| Phase Unwrapping algorithm in IDL [message #20446] |
Thu, 22 June 2000 00:00  |
Richard Tyc
Messages: 69
Registered: June 1999
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Member |
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Would anyone have a 2D phase image unwrapping algorithm they would be
willing to share ? (an algorithm which corrects for phase spillover on
images which may only contain data between 0 and 2PI but in fact the data
has a larger range which gets wrapped into the 0 -> 2PI range)
If not in IDL, one in C or Fortran would also help.
Thanks in Advance
Richard Tyc
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| Re: phase unwrapping [message #26689 is a reply to message #20446] |
Tue, 18 September 2001 11:36  |
Clay Kirkendall
Messages: 5
Registered: August 2001
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Junior Member |
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Alexander Rauscher wrote:
> hi everybody
>
> i need a phase unwrapping algorithm (MRI, buti think it doenst really
> matter what type of data it is. does anyone have experience with
> this? it turnded out to be quite a tough problem...
> alex
Alex,
Here is a routine that I have been using for several years without
problems.
It defaults to 2pi phase resets but by using thresh and step it will
correct
for any step size. Depending on your data you may need to manually set
thresh and
step.
Good luck,
Clay
Function unwrap, x, thresh, step
;
; This routine removes resets from data vectors that have a
;modulus reset of size step. The data record is scanned for
;|resets| > |thresh| and adjusts the x by multiples of step
;
;
;
;MODIFICATIONS: 2/99 - added defaults for thresh and step
; 000831 - let x be an array
;
if n_params() eq 1 then $
Begin
thresh = !pi * 1.5
step = 2 * !pi
EndIf
sx=size(x)
if sx(0) EQ 0 then $
BEGIN
print, 'X must be a vector for this routine'
return, NaN
ENDIF
if sx[0] EQ 2 then $ ;Input is a two dimensional array
Begin
lx = length(x)
;get the derivative
dt=x(*, 0:lx-2) - x(*, 1:lx-1)
;search for steps greater then thresh
ddt=float(dt ge thresh) - (dt le (-thresh))
iddt=[ [replicate(0.0, sx[1])], [total(ddt, 2,
/CUMULATIVE)] ] * step
return, x + iddt
EndIf Else $
Begin
lx = max(sx(1:sx(0)), dim)
;get the derivative
dt=x(0:lx-2) - x(1:lx-1)
;search for steps greater then thresh
ddt=(dt ge thresh)*1. - (dt le (-thresh))
iddt=[0, total(ddt, /CUMULATIVE)] * step
return, x + iddt
EndElse
END
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| Re: phase unwrapping [message #26710 is a reply to message #20446] |
Fri, 14 September 2001 11:37 |
Craig Markwardt
Messages: 1869
Registered: November 1996
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Senior Member |
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Alexander Rauscher <e9121161@stud4.tuwien.ac.at> writes:
>
> i need a phase unwrapping algorithm (MRI, buti think it doenst really
> matter what type of data it is. does anyone have experience with
> this? it turnded out to be quite a tough problem...
> alex
Hi Alexander--
Answers to these questions have been discussed by "R. G. S.", Robert
Weiss, and Nando Ivarone in the past year and a half. The first two
posters provided actual code. I have provided some message id's
below.
For some reason Google Groups has discarded the actual code from these
posts, but you can still find it at my newsgroup archive, using this
search query:
http://cow.physics.wisc.edu/cgi-bin/msearch?keyall=phase+unw rapping
Craig
Message-Id: fL4F4.16761$1g1.495467@den-news1.rmi.net
Message-Id: 3953658A.EB723200@mpia-hd.mpg.de
Message-Id: 3A80F590.95C94E2A@acsys.it
--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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