparatus and method for skew control of document images

A method of determining a predominant angle of orientation of an image with respect to a reference angle, characterized by the steps of

• generating a file of picture elements depicting the image with respect to the reference angle,
• iteratively computing the number of picture elements that are projected onto each of a plurality of contiguous segments of an imaginary line by projections of the picture elements onto the imaginary line at selected angles across the file, wherein each imaginary line is perpendicular to the direction of projection,
• applying an enhancement function to the segment counts of each projection, wherein the enhancement function increases in value faster than a linear function,
• selecting as the dominant angle of orientation of the image that projection angle which generates the largest value of the enhancement function.

Apparatus for determining a predominant angle of orientation of an image with respect to a reference angle, characterized by

• means for generating a file of picture elements depicting the image with respect to the reference angle,
• means for projecting the picture elements onto a plurality of contiguous segments of imaginary lines at selected angles across the file, wherein each imaginary line is perpendicular to its associated direction of projection,
• means for counting the number of picture elements that fall into the segments for each projection,
• means for applying an enhancement function to the segment counts of each projection, and
• means for selecting the projection that generates the largest value of the enhancement function.

Apparatus for determining a predominant angle of orientation of an image with respect to a reference angle, characterized by

• means for processing a file of information depicting the image in terms of picture elements with respect to the reference angle, wherein the means for processing includes
• means for iteratively computing the number of picture elements that are projected onto each of a plurality of contiguous segments of an imaginary line by projections of the picture elements onto the imaginary line at selected angles across the file, wherein each imaginary line is perpendicular to the direction of projection,
• means for calculating an enhancement function applied to the segment counts of each projection to form an enhanced distribution function for each projection, wherein the enhancement function increases in value faster than a linear function, and
• means for selecting as the dominant angle of orientation of the image that projection angle which generates the largest value of the enhancement function.