code: """
  Mask R-CNN
  The main Mask R-CNN model implementation.
  
  Copyright (c) 2017 Matterport, Inc.
  Licensed under the MIT License (see LICENSE for details)
  Written by Waleed Abdulla
  """
  
  import os
  import datetime
  import re
  import math
  from collections import OrderedDict
  import multiprocessing
  import numpy as np
  import tensorflow as tf
  import tensorflow.keras as keras
  import tensorflow.keras.backend as K
  import tensorflow.keras.layers as KL
  import tensorflow.keras.layers as KE
  import tensorflow.keras.utils as KU
  import tensorflow.keras.models as KM
  
  from mrcnn import utils
  
  # Requires TensorFlow 2.0+
  from distutils.version import LooseVersion
  assert LooseVersion(tf.__version__) >= LooseVersion("2.0")
  
  
  ############################################################
  #  Utility Functions
  ############################################################
  
  def log(text, array=None):
      """Prints a text message. And, optionally, if a Numpy array is provided it
      prints it's shape, min, and max values.
      """
      if array is not None:
          text = text.ljust(25)
          text += ("shape: {:20}  ".format(str(array.shape)))
          if array.size:
              text += ("min: {:10.5f}  max: {:10.5f}".format(array.min(), array.max()))
          else:
              text += ("min: {:10}  max: {:10}".format("", ""))
          text += "  {}".format(array.dtype)
      print(text)
  
  
  class BatchNorm(KL.BatchNormalization):
      """Extends the Keras BatchNormalization class to allow a central place
      to make changes if needed.
  
      Batch normalization has a negative effect on training if batches are small
      so this layer is often frozen (via setting in Config class) and functions
      as linear layer.
      """
  
      def call(self, inputs, training=None):
          """
          Note about training values:
              None: Train BN layers. This is the normal mode
              False: Freeze BN layers. Good when batch size is small
              True: (don't use). Set layer in training mode even when making inferences
          """
          return super(self.__class__, self).call(inputs, training=training)
  
  
  def compute_backbone_shapes(config, image_shape):
      """Computes the width and height of each stage of the backbone network.
  
      Returns:
          [N, (height, width)]. Where N is the number of stages
      """
      if callable(config.BACKBONE):
          return config.COMPUTE_BACKBONE_SHAPE(image_shape)
  
      # Currently supports ResNet only
      assert config.BACKBONE in ["resnet50", "resnet101"]
      return np.array(
          [[int(math.ceil(image_shape[0] / stride)),
              int(math.ceil(image_shape[1] / stride))]
              for stride in config.BACKBONE_STRIDES])
  
  
  ############################################################
  #  Resnet Graph
  ############################################################
  
  # Code adopted from:
  # https://github.com/fchollet/deep-learning-models/blob/master/resnet50.py
  
  def identity_block(input_tensor, kernel_size, filters, stage, block,
                     use_bias=True, train_bn=True):
      """The identity_block is the block that has no conv layer at shortcut
      # Arguments
          input_tensor: input tensor
          kernel_size: default 3, the kernel size of middle conv layer at main path
          filters: list of integers, the nb_filters of 3 conv layer at main path
          stage: integer, current stage label, used for generating layer names
          block: 'a','b'..., current block label, used for generating layer names
          use_bias: Boolean. To use or not use a bias in conv layers.
          train_bn: Boolean. Train or freeze Batch Norm layers
      """
      nb_filter1, nb_filter2, nb_filter3 = filters
      conv_name_base = 'res' + str(stage) + block + '_branch'
      bn_name_base = 'bn' + str(stage) + block + '_branch'
  
      x = KL.Conv2D(nb_filter1, (1, 1), name=conv_name_base + '2a',
                    use_bias=use_bias)(input_tensor)
      x = BatchNorm(name=bn_name_base + '2a')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.Conv2D(nb_filter2, (kernel_size, kernel_size), padding='same',
                    name=conv_name_base + '2b', use_bias=use_bias)(x)
      x = BatchNorm(name=bn_name_base + '2b')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.Conv2D(nb_filter3, (1, 1), name=conv_name_base + '2c',
                    use_bias=use_bias)(x)
      x = BatchNorm(name=bn_name_base + '2c')(x, training=train_bn)
  
      x = KL.Add()([x, input_tensor])
      x = KL.Activation('relu', name='res' + str(stage) + block + '_out')(x)
      return x
  
  
  def conv_block(input_tensor, kernel_size, filters, stage, block,
                 strides=(2, 2), use_bias=True, train_bn=True):
      """conv_block is the block that has a conv layer at shortcut
      # Arguments
          input_tensor: input tensor
          kernel_size: default 3, the kernel size of middle conv layer at main path
          filters: list of integers, the nb_filters of 3 conv layer at main path
          stage: integer, current stage label, used for generating layer names
          block: 'a','b'..., current block label, used for generating layer names
          use_bias: Boolean. To use or not use a bias in conv layers.
          train_bn: Boolean. Train or freeze Batch Norm layers
      Note that from stage 3, the first conv layer at main path is with subsample=(2,2)
      And the shortcut should have subsample=(2,2) as well
      """
      nb_filter1, nb_filter2, nb_filter3 = filters
      conv_name_base = 'res' + str(stage) + block + '_branch'
      bn_name_base = 'bn' + str(stage) + block + '_branch'
  
      x = KL.Conv2D(nb_filter1, (1, 1), strides=strides,
                    name=conv_name_base + '2a', use_bias=use_bias)(input_tensor)
      x = BatchNorm(name=bn_name_base + '2a')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.Conv2D(nb_filter2, (kernel_size, kernel_size), padding='same',
                    name=conv_name_base + '2b', use_bias=use_bias)(x)
      x = BatchNorm(name=bn_name_base + '2b')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.Conv2D(nb_filter3, (1, 1), name=conv_name_base +
                    '2c', use_bias=use_bias)(x)
      x = BatchNorm(name=bn_name_base + '2c')(x, training=train_bn)
  
      shortcut = KL.Conv2D(nb_filter3, (1, 1), strides=strides,
                           name=conv_name_base + '1', use_bias=use_bias)(input_tensor)
      shortcut = BatchNorm(name=bn_name_base + '1')(shortcut, training=train_bn)
  
      x = KL.Add()([x, shortcut])
      x = KL.Activation('relu', name='res' + str(stage) + block + '_out')(x)
      return x
  
  
  def resnet_graph(input_image, architecture, stage5=False, train_bn=True):
      """Build a ResNet graph.
          architecture: Can be resnet50 or resnet101
          stage5: Boolean. If False, stage5 of the network is not created
          train_bn: Boolean. Train or freeze Batch Norm layers
      """
      assert architecture in ["resnet50", "resnet101"]
      # Stage 1
      x = KL.ZeroPadding2D((3, 3))(input_image)
      x = KL.Conv2D(64, (7, 7), strides=(2, 2), name='conv1', use_bias=True)(x)
      x = BatchNorm(name='bn_conv1')(x, training=train_bn)
      x = KL.Activation('relu')(x)
      C1 = x = KL.MaxPooling2D((3, 3), strides=(2, 2), padding="same")(x)
      # Stage 2
      x = conv_block(x, 3, [64, 64, 256], stage=2, block='a', strides=(1, 1), train_bn=train_bn)
      x = identity_block(x, 3, [64, 64, 256], stage=2, block='b', train_bn=train_bn)
      C2 = x = identity_block(x, 3, [64, 64, 256], stage=2, block='c', train_bn=train_bn)
      # Stage 3
      x = conv_block(x, 3, [128, 128, 512], stage=3, block='a', train_bn=train_bn)
      x = identity_block(x, 3, [128, 128, 512], stage=3, block='b', train_bn=train_bn)
      x = identity_block(x, 3, [128, 128, 512], stage=3, block='c', train_bn=train_bn)
      C3 = x = identity_block(x, 3, [128, 128, 512], stage=3, block='d', train_bn=train_bn)
      # Stage 4
      x = conv_block(x, 3, [256, 256, 1024], stage=4, block='a', train_bn=train_bn)
      block_count = {"resnet50": 5, "resnet101": 22}[architecture]
      for i in range(block_count):
          x = identity_block(x, 3, [256, 256, 1024], stage=4, block=chr(98 + i), train_bn=train_bn)
      C4 = x
      # Stage 5
      if stage5:
          x = conv_block(x, 3, [512, 512, 2048], stage=5, block='a', train_bn=train_bn)
          x = identity_block(x, 3, [512, 512, 2048], stage=5, block='b', train_bn=train_bn)
          C5 = x = identity_block(x, 3, [512, 512, 2048], stage=5, block='c', train_bn=train_bn)
      else:
          C5 = None
      return [C1, C2, C3, C4, C5]
  
  
  ############################################################
  #  Proposal Layer
  ############################################################
  
  def apply_box_deltas_graph(boxes, deltas):
      """Applies the given deltas to the given boxes.
      boxes: [N, (y1, x1, y2, x2)] boxes to update
      deltas: [N, (dy, dx, log(dh), log(dw))] refinements to apply
      """
      # Convert to y, x, h, w
      height = boxes[:, 2] - boxes[:, 0]
      width = boxes[:, 3] - boxes[:, 1]
      center_y = boxes[:, 0] + 0.5 * height
      center_x = boxes[:, 1] + 0.5 * width
      # Apply deltas
      center_y += deltas[:, 0] * height
      center_x += deltas[:, 1] * width
      height *= tf.exp(deltas[:, 2])
      width *= tf.exp(deltas[:, 3])
      # Convert back to y1, x1, y2, x2
      y1 = center_y - 0.5 * height
      x1 = center_x - 0.5 * width
      y2 = y1 + height
      x2 = x1 + width
      result = tf.stack([y1, x1, y2, x2], axis=1, name="apply_box_deltas_out")
      return result
  
  
  def clip_boxes_graph(boxes, window):
      """
      boxes: [N, (y1, x1, y2, x2)]
      window: [4] in the form y1, x1, y2, x2
      """
      # Split
      wy1, wx1, wy2, wx2 = tf.split(window, 4)
      y1, x1, y2, x2 = tf.split(boxes, 4, axis=1)
      # Clip
      y1 = tf.maximum(tf.minimum(y1, wy2), wy1)
      x1 = tf.maximum(tf.minimum(x1, wx2), wx1)
      y2 = tf.maximum(tf.minimum(y2, wy2), wy1)
      x2 = tf.maximum(tf.minimum(x2, wx2), wx1)
      clipped = tf.concat([y1, x1, y2, x2], axis=1, name="clipped_boxes")
      clipped.set_shape((clipped.shape[0], 4))
      return clipped
  
  
  class ProposalLayer(KE.Layer):
      """Receives anchor scores and selects a subset to pass as proposals
      to the second stage. Filtering is done based on anchor scores and
      non-max suppression to remove overlaps. It also applies bounding
      box refinement deltas to anchors.
  
      Inputs:
          rpn_probs: [batch, num_anchors, (bg prob, fg prob)]
          rpn_bbox: [batch, num_anchors, (dy, dx, log(dh), log(dw))]
          anchors: [batch, num_anchors, (y1, x1, y2, x2)] anchors in normalized coordinates
  
      Returns:
          Proposals in normalized coordinates [batch, rois, (y1, x1, y2, x2)]
      """
  
      def __init__(self, proposal_count, nms_threshold, config=None, **kwargs):
          super(ProposalLayer, self).__init__(**kwargs)
          self.config = config
          self.proposal_count = proposal_count
          self.nms_threshold = nms_threshold
  
      def call(self, inputs):
          # Box Scores. Use the foreground class confidence. [Batch, num_rois, 1]
          scores = inputs[0][:, :, 1]
          # Box deltas [batch, num_rois, 4]
          deltas = inputs[1]
          deltas = deltas * np.reshape(self.config.RPN_BBOX_STD_DEV, [1, 1, 4])
          # Anchors
          anchors = inputs[2]
  
          # Improve performance by trimming to top anchors by score
          # and doing the rest on the smaller subset.
          pre_nms_limit = tf.minimum(self.config.PRE_NMS_LIMIT, tf.shape(anchors)[1])
          ix = tf.nn.top_k(scores, pre_nms_limit, sorted=True,
                           name="top_anchors").indices
          scores = utils.batch_slice([scores, ix], lambda x, y: tf.gather(x, y),
                                     self.config.IMAGES_PER_GPU)
          deltas = utils.batch_slice([deltas, ix], lambda x, y: tf.gather(x, y),
                                     self.config.IMAGES_PER_GPU)
          pre_nms_anchors = utils.batch_slice([anchors, ix], lambda a, x: tf.gather(a, x),
                                              self.config.IMAGES_PER_GPU,
                                              names=["pre_nms_anchors"])
  
          # Apply deltas to anchors to get refined anchors.
          # [batch, N, (y1, x1, y2, x2)]
          boxes = utils.batch_slice([pre_nms_anchors, deltas],
                                    lambda x, y: apply_box_deltas_graph(x, y),
                                    self.config.IMAGES_PER_GPU,
                                    names=["refined_anchors"])
  
          # Clip to image boundaries. Since we're in normalized coordinates,
          # clip to 0..1 range. [batch, N, (y1, x1, y2, x2)]
          window = np.array([0, 0, 1, 1], dtype=np.float32)
          boxes = utils.batch_slice(boxes,
                                    lambda x: clip_boxes_graph(x, window),
                                    self.config.IMAGES_PER_GPU,
                                    names=["refined_anchors_clipped"])
  
          # Filter out small boxes
          # According to Xinlei Chen's paper, this reduces detection accuracy
          # for small objects, so we're skipping it.
  
          # Non-max suppression
          def nms(boxes, scores):
              indices = tf.image.non_max_suppression(
                  boxes, scores, self.proposal_count,
                  self.nms_threshold, name="rpn_non_max_suppression")
              proposals = tf.gather(boxes, indices)
              # Pad if needed
              padding = tf.maximum(self.proposal_count - tf.shape(proposals)[0], 0)
              proposals = tf.pad(proposals, [(0, padding), (0, 0)])
              return proposals
          proposals = utils.batch_slice([boxes, scores], nms,
                                        self.config.IMAGES_PER_GPU)
          return proposals
  
      def compute_output_shape(self, input_shape):
          return (None, self.proposal_count, 4)
  
  
  ############################################################
  #  ROIAlign Layer
  ############################################################
  
  def log2_graph(x):
      """Implementation of Log2. TF doesn't have a native implementation."""
      return tf.math.log(x) / tf.math.log(2.0)
  
  
  class PyramidROIAlign(KE.Layer):
      """Implements ROI Pooling on multiple levels of the feature pyramid.
  
