Gradient vector flow
Gradient Vector Flow
Chenyang Xu, Silicon Valley Future Academy
Jerry L. Prince, Johns Hopkins University
Synonyms: GVF
Gradient vector flow is the vector field that is produced by a process that smooths and diffuses an input vector field, and is usually used to create a vector field that points to object edges from a distance.
Background
Finding objects or homogeneous regions in images is a process known as
image segmentation. In many applications, the locations of object edges can be
estimated using local operators that yield a new image called an edge map. The
edge map can then be used to guide a deformable model, sometimes called an
active contour or a snake, so that it passes through the edge map in a smooth
way, therefore defining the object itself.
A common way to encourage a deformable model to move toward the edge
map is to take the spatial gradient of the edge map, yielding a vector field.
Since the edge map has its highest intensities directly on the edge and drops to
zero away from the edge, these gradient vectors provide directions for the active
contour to move. When the gradient vectors are zero, the active contour will not
move, and this is the correct behavior when the contour rests on the peak of the
edge map itself. However, because the edge itself is defined by local operators,
these gradient vectors will also be zero far away from the edge and therefore the
active contour will not move toward the edge when initialized far away from the
edge.