6765 update GeneralizedDiceLoss (#6775)

Fixes #6765

### Description
as discussed in #6765, when `batch=True` the loss should still return 1
aggregated value instead of C channels.
#5466 is not actually
achievable with this formulation.

### Types of changes
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [x] Non-breaking change (fix or new feature that would not break
existing functionality).
- [ ] Breaking change (fix or new feature that would cause existing
functionality to change).
- [ ] New tests added to cover the changes.
- [ ] Integration tests passed locally by running `./runtests.sh -f -u
--net --coverage`.
- [ ] Quick tests passed locally by running `./runtests.sh --quick
--unittests --disttests`.
- [ ] In-line docstrings updated.
- [ ] Documentation updated, tested `make html` command in the `docs/`
folder.

---------

Signed-off-by: Wenqi Li <wenqil@nvidia.com>

monai/losses/dice.py

@@ -268,6 +268,7 @@ def __init__(
             smooth_dr: a small constant added to the denominator to avoid nan.
             batch: whether to sum the intersection and union areas over the batch dimension before the dividing.
                 Defaults to False, intersection over union is computed from each item in the batch.
+                If True, the class-weighted intersection and union areas are first summed across the batches.
 
         Raises:
             TypeError: When ``other_act`` is not an ``Optional[Callable]``.
@@ -360,8 +361,9 @@ def forward(self, input: torch.Tensor, target: torch.Tensor) -> torch.Tensor:
             max_values = torch.max(w, dim=1)[0].unsqueeze(dim=1)
             w = w + infs * max_values
 
-        numer = 2.0 * (intersection * w) + self.smooth_nr
-        denom = (denominator * w) + self.smooth_dr
+        final_reduce_dim = 0 if self.batch else 1
+        numer = 2.0 * (intersection * w).sum(final_reduce_dim, keepdim=True) + self.smooth_nr
+        denom = (denominator * w).sum(final_reduce_dim, keepdim=True) + self.smooth_dr
         f: torch.Tensor = 1.0 - (numer / denom)
 
         if self.reduction == LossReduction.MEAN.value:

tests/test_generalized_dice_loss.py

@@ -48,15 +48,15 @@
             "input": torch.tensor([[[-1.0, 0.0, 1.0], [1.0, 0.0, -1.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1.0, 0.0, 0.0]], [[1.0, 1.0, 0.0]]]),
         },
-        0.435035,
+        0.469964,
     ],
     [  # shape: (2, 2, 3), (2, 1, 3)
         {"include_background": True, "to_onehot_y": True, "softmax": True, "smooth_nr": 1e-4, "smooth_dr": 1e-4},
         {
             "input": torch.tensor([[[-1.0, 0.0, 1.0], [1.0, 0.0, -1.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1.0, 0.0, 0.0]], [[1.0, 1.0, 0.0]]]),
         },
-        0.3837,
+        0.414507,
     ],
     [  # shape: (2, 2, 3), (2, 1, 3)
         {
@@ -71,7 +71,7 @@
             "input": torch.tensor([[[-1.0, 0.0, 1.0], [1.0, 0.0, -1.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1.0, 0.0, 0.0]], [[1.0, 1.0, 0.0]]]),
         },
-        1.5348,
+        0.829015,
     ],
     [  # shape: (2, 2, 3), (2, 1, 3)
         {
@@ -86,7 +86,7 @@
             "input": torch.tensor([[[-1.0, 0.0, 1.0], [1.0, 0.0, -1.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1.0, 0.0, 0.0]], [[1.0, 1.0, 0.0]]]),
         },
-        [[[0.210949], [0.295351]], [[0.599976], [0.428522]]],
+        [[[0.273476]], [[0.555539]]],
     ],
     [  # shape: (2, 2, 3), (2, 1, 3)
         {"include_background": False, "to_onehot_y": True, "smooth_nr": 1e-8, "smooth_dr": 1e-8},
@@ -114,7 +114,7 @@
             "input": torch.tensor([[[0.0, 10.0, 10.0, 10.0], [10.0, 0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1, 1, 0, 0]]]),
         },
-        0.26669,
+        0.250023,
     ],
     [  # shape: (2, 1, 2, 2), (2, 1, 2, 2)
         {"include_background": True, "other_act": torch.tanh, "smooth_nr": 1e-4, "smooth_dr": 1e-4},
@@ -136,7 +136,7 @@
             "input": torch.tensor([[[-1.0, 0.0, 1.0], [1.0, 0.0, -1.0]], [[0.0, 0.0, 0.0], [0.0, 0.0, 0.0]]]),
             "target": torch.tensor([[[1.0, 0.0, 0.0]], [[1.0, 1.0, 0.0]]]),
         },
-        -8.55485,
+        -0.097833,
     ],
 ]