Peak Width at Half Height

Question

Laiba Qadeer 2020-3-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510144-peak-width-at-half-height

评论： Rufus Adjetey 2020-11-13

I started using MATLAB only a few days ago. And I have trouble finding the width of peak. I have two subplots, both of which represent one peak from the data only. I want to know the width of peak at half distance. I also want the line representing width to be displayed on the plot. Please tell me how this can be done.

I searched the internet for help but could not get the desired result.

Here is my code for both graphs:

subplot(2,1,1)

plot(Hwave,Hintense,'.'),title('Original data'),xlabel('Wavelength'),ylabel('Intensity')

axis tight, grid

subplot(2,1,2)

plot(Hwaveinter,Hreal,'.'),title('Eight Times Interpolated Data'),xlabel('Wavelength'),ylabel('Intensity')

axis tight, grid

Thanks

3 个评论
显示 1更早的评论隐藏 1更早的评论

Laiba Qadeer 2020-3-10

10march run1.jpg

I have attached the image

Adam Danz 2020-3-10

Image Analyst's demo will work well with your data.

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Image Analyst 2020-3-10

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/510144-peak-width-at-half-height#answer_419495

编辑：Image Analyst 2020-3-10

在 MATLAB Online 中打开

See this demo:

% Initialization steps.
clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 24;
% Make Gaussian https://en.wikipedia.org/wiki/Gaussian_function
x = linspace(0, 100, 1024);
amp = 50;
mu = 35;
sigma = 20;
y = amp * exp(-(x - mu).^2 / (2 * sigma^2));
hFig = figure;
plot(x, y, 'b-', 'LineWidth', 2);
grid on;
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
hFig.WindowState = 'maximized';
% Find the half height - midway between min and max y values.
halfHeight = (min(y) + max(y)) / 2;
hold on;
yline(halfHeight, 'Color', 'g', 'LineWidth', 2);
% Find left edge
index1 = find(y >= halfHeight, 1, 'first');
x1 = x(index1)
line([x1, x1], [0, y(index1)], 'Color', 'r', 'LineWidth', 2);
text(x1+1, 5, sprintf('x1 = %.2f', x1), 'FontSize', fontSize, 'Color', 'r');
% Find right edge
index2 = find(y >= halfHeight, 1, 'last');
x2 = x(index2)
line([x2, x2], [0, y(index2)], 'Color', 'r', 'LineWidth', 2);
text(x2+1, 5, sprintf('x2 = %.2f', x2), 'FontSize', fontSize, 'Color', 'r');
% Compute the full width, half max.
fwhm = x2 - x1
text(mu, halfHeight+2, sprintf('width = %.2f', fwhm), 'FontSize', fontSize, 'Color', 'r', 'HorizontalAlignment', 'center');
caption = sprintf('Full Width, Half Max = %.2f', x2 - x1);
title(caption,  'FontSize', fontSize);

Adapt code as needed for your variable names.

12 个评论
显示 10更早的评论隐藏 10更早的评论

Rufus Adjetey 2020-11-12

% Initialization steps.

clc; % Clear the command window.

workspace; % Make sure the workspace panel is showing.

format long g;

format compact;

fontSize = 24;

% Make Gaussian https://en.wikipedia.org/wiki/Gaussian_function

x = linspace(0, 100, 1024);

amp = 100;

y = amp*sin(x);

hFig = figure;

plot(x, y, 'b-', 'LineWidth', 2);

grid on;

xlabel('x', 'FontSize', fontSize);

ylabel('y', 'FontSize', fontSize);

hFig.WindowState = 'maximized';

% Find the half height - midway between min and max y values.

halfHeight = 60;

hold on;

yline(halfHeight, 'Color', 'g', 'LineWidth', 2);

% Find left edge

index1 = find(y >= halfHeight, 1, 'first');

x1 = x(index1);

line([x1, x1], [0, y(index1)], 'Color', 'r', 'LineWidth', 2);

text(x1+1, 5, sprintf('x1 = %.2f', x1), 'FontSize', fontSize, 'Color', 'r');

% Find right edge

index2 = find(y >= halfHeight, 1, 'last');

x2 = x(index2);

line([x2, x2], [0, y(index2)], 'Color', 'r', 'LineWidth', 2);

text(x2+1, 5, sprintf('x2 = %.2f', x2), 'FontSize', fontSize, 'Color', 'r');

% Compute the full width, half max.

fwhm = x2 - x1;

for k=1:4:100

fwhm(k) = x2 - x1;

end

caption = sprintf('Full Width, Half Max = %.2f', x2 - x1);

title(caption, 'FontSize', fontSize);

Thanks for the initial suggestion

I did this but it seems to calcultae the first and last and ignores all the curves in the middle. Could all the x-points be stored into at the given halfHeight be stored in an array?

