object_detection/metrics/coco_tools.py

# Copyright 2017 The TensorFlow 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
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# ==============================================================================
"""Wrappers for third party pycocotools to be used within object_detection.

Note that nothing in this file is tensorflow related and thus cannot
be called directly as a slim metric, for example.

TODO(jonathanhuang): wrap as a slim metric in metrics.py


Usage example: given a set of images with ids in the list image_ids
and corresponding lists of numpy arrays encoding groundtruth (boxes and classes)
and detections (boxes, scores and classes), where elements of each list
correspond to detections/annotations of a single image,
then evaluation (in multi-class mode) can be invoked as follows:

  groundtruth_dict = coco_tools.ExportGroundtruthToCOCO(
      image_ids, groundtruth_boxes_list, groundtruth_classes_list,
      max_num_classes, output_path=None)
  detections_list = coco_tools.ExportDetectionsToCOCO(
      image_ids, detection_boxes_list, detection_scores_list,
      detection_classes_list, output_path=None)
  groundtruth = coco_tools.COCOWrapper(groundtruth_dict)
  detections = groundtruth.LoadAnnotations(detections_list)
  evaluator = coco_tools.COCOEvalWrapper(groundtruth, detections,
                                         agnostic_mode=False)
  metrics = evaluator.ComputeMetrics()

"""
from collections import OrderedDict
import copy
import time
import numpy as np

from pycocotools import coco
from pycocotools import cocoeval
from pycocotools import mask

import tensorflow as tf

from object_detection.utils import json_utils


class COCOWrapper(coco.COCO):
  """Wrapper for the pycocotools COCO class."""

  def __init__(self, dataset, detection_type='bbox'):
    """COCOWrapper constructor.

    See http://mscoco.org/dataset/#format for a description of the format.
    By default, the coco.COCO class constructor reads from a JSON file.
    This function duplicates the same behavior but loads from a dictionary,
    allowing us to perform evaluation without writing to external storage.

    Args:
      dataset: a dictionary holding bounding box annotations in the COCO format.
      detection_type: type of detections being wrapped. Can be one of ['bbox',
        'segmentation']

    Raises:
      ValueError: if detection_type is unsupported.
    """
    supported_detection_types = ['bbox', 'segmentation']
    if detection_type not in supported_detection_types:
      raise ValueError('Unsupported detection type: {}. '
                       'Supported values are: {}'.format(
                           detection_type, supported_detection_types))
    self._detection_type = detection_type
    coco.COCO.__init__(self)
    self.dataset = dataset
    self.createIndex()

  def LoadAnnotations(self, annotations):
    """Load annotations dictionary into COCO datastructure.

    See http://mscoco.org/dataset/#format for a description of the annotations
    format.  As above, this function replicates the default behavior of the API
    but does not require writing to external storage.

    Args:
      annotations: python list holding object detection results where each
        detection is encoded as a dict with required keys ['image_id',
        'category_id', 'score'] and one of ['bbox', 'segmentation'] based on
        `detection_type`.

    Returns:
      a coco.COCO datastructure holding object detection annotations results

    Raises:
      ValueError: if annotations is not a list
      ValueError: if annotations do not correspond to the images contained
        in self.
    """
    results = coco.COCO()
    results.dataset['images'] = [img for img in self.dataset['images']]

    tf.logging.info('Loading and preparing annotation results...')
    tic = time.time()

    if not isinstance(annotations, list):
      raise ValueError('annotations is not a list of objects')
    annotation_img_ids = [ann['image_id'] for ann in annotations]
    if (set(annotation_img_ids) != (set(annotation_img_ids)
                                    & set(self.getImgIds()))):
      raise ValueError('Results do not correspond to current coco set')
    results.dataset['categories'] = copy.deepcopy(self.dataset['categories'])
    if self._detection_type == 'bbox':
      for idx, ann in enumerate(annotations):
        bb = ann['bbox']
        ann['area'] = bb[2] * bb[3]
        ann['id'] = idx + 1
        ann['iscrowd'] = 0
    elif self._detection_type == 'segmentation':
      for idx, ann in enumerate(annotations):
        ann['area'] = mask.area(ann['segmentation'])
        ann['bbox'] = mask.toBbox(ann['segmentation'])
        ann['id'] = idx + 1
        ann['iscrowd'] = 0
    tf.logging.info('DONE (t=%0.2fs)', (time.time() - tic))

    results.dataset['annotations'] = annotations
    results.createIndex()
    return results


class COCOEvalWrapper(cocoeval.COCOeval):
  """Wrapper for the pycocotools COCOeval class.

