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# Copyright Niantic 2019. Patent Pending. All rights reserved.
#
# This software is licensed under the terms of the Monodepth2 licence
# which allows for non-commercial use only, the full terms of which are made
# available in the LICENSE file.
from __future__ import absolute_import, division, print_function
import numpy as np
import torch
import torch.nn as nn
import torchvision.models as models
import torch.utils.model_zoo as model_zoo
class ResNetMultiImageInput(models.ResNet):
"""Constructs a resnet model with varying number of input images.
Adapted from https://github.com/pytorch/vision/blob/master/torchvision/models/resnet.py
"""
def __init__(self, block, layers, num_classes=1000, num_input_images=1):
super(ResNetMultiImageInput, self).__init__(block, layers)
self.inplanes = 64
self.conv1 = nn.Conv2d(
num_input_images * 3, 64, kernel_size=7, stride=2, padding=3, bias=False)
self.bn1 = nn.BatchNorm2d(64)
self.relu = nn.ReLU(inplace=True)
self.maxpool = nn.MaxPool2d(kernel_size=3, stride=2, padding=1)
self.layer1 = self._make_layer(block, 64, layers[0])
self.layer2 = self._make_layer(block, 128, layers[1], stride=2)
self.layer3 = self._make_layer(block, 256, layers[2], stride=2)
self.layer4 = self._make_layer(block, 512, layers[3], stride=2)
for m in self.modules():
if isinstance(m, nn.Conv2d):
nn.init.kaiming_normal_(m.weight, mode='fan_out', nonlinearity='relu')
elif isinstance(m, nn.BatchNorm2d):
nn.init.constant_(m.weight, 1)
nn.init.constant_(m.bias, 0)
def resnet_multiimage_input(num_layers, pretrained=False, num_input_images=1):
"""Constructs a ResNet model.
Args:
num_layers (int): Number of resnet layers. Must be 18 or 50
pretrained (bool): If True, returns a model pre-trained on ImageNet
num_input_images (int): Number of frames stacked as input
"""
assert num_layers in [18, 50], "Can only run with 18 or 50 layer resnet"
blocks = {18: [2, 2, 2, 2], 50: [3, 4, 6, 3]}[num_layers]
block_type = {18: models.resnet.BasicBlock, 50: models.resnet.Bottleneck}[num_layers]
model = ResNetMultiImageInput(block_type, blocks, num_input_images=num_input_images)
if pretrained:
loaded = model_zoo.load_url(models.resnet.model_urls['resnet{}'.format(num_layers)])
loaded['conv1.weight'] = torch.cat(
[loaded['conv1.weight']] * num_input_images, 1) / num_input_images
model.load_state_dict(loaded)
return model
class ResnetEncoder(nn.Module):
"""Pytorch module for a resnet encoder
"""
def __init__(self, num_layers, pretrained, num_input_images=1):
super(ResnetEncoder, self).__init__()
self.num_ch_enc = np.array([64, 64, 128, 256, 512])
resnets = {18: models.resnet18,
34: models.resnet34,
50: models.resnet50,
101: models.resnet101,
152: models.resnet152}
if num_layers not in resnets:
raise ValueError("{} is not a valid number of resnet layers".format(num_layers))
if num_input_images > 1:
self.encoder = resnet_multiimage_input(num_layers, pretrained, num_input_images)
else:
self.encoder = resnets[num_layers](pretrained)
if num_layers > 34:
self.num_ch_enc[1:] *= 4
def forward(self, input_image):
self.features = []
x = (input_image - 0.45) / 0.225
x = self.encoder.conv1(x)
x = self.encoder.bn1(x)
self.features.append(self.encoder.relu(x))
self.features.append(self.encoder.layer1(self.encoder.maxpool(self.features[-1])))
self.features.append(self.encoder.layer2(self.features[-1]))
self.features.append(self.encoder.layer3(self.features[-1]))
self.features.append(self.encoder.layer4(self.features[-1]))
return self.features
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