MATLAB TUTORIAL SEVEN

Edge Detection Methods for images using Matlab.

Perwitt Operator based Edge Detection of given image

clc;

clear all;

close all;

aa = imread('Arjundiscontinuity.JPG');

a = double(aa);

[row col] = size(a);

w1 = [-1 0 1;-1 0 1;-1 0 1];

w2 = [-1 -1 -1;0 0 0;1 1 1];

for x=2:1:size(a,1)-1;

    for y=2:1:size(a,2)-1;

a1=w1(1)*a(x-1,y-1)+w1(2)*a(x-1,y)+w1(3)*a(x-1,y+1)+w1(4)*a(x,y-1)+w1(5)*a(x,y)+w1(6)*a(x,y+1)+w1(7)*a(x+1,y-1)+w1(8)*a(x+1,y)+w1(9)*a(x+1,y+1);

size(a1);

a2=w2(1)*a(x-1,y-1)+w2(2)*a(x-1,y)+w2(3)*a(x-1,y+1)+w2(4)*a(x,y-1)+w2(5)*a(x,y)+w2(6)*a(x,y+1)+w2(7)*a(x+1,y-1)+w2(8)*a(x+1,y)+w2(9)*a(x+1,y+1);

size(a2);

    a11(x,y) = (a1);

    a12(x,y) = (a2);

    a3(x,y) = ((a1+a2));

    size(a3);

    end

end

Thresh=200;

a3=max(a3,Thresh);

a3(a3==round(Thresh))=0;

B1=uint8(a3);

a11=max(a11,Thresh);

a11(a11==round(Thresh))=0;

Bx1=uint8(a11);

a12=max(a12,Thresh);

a12(a12==round(Thresh))=0;

By1=uint8(a12);

subplot(2,2,1)

imshow(Bx1); title('Perwitt X direction gradient')

subplot(2,2,2)

imshow(By1); title('Perwitt Y direction gradient');

subplot(2,2,3)

imshow(a3); title('Perwitt Gradient image');

subplot(2,2,4)

imshow(~a3); title('Edge Detected Image');

Sobel Operator based Edge Detection of given image

clear all;

close all;

aa = imread('Arjundiscontinuity.JPG');

a = double(aa);

[row col] = size(a);

w2 = [-1 -2 -1;0 0 0;1 2 1];

w1 = [-1 0 1;-2 0 2;-1 0 1];

for x=2:1:size(a,1)-1;

    for y=2:1:size(a,2)-1;

a1=w1(1)*a(x-1,y-1)+w1(2)*a(x-1,y)+w1(3)*a(x-1,y+1)+w1(4)*a(x,y-1)+w1(5)*a(x,y)+w1(6)*a(x,y+1)+w1(7)*a(x+1,y-1)+w1(8)*a(x+1,y)+w1(9)*a(x+1,y+1);

size(a1);

a2=w2(1)*a(x-1,y-1)+w2(2)*a(x-1,y)+w2(3)*a(x-1,y+1)+w2(4)*a(x,y-1)+w2(5)*a(x,y)+w2(6)*a(x,y+1)+w2(7)*a(x+1,y-1)+w2(8)*a(x+1,y)+w2(9)*a(x+1,y+1);

size(a2);

    a11(x,y) = (a1);

    a12(x,y) = (a2);

    a3(x,y) = ((a1+a2));

    size(a3);

    end

end

Thresh=200;

a3=max(a3,Thresh);

a3(a3==round(Thresh))=0;

B1=uint8(a3);

a11=max(a11,Thresh);

a11(a11==round(Thresh))=0;

Bx1=uint8(a11);

a12=max(a12,Thresh)

a12(a12==round(Thresh))=0;

By1=uint8(a12);

subplot(2,2,1)

imshow(aa); title('Original Image')

subplot(2,2,2)

imshow(Bx1); title('Sobel X direction gradient');

subplot(2,2,3)

imshow(By1); title('Sobel Y direction gradient');

subplot(2,2,4)

imshow(a3); title('Sobel Gradient image');

Canny operator Comparison with Perwitt & Soble Operators based

Edge Detection using inbuit matlab commands :

I1 = imread('discontinuity.JPG');

I = rgb2gray(I1);

A1 = edge(I,'sobel')

A2 = edge(I,'prewitt');

A3 = edge(I,'canny');

figure

imshow(I); title('Original Image');

figure

imshow(A1); title('Sobel');

figure

imshow(A2); title('Perwitt');

figure

imshow(A3); title('canny');