  To evaluate, create two objects (groundtruth_dict and detections_list)
  using the conventions listed at http://mscoco.org/dataset/#format.
  Then call evaluation as follows:

    groundtruth = coco_tools.COCOWrapper(groundtruth_dict)
    detections = groundtruth.LoadAnnotations(detections_list)
    evaluator = coco_tools.COCOEvalWrapper(groundtruth, detections,
                                           agnostic_mode=False)

    metrics = evaluator.ComputeMetrics()
  """

  def __init__(self, groundtruth=None, detections=None, agnostic_mode=False,
               iou_type='bbox'):
    """COCOEvalWrapper constructor.

    Note that for the area-based metrics to be meaningful, detection and
    groundtruth boxes must be in image coordinates measured in pixels.

    Args:
      groundtruth: a coco.COCO (or coco_tools.COCOWrapper) object holding
        groundtruth annotations
      detections: a coco.COCO (or coco_tools.COCOWrapper) object holding
        detections
      agnostic_mode: boolean (default: False).  If True, evaluation ignores
        class labels, treating all detections as proposals.
      iou_type: IOU type to use for evaluation. Supports `bbox` or `segm`.
    """
    cocoeval.COCOeval.__init__(self, groundtruth, detections,
                               iouType=iou_type)
    if agnostic_mode:
      self.params.useCats = 0

  def GetCategory(self, category_id):
    """Fetches dictionary holding category information given category id.

    Args:
      category_id: integer id
    Returns:
      dictionary holding 'id', 'name'.
    """
    return self.cocoGt.cats[category_id]

  def GetAgnosticMode(self):
    """Returns true if COCO Eval is configured to evaluate in agnostic mode."""
    return self.params.useCats == 0

  def GetCategoryIdList(self):
    """Returns list of valid category ids."""
    return self.params.catIds

  def ComputeMetrics(self,
                     include_metrics_per_category=False,
                     all_metrics_per_category=False):
    """Computes detection metrics.

    Args:
      include_metrics_per_category: If True, will include metrics per category.
      all_metrics_per_category: If true, include all the summery metrics for
        each category in per_category_ap. Be careful with setting it to true if
        you have more than handful of categories, because it will pollute
        your mldash.

    Returns:
      1. summary_metrics: a dictionary holding:
        'Precision/mAP': mean average precision over classes averaged over IOU
          thresholds ranging from .5 to .95 with .05 increments
        'Precision/mAP@.50IOU': mean average precision at 50% IOU
        'Precision/mAP@.75IOU': mean average precision at 75% IOU
        'Precision/mAP (small)': mean average precision for small objects
                        (area < 32^2 pixels)
        'Precision/mAP (medium)': mean average precision for medium sized
                        objects (32^2 pixels < area < 96^2 pixels)
        'Precision/mAP (large)': mean average precision for large objects
                        (96^2 pixels < area < 10000^2 pixels)
        'Recall/AR@1': average recall with 1 detection
        'Recall/AR@10': average recall with 10 detections
        'Recall/AR@100': average recall with 100 detections
        'Recall/AR@100 (small)': average recall for small objects with 100
          detections
        'Recall/AR@100 (medium)': average recall for medium objects with 100
          detections
        'Recall/AR@100 (large)': average recall for large objects with 100
          detections
      2. per_category_ap: a dictionary holding category specific results with
        keys of the form: 'Precision mAP ByCategory/category'
        (without the supercategory part if no supercategories exist).
        For backward compatibility 'PerformanceByCategory' is included in the
        output regardless of all_metrics_per_category.
        If evaluating class-agnostic mode, per_category_ap is an empty
        dictionary.

