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(Matlab) Image processing - Detect multiple circle

Dear All..

I need your help about hough transform..

I have problem with detecting multiple circle

I have program to detect a circle and show the radius of it..

but the problem is I want to detect another circle in a picture and shown the radius as well..

here is the program

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%circle equation = (x-a)^2 + (y-b)^2 = R^2

I = imread('pic23.bmp');

% function [radian]= hough (I)

I =im2bw(I);

[y,x]=find(I);

[sy,sx]=size(I);

totalpix = length(x); %totalpix is the numbers of '1' in the image (white)

HM = zeros(sy,sx,50); %Preallocate memory

R = 1:50; %R is known in the range from 1 to 50

R2 = R.^2;

sz = sy*sx; %column x row

% Hough Transform

for cnt = 1:totalpix

for cntR = 1:50

b = 1:sy;

a = (round(x(cnt) - sqrt(R2(cntR) - (y(cnt) - [1:sy]).^2))); %(x-a)^2 + (y-b)^2 = R^2

b = b(imag(a)==0 & a>0);

a = a(imag(a)==0 & a>0);

ind = sub2ind([sy,sx],b,a);

HM(sz*(cntR-1)+ind) = HM(sz*(cntR-1)+ind) + 1;

end

end

% Find for the maximum value for each layer, or in other words, the layer

% with maximum value will indicate the correspond R for the circle

for cnt = 1:50

H(cnt) = max(max(HM(:,:,cnt)));

end

[maxval, maxind] = max(H);

[B,A] = find(HM(:,:,maxind)==maxval);

imshow(I); hold on;

plot(mean(A),mean(B),'xr')

text(mean(A),mean(B),num2str(maxind),'color','gree n')

radian = maxind

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and the result of the image i put on attachment .

It shows only the radius of the biggest circle.

I want to know the small one also, or if there is another circle.

Thank you very much for any help..