A simple criterion is proposed for the selection of contour points from a hierarchy of filter responses. The operators are the first derivatives of 2-dimensional Gaussians with different widths whose positive and negative parts are separately normalized to +1 and -1, respectively. The responses of the convolution of this 2-dimensional gradient operator with a gray value picture are vectors whose magnitudes and phases give useful information about differences of mean gray values across contours, and about the exact direction of the maximal intensity changes. Closed chains of contour points define regions whose gray values can be reconstructed approximately from the attributes of contour points. The regions of the segmented pictures are appropriate features which facilitate the matching process with scene models.