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executable file 91 lines (72 sloc) 2.713 kB
% [PYR, INDICES, STEERMTX, HARMONICS] = buildSCFpyr(IM, HEIGHT, ORDER, TWIDTH)
%
% This is a modified version of buildSFpyr, that constructs a
% complex-valued steerable pyramid using Hilbert-transform pairs
% of filters. Note that the imaginary parts will *not* be steerable.
%
% To reconstruct from this representation, either call reconSFpyr
% on the real part of the pyramid, *or* call reconSCFpyr which will
% use both real and imaginary parts (forcing analyticity).
%
% Description of this transform appears in: Portilla & Simoncelli,
% Int'l Journal of Computer Vision, 40(1):49-71, Oct 2000.
% Further information: http://www.cns.nyu.edu/~eero/STEERPYR/
% Original code: Eero Simoncelli, 5/97.
% Modified by Javier Portilla to return complex (quadrature pair) channels,
% 9/97.
function [pyr,pind,steermtx,harmonics] = buildSCFpyr(im, ht, order, twidth)
%-----------------------------------------------------------------
%% DEFAULTS:
max_ht = floor(log2(min(size(im)))) - 2;
if (exist('ht') ~= 1)
ht = max_ht;
else
if (ht > max_ht)
error(sprintf('Cannot build pyramid higher than %d levels.',max_ht));
end
end
if (exist('order') ~= 1)
order = 3;
elseif ((order > 15) | (order < 0))
fprintf(1,'Warning: ORDER must be an integer in the range [0,15]. Truncating.\n');
order = min(max(order,0),15);
else
order = round(order);
end
nbands = order+1;
if (exist('twidth') ~= 1)
twidth = 1;
elseif (twidth <= 0)
fprintf(1,'Warning: TWIDTH must be positive. Setting to 1.\n');
twidth = 1;
end
%-----------------------------------------------------------------
%% Steering stuff:
if (mod((nbands),2) == 0)
harmonics = [0:(nbands/2)-1]'*2 + 1;
else
harmonics = [0:(nbands-1)/2]'*2;
end
steermtx = steer2HarmMtx(harmonics, pi*[0:nbands-1]/nbands, 'even');
%-----------------------------------------------------------------
dims = size(im);
ctr = ceil((dims+0.5)/2);
[xramp,yramp] = meshgrid( ([1:dims(2)]-ctr(2))./(dims(2)/2), ...
([1:dims(1)]-ctr(1))./(dims(1)/2) );
angle = atan2(yramp,xramp);
log_rad = sqrt(xramp.^2 + yramp.^2);
log_rad(ctr(1),ctr(2)) = log_rad(ctr(1),ctr(2)-1);
log_rad = log2(log_rad);
%% Radial transition function (a raised cosine in log-frequency):
[Xrcos,Yrcos] = rcosFn(twidth,(-twidth/2),[0 1]);
Yrcos = sqrt(Yrcos);
YIrcos = sqrt(1.0 - Yrcos.^2);
lo0mask = pointOp(log_rad, YIrcos, Xrcos(1), Xrcos(2)-Xrcos(1), 0);
imdft = fftshift(fft2(im));
lo0dft = imdft .* lo0mask;
[pyr,pind] = buildSCFpyrLevs(lo0dft, log_rad, Xrcos, Yrcos, angle, ht, nbands);
hi0mask = pointOp(log_rad, Yrcos, Xrcos(1), Xrcos(2)-Xrcos(1), 0);
hi0dft = imdft .* hi0mask;
hi0 = ifft2(ifftshift(hi0dft));
pyr = [real(hi0(:)) ; pyr];
pind = [size(hi0); pind];
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