How to get spectrum of an image?

I have an image :

img = imread('pic.jpg');

Now, How can I get spectrum of that image?

Answer 1

[Image Analyst]

theSpectrum = fft2(img);

[Hamed]

Thank You but, I want to know what's happened in fft2() function. What is body of fft2() ?

[Image Analyst]

I took a full year on Fourier stuff in graduate school. If you don't know what a Fourier Transform is yet, then you'll have some studying up to do. Start here:

http://blogs.mathworks.com/steve/category/fourier-transforms/

http://www.mathworks.com/matlabcentral/fileexchange/28810-fourier-transform-demonstration/content/fourier_demo/html/fourier_demo.html

http://en.wikipedia.org/wiki/Fourier_transform#Functional_relationships

http://cns-alumni.bu.edu/~slehar/fourier/fourier.html