    Raises:
      ValueError: If category_stats does not exist.
    """
    self.evaluate()
    self.accumulate()
    self.summarize()

    summary_metrics = OrderedDict([
        ('Precision/mAP', self.stats[0]),
        ('Precision/mAP@.50IOU', self.stats[1]),
        ('Precision/mAP@.75IOU', self.stats[2]),
        ('Precision/mAP (small)', self.stats[3]),
        ('Precision/mAP (medium)', self.stats[4]),
        ('Precision/mAP (large)', self.stats[5]),
        ('Recall/AR@1', self.stats[6]),
        ('Recall/AR@10', self.stats[7]),
        ('Recall/AR@100', self.stats[8]),
        ('Recall/AR@100 (small)', self.stats[9]),
        ('Recall/AR@100 (medium)', self.stats[10]),
        ('Recall/AR@100 (large)', self.stats[11])
    ])
    if not include_metrics_per_category:
      return summary_metrics, {}
    if not hasattr(self, 'category_stats'):
      raise ValueError('Category stats do not exist')
    per_category_ap = OrderedDict([])
    if self.GetAgnosticMode():
      return summary_metrics, per_category_ap
    for category_index, category_id in enumerate(self.GetCategoryIdList()):
      category = self.GetCategory(category_id)['name']
      # Kept for backward compatilbility
      per_category_ap['PerformanceByCategory/mAP/{}'.format(
          category)] = self.category_stats[0][category_index]
      if all_metrics_per_category:
        per_category_ap['Precision mAP ByCategory/{}'.format(
            category)] = self.category_stats[0][category_index]
        per_category_ap['Precision mAP@.50IOU ByCategory/{}'.format(
            category)] = self.category_stats[1][category_index]
        per_category_ap['Precision mAP@.75IOU ByCategory/{}'.format(
            category)] = self.category_stats[2][category_index]
        per_category_ap['Precision mAP (small) ByCategory/{}'.format(
            category)] = self.category_stats[3][category_index]
        per_category_ap['Precision mAP (medium) ByCategory/{}'.format(
            category)] = self.category_stats[4][category_index]
        per_category_ap['Precision mAP (large) ByCategory/{}'.format(
            category)] = self.category_stats[5][category_index]
        per_category_ap['Recall AR@1 ByCategory/{}'.format(
            category)] = self.category_stats[6][category_index]
        per_category_ap['Recall AR@10 ByCategory/{}'.format(
            category)] = self.category_stats[7][category_index]
        per_category_ap['Recall AR@100 ByCategory/{}'.format(
            category)] = self.category_stats[8][category_index]
        per_category_ap['Recall AR@100 (small) ByCategory/{}'.format(
            category)] = self.category_stats[9][category_index]
        per_category_ap['Recall AR@100 (medium) ByCategory/{}'.format(
            category)] = self.category_stats[10][category_index]
        per_category_ap['Recall AR@100 (large) ByCategory/{}'.format(
            category)] = self.category_stats[11][category_index]

    return summary_metrics, per_category_ap


def _ConvertBoxToCOCOFormat(box):
  """Converts a box in [ymin, xmin, ymax, xmax] format to COCO format.

  This is a utility function for converting from our internal
  [ymin, xmin, ymax, xmax] convention to the convention used by the COCO API
  i.e., [xmin, ymin, width, height].

  Args:
    box: a [ymin, xmin, ymax, xmax] numpy array

  Returns:
    a list of floats representing [xmin, ymin, width, height]
  """
  return [float(box[1]), float(box[0]), float(box[3] - box[1]),
          float(box[2] - box[0])]


def _RleCompress(masks):
  """Compresses mask using Run-length encoding provided by pycocotools.

  Args:
    masks: uint8 numpy array of shape [mask_height, mask_width] with values in
    {0, 1}.

  Returns:
    A pycocotools Run-length encoding of the mask.
  """
  return mask.encode(np.asfortranarray(masks))


def ExportSingleImageGroundtruthToCoco(image_id,
                                       next_annotation_id,
                                       category_id_set,
                                       groundtruth_boxes,
                                       groundtruth_classes,
                                       groundtruth_masks=None,
                                       groundtruth_is_crowd=None):
  """Export groundtruth of a single image to COCO format.

