How to label the centers of circles according to their position on axes?

Hello all.

I have found and masked circles in an image. Now, I wish to label the circles as 1, 2, 3....end (please see the attached image) , and I want the numbers to appear at the center of the circles. The attached image is how I want the output to be.

Tried implementing it using text(). I used the following code which definitely has errors; as it is not giving the desired output.

for i=1:sorted_centers_x    % sorted_centers_x is an array with all the X coordinates of the centers of the circles
    for j=1:sorted_centers_y    % sorted_centers_y is an array with all the Y coordinates of the centers of the circles
        if (sorted_centers_y(j) >=0) && (sorted_centers_y(j)<20)    % iterating with different range of values. so as to label 1-6 on the circles in the upper row and so on..
            text(double(sorted_centers_x(j)),double(sorted_centers_y(i)),num2str(j),'Color','g','FontSize', 14,'FontWeight','bold'); 
        else
            text(double(sorted_centers_x(j)),double(sorted_centers_y(i)),num2str(j),'Color','g','FontSize', 14,'FontWeight','bold');
        end
    end
end

Any help would be appreciated! Thanks in advance :)

Answer 1

[Simon Chan]

Try this and still using function text:

clear; clc;
I = ones(400,600);
sorted_centers_x = repmat(50:100:550,1,4);
sorted_centers_y = repelem(50:100:350,1,6);
imshow(I)
text(sorted_centers_x,sorted_centers_y,num2str([1:24]'))

[Shailly Vaidya]

Thanks @Simon Chan, for the code, it is working perfectly.

But actually the whole purpose of this is to make the process of labelling automatic, so that the image dimensions and other parameters don't need to be altered everytime. Thats why am looking for a loop which automatically adjusts according to the number and centers of circles in the image.

[Simon Chan]

May I know how many centers and circles are detecting before writing the text on the image.

[Image Analyst]

@Shailly Vaidya, it looks like you have some sort of template, like a 96 well plate or something. Therefore the centers of the circles will always be at the same locations regardless of how many pixels got segmented and are white within the circle. Therefore @Simon Chan's solution is automatic. It's automatic because it puts numbers at the known locations of the circles and does not require any manual user interaction to locate the centers.

[Shailly Vaidya]

@Simon Chan there are 24 circles detected and hence 24 pairs of X and Y coordiantes of centers stored in sorted_centers_x and sorted_centers_y respectively.

Thanks for helping! :)

[Shailly Vaidya]

@Image Analyst yes sir, am using 96 well plate template. You are right, after a few rounds of testing, I can fix the positions of the numbers on the image.

Thanks a lot for helping!

Answer 2

[Devyani Maladkar]

Hello,

It is my understanding that you want to label the masked circle by placing a number at the centre of the circle.

The text function can be used to insert text at the desired position in the current axes. The documentation here can be used to understand more about the text function use.

I have provided the code below for the implementation of labelling the circles with appropriate numbers. I have used sample data to demonstrate that the numbering takes place depending on where the (0,0) reference point is.

In the below code the reference point (0,0) is in the bottom-left corner of the plot, and the circle with maximum y-coordinate and minimum x-coordinate gets labelled 1 (upper-left corner). The labelling proceeds with increasing x-coordinate and decreasing y-coordinate hence the for-loop iteration is on ascending x values and descending y values.

%Sample data 
sorted_centers_x=sort([0.1 ,0.2,0.3,0.4,0.5],'ascend') 
sorted_centers_y=sort([0.1,0.2,0.3],'descend') 


for j=1:numel(sorted_centers_y) % sorted_centers_x is an array with all the X coordinates of the centers of the circles 
    for i=1:numel(sorted_centers_x) % sorted_centers_y is an array with all the Y coordinates of the centers of the circles 
        if (sorted_centers_y(j) >=0) && (sorted_centers_y(j)<20) % iterating with different range of values. so as to label 1-6 on the circles in the upper row and so on.. 
            text(double(sorted_centers_x(i)),double(sorted_centers_y(j)),num2str((j-1)*numel(sorted_centers_x)+i),'Color','g','FontSize', 14,'FontWeight','bold');  
        else 
            ext(double(sorted_centers_x(i)),double(sorted_centers_y(j)),num2str((j-1)*numel(sorted_centers_x)+i),'Color','r','FontSize', 14,'FontWeight','bold'); 
        end 
    end 
end 

[Shailly Vaidya]

Hey thanks @Devyani Maladkar! I have altered the code that you provided.

%Sample data 
sorted_centers_x=sort(sorted_centers_x,'descend') 
sorted_centers_y=sort(sorted_centers_y,'ascend') 
for j=1:numel(sorted_centers_y) % sorted_centers_x is an array with all the X coordinates of the centers of the circles 
    for i=1:numel(sorted_centers_x) % sorted_centers_y is an array with all the Y coordinates of the centers of the circles 
        if (sorted_centers_y(j) >=0) && (sorted_centers_y(j)<135) % iterating with different range of values. so as to label 1-6 on the circles in the upper row and so on.. 
            text(double(sorted_centers_x(i)),double(sorted_centers_y(j)),num2str((j-1)*numel(sorted_centers_x)+i),'Color','g','FontSize', 14,'FontWeight','bold');  
        else 
            text(double(sorted_centers_x(i)),double(sorted_centers_y(j)),num2str((j-1)*numel(sorted_centers_x)+i),'Color','r','FontSize', 14,'FontWeight','bold'); 
        end 
    end 
end 

and getting this output. Here, all the numbers are getting printed on top of each other, and hence creating the red-patch over it. How can I resolve this issue?

[Devyani Maladkar]

This could be due to the values populated in sorted_centers_x and sorted_centers_y you may want to look into those