Create a simple rectangular image

So I was wondering if I could create a small image of 100x100 pixels where the outside is dark whilst the inside is completely clear (1's) I know how to fill a matrix by doing zeroes(100,100) but I now want to replace within this area a space of ones(40,60) but How do i exactly overlay this?

Answer 1

[Walter Roberson]

img(row_white_start:row_white_start+num_white_rows-1, col_white_start:col_white_start+num_white_cols-1) = 1;

Answer 2

[Image Analyst]

Do you want to overlay an image or replace the image there? You said it both ways.

Do you mean like this:

img = zeros(100, 100);
img(31:70, 21:80) = 1
imshow(img, [], 'InitialMagnification', 1000);
grid on;
axis('on', 'image');

Answer 3

[DGM]

If you're describing a white image with a black border, then I'll offer a different method:

testpict = padarray(ones(40,60),[30 20]);

EDIT: If you don't have Image Processing Toolbox and you still want to use something with a convenient syntax, MIMT has you covered.

https://www.mathworks.com/matlabcentral/fileexchange/53786-image-manipulation-toolbox?s_tid=srchtitle

testpict1 = padarrayFB(ones(40,60),[30 20]); % works with or without IPT
testpict2 = addborder(ones(40,60),[30 20]); % addborder can do the same things as padarray()
testpict3 = addborder(ones(40,60,3),[20 40 30 10],[0.12 0.23 0.5]); % but it can do many other things too