# Copyright 2021 Huawei Technologies Co., Ltd
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# Licensed under the Apache License, Version 2.0 (the "License");
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# http://www.apache.org/licenses/LICENSE-2.0
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# ============================================================================
"""MeanSurfaceDistance."""
from __future__ import absolute_import
from scipy.ndimage import morphology
import numpy as np
from mindspore._checkparam import Validator as validator
from mindspore.nn.metrics.metric import Metric, rearrange_inputs
[docs]class MeanSurfaceDistance(Metric):
r"""
Computes the Average Surface Distance from `y_pred` to `y` under the default setting. It measures how much,
on average, the surface varies between the segmentation and the GT (ground truth).
Given two sets A and B, S(A) denotes the set of surface voxels of A, the shortest distance of an arbitrary voxel v
to S(A) is defined as:
.. math::
{\text{dis}}\left (v, S(A)\right ) = \underset{s_{A} \in S(A)}{\text{min }}\rVert v - s_{A} \rVert
The Average Surface Distance from set(B) to set(A) is given by:
.. math::
AvgSurDis(B \rightarrow A) = \frac{\sum_{s_{B} \in S(B)}^{} {\text{dis} \left
( s_{B}, S(A) \right )} } {\left | S(B) \right |}
Where the \|\|\*\|\| denotes a distance measure. \|\*\| denotes the number of elements.
The mean of surface distance from set(B) to set(A) and from set(A) to set(B) is:
.. math::
MeanSurDis(A \leftrightarrow B) = \frac{\sum_{s_{A} \in S(A)}^{} {\text{dis} \left ( s_{A}, S(B) \right )}
+ \sum_{s_{B} \in S(B)}^{} {\text{dis} \left ( s_{B}, S(A) \right )} }{\left | S(A) \right | +
\left | S(B) \right |}
Args:
distance_metric (string): Three measurement methods are supported: "euclidean", "chessboard" or "taxicab".
Default: "euclidean".
symmetric (bool): Whether to calculate the Mean Surface Distance between y_pred and y.
If False, it only calculates :math:`AvgSurDis({y\_pred} \rightarrow y)`,
otherwise, the mean of distance from `y_pred` to `y` and from `y` to `y_pred`, i.e.
:math:`MeanSurDis(y_{pred} \leftrightarrow y)`, will be returned. Default: False.
Supported Platforms:
``Ascend`` ``GPU`` ``CPU``
Examples:
>>> import numpy as np
>>> from mindspore import nn, Tensor
>>> x = Tensor(np.array([[3, 0, 1], [1, 3, 0], [1, 0, 2]]))
>>> y = Tensor(np.array([[0, 2, 1], [1, 2, 1], [0, 0, 1]]))
>>> metric = nn.MeanSurfaceDistance(symmetric=False, distance_metric="euclidean")
>>> metric.clear()
>>> metric.update(x, y, 0)
>>> mean_average_distance = metric.eval()
>>> print(mean_average_distance)
0.8047378541243649
"""
def __init__(self, symmetric=False, distance_metric="euclidean"):
super(MeanSurfaceDistance, self).__init__()
self.distance_metric_list = ["euclidean", "chessboard", "taxicab"]
distance_metric = validator.check_value_type("distance_metric", distance_metric, [str])
self.distance_metric = validator.check_string(distance_metric, self.distance_metric_list, "distance_metric")
self.symmetric = validator.check_value_type("symmetric", symmetric, [bool])
self.clear()
self._is_update = None
self._y_edges = None
self._y_pred_edges = None
[docs] def clear(self):
"""Clears the internal evaluation result."""
self._y_pred_edges = 0
self._y_edges = 0
self._is_update = False
def _get_surface_distance(self, y_pred_edges, y_edges):
"""
Calculate the surface distances from `y_pred_edges` to `y_edges`.
Args:
y_pred_edges (np.ndarray): the edge of the predictions.
y_edges (np.ndarray): the edge of the ground truth.
"""
if not np.any(y_pred_edges):
return np.array([])
if np.any(y_edges):
if self.distance_metric == "euclidean":
dis = morphology.distance_transform_edt(~y_edges)
elif self.distance_metric in self.distance_metric_list[-2:]:
dis = morphology.distance_transform_cdt(~y_edges, metric=self.distance_metric)
else:
dis = np.full(y_edges.shape, np.inf)
return dis[y_pred_edges]
[docs] @rearrange_inputs
def update(self, *inputs):
"""
Updates the internal evaluation result 'y_pred', 'y' and 'label_idx'.
Args:
inputs: Input 'y_pred', 'y' and 'label_idx'. 'y_pred' and 'y' are a Tensor, list or numpy.ndarray.
'y_pred' is the predicted binary image. 'y' is the actual binary image. 'label_idx', the data
type of `label_idx` is int.
Raises:
ValueError: If the number of the inputs is not 3.
TypeError: If the data type of label_idx is not int or float.
ValueError: If the value of label_idx is not in y_pred or y.
ValueError: If y_pred and y have different shapes.
"""
if len(inputs) != 3:
raise ValueError("For 'MeanSurfaceDistance.update', it needs 3 inputs (predicted value, true value, "
"label index), but got {}".format(len(inputs)))
y_pred = self._convert_data(inputs[0])
y = self._convert_data(inputs[1])
label_idx = inputs[2]
if not isinstance(label_idx, (int, float)):
raise ValueError(f"For 'MeanSurfaceDistance.update', the label index (input[2]) must be int or float, "
f"but got {type(label_idx)}.")
if label_idx not in y_pred and label_idx not in y:
raise ValueError("For 'MeanSurfaceDistance.update', the label index (input[2]) must be in predicted "
"value (input[0]) or true value (input[1]), but {} is not.".format(label_idx))
if y_pred.size == 0 or y_pred.shape != y.shape:
raise ValueError(f"For 'MeanSurfaceDistance.update', the size of predicted value (input[0]) and true "
f"value (input[1]) must be greater than 0, in addition to that, predicted value and "
f"true value must have the same shape, but got predicted value size: {y_pred.size}, "
f"shape: {y_pred.shape}, true value size: {y.size}, shape: {y.shape}.")
if y_pred.dtype != bool:
y_pred = y_pred == label_idx
if y.dtype != bool:
y = y == label_idx
self._y_pred_edges = morphology.binary_erosion(y_pred) ^ y_pred
self._y_edges = morphology.binary_erosion(y) ^ y
self._is_update = True
[docs] def eval(self):
"""
Calculate mean surface distance.
Returns:
numpy.float64. The mean surface distance value.
Raises:
RuntimeError: If the update method is not called first, an error will be reported.
"""
if self._is_update is False:
raise RuntimeError("Please call the 'update' method before calling 'eval' method.")
mean_surface_distance = self._get_surface_distance(self._y_pred_edges, self._y_edges)
if mean_surface_distance.shape == (0,):
return np.inf
avg_surface_distance = mean_surface_distance.mean()
if not self.symmetric:
return avg_surface_distance
contrary_mean_surface_distance = self._get_surface_distance(self._y_edges, self._y_pred_edges)
if contrary_mean_surface_distance.shape == (0,):
return np.inf
contrary_avg_surface_distance = contrary_mean_surface_distance.mean()
return np.mean((avg_surface_distance, contrary_avg_surface_distance))