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"""
UNet Network in PyTorch, modified from https://github.com/milesial/Pytorch-UNet
with architecture referenced from https://keras.io/examples/vision/depth_estimation
for monocular depth estimation from RGB images, i.e. one output channel.
"""
import torch
from torch import nn
class UNet(nn.Module):
"""
The overall UNet architecture.
"""
def __init__(self):
super().__init__()
self.downscale_blocks = nn.ModuleList(
[
DownBlock(16, 32),
DownBlock(32, 64),
DownBlock(64, 128),
DownBlock(128, 256),
]
)
self.upscale_blocks = nn.ModuleList(
[
UpBlock(256, 128),
UpBlock(128, 64),
UpBlock(64, 32),
UpBlock(32, 16),
]
)
self.input_conv = nn.Conv2d(3, 16, kernel_size=3, padding="same")
self.output_conv = nn.Conv2d(16, 1, kernel_size=1)
self.bridge = BottleNeckBlock(256)
self.activation = nn.Sigmoid()
def forward(self, x):
x = self.input_conv(x)
skip_features = []
for block in self.downscale_blocks:
c, x = block(x)
skip_features.append(c)
x = self.bridge(x)
skip_features.reverse()
for block, skip in zip(self.upscale_blocks, skip_features):
x = block(x, skip)
x = self.output_conv(x)
x = self.activation(x)
return x
class DownBlock(nn.Module):
"""
Module that performs downscaling with residual connections.
"""
def __init__(self, in_channels, out_channels, padding="same", stride=1):
super().__init__()
self.conv1 = nn.Conv2d(
in_channels,
out_channels,
kernel_size=3,
stride=stride,
padding=padding,
bias=False,
)
self.conv2 = nn.Conv2d(
out_channels,
out_channels,
kernel_size=3,
stride=stride,
padding=padding,
bias=False,
)
self.bn1 = nn.BatchNorm2d(out_channels)
self.bn2 = nn.BatchNorm2d(out_channels)
self.relu = nn.LeakyReLU(0.2)
self.maxpool = nn.MaxPool2d(2)
def forward(self, x):
d = self.conv1(x)
x = self.bn1(d)
x = self.relu(x)
x = self.conv2(x)
x = self.bn2(x)
x = self.relu(x)
x = x + d
p = self.maxpool(x)
return x, p
class UpBlock(nn.Module):
"""
Module that performs upscaling after concatenation with skip connections.
"""
def __init__(self, in_channels, out_channels, padding="same", stride=1):
super().__init__()
self.up = nn.Upsample(scale_factor=2, mode="bilinear", align_corners=True)
self.conv1 = nn.Conv2d(
in_channels * 2,
in_channels,
kernel_size=3,
stride=stride,
padding=padding,
bias=False,
)
self.conv2 = nn.Conv2d(
in_channels,
out_channels,
kernel_size=3,
stride=stride,
padding=padding,
bias=False,
)
self.bn1 = nn.BatchNorm2d(in_channels)
self.bn2 = nn.BatchNorm2d(out_channels)
self.relu = nn.LeakyReLU(0.2)
def forward(self, x, skip):
x = self.up(x)
x = torch.cat([x, skip], dim=1)
x = self.conv1(x)
x = self.bn1(x)
x = self.relu(x)
x = self.conv2(x)
x = self.bn2(x)
x = self.relu(x)
return x
class BottleNeckBlock(nn.Module):
"""
BottleNeckBlock that serves as the UNet bridge.
"""
def __init__(self, channels, padding="same", strides=1):
super().__init__()
self.conv1 = nn.Conv2d(channels, channels, 3, 1, "same")
self.conv2 = nn.Conv2d(channels, channels, 3, 1, "same")
self.relu = nn.LeakyReLU(0.2)
def forward(self, x):
x = self.conv1(x)
x = self.relu(x)
x = self.conv2(x)
x = self.relu(x)
return x |