image plot after is calculating hilbert spectrum

I have used th matlab function [hs,f,t,imfinsf,imfinse] = hht(imf,fs); to do hilbert haung transform.

The hilbert spectrum (hs) is a sparse matrix. How could this be plotted as an image plot? I tried to convert this to a double matrix using full(hs). But this doesn't give a hilbert spectrum. Its just blank. How to resolve this?

[jiayun zhang]

I am also studying HHT transformation recently. I have met the same problem as you. I want to plot the instantaneous energy spectrum, but I don't know how to achieve it. Have you solved the problem

Answer 1

[Michael Madelaire]

There shouldn't be any problem. But you have attached no code, so it is hard to know.

Without for information many things could be the problem. Below is a test. There show be no problem in plotting a sparse matrix.

a = diag(1:20); % Create diagonal matrix
b = sparse(a); % Convert into sparse matrix
c = full(b); % Convert sparse matrix back into full matrix
figure();
imagesc(a); title('Original full matrix'); colorbar();
figure();
imagesc(b); title('Sparse matrix');  colorbar();
figure();
imagesc(c); title('Converted full matrix');  colorbar();

I do not know anything about the Hilbert-Huang Transformation. But by taking the initial example from: https://se.mathworks.com/help/signal/ref/hht.html

I converted the sparse matrix into full. No problem

Plotted the sparse matrix. No problem

Plotted the converted matrix (into full). No problem

load('sinusoidalSignalExampleData.mat','X','fs')
t = (0:length(X)-1)/fs;
figure();
plot(t,X)
xlabel('Time(s)')

[imf,residual,info] = emd(X,'Interpolation','pchip');

hs = hht(imf,fs);

q = full(hs);
figure();
imagesc(hs); colorbar()
figure();
imagesc(q); colorbar()

[Ramya Raman]

Thank you for your response. What I am try to do is,

%%%%

[hs,f,t,imfinsf,imfinse] = hht(imf,fs);

q = full(hs);

imagesc(imfinsf(:,1),f,q);

However, this is not close to the plot when I directly plot hht(imf,fs); without getting the return values.

[Michael Madelaire]

It is unclear to me what it is you want illustrated?

imagesc(imfinsf(:,1),f,q);

Does not make any sense.

The imagesc specification states:

"imagesc(x,y,C) specifies the image location. Use x and y to specify the locations of the corners corresponding to C(1,1) and C(m,n). To specify both corners, set x and y as two-element vectors. To specify the first corner and let imagesc determine the other, set x and y as scalar values. The image is stretched and oriented as applicable."

When you say "I directly plot hht(imf,fs); without getting the return values" what does that mean? There has to be a return value otherwise nothing is plotted. Do you mean hs?