Full Width at Half Max Peaks
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I have 3 peaks close to eachother and I would like to find the FWHM and draw some lines like the graph produced by the Image Analyst here: https://au.mathworks.com/matlabcentral/answers/510144-peak-width-at-half-height
I have loaded my data and normalized already then I utilized this following code (with very slight modification) produced by the Image Analyat here:
% Find the half height - midway between min and max y values.
halfHeight = (min(normy) + max(normy)) / 2;
yline(halfHeight, 'Color', 'g', 'LineWidth', 2);
% Find left edge
index1 = find(normy >= halfHeight, 1, 'first');
x1 = x(index1)
line([x1, x1], [0, normy(index1)], 'Color', 'r', 'LineWidth', 2);
text(x1+1, 5, sprintf('x1 = %.2f', x1), 'FontSize', 1, 'Color', 'r');
% Find right edge
index2 = find(normy >= halfHeight, 1, 'last');
x2 = x(index2)
line([x2, x2], [0, normy(index2)], 'Color', 'r', 'LineWidth', 2);
text(x2+1, 5, sprintf('x2 = %.2f', x2), 'FontSize', 1, 'Color', 'r');
% Compute the full width, half max.
fwhm = x2 - x1
text( -0.02688, halfHeight+2, sprintf('width = %.2f', fwhm), 'FontSize', 1, 'Color', 'r', 'HorizontalAlignment', 'center');
caption = sprintf('Full Width, Half Max = %.2f', x2 - x1);
title(caption, 'FontSize', 1);
The "normy" is the y-axis values normalized. The value -0.02688 in the "text" command is the c1 value which is used here in the fwhm equation:
f(x)=a1*exp(-((x-b1)/c1)^2). The produced graph shows the right edge is not accurate and it rather picked up the centre of the peak itself.
Is there anything I am missing here?