      Params:
      - pool_shape: [pool_height, pool_width] of the output pooled regions. Usually [7, 7]
  
      Inputs:
      - boxes: [batch, num_boxes, (y1, x1, y2, x2)] in normalized
               coordinates. Possibly padded with zeros if not enough
               boxes to fill the array.
      - image_meta: [batch, (meta data)] Image details. See compose_image_meta()
      - feature_maps: List of feature maps from different levels of the pyramid.
                      Each is [batch, height, width, channels]
  
      Output:
      Pooled regions in the shape: [batch, num_boxes, pool_height, pool_width, channels].
      The width and height are those specific in the pool_shape in the layer
      constructor.
      """
  
      def __init__(self, pool_shape, **kwargs):
          super(PyramidROIAlign, self).__init__(**kwargs)
          self.pool_shape = tuple(pool_shape)
  
      def call(self, inputs):
          # Crop boxes [batch, num_boxes, (y1, x1, y2, x2)] in normalized coords
          boxes = inputs[0]
  
          # Image meta
          # Holds details about the image. See compose_image_meta()
          image_meta = inputs[1]
  
          # Feature Maps. List of feature maps from different level of the
          # feature pyramid. Each is [batch, height, width, channels]
          feature_maps = inputs[2:]
  
          # Assign each ROI to a level in the pyramid based on the ROI area.
          y1, x1, y2, x2 = tf.split(boxes, 4, axis=2)
          h = y2 - y1
          w = x2 - x1
          # Use shape of first image. Images in a batch must have the same size.
          image_shape = parse_image_meta_graph(image_meta)['image_shape'][0]
          # Equation 1 in the Feature Pyramid Networks paper. Account for
          # the fact that our coordinates are normalized here.
          # e.g. a 224x224 ROI (in pixels) maps to P4
          image_area = tf.cast(image_shape[0] * image_shape[1], tf.float32)
          roi_level = log2_graph(tf.sqrt(h * w) / (224.0 / tf.sqrt(image_area)))
          roi_level = tf.minimum(5, tf.maximum(
              2, 4 + tf.cast(tf.round(roi_level), tf.int32)))
          roi_level = tf.squeeze(roi_level, 2)
  
          # Loop through levels and apply ROI pooling to each. P2 to P5.
          pooled = []
          box_to_level = []
          for i, level in enumerate(range(2, 6)):
              ix = tf.where(tf.equal(roi_level, level))
              level_boxes = tf.gather_nd(boxes, ix)
  
              # Box indices for crop_and_resize.
              box_indices = tf.cast(ix[:, 0], tf.int32)
  
              # Keep track of which box is mapped to which level
              box_to_level.append(ix)
  
              # Stop gradient propogation to ROI proposals
              level_boxes = tf.stop_gradient(level_boxes)
              box_indices = tf.stop_gradient(box_indices)
  
              # Crop and Resize
              # From Mask R-CNN paper: "We sample four regular locations, so
              # that we can evaluate either max or average pooling. In fact,
              # interpolating only a single value at each bin center (without
              # pooling) is nearly as effective."
              #
              # Here we use the simplified approach of a single value per bin,
              # which is how it's done in tf.crop_and_resize()
              # Result: [batch * num_boxes, pool_height, pool_width, channels]
              pooled.append(tf.image.crop_and_resize(
                  feature_maps[i], level_boxes, box_indices, self.pool_shape,
                  method="bilinear"))
  
          # Pack pooled features into one tensor
          pooled = tf.concat(pooled, axis=0)
  
          # Pack box_to_level mapping into one array and add another
          # column representing the order of pooled boxes
          box_to_level = tf.concat(box_to_level, axis=0)
          box_range = tf.expand_dims(tf.range(tf.shape(box_to_level)[0]), 1)
          box_to_level = tf.concat([tf.cast(box_to_level, tf.int32), box_range],
                                   axis=1)
  
          # Rearrange pooled features to match the order of the original boxes
          # Sort box_to_level by batch then box index
          # TF doesn't have a way to sort by two columns, so merge them and sort.
          sorting_tensor = box_to_level[:, 0] * 100000 + box_to_level[:, 1]
          ix = tf.nn.top_k(sorting_tensor, k=tf.shape(
              box_to_level)[0]).indices[::-1]
          ix = tf.gather(box_to_level[:, 2], ix)
          pooled = tf.gather(pooled, ix)
  
          # Re-add the batch dimension
          shape = tf.concat([tf.shape(boxes)[:2], tf.shape(pooled)[1:]], axis=0)
          pooled = tf.reshape(pooled, shape)
          return pooled
  
      def compute_output_shape(self, input_shape):
          return input_shape[0][:2] + self.pool_shape + (input_shape[2][-1], )
  
  
  ############################################################
  #  Detection Target Layer
  ############################################################
  
  def overlaps_graph(boxes1, boxes2):
      """Computes IoU overlaps between two sets of boxes.
      boxes1, boxes2: [N, (y1, x1, y2, x2)].
      """
      # 1. Tile boxes2 and repeat boxes1. This allows us to compare
      # every boxes1 against every boxes2 without loops.
      # TF doesn't have an equivalent to np.repeat() so simulate it
      # using tf.tile() and tf.reshape.
      b1 = tf.reshape(tf.tile(tf.expand_dims(boxes1, 1),
                              [1, 1, tf.shape(boxes2)[0]]), [-1, 4])
      b2 = tf.tile(boxes2, [tf.shape(boxes1)[0], 1])
      # 2. Compute intersections
      b1_y1, b1_x1, b1_y2, b1_x2 = tf.split(b1, 4, axis=1)
      b2_y1, b2_x1, b2_y2, b2_x2 = tf.split(b2, 4, axis=1)
      y1 = tf.maximum(b1_y1, b2_y1)
      x1 = tf.maximum(b1_x1, b2_x1)
      y2 = tf.minimum(b1_y2, b2_y2)
      x2 = tf.minimum(b1_x2, b2_x2)
      intersection = tf.maximum(x2 - x1, 0) * tf.maximum(y2 - y1, 0)
      # 3. Compute unions
      b1_area = (b1_y2 - b1_y1) * (b1_x2 - b1_x1)
      b2_area = (b2_y2 - b2_y1) * (b2_x2 - b2_x1)
      union = b1_area + b2_area - intersection
      # 4. Compute IoU and reshape to [boxes1, boxes2]
      iou = intersection / union
      overlaps = tf.reshape(iou, [tf.shape(boxes1)[0], tf.shape(boxes2)[0]])
      return overlaps
  
  
  def detection_targets_graph(proposals, gt_class_ids, gt_boxes, gt_masks, config):
      """Generates detection targets for one image. Subsamples proposals and
      generates target class IDs, bounding box deltas, and masks for each.
  
      Inputs:
      proposals: [POST_NMS_ROIS_TRAINING, (y1, x1, y2, x2)] in normalized coordinates. Might
                 be zero padded if there are not enough proposals.
      gt_class_ids: [MAX_GT_INSTANCES] int class IDs
      gt_boxes: [MAX_GT_INSTANCES, (y1, x1, y2, x2)] in normalized coordinates.
      gt_masks: [height, width, MAX_GT_INSTANCES] of boolean type.
  
      Returns: Target ROIs and corresponding class IDs, bounding box shifts,
      and masks.
      rois: [TRAIN_ROIS_PER_IMAGE, (y1, x1, y2, x2)] in normalized coordinates
      class_ids: [TRAIN_ROIS_PER_IMAGE]. Integer class IDs. Zero padded.
      deltas: [TRAIN_ROIS_PER_IMAGE, (dy, dx, log(dh), log(dw))]
      masks: [TRAIN_ROIS_PER_IMAGE, height, width]. Masks cropped to bbox
             boundaries and resized to neural network output size.
  
      Note: Returned arrays might be zero padded if not enough target ROIs.
      """
      # Assertions
      asserts = [
          tf.Assert(tf.greater(tf.shape(proposals)[0], 0), [proposals],
                    name="roi_assertion"),
      ]
      with tf.control_dependencies(asserts):
          proposals = tf.identity(proposals)
  
      # Remove zero padding
      proposals, _ = trim_zeros_graph(proposals, name="trim_proposals")
      gt_boxes, non_zeros = trim_zeros_graph(gt_boxes, name="trim_gt_boxes")
      gt_class_ids = tf.boolean_mask(gt_class_ids, non_zeros,
                                     name="trim_gt_class_ids")
      gt_masks = tf.gather(gt_masks, tf.where(non_zeros)[:, 0], axis=2,
                           name="trim_gt_masks")
  
      # Handle COCO crowds
      # A crowd box in COCO is a bounding box around several instances. Exclude
      # them from training. A crowd box is given a negative class ID.
      crowd_ix = tf.where(gt_class_ids < 0)[:, 0]
      non_crowd_ix = tf.where(gt_class_ids > 0)[:, 0]
      crowd_boxes = tf.gather(gt_boxes, crowd_ix)
      gt_class_ids = tf.gather(gt_class_ids, non_crowd_ix)
      gt_boxes = tf.gather(gt_boxes, non_crowd_ix)
      gt_masks = tf.gather(gt_masks, non_crowd_ix, axis=2)
  
      # Compute overlaps matrix [proposals, gt_boxes]
      overlaps = overlaps_graph(proposals, gt_boxes)
  
      # Compute overlaps with crowd boxes [proposals, crowd_boxes]
      crowd_overlaps = overlaps_graph(proposals, crowd_boxes)
      crowd_iou_max = tf.reduce_max(crowd_overlaps, axis=1)
      no_crowd_bool = (crowd_iou_max < 0.001)
  
      # Determine positive and negative ROIs
      roi_iou_max = tf.reduce_max(overlaps, axis=1)
      # 1. Positive ROIs are those with >= 0.5 IoU with a GT box
      positive_roi_bool = (roi_iou_max >= 0.5)
      positive_indices = tf.where(positive_roi_bool)[:, 0]
      # 2. Negative ROIs are those with < 0.5 with every GT box. Skip crowds.
      negative_indices = tf.where(tf.logical_and(roi_iou_max < 0.5, no_crowd_bool))[:, 0]
  
      # Subsample ROIs. Aim for 33% positive
      # Positive ROIs
      positive_count = int(config.TRAIN_ROIS_PER_IMAGE *
                           config.ROI_POSITIVE_RATIO)
      positive_indices = tf.random.shuffle(positive_indices)[:positive_count]
      positive_count = tf.shape(positive_indices)[0]
      # Negative ROIs. Add enough to maintain positive:negative ratio.
      r = 1.0 / config.ROI_POSITIVE_RATIO
      negative_count = tf.cast(r * tf.cast(positive_count, tf.float32), tf.int32) - positive_count
      negative_indices = tf.random.shuffle(negative_indices)[:negative_count]
      # Gather selected ROIs
      positive_rois = tf.gather(proposals, positive_indices)
      negative_rois = tf.gather(proposals, negative_indices)
  
      # Assign positive ROIs to GT boxes.
      positive_overlaps = tf.gather(overlaps, positive_indices)
      roi_gt_box_assignment = tf.cond(
          tf.greater(tf.shape(positive_overlaps)[1], 0),
          true_fn=lambda: tf.argmax(positive_overlaps, axis=1),
          false_fn=lambda: tf.cast(tf.constant([]), tf.int64)
      )
      roi_gt_boxes = tf.gather(gt_boxes, roi_gt_box_assignment)
      roi_gt_class_ids = tf.gather(gt_class_ids, roi_gt_box_assignment)
  
      # Compute bbox refinement for positive ROIs
      deltas = utils.box_refinement_graph(positive_rois, roi_gt_boxes)
      deltas /= config.BBOX_STD_DEV
  
      # Assign positive ROIs to GT masks
      # Permute masks to [N, height, width, 1]
      transposed_masks = tf.expand_dims(tf.transpose(gt_masks, [2, 0, 1]), -1)
      # Pick the right mask for each ROI
      roi_masks = tf.gather(transposed_masks, roi_gt_box_assignment)
  
      # Compute mask targets
      boxes = positive_rois
      if config.USE_MINI_MASK:
          # Transform ROI coordinates from normalized image space
          # to normalized mini-mask space.
          y1, x1, y2, x2 = tf.split(positive_rois, 4, axis=1)
          gt_y1, gt_x1, gt_y2, gt_x2 = tf.split(roi_gt_boxes, 4, axis=1)
          gt_h = gt_y2 - gt_y1
          gt_w = gt_x2 - gt_x1
          y1 = (y1 - gt_y1) / gt_h
          x1 = (x1 - gt_x1) / gt_w
          y2 = (y2 - gt_y1) / gt_h
          x2 = (x2 - gt_x1) / gt_w
          boxes = tf.concat([y1, x1, y2, x2], 1)
      box_ids = tf.range(0, tf.shape(roi_masks)[0])
      masks = tf.image.crop_and_resize(tf.cast(roi_masks, tf.float32), boxes,
                                       box_ids,
                                       config.MASK_SHAPE)
      # Remove the extra dimension from masks.
      masks = tf.squeeze(masks, axis=3)
  
      # Threshold mask pixels at 0.5 to have GT masks be 0 or 1 to use with
      # binary cross entropy loss.
      masks = tf.round(masks)
  
      # Append negative ROIs and pad bbox deltas and masks that
      # are not used for negative ROIs with zeros.
      rois = tf.concat([positive_rois, negative_rois], axis=0)
      N = tf.shape(negative_rois)[0]
      P = tf.maximum(config.TRAIN_ROIS_PER_IMAGE - tf.shape(rois)[0], 0)
      rois = tf.pad(rois, [(0, P), (0, 0)])
      roi_gt_boxes = tf.pad(roi_gt_boxes, [(0, N + P), (0, 0)])
      roi_gt_class_ids = tf.pad(roi_gt_class_ids, [(0, N + P)])
      deltas = tf.pad(deltas, [(0, N + P), (0, 0)])
      masks = tf.pad(masks, [[0, N + P], (0, 0), (0, 0)])
  
      return rois, roi_gt_class_ids, deltas, masks
  
  
  class DetectionTargetLayer(KE.Layer):
      """Subsamples proposals and generates target box refinement, class_ids,
      and masks for each.
  
      Inputs:
      proposals: [batch, N, (y1, x1, y2, x2)] in normalized coordinates. Might
                 be zero padded if there are not enough proposals.
      gt_class_ids: [batch, MAX_GT_INSTANCES] Integer class IDs.
      gt_boxes: [batch, MAX_GT_INSTANCES, (y1, x1, y2, x2)] in normalized
                coordinates.
      gt_masks: [batch, height, width, MAX_GT_INSTANCES] of boolean type
  
      Returns: Target ROIs and corresponding class IDs, bounding box shifts,
      and masks.
      rois: [batch, TRAIN_ROIS_PER_IMAGE, (y1, x1, y2, x2)] in normalized
            coordinates
      target_class_ids: [batch, TRAIN_ROIS_PER_IMAGE]. Integer class IDs.
      target_deltas: [batch, TRAIN_ROIS_PER_IMAGE, (dy, dx, log(dh), log(dw)]
      target_mask: [batch, TRAIN_ROIS_PER_IMAGE, height, width]
                   Masks cropped to bbox boundaries and resized to neural
                   network output size.
  
      Note: Returned arrays might be zero padded if not enough target ROIs.
      """
  
      def __init__(self, config, **kwargs):
          super(DetectionTargetLayer, self).__init__(**kwargs)
          self.config = config
  
      def call(self, inputs):
          proposals = inputs[0]
          gt_class_ids = inputs[1]
          gt_boxes = inputs[2]
          gt_masks = inputs[3]
  
          # Slice the batch and run a graph for each slice
          # TODO: Rename target_bbox to target_deltas for clarity
          names = ["rois", "target_class_ids", "target_bbox", "target_mask"]
          outputs = utils.batch_slice(
              [proposals, gt_class_ids, gt_boxes, gt_masks],
              lambda w, x, y, z: detection_targets_graph(
                  w, x, y, z, self.config),
              self.config.IMAGES_PER_GPU, names=names)
          return outputs
  
      def compute_output_shape(self, input_shape):
          return [
              (None, self.config.TRAIN_ROIS_PER_IMAGE, 4),  # rois
              (None, self.config.TRAIN_ROIS_PER_IMAGE),  # class_ids
              (None, self.config.TRAIN_ROIS_PER_IMAGE, 4),  # deltas
              (None, self.config.TRAIN_ROIS_PER_IMAGE, self.config.MASK_SHAPE[0],
               self.config.MASK_SHAPE[1])  # masks
          ]
  
      def compute_mask(self, inputs, mask=None):
          return [None, None, None, None]
  
  
  ############################################################
  #  Detection Layer
  ############################################################
  
  def refine_detections_graph(rois, probs, deltas, window, config):
      """Refine classified proposals and filter overlaps and return final
      detections.
  
      Inputs:
          rois: [N, (y1, x1, y2, x2)] in normalized coordinates
          probs: [N, num_classes]. Class probabilities.
          deltas: [N, num_classes, (dy, dx, log(dh), log(dw))]. Class-specific
                  bounding box deltas.
          window: (y1, x1, y2, x2) in normalized coordinates. The part of the image
              that contains the image excluding the padding.
  
