nms.m

function pick = nms(boxes, overlap)
% top = nms(boxes, overlap)
% Non-maximum suppression. (FAST VERSION)
% Greedily select high-scoring detections and skip detections
% that are significantly covered by a previously selected
% detection.
%
% NOTE: This is adapted from Pedro Felzenszwalb's version (nms.m),
% but an inner loop has been eliminated to significantly speed it
% up in the case of a large number of boxes

% Copyright (C) 2011-12 by Tomasz Malisiewicz
% All rights reserved.
%
% This file is part of the Exemplar-SVM library and is made
% available under the terms of the MIT license (see COPYING file).
% Project homepage: https://github.com/quantombone/exemplarsvm


if isempty(boxes)
  pick = [];
  return;
end

x1 = boxes(:,1);
y1 = boxes(:,2);
x2 = boxes(:,3);
y2 = boxes(:,4);
s = boxes(:,end);

area = (x2-x1+1) .* (y2-y1+1);
[vals, I] = sort(s);

pick = s*0;
counter = 1;
while ~isempty(I)
  last = length(I);
  i = I(last);
  pick(counter) = i;
  counter = counter + 1;

  xx1 = max(x1(i), x1(I(1:last-1)));
  yy1 = max(y1(i), y1(I(1:last-1)));
  xx2 = min(x2(i), x2(I(1:last-1)));
  yy2 = min(y2(i), y2(I(1:last-1)));

  w = max(0.0, xx2-xx1+1);
  h = max(0.0, yy2-yy1+1);

  inter = w.*h;
  o = inter ./ (area(i) + area(I(1:last-1)) - inter);

  I = I(find(o<=overlap));
end

pick = pick(1:(counter-1));