How to set radii in imfindingcircles function?

dear all, i'm trying to create a mask for this image based on the fuction imfindingcircles. I tried setting different thresholds but I didn't get the rigth result. Can anybody help me? than I would like to set NaN to the mask. Thank you in advance!

clear all
close all
clc
A= imread('image_1567.png');
[rows, columns, numberOfColorChannels] = size(A)
%imshow(A)
[centers,radii] = imfindcircles(A,[50 100],Sensitivity=0.9);
mask = circles2mask(centers,radii,size(A));
figure
montage({A,mask})
A(~(A == mask)) = nan

[Shantanu Dixit]

Hi Elisa, can you share the image you are working on?

[Elisa]

yes sure, it was missed, sorry

Answer 1

[Deepak]

Hi,

The radius range set in the “imfindcircles” method is "[50 100]". It needs to be in the range "[500 650]" to detect the circle present in the PNG image provided by you.

Also, the sensitivity parameters need to be set to “0.95” instead of “0.9” due to the low contrast difference between black background and grey circle.

Here is the updated code snippet that will detect the circle to mask –

[centers,radii] = imfindcircles(A,[500 650],Sensitivity=0.95); 

Attaching the documentation of “imfindcircles” for reference –

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