Automatic extraction of contour lines and feature points from profile images

The paper proposes a new extraction algorithm for contour lines and feature points from profile images for automatic personal identification. First the authors input a side view of a human head within a dark background under uniform lighting conditions by a CCD camera, then transform the input to a color difference signal image. After enhancing edges of the image using Sobel operators they binarize the luminance level of each pixel and portray a black profile in a white background. Next they differentiate the black profile, binarize the differentiated results, and depict a contour line using a thinning operator. Finally they encode the extracted contour line using Freeman's chain code and, using the encoded data, calculate the digital curvature in concave sections of the contour line and determine the concave feature points. Next they draw straight lines connecting the adjacent feature points and specify the convex feature points on the contour line which are farthest from the straight lines. They can obtain feature points of the profile automatically and reliably.