Feature extraction of edge by directional computation of gray-scale variation

The process of edge detection and feature extraction methods is based on converting a change of gray level between two regions of an image into a variation function that gives the difference between the gray level of each region and the gray level of the line of discontinuity. The process of computing the relative difference yields the magnitude, direction, and slope sign of the magnitude, which in turn characterize the features of an edge. By focusing on the relative variation of gray level for pixels between small regions, the filtering process of the local region identifies and smoothes uncorrelated features for a truer edge than is possible by smoothing a larger region