      Returns detections shaped: [num_detections, (y1, x1, y2, x2, class_id, score)] where
          coordinates are normalized.
      """
      # Class IDs per ROI
      class_ids = tf.argmax(probs, axis=1, output_type=tf.int32)
      # Class probability of the top class of each ROI
      indices = tf.stack([tf.range(tf.shape(probs)[0]), class_ids], axis=1)
      class_scores = tf.gather_nd(probs, indices)
      # Class-specific bounding box deltas
      deltas_specific = tf.gather_nd(deltas, indices)
      # Apply bounding box deltas
      # Shape: [boxes, (y1, x1, y2, x2)] in normalized coordinates
      refined_rois = apply_box_deltas_graph(
          rois, deltas_specific * config.BBOX_STD_DEV)
      # Clip boxes to image window
      refined_rois = clip_boxes_graph(refined_rois, window)
  
      # TODO: Filter out boxes with zero area
  
      # Filter out background boxes
      keep = tf.where(class_ids > 0)[:, 0]
      # Filter out low confidence boxes
      if config.DETECTION_MIN_CONFIDENCE:
          conf_keep = tf.where(class_scores >= config.DETECTION_MIN_CONFIDENCE)[:, 0]
          keep = tf.sets.intersection(tf.expand_dims(keep, 0),
                                      tf.expand_dims(conf_keep, 0))
          keep = tf.sparse.to_dense(keep)[0]
  
      # Apply per-class NMS
      # 1. Prepare variables
      pre_nms_class_ids = tf.gather(class_ids, keep)
      pre_nms_scores = tf.gather(class_scores, keep)
      pre_nms_rois = tf.gather(refined_rois,   keep)
      unique_pre_nms_class_ids = tf.unique(pre_nms_class_ids)[0]
  
      def nms_keep_map(class_id):
          """Apply Non-Maximum Suppression on ROIs of the given class."""
          # Indices of ROIs of the given class
          ixs = tf.where(tf.equal(pre_nms_class_ids, class_id))[:, 0]
          # Apply NMS
          class_keep = tf.image.non_max_suppression(
              tf.gather(pre_nms_rois, ixs),
              tf.gather(pre_nms_scores, ixs),
              max_output_size=config.DETECTION_MAX_INSTANCES,
              iou_threshold=config.DETECTION_NMS_THRESHOLD)
          # Map indices
          class_keep = tf.gather(keep, tf.gather(ixs, class_keep))
          # Pad with -1 so returned tensors have the same shape
          gap = config.DETECTION_MAX_INSTANCES - tf.shape(class_keep)[0]
          class_keep = tf.pad(class_keep, [(0, gap)],
                              mode='CONSTANT', constant_values=-1)
          # Set shape so map_fn() can infer result shape
          class_keep.set_shape([config.DETECTION_MAX_INSTANCES])
          return class_keep
  
      # 2. Map over class IDs
      nms_keep = tf.map_fn(nms_keep_map, unique_pre_nms_class_ids,
                           dtype=tf.int64)
      # 3. Merge results into one list, and remove -1 padding
      nms_keep = tf.reshape(nms_keep, [-1])
      nms_keep = tf.gather(nms_keep, tf.where(nms_keep > -1)[:, 0])
      # 4. Compute intersection between keep and nms_keep
      keep = tf.sets.intersection(tf.expand_dims(keep, 0),
                                  tf.expand_dims(nms_keep, 0))
      keep = tf.sparse.to_dense(keep)[0]
      # Keep top detections
      roi_count = config.DETECTION_MAX_INSTANCES
      class_scores_keep = tf.gather(class_scores, keep)
      num_keep = tf.minimum(tf.shape(class_scores_keep)[0], roi_count)
      top_ids = tf.nn.top_k(class_scores_keep, k=num_keep, sorted=True)[1]
      keep = tf.gather(keep, top_ids)
  
      # Arrange output as [N, (y1, x1, y2, x2, class_id, score)]
      # Coordinates are normalized.
      detections = tf.concat([
          tf.gather(refined_rois, keep),
          tf.cast(tf.gather(class_ids, keep), tf.float32)[..., tf.newaxis],
          tf.gather(class_scores, keep)[..., tf.newaxis]
      ], axis=1)
  
      # Pad with zeros if detections < DETECTION_MAX_INSTANCES
      gap = config.DETECTION_MAX_INSTANCES - tf.shape(detections)[0]
      detections = tf.pad(detections, [(0, gap), (0, 0)], "CONSTANT")
      return detections
  
  
  class DetectionLayer(KE.Layer):
      """Takes classified proposal boxes and their bounding box deltas and
      returns the final detection boxes.
  
      Returns:
      [batch, num_detections, (y1, x1, y2, x2, class_id, class_score)] where
      coordinates are normalized.
      """
  
      def __init__(self, config=None, **kwargs):
          super(DetectionLayer, self).__init__(**kwargs)
          self.config = config
  
      def call(self, inputs):
          rois = inputs[0]
          mrcnn_class = inputs[1]
          mrcnn_bbox = inputs[2]
          image_meta = inputs[3]
  
          # Get windows of images in normalized coordinates. Windows are the area
          # in the image that excludes the padding.
          # Use the shape of the first image in the batch to normalize the window
          # because we know that all images get resized to the same size.
          m = parse_image_meta_graph(image_meta)
          image_shape = m['image_shape'][0]
          window = norm_boxes_graph(m['window'], image_shape[:2])
  
          # Run detection refinement graph on each item in the batch
          detections_batch = utils.batch_slice(
              [rois, mrcnn_class, mrcnn_bbox, window],
              lambda x, y, w, z: refine_detections_graph(x, y, w, z, self.config),
              self.config.IMAGES_PER_GPU)
  
          # Reshape output
          # [batch, num_detections, (y1, x1, y2, x2, class_id, class_score)] in
          # normalized coordinates
          return tf.reshape(
              detections_batch,
              [self.config.BATCH_SIZE, self.config.DETECTION_MAX_INSTANCES, 6])
  
      def compute_output_shape(self, input_shape):
          return (None, self.config.DETECTION_MAX_INSTANCES, 6)
  
  
  ############################################################
  #  Region Proposal Network (RPN)
  ############################################################
  
  def rpn_graph(feature_map, anchors_per_location, anchor_stride):
      """Builds the computation graph of Region Proposal Network.
  
      feature_map: backbone features [batch, height, width, depth]
      anchors_per_location: number of anchors per pixel in the feature map
      anchor_stride: Controls the density of anchors. Typically 1 (anchors for
                     every pixel in the feature map), or 2 (every other pixel).
  
      Returns:
          rpn_class_logits: [batch, H * W * anchors_per_location, 2] Anchor classifier logits (before softmax)
          rpn_probs: [batch, H * W * anchors_per_location, 2] Anchor classifier probabilities.
          rpn_bbox: [batch, H * W * anchors_per_location, (dy, dx, log(dh), log(dw))] Deltas to be
                    applied to anchors.
      """
      # TODO: check if stride of 2 causes alignment issues if the feature map
      # is not even.
      # Shared convolutional base of the RPN
      shared = KL.Conv2D(512, (3, 3), padding='same', activation='relu',
                         strides=anchor_stride,
                         name='rpn_conv_shared')(feature_map)
  
      # Anchor Score. [batch, height, width, anchors per location * 2].
      x = KL.Conv2D(2 * anchors_per_location, (1, 1), padding='valid',
                    activation='linear', name='rpn_class_raw')(shared)
  
      # Reshape to [batch, anchors, 2]
      rpn_class_logits = KL.Lambda(
          lambda t: tf.reshape(t, [tf.shape(t)[0], -1, 2]))(x)
  
      # Softmax on last dimension of BG/FG.
      rpn_probs = KL.Activation(
          "softmax", name="rpn_class_xxx")(rpn_class_logits)
  
      # Bounding box refinement. [batch, H, W, anchors per location * depth]
      # where depth is [x, y, log(w), log(h)]
      x = KL.Conv2D(anchors_per_location * 4, (1, 1), padding="valid",
                    activation='linear', name='rpn_bbox_pred')(shared)
  
      # Reshape to [batch, anchors, 4]
      rpn_bbox = KL.Lambda(lambda t: tf.reshape(t, [tf.shape(t)[0], -1, 4]))(x)
  
      return [rpn_class_logits, rpn_probs, rpn_bbox]
  
  
  def build_rpn_model(anchor_stride, anchors_per_location, depth):
      """Builds a Keras model of the Region Proposal Network.
      It wraps the RPN graph so it can be used multiple times with shared
      weights.
  
      anchors_per_location: number of anchors per pixel in the feature map
      anchor_stride: Controls the density of anchors. Typically 1 (anchors for
                     every pixel in the feature map), or 2 (every other pixel).
      depth: Depth of the backbone feature map.
  
      Returns a Keras Model object. The model outputs, when called, are:
      rpn_class_logits: [batch, H * W * anchors_per_location, 2] Anchor classifier logits (before softmax)
      rpn_probs: [batch, H * W * anchors_per_location, 2] Anchor classifier probabilities.
      rpn_bbox: [batch, H * W * anchors_per_location, (dy, dx, log(dh), log(dw))] Deltas to be
                  applied to anchors.
      """
      input_feature_map = KL.Input(shape=[None, None, depth],
                                   name="input_rpn_feature_map")
      outputs = rpn_graph(input_feature_map, anchors_per_location, anchor_stride)
      return KM.Model([input_feature_map], outputs, name="rpn_model")
  
  
  ############################################################
  #  Feature Pyramid Network Heads
  ############################################################
  
  def fpn_classifier_graph(rois, feature_maps, image_meta,
                           pool_size, num_classes, train_bn=True,
                           fc_layers_size=1024):
      """Builds the computation graph of the feature pyramid network classifier
      and regressor heads.
  
      rois: [batch, num_rois, (y1, x1, y2, x2)] Proposal boxes in normalized
            coordinates.
      feature_maps: List of feature maps from different layers of the pyramid,
                    [P2, P3, P4, P5]. Each has a different resolution.
      image_meta: [batch, (meta data)] Image details. See compose_image_meta()
      pool_size: The width of the square feature map generated from ROI Pooling.
      num_classes: number of classes, which determines the depth of the results
      train_bn: Boolean. Train or freeze Batch Norm layers
      fc_layers_size: Size of the 2 FC layers
  
      Returns:
          logits: [batch, num_rois, NUM_CLASSES] classifier logits (before softmax)
          probs: [batch, num_rois, NUM_CLASSES] classifier probabilities
          bbox_deltas: [batch, num_rois, NUM_CLASSES, (dy, dx, log(dh), log(dw))] Deltas to apply to
                       proposal boxes
      """
      # ROI Pooling
      # Shape: [batch, num_rois, POOL_SIZE, POOL_SIZE, channels]
      x = PyramidROIAlign([pool_size, pool_size],
                          name="roi_align_classifier")([rois, image_meta] + feature_maps)
      # Two 1024 FC layers (implemented with Conv2D for consistency)
      x = KL.TimeDistributed(KL.Conv2D(fc_layers_size, (pool_size, pool_size), padding="valid"),
                             name="mrcnn_class_conv1")(x)
      x = KL.TimeDistributed(BatchNorm(), name='mrcnn_class_bn1')(x, training=train_bn)
      x = KL.Activation('relu')(x)
      x = KL.TimeDistributed(KL.Conv2D(fc_layers_size, (1, 1)),
                             name="mrcnn_class_conv2")(x)
      x = KL.TimeDistributed(BatchNorm(), name='mrcnn_class_bn2')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      shared = KL.Lambda(lambda x: K.squeeze(K.squeeze(x, 3), 2),
                         name="pool_squeeze")(x)
  
      # Classifier head
      mrcnn_class_logits = KL.TimeDistributed(KL.Dense(num_classes),
                                              name='mrcnn_class_logits')(shared)
      mrcnn_probs = KL.TimeDistributed(KL.Activation("softmax"),
                                       name="mrcnn_class")(mrcnn_class_logits)
  
      # BBox head
      # [batch, num_rois, NUM_CLASSES * (dy, dx, log(dh), log(dw))]
      x = KL.TimeDistributed(KL.Dense(num_classes * 4, activation='linear'),
                             name='mrcnn_bbox_fc')(shared)
      # Reshape to [batch, num_rois, NUM_CLASSES, (dy, dx, log(dh), log(dw))]
      s = K.int_shape(x)
      s1 = s[1] if s[1] != None else -1
      mrcnn_bbox = KL.Reshape((s1, num_classes, 4), name="mrcnn_bbox")(x)
  
      return mrcnn_class_logits, mrcnn_probs, mrcnn_bbox
  
  
  def build_fpn_mask_graph(rois, feature_maps, image_meta,
                           pool_size, num_classes, train_bn=True):
      """Builds the computation graph of the mask head of Feature Pyramid Network.
  
      rois: [batch, num_rois, (y1, x1, y2, x2)] Proposal boxes in normalized
            coordinates.
      feature_maps: List of feature maps from different layers of the pyramid,
                    [P2, P3, P4, P5]. Each has a different resolution.
      image_meta: [batch, (meta data)] Image details. See compose_image_meta()
      pool_size: The width of the square feature map generated from ROI Pooling.
      num_classes: number of classes, which determines the depth of the results
      train_bn: Boolean. Train or freeze Batch Norm layers
  
      Returns: Masks [batch, num_rois, MASK_POOL_SIZE, MASK_POOL_SIZE, NUM_CLASSES]
      """
      # ROI Pooling
      # Shape: [batch, num_rois, MASK_POOL_SIZE, MASK_POOL_SIZE, channels]
      x = PyramidROIAlign([pool_size, pool_size],
                          name="roi_align_mask")([rois, image_meta] + feature_maps)
  
      # Conv layers
      x = KL.TimeDistributed(KL.Conv2D(256, (3, 3), padding="same"),
                             name="mrcnn_mask_conv1")(x)
      x = KL.TimeDistributed(BatchNorm(),
                             name='mrcnn_mask_bn1')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.TimeDistributed(KL.Conv2D(256, (3, 3), padding="same"),
                             name="mrcnn_mask_conv2")(x)
      x = KL.TimeDistributed(BatchNorm(),
                             name='mrcnn_mask_bn2')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.TimeDistributed(KL.Conv2D(256, (3, 3), padding="same"),
                             name="mrcnn_mask_conv3")(x)
      x = KL.TimeDistributed(BatchNorm(),
                             name='mrcnn_mask_bn3')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.TimeDistributed(KL.Conv2D(256, (3, 3), padding="same"),
                             name="mrcnn_mask_conv4")(x)
      x = KL.TimeDistributed(BatchNorm(),
                             name='mrcnn_mask_bn4')(x, training=train_bn)
      x = KL.Activation('relu')(x)
  
      x = KL.TimeDistributed(KL.Conv2DTranspose(256, (2, 2), strides=2, activation="relu"),
                             name="mrcnn_mask_deconv")(x)
      x = KL.TimeDistributed(KL.Conv2D(num_classes, (1, 1), strides=1, activation="sigmoid"),
                             name="mrcnn_mask")(x)
      return x
  
  
  ############################################################
  #  Loss Functions
  ############################################################
  
  def smooth_l1_loss(y_true, y_pred):
      """Implements Smooth-L1 loss.
      y_true and y_pred are typically: [N, 4], but could be any shape.
      """
      diff = K.abs(y_true - y_pred)
      less_than_one = K.cast(K.less(diff, 1.0), "float32")
      loss = (less_than_one * 0.5 * diff**2) + (1 - less_than_one) * (diff - 0.5)
      return loss
  
  
  def rpn_class_loss_graph(rpn_match, rpn_class_logits):
      """RPN anchor classifier loss.
  
      rpn_match: [batch, anchors, 1]. Anchor match type. 1=positive,
                 -1=negative, 0=neutral anchor.
      rpn_class_logits: [batch, anchors, 2]. RPN classifier logits for BG/FG.
      """
      # Squeeze last dim to simplify
      rpn_match = tf.squeeze(rpn_match, -1)
      # Get anchor classes. Convert the -1/+1 match to 0/1 values.
      anchor_class = K.cast(K.equal(rpn_match, 1), tf.int32)
      # Positive and Negative anchors contribute to the loss,
      # but neutral anchors (match value = 0) don't.
      indices = tf.where(K.not_equal(rpn_match, 0))
      # Pick rows that contribute to the loss and filter out the rest.
      rpn_class_logits = tf.gather_nd(rpn_class_logits, indices)
      anchor_class = tf.gather_nd(anchor_class, indices)
      # Cross entropy loss
      loss = K.sparse_categorical_crossentropy(target=anchor_class,
                                               output=rpn_class_logits,
                                               from_logits=True)
      loss = K.switch(tf.size(loss) > 0, K.mean(loss), tf.constant(0.0))
      return loss
  
  
  def rpn_bbox_loss_graph(config, target_bbox, rpn_match, rpn_bbox):
      """Return the RPN bounding box loss graph.
  
      config: the model config object.
      target_bbox: [batch, max positive anchors, (dy, dx, log(dh), log(dw))].
          Uses 0 padding to fill in unsed bbox deltas.
      rpn_match: [batch, anchors, 1]. Anchor match type. 1=positive,
                 -1=negative, 0=neutral anchor.
      rpn_bbox: [batch, anchors, (dy, dx, log(dh), log(dw))]
      """
      # Positive anchors contribute to the loss, but negative and
      # neutral anchors (match value of 0 or -1) don't.
      rpn_match = K.squeeze(rpn_match, -1)
      indices = tf.where(K.equal(rpn_match, 1))
  
