visualizeHOG.m

function visualizeHOG(I, bins)
    hogs = features(double(I), bins);
    im = visualizeHOGfeatures(hogs, bins);
    imshow(im);
end

function im = visualizeHOGfeatures(w, bs)
    % Make picture of positive HOG weights.
    % im = HOGpicture(w, bs)

    % AUTORIGHTS
    % -------------------------------------------------------
    % Copyright (C) 2011-2012 Ross Girshick
    % Copyright (C) 2008, 2009, 2010 Pedro Felzenszwalb, Ross Girshick
    % Copyright (C) 2007 Pedro Felzenszwalb, Deva Ramanan
    %
    % This file is part of the voc-releaseX code
    % (http://people.cs.uchicago.edu/~rbg/latent/)
    % and is available under the terms of an MIT-like license
    % provided in COPYING. Please retain this notice and
    % COPYING if you use this file (or a portion of it) in
    % your project.
    % -------------------------------------------------------

    % construct a "glyph" for each orientaion
    bim1 = zeros(bs, bs);
    bim1(:,round(bs/2):round(bs/2)+1) = 1;
    bim = zeros([size(bim1) 9]);
    bim(:,:,1) = bim1;
    for i = 2:9,
      bim(:,:,i) = imrotate(bim1, -(i-1)*20, 'crop');
    end

    % make pictures of positive weights bs adding up weighted glyphs
    s = size(w);
    w(w < 0) = 0;
    im = zeros(bs*s(1), bs*s(2));
    for i = 1:s(1),
      iis = (i-1)*bs+1:i*bs;
      for j = 1:s(2),
        jjs = (j-1)*bs+1:j*bs;
        for k = 1:9,
          im(iis,jjs) = im(iis,jjs) + bim(:,:,k) * w(i,j,k);
        end
      end
    end
end