Asked by lara
on 21 Jul 2011

i have created white boxes inside a big black box as follows:

A=zeros(70,70); % black box

A(15:23,50:55)=1;% white box

A(50:60,50:55)=1;% white box

A(20:23,10:13)=1 ;% white box

imshow(A,[])

how can i add to the same matrix A a white circle or a white sphere?thanks in advance.

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Answer by Andrei Bobrov
on 21 Jul 2011

Accepted answer

A=zeros(70,70); r = 10; %radius m = {40,40}; %midpoint A(m{:})=1; B = imdilate(A,strel('disk', r,0) ); imshow(B)

**ADD** wutout Image Processing Toolbox

A=zeros(70,70); r = 10; %radius P = [40,40]; %midpoint [m n ] = size(A); X = bsxfun(@plus,(1:m)',zeros(1,n)); Y = bsxfun(@plus,(1:n),zeros(m,1)); B = sqrt(sum(bsxfun(@minus,cat(3,X,Y),reshape(P,1,1,[])).^2,3))<=r; imagesc(B)

Show 1 older comment

Andrei Bobrov
on 21 Jul 2011

A=zeros(70,70);

r = 10; %radius

m = {40,40}; %midpoint

A(m{:})=1;

B = bwdist(A) <= r;

imshow(B)

Friedrich
on 21 Jul 2011

Nice. +1

Andrei Bobrov
on 21 Jul 2011

Thanks, Friedrich!

Adding my variant without Image Processing Toolbox

Answer by Friedrich
on 21 Jul 2011

Hi,

can this help?

function out = my_circ( A, midpoint, radius )

out = A; [ m n] = size(A);

for i=1:m for j=1:n if norm( [i,j] - midpoint ) <= radius out(i,j) = 1; end end end

end

And call it through:

>> A = zeros(100); >> B = my_circ(A,[40,40],10); >> imshow(B,[]);

Answer by Ujitha
on 3 Mar 2013

Hi this was really helpful. How do you do this to create two different sizes of circles.

Thanks inadvance

Image Analyst
on 3 Mar 2013

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