imdb_from_voc.m

function imdb = imdb_from_voc(root_dir, image_set, year, flip)
% imdb = imdb_from_voc(root_dir, image_set, year)
%   Builds an image database for the PASCAL VOC devkit located
%   at root_dir using the image_set and year.
%
%   Inspired by Andrea Vedaldi's MKL imdb and roidb code.

% AUTORIGHTS
% ---------------------------------------------------------
% Copyright (c) 2014, Ross Girshick
% 
% This file is part of the R-CNN code and is available 
% under the terms of the Simplified BSD License provided in 
% LICENSE. Please retain this notice and LICENSE if you use 
% this file (or any portion of it) in your project.
% ---------------------------------------------------------

%imdb.name = 'voc_train_2007'
%imdb.image_dir = '/work4/rbg/VOC2007/VOCdevkit/VOC2007/JPEGImages/'
%imdb.extension = '.jpg'
%imdb.image_ids = {'000001', ... }
%imdb.sizes = [numimages x 2]
%imdb.classes = {'aeroplane', ... }
%imdb.num_classes
%imdb.class_to_id
%imdb.class_ids
%imdb.eval_func = pointer to the function that evaluates detections
%imdb.roidb_func = pointer to the function that returns regions of interest

if nargin < 4
    flip = false;
end

cache_file = ['./imdb/cache/imdb_voc_' year '_' image_set];
if flip
    cache_file = [cache_file, '_flip'];
end
try
  load(cache_file);
catch
  VOCopts = get_voc_opts(root_dir);
  VOCopts.testset = image_set;

  imdb.name = ['voc_' year '_' image_set];
  imdb.image_dir = fileparts(VOCopts.imgpath);
  imdb.image_ids = textread(sprintf(VOCopts.imgsetpath, image_set), '%s');
  imdb.extension = 'jpg';
  imdb.flip = flip;
  if flip
      image_at = @(i) sprintf('%s/%s.%s', imdb.image_dir, imdb.image_ids{i}, imdb.extension);
      flip_image_at = @(i) sprintf('%s/%s_flip.%s', imdb.image_dir, imdb.image_ids{i}, imdb.extension);
      for i = 1:length(imdb.image_ids)
          if ~exist(flip_image_at(i), 'file')
             im = imread(image_at(i));
             imwrite(fliplr(im), flip_image_at(i));
          end
      end
      img_num = length(imdb.image_ids)*2;
      image_ids = imdb.image_ids;
      imdb.image_ids(1:2:img_num) = image_ids;
      imdb.image_ids(2:2:img_num) = cellfun(@(x) [x, '_flip'], image_ids, 'UniformOutput', false);
      imdb.flip_from = zeros(img_num, 1);
      imdb.flip_from(2:2:img_num) = 1:2:img_num;
  end
  imdb.classes = VOCopts.classes;
  imdb.num_classes = length(imdb.classes);
  imdb.class_to_id = ...
    containers.Map(imdb.classes, 1:imdb.num_classes);
  imdb.class_ids = 1:imdb.num_classes;

  % private VOC details
  imdb.details.VOCopts = VOCopts;

  % VOC specific functions for evaluation and region of interest DB
  imdb.eval_func = @imdb_eval_voc;
  imdb.roidb_func = @roidb_from_voc;
  imdb.image_at = @(i) ...
      sprintf('%s/%s.%s', imdb.image_dir, imdb.image_ids{i}, imdb.extension);

  for i = 1:length(imdb.image_ids)
    tic_toc_print('imdb (%s): %d/%d\n', imdb.name, i, length(imdb.image_ids));
    info = imfinfo(sprintf(VOCopts.imgpath, imdb.image_ids{i}));
    imdb.sizes(i, :) = [info.Height info.Width];
  end

  fprintf('Saving imdb to cache...');
  save(cache_file, 'imdb', '-v7.3');
  fprintf('done\n');
end