Creation of a black and white image

Hello, I tried to create an image of 512 X 512 pixels filled with black and in its center a square of white pixels of width 100 pixels for the moment I use this code to display an image in black but I can not do it at all is it you have a solution ?

image=zeros(512,512,3); %initialize
image(:,1)=0.5;   %(dark )
figure, imshow(image)

Answer 1

[Stephan]

image=zeros(512,512);
image(206:305,206:305)=255;
imshow(image)

[Damien Dubois]

Thank you very much.