create a white circle or sphere inside a black box

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.

Answer 1

[Andrei Bobrov]

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)

[Friedrich]

If she has Image Processing Toolbox your code will work. Maybe consider using bwdist. This should be possible too and should result in short code ;)

[Andrei Bobrov]

A=zeros(70,70);

r = 10; %radius

m = {40,40}; %midpoint

A(m{:})=1;

B = bwdist(A) <= r;

imshow(B)

[Friedrich]

Nice. +1

[Andrei Bobrov]

Thanks, Friedrich!

Adding my variant without Image Processing Toolbox

Answer 2

[Friedrich]

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 3

[Ujitha]

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

Thanks inadvance

[Image Analyst]

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_a_circle.3F

Answer 4

[Ujitha]

Thanks a lot. It was really helpful..!