What are (r min) & (r max) in "imfindcircles"?

To count some cells in an image, I set the radii range [20 80] in "imfindcircles" and around 70 circles were found with the largest radius < 60. After changing the radii range to [20 2000], more than 120 circle were found with the largest radius < 80! I don't understand if the largest radius is <80, why is it not found by setting the first range [20 80]?

[Suraj Mankulangara]

Could you provide the code and the image on which you are trying to use "imfindcircles" ?

[KSSV]

Can you show your image?

[Shahin Safazadeh]

    img = imread('normal.jpg');
    subplot(2,2,3),imshow(img),title('Found cells')
    hold on

    img_gray = rgb2gray(img);
    subplot(2,2,1),imshow(img_gray), title('RGB to gray conversion')

    edges_gray = edge(img_gray,'Canny');
    subplot(2,2,2),imshow(edges_gray), title('Edges by Canny')

    [centers1,radii1] = imfindcircles(edges_gray,[20 100]);
    subplot(2,2,3),viscircles(centers1,radii1,'EdgeColor','r','LineWidth',0.6);

[Image Analyst]

You forgot to attach 'D:\KUL\CV\assignment\assignment_2\circles_on_original_img.png' and 'D:\KUL\CV\assignment\assignment_2\normal.jpg'.

And you have never read this link so please read it now.

Answer 1

[Abhishek Ballaney]

https://in.mathworks.com/help/images/ref/imfindcircles.html

[Shahin Safazadeh]

Would you please let me know what you are going to say by that link? I had already used this syntax!

Answer 2

[Suraj Mankulangara]

Hello Shahin,

I suspect that this is an accuracy issue. The recommendation from MathWorks is that for best results, the conditions rmax < 3*rmin and (rmax-rmin) < 100 should hold:

https://in.mathworks.com/help/images/ref/imfindcircles.html#Tips

It could very well be that "imfindcircles" fails since these conditions are not met when the radius range is specified as [20, 2000]

- Suraj Mankulangara

[Shahin Safazadeh]

Hi Suraj,

Seeing the warning in MATLAB, I already realized that I should respect those 2 conditions. Although, MATLAB can't find all the circles within the interval, when I set the interval, [20 80]! On the other hand, increasing the interval takes too long to get the result. So, I believe, this syntax is not that useful for counting cells.