  This function converts groundtruth detection annotations represented as numpy
  arrays to dictionaries that can be ingested by the COCO evaluation API. Note
  that the image_ids provided here must match the ones given to
  ExportSingleImageDetectionsToCoco. We assume that boxes and classes are in
  correspondence - that is: groundtruth_boxes[i, :], and
  groundtruth_classes[i] are associated with the same groundtruth annotation.

  In the exported result, "area" fields are always set to the area of the
  groundtruth bounding box.

  Args:
    image_id: a unique image identifier either of type integer or string.
    next_annotation_id: integer specifying the first id to use for the
      groundtruth annotations. All annotations are assigned a continuous integer
      id starting from this value.
    category_id_set: A set of valid class ids. Groundtruth with classes not in
      category_id_set are dropped.
    groundtruth_boxes: numpy array (float32) with shape [num_gt_boxes, 4]
    groundtruth_classes: numpy array (int) with shape [num_gt_boxes]
    groundtruth_masks: optional uint8 numpy array of shape [num_detections,
      image_height, image_width] containing detection_masks.
    groundtruth_is_crowd: optional numpy array (int) with shape [num_gt_boxes]
      indicating whether groundtruth boxes are crowd.

  Returns:
    a list of groundtruth annotations for a single image in the COCO format.

  Raises:
    ValueError: if (1) groundtruth_boxes and groundtruth_classes do not have the
      right lengths or (2) if each of the elements inside these lists do not
      have the correct shapes or (3) if image_ids are not integers
  """

  if len(groundtruth_classes.shape) != 1:
    raise ValueError('groundtruth_classes is '
                     'expected to be of rank 1.')
  if len(groundtruth_boxes.shape) != 2:
    raise ValueError('groundtruth_boxes is expected to be of '
                     'rank 2.')
  if groundtruth_boxes.shape[1] != 4:
    raise ValueError('groundtruth_boxes should have '
                     'shape[1] == 4.')
  num_boxes = groundtruth_classes.shape[0]
  if num_boxes != groundtruth_boxes.shape[0]:
    raise ValueError('Corresponding entries in groundtruth_classes, '
                     'and groundtruth_boxes should have '
                     'compatible shapes (i.e., agree on the 0th dimension).'
                     'Classes shape: %d. Boxes shape: %d. Image ID: %s' % (
                         groundtruth_classes.shape[0],
                         groundtruth_boxes.shape[0], image_id))
  has_is_crowd = groundtruth_is_crowd is not None
  if has_is_crowd and len(groundtruth_is_crowd.shape) != 1:
    raise ValueError('groundtruth_is_crowd is expected to be of rank 1.')
  groundtruth_list = []
  for i in range(num_boxes):
    if groundtruth_classes[i] in category_id_set:
      iscrowd = groundtruth_is_crowd[i] if has_is_crowd else 0
      export_dict = {
          'id':
              next_annotation_id + i,
          'image_id':
              image_id,
          'category_id':
              int(groundtruth_classes[i]),
          'bbox':
              list(_ConvertBoxToCOCOFormat(groundtruth_boxes[i, :])),
          'area':
              float((groundtruth_boxes[i, 2] - groundtruth_boxes[i, 0]) *
                    (groundtruth_boxes[i, 3] - groundtruth_boxes[i, 1])),
          'iscrowd':
              iscrowd
      }
      if groundtruth_masks is not None:
        export_dict['segmentation'] = _RleCompress(groundtruth_masks[i])
      groundtruth_list.append(export_dict)
  return groundtruth_list


def ExportGroundtruthToCOCO(image_ids,
                            groundtruth_boxes,
                            groundtruth_classes,
                            categories,
                            output_path=None):
  """Export groundtruth detection annotations in numpy arrays to COCO API.

  This function converts a set of groundtruth detection annotations represented
  as numpy arrays to dictionaries that can be ingested by the COCO API.
  Inputs to this function are three lists: image ids for each groundtruth image,
  groundtruth boxes for each image and groundtruth classes respectively.
  Note that the image_ids provided here must match the ones given to the
  ExportDetectionsToCOCO function in order for evaluation to work properly.
  We assume that for each image, boxes, scores and classes are in
  correspondence --- that is: image_id[i], groundtruth_boxes[i, :] and
  groundtruth_classes[i] are associated with the same groundtruth annotation.

