Im=imread('0002_m_l_01.jpg');                       
Im=ceil(Im);
Fl=medfilt2(Im,[17 17]);         
B2=im2bw(Fl,0.1);               
boundary=bwboundaries(B2);
b=boundary{1};                  
Ol(284,384)=0;
for m=1:(size(b))(1)
Ol(b(m,1),b(m,2))=1;
end               
请问从b=boundary{1}往下面每句是什么意思？