Fourier Transform Computer Vision Textbook
Thats funny,  I was exactly trying to fill the same gap.
I found the several sites which helped me

this is one of them : 
http://homepages.inf.ed.ac.uk/rbf/HIPR2/fourier.htm

Moreover , I recommend on creating a black image and playing with it.

e.g.

black = false(500,500);
black(10:40:end,:) = true;
black = imrotate(black , 45 , 'crop');
ffim = fftshift ( abs ( fft2 ( black ) ) );
lffim = log ( ffim ) ;
fs(lffim,[]);