bdg_mhaSampLazy.m

classdef bdg_mhaSampLazy < bdg_i
  %bdg_mhaSamp producing mini-batch by lazy sampling 
  %   Pass the handle to get_x and get_y
  %   Set function handles for how to get instances x and labels y
  %
  %   A typical senario:
  %   ------------------
  %   The instatces are a cube:
  %   X: [32,32,32,N], ndims(X) = 4
  %   The lables are 0/1 mask for the pre-specified points in the cube
  %   Y: [K,N], each clumn is 1-hot response for the fg; Or 0/1 bg/fg 
  %      coding when K = 1; bg, fg are balanced
  %
  
  properties
    mha;
    mk_fgbg;
    ix_fgbg; % [M] # fg+bg pixels index
    ix_fg;
    ix_bg;
    
    h_get_x; % handle to how to get instances x
    h_get_y; % handle to how to get labels y

    hb; % handle to a  bat_gentor
  end
   
  methods % implement the bdg_i interfaces
    function ob = bdg_mhaSampLazy (mha, mk_fgbg, bs, h_get_x, h_get_y)
    % ob = bdg_mhaSampInPlace (mha, mk_fgbg, bs, h_get_x, h_get_y)
    
      % setting and checking
      assert( all( size(mha)==size(mk_fgbg) ) );
      ob.mha = mha;
      ob.mk_fgbg = mk_fgbg;
      
      % sampling
      ob.ix_fg  = find(mk_fgbg == 255);
      ob.ix_bg  = find(mk_fgbg == 128);
      ob.ix_fgbg = [ob.ix_fg(:); ob.ix_bg(:)];
      
      % create internal batch generator
      N = numel(ob.ix_fgbg);
      ob.hb = bat_gentor();
      ob.hb = reset(ob.hb, N,bs);
      
      % function handles: how to get instances x and labels y?
      ob.h_get_x = h_get_x;
      ob.h_get_y = h_get_y;
    end % bdg_mhaSamp
    
    function ob = reset_epoch(ob)
    % reset for a new epoch
      N = numel(ob.ix_fgbg);
      bs = get_bdsz(ob, 1);
      ob.hb = reset(ob.hb, N,bs);
    end
    
    function [data, idx] = get_bd (ob, i_bat)
    % get the i_bat-th batch data
      % the instance index
      idx = get_idx(ob.hb, i_bat);
      data = get_bd_from_idx(ob, idx);
    end
    
    function [data, idx] = get_bd_orig (ob, i_bat)
    % get the i_bat-th batch data
      % the instance index
      idx = get_idx_orig(ob.hb, i_bat);
      data = get_bd_from_idx(ob, idx);
    end
    
    function N = get_bdsz (ob, i_bat)
    % get the size of the i_bat-th batch data
      N = numel( get_idx_orig(ob.hb, i_bat) );
    end
    
    function nb = get_numbat (ob)
    % get number of batchs in an epoch
      nb = ob.hb.num_bat;
    end
    
    function ni = get_numinst (ob)
    % get number of the total instances
      ni = numel(ob.ix_fgbg);
    end
  end % methods
  
  methods % auxiliary, extra interfaces
    function data = get_bd_from_idx (ob, idx)
      % the fg, bg mask index: should never be out of boundary
      ind_fgbg = ob.ix_fgbg(idx);
      
      % the instaces: X
      data{1} = ob.h_get_x(ob.mha, ind_fgbg);
      % the labels: Y
      data{2} = ob.h_get_y(ob.mk_fgbg, ind_fgbg);
    end
        
    function Ygt = get_all_Ygt (ob)
      Ygt = ob.h_get_y(ob.mk_fgbg, ob.ix_fgbg);
    end
    
  end % auxiliary 
  
end % bdg_mhaSampBal