Computing change in phase of a signal using hilbert transform

How do I compute the change in phase of a signal using hilbert transform? My input signal is a video, so i want to compute the phase change from frame to frame.

Answer 1

[Balaji]

Hi Anisia

I Understand that you want to find the phase shift in the of the Hilbert transform of an input video.

For that I suggest you do the following steps:

1. Read the video file and convert the frames into a grayscale.
2. Apply Hilbert transform using the ‘hilbert’ function in MATLAB.
3. Calculate the phase angle in MATLAB using the ‘angle’ function
4. Find out the difference between the two phases.

Here is a reference code:

% Read the video 
video = VideoReader('video.mp4'); 

%Define two frames to be compared 
index1 = 15; 
index2 = 20; 
%Read the corresponding frames 
frame1 = read(video, index1); 
frame2 = read(video, index2); 

signal1 = rgb2gray(frame1); 
signal2 = rgb2gray(frame2); 

% Apply the Hilbert transform 
analyticSignal1 = hilbert(signal1); 
analyticSignal2 = hilbert(signal2); 

% Extract the phase angle 
phase1 = angle(analyticSignal1); 
phase2 = angle(analyticSignal2); 

%Calculate the phase difference 
phaseDifference = phase1 - phase2; 

I suggest you refer the following documentation for more information:

https://www.mathworks.com/help/signal/ug/hilbert-transform.html

Hope this helps!

Thanks

Balaji