Cannot detect dots in calibration image with detectCircleGridPoints

Hi all,

I'm trying to calibrate my camera based on a dotted pattern on a board. I see I can use the detectCircleGridPoints algorithm, but cannot get it to detect any of the points and get imagePoints = []. Below my code.

What am I doing wrong?

Best,

clc; clear all; close all;
fileName = 'dotted_cali_fig.tiff';  %to attach the file I had to put it in .png 
img = imread(fileName);

patternDims = [7 35];
imagePoints = detectCircleGridPoints(img,patternDims,PatternType="symmetric")

Answer 1

[Antoni Garcia-Herreros]

Hello Jos,

I'm not sure why detectCirlceGridPoints is not working, however, you could try using regionprops:

BW=imbinarize(img);
r=regionprops('table',imcomplement(BW),'Centroid','Circularity','Area');
R=table2array(r);
R=R(R(:,1)>5,:); % Filter by Area > 5 pixels
ListPoints=R(R(:,4)>prctile(R(:,4),5),:); % Filter by circularity

Hope this helps

[Jos Muller]

Thanks Antoni,

It works for most of the points in my example figure. Some more conservative 'area' threshold works beter. The circularity filter is a nice suggestion, allthough in my example I lose to much points. I can continue to work from this, thanks!

Best,

Jos