Draw a circle inside a black image

I want to draw a circle in this 500x500 black matrix, but it deos not appear idk

here is the code

E = zeros(500,500); 
E2 = insertShape(E, 'Circle',[250 250 100], ...
    'Color','white', 'LineWidth',5); 
figure(5),imshow(uint8(E2));

Answer 1

[Voss]

E = zeros(500,500); 
E2 = insertShape(E, 'Circle',[250 250 100], ...
    'Color','white', 'LineWidth',5);

figure(5);
% imshow(uint8(255*E2));
% or:
imshow(E2);

[Maha Almuaikel]

@_

Can I ask you why did you delete uint8?

[Voss]

E2 is a double matrix with values between 0 and 1.

uint8(E2) gives you a uint8 matrix with values between 0 and 1.

uint8([0 0 0]) is black, and uint8([1 1 1]) is very close to black.

uint8([255 255 255]) is white, which is what you want, so either multiply by 255 before doing uint8() (so that 0 goes to 0 and 1 goes to 255) or just use the double values (between 0 and 1) as they already are.

[Image Analyst]

Do you need double? You just cast the whole thing to double at the end, so why didn't you like my solution where I just start out with the matrix being double right from the start, thus avoiding the need to cast it to double?

Or you can leave it as double - don't cast to uint8 - and it works fine:

E = zeros(500,500); 
E2 = insertShape(E, 'Circle',[250 250 100], ...
    'Color','white', 'LineWidth',5); 
figure(5),imshow(E2);

[Maha Almuaikel]

@_ @Image Analyst Thank you! got it

Answer 2

[Image Analyst]

Try this:

E = zeros(500,500, 'uint8'); % Make image as uint8 right from the beginning.
E2 = insertShape(E, 'Circle', [250 250 100], ...
    'Color','white', 'LineWidth',5); 
imshow(E2, []); % Display it with [] to expand the contrast.

[Maha Almuaikel]

@Image Analyst

Thanks!!