🚀 go-pugleaf

In article <1992Aug6.111336.9896@waikato.ac.nz> singlis@waikato.ac.nz writes:

> How do you calculate the FFT of a 2-D image? I assume you calculate the FFT
> of the row/col of the element (pixel) you are working with.

The equation that describes the 2-D FFT is `separable', which means
that it can be decomposed into a series of 1-D FFTs.  In other words,
you FFT along all the rows, then FFT down all the columns.  (This is
not, however a very efficient way to do it!)  Most image processing
books go into this topic in a little detail.

> BUT how do they display this as an intensity diagram? An FFT creates a freq.
> breakdown, how do you display this as a single intensity???

The result of a FT is complex: for every pixel, there is a real part
and an imaginary part.  To display the FT, it is common (but by no
means universal) to convert the real-imaginary representation to
modulus-phase, and then display the modulus (or maybe modulus-square),
since this is what happens in real life (i.e., optics).  But don't
just discard the phase: the information it contains is at least as
important as that in the modulus!

--
 Dr Adrian F. Clark                                   JANET: alien@uk.ac.essex
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 Dept ESE, University of Essex, Wivenhoe Park, Colchester, Essex, C04 3SQ, UK.