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- % [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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