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ppocr/losses/rec_ctc_loss.py

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+# copyright (c) 2019 PaddlePaddle Authors. All Rights Reserve.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import paddle
+from paddle import nn
+
+
+class CTCLoss(nn.Layer):
+    def __init__(self, use_focal_loss=False, **kwargs):
+        super(CTCLoss, self).__init__()
+        self.loss_func = nn.CTCLoss(blank=0, reduction="none")
+        self.use_focal_loss = use_focal_loss
+
+    def forward(self, predicts, batch):
+        if isinstance(predicts, (list, tuple)):
+            predicts = predicts[-1]
+        predicts = predicts.transpose((1, 0, 2))
+        N, B, _ = predicts.shape
+        preds_lengths = paddle.to_tensor(
+            [N] * B, dtype="int64", place=paddle.CPUPlace()
+        )
+        labels = batch[1].astype("int32")
+        label_lengths = batch[2].astype("int64")
+        loss = self.loss_func(predicts, labels, preds_lengths, label_lengths)
+        if self.use_focal_loss:
+            weight = paddle.exp(-loss)
+            weight = paddle.subtract(paddle.to_tensor([1.0]), weight)
+            weight = paddle.square(weight)
+            loss = paddle.multiply(loss, weight)
+        loss = loss.mean()
+        return {"loss": loss}