coco_loader.py

# Copyright (c) 2019 PaddlePaddle Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import numpy as np
from pycocotools.coco import COCO

import logging
logger = logging.getLogger(__name__)


def load(anno_path, sample_num=-1, with_background=True):
    """
    Load COCO records with annotations in json file 'anno_path'

    Args:
        anno_path (str): json file path
        sample_num (int): number of samples to load, -1 means all
        with_background (bool): whether load background as a class.
                                if True, total class number will
                                be 81. default True

    Returns:
        (records, cname2cid)
        'records' is list of dict whose structure is:
        {
            'im_file': im_fname, # image file name
            'im_id': img_id, # image id
            'h': im_h, # height of image
            'w': im_w, # width
            'is_crowd': is_crowd,
            'gt_score': gt_score,
            'gt_class': gt_class,
            'gt_bbox': gt_bbox,
            'gt_poly': gt_poly,
        }
        'cname2cid' is a dict used to map category name to class id
    """
    assert anno_path.endswith('.json'), 'invalid coco annotation file: ' \
        + anno_path
    coco = COCO(anno_path)
    img_ids = coco.getImgIds()
    cat_ids = coco.getCatIds()
    records = []
    ct = 0

    # when with_background = True, mapping category to classid, like:
    #   background:0, first_class:1, second_class:2, ...
    catid2clsid = dict(
        {catid: i + int(with_background)
         for i, catid in enumerate(cat_ids)})
    cname2cid = dict({
        coco.loadCats(catid)[0]['name']: clsid
        for catid, clsid in catid2clsid.items()
    })

    for img_id in img_ids:
        img_anno = coco.loadImgs(img_id)[0]
        im_fname = img_anno['file_name']
        im_w = float(img_anno['width'])
        im_h = float(img_anno['height'])

        ins_anno_ids = coco.getAnnIds(imgIds=img_id, iscrowd=False)
        instances = coco.loadAnns(ins_anno_ids)

        bboxes = []
        for inst in instances:
            x, y, box_w, box_h = inst['bbox']
            x1 = max(0, x)
            y1 = max(0, y)
            x2 = min(im_w - 1, x1 + max(0, box_w - 1))
            y2 = min(im_h - 1, y1 + max(0, box_h - 1))
            if inst['area'] > 0 and x2 >= x1 and y2 >= y1:
                inst['clean_bbox'] = [x1, y1, x2, y2]
                bboxes.append(inst)
            else:
                logger.warn(
                    'Found an invalid bbox in annotations: im_id: {}, area: {} x1: {}, y1: {}, x2: {}, y2: {}.'.
                    format(img_id, float(inst['area']), x1, y1, x2, y2))
        num_bbox = len(bboxes)

        gt_bbox = np.zeros((num_bbox, 4), dtype=np.float32)
        gt_class = np.zeros((num_bbox, 1), dtype=np.int32)
        gt_score = np.ones((num_bbox, 1), dtype=np.float32)
        is_crowd = np.zeros((num_bbox, 1), dtype=np.int32)
        difficult = np.zeros((num_bbox, 1), dtype=np.int32)
        gt_poly = [None] * num_bbox

        for i, box in enumerate(bboxes):
            catid = box['category_id']
            gt_class[i][0] = catid2clsid[catid]
            gt_bbox[i, :] = box['clean_bbox']
            is_crowd[i][0] = box['iscrowd']
            if 'segmentation' in box:
                gt_poly[i] = box['segmentation']

        coco_rec = {
            'im_file': im_fname,
            'im_id': np.array([img_id]),
            'h': im_h,
            'w': im_w,
            'is_crowd': is_crowd,
            'gt_class': gt_class,
            'gt_bbox': gt_bbox,
            'gt_score': gt_score,
            'gt_poly': gt_poly,
            'difficult': difficult
        }

        logger.debug('Load file: {}, im_id: {}, h: {}, w: {}.'.format(
            im_fname, img_id, im_h, im_w))
        records.append(coco_rec)
        ct += 1
        if sample_num > 0 and ct >= sample_num:
            break
    assert len(records) > 0, 'not found any coco record in %s' % (anno_path)
    logger.info('{} samples in file {}'.format(ct, anno_path))
    return records, cname2cid