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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 | |
| """ | |
| from __future__ import absolute_import | |
| from __future__ import division | |
| from __future__ import print_function | |
| 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 | |