Contact angle measurements for droplets with a capillary

Question

Baraa 2024-6-25

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2131701-contact-angle-measurements-for-droplets-with-a-capillary

回答： Umang Pandey 2024-7-16

Hello everyone

My name is Baraa, I recently started using Matlab (Bigginner), and I need your help in explaining the error I keep making in the following code. The code is supposed to measure the contact angle of a droplet based on defining the edges of the droplet, masking the capillary, dividing the pixels on the edges of the droplet by 2 (so we can have left and right), finding the reflection of each side to define the contact points between the surface and the droplet on each side, and finally connecting the contact points together. The code then fits the pixels to find the tangent and calculates the contact angle between the tangent and the line between the contact points.

The main problem is that the code doesn't work with all droplets and most of the time I have errors with droplets with high wettability and high volume (the droplets spread on the surface). The error message is as follows:

Index in position 1 exceeds array bounds. Index must not exceed 1113.

Error in findreflection (line 50)

x2=trace(index+n2:index+n-1,2);

Error in contactAngleImageAnalysis (line 104)

[x0L,y0L,indexL]=findreflection([edgeL.x,edgeL.y],70,0); % change the last entry (160) to zero and see what happens

How can I modify the code to make it suitable for any droplet volume?

P.S

The code always fails to read this image (Co-Eth-1, see attached) and it reads probably reads this image (Co-Eth-1b, see attached). Please refer to the two images.

Thank you very much in advance

clc
clear all
close all
addpath(genpath("C:\Users\Bara'a Al-khateeb\Desktop\Others\Students\Gideon Mensah\Laptop\codes\Contact Angle Fitting\Scripts\Subpixel Matlab v2.11"));
addpath(genpath("C:\Users\Bara'a Al-khateeb\Desktop\Others\Students\Gideon Mensah\Laptop\codes\Contact Angle Fitting\Scripts"));
main_path = "C:\Users\Bara'a Al-khateeb\Desktop\Others\Students\Gideon Mensah\Laptop\IMAGES\25.06.24";
output_folder = "C:\Users\Bara'a Al-khateeb\Desktop\Others\Students\Gideon Mensah\Laptop\sessileDrop_processed\";
%these are the coordinates of the polygon to mask the cannula
Xright=3100;%this the X value on the right side of the ploygon and it represents top and bottom if the right side of the polygon.
Xleft=2800;%this is the X value of the left side of the ploygon and it represents both top and bottom x cordinates 
Y_top=0;% this is the y value on the top side of the polygon for both left and right side 
Y_bottom=2050;% this is the y value of the bottom side of the ploygon for both left and right side 
%******************************pixel intensity***************************
pixelValue=255;
%***********************threshold to be used*****************************
trsh_sub=4;
% Read a group of images from a folder
imageFiles = dir(fullfile(main_path, '*.png')); % Assuming images are in PNG format
numImages = input('Enter the number of images to work with: ');
% Create cell arrays to store data
imageNumbers = zeros(numImages, 1);
CAL_values = zeros(numImages, 1);
CAR_values = zeros(numImages, 1);
for k = 1:numImages
    % Load image
    filename = imageFiles(k).name;
    im_load = fullfile(main_path, filename);
    im = imread(im_load);
    %-----------------------------------------------------------------
    %       Masking the cannula
    %-----------------------------------------------------------------
    
    % Define the coordinates of the four points
    maskSize = size(im);
    pointCoordinates = [Xleft, Y_bottom; Xright, Y_bottom; Xright, Y_top; Xleft, Y_top];
    mask = zeros(maskSize(1), maskSize(2));
    mask = poly2mask(pointCoordinates(:, 1), pointCoordinates(:, 2), maskSize(1), maskSize(2));
    burnedImage = im;
    burnedImage(mask) = pixelValue;
    
    %---------------------------------------------------------------
    %         Step 2 Detect boundaries in image
    %---------------------------------------------------------------
    [edges, RI] = subpixelEdges(burnedImage, trsh_sub);
    
    im_size=size(burnedImage);
    im_size=size(burnedImage);
    points = detectHarrisFeatures(burnedImage);
    strongest = selectStrongest(points,10);
    
    f2h=figure;
    imshow(burnedImage)
    hold on
    plot(edges.x,edges.y,'r.','LineWidth',2)
    % plot(edges.x(1), edges.y(1),'b*')
    % plot(edges.x(im_size(1)),edges.y(im_size(2)),'g*')
    plot(strongest)
    set(f2h,'Units','normalized','Position',[0.31,0.6,0.3,0.3])
    
    %---------------------------------------------------------------
    %         Step 3 Select longes boundary in image
    %---------------------------------------------------------------
    
    longestedge=findlongestedge(edges,size(burnedImage),5);
    f3h=figure;
    imshow(burnedImage)
    hold on
    plot(longestedge.x,longestedge.y,'r.','LineWidth',2)
    set(f3h,'Units','normalized','Position',[0.62,0.6,0.3,0.3])
    %---------------------------------------------------------------
    %         Step 4 Split edge into left and right and sort it
    %---------------------------------------------------------------
    
    [edgeL,edgeR]=leftrightedges(longestedge);
    f4h=figure;
    imshow(burnedImage)
    hold on
    plot(edgeL.x,edgeL.y,'r','LineWidth',2)
    plot(edgeR.x,edgeR.y,'b','LineWidth',2)
    set(f4h,'Units','normalized','Position',[0.0,0.3,0.3,0.3])
    %---------------------------------------------------------------
    %         Step 5 Find reflection
    %---------------------------------------------------------------
    
