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Aide Scilab >> Traitement du Signal > fft2

fft2

two-dimension fast Fourier transform

Calling Sequence

y=fft2(x)
y=fft2(x,n,m)

Arguments

x

a vector/matrix/array (Real or Complex)

y

a vector/matrix/array (Real or Complex)

m

integer, number of rows.

n

integer, number of columns.

Description

This functions performs the two-dimension discrete Fourier transform.

y=fft2(x)y and x have the same size

y=fft2(x,m,n): If m (respectively n) is less than the rows number (respectively columns) of x then the x rows number (resp. columns) is truncated, else if m (resp. n) is more than the rows number (resp. columns) of x then x rows are completed by zero (resp. columns) .

if x is a matrix then y is a matrix, if x is a hypermatrix then y is a hypermatrix, with the size of the first dimension of y is equal to m, the size of the second dimension of y is equal to n, the size of the ith dimension of y (for i>2, case hypermatrix) equal to the size of the ith dimension of x. (i.e size(y,1)=m, size(y,2)=n and size(y,i)=size(x,i) for i>2)

Examples

//Comparison with explicit formula
a=[1 2 3 ;4 5 6 ;7 8 9 ;10 11 12]  
m=size(a,1)
n=size(a,2)

// fourier transform along the rows
for i=1:n
a1(:,i)=exp(-2*%i*%pi*(0:m-1)'.*.(0:m-1)/m)*a(:,i) 
end

// fourier transform along the columns
for j=1:m
a2temp=exp(-2*%i*%pi*(0:n-1)'.*.(0:n-1)/n)*(a1(j,:)).' 
a2(j,:)=a2temp.'
end
norm(a2-fft2(a))

See Also

  • fft — Transformée de Fourier discrète rapide.
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Last updated:
Wed Oct 05 12:10:56 CEST 2011