Source code for monai.networks.nets.regressor

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# 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
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from typing import Optional, Sequence, Union

import numpy as np
import torch
import torch.nn as nn

from monai.networks.blocks import Convolution, ResidualUnit
from monai.networks.layers.convutils import calculate_out_shape, same_padding
from monai.networks.layers.factories import Act, Norm
from monai.networks.layers.simplelayers import Reshape
from monai.utils import ensure_tuple, ensure_tuple_rep


[docs]class Regressor(nn.Module): """ This defines a network for relating large-sized input tensors to small output tensors, ie. regressing large values to a prediction. An output of a single dimension can be used as value regression or multi-label classification prediction, an output of a single value can be used as a discriminator or critic prediction. """ def __init__( self, in_shape: Sequence[int], out_shape: Sequence[int], channels: Sequence[int], strides: Sequence[int], kernel_size: Union[Sequence[int], int] = 3, num_res_units: int = 2, act=Act.PRELU, norm=Norm.INSTANCE, dropout: Optional[float] = None, bias: bool = True, ) -> None: """ Construct the regressor network with the number of layers defined by `channels` and `strides`. Inputs are first passed through the convolutional layers in the forward pass, the output from this is then pass through a fully connected layer to relate them to the final output tensor. Args: in_shape: tuple of integers stating the dimension of the input tensor (minus batch dimension) out_shape: tuple of integers stating the dimension of the final output tensor channels: tuple of integers stating the output channels of each convolutional layer strides: tuple of integers stating the stride (downscale factor) of each convolutional layer kernel_size: integer or tuple of integers stating size of convolutional kernels num_res_units: integer stating number of convolutions in residual units, 0 means no residual units act: name or type defining activation layers norm: name or type defining normalization layers dropout: optional float value in range [0, 1] stating dropout probability for layers, None for no dropout bias: boolean stating if convolution layers should have a bias component """ super().__init__() self.in_channels, *self.in_shape = ensure_tuple(in_shape) self.dimensions = len(self.in_shape) self.channels = ensure_tuple(channels) self.strides = ensure_tuple(strides) self.out_shape = ensure_tuple(out_shape) self.kernel_size = ensure_tuple_rep(kernel_size, self.dimensions) self.num_res_units = num_res_units self.act = act self.norm = norm self.dropout = dropout self.bias = bias self.net = nn.Sequential() echannel = self.in_channels padding = same_padding(kernel_size) self.final_size = np.asarray(self.in_shape, np.int) self.reshape = Reshape(*self.out_shape) # encode stage for i, (c, s) in enumerate(zip(self.channels, self.strides)): layer = self._get_layer(echannel, c, s, i == len(channels) - 1) echannel = c # use the output channel number as the input for the next loop self.net.add_module("layer_%i" % i, layer) self.final_size = calculate_out_shape(self.final_size, kernel_size, s, padding) self.final = self._get_final_layer((echannel,) + self.final_size) def _get_layer( self, in_channels: int, out_channels: int, strides: int, is_last: bool ) -> Union[ResidualUnit, Convolution]: """ Returns a layer accepting inputs with `in_channels` number of channels and producing outputs of `out_channels` number of channels. The `strides` indicates downsampling factor, ie. convolutional stride. If `is_last` is True this is the final layer and is not expected to include activation and normalization layers. """ layer: Union[ResidualUnit, Convolution] if self.num_res_units > 0: layer = ResidualUnit( subunits=self.num_res_units, last_conv_only=is_last, dimensions=self.dimensions, in_channels=in_channels, out_channels=out_channels, strides=strides, kernel_size=self.kernel_size, act=self.act, norm=self.norm, dropout=self.dropout, bias=self.bias, ) else: layer = Convolution( conv_only=is_last, dimensions=self.dimensions, in_channels=in_channels, out_channels=out_channels, strides=strides, kernel_size=self.kernel_size, act=self.act, norm=self.norm, dropout=self.dropout, bias=self.bias, ) return layer def _get_final_layer(self, in_shape: Sequence[int]): linear = nn.Linear(int(np.product(in_shape)), int(np.product(self.out_shape))) return nn.Sequential(nn.Flatten(), linear)
[docs] def forward(self, x: torch.Tensor) -> torch.Tensor: x = self.net(x) x = self.final(x) x = self.reshape(x) return x