How to convert an image to frequency domain in MATLAB?

I did it with this below code.

r=imread('C:\Users\Nayana22\Desktop\k.jpg');
figure,imshow(r)
F=fft2(r);
S=fftshift(log(1+abs(F)));
figure,imshow(S,[])

The output of second figure is full blank white page. Please can u tell me what's mistake with this code?

My MATLAB version is R2012a.

Thank u

Answer 1

[Image Analyst]

r is not an RGB image is it? Verify and run this and tell me what it says

[rows, columns, numberOfColorChannels] = size(r)

I know this works for the RGB demo image because I convert it to grayscale:

grayImage = imread('peppers.png');
% Get the dimensions of the image.  
% numberOfColorBands should be = 1.
[rows, columns, numberOfColorBands] = size(grayImage);
if numberOfColorBands > 1
  % It's not really gray scale like we expected - it's color.
  % Convert it to gray scale by taking only the green channel.
  grayImage = grayImage(:, :, 2); % Take green channel.
end
% Display the original gray scale image.
subplot(2, 1, 1);
imshow(grayImage, []);
fontSize = 20;
title('Original Grayscale Image', 'FontSize', fontSize, 'Interpreter', 'None');

% Set up figure properties:
% Enlarge figure to full screen.
set(gcf, 'Units', 'Normalized', 'OuterPosition', [0 0 1 1]);
% Get rid of tool bar and pulldown menus that are along top of figure.
set(gcf, 'Toolbar', 'none', 'Menu', 'none');
% Give a name to the title bar.
set(gcf, 'Name', 'Demo by ImageAnalyst', 'NumberTitle', 'Off') 

% Display the original gray scale image.
subplot(2, 1, 2);
F=fft2(grayImage);
S=fftshift(log(1+abs(F)));
imshow(S,[]);
title('Spectrum Image', 'FontSize', fontSize, 'Interpreter', 'None');

[Nayana Hammini]

its absolutely working.. thank u so much

[roni zidane]

Hi @Image analyst,

How will i reconstruct my filtered freqency domain image data to original image after using the following code..

F=fft2(grayImage);
S=fftshift(log(1+abs(F)));
W = wiener2(S);   % filter a gray image by 3x3 neighbourhood in freq domain.
% now i want to get a resulting filtered gray image
% which steps to follow?
FiltImg = ...      % how do i convert the freq domain to spacial/time domain?

[Seyed Amirreza Kabodian]

why do you do this?

--> S=fftshift(log(1+abs(F)));

is that any reason for this ?