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function feat = phow(conf, im)
% PHOW Extract PHOW features
%
% Author:: Andrea Vedaldi
conf_.color = false ;
conf_.sizes = [10 20] ;
conf_.step = 5 ;
conf_.fast = false ;
conf = override(conf_, conf) ;
im = im2double(im) ;
opts = {'windowsize', 1, 'verbose'} ;
if conf.fast, opts{end+1} = 'fast' ; end
if conf.color
if size(im, 3) == 1, im = cat(3, im, im, im) ; end
frames = [] ;
descrs = [] ;
for si = 1:length(conf.sizes)
s = conf.sizes(si) ;
ims = imsmooth(im, sqrt((s/6)^2 - 0)) ;
hsv = rgb2hsv(ims) ;
hsv = im2single(hsv) ;
d_ = [] ;
for k=1:3
% This offset causes features of different scales to have the same
% centers. While not strictly required, it makes the
% representation much more compact.
off = 3/2 * max(conf.sizes) + 1 - 3/2 * s ;
[f, d] = vl_dsift(squeeze(hsv(:,:,k)), ...
'step', conf.step, ...
'size', s, ...
'bounds', [off off +inf +inf], ...
'norm', opts{:}) ;
sel = find(f(3,:) < 0.002) ;
d(:,sel) = 0 ;
f = [f(1:2,:) ; 2*s * ones(1, size(f,2))] ;
d_ = cat(1, d_, d) ;
end
frames = cat(2, frames, f) ;
descrs = cat(2, descrs, d_) ;
end
else
if size(im, 3) == 3, im = rgb2gray(im) ; end
im = im2single(im) ;
frames = [] ;
descrs = [] ;
for si = 1:length(conf.sizes)
s = conf.sizes(si) ;
% This offset causes features of different scales to have the same
% centers. While not strictly required, it makes the
% representation much more compact.
off = 3/2 * max(conf.sizes) + 1 - 3/2 * s ;
ims = imsmooth(im, sqrt(max((s/6)^2 -.25,0))) ;
[f, d] = vl_dsift(ims, ...
'step', conf.step, ...
'size', s, ...
'bounds', [off off +inf +inf], ...
'norm', opts{:}) ;
sel = find(f(3,:) < 0.005) ;
d(:,sel) = 0 ;
% figure ; hist(f(3,:),100) ;
%drawnow ;
f = [f(1:2,:) ; 2*s * ones(1, size(f,2))] ;
frames = cat(2, frames, f) ;
descrs = cat(2, descrs, d) ;
end
end
feat = struct('frames', frames, 'descrs', descrs) ;
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