p3d-hdrvdp-2/matlabPyrTools_1.4_fixed/modulateFlip.m

% [HFILT] = modulateFlipShift(LFILT)
%
% QMF/Wavelet highpass filter construction: modulate by (-1)^n,
% reverse order (and shift by one, which is handled by the convolution
% routines).  This is an extension of the original definition of QMF's
% (e.g., see Simoncelli90).

% Eero Simoncelli, 7/96.

function [hfilt] = modulateFlipShift(lfilt)

lfilt = lfilt(:);

sz = size(lfilt,1);
sz2 = ceil(sz/2);

ind = [sz:-1:1]';

hfilt = lfilt(ind) .* (-1).^(ind-sz2);