How to generate point on edge of circle so that input to other code?

https://kr.mathworks.com/matlabcentral/fileexchange/19083-calccircle

I want pick 3 points on this image and recover this circle by using code in link above.

I used bwboundaries function to define coordinates of 3 points

but have no idea how to pick 3 random points and connect it to code in link.

No need to use bwboundaries function if there are solutions!

Any small help would be my big appreciate!

Here is trial and error found on defining p1, p2, p3 part..

out = imread('noname1.png');
out = rgb2gray(out);
figure; imshow(out); hold on;

   [B,L,N] = bwboundaries(out,4,'holes');
   a = bwboundaries(out,4,'holes');
   figure; imshow(out); axis equal; hold on;

   for k = 1 : length(B),
       boundary = B{k};
       if(k > N)
           plot(boundary(:,2), boundary(:,1), 'g', 'LineWidth', 2);
       else
           plot(boundary(:,2), boundary(:,1), 'r', 'LineWidth', 2);
       end
   end

%%%%%%error %%%%%%%%%
p1 = (469,441);
p2 = (680,241);
p3 = (1025,512);
%%%%%%error %%%%%%%%%

[c r] = calc_circle(p1, p2, p3);

axis equal
hold on
if r == -1
    disp('COLLINEAR')
else
    rectangle('Position', [c(1)-r,c(2)-r,2*r,2*r],...
'Curvature', [1,1], 'EdgeColor', 'g')
end
plot(p1(1), p1(2), '*')
plot(p2(1), p2(2), '*')
plot(p3(1), p3(2), '*')

[hyong suk choo]

It works changing () to []!

Answer 1

[KSSV]

I = imread('yourimage') ;
[y,x] = find(I(:,:,1)) ;   % your required points 

imshow(I) ;
hold on
plot(x,y,'.r')

[hyong suk choo]

Thank you for your answer! I just tried this way but it didn't work.

index exceeds matrix of dimension. when boundaries tracked too.

out = imread('C:\Users\Choo Hyong Suk\Desktop\noname1.png');
out = rgb2gray(out);

 %%%%%%%%%%%%%%%try 1 %%%%%%%%%%%%%%%%
  [y1,x1] = find(out(469,441,1));
  [y2,x2] = find(out(680,241,1));
  [y3,x3] = find(out(1025,512,1));

imshow(out);
hold on

   p1 = [x1,y1];
   p2 = [x2,y2];
   p3 = [x3,y3];

 %%%%%%%%%%%%%%%try1 %%%%%%%%%%%%%%%%

 %%%%%%%%%%%%%%%try2 %%%%%%%%%%%%%%%%

 p1 = find(out(469,441,1));
 p2 = find(out(680,241,1));
 p3 = find(out(1025,512,1));

 %%%%%%%%%%%%%%%try2 %%%%%%%%%%%%%%%%

[c r] = calc_circle(p1, p2, p3);

Is there anything missed?

[KSSV]

Simply try [y,x] = find(out); It gives all the points lying on the circle.

[hyong suk choo]

Useful tool. thanks! I'm sure find code would be used someday.