  In the exported result, "area" fields are always set to the area of the
  groundtruth bounding box and "iscrowd" fields are always set to 0.
  TODO(jonathanhuang): pass in "iscrowd" array for evaluating on COCO dataset.

  Args:
    image_ids: a list of unique image identifier either of type integer or
      string.
    groundtruth_boxes: list of numpy arrays with shape [num_gt_boxes, 4]
      (note that num_gt_boxes can be different for each entry in the list)
    groundtruth_classes: list of numpy arrays (int) with shape [num_gt_boxes]
      (note that num_gt_boxes can be different for each entry in the list)
    categories: a list of dictionaries representing all possible categories.
        Each dict in this list has the following keys:
          'id': (required) an integer id uniquely identifying this category
          'name': (required) string representing category name
            e.g., 'cat', 'dog', 'pizza'
          'supercategory': (optional) string representing the supercategory
            e.g., 'animal', 'vehicle', 'food', etc
    output_path: (optional) path for exporting result to JSON
  Returns:
    dictionary that can be read by COCO API
  Raises:
    ValueError: if (1) groundtruth_boxes and groundtruth_classes do not have the
      right lengths or (2) if each of the elements inside these lists do not
      have the correct shapes or (3) if image_ids are not integers
  """
  category_id_set = set([cat['id'] for cat in categories])
  groundtruth_export_list = []
  image_export_list = []
  if not len(image_ids) == len(groundtruth_boxes) == len(groundtruth_classes):
    raise ValueError('Input lists must have the same length')

  # For reasons internal to the COCO API, it is important that annotation ids
  # are not equal to zero; we thus start counting from 1.
  annotation_id = 1
  for image_id, boxes, classes in zip(image_ids, groundtruth_boxes,
                                      groundtruth_classes):
    image_export_list.append({'id': image_id})
    groundtruth_export_list.extend(ExportSingleImageGroundtruthToCoco(
        image_id,
        annotation_id,
        category_id_set,
        boxes,
        classes))
    num_boxes = classes.shape[0]
    annotation_id += num_boxes

  groundtruth_dict = {
      'annotations': groundtruth_export_list,
      'images': image_export_list,
      'categories': categories
  }
  if output_path:
    with tf.gfile.GFile(output_path, 'w') as fid:
      json_utils.Dump(groundtruth_dict, fid, float_digits=4, indent=2)
  return groundtruth_dict


def ExportSingleImageDetectionBoxesToCoco(image_id,
                                          category_id_set,
                                          detection_boxes,
                                          detection_scores,
                                          detection_classes):
  """Export detections of a single image to COCO format.

  This function converts detections represented as numpy arrays to dictionaries
  that can be ingested by the COCO evaluation API. Note that the image_ids
  provided here must match the ones given to the
  ExporSingleImageDetectionBoxesToCoco. We assume that boxes, and classes are in
  correspondence - that is: boxes[i, :], and classes[i]
  are associated with the same groundtruth annotation.

  Args:
    image_id: unique image identifier either of type integer or string.
    category_id_set: A set of valid class ids. Detections with classes not in
      category_id_set are dropped.
    detection_boxes: float numpy array of shape [num_detections, 4] containing
      detection boxes.
    detection_scores: float numpy array of shape [num_detections] containing
      scored for the detection boxes.
    detection_classes: integer numpy array of shape [num_detections] containing
      the classes for detection boxes.

  Returns:
    a list of detection annotations for a single image in the COCO format.

  Raises:
    ValueError: if (1) detection_boxes, detection_scores and detection_classes
      do not have the right lengths or (2) if each of the elements inside these
      lists do not have the correct shapes or (3) if image_ids are not integers.
  """

