Re: image 2-d Fouriertransform ?

*To*: mathgroup at smc.vnet.net*Subject*: [mg21902] Re: image 2-d Fouriertransform ?*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 4 Feb 2000 02:54:36 -0500 (EST)*Organization*: Universitaet Leipzig*References*: <87av1h$nun@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, the result of the 2d Fourier[] call is in the interval kx,ky \in [0,2Pi]. "Important" are the kx,ky with small absolute values , but with the periodic condition in kx and ky. So every quadrant in your image is important because a ki near 2Pi will map to a small ki in the periodic repeated area. You can use ShiftMatrix[m_?MatrixQ] := RotateLeft[RotateLeft[#, Length[#]/2] & /@ m, Length[m]/2] on your Fourier output. This shift the interval from ki \in [0,2Pi] to ki \in [-Pi,Pi] and all what is close to the center (the origin) of the image is important. Hope that helps Jens maurus wrote: > > Hello, > > sorry for this question but .. > > i have a 2-d image with 8 bit grey level. > Now i make a 2-d-Fouriertransform of the image (in Mathematica) > The result is a Picture with 4 quadrants, were the signals are > significant. > > Now my questions: > I think, only the first quadrant ist important ? Rest ist random ? > What does the axis, the results means ? > > If someone canl help me, i can send an example for better understanding. > > In this case, the Helpfunktion in Mathematica ist not to good. > > Thanks in advance > > Maurus