rnn.py

# copyright (c) 2020 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

from paddle import nn

from ppocr.modeling.heads.rec_ctc_head import get_para_bias_attr


class Im2Seq(nn.Layer):
    def __init__(self, in_channels, **kwargs):
        super().__init__()
        self.out_channels = in_channels

    def forward(self, x):
        B, C, H, W = x.shape
        assert H == 1
        x = x.squeeze(axis=2)
        x = x.transpose([0, 2, 1])  # (NTC)(batch, width, channels)
        return x


class EncoderWithRNN(nn.Layer):
    def __init__(self, in_channels, hidden_size):
        super(EncoderWithRNN, self).__init__()
        self.out_channels = hidden_size * 2
        self.lstm = nn.LSTM(
            in_channels, hidden_size, direction='bidirectional', num_layers=2)

    def forward(self, x):
        x, _ = self.lstm(x)
        return x


class EncoderWithFC(nn.Layer):
    def __init__(self, in_channels, hidden_size):
        super(EncoderWithFC, self).__init__()
        self.out_channels = hidden_size
        weight_attr, bias_attr = get_para_bias_attr(
            l2_decay=0.00001, k=in_channels, name='reduce_encoder_fea')
        self.fc = nn.Linear(
            in_channels,
            hidden_size,
            weight_attr=weight_attr,
            bias_attr=bias_attr,
            name='reduce_encoder_fea')

    def forward(self, x):
        x = self.fc(x)
        return x


class SequenceEncoder(nn.Layer):
    def __init__(self, in_channels, encoder_type, hidden_size=48, **kwargs):
        super(SequenceEncoder, self).__init__()
        self.encoder_reshape = Im2Seq(in_channels)
        self.out_channels = self.encoder_reshape.out_channels
        if encoder_type == 'reshape':
            self.only_reshape = True
        else:
            support_encoder_dict = {
                'reshape': Im2Seq,
                'fc': EncoderWithFC,
                'rnn': EncoderWithRNN
            }
            assert encoder_type in support_encoder_dict, '{} must in {}'.format(
                encoder_type, support_encoder_dict.keys())

            self.encoder = support_encoder_dict[encoder_type](
                self.encoder_reshape.out_channels, hidden_size)
            self.out_channels = self.encoder.out_channels
            self.only_reshape = False

    def forward(self, x):
        x = self.encoder_reshape(x)
        if not self.only_reshape:
            x = self.encoder(x)
        return x