How to determine the contact angle of droplet with a cannula in place

I have been using a code I found on the Matlab community to calculate the contact angle of a droplet on a solid surface. The code works well in detecting almost all contact angles, but I have encountered an error when trying to determine the contact angle of a sessile droplet with the cannula still in place. The issue is that the code is unable to determine the contour of the droplet for the calculation of the contact angle. How can I separate the cannula from the droplet profile in order to calculate the contact angle accurately?

Answer 1

[Image Analyst]

Is the cannula always in the same place? Then just mask it out.

[Gideon Mensah]

Yes the cannula is always fixed and the droplet image is taken through the window of the pressure chamber.

[Image Analyst]

% 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 = "untitled.jpg";
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
    % Convert to gray scale.
    grayImage = grayImage(:,:,2);
end
% Display the image.
subplot(2, 2, 1);
imshow(grayImage);
axis('on', 'image');
impixelinfo;
title('Original Image', 'FontSize', fontSize, 'Interpreter', 'None');
%--------------------------------------------------------------------------------------------------------
% Read in mask
mask = logical(imread('Cannula Mask.png'));
% Display the image.
subplot(2, 2, 2);
imshow(mask);
axis('on', 'image');
impixelinfo;
title('Mask Image', 'FontSize', fontSize, 'Interpreter', 'None');
% Maximize window.
g = gcf;
g.WindowState = 'maximized';
g.Name = 'Demo by Image Analyst';
g.NumberTitle = 'off';
drawnow;
%--------------------------------------------------------------------------------------------------------
% Mask the original image.
grayImage(mask) = 255;
% Display the image.
subplot(2, 2, 3);
imshow(grayImage, []);
impixelinfo;
axis('on', 'image');
title('Masked Image', 'FontSize', fontSize, 'Interpreter', 'None');

If youir droplet grows larger such that the cannula mask pierces it, it won't really matter since you'll still have enough coordinates to fit an ellipse to.

https://matlab.fandom.com/wiki/FAQ#How_can_I_fit_an_ellipse_or_other_shape_to_a_set_of_XY_data?

I'm also attaching a contact angle demo that I've used before.

[Gideon Mensah]

Thank you for the rapid response

I edited the following part of the code : % Read in mask

mask = logical(imread('Cannula Mask.png'));

I replaced cannula mask.png with (grayImage) as the error message indicates the file name (cannula mask.png ) did not exsist. this has lead to a different results which i have attached to this responds

[Image Analyst]

See attached mask that I forgot to include last time.