1 files changed, 69 insertions, 0 deletions
diff --git a/src/text_recognizer/networks/loss/loss.py b/src/text_recognizer/networks/loss/loss.py
new file mode 100644
index 0000000..cf9fa0d
--- /dev/null
+++ b/src/text_recognizer/networks/loss/loss.py
@@ -0,0 +1,69 @@
+"""Implementations of custom loss functions."""
+from pytorch_metric_learning import distances, losses, miners, reducers
+import torch
+from torch import nn
+from torch import Tensor
+from torch.autograd import Variable
+import torch.nn.functional as F
+
+__all__ = ["EmbeddingLoss", "LabelSmoothingCrossEntropy"]
+
+
+class EmbeddingLoss:
+    """Metric loss for training encoders to produce information-rich latent embeddings."""
+
+    def __init__(self, margin: float = 0.2, type_of_triplets: str = "semihard") -> None:
+        self.distance = distances.CosineSimilarity()
+        self.reducer = reducers.ThresholdReducer(low=0)
+        self.loss_fn = losses.TripletMarginLoss(
+            margin=margin, distance=self.distance, reducer=self.reducer
+        )
+        self.miner = miners.MultiSimilarityMiner(epsilon=margin, distance=self.distance)
+
+    def __call__(self, embeddings: Tensor, labels: Tensor) -> Tensor:
+        """Computes the metric loss for the embeddings based on their labels.
+
+        Args:
+            embeddings (Tensor): The laten vectors encoded by the network.
+            labels (Tensor): Labels of the embeddings.
+
+        Returns:
+            Tensor: The metric loss for the embeddings.
+
+        """
+        hard_pairs = self.miner(embeddings, labels)
+        loss = self.loss_fn(embeddings, labels, hard_pairs)
+        return loss
+
+
+class LabelSmoothingCrossEntropy(nn.Module):
+    """Label smoothing loss function."""
+
+    def __init__(
+        self,
+        classes: int,
+        smoothing: float = 0.0,
+        ignore_index: int = None,
+        dim: int = -1,
+    ) -> None:
+        super().__init__()
+        self.confidence = 1.0 - smoothing
+        self.smoothing = smoothing
+        self.ignore_index = ignore_index
+        self.cls = classes
+        self.dim = dim
+
+    def forward(self, pred: Tensor, target: Tensor) -> Tensor:
+        """Calculates the loss."""
+        pred = pred.log_softmax(dim=self.dim)
+        with torch.no_grad():
+            # true_dist = pred.data.clone()
+            true_dist = torch.zeros_like(pred)
+            true_dist.fill_(self.smoothing / (self.cls - 1))
+            true_dist.scatter_(1, target.data.unsqueeze(1), self.confidence)
+            if self.ignore_index is not None:
+                true_dist[:, self.ignore_index] = 0
+                mask = torch.nonzero(target == self.ignore_index, as_tuple=False)
+                if mask.dim() > 0:
+                    true_dist.index_fill_(0, mask.squeeze(), 0.0)
+        return torch.mean(torch.sum(-true_dist * pred, dim=self.dim))