  Contours are salient features for image description, but the detection and
localization of boundary contours is still considered a challenging problem.
This paper introduces a new tool for edge processing implementing the
Gestaltism idea of edge grouping. This tool is a mid-level image operator,
called the Torque operator, that is designed to help detect closed contours in
images. The torque operator takes as input the raw image and creates an image
map by computing from the image gradients within regions of multiple sizes a
measure of how well the edges are aligned to form closed convex contours.
Fundamental properties of the torque are explored and illustrated through
examples. Then it is applied in pure bottom-up processing in a variety of
applications, including edge detection, visual attention and segmentation and
experimentally demonstrated a useful tool that can improve existing techniques.
Finally, its extension as a more general grouping mechanism and application in
object recognition is discussed.