      # Pick bbox deltas that contribute to the loss
      rpn_bbox = tf.gather_nd(rpn_bbox, indices)
  
      # Trim target bounding box deltas to the same length as rpn_bbox.
      batch_counts = K.sum(K.cast(K.equal(rpn_match, 1), tf.int32), axis=1)
      target_bbox = batch_pack_graph(target_bbox, batch_counts,
                                     config.IMAGES_PER_GPU)
  
      loss = smooth_l1_loss(target_bbox, rpn_bbox)
  
      loss = K.switch(tf.size(loss) > 0, K.mean(loss), tf.constant(0.0))
      return loss
  
  
  def mrcnn_class_loss_graph(target_class_ids, pred_class_logits,
                             active_class_ids):
      """Loss for the classifier head of Mask RCNN.
  
      target_class_ids: [batch, num_rois]. Integer class IDs. Uses zero
          padding to fill in the array.
      pred_class_logits: [batch, num_rois, num_classes]
      active_class_ids: [batch, num_classes]. Has a value of 1 for
          classes that are in the dataset of the image, and 0
          for classes that are not in the dataset.
      """
      # During model building, Keras calls this function with
      # target_class_ids of type float32. Unclear why. Cast it
      # to int to get around it.
      target_class_ids = tf.cast(target_class_ids, 'int64')
  
      # Find predictions of classes that are not in the dataset.
      pred_class_ids = tf.argmax(pred_class_logits, axis=2)
      # TODO: Update this line to work with batch > 1. Right now it assumes all
      #       images in a batch have the same active_class_ids
      pred_active = tf.gather(active_class_ids[0], pred_class_ids)
  
      # Loss
      loss = tf.nn.sparse_softmax_cross_entropy_with_logits(
          labels=target_class_ids, logits=pred_class_logits)
  
      # Erase losses of predictions of classes that are not in the active
      # classes of the image.
      loss = loss * pred_active
  
      # Computer loss mean. Use only predictions that contribute
      # to the loss to get a correct mean.
      loss = tf.reduce_sum(loss) / tf.reduce_sum(pred_active)
      return loss
  
  
  def mrcnn_bbox_loss_graph(target_bbox, target_class_ids, pred_bbox):
      """Loss for Mask R-CNN bounding box refinement.
  
      target_bbox: [batch, num_rois, (dy, dx, log(dh), log(dw))]
      target_class_ids: [batch, num_rois]. Integer class IDs.
      pred_bbox: [batch, num_rois, num_classes, (dy, dx, log(dh), log(dw))]
      """
      # Reshape to merge batch and roi dimensions for simplicity.
      target_class_ids = K.reshape(target_class_ids, (-1,))
      target_bbox = K.reshape(target_bbox, (-1, 4))
      pred_bbox = K.reshape(pred_bbox, (-1, K.int_shape(pred_bbox)[2], 4))
  
      # Only positive ROIs contribute to the loss. And only
      # the right class_id of each ROI. Get their indices.
      positive_roi_ix = tf.where(target_class_ids > 0)[:, 0]
      positive_roi_class_ids = tf.cast(
          tf.gather(target_class_ids, positive_roi_ix), tf.int64)
      indices = tf.stack([positive_roi_ix, positive_roi_class_ids], axis=1)
  
      # Gather the deltas (predicted and true) that contribute to loss
      target_bbox = tf.gather(target_bbox, positive_roi_ix)
      pred_bbox = tf.gather_nd(pred_bbox, indices)
  
      # Smooth-L1 Loss
      loss = K.switch(tf.size(target_bbox) > 0,
                      smooth_l1_loss(y_true=target_bbox, y_pred=pred_bbox),
                      tf.constant(0.0))
      loss = K.mean(loss)
      return loss
  
  
  def mrcnn_mask_loss_graph(target_masks, target_class_ids, pred_masks):
      """Mask binary cross-entropy loss for the masks head.
  
      target_masks: [batch, num_rois, height, width].
          A float32 tensor of values 0 or 1. Uses zero padding to fill array.
      target_class_ids: [batch, num_rois]. Integer class IDs. Zero padded.
      pred_masks: [batch, proposals, height, width, num_classes] float32 tensor
                  with values from 0 to 1.
      """
      # Reshape for simplicity. Merge first two dimensions into one.
      target_class_ids = K.reshape(target_class_ids, (-1,))
      mask_shape = tf.shape(target_masks)
      target_masks = K.reshape(target_masks, (-1, mask_shape[2], mask_shape[3]))
      pred_shape = tf.shape(pred_masks)
      pred_masks = K.reshape(pred_masks,
                             (-1, pred_shape[2], pred_shape[3], pred_shape[4]))
      # Permute predicted masks to [N, num_classes, height, width]
      pred_masks = tf.transpose(pred_masks, [0, 3, 1, 2])
  
      # Only positive ROIs contribute to the loss. And only
      # the class specific mask of each ROI.
      positive_ix = tf.where(target_class_ids > 0)[:, 0]
      positive_class_ids = tf.cast(
          tf.gather(target_class_ids, positive_ix), tf.int64)
      indices = tf.stack([positive_ix, positive_class_ids], axis=1)
  
      # Gather the masks (predicted and true) that contribute to loss
      y_true = tf.gather(target_masks, positive_ix)
      y_pred = tf.gather_nd(pred_masks, indices)
  
      # Compute binary cross entropy. If no positive ROIs, then return 0.
      # shape: [batch, roi, num_classes]
      loss = K.switch(tf.size(y_true) > 0,
                      K.binary_crossentropy(target=y_true, output=y_pred),
                      tf.constant(0.0))
      loss = K.mean(loss)
      return loss
  
  
  ############################################################
  #  Data Generator
  ############################################################
  
  def load_image_gt(dataset, config, image_id, augmentation=None,
                    use_mini_mask=False):
      """Load and return ground truth data for an image (image, mask, bounding boxes).
  
      augmentation: Optional. An imgaug (https://github.com/aleju/imgaug) augmentation.
          For example, passing imgaug.augmenters.Fliplr(0.5) flips images
          right/left 50% of the time.
      use_mini_mask: If False, returns full-size masks that are the same height
          and width as the original image. These can be big, for example
          1024x1024x100 (for 100 instances). Mini masks are smaller, typically,
          224x224 and are generated by extracting the bounding box of the
          object and resizing it to MINI_MASK_SHAPE.
  
      Returns:
          image: [height, width, 3]
          shape: the original shape of the image before resizing and cropping.
          class_ids: [instance_count] Integer class IDs
          bbox: [instance_count, (y1, x1, y2, x2)]
          mask: [height, width, instance_count]. The height and width are those
              of the image unless use_mini_mask is True, in which case they are
              defined in MINI_MASK_SHAPE.
      """
      # Load image and mask
      image = dataset.load_image(image_id)
      mask, class_ids = dataset.load_mask(image_id)
      original_shape = image.shape
      image, window, scale, padding, crop = utils.resize_image(
          image,
          min_dim=config.IMAGE_MIN_DIM,
          min_scale=config.IMAGE_MIN_SCALE,
          max_dim=config.IMAGE_MAX_DIM,
          mode=config.IMAGE_RESIZE_MODE)
      mask = utils.resize_mask(mask, scale, padding, crop)
  
      # Augmentation
      # This requires the imgaug lib (https://github.com/aleju/imgaug)
      if augmentation:
          import imgaug
  
          # Augmenters that are safe to apply to masks
          # Some, such as Affine, have settings that make them unsafe, so always
          # test your augmentation on masks
          MASK_AUGMENTERS = ["Sequential", "SomeOf", "OneOf", "Sometimes",
                             "Fliplr", "Flipud", "CropAndPad",
                             "Affine", "PiecewiseAffine"]
  
          def hook(images, augmenter, parents, default):
              """Determines which augmenters to apply to masks."""
              return augmenter.__class__.__name__ in MASK_AUGMENTERS
  
          # Store shapes before augmentation to compare
          image_shape = image.shape
          mask_shape = mask.shape
          # Make augmenters deterministic to apply similarly to images and masks
          det = augmentation.to_deterministic()
          image = det.augment_image(image)
          # Change mask to np.uint8 because imgaug doesn't support np.bool
          mask = det.augment_image(mask.astype(np.uint8),
                                   hooks=imgaug.HooksImages(activator=hook))
          # Verify that shapes didn't change
          assert image.shape == image_shape, "Augmentation shouldn't change image size"
          assert mask.shape == mask_shape, "Augmentation shouldn't change mask size"
          # Change mask back to bool
          mask = mask.astype(np.bool)
  
      # Note that some boxes might be all zeros if the corresponding mask got cropped out.
      # and here is to filter them out
      _idx = np.sum(mask, axis=(0, 1)) > 0
      mask = mask[:, :, _idx]
      class_ids = class_ids[_idx]
      # Bounding boxes. Note that some boxes might be all zeros
      # if the corresponding mask got cropped out.
      # bbox: [num_instances, (y1, x1, y2, x2)]
      bbox = utils.extract_bboxes(mask)
  
      # Active classes
      # Different datasets have different classes, so track the
      # classes supported in the dataset of this image.
      active_class_ids = np.zeros([dataset.num_classes], dtype=np.int32)
      source_class_ids = dataset.source_class_ids[dataset.image_info[image_id]["source"]]
      active_class_ids[source_class_ids] = 1
  
      # Resize masks to smaller size to reduce memory usage
      if use_mini_mask:
          mask = utils.minimize_mask(bbox, mask, config.MINI_MASK_SHAPE)
  
      # Image meta data
      image_meta = compose_image_meta(image_id, original_shape, image.shape,
                                      window, scale, active_class_ids)
  
      return image, image_meta, class_ids, bbox, mask
  
  
  def build_detection_targets(rpn_rois, gt_class_ids, gt_boxes, gt_masks, config):
      """Generate targets for training Stage 2 classifier and mask heads.
      This is not used in normal training. It's useful for debugging or to train
      the Mask RCNN heads without using the RPN head.
  
      Inputs:
      rpn_rois: [N, (y1, x1, y2, x2)] proposal boxes.
      gt_class_ids: [instance count] Integer class IDs
      gt_boxes: [instance count, (y1, x1, y2, x2)]
      gt_masks: [height, width, instance count] Ground truth masks. Can be full
                size or mini-masks.
  
      Returns:
      rois: [TRAIN_ROIS_PER_IMAGE, (y1, x1, y2, x2)]
      class_ids: [TRAIN_ROIS_PER_IMAGE]. Integer class IDs.
      bboxes: [TRAIN_ROIS_PER_IMAGE, NUM_CLASSES, (y, x, log(h), log(w))]. Class-specific
              bbox refinements.
      masks: [TRAIN_ROIS_PER_IMAGE, height, width, NUM_CLASSES). Class specific masks cropped
             to bbox boundaries and resized to neural network output size.
      """
      assert rpn_rois.shape[0] > 0
      assert gt_class_ids.dtype == np.int32, "Expected int but got {}".format(
          gt_class_ids.dtype)
      assert gt_boxes.dtype == np.int32, "Expected int but got {}".format(
          gt_boxes.dtype)
      assert gt_masks.dtype == np.bool_, "Expected bool but got {}".format(
          gt_masks.dtype)
  
      # It's common to add GT Boxes to ROIs but we don't do that here because
      # according to XinLei Chen's paper, it doesn't help.
  
      # Trim empty padding in gt_boxes and gt_masks parts
      instance_ids = np.where(gt_class_ids > 0)[0]
      assert instance_ids.shape[0] > 0, "Image must contain instances."
      gt_class_ids = gt_class_ids[instance_ids]
      gt_boxes = gt_boxes[instance_ids]
      gt_masks = gt_masks[:, :, instance_ids]
  
      # Compute areas of ROIs and ground truth boxes.
      rpn_roi_area = (rpn_rois[:, 2] - rpn_rois[:, 0]) * \
          (rpn_rois[:, 3] - rpn_rois[:, 1])
      gt_box_area = (gt_boxes[:, 2] - gt_boxes[:, 0]) * \
          (gt_boxes[:, 3] - gt_boxes[:, 1])
  
      # Compute overlaps [rpn_rois, gt_boxes]
      overlaps = np.zeros((rpn_rois.shape[0], gt_boxes.shape[0]))
      for i in range(overlaps.shape[1]):
          gt = gt_boxes[i]
          overlaps[:, i] = utils.compute_iou(
              gt, rpn_rois, gt_box_area[i], rpn_roi_area)
  
      # Assign ROIs to GT boxes
      rpn_roi_iou_argmax = np.argmax(overlaps, axis=1)
      rpn_roi_iou_max = overlaps[np.arange(
          overlaps.shape[0]), rpn_roi_iou_argmax]
      # GT box assigned to each ROI
      rpn_roi_gt_boxes = gt_boxes[rpn_roi_iou_argmax]
      rpn_roi_gt_class_ids = gt_class_ids[rpn_roi_iou_argmax]
  
      # Positive ROIs are those with >= 0.5 IoU with a GT box.
      fg_ids = np.where(rpn_roi_iou_max > 0.5)[0]
  
      # Negative ROIs are those with max IoU 0.1-0.5 (hard example mining)
      # TODO: To hard example mine or not to hard example mine, that's the question
      # bg_ids = np.where((rpn_roi_iou_max >= 0.1) & (rpn_roi_iou_max < 0.5))[0]
      bg_ids = np.where(rpn_roi_iou_max < 0.5)[0]
  
      # Subsample ROIs. Aim for 33% foreground.
      # FG
      fg_roi_count = int(config.TRAIN_ROIS_PER_IMAGE * config.ROI_POSITIVE_RATIO)
      if fg_ids.shape[0] > fg_roi_count:
          keep_fg_ids = np.random.choice(fg_ids, fg_roi_count, replace=False)
      else:
          keep_fg_ids = fg_ids
      # BG
      remaining = config.TRAIN_ROIS_PER_IMAGE - keep_fg_ids.shape[0]
      if bg_ids.shape[0] > remaining:
          keep_bg_ids = np.random.choice(bg_ids, remaining, replace=False)
      else:
          keep_bg_ids = bg_ids
      # Combine indices of ROIs to keep
      keep = np.concatenate([keep_fg_ids, keep_bg_ids])
      # Need more?
      remaining = config.TRAIN_ROIS_PER_IMAGE - keep.shape[0]
      if remaining > 0:
          # Looks like we don't have enough samples to maintain the desired
          # balance. Reduce requirements and fill in the rest. This is
          # likely different from the Mask RCNN paper.
  
