'fill basic information to initialize imdb
:param image_set: 2007_trainval, 2007_test, etc
:param root_path: \'selective_search_data\' and \'cache\'
:param devkit_path: data and results
:return: imdb object'

def __init__(self, image_set, root_path, devkit_path):

    (year, image_set) = image_set.split('_')
    super(PascalVOC, self).__init__(('voc_' + year), image_set, root_path, devkit_path)
    self.year = year
    self.root_path = root_path
    self.devkit_path = devkit_path
    self.data_path = os.path.join(devkit_path, ('VOC' + year))
    self.classes = ['__background__', 'aeroplane', 'bicycle', 'bird', 'boat', 'bottle', 'bus', 'car', 'cat', 'chair', 'cow', 'diningtable', 'dog', 'horse', 'motorbike', 'person', 'pottedplant', 'sheep', 'sofa', 'train', 'tvmonitor']
    self.num_classes = len(self.classes)
    self.image_set_index = self.load_image_set_index()
    self.num_images = len(self.image_set_index)
    logger.info(('%s    num_images    %d' % (self.name, self.num_images)))
    self.config = {'comp_id': 'comp4', 'use_diff': False, 'min_size': 2}
