nullevels.imwd          package:wavethresh          R Documentation

_S_e_t_s _w_h_o_l_e _r_e_s_o_l_u_t_i_o_n _l_e_v_e_l_s _o_f _c_o_e_f_f_i_c_i_e_n_t_s _e_q_u_a_l _t_o _z_e_r_o _i_n _a _i_m_w_d _o_b_j_e_c_t.

_D_e_s_c_r_i_p_t_i_o_n:

     Sets whole resolution levels of coefficients equal to zero in a
     'imwd.object'

_U_s_a_g_e:

     nullevels.imwd(imwd, levelstonull, ...)

_A_r_g_u_m_e_n_t_s:

    imwd: An object of class 'imwd'.

levelstonull: An integer vector specifying which resolution levels of
          coefficients of 'imwd' that you wish to set to zero. 

     ...: any other arguments

_D_e_t_a_i_l_s:

     Setting whole resolution levels of coefficients to zero can be
     very useful. For example, one can construct a linear smoothing
     method by setting all coefficients above a particular resolution
     (the _primary resolution_ equal to zero. Also setting particular
     levels equal to zero can also be useful for removing noise which
     is specific to a particular resolution level (as long as important
     signal is not also contained at that level). 

     Note that this function removes the horiztonal, diagonal and
     vertical detail coefficients at the resolution level specified. It
     does not remove the father wavelet coefficients at those
     resolution levels. 

     To remove individual coefficients on a systematic basis you
     probably want to look at the 'threshold' function.

_V_a_l_u_e:

     An object of class 'imwd' where the coefficients in resolution
     levels specified by levelstonull have been set to zero.

_R_E_L_E_A_S_E:

     Version 3.9.5 Copyright Guy Nason 1998

_S_e_e _A_l_s_o:

     'nullevels', 'imwd', 'imwd.object', 'threshold'.

_E_x_a_m_p_l_e_s:

     #
     # Do the wavelet transform of the Lennon image
     #
     #lenimwd <- imwd(lennon)
     #
     # Set scales (resolution levels) 2, 4 and 6 equal to zero.
     #
     #lenwdNL <- nullevels(lenimwd, levelstonull=c(2,4,6))
     #
     # Now let's plot the coefficients using a nice blue-heat colour map
     #
     # You will see that coefficients at levels 2, 4 and 6 are black (i.e. zero)
     # You can see that coefficients at other levels are unaffected and still
     # show the Lennon coefficients.
     #
     #plot(lenwdNL)