          # There is a small chance we have neither fg nor bg samples.
          if keep.shape[0] == 0:
              # Pick bg regions with easier IoU threshold
              bg_ids = np.where(rpn_roi_iou_max < 0.5)[0]
              assert bg_ids.shape[0] >= remaining
              keep_bg_ids = np.random.choice(bg_ids, remaining, replace=False)
              assert keep_bg_ids.shape[0] == remaining
              keep = np.concatenate([keep, keep_bg_ids])
          else:
              # Fill the rest with repeated bg rois.
              keep_extra_ids = np.random.choice(
                  keep_bg_ids, remaining, replace=True)
              keep = np.concatenate([keep, keep_extra_ids])
      assert keep.shape[0] == config.TRAIN_ROIS_PER_IMAGE, \
          "keep doesn't match ROI batch size {}, {}".format(
              keep.shape[0], config.TRAIN_ROIS_PER_IMAGE)
  
      # Reset the gt boxes assigned to BG ROIs.
      rpn_roi_gt_boxes[keep_bg_ids, :] = 0
      rpn_roi_gt_class_ids[keep_bg_ids] = 0
  
      # For each kept ROI, assign a class_id, and for FG ROIs also add bbox refinement.
      rois = rpn_rois[keep]
      roi_gt_boxes = rpn_roi_gt_boxes[keep]
      roi_gt_class_ids = rpn_roi_gt_class_ids[keep]
      roi_gt_assignment = rpn_roi_iou_argmax[keep]
  
      # Class-aware bbox deltas. [y, x, log(h), log(w)]
      bboxes = np.zeros((config.TRAIN_ROIS_PER_IMAGE,
                         config.NUM_CLASSES, 4), dtype=np.float32)
      pos_ids = np.where(roi_gt_class_ids > 0)[0]
      bboxes[pos_ids, roi_gt_class_ids[pos_ids]] = utils.box_refinement(
          rois[pos_ids], roi_gt_boxes[pos_ids, :4])
      # Normalize bbox refinements
      bboxes /= config.BBOX_STD_DEV
  
      # Generate class-specific target masks
      masks = np.zeros((config.TRAIN_ROIS_PER_IMAGE, config.MASK_SHAPE[0], config.MASK_SHAPE[1], config.NUM_CLASSES),
                       dtype=np.float32)
      for i in pos_ids:
          class_id = roi_gt_class_ids[i]
          assert class_id > 0, "class id must be greater than 0"
          gt_id = roi_gt_assignment[i]
          class_mask = gt_masks[:, :, gt_id]
  
          if config.USE_MINI_MASK:
              # Create a mask placeholder, the size of the image
              placeholder = np.zeros(config.IMAGE_SHAPE[:2], dtype=bool)
              # GT box
              gt_y1, gt_x1, gt_y2, gt_x2 = gt_boxes[gt_id]
              gt_w = gt_x2 - gt_x1
              gt_h = gt_y2 - gt_y1
              # Resize mini mask to size of GT box
              placeholder[gt_y1:gt_y2, gt_x1:gt_x2] = \
                  np.round(utils.resize(class_mask, (gt_h, gt_w))).astype(bool)
              # Place the mini batch in the placeholder
              class_mask = placeholder
  
          # Pick part of the mask and resize it
          y1, x1, y2, x2 = rois[i].astype(np.int32)
          m = class_mask[y1:y2, x1:x2]
          mask = utils.resize(m, config.MASK_SHAPE)
          masks[i, :, :, class_id] = mask
  
      return rois, roi_gt_class_ids, bboxes, masks
  
  
  def build_rpn_targets(image_shape, anchors, gt_class_ids, gt_boxes, config):
      """Given the anchors and GT boxes, compute overlaps and identify positive
      anchors and deltas to refine them to match their corresponding GT boxes.
  
      anchors: [num_anchors, (y1, x1, y2, x2)]
      gt_class_ids: [num_gt_boxes] Integer class IDs.
      gt_boxes: [num_gt_boxes, (y1, x1, y2, x2)]
  
      Returns:
      rpn_match: [N] (int32) matches between anchors and GT boxes.
                 1 = positive anchor, -1 = negative anchor, 0 = neutral
      rpn_bbox: [N, (dy, dx, log(dh), log(dw))] Anchor bbox deltas.
      """
      # RPN Match: 1 = positive anchor, -1 = negative anchor, 0 = neutral
      rpn_match = np.zeros([anchors.shape[0]], dtype=np.int32)
      # RPN bounding boxes: [max anchors per image, (dy, dx, log(dh), log(dw))]
      rpn_bbox = np.zeros((config.RPN_TRAIN_ANCHORS_PER_IMAGE, 4))
  
      # Handle COCO crowds
      # A crowd box in COCO is a bounding box around several instances. Exclude
      # them from training. A crowd box is given a negative class ID.
      crowd_ix = np.where(gt_class_ids < 0)[0]
      if crowd_ix.shape[0] > 0:
          # Filter out crowds from ground truth class IDs and boxes
          non_crowd_ix = np.where(gt_class_ids > 0)[0]
          crowd_boxes = gt_boxes[crowd_ix]
          gt_class_ids = gt_class_ids[non_crowd_ix]
          gt_boxes = gt_boxes[non_crowd_ix]
          # Compute overlaps with crowd boxes [anchors, crowds]
          crowd_overlaps = utils.compute_overlaps(anchors, crowd_boxes)
          crowd_iou_max = np.amax(crowd_overlaps, axis=1)
          no_crowd_bool = (crowd_iou_max < 0.001)
      else:
          # All anchors don't intersect a crowd
          no_crowd_bool = np.ones([anchors.shape[0]], dtype=bool)
  
      # Compute overlaps [num_anchors, num_gt_boxes]
      overlaps = utils.compute_overlaps(anchors, gt_boxes)
  
      # Match anchors to GT Boxes
      # If an anchor overlaps a GT box with IoU >= 0.7 then it's positive.
      # If an anchor overlaps a GT box with IoU < 0.3 then it's negative.
      # Neutral anchors are those that don't match the conditions above,
      # and they don't influence the loss function.
      # However, don't keep any GT box unmatched (rare, but happens). Instead,
      # match it to the closest anchor (even if its max IoU is < 0.3).
      #
      # 1. Set negative anchors first. They get overwritten below if a GT box is
      # matched to them. Skip boxes in crowd areas.
      anchor_iou_argmax = np.argmax(overlaps, axis=1)
      anchor_iou_max = overlaps[np.arange(overlaps.shape[0]), anchor_iou_argmax]
      rpn_match[(anchor_iou_max < 0.3) & (no_crowd_bool)] = -1
      # 2. Set an anchor for each GT box (regardless of IoU value).
      # If multiple anchors have the same IoU match all of them
      gt_iou_argmax = np.argwhere(overlaps == np.max(overlaps, axis=0))[:, 0]
      rpn_match[gt_iou_argmax] = 1
      # 3. Set anchors with high overlap as positive.
      rpn_match[anchor_iou_max >= 0.7] = 1
  
      # Subsample to balance positive and negative anchors
      # Don't let positives be more than half the anchors
      ids = np.where(rpn_match == 1)[0]
      extra = len(ids) - (config.RPN_TRAIN_ANCHORS_PER_IMAGE // 2)
      if extra > 0:
          # Reset the extra ones to neutral
          ids = np.random.choice(ids, extra, replace=False)
          rpn_match[ids] = 0
      # Same for negative proposals
      ids = np.where(rpn_match == -1)[0]
      extra = len(ids) - (config.RPN_TRAIN_ANCHORS_PER_IMAGE -
                          np.sum(rpn_match == 1))
      if extra > 0:
          # Rest the extra ones to neutral
          ids = np.random.choice(ids, extra, replace=False)
          rpn_match[ids] = 0
  
      # For positive anchors, compute shift and scale needed to transform them
      # to match the corresponding GT boxes.
      ids = np.where(rpn_match == 1)[0]
      ix = 0  # index into rpn_bbox
      # TODO: use box_refinement() rather than duplicating the code here
      for i, a in zip(ids, anchors[ids]):
          # Closest gt box (it might have IoU < 0.7)
          gt = gt_boxes[anchor_iou_argmax[i]]
  
          # Convert coordinates to center plus width/height.
          # GT Box
          gt_h = gt[2] - gt[0]
          gt_w = gt[3] - gt[1]
          gt_center_y = gt[0] + 0.5 * gt_h
          gt_center_x = gt[1] + 0.5 * gt_w
          # Anchor
          a_h = a[2] - a[0]
          a_w = a[3] - a[1]
          a_center_y = a[0] + 0.5 * a_h
          a_center_x = a[1] + 0.5 * a_w
  
          # Compute the bbox refinement that the RPN should predict.
          rpn_bbox[ix] = [
              (gt_center_y - a_center_y) / a_h,
              (gt_center_x - a_center_x) / a_w,
              np.log(gt_h / a_h),
              np.log(gt_w / a_w),
          ]
          # Normalize
          rpn_bbox[ix] /= config.RPN_BBOX_STD_DEV
          ix += 1
  
      return rpn_match, rpn_bbox
  
  
  def generate_random_rois(image_shape, count, gt_class_ids, gt_boxes):
      """Generates ROI proposals similar to what a region proposal network
      would generate.
  
      image_shape: [Height, Width, Depth]
      count: Number of ROIs to generate
      gt_class_ids: [N] Integer ground truth class IDs
      gt_boxes: [N, (y1, x1, y2, x2)] Ground truth boxes in pixels.
  
      Returns: [count, (y1, x1, y2, x2)] ROI boxes in pixels.
      """
      # placeholder
      rois = np.zeros((count, 4), dtype=np.int32)
  
      # Generate random ROIs around GT boxes (90% of count)
      rois_per_box = int(0.9 * count / gt_boxes.shape[0])
      for i in range(gt_boxes.shape[0]):
          gt_y1, gt_x1, gt_y2, gt_x2 = gt_boxes[i]
          h = gt_y2 - gt_y1
          w = gt_x2 - gt_x1
          # random boundaries
          r_y1 = max(gt_y1 - h, 0)
          r_y2 = min(gt_y2 + h, image_shape[0])
          r_x1 = max(gt_x1 - w, 0)
          r_x2 = min(gt_x2 + w, image_shape[1])
  
          # To avoid generating boxes with zero area, we generate double what
          # we need and filter out the extra. If we get fewer valid boxes
          # than we need, we loop and try again.
          while True:
              y1y2 = np.random.randint(r_y1, r_y2, (rois_per_box * 2, 2))
              x1x2 = np.random.randint(r_x1, r_x2, (rois_per_box * 2, 2))
              # Filter out zero area boxes
              threshold = 1
              y1y2 = y1y2[np.abs(y1y2[:, 0] - y1y2[:, 1]) >=
                          threshold][:rois_per_box]
              x1x2 = x1x2[np.abs(x1x2[:, 0] - x1x2[:, 1]) >=
                          threshold][:rois_per_box]
              if y1y2.shape[0] == rois_per_box and x1x2.shape[0] == rois_per_box:
                  break
  
          # Sort on axis 1 to ensure x1 <= x2 and y1 <= y2 and then reshape
          # into x1, y1, x2, y2 order
          x1, x2 = np.split(np.sort(x1x2, axis=1), 2, axis=1)
          y1, y2 = np.split(np.sort(y1y2, axis=1), 2, axis=1)
          box_rois = np.hstack([y1, x1, y2, x2])
          rois[rois_per_box * i:rois_per_box * (i + 1)] = box_rois
  
      # Generate random ROIs anywhere in the image (10% of count)
      remaining_count = count - (rois_per_box * gt_boxes.shape[0])
      # To avoid generating boxes with zero area, we generate double what
      # we need and filter out the extra. If we get fewer valid boxes
      # than we need, we loop and try again.
      while True:
          y1y2 = np.random.randint(0, image_shape[0], (remaining_count * 2, 2))
          x1x2 = np.random.randint(0, image_shape[1], (remaining_count * 2, 2))
          # Filter out zero area boxes
          threshold = 1
          y1y2 = y1y2[np.abs(y1y2[:, 0] - y1y2[:, 1]) >=
                      threshold][:remaining_count]
          x1x2 = x1x2[np.abs(x1x2[:, 0] - x1x2[:, 1]) >=
                      threshold][:remaining_count]
          if y1y2.shape[0] == remaining_count and x1x2.shape[0] == remaining_count:
              break
  
      # Sort on axis 1 to ensure x1 <= x2 and y1 <= y2 and then reshape
      # into x1, y1, x2, y2 order
      x1, x2 = np.split(np.sort(x1x2, axis=1), 2, axis=1)
      y1, y2 = np.split(np.sort(y1y2, axis=1), 2, axis=1)
      global_rois = np.hstack([y1, x1, y2, x2])
      rois[-remaining_count:] = global_rois
      return rois
  
  
  class DataGenerator(KU.Sequence):
      """An iterable that returns images and corresponding target class ids,
      bounding box deltas, and masks.
      It inherits from keras.utils.Sequence to avoid data redundancy when multiprocessing=True.
  
      dataset: The Dataset object to pick data from
      config: The model config object
      shuffle: If True, shuffles the samples before every epoch
      augmentation: Optional. An imgaug (https://github.com/aleju/imgaug) augmentation.
          For example, passing imgaug.augmenters.Fliplr(0.5) flips images
          right/left 50% of the time.
      random_rois: If > 0 then generate proposals to be used to train the
                   network classifier and mask heads. Useful if training
                   the Mask RCNN part without the RPN.
      batch_size: How many images to return in each call
      detection_targets: If True, generate detection targets (class IDs, bbox
          deltas, and masks). Typically for debugging or visualizations because
          in trainig detection targets are generated by DetectionTargetLayer.
  
      Returns a Python iterable. Upon calling __getitem__() on it, the
      iterable returns two lists, inputs and outputs. The contents
      of the lists differ depending on the received arguments:
      inputs list:
      - images: [batch, H, W, C]
      - image_meta: [batch, (meta data)] Image details. See compose_image_meta()
      - rpn_match: [batch, N] Integer (1=positive anchor, -1=negative, 0=neutral)
      - rpn_bbox: [batch, N, (dy, dx, log(dh), log(dw))] Anchor bbox deltas.
      - gt_class_ids: [batch, MAX_GT_INSTANCES] Integer class IDs
      - gt_boxes: [batch, MAX_GT_INSTANCES, (y1, x1, y2, x2)]
      - gt_masks: [batch, height, width, MAX_GT_INSTANCES]. The height and width
                  are those of the image unless use_mini_mask is True, in which
                  case they are defined in MINI_MASK_SHAPE.
  
      outputs list: Usually empty in regular training. But if detection_targets
          is True then the outputs list contains target class_ids, bbox deltas,
          and masks.
      """
  
      def __init__(self, dataset, config, shuffle=True, augmentation=None,
                   random_rois=0, batch_size=1, detection_targets=False):
          self.dataset = dataset
          self.config = config
          self.shuffle = shuffle
          self.augmentation = augmentation
          self.random_rois = random_rois
          self.batch_size = batch_size
          self.detection_targets = detection_targets
          self.image_ids = np.copy(dataset.image_ids)
  
          # Anchors
          # [anchor_count, (y1, x1, y2, x2)]
          self.backbone_shapes = compute_backbone_shapes(config, config.IMAGE_SHAPE)
          self.anchors = utils.generate_pyramid_anchors(config.RPN_ANCHOR_SCALES,
                                                        config.RPN_ANCHOR_RATIOS,
                                                        self.backbone_shapes,
                                                        config.BACKBONE_STRIDES,
                                                        config.RPN_ANCHOR_STRIDE)
  
      def __len__(self):
          return int(np.ceil(len(self.image_ids) / float(self.batch_size)))
  
      def __getitem__(self, idx):
          b = 0  # batch item index
          image_index = -1
          while b < self.batch_size:
              # Increment index to pick next image. Shuffle if at the start of an epoch.
              image_index = (image_index + 1) % len(self.image_ids)
              if self.shuffle and image_index == 0:
                  np.random.shuffle(self.image_ids)
  
              # Get GT bounding boxes and masks for image.
              image_id = self.image_ids[image_index]
              image, image_meta, gt_class_ids, gt_boxes, gt_masks = \
                  load_image_gt(self.dataset, self.config, image_id,
                                augmentation=self.augmentation,
                                use_mini_mask=self.config.USE_MINI_MASK)
  
              # Skip images that have no instances. This can happen in cases
              # where we train on a subset of classes and the image doesn't
              # have any of the classes we care about.
              if not np.any(gt_class_ids > 0):
                  continue
  
              # RPN Targets
              rpn_match, rpn_bbox = build_rpn_targets(image.shape, self.anchors,
                                                      gt_class_ids, gt_boxes, self.config)
  
              # Mask R-CNN Targets
              if self.random_rois:
                  rpn_rois = generate_random_rois(
                      image.shape, self.random_rois, gt_class_ids, gt_boxes)
                  if self.detection_targets:
                      rois, mrcnn_class_ids, mrcnn_bbox, mrcnn_mask = \
                          build_detection_targets(
                              rpn_rois, gt_class_ids, gt_boxes, gt_masks, self.config)
  
              # Init batch arrays
              if b == 0:
                  batch_image_meta = np.zeros(
                      (self.batch_size,) + image_meta.shape, dtype=image_meta.dtype)
                  batch_rpn_match = np.zeros(
                      [self.batch_size, self.anchors.shape[0], 1], dtype=rpn_match.dtype)
                  batch_rpn_bbox = np.zeros(
                      [self.batch_size, self.config.RPN_TRAIN_ANCHORS_PER_IMAGE, 4], dtype=rpn_bbox.dtype)
                  batch_images = np.zeros(
                      (self.batch_size,) + image.shape, dtype=np.float32)
                  batch_gt_class_ids = np.zeros(
                      (self.batch_size, self.config.MAX_GT_INSTANCES), dtype=np.int32)
                  batch_gt_boxes = np.zeros(
                      (self.batch_size, self.config.MAX_GT_INSTANCES, 4), dtype=np.int32)
                  batch_gt_masks = np.zeros(
                      (self.batch_size, gt_masks.shape[0], gt_masks.shape[1],
                          self.config.MAX_GT_INSTANCES), dtype=gt_masks.dtype)
                  if self.random_rois:
                      batch_rpn_rois = np.zeros(
                          (self.batch_size, rpn_rois.shape[0], 4), dtype=rpn_rois.dtype)
                      if self.detection_targets:
                          batch_rois = np.zeros(
                              (self.batch_size,) + rois.shape, dtype=rois.dtype)
                          batch_mrcnn_class_ids = np.zeros(
                              (self.batch_size,) + mrcnn_class_ids.shape, dtype=mrcnn_class_ids.dtype)
                          batch_mrcnn_bbox = np.zeros(
                              (self.batch_size,) + mrcnn_bbox.shape, dtype=mrcnn_bbox.dtype)
                          batch_mrcnn_mask = np.zeros(
                              (self.batch_size,) + mrcnn_mask.shape, dtype=mrcnn_mask.dtype)
  
