On interpreting views of Fourier Transforms

[isoparix]

Question on Fourier transforms: 
  
If I take a simple rectangular bar image, 
<http://octave.1599824.n4.nabble.com/file/n4672032/rectangle_500x7.jpg> 
and engineer an FT via ImageAnalyser
(http://meesoft.logicnet.dk/Analyzer/index.htm), I get an FT 

<http://octave.1599824.n4.nabble.com/file/n4672032/classic_FFT_of_bar.png> 

that conforms to what I read in the literature.   See for instance,  page 15
of 
http://www.robots.ox.ac.uk/~az/lectures/ia/lect2.pdf
<http://www.robots.ox.ac.uk/~az/lectures/ia/lect2.pdf>  

Octave produces something very different.  

My question is, are we all talking at cross-purposes here?   I'm sure
Octave's understanding of FFT cannot be utterly different to everyone
else's.  And the Octave FFT certainly, using 'ifft', transforms exactly back
to the original image, *but* why doesn't Octave's FFT look like the FFT
produced by Image Analyser, or described in the Oxford lectures in the PDF,
or in other literature?

What am I misinterpreting?   Thank you.

To see what Octave does, try:

%Import image
origimage = imread('rectangle_500x7','jpg');
%Plot image
figure, imagesc(origimage)
axis square
colormap gray
title('Original Image')
%Perform 2D FFT
fftimage = fft2(double(origimage));
%Display Image of FFT
figure, imagesc(abs(fftimage))
axis square
title('FFT of Image')
colormap gray
set(gca, 'XTick', [], 'YTick', [])
%Perform Inverse 2D FFT
backimage = ifft2(fftimage);
%Display Image of FFT
figure, imagesc(abs(backimage))
axis square
title('Inverse FFT')
colormap gray
set(gca, 'XTick', [], 'YTick', [])



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