i m taking videoframes&applying 3-D FFT.but takes 2-3 hours for execution.Is there any way to speed up the code from 2-3 hours to few minutes (using e.g.vectorization,preallocation or any other way)????

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ramdas patil 2014-4-9

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https://ww2.mathworks.cn/matlabcentral/answers/125098-i-m-taking-videoframes-applying-3-d-fft-but-takes-2-3-hours-for-execution-is-there-any-way-to-speed

编辑： ramdas patil 2014-4-21

for t=1:100:T-31; %T is no of frames.... and i am taking selective frames from video f1= read(video,t); %read frames from video file video f2=rgb2gray(f1); I(:,:,t)=f2; %I is for storing database of all frames end

%code for 3-D Fourier Transform

for s=1:100:T-31

    for u=1:r1 %r1 and c1 are dimensions of frame
        for v=1:c1        
            dft=0; 
            mag(u,v,s)=0;
            phase(u,v,s)=0;
            for t=1:100:T-31                  
                    for x=1:r1          
                        for y=1:c1                
                        v1=exp(((-1j)*2*pi*(x-1)*(u-1))/r1);                 
                        v2=exp(((-1j)*2*pi*(y-1)*(v-1))/c1);                 
                        v3=exp(((-1j)*2*pi*(t-1)*(s-1))/(T-31));                                     
                        dft=dft+ I(x,y,t)*((v1)*(v2)*(v3))/(r1*c1*(T-31)); 
                        dft1=(fftshift(dft));
                        mag(u,v,s)=mag(u,v,s)+log(1+abs(dft1));%magnitude spectrum
                       phase(u,v,s)=phase(u,v,s)+exp(1j*angle(dft));%phase spectrum              
                        end
                    end
            end
        end
    end
    magstruct(s)=struct('magnitude',mag(:,:,s));%use of structure for storing magnitude data
    phasestruct(s)=struct('phase',phase(:,:,s));%use of structure for storing phase data

end

%code for 3-d Inverse Fourier Transform

for t=1:100:T-31 for x=1:r1 for y=1:c1 idft(x,y,t)=0;

            for s=1:100:T-31
                for u=1:r1
                    for v=1:c1   
                        z1=exp(((1j)*2*pi*(x-1)*(u-1))/r1);                 
                        z2=exp(((1j)*2*pi*(y-1)*(v-1))/c1);                 
                        z3=exp(((1j)*2*pi*(t-1)*(s-1))/(T-31));   
                        idft(x,y,t)=idft(x,y,t)+ (phasestruct(s).phase(u,v))*((z1)*(z2)*(z3)); %reconstructin frm phase only   
                        idft2(x,y,t)=idft(x,y,t).*conj(idft(x,y,t));            
                    end
                end
            end
        end
    end
    reconstruct(t)=struct('reconstructed',idft(:,:,t));
end