              # If more instances than fits in the array, sub-sample from them.
              if gt_boxes.shape[0] > self.config.MAX_GT_INSTANCES:
                  ids = np.random.choice(
                      np.arange(gt_boxes.shape[0]), self.config.MAX_GT_INSTANCES, replace=False)
                  gt_class_ids = gt_class_ids[ids]
                  gt_boxes = gt_boxes[ids]
                  gt_masks = gt_masks[:, :, ids]
  
              # Add to batch
              batch_image_meta[b] = image_meta
              batch_rpn_match[b] = rpn_match[:, np.newaxis]
              batch_rpn_bbox[b] = rpn_bbox
              batch_images[b] = mold_image(image.astype(np.float32), self.config)
              batch_gt_class_ids[b, :gt_class_ids.shape[0]] = gt_class_ids
              batch_gt_boxes[b, :gt_boxes.shape[0]] = gt_boxes
              batch_gt_masks[b, :, :, :gt_masks.shape[-1]] = gt_masks
              if self.random_rois:
                  batch_rpn_rois[b] = rpn_rois
                  if self.detection_targets:
                      batch_rois[b] = rois
                      batch_mrcnn_class_ids[b] = mrcnn_class_ids
                      batch_mrcnn_bbox[b] = mrcnn_bbox
                      batch_mrcnn_mask[b] = mrcnn_mask
              b += 1
  
          inputs = [batch_images, batch_image_meta, batch_rpn_match, batch_rpn_bbox,
                    batch_gt_class_ids, batch_gt_boxes, batch_gt_masks]
          outputs = []
  
          if self.random_rois:
              inputs.extend([batch_rpn_rois])
              if self.detection_targets:
                  inputs.extend([batch_rois])
                  # Keras requires that output and targets have the same number of dimensions
                  batch_mrcnn_class_ids = np.expand_dims(
                      batch_mrcnn_class_ids, -1)
                  outputs.extend(
                      [batch_mrcnn_class_ids, batch_mrcnn_bbox, batch_mrcnn_mask])
  
          return inputs, outputs
  
  
  ############################################################
  #  MaskRCNN Class
  ############################################################
  
  class MaskRCNN():
      """Encapsulates the Mask RCNN model functionality.
  
      The actual Keras model is in the keras_model property.
      """
  
      def __init__(self, mode, config, model_dir):
          """
          mode: Either "training" or "inference"
          config: A Sub-class of the Config class
          model_dir: Directory to save training logs and trained weights
          """
          assert mode in ['training', 'inference']
          self.mode = mode
          self.config = config
          self.model_dir = model_dir
          self.set_log_dir()
          self.keras_model = self.build(mode=mode, config=config)
  
      def build(self, mode, config):
          """Build Mask R-CNN architecture.
              input_shape: The shape of the input image.
              mode: Either "training" or "inference". The inputs and
                  outputs of the model differ accordingly.
          """
          assert mode in ['training', 'inference']
  
          # Image size must be dividable by 2 multiple times
          h, w = config.IMAGE_SHAPE[:2]
          if h / 2**6 != int(h / 2**6) or w / 2**6 != int(w / 2**6):
              raise Exception("Image size must be dividable by 2 at least 6 times "
                              "to avoid fractions when downscaling and upscaling."
                              "For example, use 256, 320, 384, 448, 512, ... etc. ")
  
          # Inputs
          input_image = KL.Input(
              shape=[None, None, config.IMAGE_SHAPE[2]], name="input_image")
          input_image_meta = KL.Input(shape=[config.IMAGE_META_SIZE],
                                      name="input_image_meta")
          if mode == "training":
              # RPN GT
              input_rpn_match = KL.Input(
                  shape=[None, 1], name="input_rpn_match", dtype=tf.int32)
              input_rpn_bbox = KL.Input(
                  shape=[None, 4], name="input_rpn_bbox", dtype=tf.float32)
  
              # Detection GT (class IDs, bounding boxes, and masks)
              # 1. GT Class IDs (zero padded)
              input_gt_class_ids = KL.Input(
                  shape=[None], name="input_gt_class_ids", dtype=tf.int32)
              # 2. GT Boxes in pixels (zero padded)
              # [batch, MAX_GT_INSTANCES, (y1, x1, y2, x2)] in image coordinates
              input_gt_boxes = KL.Input(
                  shape=[None, 4], name="input_gt_boxes", dtype=tf.float32)
              # Normalize coordinates
              gt_boxes = KL.Lambda(lambda x: norm_boxes_graph(
                  x, K.shape(input_image)[1:3]))(input_gt_boxes)
              # 3. GT Masks (zero padded)
              # [batch, height, width, MAX_GT_INSTANCES]
              if config.USE_MINI_MASK:
                  input_gt_masks = KL.Input(
                      shape=[config.MINI_MASK_SHAPE[0],
                             config.MINI_MASK_SHAPE[1], None],
                      name="input_gt_masks", dtype=bool)
              else:
                  input_gt_masks = KL.Input(
                      shape=[config.IMAGE_SHAPE[0], config.IMAGE_SHAPE[1], None],
                      name="input_gt_masks", dtype=bool)
          elif mode == "inference":
              # Anchors in normalized coordinates
              input_anchors = KL.Input(shape=[None, 4], name="input_anchors")
  
          # Build the shared convolutional layers.
          # Bottom-up Layers
          # Returns a list of the last layers of each stage, 5 in total.
          # Don't create the thead (stage 5), so we pick the 4th item in the list.
          if callable(config.BACKBONE):
              _, C2, C3, C4, C5 = config.BACKBONE(input_image, stage5=True,
                                                  train_bn=config.TRAIN_BN)
          else:
              _, C2, C3, C4, C5 = resnet_graph(input_image, config.BACKBONE,
                                               stage5=True, train_bn=config.TRAIN_BN)
          # Top-down Layers
          # TODO: add assert to varify feature map sizes match what's in config
          P5 = KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (1, 1), name='fpn_c5p5')(C5)
          P4 = KL.Add(name="fpn_p4add")([
              KL.UpSampling2D(size=(2, 2), name="fpn_p5upsampled")(P5),
              KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (1, 1), name='fpn_c4p4')(C4)])
          P3 = KL.Add(name="fpn_p3add")([
              KL.UpSampling2D(size=(2, 2), name="fpn_p4upsampled")(P4),
              KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (1, 1), name='fpn_c3p3')(C3)])
          P2 = KL.Add(name="fpn_p2add")([
              KL.UpSampling2D(size=(2, 2), name="fpn_p3upsampled")(P3),
              KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (1, 1), name='fpn_c2p2')(C2)])
          # Attach 3x3 conv to all P layers to get the final feature maps.
          P2 = KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (3, 3), padding="SAME", name="fpn_p2")(P2)
          P3 = KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (3, 3), padding="SAME", name="fpn_p3")(P3)
          P4 = KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (3, 3), padding="SAME", name="fpn_p4")(P4)
          P5 = KL.Conv2D(config.TOP_DOWN_PYRAMID_SIZE, (3, 3), padding="SAME", name="fpn_p5")(P5)
          # P6 is used for the 5th anchor scale in RPN. Generated by
          # subsampling from P5 with stride of 2.
          P6 = KL.MaxPooling2D(pool_size=(1, 1), strides=2, name="fpn_p6")(P5)
  
          # Note that P6 is used in RPN, but not in the classifier heads.
          rpn_feature_maps = [P2, P3, P4, P5, P6]
          mrcnn_feature_maps = [P2, P3, P4, P5]
  
          # Anchors
          if mode == "training":
              anchors = self.get_anchors(config.IMAGE_SHAPE)
              # Duplicate across the batch dimension because Keras requires it
              # TODO: can this be optimized to avoid duplicating the anchors?
              anchors = np.broadcast_to(anchors, (config.BATCH_SIZE,) + anchors.shape)
  
              # A hack to get around Keras's bad support for constants
              # This class returns a constant layer
              class ConstLayer(KE.Layer):
                  def __init__(self, x, name=None):
                      super(ConstLayer, self).__init__(name=name)
                      self.x = tf.Variable(x)
  
                  def call(self, input):
                      return self.x
  
              anchors = ConstLayer(anchors, name="anchors")(input_image)
          else:
              anchors = input_anchors
  
          # RPN Model
          rpn = build_rpn_model(config.RPN_ANCHOR_STRIDE,
                                len(config.RPN_ANCHOR_RATIOS), config.TOP_DOWN_PYRAMID_SIZE)
          # Loop through pyramid layers
          layer_outputs = []  # list of lists
          for p in rpn_feature_maps:
              layer_outputs.append(rpn([p]))
          # Concatenate layer outputs
          # Convert from list of lists of level outputs to list of lists
          # of outputs across levels.
          # e.g. [[a1, b1, c1], [a2, b2, c2]] => [[a1, a2], [b1, b2], [c1, c2]]
          output_names = ["rpn_class_logits", "rpn_class", "rpn_bbox"]
          outputs = list(zip(*layer_outputs))
          outputs = [KL.Concatenate(axis=1, name=n)(list(o))
                     for o, n in zip(outputs, output_names)]
  
          rpn_class_logits, rpn_class, rpn_bbox = outputs
  
          # Generate proposals
          # Proposals are [batch, N, (y1, x1, y2, x2)] in normalized coordinates
          # and zero padded.
          proposal_count = config.POST_NMS_ROIS_TRAINING if mode == "training"\
              else config.POST_NMS_ROIS_INFERENCE
          rpn_rois = ProposalLayer(
              proposal_count=proposal_count,
              nms_threshold=config.RPN_NMS_THRESHOLD,
              name="ROI",
              config=config)([rpn_class, rpn_bbox, anchors])
  
          if mode == "training":
              # Class ID mask to mark class IDs supported by the dataset the image
              # came from.
              active_class_ids = KL.Lambda(
                  lambda x: parse_image_meta_graph(x)["active_class_ids"]
              )(input_image_meta)
  
              if not config.USE_RPN_ROIS:
                  # Ignore predicted ROIs and use ROIs provided as an input.
                  input_rois = KL.Input(shape=[config.POST_NMS_ROIS_TRAINING, 4],
                                        name="input_roi", dtype=np.int32)
                  # Normalize coordinates
                  target_rois = KL.Lambda(lambda x: norm_boxes_graph(
                      x, K.shape(input_image)[1:3]))(input_rois)
              else:
                  target_rois = rpn_rois
  
              # Generate detection targets
              # Subsamples proposals and generates target outputs for training
              # Note that proposal class IDs, gt_boxes, and gt_masks are zero
              # padded. Equally, returned rois and targets are zero padded.
              rois, target_class_ids, target_bbox, target_mask =\
                  DetectionTargetLayer(config, name="proposal_targets")([
                      target_rois, input_gt_class_ids, gt_boxes, input_gt_masks])
  
              # Network Heads
              # TODO: verify that this handles zero padded ROIs
              mrcnn_class_logits, mrcnn_class, mrcnn_bbox =\
                  fpn_classifier_graph(rois, mrcnn_feature_maps, input_image_meta,
                                       config.POOL_SIZE, config.NUM_CLASSES,
                                       train_bn=config.TRAIN_BN,
                                       fc_layers_size=config.FPN_CLASSIF_FC_LAYERS_SIZE)
  
              mrcnn_mask = build_fpn_mask_graph(rois, mrcnn_feature_maps,
                                                input_image_meta,
                                                config.MASK_POOL_SIZE,
                                                config.NUM_CLASSES,
                                                train_bn=config.TRAIN_BN)
  
              # TODO: clean up (use tf.identify if necessary)
              output_rois = KL.Lambda(lambda x: x * 1, name="output_rois")(rois)
  
              # Losses
              rpn_class_loss = KL.Lambda(lambda x: rpn_class_loss_graph(*x), name="rpn_class_loss")(
                  [input_rpn_match, rpn_class_logits])
              rpn_bbox_loss = KL.Lambda(lambda x: rpn_bbox_loss_graph(config, *x), name="rpn_bbox_loss")(
                  [input_rpn_bbox, input_rpn_match, rpn_bbox])
              class_loss = KL.Lambda(lambda x: mrcnn_class_loss_graph(*x), name="mrcnn_class_loss")(
                  [target_class_ids, mrcnn_class_logits, active_class_ids])
              bbox_loss = KL.Lambda(lambda x: mrcnn_bbox_loss_graph(*x), name="mrcnn_bbox_loss")(
                  [target_bbox, target_class_ids, mrcnn_bbox])
              mask_loss = KL.Lambda(lambda x: mrcnn_mask_loss_graph(*x), name="mrcnn_mask_loss")(
                  [target_mask, target_class_ids, mrcnn_mask])
  
              # Model
              inputs = [input_image, input_image_meta,
                        input_rpn_match, input_rpn_bbox, input_gt_class_ids, input_gt_boxes, input_gt_masks]
              if not config.USE_RPN_ROIS:
                  inputs.append(input_rois)
              outputs = [rpn_class_logits, rpn_class, rpn_bbox,
                         mrcnn_class_logits, mrcnn_class, mrcnn_bbox, mrcnn_mask,
                         rpn_rois, output_rois,
                         rpn_class_loss, rpn_bbox_loss, class_loss, bbox_loss, mask_loss]
              model = KM.Model(inputs, outputs, name='mask_rcnn')
          else:
              # Network Heads
              # Proposal classifier and BBox regressor heads
              mrcnn_class_logits, mrcnn_class, mrcnn_bbox =\
                  fpn_classifier_graph(rpn_rois, mrcnn_feature_maps, input_image_meta,
                                       config.POOL_SIZE, config.NUM_CLASSES,
                                       train_bn=config.TRAIN_BN,
                                       fc_layers_size=config.FPN_CLASSIF_FC_LAYERS_SIZE)
  
              # Detections
              # output is [batch, num_detections, (y1, x1, y2, x2, class_id, score)] in
              # normalized coordinates
              detections = DetectionLayer(config, name="mrcnn_detection")(
                  [rpn_rois, mrcnn_class, mrcnn_bbox, input_image_meta])
  
              # Create masks for detections
              detection_boxes = KL.Lambda(lambda x: x[..., :4])(detections)
              mrcnn_mask = build_fpn_mask_graph(detection_boxes, mrcnn_feature_maps,
                                                input_image_meta,
                                                config.MASK_POOL_SIZE,
                                                config.NUM_CLASSES,
                                                train_bn=config.TRAIN_BN)
  
              model = KM.Model([input_image, input_image_meta, input_anchors],
                               [detections, mrcnn_class, mrcnn_bbox,
                                   mrcnn_mask, rpn_rois, rpn_class, rpn_bbox],
                               name='mask_rcnn')
  
          # Add multi-GPU support.
          if config.GPU_COUNT > 1:
              from mrcnn.parallel_model import ParallelModel
              model = ParallelModel(model, config.GPU_COUNT)
  
          return model
  
      def find_last(self):
          """Finds the last checkpoint file of the last trained model in the
          model directory.
          Returns:
              The path of the last checkpoint file
          """
          # Get directory names. Each directory corresponds to a model
          dir_names = next(os.walk(self.model_dir))[1]
          key = self.config.NAME.lower()
          dir_names = filter(lambda f: f.startswith(key), dir_names)
          dir_names = sorted(dir_names)
          if not dir_names:
              import errno
              raise FileNotFoundError(
                  errno.ENOENT,
                  "Could not find model directory under {}".format(self.model_dir))
          # Pick last directory
          dir_name = os.path.join(self.model_dir, dir_names[-1])
          # Find the last checkpoint
          checkpoints = next(os.walk(dir_name))[2]
          checkpoints = filter(lambda f: f.startswith("mask_rcnn"), checkpoints)
          checkpoints = sorted(checkpoints)
          if not checkpoints:
              import errno
              raise FileNotFoundError(
                  errno.ENOENT, "Could not find weight files in {}".format(dir_name))
          checkpoint = os.path.join(dir_name, checkpoints[-1])
          return checkpoint
  
      def load_weights(self, filepath, by_name=False, exclude=None):
          """Modified version of the corresponding Keras function with
          the addition of multi-GPU support and the ability to exclude
          some layers from loading.
          exclude: list of layer names to exclude
          """
          import h5py
          from tensorflow.python.keras.saving import hdf5_format
  
          if exclude:
              by_name = True
  
          if h5py is None:
              raise ImportError('`load_weights` requires h5py.')
          with h5py.File(filepath, mode='r') as f:
              if 'layer_names' not in f.attrs and 'model_weights' in f:
                  f = f['model_weights']
  
