nms(boxes, overlap)

function pick = nms(boxes, overlap)

% pick = nms(boxes, overlap)
% Non-maximum suppression.
% Greedily select high-scoring detections and skip detections
% that are significantly covered by a previously selected detection.

if isempty(boxes)
    pick = [];
else
    x1   = boxes(1 , :);
    y1   = boxes(2 , :);
    s    = boxes(3 , :);
    x2   = x1 + s;
    y2   = y1 + s;
    fx   = boxes(4 , :);
    area = (x2-x1+1) .* (y2-y1+1);
    
    [vals, I] = sort(fx);
    pick = [];
    while (~isempty(I))
        last      = length(I);
        i         = I(last);
        pick      = [pick, i];
        suppress  = [last];
        for pos = 1:last-1
            j       = I(pos);
            xx1     = max(x1(i), x1(j));
            yy1     = max(y1(i), y1(j));
            xx2     = min(x2(i), x2(j));
            yy2     = min(y2(i), y2(j));
            w       = xx2-xx1+1;
            h       = yy2-yy1+1;
            if (w > 0 && h > 0)
                % compute overlap
                o = w * h / area(j);
                if (o > overlap)
                    suppress = [suppress; pos];
                end
            end
        end
        I(suppress) = [];
    end
end