HHT and how to plot the Hilbert spectrum NOTE:
The following is based on an unanswered question posted here:
How to plot the Hilbert Spectrum in Hilbert-Huang transform?
, based on the usage of the "plot_hht" from here:
(https://www.mathworks.com/matlabcentral/fileexchange/19681-hilbert-huang-transform)



From what I understand the "plot_hht" does, 
after applying EMD to a signal, the IMF's of the signal remain.
The Hilbert Transform is then applied to each IMF, and the resulting phase angles are somehow used to help find the instantaneous frequency (with respect to time). 

Is it possible to represent these instantaneous frequencies vs time, with a third dimension, its strength/amplitude?

Thanks in advance.



EDIT P.S.: For clarity, the desired result is a graph that looks like this:
,
as taken from an article titled "Detecting position dependent tremor with the Empirical mode decomposition".
I figured out an answer.

From here:
https://web.cs.dal.ca/~tt/CSCI690611/papers/HHT.pdf

The Hilbert spectrum x(t) is:



where "a" is the instantaneous amplitude of the resulting IMF's 
(i.e.: absolute value of the Hilbert Transform applied to every point of one IMF),
and "w" is the instantanous frequency of the resulting IMF', calculated from the inverse tan of the imaginary divided by real components.

So adding the results using all the IMF's should provide the 3D time-frequency-amplitude information.