a = ones(240,320,3,70);

SE = strel('square',4);

for k=1:70
   a(45:195, 60:260,:,k)=0;

   if( k>=1 && k<=20 )
       x = round(60 + 10*(k-1));
       y = round(46);
   end
   if( k>=21 && k<=35 )
       y = round(45+10*(k-21));
   end
   if( k>=36 && k<=55 )
       x = round(260 - 10*(k-36));
   end
   if( k>=56 && k<=70 )
       y = round(185-10*(k-56));
   end
       a(y,x,1,k) = 0;
       a(y,x,2,k) = 1;
       a(y,x,3,k) = 0;
       a(:,:,:,k) = imdilate( a(:,:,:,k),SE );
end

prev = a(:,:,:,1);
for i=2:70
   prev(:,:,:,i) = a(:,:,:,i)+prev(:,:,:,i-1);
end
implay(prev);