  if len(detection_classes.shape) != 1 or len(detection_scores.shape) != 1:
    raise ValueError('All entries in detection_classes and detection_scores'
                     'expected to be of rank 1.')
  if len(detection_boxes.shape) != 2:
    raise ValueError('All entries in detection_boxes expected to be of '
                     'rank 2.')
  if detection_boxes.shape[1] != 4:
    raise ValueError('All entries in detection_boxes should have '
                     'shape[1] == 4.')
  num_boxes = detection_classes.shape[0]
  if not num_boxes == detection_boxes.shape[0] == detection_scores.shape[0]:
    raise ValueError('Corresponding entries in detection_classes, '
                     'detection_scores and detection_boxes should have '
                     'compatible shapes (i.e., agree on the 0th dimension). '
                     'Classes shape: %d. Boxes shape: %d. '
                     'Scores shape: %d' % (
                         detection_classes.shape[0], detection_boxes.shape[0],
                         detection_scores.shape[0]
                     ))
  detections_list = []
  for i in range(num_boxes):
    if detection_classes[i] in category_id_set:
      detections_list.append({
          'image_id': image_id,
          'category_id': int(detection_classes[i]),
          'bbox': list(_ConvertBoxToCOCOFormat(detection_boxes[i, :])),
          'score': float(detection_scores[i])
      })
  return detections_list


def ExportSingleImageDetectionMasksToCoco(image_id,
                                          category_id_set,
                                          detection_masks,
                                          detection_scores,
                                          detection_classes):
  """Export detection masks of a single image to COCO format.

  This function converts detections represented as numpy arrays to dictionaries
  that can be ingested by the COCO evaluation API. We assume that
  detection_masks, detection_scores, and detection_classes are in correspondence
  - that is: detection_masks[i, :], detection_classes[i] and detection_scores[i]
    are associated with the same annotation.

  Args:
    image_id: unique image identifier either of type integer or string.
    category_id_set: A set of valid class ids. Detections with classes not in
      category_id_set are dropped.
    detection_masks: uint8 numpy array of shape [num_detections, image_height,
      image_width] containing detection_masks.
    detection_scores: float numpy array of shape [num_detections] containing
      scores for detection masks.
    detection_classes: integer numpy array of shape [num_detections] containing
      the classes for detection masks.

  Returns:
    a list of detection mask annotations for a single image in the COCO format.

  Raises:
    ValueError: if (1) detection_masks, detection_scores and detection_classes
      do not have the right lengths or (2) if each of the elements inside these
      lists do not have the correct shapes or (3) if image_ids are not integers.
  """

  if len(detection_classes.shape) != 1 or len(detection_scores.shape) != 1:
    raise ValueError('All entries in detection_classes and detection_scores'
                     'expected to be of rank 1.')
  num_boxes = detection_classes.shape[0]
  if not num_boxes == len(detection_masks) == detection_scores.shape[0]:
    raise ValueError('Corresponding entries in detection_classes, '
                     'detection_scores and detection_masks should have '
                     'compatible lengths and shapes '
                     'Classes length: %d.  Masks length: %d. '
                     'Scores length: %d' % (
                         detection_classes.shape[0], len(detection_masks),
                         detection_scores.shape[0]
                     ))
  detections_list = []
  for i in range(num_boxes):
    if detection_classes[i] in category_id_set:
      detections_list.append({
          'image_id': image_id,
          'category_id': int(detection_classes[i]),
          'segmentation': _RleCompress(detection_masks[i]),
          'score': float(detection_scores[i])
      })
  return detections_list


def ExportDetectionsToCOCO(image_ids,
                           detection_boxes,
                           detection_scores,
                           detection_classes,
                           categories,
                           output_path=None):
  """Export detection annotations in numpy arrays to COCO API.

  This function converts a set of predicted detections represented
  as numpy arrays to dictionaries that can be ingested by the COCO API.
  Inputs to this function are lists, consisting of boxes, scores and
  classes, respectively, corresponding to each image for which detections
  have been produced.  Note that the image_ids provided here must
  match the ones given to the ExportGroundtruthToCOCO function in order
  for evaluation to work properly.

  We assume that for each image, boxes, scores and classes are in
  correspondence --- that is: detection_boxes[i, :], detection_scores[i] and
  detection_classes[i] are associated with the same detection.

