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- # Copyright 2017 The TensorFlow Authors. All Rights Reserved.
- #
- # Licensed under the Apache License, Version 2.0 (the "License");
- # you may not use this file except in compliance with the License.
- # You may obtain a copy of the License at
- #
- # http://www.apache.org/licenses/LICENSE-2.0
- #
- # Unless required by applicable law or agreed to in writing, software
- # distributed under the License is distributed on an "AS IS" BASIS,
- # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- # See the License for the specific language governing permissions and
- # limitations under the License.
- # ==============================================================================
-
- """Operations for [N, 4] numpy arrays representing bounding boxes.
-
- Example box operations that are supported:
- * Areas: compute bounding box areas
- * IOU: pairwise intersection-over-union scores
- """
- import numpy as np
-
-
- def area(boxes):
- """Computes area of boxes.
-
- Args:
- boxes: Numpy array with shape [N, 4] holding N boxes
-
- Returns:
- a numpy array with shape [N*1] representing box areas
- """
- return (boxes[:, 2] - boxes[:, 0]) * (boxes[:, 3] - boxes[:, 1])
-
-
- def intersection(boxes1, boxes2):
- """Compute pairwise intersection areas between boxes.
-
- Args:
- boxes1: a numpy array with shape [N, 4] holding N boxes
- boxes2: a numpy array with shape [M, 4] holding M boxes
-
- Returns:
- a numpy array with shape [N*M] representing pairwise intersection area
- """
- [y_min1, x_min1, y_max1, x_max1] = np.split(boxes1, 4, axis=1)
- [y_min2, x_min2, y_max2, x_max2] = np.split(boxes2, 4, axis=1)
-
- all_pairs_min_ymax = np.minimum(y_max1, np.transpose(y_max2))
- all_pairs_max_ymin = np.maximum(y_min1, np.transpose(y_min2))
- intersect_heights = np.maximum(
- np.zeros(all_pairs_max_ymin.shape),
- all_pairs_min_ymax - all_pairs_max_ymin)
- all_pairs_min_xmax = np.minimum(x_max1, np.transpose(x_max2))
- all_pairs_max_xmin = np.maximum(x_min1, np.transpose(x_min2))
- intersect_widths = np.maximum(
- np.zeros(all_pairs_max_xmin.shape),
- all_pairs_min_xmax - all_pairs_max_xmin)
- return intersect_heights * intersect_widths
-
-
- def iou(boxes1, boxes2):
- """Computes pairwise intersection-over-union between box collections.
-
- Args:
- boxes1: a numpy array with shape [N, 4] holding N boxes.
- boxes2: a numpy array with shape [M, 4] holding N boxes.
-
- Returns:
- a numpy array with shape [N, M] representing pairwise iou scores.
- """
- intersect = intersection(boxes1, boxes2)
- area1 = area(boxes1)
- area2 = area(boxes2)
- union = np.expand_dims(area1, axis=1) + np.expand_dims(
- area2, axis=0) - intersect
- return intersect / union
-
-
- def ioa(boxes1, boxes2):
- """Computes pairwise intersection-over-area between box collections.
-
- Intersection-over-area (ioa) between two boxes box1 and box2 is defined as
- their intersection area over box2's area. Note that ioa is not symmetric,
- that is, IOA(box1, box2) != IOA(box2, box1).
-
- Args:
- boxes1: a numpy array with shape [N, 4] holding N boxes.
- boxes2: a numpy array with shape [M, 4] holding N boxes.
-
- Returns:
- a numpy array with shape [N, M] representing pairwise ioa scores.
- """
- intersect = intersection(boxes1, boxes2)
- areas = np.expand_dims(area(boxes2), axis=0)
- return intersect / areas
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