              # In multi-GPU training, we wrap the model. Get layers
              # of the inner model because they have the weights.
              keras_model = self.keras_model
              layers = keras_model.inner_model.layers if hasattr(keras_model, "inner_model")\
                  else keras_model.layers
  
              # Exclude some layers
              if exclude:
                  layers = filter(lambda l: l.name not in exclude, layers)
  
              if by_name:
                  hdf5_format.load_weights_from_hdf5_group_by_name(f, layers)
              else:
                  hdf5_format.load_weights_from_hdf5_group(f, layers)
  
          # Update the log directory
          self.set_log_dir(filepath)
  
      def get_imagenet_weights(self):
          """Downloads ImageNet trained weights from Keras.
          Returns path to weights file.
          """
          from keras.utils.data_utils import get_file
          TF_WEIGHTS_PATH_NO_TOP = 'https://github.com/fchollet/deep-learning-models/'\
                                   'releases/download/v0.2/'\
                                   'resnet50_weights_tf_dim_ordering_tf_kernels_notop.h5'
          weights_path = get_file('resnet50_weights_tf_dim_ordering_tf_kernels_notop.h5',
                                  TF_WEIGHTS_PATH_NO_TOP,
                                  cache_subdir='models',
                                  md5_hash='a268eb855778b3df3c7506639542a6af')
          return weights_path
  
      def compile(self, learning_rate, momentum):
          """Gets the model ready for training. Adds losses, regularization, and
          metrics. Then calls the Keras compile() function.
          """
          # Optimizer object
          optimizer = keras.optimizers.SGD(
              lr=learning_rate, momentum=momentum,
              clipnorm=self.config.GRADIENT_CLIP_NORM)
          # Add Losses
          # First, clear previously set losses to avoid duplication
          self.keras_model._losses = []
          self.keras_model._per_input_losses = {}
          loss_names = [
              "rpn_class_loss",  "rpn_bbox_loss",
              "mrcnn_class_loss", "mrcnn_bbox_loss", "mrcnn_mask_loss"]
          for name in loss_names:
              layer = self.keras_model.get_layer(name)
              if layer.output in self.keras_model.losses:
                  continue
              loss = (
                  tf.reduce_mean(layer.output, keepdims=True)
                  * self.config.LOSS_WEIGHTS.get(name, 1.))
              self.keras_model.add_loss(loss)
  
          # Add L2 Regularization
          # Skip gamma and beta weights of batch normalization layers.
          reg_losses = [
              keras.regularizers.l2(self.config.WEIGHT_DECAY)(w) / tf.cast(tf.size(w), tf.float32)
              for w in self.keras_model.trainable_weights
              if 'gamma' not in w.name and 'beta' not in w.name]
          self.keras_model.add_loss(tf.add_n(reg_losses))
  
          # Compile
          self.keras_model.compile(
              optimizer=optimizer,
              loss=[None] * len(self.keras_model.outputs))
  
          # Add metrics for losses
          for name in loss_names:
              if name in self.keras_model.metrics_names:
                  continue
              layer = self.keras_model.get_layer(name)
              self.keras_model.metrics_names.append(name)
              loss = (
                  tf.reduce_mean(layer.output, keepdims=True)
                  * self.config.LOSS_WEIGHTS.get(name, 1.))
              self.keras_model.add_metric(loss, name, aggregation='mean')
  
      def set_trainable(self, layer_regex, keras_model=None, indent=0, verbose=1):
          """Sets model layers as trainable if their names match
          the given regular expression.
          """
          # Print message on the first call (but not on recursive calls)
          if verbose > 0 and keras_model is None:
              log("Selecting layers to train")
  
          keras_model = keras_model or self.keras_model
  
          # In multi-GPU training, we wrap the model. Get layers
          # of the inner model because they have the weights.
          layers = keras_model.inner_model.layers if hasattr(keras_model, "inner_model")\
              else keras_model.layers
  
          for layer in layers:
              # Is the layer a model?
              if layer.__class__.__name__ == 'Model':
                  print("In model: ", layer.name)
                  self.set_trainable(
                      layer_regex, keras_model=layer, indent=indent + 4)
                  continue
  
              if not layer.weights:
                  continue
              # Is it trainable?
              trainable = bool(re.fullmatch(layer_regex, layer.name))
              # Update layer. If layer is a container, update inner layer.
              if layer.__class__.__name__ == 'TimeDistributed':
                  layer.layer.trainable = trainable
              else:
                  layer.trainable = trainable
              # Print trainable layer names
              if trainable and verbose > 0:
                  log("{}{:20}   ({})".format(" " * indent, layer.name,
                                              layer.__class__.__name__))
  
      def set_log_dir(self, model_path=None):
          """Sets the model log directory and epoch counter.
  
          model_path: If None, or a format different from what this code uses
              then set a new log directory and start epochs from 0. Otherwise,
              extract the log directory and the epoch counter from the file
              name.
          """
          # Set date and epoch counter as if starting a new model
          self.epoch = 0
          now = datetime.datetime.now()
  
          # If we have a model path with date and epochs use them
          if model_path:
              # Continue from we left of. Get epoch and date from the file name
              # A sample model path might look like:
              # \path\to\logs\coco20171029T2315\mask_rcnn_coco_0001.h5 (Windows)
              # /path/to/logs/coco20171029T2315/mask_rcnn_coco_0001.h5 (Linux)
              regex = r".*[/\\][\w-]+(\d{4})(\d{2})(\d{2})T(\d{2})(\d{2})[/\\]mask\_rcnn\_[\w-]+(\d{4})\.h5"
              # Use string for regex since we might want to use pathlib.Path as model_path
              m = re.match(regex, str(model_path))
              if m:
                  now = datetime.datetime(int(m.group(1)), int(m.group(2)), int(m.group(3)),
                                          int(m.group(4)), int(m.group(5)))
                  # Epoch number in file is 1-based, and in Keras code it's 0-based.
                  # So, adjust for that then increment by one to start from the next epoch
                  self.epoch = int(m.group(6)) - 1 + 1
                  print('Re-starting from epoch %d' % self.epoch)
  
          # Directory for training logs
          self.log_dir = os.path.join(self.model_dir, "{}{:%Y%m%dT%H%M}".format(
              self.config.NAME.lower(), now))
  
          # Path to save after each epoch. Include placeholders that get filled by Keras.
          self.checkpoint_path = os.path.join(self.log_dir, "mask_rcnn_{}_*epoch*.h5".format(
              self.config.NAME.lower()))
          self.checkpoint_path = self.checkpoint_path.replace(
              "*epoch*", "{epoch:04d}")
  
      def train(self, train_dataset, val_dataset, learning_rate, epochs, layers,
                augmentation=None, custom_callbacks=None):
          """Train the model.
          train_dataset, val_dataset: Training and validation Dataset objects.
          learning_rate: The learning rate to train with
          epochs: Number of training epochs. Note that previous training epochs
                  are considered to be done alreay, so this actually determines
                  the epochs to train in total rather than in this particaular
                  call.
          layers: Allows selecting wich layers to train. It can be:
              - A regular expression to match layer names to train
              - One of these predefined values:
                heads: The RPN, classifier and mask heads of the network
                all: All the layers
                3+: Train Resnet stage 3 and up
                4+: Train Resnet stage 4 and up
                5+: Train Resnet stage 5 and up
          augmentation: Optional. An imgaug (https://github.com/aleju/imgaug)
              augmentation. For example, passing imgaug.augmenters.Fliplr(0.5)
              flips images right/left 50% of the time. You can pass complex
              augmentations as well. This augmentation applies 50% of the
              time, and when it does it flips images right/left half the time
              and adds a Gaussian blur with a random sigma in range 0 to 5.
                  augmentation = imgaug.augmenters.Sometimes(0.5, [
                      imgaug.augmenters.Fliplr(0.5),
                      imgaug.augmenters.GaussianBlur(sigma=(0.0, 5.0))
                  ])
          custom_callbacks: Optional. Add custom callbacks to be called
              with the keras fit_generator method. Must be list of type keras.callbacks.
          """
          assert self.mode == "training", "Create model in training mode."
  
          # Pre-defined layer regular expressions
          layer_regex = {
              # all layers but the backbone
              "heads": r"(mrcnn\_.*)|(rpn\_.*)|(fpn\_.*)",
              # From a specific Resnet stage and up
              "3+": r"(res3.*)|(bn3.*)|(res4.*)|(bn4.*)|(res5.*)|(bn5.*)|(mrcnn\_.*)|(rpn\_.*)|(fpn\_.*)",
              "4+": r"(res4.*)|(bn4.*)|(res5.*)|(bn5.*)|(mrcnn\_.*)|(rpn\_.*)|(fpn\_.*)",
              "5+": r"(res5.*)|(bn5.*)|(mrcnn\_.*)|(rpn\_.*)|(fpn\_.*)",
              # All layers
              "all": ".*",
          }
          if layers in layer_regex.keys():
              layers = layer_regex[layers]
  
          # Data generators
          train_generator = DataGenerator(train_dataset, self.config, shuffle=True,
                                          augmentation=augmentation,
                                          batch_size=self.config.BATCH_SIZE)
          val_generator = DataGenerator(val_dataset, self.config, shuffle=True,
                                        batch_size=self.config.BATCH_SIZE)
  
          # Create log_dir if it does not exist
          if not os.path.exists(self.log_dir):
              os.makedirs(self.log_dir)
  
          # Callbacks
          callbacks = [
              keras.callbacks.TensorBoard(log_dir=self.log_dir,
                                          histogram_freq=0, write_graph=True, write_images=False),
              keras.callbacks.ModelCheckpoint(self.checkpoint_path,
                                              verbose=0, save_weights_only=True),
          ]
  
          # Add custom callbacks to the list
          if custom_callbacks:
              callbacks += custom_callbacks
  
          # Train
          log("\nStarting at epoch {}. LR={}\n".format(self.epoch, learning_rate))
          log("Checkpoint Path: {}".format(self.checkpoint_path))
          self.set_trainable(layers)
          self.compile(learning_rate, self.config.LEARNING_MOMENTUM)
  
          # Work-around for Windows: Keras fails on Windows when using
          # multiprocessing workers. See discussion here:
          # https://github.com/matterport/Mask_RCNN/issues/13#issuecomment-353124009
          if os.name == 'nt':
              workers = 0
          else:
              workers = multiprocessing.cpu_count()
  
          self.keras_model.fit(
              train_generator,
              initial_epoch=self.epoch,
              epochs=epochs,
              steps_per_epoch=self.config.STEPS_PER_EPOCH,
              callbacks=callbacks,
              validation_data=val_generator,
              validation_steps=self.config.VALIDATION_STEPS,
              max_queue_size=100,
              workers=workers,
              use_multiprocessing=(1 < workers),
          )
          self.epoch = max(self.epoch, epochs)
  
      def mold_inputs(self, images):
          """Takes a list of images and modifies them to the format expected
          as an input to the neural network.
          images: List of image matrices [height,width,depth]. Images can have
              different sizes.
  
          Returns 3 Numpy matrices:
          molded_images: [N, h, w, 3]. Images resized and normalized.
          image_metas: [N, length of meta data]. Details about each image.
          windows: [N, (y1, x1, y2, x2)]. The portion of the image that has the
              original image (padding excluded).
          """
          molded_images = []
          image_metas = []
          windows = []
          for image in images:
              # Resize image
              # TODO: move resizing to mold_image()
              molded_image, window, scale, padding, crop = utils.resize_image(
                  image,
                  min_dim=self.config.IMAGE_MIN_DIM,
                  min_scale=self.config.IMAGE_MIN_SCALE,
                  max_dim=self.config.IMAGE_MAX_DIM,
                  mode=self.config.IMAGE_RESIZE_MODE)
              molded_image = mold_image(molded_image, self.config)
              # Build image_meta
              image_meta = compose_image_meta(
                  0, image.shape, molded_image.shape, window, scale,
                  np.zeros([self.config.NUM_CLASSES], dtype=np.int32))
              # Append
              molded_images.append(molded_image)
              windows.append(window)
              image_metas.append(image_meta)
          # Pack into arrays
          molded_images = np.stack(molded_images)
          image_metas = np.stack(image_metas)
          windows = np.stack(windows)
          return molded_images, image_metas, windows
  
      def unmold_detections(self, detections, mrcnn_mask, original_image_shape,
                            image_shape, window):
          """Reformats the detections of one image from the format of the neural
          network output to a format suitable for use in the rest of the
          application.
  
          detections: [N, (y1, x1, y2, x2, class_id, score)] in normalized coordinates
          mrcnn_mask: [N, height, width, num_classes]
          original_image_shape: [H, W, C] Original image shape before resizing
          image_shape: [H, W, C] Shape of the image after resizing and padding
          window: [y1, x1, y2, x2] Pixel coordinates of box in the image where the real
                  image is excluding the padding.
  
          Returns:
          boxes: [N, (y1, x1, y2, x2)] Bounding boxes in pixels
          class_ids: [N] Integer class IDs for each bounding box
          scores: [N] Float probability scores of the class_id
          masks: [height, width, num_instances] Instance masks
          """
          # How many detections do we have?
          # Detections array is padded with zeros. Find the first class_id == 0.
          zero_ix = np.where(detections[:, 4] == 0)[0]
          N = zero_ix[0] if zero_ix.shape[0] > 0 else detections.shape[0]
  
          # Extract boxes, class_ids, scores, and class-specific masks
          boxes = detections[:N, :4]
          class_ids = detections[:N, 4].astype(np.int32)
          scores = detections[:N, 5]
          masks = mrcnn_mask[np.arange(N), :, :, class_ids]
  
          # Translate normalized coordinates in the resized image to pixel
          # coordinates in the original image before resizing
          window = utils.norm_boxes(window, image_shape[:2])
          wy1, wx1, wy2, wx2 = window
          shift = np.array([wy1, wx1, wy1, wx1])
          wh = wy2 - wy1  # window height
          ww = wx2 - wx1  # window width
          scale = np.array([wh, ww, wh, ww])
          # Convert boxes to normalized coordinates on the window
          boxes = np.divide(boxes - shift, scale)
          # Convert boxes to pixel coordinates on the original image
          boxes = utils.denorm_boxes(boxes, original_image_shape[:2])
  
          # Filter out detections with zero area. Happens in early training when
          # network weights are still random
          exclude_ix = np.where(
              (boxes[:, 2] - boxes[:, 0]) * (boxes[:, 3] - boxes[:, 1]) <= 0)[0]
          if exclude_ix.shape[0] > 0:
              boxes = np.delete(boxes, exclude_ix, axis=0)
              class_ids = np.delete(class_ids, exclude_ix, axis=0)
              scores = np.delete(scores, exclude_ix, axis=0)
              masks = np.delete(masks, exclude_ix, axis=0)
              N = class_ids.shape[0]
  
          # Resize masks to original image size and set boundary threshold.
          full_masks = []
          for i in range(N):
              # Convert neural network mask to full size mask
              full_mask = utils.unmold_mask(masks[i], boxes[i], original_image_shape)
              full_masks.append(full_mask)
          full_masks = np.stack(full_masks, axis=-1)\
              if full_masks else np.empty(original_image_shape[:2] + (0,))
  
          return boxes, class_ids, scores, full_masks
  
      def detect(self, images, verbose=0):
          """Runs the detection pipeline.
  
          images: List of images, potentially of different sizes.
  
