Droplet Contact Angle Measurement

Hi,

I am using the code below to generate the droplet image and measure the contact angle. After truncation, I only can get the subtrate image but not the actual droplet image i need. Can somebody help me to look into it?

Thanks you.

% Surface Tension Measurements Using the Pendant Drop Method

[filename, pathname] = ...
     uigetfile({'*.jpg';'*.tif';'*.gif';'*.*'},'Select an image');  %Open standard dialog box for retrieving files

rgbImage = imread([pathname,filename]);
im = im2double(rgb2gray(rgbImage)); % Convert image to gray
imshow(im); % Display image

BW = im2bw(im);
L = bwlabeln(1-BW, 4); % Label White Spots
S = regionprops(L, 'Area'); % Measure Area of Spots
BW2 = ismember(L, find([S.Area] ==max( [S.Area]) )); % Find Largest Spot
BW2(1,:) = 1; % Turn First Row White
imshow(BW2);

figure(2);clf;
BW3 = imfill( BW2, 'holes' ); % Fill In Holes in Image
imshow(BW3);

[x_coordinates y_coordinates Pixel_vals] = impixel;
rot_line = polyfit(x_coordinates ,y_coordinates ,1 ); % Replicate Substrate
rot_point = round( polyval( rot_line, 1 )); % Truncation Point
rot_angle = atan( rot_line(1) ); % Correction Angle
BW4 = BW3( rot_point:end,: ); % Truncation
BW4 = imrotate( BW4, -rot_angle*180/pi ); % Correction
BW4 = BW4( -y_coordinates(2) + rot_point:end,: ); % Truncation Correction
imshow( BW4 ); % Display Image

Function_ContactAngleb([200 300], 250, BW4)
[val, status, message] = fminsearch( @(cntr_radius) ...
    Function_ContactAngleb( cntr_radius(1:2), cntr_radius(3), BW4 ), ...
    [200, 200, 100], optimset('display', 'iter' ) );

crcl = Function_ContactAngle( val(1:2), val(3), size(BW4) ); % Optimized Generated Circle
imagesc( 10*crcl+BW4 ); % Picture/Optimization Overlay
axis image; % Show axes

% Math manipulation to calculate contact points based on radius and
% location of the center of the circle
contact_pt = [ (sqrt( val(3)^2 - ( 1-val(1) )^2 ) + val(2)), ...
    -(sqrt( val(3)^2 - ( 1-val(1) )^2 ) + val(2)) ];
% Determine tangent lines of contact points
tangent_slope = -( contact_pt-val(2) )/( 1-val(1) );
contact_angle = atan(tangent_slope); % Contact Angle
contact_angle = (contact_angle*180/pi); % Radians to Degrees
corrected_angle = [ mod( 180-contact_angle(1), 180 ),...
    mod( 180+contact_angle(2), 180)]; % Correction for proper domain
return
%*******************************************************************************
% Finish Main Program

And how can we do that? (Put yourself in our position and think a minute.)

... For example, is the cameraman image a suitable input?

Answer 1

Your array Function_ContactAngle is not initialized anywhere in the code you show.

The portion of your code starting at "Math manipulation" references the variable "val" which is previously unreferenced.

A reasonable hypothesis would be that the portion of your code starting at "Math manipulation" should be a function named Function_ContactAngle .

With regards to plotting not working as you expect, please read my graphics advice in http://www.mathworks.co.uk/matlabcentral/answers/22208-show-figure

Sorry about that. I am here attached the function code for you.

function subim = Function_ContactAngle( center, radius, sz) % Function called Function_ContactAngle
[a,b] = ndgrid( -radius:radius ); % Restrict domain to radius
tmp = a.^2+b.^2<= radius^2; % Make Domain Circular
subim = zeros( sz ); % Matrix of Zeros
subim(round(min(end, max(1,center(1)+[-radius:radius]) )), ...
    round(min(end, max(1,center(2)+[-radius:radius]) )) ) = tmp; % Draw Circle
return;

function [val] = Function_ContactAngleb( center, radius, im ) % Function called Function_ContactAngleb
crcl = Function_ContactAngle( center, radius, size( im ) ); % Create Circle
val = 1/abs(sum(sum(im&crcl) )-sum(sum(crcl&~im))); % Value Drawing’s Accuracy
return;

These are the two function code for the matlab.

Thank you.

Best regards.

I would be concerned about your lines

 subim(round(min(end, max(1,center(1)+[-radius:radius]) )), ...
    round(min(end, max(1,center(2)+[-radius:radius]) )) ) = tmp; % Draw Circle

In those lines, you may vary the index range to write into (to prevent writing past the beginning or end of the array), but you do not adjust the size of "tmp" when you do that. If the restriction conditions can ever be met then you would get dimension mismatches; if the restriction conditions cannot be met then there is no point in putting in the restrictions.

Hi,

Thanks for your reply.

I have a problem when I need to truncate the substrate in order to get my actual droplet especially when those droplet with reflection on the substrate. Is it the problem with the truncation?

[x_coordinates y_coordinates Pixel_vals] = impixel;
rot_line = polyfit(x_coordinates ,y_coordinates ,1 ); % Replicate Substrate
rot_point = round( polyval( rot_line, 1 )); % Truncation Point
rot_angle = atan( rot_line(1) ); % Correction Angle
BW4 = BW3( rot_point:end,: ); % Truncation
BW4 = imrotate( BW4, -rot_angle*180/pi ); % Correction
BW4 = BW4( -y_coordinates(2) + rot_point:end,: ); % Truncation Correction
imshow( BW4 ); % Display Image

Kind regards,

Voon Loong

I do not understand what you mean by "truncation" in this context?