Edge detection

An edge in an image is a boundary or contour at which a significant change occurs in some physical aspect of an image, such as the surface reflectance, illumination or the distances of the visible surfaces from the viewer. Changes in physical aspects manifest themselves in a variety of ways, including changes in intensity, color, and texture.

Detecting edges is very useful in a no of contexts. For example in a typical image understanding task such as object identification, an essential step is to segment an image into different regions corresponded to different objects in the scene. Edge detection is the 1 st step in image segmentation.

Another example, is in the development of a low bit rate image coding system in which we can code only edges. It is well known that an image that consists of only edges is highly intelligible. The significance of a physical change in an image depends on the application. An intensity change that would be classified as an edge in some application might not be considered an edge in other application.

In object identification system, an object's boundaries may be sufficient for identify and contours that represent additional details within the object may not be considered edges. An edge cannot be defined outside of the context of an application.