'example: images / train2014 / COCO_train2014_000000119993.jpg'

def image_path_from_index(self, index):

    filename = ('COCO_%s_%012d.jpg' % (self.data_name, index))
    image_path = os.path.join(self.data_path, 'images', self.data_name, filename)
    assert os.path.exists(image_path), 'Path    does    not    exist:    {}'.format(image_path)
    return image_path