    [x0L,y0L,indexL]=findreflection([edgeL.x,edgeL.y],70,0); % change the last entry (160) to zero and see what happens
    [x0R,y0R,indexR]=findreflection([edgeR.x,edgeR.y],60,0);
    f5h=figure;
    imshow(burnedImage)
    hold on
    plot(edgeL.x,edgeL.y,'r','LineWidth',2)
    plot(edgeR.x,edgeR.y,'b','LineWidth',2)
    plot(x0L,y0L,'yx','MarkerSize',10,'LineWidth',2)
    plot(x0R,y0R,'yx','MarkerSize',10,'LineWidth',2)
    t=linspace(-3,3);
    plot((x0L-x0R)*t+x0R,(y0L-y0R)*t+y0R,'r--','LineWidth',2)
    
    set(f5h,'Units','normalized','Position',[0.31,0.3,0.3,0.3])
    %---------------------------------------------------------------
    %         Step 6 Fit data to polynomial
    %---------------------------------------------------------------
    
    PolyData=polynomialfit(edgeL,edgeR,[x0L,y0L],[x0R,y0R]);
    
    f6h=figure;
    imshow(burnedImage)
    hold on
    
    t=linspace(-3,3);
    plot((x0L-x0R)*t+x0R,(y0L-y0R)*t+y0R,'r--','LineWidth',2)
    
    plot(PolyData.EvalPolyL(:,1),PolyData.EvalPolyL(:,2),'r','LineWidth',2)
    plot(PolyData.EvalPolyR(:,1),PolyData.EvalPolyR(:,2),'b','LineWidth',2)
    
    radius=500;
    tilt=atand((y0R-y0L)/(x0R-x0L));
    plot([PolyData.TLL(1),PolyData.TLL(1)+radius*cosd(PolyData.CAL-tilt)],[PolyData.TLL(2),PolyData.TLL(2)-radius*sind(PolyData.CAL-tilt)],'LineWidth', 2,'color','g')
    plot([PolyData.TLR(1),PolyData.TLR(1)-radius*cosd(PolyData.CAR+tilt)],[PolyData.TLR(2),PolyData.TLR(2)-radius*sind(PolyData.CAR+tilt)],'LineWidth', 2,'color','g')
    legend(['contact angles, CA left= ',num2str(PolyData.CAL),' CA Right= ',num2str(PolyData.CAR)])
    set(f6h,'Units','normalized','Position',[0.62,0.3,0.3,0.3])
    
    display(['Polynomial fit return the contact angles, CA Left=',num2str(PolyData.CAL),' CA Right=',num2str(PolyData.CAR)])
    % % Store data in the table
    
    imageNumbers(k) = k;
    CAL_values(k) = PolyData.CAL;
    CAR_values(k) = PolyData.CAR;
    % Save processed image to a new folder
    if ~exist(output_folder, 'dir')
        mkdir(output_folder);
    end
    % Save processed image in the specified formats
    [~, name, ext] = fileparts(filename);
    processed_filename = [name '_processed'];
    % Check if the filename already exists, if so, append a unique identifier
    index = 1;
    while exist(fullfile(output_folder, [processed_filename, '_', num2str(index), '.jpg']), 'file')
        index = index + 1;
    end
    % Save as JPG
    imwrite(burnedImage, fullfile(output_folder, [processed_filename, '_', num2str(index), '.jpg']));
    % Save as FIG
    saveas(f6h, fullfile(output_folder, [processed_filename, '_', num2str(index), '.fig']));
    % Save result to TXT
    nsave = fullfile(output_folder, [name, '_', num2str(index), '.txt']);
    result_vary = rand(10); % Example data, replace with your actual data
    save(nsave, 'result_vary', '-ASCII');
    
    disp(['Processed image saved as: ', processed_filename]);
    
end
% Create table from cell arrays
tableData = table(imageNumbers, CAL_values, CAR_values);
% Save table to a text file
output_filename = fullfile(output_folder, 'contactAngle_table_data.txt');
writetable(tableData, output_filename, 'Delimiter', '\t');
disp(['Table data saved as: ', output_filename]);
% Display the table
disp(tableData);

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Image Analyst 2024-7-3

If you have any more questions, then attach your images and code to read it in with the paperclip icon after you read this:

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Attach one or two images that this code works well for, and some that it does not work well for, as well as the missing functions like findlongestedge, etc.

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Answer 1

Umang Pandey 2024-7-16

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2131701-contact-angle-measurements-for-droplets-with-a-capillary#answer_1485908

Hi Baraa,

The error in your code is coming from the "findreflection" function, specifically from the indicated line. Unfortunately, it would be difficult to pin-point the exact issue since you have not provided the implementation for functions you have used in your code. But on a high-level, the error message indicates that an index exceeds the array bounds.

Firstly, "trace" is an inbuilt MATLAB function used to calculate trace of a Matrix, i.e. sum of its diagonal. Since I do not have the access to "findreflection", I am not sure how is trace being used here but looks like you are using it as an array to extract values.

Secondly, the index out of bounds error indicates that the array indices you are trying to process are not within the range of that array. You need to verify the inputs you are passing and operations you are performing to check the indices are within valid range.

Additionally, I found some MATLAB answers where users are trying to achieve the same thing which you are attempting, these might be of help:

Hope this helps!

Best,

Umang