How can I use imfindcircles function to find circle centers without sorting

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li yan
li yan le 25 Nov 2014
Commenté : li yan le 28 Nov 2014
I used imfindcircles to find circles in an image, but the circles found are also sorted based on the strgenth of the circles! I do not want to this function to sort the circles, how can I to do this?

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David Young
David Young le 27 Nov 2014
Your comment suggests that you do want the results to be sorted, but according to position rather than strength. (Strength means the number of votes the circle gets in the Hough accumulator.)
There is no natural position ordering. You have to decide what you want and implement a sort as required. For example, if you want to sort by y-coordinate, you'd do this:
% example data
A = imread('coins.png');
[centres, radii] = imfindcircles(A, [15 30]);
% sort by y coordinate
[~, index] = sort(centres(:,2)); % 1 instead of 2 would sort by x coord
centres = centres(index, :);
radii = radii(index, :);
% display the ordering
viscircles(centres, radii);
for c = 1:length(radii)
text(centres(c,1), centres(c,2), sprintf('%2u', c));
If your circles are on a kind of grid, it is unlikely that sorting by x or y will give exactly what you want. You probably have to work out which cell of the grid each circle is in, then sort the results accordingly. Here's a simple approach, but you'll need to think through how to make the quantisation step work reliably for your data.
% sort by quantised x and y coordinates
gridstep = 50; % needs to be equal to the grid size
qcentres = gridstep * round(centres/gridstep); % quantised coords
[~, index] = sort(qcentres(:,1)*size(A,1) + qcentres(:,2)); % sort on x then on y
centres = centres(index, :);
radii = radii(index, :);
You can visualise the ordering using the same code as before.
  1 commentaire
li yan
li yan le 28 Nov 2014
Thank you very much. Your answer really helped me.

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Plus de réponses (2)

Image Analyst
Image Analyst le 25 Nov 2014
I don't see anything in the documentation about it doing any kind of sorting, though it might. Let's say you have a dozen circles of different diameters randomly placed around the image. What would you consider to be an unsorted list? Which circle would you put first and which would you put last .
  5 commentaires
li yan
li yan le 28 Nov 2014
Thank you for your patience to answer really. I do not look at 96 well plate or microarray. I just do camera calibration with the target consists of circles ordered regularly.

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Anand le 25 Nov 2014
Modifié(e) : Anand le 25 Nov 2014
If you mean to say that you'd like imfindcircles to also detect even 'weak' circles, than set the 'Sensitivity' parameter to a high value (close to 1).

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