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