Sub-Pixel Edge Peak Detection
In addition to generating whole-pixel edge peak locations, the Edge tool can also determine the locations of edge peaks with sub-pixel accuracy. If you request sub-pixel edge peak locations, the Edge tool returns a list of edgelets. An edgelet is simply the sub-pixel location of the true edge peak associated with an edge pixel, along with the edge magnitude and angle.
An edgelet’s location is provided with sub-pixel accuracy in both the x- and y-direction, although the only meaningful sub-pixel information about an edge is the one-dimensional offset along a line perpendicular to the edge and passing through the center of the edge pixel, as shown in the figure below.
The collection of sub-pixel locations found in an input image are returned as an edgelet set, rather than an image. If the programming interface you are using supports transformations, the edgelet set also includes a transformation that lets you map edgelet points to the client coordinate system of the input image.