With Scilab 5.4.0 Windows versions using the MKL library, the dct and
dst function does not work (the associated routines are not present in
the MKL library)
One solution is to use a non MKL version
You can also use the attached Scilab function based on fft (slower)
Serge Steer
Le 26/03/2013 09:36, TViT a écrit :
Say please why the example, given in the help does not work? What
communication(connection) DCT and FFTw?
In my representation FFT through one script is carried out, and DCT through
another script however dct.sci has not found in Scilab 5.4.0
//--
--d=dct(s);
!--error 999
dct: Creation of requested fftw plan failed.
//--
// build a sampled at 1000hz containing pure frequencies
// at 50 and 70 Hz
sample_rate=1000;
t = 0:1/sample_rate:0.6;
N=size(t,'*'); //number of samples
s=sin(2*%pi*50*t)+sin(2*%pi*70*t+%pi/4)+grand(1,N,'nor',0,1);
d=dct(s);
// zero low energy components
d(abs(d)1)=0;
size(find(y10),'*') //only 30 non zero coefficients out of 600
clf;plot(s,'b'),plot(dct(d,1),'r')
--
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function y=dct(A,varargin)
if A==[] then y=A;return;end
if size(A,'*')==1 then y=A;return;end
if size(varargin)==0 then
d=-1
else
d=varargin(1)
varargin(1)=null()
end
select size(varargin)
case 0 then //dct(A [,sign])
y=dct_nd(A,d)
case 1 then //dct(A [,sign],selection)
case 3 then //dct(A [,sign],dims,incrs)
end
endfunction
function y= dct_nd(y,flag)
for k=1:ndims(y)
y=dct_1d(y,flag,k)
end
endfunction
function y = dct_1d (x,flag,sel)
//Ref: A. K. Jain, Fundamentals of Digital Image Processing, pp. 150-153.
if x==[] then y=x,return,end
if argn(2)==1 then flag=-1,end
szx=size(x);
if argn(2)3 then
if size(find(szx1),'*')==1 then sel=k;else sel=1;end
end
n=szx(sel)
if n==1 then y=x,return,end
if sel1 then
sz1=1:ndims(x);sz1([1 sel])=sz1([sel 1]);
x=permute(x,sz1)
szx=permute(szx,sz1)
end
x=matrix(x,n,-1);
m=size(x,2);
if flag==-1 then
w=[sqrt(0.25/n);sqrt(0.5/n)*exp((-%i*%pi/2/n)*(1:n-1)')]*ones(1,m);
if isreal(x)modulo(n,2)==0 then
y=2*real(w.*fft([x(1:2:n,:); x(n:-2:2,:)],flag,1));
else
y=fft([x;x($:-1:1,:)],flag,1);
y=w.*y(1:n,:);
if isreal(x) then y=real(y); end
end
else //inverse transform
if isreal(x)modulo(n,2)==0 then
w = [sqrt(n/4);sqrt(n/2)*exp((%i*%pi/2/n)*(1:n-1)')]*ones(1,m);
y=fft(w.*x,flag,1);
y([1:2:n,n:-2:1],:)=2*real(y);
else
w = [sqrt(4*n);sqrt(2*n)*exp((%i*%pi/2/n)*(1:n-1)')]*ones(1,m);
y=[x.*w;zeros(1,nc);-%i*w(2:$,:).*x($:-1:2,:)];
y=fft([x.*w;zeros(1,nc);-%i*w(2:$,:).*x($:-1:2,:)],flag,1);
y=y(1:n,:);
if isreal(x) then y=real(y); end
end
end
if sel1 then y=permute(y,sz1) ;end
y=matrix(y,szx)
endfunction
function y=idct(x)
y=dct(x,1)
endfunction
function y=dst(x,flag)
[mx,nx]=size(x);
if argn(2)==1 then flag=-1,end
if size(x,1)==1 then
//transform x as a column vector
x=matrix(x,-1,1);
n=mx*nx;
nc=1;
else
n=mx;
nc=nx
end
if n==1 then y=matrix(x,mx,nx),return,end
y=fft([zeros(1,nc);x;zeros(1,nc);-x($:-1:1,:)],-1,1)
if isreal(x) then
y=-imag(y(2:n+1,:))/2
else
y=y(2:n+1,:)/(-2*%i)
end
if flag==1 then y=2/(n+1)*y;end
y=matrix(y,mx,nx);
endfunction
function y=idst(x)
y=dst(x,1)
endfunction
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