Hough Transform for Circles

[@ramkumarsakthivel9412]

Great video... there is a small mistake in the equation of the circle. It should be (x-a)^2+(y-b)^2=r^2 and not just r.

[@pratikian]

You are right. Thanks for pointing it out.

[@ohmy__gah159]

This helped me greatly to understand Hough Transform! Thank you

[@pratikian]

Happy to help 😇

[@drpiyushjoshi4544]

Thank you very much

[@kevinpriestley0110]

Thank you, you explained it very well.

[@akainu3668]

bro how can i modify your code for general curve like lame curve or an ellipse?

[@pratikian]

At line 14, 15 you will have to change the xp and yp xp=a*cos(ang); yp=b*sin(ang); where a is the major axis and b is the minor axis of ellipse. You can put the parametric equation of the curve you want to find here.

[@akainu3668]

@@pratikian thanks a lot for replying bro actually I had to do this for lame curve so can you help me with some code for it, as on net very complex codes are there

[@pratikian]

@@akainu3668 I could try

[@ayushprakash3890]

correction : in the first slide, the equation of the circle should contain r^2 and not r

[@pratikian]

Yes you are right. Thanks for pointing it out 😇

[@sl3w]

I dont understand. I have fixed R and I know x, y point of edge. How I can get(calculate) a and b to increment accumulator? Which a, b I must use? Which range of a,b? From what to what?

[@sl3w]

Am I right? I fixing a: a_min = X - R; a_max = X + R; after that I do for (i = a_min; i

[@pratikian]

So what do X and Y mean here? Apart from that I feel that the algorithm is fine it should work. here is an algorithm that I had used. first define a circle with radius r. ang=0:0.1:2*pi; xp=r*cos(ang); yp=r*sin(ang); Now we just have to move this circle so that it centers at the edge point (x,y). Now make an accumulator matrix which is of size (m+2*r, n+2*r) (where the image size is m x n ) now run a for loop for all the edge points x,y detected make the circle in the accumulator matrix centered at every edge point (x,y) v = x + xp; w = y + yp; increment the accumulator at v,w position accumulator(v,w) += 1; Finally choose the point which is having the maximum value in the accumulator. That is the required center of the circle. here you can see the matlab code for the above algorithm drive.google.com/drive/u/0/folders/1UTIgcj0Z-dKo67zNZj8qwmueH0g3OPp0

[@christianbarnes8963]

How did you implement detection of more than one circle with different radius

[@pratikian]

So for that you can make a vector of the radius of the different circles that is there in the image and run the algo for each radius

[@christianbarnes8963]

@@pratikian can you help me out with it in your implementation to see how it will work I tried using a for loop but so many smaller circles

[@pratikian]

Okay I will try. Acctually my code is not very robust meanwhile you can also try other implementations in.mathworks.com/matlabcentral/fileexchange/4985-circle-detection-via-standard-hough-transform Hope that helps

[@christianbarnes8963]

All right thank you

[@nehar8729]

excellent explanation

[@akainu3668]

also can you explain ur code?

[@pratikian]

here is an algorithm that I had used. first define a circle with radius r. ang=0:0.1:2*pi; xp=r*cos(ang); yp=r*sin(ang); Now we just have to move this circle so that it centers at the edge point (x,y). Now make an accumulator matrix which is of size (m+2*r, n+2*r) (where the image size is m x n ) now run a for loop for all the edge points x,y detected make the circle in the accumulator matrix centered at every edge point (x,y) v = x + xp; w = y + yp; increment the accumulator at v,w position accumulator(v,w) += 1; Finally choose the point which is having the maximum value in the accumulator. That is the required center of the circle. here you can see the matlab code for the above algorithm drive.google.com/drive/u/0/folders/1UTIgcj0Z-dKo67zNZj8qwmueH0g3OPp0

[@pratikian]

You can also look at some other implementations my code is not very Robust in.mathworks.com/matlabcentral/fileexchange/4985-circle-detection-via-standard-hough-transform

[@chetaniske9108]

can i get all coordinates of (a,b)

[@pratikian]

I did not get your question. What do you mean by all the co ordinates of (a,b)

[@chetaniske9108]

@@pratikian yes I want all centes coordinates in a given image for all detected circles

[@royalzak4019]

Thanks man i am going to practice over here

[@jm10oct]

THANK YOU

[@chetanahadadi3089]

can you please share me the code

[@pratikian]

Sure here is the link for the matlab code drive.google.com/drive/mobile/folders/1UTIgcj0Z-dKo67zNZj8qwmueH0g3OPp0?usp=sharing This code is not very robust it is for a constant r , it is good for understanding purpose

[@jtrtsay]

sooo good!

[@surajpatil3247]

greatttttttttttttttttttttttttt

[@happypumpkinpm7434]

Great video, thanks for the explanation. I have a question regarding your code, I wonder if your code is based on hough circle for unknown radius? how do you draw the accumulator array for an unknown radius? your code: drive.google.com/drive/u/0/folders/1UTIgcj0Z-dKo67zNZj8qwmueH0g3OPp0