Finding the full width half maximum (FWHM) of a rounded part of peak instead of sharp peaks

Hi, I have this plot where I want to find the FWHM around the main "bulge" of the plot (around the red line I have crudely drawn), ignoring the other sharper peaks. I have attached a file of the XY coordinates and would appreciate any help! Many thanks

Answer 1

[Adam Danz]

This uses rmoutliers to remove the spike and then computes the FWHM of the resultant curve. You can play around with rmoutliers to get the expected curve or use a different method if you find something more suitable.

Other approaces:

• fit the curve to a gaussian and use the fit parameters to compute FWHM.
• Use findpeaks along with the half-height width reference. See demo.

data = load('FWHM_Help_Plot_Data.mat');

% Plot raw data
h(1) = plot(data.X, data.Z, 'DisplayName', 'RawData');
hold on

% Remove outliers
[Zm,idx] = rmoutliers(data.Z, 'movmedian', 300); 
h(2) = plot(data.X(~idx), Zm, 'DisplayName', 'rmOutlier');

% Compute FWHM
halfMax = max(Zm)/2;  % simple since the baseline is near 0 
lrIdx = [find(Zm >= halfMax, 1, 'first'), find(Zm >= halfMax, 1, 'last')]; % L/R index of width
fwhm = diff(data.X(lrIdx));

% Show bounds
h(3) = yline(halfMax, 'k--', 'DisplayName', 'HalfHeight');
h(4) = xline(data.X(lrIdx(1)), 'DisplayName', 'WidthBounds');
xline(data.X(lrIdx(2))); 
legend(h)

title(sprintf('FWHM = %g', fwhm))

[Manny Kins]

Many thanks Adam Danz, this is working very well for me, I played around with rmoutliers and set the value to 400 and got some really nice results! thanks again

[Adam Danz]

It was equally fun for me 😎