rebacksamp.m

contourlet算法作为二阶小波算法的延续

function y = rebacksamp(y)
% REBACKSAMP   Re-backsampling the subband images of the DFB
%
%	y = rebacksamp(y)
%
% Input and output are cell vector of dyadic length
%
% This function is call at the begin of the DFBREC to undo the operation
% of BACKSAMP before process filter bank reconstruction.  In otherword,
% it is inverse operation of BACKSAMP
%
% See also:	BACKSAMP, DFBREC

% Number of decomposition tree levels
n = log2(length(y));

if (n ~= round(n)) | (n < 1)
    error('Input must be a cell vector of dyadic length');
end

if n == 1
    % One level, the reconstruction filterbank shoud be Q1r
    % Redo the first resampling (Q1r = R2 * D1 * R3)
    for k = 1:2
	y{k}(:, 1:2:end) = resamp(y{k}(:, 1:2:end), 2);
	y{k}(:, 2:2:end) = resamp(y{k}(:, 2:2:end), 2);		
	y{k} = resamp(y{k}, 3);
    end

elseif n > 2
    N = 2^(n-1);
    
    for k = 1:2^(n-2)
	shift = 2*k - (2^(n-2) + 1);
	
	% The first half channels
	y{2*k-1} = resamp(y{2*k-1}, 3, -shift);
	y{2*k} = resamp(y{2*k}, 3, -shift);
	
	% The second half channels
	y{2*k-1+N} = resamp(y{2*k-1+N}, 1, -shift);
	y{2*k+N} = resamp(y{2*k+N}, 1, -shift);	
    end
end