Convert to png and save json with path. This currently only contains
    the segmentation labels for objects+stuff in cocostuff - if we need to
    combine with other labels from original COCO that will be a TODO.

def convert_coco_stuff_mat(data_dir, out_dir):
    """Convert to png and save json with path. This currently only contains
    the segmentation labels for objects+stuff in cocostuff - if we need to
    combine with other labels from original COCO that will be a TODO."""
    sets = ['train', 'val']
    categories = []
    json_name = 'coco_stuff_%s.json'
    ann_dict = {}
    for data_set in sets:
        file_list = os.path.join(data_dir, '%s.txt')
        images = []
        with open(file_list % data_set) as f:
            for img_id, img_name in enumerate(f):
                img_name = img_name.replace('coco', 'COCO').strip('\n')
                image = {}
                mat_file = os.path.join(
                    data_dir, 'annotations/%s.mat' % img_name)
                data = h5py.File(mat_file, 'r')
                labelMap = data.get('S')
                if len(categories) == 0:
                    labelNames = data.get('names')
                    for idx, n in enumerate(labelNames):
                        categories.append(
                            {"id": idx, "name": ''.join(chr(i) for i in data[
                                n[0]])})
                    ann_dict['categories'] = categories
                scipy.misc.imsave(
                    os.path.join(data_dir, img_name + '.png'), labelMap)
                image['width'] = labelMap.shape[0]
                image['height'] = labelMap.shape[1]
                image['file_name'] = img_name
                image['seg_file_name'] = img_name
                image['id'] = img_id
                images.append(image)
        ann_dict['images'] = images
        print("Num images: %s" % len(images))
        with open(os.path.join(out_dir, json_name % data_set), 'wb') as outfile:
            outfile.write(json.dumps(ann_dict))