Calculation of level pixel heights

clc;clear all;
%% 1. Read picture
I = imread('orange.jpg');

Error using imread>get_full_filename
File "orange.jpg" does not exist.

Error in imread (line 371)
fullname = get_full_filename(filename);

figure();
imshow(I);

%% 2. Image binarization
thresh = graythresh(I);     %threshold
thresh = thresh+0.035;
I2 = im2bw(I,thresh);       
I2 = imcomplement(I2);      
 figure();
 imshow(I2);

%% 3. Finding the Maximum Connected Domain
img_reg = regionprops(I2,  'area', 'boundingbox');  
areas = [img_reg.Area];  
rects = cat(1,img_reg.BoundingBox);  

[~, max_id] = max(areas);  
max_rect = rects(max_id, :);  

% show the largest connected region  
figure(),   
imshow(I2);  
rectangle('position', max_rect, 'EdgeColor', 'r');  

% 
D = max_rect(3);
H = max_rect(4); 

%% boundary 
TH_D1 = D*0.9;
for i = floor(max_rect(2)):(floor(max_rect(2))+ H-1)
    num = 0;
    for j = floor(max_rect(1)):(floor(max_rect(1))+ D-1)
        if I2(i,j) == 1
            num = num + 1;
        end
    end
    if num > TH_D1
        line_1 = i;
        break
    end
end


TH_D2 = D*0.9;
for i = (floor(max_rect(2))+ H-1):-1:floor(max_rect(2))
    num = 0;
    for j = floor(max_rect(1)):(floor(max_rect(1))+ D-1)
        if I2(i,j) == 1
            num = num + 1;
        end
    end
    if num > TH_D2
        line_2 = i;
        break
    end
end

I'm trying to measure the pixel height of transparent liquids and I've designed a measurement method based on the maximum connected area which is only capable of measuring the level of coloured liquids.

[Benjamin Kraus]

Sounds like you have some code as a starting point. What have you tried already? Can you share any of the code you've written so far?

[Runyu Liu]

Hi I have just uploaded my code

[Benjamin Thompson]

What is the question? Is there a problem with the code that you wrote?

[Walter Roberson]

I believe that they are indicating that they are having trouble detecting level of transparent fluids but are ok with orange fluid

[Runyu Liu]

My tutor suggested that I use edge detection to measure liquid levels, but I could not think of a suitable method based on edge detection. This method works well for measuring coloured liquids, but not so well for identifying clear levels in labelled test tubes.

Answer 1

[Varun]

Hi Runyu,

I understand that you are facing issues with your code that calculates the height of the coloured as well as transparent liquid. You have already provided a good approach to calculate this using MATLAB functions like “imread” to read the image, “graythresh” for image binarization, followed by finding the maximum connected area using “regionprop”.

Here are the precautions which you can take to achieve your goal:

• Resolve the following error:

File “orange.jpg” does not exist.

You have the file with name “orange.png” i.e., “.png” extension but you are giving input as “orange.jpg”. Hence it is not able to find this file and throws this error.

• I executed your code on my machine for these both coloured and transparent image, your idea to find the height using maximum connected area is working. It is able to detect both coloured as well as transparent liquid. However, in case of transparent liquid it will give wrong answer because there is a paper label on the test-tube which is making the “regionprop” function to calculate the unintended area due this paper label as well.To resolve this issue, make sure that you take a clear pic/image of the test-tube at such an angle that there is no obscuration of this paper label.

Please refer to the following documentations to learn more:

“imread”: https://www.mathworks.com/help/matlab/ref/imread.html

“graythresh”: https://www.mathworks.com/help/images/ref/graythresh.html

“regionprop”: https://www.mathworks.com/help/images/ref/regionprops.html

Hope this helps!