  Args:
    image_ids: a list of unique image identifier either of type integer or
      string.
    detection_boxes: list of numpy arrays with shape [num_detection_boxes, 4]
    detection_scores: list of numpy arrays (float) with shape
      [num_detection_boxes]. Note that num_detection_boxes can be different
      for each entry in the list.
    detection_classes: list of numpy arrays (int) with shape
      [num_detection_boxes]. Note that num_detection_boxes can be different
      for each entry in the list.
    categories: a list of dictionaries representing all possible categories.
      Each dict in this list must have an integer 'id' key uniquely identifying
      this category.
    output_path: (optional) path for exporting result to JSON

  Returns:
    list of dictionaries that can be read by COCO API, where each entry
    corresponds to a single detection and has keys from:
    ['image_id', 'category_id', 'bbox', 'score'].
  Raises:
    ValueError: if (1) detection_boxes and detection_classes do not have the
      right lengths or (2) if each of the elements inside these lists do not
      have the correct shapes or (3) if image_ids are not integers.
  """
  category_id_set = set([cat['id'] for cat in categories])
  detections_export_list = []
  if not (len(image_ids) == len(detection_boxes) == len(detection_scores) ==
          len(detection_classes)):
    raise ValueError('Input lists must have the same length')
  for image_id, boxes, scores, classes in zip(image_ids, detection_boxes,
                                              detection_scores,
                                              detection_classes):
    detections_export_list.extend(ExportSingleImageDetectionBoxesToCoco(
        image_id,
        category_id_set,
        boxes,
        scores,
        classes))
  if output_path:
    with tf.gfile.GFile(output_path, 'w') as fid:
      json_utils.Dump(detections_export_list, fid, float_digits=4, indent=2)
  return detections_export_list


def ExportSegmentsToCOCO(image_ids,
                         detection_masks,
                         detection_scores,
                         detection_classes,
                         categories,
                         output_path=None):
  """Export segmentation masks in numpy arrays to COCO API.

  This function converts a set of predicted instance masks represented
  as numpy arrays to dictionaries that can be ingested by the COCO API.
  Inputs to this function are lists, consisting of segments, scores and
  classes, respectively, corresponding to each image for which detections
  have been produced.

  Note this function is recommended to use for small dataset.
  For large dataset, it should be used with a merge function
  (e.g. in map reduce), otherwise the memory consumption is large.

  We assume that for each image, masks, scores and classes are in
  correspondence --- that is: detection_masks[i, :, :, :], detection_scores[i]
  and detection_classes[i] are associated with the same detection.

  Args:
    image_ids: list of image ids (typically ints or strings)
    detection_masks: list of numpy arrays with shape [num_detection, h, w, 1]
      and type uint8. The height and width should match the shape of
      corresponding image.
    detection_scores: list of numpy arrays (float) with shape
      [num_detection]. Note that num_detection can be different
      for each entry in the list.
    detection_classes: list of numpy arrays (int) with shape
      [num_detection]. Note that num_detection can be different
      for each entry in the list.
    categories: a list of dictionaries representing all possible categories.
      Each dict in this list must have an integer 'id' key uniquely identifying
      this category.
    output_path: (optional) path for exporting result to JSON

  Returns:
    list of dictionaries that can be read by COCO API, where each entry
    corresponds to a single detection and has keys from:
    ['image_id', 'category_id', 'segmentation', 'score'].

  Raises:
    ValueError: if detection_masks and detection_classes do not have the
      right lengths or if each of the elements inside these lists do not
      have the correct shapes.
  """
  if not (len(image_ids) == len(detection_masks) == len(detection_scores) ==
          len(detection_classes)):
    raise ValueError('Input lists must have the same length')

  segment_export_list = []
  for image_id, masks, scores, classes in zip(image_ids, detection_masks,
                                              detection_scores,
                                              detection_classes):

    if len(classes.shape) != 1 or len(scores.shape) != 1:
      raise ValueError('All entries in detection_classes and detection_scores'
                       'expected to be of rank 1.')
    if len(masks.shape) != 4:
      raise ValueError('All entries in masks expected to be of '
                       'rank 4. Given {}'.format(masks.shape))

    num_boxes = classes.shape[0]
    if not num_boxes == masks.shape[0] == scores.shape[0]:
      raise ValueError('Corresponding entries in segment_classes, '
                       'detection_scores and detection_boxes should have '
                       'compatible shapes (i.e., agree on the 0th dimension).')

    category_id_set = set([cat['id'] for cat in categories])
    segment_export_list.extend(ExportSingleImageDetectionMasksToCoco(
        image_id, category_id_set, np.squeeze(masks, axis=3), scores, classes))

  if output_path:
    with tf.gfile.GFile(output_path, 'w') as fid:
      json_utils.Dump(segment_export_list, fid, float_digits=4, indent=2)
  return segment_export_list


def ExportKeypointsToCOCO(image_ids,
                          detection_keypoints,
                          detection_scores,
                          detection_classes,
                          categories,
                          output_path=None):
  """Exports keypoints in numpy arrays to COCO API.

