Analog output signal after applying DFT

Hello Team,

I need to apply Discrete Fourier Transform to a vector following the equation attached to this post. So I have written this code. The output will be a digital vector, am I right?

if true
  % code
function [horFourier, verFourier] = DFT(hProfile, vProfile)

    lengthH = length(hProfile);
    lengthV = length(vProfile);

    for xH=1:1:lengthH
        sumH =0;
        for yH=1:1:lengthH
            sumH = sumH + hProfile(yH)*exp((-1j)*2*pi*yH*xH/lengthH-1);
        end
        horFourier(xH) = abs(sumH);
    end

    for xV=1:1:lengthV
        sumV = 0;
        for yV=1:1:lengthV
            sumV = sumV + vProfile(yV)*exp((-1j)*2*pi*yV*xV/lengthV-1);
        end
        verFourier(xV) = abs(sumV);
    end

end end

What should I do to have an analog signal? The output should be an analog signal so that I can compute the other steps.

Answer 1

[Walter Roberson]

You can never use an analog signal for computation on a digital computer. There are computations that can be done at the analog level, including gain (voltage multiplier), filters (inductors, transformers, resistors), integration (charging a capacitor), and so on, and if you have external hardware that is doing those kinds of operations then you need a digital to analog converter of some sort.

[Matlab Student]

Right, but the next step of this method is to use the output signal after DFT is applied in order to compute the blockiness of the image (equation is attached). At some points it will require the value of non-integer indices which will result an error in Matlab.

What should I do to apply the same method documented in this paper?

[Walter Roberson]

What does this have to do with converting to analog?

Why do you need to index an array at a nonzero index?

Hint:

t = 0:.1:2;
y = @(t) t.^2;
Y = y(t) ;

Y(1) corresponds to y(0) but does not require indexing at a nonintegral location.

[Matlab Student]

Thanks Walter, I got your point. I will try to implement the method in this way.

[Matlab Student]

Good Morning Walter,

After digging deeper, I found they have plot the DFT coefficients as an analog signal (attached picture) hence they were able to provide the output of any value (integer or non-integer).

Can I do the same?

[Walter Roberson]

That picture does not show an analog signal. It shows a plot of dft coefficients, which are calculated as digital values.