the 2d convolution result dosen't match my expectation

%i
x = 1:317;
y = 1:317;
[xx,yy] = meshgrid(x,y);
z = (xx-158.5).^2+(yy-158.5).^2;
circle = zeros(317,317);
for i = 1:317
  for j = 1: 317
      if z(j,i) < 158.5^2
          circle(j,i) = 1;
      end
  end
end
c = conv2(circle,circle);
c = c./max(c);
imshow(c)

I use simple code, simple object. However the result isn't correct.

Why did this result come out?

p.s. The second image is square and square case.

[Rena Berman]

(Answers Dev) Restored question with images as attachments

Answer 1

[Bruno Luong]

Not sure what is your expectation, and intention but shooting on the dark, try to replace

c = c./max(c);

with

c = c./max(c(:));

[Bruno Luong]

Please accept the answer if it resolves your question. Thanks