[Feature] huasdorff distance loss (#2820)

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## Motivation

Add Huasdorff distance loss

---------

Co-authored-by: xiexinch <[email protected]>

mmseg/models/losses/__init__.py

@@ -5,6 +5,7 @@
                                  cross_entropy, mask_cross_entropy)
 from .dice_loss import DiceLoss
 from .focal_loss import FocalLoss
+from .huasdorff_distance_loss import HuasdorffDisstanceLoss
 from .lovasz_loss import LovaszLoss
 from .ohem_cross_entropy_loss import OhemCrossEntropy
 from .tversky_loss import TverskyLoss
@@ -14,5 +15,6 @@
     'accuracy', 'Accuracy', 'cross_entropy', 'binary_cross_entropy',
     'mask_cross_entropy', 'CrossEntropyLoss', 'reduce_loss',
     'weight_reduce_loss', 'weighted_loss', 'LovaszLoss', 'DiceLoss',
-    'FocalLoss', 'TverskyLoss', 'OhemCrossEntropy', 'BoundaryLoss'
+    'FocalLoss', 'TverskyLoss', 'OhemCrossEntropy', 'BoundaryLoss',
+    'HuasdorffDisstanceLoss'
 ]

mmseg/models/losses/huasdorff_distance_loss.py

@@ -0,0 +1,160 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+"""Modified from https://github.com/JunMa11/SegWithDistMap/blob/
+master/code/train_LA_HD.py (Apache-2.0 License)"""
+import torch
+import torch.nn as nn
+import torch.nn.functional as F
+from scipy.ndimage import distance_transform_edt as distance
+from torch import Tensor
+
+from mmseg.registry import MODELS
+from .utils import get_class_weight, weighted_loss
+
+
+def compute_dtm(img_gt: Tensor, pred: Tensor) -> Tensor:
+    """
+    compute the distance transform map of foreground in mask
+    Args:
+        img_gt: Ground truth of the image, (b, h, w)
+        pred: Predictions of the segmentation head after softmax, (b, c, h, w)
+
+    Returns:
+        output: the foreground Distance Map (SDM)
+        dtm(x) = 0; x in segmentation boundary
+                inf|x-y|; x in segmentation
+    """
+
+    fg_dtm = torch.zeros_like(pred)
+    out_shape = pred.shape
+    for b in range(out_shape[0]):  # batch size
+        for c in range(1, out_shape[1]):  # default 0 channel is background
+            posmask = img_gt[b].byte()
+            if posmask.any():
+                posdis = distance(posmask)
+                fg_dtm[b][c] = torch.from_numpy(posdis)
+
+    return fg_dtm
+
+
+@weighted_loss
+def hd_loss(seg_soft: Tensor,
+            gt: Tensor,
+            seg_dtm: Tensor,
+            gt_dtm: Tensor,
+            class_weight=None,
+            ignore_index=255) -> Tensor:
+    """
+    compute huasdorff distance loss for segmentation
+    Args:
+        seg_soft: softmax results, shape=(b,c,x,y)
+        gt: ground truth, shape=(b,x,y)
+        seg_dtm: segmentation distance transform map, shape=(b,c,x,y)
+        gt_dtm: ground truth distance transform map, shape=(b,c,x,y)
+
+    Returns:
+        output: hd_loss
+    """
+    assert seg_soft.shape[0] == gt.shape[0]
+    total_loss = 0
+    num_class = seg_soft.shape[1]
+    if class_weight is not None:
+        assert class_weight.ndim == num_class
+    for i in range(1, num_class):
+        if i != ignore_index:
+            delta_s = (seg_soft[:, i, ...] - gt.float())**2
+            s_dtm = seg_dtm[:, i, ...]**2
+            g_dtm = gt_dtm[:, i, ...]**2
+            dtm = s_dtm + g_dtm
+            multiplied = torch.einsum('bxy, bxy->bxy', delta_s, dtm)
+            hd_loss = multiplied.mean()
+        if class_weight is not None:
+            hd_loss *= class_weight[i]
+        total_loss += hd_loss
+
+    return total_loss / num_class
+
+
+@MODELS.register_module()
+class HuasdorffDisstanceLoss(nn.Module):
+    """HuasdorffDisstanceLoss. This loss is proposed in `How Distance Transform
+    Maps Boost Segmentation CNNs: An Empirical Study.
+
+    <http://proceedings.mlr.press/v121/ma20b.html>`_.
+    Args:
+        reduction (str, optional): The method used to reduce the loss into
+            a scalar. Defaults to 'mean'.
+        class_weight (list[float] | str, optional): Weight of each class. If in
