Edge Detection

Within an image, the boundary between two regions with different pixel values is called an edge. An edge has a magnitude which is related to the difference in pixel values for pixels on either side of the edge. The following figure shows an edge.

A pixel in an image that lies on an edge in the image is called an edge pixel. The process of determining which pixels in an image are edge pixels is called edge detection.

In order to be considered to be an edge pixel by CNLSearch, a pixel must be one of a group of connected pixels where the average difference in pixel values between the regions on either side of the edge is greater than an edge threshold that you can specify.

The following figure shows an idealized representation of an edge along with a graph showing the edge peak.

The only information contained in images that have undergone nonlinear brightness changes that does not change as a result of the brightness changes is the location of edges within the image. The following figure shows how the edge peak occurs in the same location despite a nonlinear change in brightness between the images.