Active contour model with gradient directional information: Directional snake

Active contours or snakes are an effective edge-based method in segmenting an object of interest, However, the segmented boundary of a moving object in one video frame may lie far from the same moving object in the next frame due to its rapid motion, causing the snake to converge on the wrong edges. To guide the snake toward the appropriate edges, we have added gradient-directional information to the external image force to create a "directional snake." Thus, in minimizing the snake energy, the new method considers both the gradient strength and gradient direction of the image. Experimental results demonstrate that the directional snake can provide a better segmentation than the conventional method in certain situations, e.g., when there are multiple edge candidates in the neighborhood with different directions. The directional snake is significant because it provides a framework to incorporate directional information in digital video segmentation.