Question

MATLAB THEORY QUESTION

Write a detailed report about Edge detection, then sobel edge detector in Least squares fitting for linear line detection, explaining the MATLAB Functions to used.

Answer 1

Edge detection is an important task in image processing based applications. There are numerous cases where edges are required. For example, in every pattern recognition task, edges are required to get the shape perimeter and size estimation. Edges gives a separation between regions of different properties in an image like brightness, contrast, texture etc. Edge detection algorithms are primarily based upon the image intensity derivative. At edge points, there is sharp change in intensity as one enters from one region to other region. Normally when moving within the same region, the image intensity is constant and thereby, the image intensity derivative is also zero, however, when there is sudden rise in image intensity derivative, the edge point occurs. Edge detection gives about the shape information. There are different kernels that are used in image processing to detect the edges: These are:

• Canny Operator
• Prewitt Operator
• Roberts Operator
• Sobel Operator
• Laplacian Operator
• Logarithmic Operator

Sobel Operator

Sobel Operator is a 3x3 kernel used to extract the boundary of an object in binary image. The kernel is given by:

Sobel = [-1, -2, -1 ; 0, 0, 0 ; 1, 2, 1]

Matlab Code

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close all,

clear all,

clc,

ProjectPath = pwd;
ImagePath = strcat(ProjectPath,'\CameraMan.jpg');
Orig = imread(ImagePath);

Gray = rgb2gray(Orig);
subplot(2,4,1); imshow(Gray); title('Original Image');

BW = edge(Gray,'sobel');subplot(2,4,2); imshow(BW); title('Edge Detection using SOBEL');

BW = edge(Gray,'prewitt');subplot(2,4,3); imshow(BW); title('Edge Detection using PREITT');

BW = edge(Gray,'roberts');subplot(2,4,4); imshow(BW); title('Edge Detection using ROBERTS');

BW = edge(Gray,'log');subplot(2,4,5); imshow(BW); title('Edge Detection using LOG');

BW = edge(Gray,'zerocross');subplot(2,4,6); imshow(BW); title('Edge Detection using ZERO CROSS');

BW = edge(Gray,'canny');subplot(2,4,7); imshow(BW); title('Edge Detection using CANNY');

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Original Image Edge Detection using SOBEL Edge Detection using PREITT Edge Detection using ROBERTS Edge Detection using ZERO CROSS Edge Detection using CANNY Edge Detection using LOG