how displaying subband coefficient matrix of dwt in matlab?

hi i apply dwt2 on image [ll,lh,hl,hh]=dwt2(i,'haar') is hh a coeffiecients matrix? is it correct i show it by imtool(hh)? i want to manipulating one of subband coeffiecient(in binary)but they are negative and decimal and if i convert them to uint8 or mat2gray() after apply idwt and again dwt cause changed pixels .what can i do? i read a lot of article about this method but None of them do not talk about this problem (Select one sub-band for embedding the secret message. i want to replace 3 least significant bits of wavelet coefficients by the 3 bits of bit stream )i do not know hoص to modify the coefficients?