That matrix is already the ROI.
Potentially you might want to do something like
ROI = imfill(YourMatrix, 'holes');
if you want to convert things like
0 0 0 0 0
0 1 1 1 0
0 1 0 1 0
0 1 1 1 0
0 0 0 0 0
to
0 0 0 0 0
0 1 1 1 0
0 1 1 1 0
0 1 1 1 0
0 0 0 0 0
If for some reason you only want the coordinates of the outside boundary (which is not how you typically use ROIs) then https://www.mathworks.com/help/images/ref/bwboundaries.html or https://www.mathworks.com/help/images/ref/bwtraceboundary.html
If you want the smallest enclosing rectangle around the area that has 1's (which is often used with ROIs), then use regionprops() with the 'boundingbox' option.
