🚀 go-pugleaf

> From: susanm@hp-and.an.hp.com (Susan Margulies)

>Basically, I am trying to come up with a way of visualizing the
>phase information as a function of position. ...

Hello!

    I was interested in the same problem, and have heard other people
mension that displaying the phase as colour was effective.

    I have tried this, and it can produce some very pretty pictures.
A good colour mapping seems to be

  0 degrees -> red
 90 degrees -> blue
180 degrees -> green
270 degrees -> yellow

    As well as producing pretty pictures, this mapping has some nice
perceptual properties: colours that are 180 degrees apart are also
complementary as far as the human visual system is concerned, because
colour information gets into the brain as a luminance, blue/yellow
balance and green/red balance (I think!).

    I've put a pretty picture generated by this method in the
anonymous ftp area on our machine here; the directory is
/anonymous@csis.dit.csiro.au:pub/fft , and the two files are fft.ras.Z
(an eight bit rasterfile with phase/amplitude colurmap) and
input.ras.Z, which was the input file used to generate the pretty
picture.

    Note that to actually produce the fft image here, it is actually
necessary to translate the input image so that its centre is on the
origin, not in the middle of the space; if you perform an fft on the
untranslated image, you get a phase modulation of 180 degrees per
pixel, which smears out the colours and makes them impossible to see.

    Unfortunately, the phase examined in this way in any real (as in
real-life) image looks like gobbledygook.

-peter
--
Peter Fletcher,            Internet : peterf@csis.dit.csiro.au
PhD Student                Physical : CSIRO Division of Information Technology,
Phone    : +61-6-2750914              ANU, Acton, Canberra ACT AUSTRALIA
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