This document summarizes a seminar topic on edge linking presented under the guidance of Dr. Suresha M. It was submitted by student Shashikala V. Edge linking is used to group edge points detected by edge detection algorithms into meaningful boundaries. There are two types of edge linking: local processing which analyzes pixel neighborhoods, and global processing using the Hough transform which is tolerant of gaps and noise. The Hough transform maps edge points in image space to curves in parameter space to identify linear features like lines.

1. SEMINAR TOPIC ON
EDGE LINKING
UNDER THE GUIDANCE BY
Dr. SURESHA M
Associate Professor
Dept.Of.MCA
Kuvempu University
Jnana sahyadri
Shanakargatta
Submitted by
Shashikala v
Reg no: PS202537
3rd sem Mca
Dept.Of.MCA
Kuvempu university
Jnana sahyadri
ShankargattaM

2. Edge linking
 Used to group the edge points that are detected using edge
detection algorithms.
 Set of pixels from edge detecting algorithms, seldom define
a boundary completely because of noise, breaks in the
boundary etc. Therefore, Edge detecting algorithms are
typically followed by linking and other detection
procedures, designed to assemble edge pixels into
meaningful boundaries.
 2 types of edge linking
 local processing
 global processing

3. Local processing
 One of the simplest approches for linking edge ponts is to
an analyze the characteristics of pixels in a small
neighbourhood (say 3x3, or 5x5 )abou every point (x,y) in
an image that has been labeled an edge point.
 All points that are similar according to set of predefined
criteria are linked,forming an edge of pixels that those
criteria.
 The two principal properties used for establishing
similarity of edge pixels
 Strength of the response of the gradient operator used to
produce the edge pixel
 The direction of the gradient vector.

6. Global processing using Hough Transform
 Hough transform is most commonly used for the detection
of regular curves such as lines,circles,ellipses ,etc
 The main advantage of the hough transform technique is
that it is tolerant of gaps in feature boundary descriptions
and is relatively unaffected by image noise.
 It maps a straight line y=mx+c in a Cartesian coordinate
system into a single point in the (ρ,θ) plane or ρ=xcos
θ+ysin θ For a point (x,y) in the Cartesian coordinate plane
, there will be an infinite number of curves in the (ρ,θ)
plane

9. Edge linking using Hough transform
 Compute the gradient of an image and threshold it to
obtain a binary image.
 Specify subdivision in the p0(theta) plane.
 Examine the counts of the accumulator cells for high
pixels concemtrations.
 Examine the relationship (for continuity)between
pixels in a chosen cell.

11. Thank you….