Matlab DFT demonstration

We did a demonstration of fft2 function of MATLAB.

clear

clc

Irgb = imread('bricks.png');

% figure,imshow(Irgb)

Id = rgb2gray(Irgb);

Ig = rgb2gray(Irgb);

% figure,imshow(Ig)

Id = im2double(Ig);

figure,imshow(Id)

figure,imshow(Id(1:2:end,1:2:end))

figure,imshow(Id(1:3:end,1:3:end))

%figure,imshow(Id)

figure,imshow(Id(1:10:end,1:10:end))

%figure,imshow(Id)

%Lets create an synthetic image

%This part is taken from the pdf (I will provide it on the blog)

x = linspace(-pi, pi, 201);

% If you pass meshgrid only one vector, it uses that vector for both the x

% and the y coordinates.

[xx,yy] = meshgrid(x);

A = 10;

Icircles = sin(A*(xx.^2 + yy.^2));

% End of synthetic image creation

figure,imshow(Icircles)

figure,imshow(Icircles(1:3:end,1:3:end))

%imshow(Icircles)

Fcircles = fftshift(abs(fft2(Icircles)));

figure,imshow(Fcircles)

figure,imshow(Fcircles,[0,200])

FcirclesShifted = fftshift(fft2(Icircles));

%imshow(abs(Fcircles),[0,200])

size(Fcircles)

LowPassRectangle = zeros(size(Fcircles));

LowPassRectangle(69:132,69:132) = 1;

imshow(LowPassRectangle)

%imshow(LowPassRectangle.*Fcircles)

imshow(LowPassRectangle.*Fcircles,[0,200])

FcirclesLow = LowPassRectangle.*FcirclesShifted;

figure,imshow(abs(FcirclesLow),[0,200])

%IcirclesLow = ifft2(fftshift(FcirclesLow));

IcirclesLow = abs(ifft2(fftshift(FcirclesLow)));

figure,imshow(IcirclesLow)

figure,imshow(Icircles(1:3:end,1:3:end))

figure,imshow(IcirclesLow(1:3:end,1:3:end))

figure,imshow(IcirclesLow(1:2:end,1:2:end))

figure,imshow(Icircles(1:2:end,1:2:end))

Iparrot = im2double(imread('parrotsGrayscale.jpg'));

figure,imshow(Iparrot)

figure,imshow(Iparrot(1:5:end,1:5:end))

Fparrot = fft2(Iparrot);

%figure, imshow(abs(fftshift(Fparrot)))

figure, imshow(abs(fftshift(Fparrot)),[0,200])

LowPassRectangle = zeros(size(Fparrot));

%LowPassRectangle(342:382,221:258)=1;

%figure,imshow(LowPassRectangle)

%figure, imshow(abs(fftshift(Fparrot)),[0,200])

%figure,imshow(LowPassRectangle)

LowPassRectangle = zeros(size(Fparrot));

LowPassRectangle(221:257,342:382)=1;

figure,imshow(LowPassRectangle)

figure,imshow(abs(LowPassRectangle.*fftshift(Fparrot)),[0,200])

IparrotLow = abs(ifft2(fftshift(LowPassRectangle.*fftshift(Fparrot))));

figure,imshow(IparrotLow)

figure,imshow(IparrotLow(1:5:end,1:5:end))

Warning: Image is too big to fit on screen; displaying at 50%

ans =

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