  This function converts a set of predicted keypoints represented
  as numpy arrays to dictionaries that can be ingested by the COCO API.
  Inputs to this function are lists, consisting of keypoints, scores and
  classes, respectively, corresponding to each image for which detections
  have been produced.

  We assume that for each image, keypoints, scores and classes are in
  correspondence --- that is: detection_keypoints[i, :, :, :],
  detection_scores[i] and detection_classes[i] are associated with the same
  detection.

  Args:
    image_ids: list of image ids (typically ints or strings)
    detection_keypoints: list of numpy arrays with shape
      [num_detection, num_keypoints, 2] and type float32 in absolute
      x-y coordinates.
    detection_scores: list of numpy arrays (float) with shape
      [num_detection]. Note that num_detection can be different
      for each entry in the list.
    detection_classes: list of numpy arrays (int) with shape
      [num_detection]. Note that num_detection can be different
      for each entry in the list.
    categories: a list of dictionaries representing all possible categories.
      Each dict in this list must have an integer 'id' key uniquely identifying
      this category and an integer 'num_keypoints' key specifying the number of
      keypoints the category has.
    output_path: (optional) path for exporting result to JSON

  Returns:
    list of dictionaries that can be read by COCO API, where each entry
    corresponds to a single detection and has keys from:
    ['image_id', 'category_id', 'keypoints', 'score'].

  Raises:
    ValueError: if detection_keypoints and detection_classes do not have the
      right lengths or if each of the elements inside these lists do not
      have the correct shapes.
  """
  if not (len(image_ids) == len(detection_keypoints) ==
          len(detection_scores) == len(detection_classes)):
    raise ValueError('Input lists must have the same length')

  keypoints_export_list = []
  for image_id, keypoints, scores, classes in zip(
      image_ids, detection_keypoints, detection_scores, detection_classes):

    if len(classes.shape) != 1 or len(scores.shape) != 1:
      raise ValueError('All entries in detection_classes and detection_scores'
                       'expected to be of rank 1.')
    if len(keypoints.shape) != 3:
      raise ValueError('All entries in keypoints expected to be of '
                       'rank 3. Given {}'.format(keypoints.shape))

    num_boxes = classes.shape[0]
    if not num_boxes == keypoints.shape[0] == scores.shape[0]:
      raise ValueError('Corresponding entries in detection_classes, '
                       'detection_keypoints, and detection_scores should have '
                       'compatible shapes (i.e., agree on the 0th dimension).')

    category_id_set = set([cat['id'] for cat in categories])
    category_id_to_num_keypoints_map = {
        cat['id']: cat['num_keypoints'] for cat in categories
        if 'num_keypoints' in cat}

    for i in range(num_boxes):
      if classes[i] not in category_id_set:
        raise ValueError('class id should be in category_id_set\n')

      if classes[i] in category_id_to_num_keypoints_map:
        num_keypoints = category_id_to_num_keypoints_map[classes[i]]
        # Adds extra ones to indicate the visibility for each keypoint as is
        # recommended by MSCOCO.
        instance_keypoints = np.concatenate(
            [keypoints[i, 0:num_keypoints, :],
             np.expand_dims(np.ones(num_keypoints), axis=1)],
            axis=1).astype(int)

        instance_keypoints = instance_keypoints.flatten().tolist()
        keypoints_export_list.append({
            'image_id': image_id,
            'category_id': int(classes[i]),
            'keypoints': instance_keypoints,
            'score': float(scores[i])
        })

  if output_path:
    with tf.gfile.GFile(output_path, 'w') as fid:
      json_utils.Dump(keypoints_export_list, fid, float_digits=4, indent=2)
  return keypoints_export_list