+            str format, read them from a file. Defaults to None.
+        loss_weight (float): Weight of the loss. Defaults to 1.0.
+        ignore_index (int | None): The label index to be ignored. Default: 255.
+        loss_name (str): Name of the loss item. If you want this loss
+            item to be included into the backward graph, `loss_` must be the
+            prefix of the name. Defaults to 'loss_boundary'.
+    """
+
+    def __init__(self,
+                 reduction='mean',
+                 class_weight=None,
+                 loss_weight=1.0,
+                 ignore_index=255,
+                 loss_name='loss_huasdorff_disstance',
+                 **kwargs):
+        super().__init__()
+        self.reduction = reduction
+        self.loss_weight = loss_weight
+        self.class_weight = get_class_weight(class_weight)
+        self._loss_name = loss_name
+        self.ignore_index = ignore_index
+
+    def forward(self,
+                pred: Tensor,
+                target: Tensor,
+                avg_factor=None,
+                reduction_override=None,
+                **kwargs) -> Tensor:
+        """Forward function.
+
+        Args:
+            pred (Tensor): Predictions of the segmentation head. (B, C, H, W)
+            target (Tensor): Ground truth of the image. (B, H, W)
+            avg_factor (int, optional): Average factor that is used to
+                average the loss. Defaults to None.
+            reduction_override (str, optional): The reduction method used
+                to override the original reduction method of the loss.
+                Options are "none", "mean" and "sum".
+        Returns:
+            Tensor: Loss tensor.
+        """
+        assert reduction_override in (None, 'none', 'mean', 'sum')
+        reduction = (
+            reduction_override if reduction_override else self.reduction)
+        if self.class_weight is not None:
+            class_weight = pred.new_tensor(self.class_weight)
+        else:
+            class_weight = None
+
+        pred_soft = F.softmax(pred, dim=1)
+        valid_mask = (target != self.ignore_index).long()
+        target = target * valid_mask
+
+        with torch.no_grad():
+            gt_dtm = compute_dtm(target.cpu(), pred_soft)
+            gt_dtm = gt_dtm.float()
+            seg_dtm2 = compute_dtm(
+                pred_soft.argmax(dim=1, keepdim=False).cpu(), pred_soft)
+            seg_dtm2 = seg_dtm2.float()
+
+        loss_hd = self.loss_weight * hd_loss(
+            pred_soft,
+            target,
+            seg_dtm=seg_dtm2,
+            gt_dtm=gt_dtm,
+            reduction=reduction,
+            avg_factor=avg_factor,
+            class_weight=class_weight,
+            ignore_index=self.ignore_index)
+        return loss_hd
+
+    @property
+    def loss_name(self):
+        return self._loss_name

tests/test_models/test_losses/test_huasdorff_distance_loss.py

@@ -0,0 +1,29 @@
+# Copyright (c) OpenMMLab. All rights reserved.
+import pytest
+import torch
+
+from mmseg.models.losses import HuasdorffDisstanceLoss
+
+
+def test_huasdorff_distance_loss():
+    loss_class = HuasdorffDisstanceLoss
+    pred = torch.rand((10, 8, 6, 6))
+    target = torch.rand((10, 6, 6))
+    class_weight = torch.rand(8)
+
+    # Test loss forward
+    loss = loss_class()(pred, target)
+    assert isinstance(loss, torch.Tensor)
+
+    # Test loss forward with avg_factor
+    loss = loss_class()(pred, target, avg_factor=10)
+    assert isinstance(loss, torch.Tensor)
+
+    # Test loss forward with avg_factor and reduction is None, 'sum' and 'mean'
+    for reduction in [None, 'sum', 'mean']:
+        loss = loss_class()(pred, target, avg_factor=10, reduction=reduction)
+        assert isinstance(loss, torch.Tensor)
+
+    # Test loss forward with class_weight
+    with pytest.raises(AssertionError):
+        loss_class(class_weight=class_weight)(pred, target)