How to mark threshold value in image histogram?

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My input is gray scale image. After drawing histogram of that image i want to mark the threshold value in the histogram using any red mark or line. I am using simple Otsu's thresholding method for segmentation.
  1 Comment
Rik
Rik on 23 Jan 2023
Edited: Rik on 23 Jan 2023
A simple hold('on') followed by a call to plot should do it, or am I missing something? What did you try?
Also, this is your 68th question. By now you should be aware of the advice here. Try to make a MWE so we can run your code without any other dependencies and can reproduce your issue. Use the tools explained here to format your post properly.

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Accepted Answer

Image Analyst
Image Analyst on 23 Jan 2023
Try xline. Full Demo:
% Demo by Image Analyst
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 = 22;
markerSize = 40;
%--------------------------------------------------------------------------------------------------------
% READ IN IMAGE
folder = [];
baseFileName = 'cameraman.tif';
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
% The file doesn't exist -- didn't find it there in that folder.
% Check the entire search path (other folders) for the file by stripping off the folder.
fullFileNameOnSearchPath = baseFileName; % No path this time.
if ~exist(fullFileNameOnSearchPath, 'file')
% Still didn't find it. Alert user.
errorMessage = sprintf('Error: %s does not exist in the search path folders.', fullFileName);
uiwait(warndlg(errorMessage));
return;
end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels > 1
% It's not really gray scale like we expected - it's color.
fprintf('It is not really gray scale like we expected - it is color\n');
% Extract the blue channel.
grayImage = rgb2gray(grayImage);
end
%--------------------------------------------------------------------------------------------------------
% Display the image.
subplot(2, 1, 1);
imshow(grayImage);
impixelinfo;
axis('on', 'image');
title('Original Gray Scale Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Update the dimensions of the image.
% numberOfColorChannels should be = 1 for a gray scale image, and 3 for an RGB color image.
[rows, columns, numberOfColorChannels] = size(grayImage)
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
drawnow;
%--------------------------------------------------------------------------------------------------------
% Get threshold
threshold = 255 * graythresh(grayImage);
%--------------------------------------------------------------------------------------------------------
% Display histogram
subplot(2, 1, 2);
imhist(grayImage);
grid on;
xline(threshold, 'Color', 'r', 'LineWidth', 2)
%--------------------------------------------------------------------------------------------------------
% Display threshold on histogram.
caption = sprintf('Histogram with threshold of %.1f gray levels', threshold);
title(caption, 'FontSize', fontSize)
  6 Comments
Image Analyst
Image Analyst on 26 Jan 2023
Then I'd call tech support since line() and xline() are not working the same way for you as for everyone else.

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