How to generate boxes from an image

Hello, I have a .mat folder extension, it contains 3 matrix named props,superpixels and boxes ,i succesed of genrating for each props the mask from superpixels but i failed in generating boxes.In addition i want to optimize my algorithm by adding loop to generate 626 mask.this is my code .thanks for your help load('2.mat')

Nprop=size(GOP.props,1); % number of proposals

 prop=21; % pick any proposal

SP=GOP.props(prop,:); % which superpixels are in this proposal mask=SP(GOP.superpixels); imshow(mask);figure(gcf);