Thanks

Rufus Adjetey 2020-11-12

在 MATLAB Online 中打开

Sorry I mean the width within each turning point as I have indicated with a,b,c,d e, ... in the image attached above.

% Initialization steps.
clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 24;
% Make Gaussian https://en.wikipedia.org/wiki/Gaussian_function
x = linspace(0, 100, 1024);
amp = 100;
y = amp*sin(x);
hFig = figure;
plot(x, y, 'b-', 'LineWidth', 2);
grid on;
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
hFig.WindowState = 'maximized';
% Find the half height - midway between min and max y values.
halfHeight = 60;
hold on;
yline(halfHeight, 'Color', 'g', 'LineWidth', 2);
% Find left edge
index1 = find(y >= halfHeight, 1, 'first');
x1 = x(index1);
line([x1, x1], [0, y(index1)], 'Color', 'r', 'LineWidth', 2);
text(x1+1, 5, sprintf('x1 = %.2f', x1), 'FontSize', fontSize, 'Color', 'r');
% Find right edge
index2 = find(y >= halfHeight, 1, 'last');
x2 = x(index2);
line([x2, x2], [0, y(index2)], 'Color', 'r', 'LineWidth', 2);
text(x2+1, 5, sprintf('x2 = %.2f', x2), 'FontSize', fontSize, 'Color', 'r');
% Compute the full width, half max.
fwhm = x2 - x1;
for k=1:4:100
    fwhm(k) = x2 - x1;
end
caption = sprintf('Full Width, Half Max = %.2f', x2 - x1);
title(caption,  'FontSize', fontSize);

Image Analyst 2020-11-12

在 MATLAB Online 中打开

Try this:

clc;    % Clear the command window.
close all;  % Close all figures (except those of imtool.)
clear;  % Erase all existing variables. Or clearvars if you want.
workspace;  % Make sure the workspace panel is showing.
format long g;
format compact;
fontSize = 18;
fprintf('Beginning to run %s.m ...\n', mfilename);
echo off;
% Make Gaussian https://en.wikipedia.org/wiki/Gaussian_function
x = linspace(0, 100, 1024);
amp = 100;
y = amp*sin(x);
hFig = figure;
subplot(2, 1, 1);
plot(x, y, 'b-', 'LineWidth', 2);
grid on;
xlabel('x', 'FontSize', fontSize);
ylabel('y', 'FontSize', fontSize);
caption = sprintf('Original Signal');
title(caption,  'FontSize', fontSize);
hFig.WindowState = 'maximized';
% Define a threshold level.
thresholdHeight = 60;
hold on;
yline(thresholdHeight, 'Color', 'g', 'LineWidth', 2);
% Find elements where y is above the thresholdHeight
aboveThreshold = y > thresholdHeight;
% Label each group.
[groups, numRegions] = bwlabel(aboveThreshold)
smallFontSize = 8;
for k = 1 : numRegions
	% Get a mask for this particular group
	mask = groups == k; % Logical "map" of where this group is.
	indexes = find(mask); % Get actual element (index) numbers.
	% Find left edge
	index1 = min(indexes);
	x1 = x(index1);
	line([x1, x1], [0, y(index1)], 'Color', 'r', 'LineWidth', 2);
	text(x1, 7, sprintf(' x1 = %.2f', x1), 'FontSize', smallFontSize, 'Color', 'r');
	% Find right edge
	index2 = max(indexes);
	x2 = x(index2);
	line([x2, x2], [0, y(index2)], 'Color', 'r', 'LineWidth', 2);
	text(x2, 0, sprintf(' x2 = %.2f', x2), 'FontSize', smallFontSize, 'Color', 'r');
	% Compute the full width, half max.
	fwhm(k) = x2 - x1;
end
subplot(2, 1, 2);
bar(fwhm);
grid on;
caption = sprintf('Widths above a threshold of %d', thresholdHeight);
title(caption,  'FontSize', fontSize);

Image Analyst 2020-11-12

You data is discrete - it's quantized. There are no elements that are exactly 0.6 for y. So it picks the closest element above that. If you want to interpolate with interp1() or polyval(), you're certainly welcome to do that.

Rufus Adjetey 2020-11-13