          Returns a list of dicts, one dict per image. The dict contains:
          rois: [N, (y1, x1, y2, x2)] detection bounding boxes
          class_ids: [N] int class IDs
          scores: [N] float probability scores for the class IDs
          masks: [H, W, N] instance binary masks
          """
          assert self.mode == "inference", "Create model in inference mode."
          assert len(
              images) == self.config.BATCH_SIZE, "len(images) must be equal to BATCH_SIZE"
  
          if verbose:
              log("Processing {} images".format(len(images)))
              for image in images:
                  log("image", image)
  
          # Mold inputs to format expected by the neural network
          molded_images, image_metas, windows = self.mold_inputs(images)
  
          # Validate image sizes
          # All images in a batch MUST be of the same size
          image_shape = molded_images[0].shape
          for g in molded_images[1:]:
              assert g.shape == image_shape,\
                  "After resizing, all images must have the same size. Check IMAGE_RESIZE_MODE and image sizes."
  
          # Anchors
          anchors = self.get_anchors(image_shape)
          # Duplicate across the batch dimension because Keras requires it
          # TODO: can this be optimized to avoid duplicating the anchors?
          anchors = np.broadcast_to(anchors, (self.config.BATCH_SIZE,) + anchors.shape)
  
          if verbose:
              log("molded_images", molded_images)
              log("image_metas", image_metas)
              log("anchors", anchors)
          # Run object detection
          detections, _, _, mrcnn_mask, _, _, _ =\
              self.keras_model.predict([molded_images, image_metas, anchors], verbose=0)
          # Process detections
          results = []
          for i, image in enumerate(images):
              final_rois, final_class_ids, final_scores, final_masks =\
                  self.unmold_detections(detections[i], mrcnn_mask[i],
                                         image.shape, molded_images[i].shape,
                                         windows[i])
              results.append({
                  "rois": final_rois,
                  "class_ids": final_class_ids,
                  "scores": final_scores,
                  "masks": final_masks,
              })
          return results
  
      def detect_molded(self, molded_images, image_metas, verbose=0):
          """Runs the detection pipeline, but expect inputs that are
          molded already. Used mostly for debugging and inspecting
          the model.
  
          molded_images: List of images loaded using load_image_gt()
          image_metas: image meta data, also returned by load_image_gt()
  
          Returns a list of dicts, one dict per image. The dict contains:
          rois: [N, (y1, x1, y2, x2)] detection bounding boxes
          class_ids: [N] int class IDs
          scores: [N] float probability scores for the class IDs
          masks: [H, W, N] instance binary masks
          """
          assert self.mode == "inference", "Create model in inference mode."
          assert len(molded_images) == self.config.BATCH_SIZE,\
              "Number of images must be equal to BATCH_SIZE"
  
          if verbose:
              log("Processing {} images".format(len(molded_images)))
              for image in molded_images:
                  log("image", image)
  
          # Validate image sizes
          # All images in a batch MUST be of the same size
          image_shape = molded_images[0].shape
          for g in molded_images[1:]:
              assert g.shape == image_shape, "Images must have the same size"
  
          # Anchors
          anchors = self.get_anchors(image_shape)
          # Duplicate across the batch dimension because Keras requires it
          # TODO: can this be optimized to avoid duplicating the anchors?
          anchors = np.broadcast_to(anchors, (self.config.BATCH_SIZE,) + anchors.shape)
  
          if verbose:
              log("molded_images", molded_images)
              log("image_metas", image_metas)
              log("anchors", anchors)
          # Run object detection
          detections, _, _, mrcnn_mask, _, _, _ =\
              self.keras_model.predict([molded_images, image_metas, anchors], verbose=0)
          # Process detections
          results = []
          for i, image in enumerate(molded_images):
              window = [0, 0, image.shape[0], image.shape[1]]
              final_rois, final_class_ids, final_scores, final_masks =\
                  self.unmold_detections(detections[i], mrcnn_mask[i],
                                         image.shape, molded_images[i].shape,
                                         window)
              results.append({
                  "rois": final_rois,
                  "class_ids": final_class_ids,
                  "scores": final_scores,
                  "masks": final_masks,
              })
          return results
  
      def get_anchors(self, image_shape):
          """Returns anchor pyramid for the given image size."""
          backbone_shapes = compute_backbone_shapes(self.config, image_shape)
          # Cache anchors and reuse if image shape is the same
          if not hasattr(self, "_anchor_cache"):
              self._anchor_cache = {}
          if not tuple(image_shape) in self._anchor_cache:
              # Generate Anchors
              a = utils.generate_pyramid_anchors(
                  self.config.RPN_ANCHOR_SCALES,
                  self.config.RPN_ANCHOR_RATIOS,
                  backbone_shapes,
                  self.config.BACKBONE_STRIDES,
                  self.config.RPN_ANCHOR_STRIDE)
              # Keep a copy of the latest anchors in pixel coordinates because
              # it's used in inspect_model notebooks.
              # TODO: Remove this after the notebook are refactored to not use it
              self.anchors = a
              # Normalize coordinates
              self._anchor_cache[tuple(image_shape)] = utils.norm_boxes(a, image_shape[:2])
          return self._anchor_cache[tuple(image_shape)]
  
      def ancestor(self, tensor, name, checked=None):
          """Finds the ancestor of a TF tensor in the computation graph.
          tensor: TensorFlow symbolic tensor.
          name: Name of ancestor tensor to find
          checked: For internal use. A list of tensors that were already
                   searched to avoid loops in traversing the graph.
          """
          checked = checked if checked is not None else []
          # Put a limit on how deep we go to avoid very long loops
          if len(checked) > 500:
              return None
          # Convert name to a regex and allow matching a number prefix
          # because Keras adds them automatically
          if isinstance(name, str):
              name = re.compile(name.replace("/", r"(\_\d+)*/"))
  
          parents = tensor.op.inputs
          for p in parents:
              if p in checked:
                  continue
              if bool(re.fullmatch(name, p.name)):
                  return p
              checked.append(p)
              a = self.ancestor(p, name, checked)
              if a is not None:
                  return a
          return None
  
      def find_trainable_layer(self, layer):
          """If a layer is encapsulated by another layer, this function
          digs through the encapsulation and returns the layer that holds
          the weights.
          """
          if layer.__class__.__name__ == 'TimeDistributed':
              return self.find_trainable_layer(layer.layer)
          return layer
  
      def get_trainable_layers(self):
          """Returns a list of layers that have weights."""
          layers = []
          # Loop through all layers
          for l in self.keras_model.layers:
              # If layer is a wrapper, find inner trainable layer
              l = self.find_trainable_layer(l)
              # Include layer if it has weights
              if l.get_weights():
                  layers.append(l)
          return layers
  
      def run_graph(self, images, outputs, image_metas=None):
          """Runs a sub-set of the computation graph that computes the given
          outputs.
  
          image_metas: If provided, the images are assumed to be already
              molded (i.e. resized, padded, and normalized)
  
          outputs: List of tuples (name, tensor) to compute. The tensors are
              symbolic TensorFlow tensors and the names are for easy tracking.
  
          Returns an ordered dict of results. Keys are the names received in the
          input and values are Numpy arrays.
          """
          model = self.keras_model
  
          # Organize desired outputs into an ordered dict
          outputs = OrderedDict(outputs)
          for o in outputs.values():
              assert o is not None
  
          # Build a Keras function to run parts of the computation graph
          inputs = model.inputs
          if model.uses_learning_phase and not isinstance(K.learning_phase(), int):
              inputs += [K.learning_phase()]
          kf = K.function(model.inputs, list(outputs.values()))
  
          # Prepare inputs
          if image_metas is None:
              molded_images, image_metas, _ = self.mold_inputs(images)
          else:
              molded_images = images
          image_shape = molded_images[0].shape
          # Anchors
          anchors = self.get_anchors(image_shape)
          # Duplicate across the batch dimension because Keras requires it
          # TODO: can this be optimized to avoid duplicating the anchors?
          anchors = np.broadcast_to(anchors, (self.config.BATCH_SIZE,) + anchors.shape)
          model_in = [molded_images, image_metas, anchors]
  
          # Run inference
          if model.uses_learning_phase and not isinstance(K.learning_phase(), int):
              model_in.append(0.)
          outputs_np = kf(model_in)
  
          # Pack the generated Numpy arrays into a a dict and log the results.
          outputs_np = OrderedDict([(k, v)
                                    for k, v in zip(outputs.keys(), outputs_np)])
          for k, v in outputs_np.items():
              log(k, v)
          return outputs_np
  
  
  ############################################################
  #  Data Formatting
  ############################################################
  
  def compose_image_meta(image_id, original_image_shape, image_shape,
                         window, scale, active_class_ids):
      """Takes attributes of an image and puts them in one 1D array.
  
      image_id: An int ID of the image. Useful for debugging.
      original_image_shape: [H, W, C] before resizing or padding.
      image_shape: [H, W, C] after resizing and padding
      window: (y1, x1, y2, x2) in pixels. The area of the image where the real
              image is (excluding the padding)
      scale: The scaling factor applied to the original image (float32)
      active_class_ids: List of class_ids available in the dataset from which
          the image came. Useful if training on images from multiple datasets
          where not all classes are present in all datasets.
      """
      meta = np.array(
          [image_id] +                  # size=1
          list(original_image_shape) +  # size=3
          list(image_shape) +           # size=3
          list(window) +                # size=4 (y1, x1, y2, x2) in image cooredinates
          [scale] +                     # size=1
          list(active_class_ids)        # size=num_classes
      )
      return meta
  
  
  def parse_image_meta(meta):
      """Parses an array that contains image attributes to its components.
      See compose_image_meta() for more details.
  
      meta: [batch, meta length] where meta length depends on NUM_CLASSES
  
      Returns a dict of the parsed values.
      """
      image_id = meta[:, 0]
      original_image_shape = meta[:, 1:4]
      image_shape = meta[:, 4:7]
      window = meta[:, 7:11]  # (y1, x1, y2, x2) window of image in in pixels
      scale = meta[:, 11]
      active_class_ids = meta[:, 12:]
      return {
          "image_id": image_id.astype(np.int32),
          "original_image_shape": original_image_shape.astype(np.int32),
          "image_shape": image_shape.astype(np.int32),
          "window": window.astype(np.int32),
          "scale": scale.astype(np.float32),
          "active_class_ids": active_class_ids.astype(np.int32),
      }
  
  
  def parse_image_meta_graph(meta):
      """Parses a tensor that contains image attributes to its components.
      See compose_image_meta() for more details.
  
      meta: [batch, meta length] where meta length depends on NUM_CLASSES
  
      Returns a dict of the parsed tensors.
      """
      image_id = meta[:, 0]
      original_image_shape = meta[:, 1:4]
      image_shape = meta[:, 4:7]
      window = meta[:, 7:11]  # (y1, x1, y2, x2) window of image in in pixels
      scale = meta[:, 11]
      active_class_ids = meta[:, 12:]
      return {
          "image_id": image_id,
          "original_image_shape": original_image_shape,
          "image_shape": image_shape,
          "window": window,
          "scale": scale,
          "active_class_ids": active_class_ids,
      }
  
  
  def mold_image(images, config):
      """Expects an RGB image (or array of images) and subtracts
      the mean pixel and converts it to float. Expects image
      colors in RGB order.
      """
      return images.astype(np.float32) - config.MEAN_PIXEL
  
  
  def unmold_image(normalized_images, config):
      """Takes a image normalized with mold() and returns the original."""
      return (normalized_images + config.MEAN_PIXEL).astype(np.uint8)
  
  
  ############################################################
  #  Miscellenous Graph Functions
  ############################################################
  
  def trim_zeros_graph(boxes, name='trim_zeros'):
      """Often boxes are represented with matrices of shape [N, 4] and
      are padded with zeros. This removes zero boxes.
  
      boxes: [N, 4] matrix of boxes.
      non_zeros: [N] a 1D boolean mask identifying the rows to keep
      """
      non_zeros = tf.cast(tf.reduce_sum(tf.abs(boxes), axis=1), tf.bool)
      boxes = tf.boolean_mask(boxes, non_zeros, name=name)
      return boxes, non_zeros
  
  
  def batch_pack_graph(x, counts, num_rows):
      """Picks different number of values from each row
      in x depending on the values in counts.
      """
      outputs = []
      for i in range(num_rows):
          outputs.append(x[i, :counts[i]])
      return tf.concat(outputs, axis=0)
  
  
  def norm_boxes_graph(boxes, shape):
      """Converts boxes from pixel coordinates to normalized coordinates.
      boxes: [..., (y1, x1, y2, x2)] in pixel coordinates
      shape: [..., (height, width)] in pixels
  
      Note: In pixel coordinates (y2, x2) is outside the box. But in normalized
      coordinates it's inside the box.
  
      Returns:
          [..., (y1, x1, y2, x2)] in normalized coordinates
      """
      h, w = tf.split(tf.cast(shape, tf.float32), 2)
      scale = tf.concat([h, w, h, w], axis=-1) - tf.constant(1.0)
      shift = tf.constant([0., 0., 1., 1.])
      return tf.divide(boxes - shift, scale)
  
  
  def denorm_boxes_graph(boxes, shape):
      """Converts boxes from normalized coordinates to pixel coordinates.
      boxes: [..., (y1, x1, y2, x2)] in normalized coordinates
      shape: [..., (height, width)] in pixels
  
      Note: In pixel coordinates (y2, x2) is outside the box. But in normalized
      coordinates it's inside the box.
  
      Returns:
          [..., (y1, x1, y2, x2)] in pixel coordinates
      """
      h, w = tf.split(tf.cast(shape, tf.float32), 2)
      scale = tf.concat([h, w, h, w], axis=-1) - tf.constant(1.0)
      shift = tf.constant([0., 0., 1., 1.])
      return tf.cast(tf.round(tf.multiply(boxes, scale) + shift), tf.int32)
  
apis: numpy.ones tensorflow.gather_nd numpy.any tensorflow.logical_and tensorflow.keras.layers.Lambda tensorflow.keras.layers.ZeroPadding2D tensorflow.abs tensorflow.keras.layers.Conv2D tensorflow.identity numpy.stack tensorflow.python.keras.saving.hdf5_format.load_weights_from_hdf5_group tensorflow.math.log tensorflow.random.shuffle numpy.abs tensorflow.keras.backend.not_equal tensorflow.keras.backend.squeeze tensorflow.keras.layers.Conv2DTranspose tensorflow.keras.regularizers.l2 tensorflow.keras.backend.int_shape tensorflow.cast tensorflow.equal numpy.divide tensorflow.sqrt tensorflow.unique numpy.array tensorflow.keras.layers.Input tensorflow.round tensorflow.squeeze tensorflow.keras.backend.learning_phase tensorflow.Variable tensorflow.keras.backend.sparse_categorical_crossentropy tensorflow.keras.backend.less numpy.reshape tensorflow.keras.layers.Activation numpy.delete tensorflow.keras.layers.Dense tensorflow.constant tensorflow.shape tensorflow.keras.layers.MaxPooling2D numpy.argmax numpy.hstack tensorflow.boolean_mask tensorflow.keras.layers.UpSampling2D numpy.random.shuffle tensorflow.stop_gradient tensorflow.exp tensorflow.argmax tensorflow.keras.backend.equal numpy.concatenate tensorflow.gather numpy.random.randint tensorflow.keras.layers.Reshape tensorflow.maximum tensorflow.keras.callbacks.ModelCheckpoint tensorflow.keras.backend.reshape numpy.sum tensorflow.keras.layers.Concatenate numpy.copy numpy.log tensorflow.nn.sparse_softmax_cross_entropy_with_logits numpy.amax tensorflow.split tensorflow.minimum tensorflow.keras.callbacks.TensorBoard tensorflow.multiply tensorflow.transpose tensorflow.add_n numpy.zeros tensorflow.keras.backend.abs tensorflow.expand_dims tensorflow.keras.backend.binary_crossentropy numpy.arange tensorflow.keras.backend.shape numpy.sort tensorflow.control_dependencies tensorflow.size tensorflow.map_fn tensorflow.image.non_max_suppression tensorflow.reduce_max tensorflow.reshape tensorflow.nn.top_k tensorflow.python.keras.saving.hdf5_format.load_weights_from_hdf5_group_by_name tensorflow.keras.models.Model tensorflow.keras.layers.Add tensorflow.keras.optimizers.SGD tensorflow.concat tensorflow.reduce_sum tensorflow.divide tensorflow.keras.backend.mean numpy.random.choice numpy.expand_dims numpy.where tensorflow.stack tensorflow.sparse.to_dense numpy.max numpy.broadcast_to tensorflow.pad numpy.empty tensorflow.reduce_mean tensorflow.image.crop_and_resize tensorflow.where