[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: Two-dimensional fft

From: Laurent Jacques
Subject: Re: Two-dimensional fft
Date: Fri, 13 Dec 2002 10:41:41 +0100
User-agent: KMail/1.4.3

On Friday 13 December 2002 05:28, Richard Morey wrote:
| How does one interpret the output from a two-dimensional fft? I
| understand the interpretation of the one-dimensional fft and fftshift,
| but how does one interpret the matrix of values from a two-dimensional
| fft?

1D FFT -> coefficients of the decomposition of a signal in a sum of 1D 
oscillatory functions (complex exponentials) each one specified by one 
scalar, the frequency.

2D FFT -> coefficients of the decomposition of an image in a sum of 2D 
oscillatory functions (complex exponentials) each speciefied by one vector, 
the frequency vector. Thus, the 2D FFT have to be a matrix.

1D FFTSHIFT -> turns the frequency domain [0 2pi/T[ (Where T is the sampling 
period) into the centered frequency domain [-pi/T pi/T[ by flipping the 
second half part of the vector with the first one.

2D FFTSHIFT -> turns the 2D frequency domain [0 2pi/T]*[0 2pi/T'] (where T and 
T' are respectively the sampling period according columns and rows) into the 
2D centered frequency domain [-pi/T pi/T[*[-pi/T' pi/T'[ by flipping the 
quadrans I and III, and II and IV of the matrix.

Hoping this help,


Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:
How to fund new projects:
Subscription information:

reply via email to

[Prev in Thread] Current Thread [Next in Thread]