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| """Operations for [N, height, width] numpy arrays representing masks.
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| Example mask operations that are supported:
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| * Areas: compute mask areas
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| * IOU: pairwise intersection-over-union scores
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| """
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| from __future__ import absolute_import
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| from __future__ import division
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| from __future__ import print_function
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| import numpy as np
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| EPSILON = 1e-7
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| def area(masks):
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| """Computes area of masks.
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| Args:
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| masks: Numpy array with shape [N, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| Returns:
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| a numpy array with shape [N*1] representing mask areas.
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| Raises:
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| ValueError: If masks.dtype is not np.uint8
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| """
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| if masks.dtype != np.uint8:
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| raise ValueError('Masks type should be np.uint8')
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| return np.sum(masks, axis=(1, 2), dtype=np.float32)
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| def intersection(masks1, masks2):
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| """Compute pairwise intersection areas between masks.
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| Args:
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| masks1: a numpy array with shape [N, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| masks2: a numpy array with shape [M, height, width] holding M masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| Returns:
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| a numpy array with shape [N*M] representing pairwise intersection area.
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| Raises:
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| ValueError: If masks1 and masks2 are not of type np.uint8.
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| """
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| if masks1.dtype != np.uint8 or masks2.dtype != np.uint8:
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| raise ValueError('masks1 and masks2 should be of type np.uint8')
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| n = masks1.shape[0]
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| m = masks2.shape[0]
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| answer = np.zeros([n, m], dtype=np.float32)
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| for i in np.arange(n):
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| for j in np.arange(m):
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| answer[i, j] = np.sum(np.minimum(masks1[i], masks2[j]), dtype=np.float32)
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| return answer
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| def iou(masks1, masks2):
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| """Computes pairwise intersection-over-union between mask collections.
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| Args:
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| masks1: a numpy array with shape [N, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| masks2: a numpy array with shape [M, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| Returns:
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| a numpy array with shape [N, M] representing pairwise iou scores.
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| Raises:
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| ValueError: If masks1 and masks2 are not of type np.uint8.
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| """
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| if masks1.dtype != np.uint8 or masks2.dtype != np.uint8:
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| raise ValueError('masks1 and masks2 should be of type np.uint8')
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| intersect = intersection(masks1, masks2)
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| area1 = area(masks1)
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| area2 = area(masks2)
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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 / np.maximum(union, EPSILON)
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| def ioa(masks1, masks2):
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| """Computes pairwise intersection-over-area between box collections.
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| Intersection-over-area (ioa) between two masks, mask1 and mask2 is defined as
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| their intersection area over mask2's area. Note that ioa is not symmetric,
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| that is, IOA(mask1, mask2) != IOA(mask2, mask1).
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| Args:
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| masks1: a numpy array with shape [N, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| masks2: a numpy array with shape [M, height, width] holding N masks. Masks
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| values are of type np.uint8 and values are in {0,1}.
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| Returns:
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| a numpy array with shape [N, M] representing pairwise ioa scores.
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| Raises:
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| ValueError: If masks1 and masks2 are not of type np.uint8.
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| """
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| if masks1.dtype != np.uint8 or masks2.dtype != np.uint8:
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| raise ValueError('masks1 and masks2 should be of type np.uint8')
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| intersect = intersection(masks1, masks2)
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| areas = np.expand_dims(area(masks2), axis=0)
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| return intersect / (areas + EPSILON)
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|
