| looking for 2D FFT code? [message #7661] |
Tue, 17 December 1996 00:00  |
jyli
Messages: 21
Registered: November 1995
|
Junior Member |
|
|
Hi,
I am looking for a piece of IDL code that does FFT on an image with M
rows and N colums.
I can't seem to be able to find a 2D FFT routine from IDL library.
I am very surprised.
cheers
--
============================================================ ============
Jason Y. Li | Tel : (301) 286-1029
Code 913 | Fax : (301) 286-1759
NASA Goddard Space Flight Center | www : http://climate.gsfc.nasa.gov
Greenbelt, MD 20771, USA | email: jyli@climate.gsfc.nasa.gov
============================================================ ============
Beauty of style, harmony, grace and good rhythm depend on simplicity.
|
|
|
|
| Re: looking for 2D FFT code? [message #7730 is a reply to message #7661] |
Fri, 20 December 1996 00:00  |
davidf
Messages: 2866
Registered: September 1996
|
Senior Member |
|
|
William Ryu <wsryu@fas2.fas.harvard.edu >writes:
> [Question about 2D FFTs omitted.]
>
> This question comes up again and again. Maybe it is time for a
> "Getting started with IDL" FAQ?
I've added a tip on doing frequency domain image filtering and
viewing the power specturm to my IDL Programming web page.
David
-----------------------------------------------------------
David Fanning, Ph.D.
Fanning Software Consulting
2642 Bradbury Court, Fort Collins, CO 80521
Phone: 970-221-0438 Fax: 970-221-4762
E-Mail: davidf@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com
-----------------------------------------------------------
|
|
|
|
| Re: looking for 2D FFT code? [message #7734 is a reply to message #7661] |
Fri, 20 December 1996 00:00 |
jyli
Messages: 21
Registered: November 1995
|
Junior Member |
|
|
William Ryu (wsryu@fas2.fas.harvard.edu) wrote:
: While it isn't obvious from the help file, IDL's fft() function will
: do multi-dimensional ffts ("The result returned by FFT is a complex
: array that has the same dimensions as the input array.").
With the help of RSI engineers, I think I have found the answer to my
problem.
In the beginning, I fed a test image into FFT and the resulting power
spectrum was not what I expected. Well now I know it is because the way
IDL stores positive and negative frequency components in the FFT
complex arrays, one needs to do a shift operation before displaying the
spectrum. And now Page 1-280 in the IDL reference manual seems to make
a lot sense.
Thanks for those who have responded.
happy holidays and happy IDL programming !
--
============================================================ ============
Jason Y. Li | Tel : (301) 286-1029
Code 913 | Fax : (301) 286-1759
NASA Goddard Space Flight Center | www : http://climate.gsfc.nasa.gov
Greenbelt, MD 20771, USA | email: jyli@climate.gsfc.nasa.gov
============================================================ ============
Beauty of style, harmony, grace and good rhythm depend on simplicity.
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
