Try this. Adapt as needed.
% 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 = 16;
markerSize = 20;
%--------------------------------------------------------------------------------------------------------
% READ IN TEST IMAGE
folder = pwd;
baseFileName = "marcus.png";
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~isfile(fullFileName)
% 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
% Read in image file.
grayImage = imread(fullFileName);
% Get size
[rows, columns, numberOfColorChannels] = size(grayImage)
if numberOfColorChannels == 3
% If it's color, convert to gray scale.
grayImage = rgb2gray(grayImage);
end
% Display the image.
subplot(2, 1, 1);
imshow(grayImage);
axis('on', 'image');
impixelinfo;
title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
g.Name = 'Demo by Image Analyst';
g.NumberTitle = 'off';
drawnow;
%--------------------------------------------------------------------------------------------------------
% Get the mean across columns
verticalProfile = mean(grayImage, 2);
% Erase top and bottom parts.
line1 = 262;
line2 = 362;
maxGL = max(grayImage(line1:line2, :), [], 'all')
verticalProfile(1 : line1) = maxGL;
verticalProfile(line2 : end) = maxGL;
y = 1 : rows;
subplot(2, 1, 2);
plot(verticalProfile, y, 'b-', 'LineWidth', 2);
grid on;
title('Vertical Profile', 'FontSize',fontSize);
xlabel('Mean Intensity', 'FontSize',fontSize);
ylabel('Row', 'FontSize',fontSize);
%--------------------------------------------------------------------------------------------------------
% Find the first place where the mean drops below 140.
threshold = 140;
topRow = find(verticalProfile < threshold, 1, 'first')
% Draw a red line at the threshold.
xline(threshold, 'Color', 'r', 'LineWidth', 2)
% Draw a red line going across the average black lines height.
subplot(2, 1, 1);
yline(topRow, 'Color', 'r', 'LineWidth', 2)
% Draw a yellow line there
xMid = columns/2;
line([xMid, xMid], [1, topRow], 'Color', 'y', 'LineWidth', 2);
